@c Copyright (C) 1988,1989,1992,1993,1994,1995,1996,1997,1998,1999,2000,2001,2002 @c Free Software Foundation, Inc. @c This is part of the GCC manual. @c For copying conditions, see the file gcc.texi. @node Target Macros @chapter Target Description Macros and Functions @cindex machine description macros @cindex target description macros @cindex macros, target description @cindex @file{tm.h} macros In addition to the file @file{@var{machine}.md}, a machine description includes a C header file conventionally given the name @file{@var{machine}.h} and a C source file named @file{@var{machine}.c}. The header file defines numerous macros that convey the information about the target machine that does not fit into the scheme of the @file{.md} file. The file @file{tm.h} should be a link to @file{@var{machine}.h}. The header file @file{config.h} includes @file{tm.h} and most compiler source files include @file{config.h}. The source file defines a variable @code{targetm}, which is a structure containing pointers to functions and data relating to the target machine. @file{@var{machine}.c} should also contain their definitions, if they are not defined elsewhere in GCC, and other functions called through the macros defined in the @file{.h} file. @menu * Target Structure:: The @code{targetm} variable. * Driver:: Controlling how the driver runs the compilation passes. * Run-time Target:: Defining @samp{-m} options like @option{-m68000} and @option{-m68020}. * Per-Function Data:: Defining data structures for per-function information. * Storage Layout:: Defining sizes and alignments of data. * Type Layout:: Defining sizes and properties of basic user data types. * Escape Sequences:: Defining the value of target character escape sequences * Registers:: Naming and describing the hardware registers. * Register Classes:: Defining the classes of hardware registers. * Stack and Calling:: Defining which way the stack grows and by how much. * Varargs:: Defining the varargs macros. * Trampolines:: Code set up at run time to enter a nested function. * Library Calls:: Controlling how library routines are implicitly called. * Addressing Modes:: Defining addressing modes valid for memory operands. * Condition Code:: Defining how insns update the condition code. * Costs:: Defining relative costs of different operations. * Scheduling:: Adjusting the behavior of the instruction scheduler. * Sections:: Dividing storage into text, data, and other sections. * PIC:: Macros for position independent code. * Assembler Format:: Defining how to write insns and pseudo-ops to output. * Debugging Info:: Defining the format of debugging output. * Floating Point:: Handling floating point for cross-compilers. * Mode Switching:: Insertion of mode-switching instructions. * Target Attributes:: Defining target-specific uses of @code{__attribute__}. * MIPS Coprocessors:: MIPS coprocessor support and how to customize it. * Misc:: Everything else. @end menu @node Target Structure @section The Global @code{targetm} Variable @cindex target hooks @cindex target functions @deftypevar {struct gcc_target} targetm The target @file{.c} file must define the global @code{targetm} variable which contains pointers to functions and data relating to the target machine. The variable is declared in @file{target.h}; @file{target-def.h} defines the macro @code{TARGET_INITIALIZER} which is used to initialize the variable, and macros for the default initializers for elements of the structure. The @file{.c} file should override those macros for which the default definition is inappropriate. For example: @smallexample #include "target.h" #include "target-def.h" /* @r{Initialize the GCC target structure.} */ #undef TARGET_COMP_TYPE_ATTRIBUTES #define TARGET_COMP_TYPE_ATTRIBUTES @var{machine}_comp_type_attributes struct gcc_target targetm = TARGET_INITIALIZER; @end smallexample @end deftypevar Where a macro should be defined in the @file{.c} file in this manner to form part of the @code{targetm} structure, it is documented below as a ``Target Hook'' with a prototype. Many macros will change in future from being defined in the @file{.h} file to being part of the @code{targetm} structure. @node Driver @section Controlling the Compilation Driver, @file{gcc} @cindex driver @cindex controlling the compilation driver @c prevent bad page break with this line You can control the compilation driver. @table @code @findex SWITCH_TAKES_ARG @item SWITCH_TAKES_ARG (@var{char}) A C expression which determines whether the option @option{-@var{char}} takes arguments. The value should be the number of arguments that option takes--zero, for many options. By default, this macro is defined as @code{DEFAULT_SWITCH_TAKES_ARG}, which handles the standard options properly. You need not define @code{SWITCH_TAKES_ARG} unless you wish to add additional options which take arguments. Any redefinition should call @code{DEFAULT_SWITCH_TAKES_ARG} and then check for additional options. @findex WORD_SWITCH_TAKES_ARG @item WORD_SWITCH_TAKES_ARG (@var{name}) A C expression which determines whether the option @option{-@var{name}} takes arguments. The value should be the number of arguments that option takes--zero, for many options. This macro rather than @code{SWITCH_TAKES_ARG} is used for multi-character option names. By default, this macro is defined as @code{DEFAULT_WORD_SWITCH_TAKES_ARG}, which handles the standard options properly. You need not define @code{WORD_SWITCH_TAKES_ARG} unless you wish to add additional options which take arguments. Any redefinition should call @code{DEFAULT_WORD_SWITCH_TAKES_ARG} and then check for additional options. @findex SWITCH_CURTAILS_COMPILATION @item SWITCH_CURTAILS_COMPILATION (@var{char}) A C expression which determines whether the option @option{-@var{char}} stops compilation before the generation of an executable. The value is boolean, nonzero if the option does stop an executable from being generated, zero otherwise. By default, this macro is defined as @code{DEFAULT_SWITCH_CURTAILS_COMPILATION}, which handles the standard options properly. You need not define @code{SWITCH_CURTAILS_COMPILATION} unless you wish to add additional options which affect the generation of an executable. Any redefinition should call @code{DEFAULT_SWITCH_CURTAILS_COMPILATION} and then check for additional options. @findex SWITCHES_NEED_SPACES @item SWITCHES_NEED_SPACES A string-valued C expression which enumerates the options for which the linker needs a space between the option and its argument. If this macro is not defined, the default value is @code{""}. @findex TARGET_OPTION_TRANSLATE_TABLE @item TARGET_OPTION_TRANSLATE_TABLE If defined, a list of pairs of strings, the first of which is a potential command line target to the @file{gcc} driver program, and the second of which is a space-separated (tabs and other whitespace are not supported) list of options with which to replace the first option. The target defining this list is responsible for assuring that the results are valid. Replacement options may not be the @code{--opt} style, they must be the @code{-opt} style. It is the intention of this macro to provide a mechanism for substitution that affects the multilibs chosen, such as one option that enables many options, some of which select multilibs. Example nonsensical definition, where @code{-malt-abi}, @code{-EB}, and @code{-mspoo} cause different multilibs to be chosen: @smallexample #define TARGET_OPTION_TRANSLATE_TABLE \ @{ "-fast", "-march=fast-foo -malt-abi -I/usr/fast-foo" @}, \ @{ "-compat", "-EB -malign=4 -mspoo" @} @end smallexample @findex CPP_SPEC @item CPP_SPEC A C string constant that tells the GCC driver program options to pass to CPP@. It can also specify how to translate options you give to GCC into options for GCC to pass to the CPP@. Do not define this macro if it does not need to do anything. @findex CPLUSPLUS_CPP_SPEC @item CPLUSPLUS_CPP_SPEC This macro is just like @code{CPP_SPEC}, but is used for C++, rather than C@. If you do not define this macro, then the value of @code{CPP_SPEC} (if any) will be used instead. @findex CC1_SPEC @item CC1_SPEC A C string constant that tells the GCC driver program options to pass to @code{cc1}, @code{cc1plus}, @code{f771}, and the other language front ends. It can also specify how to translate options you give to GCC into options for GCC to pass to front ends. Do not define this macro if it does not need to do anything. @findex CC1PLUS_SPEC @item CC1PLUS_SPEC A C string constant that tells the GCC driver program options to pass to @code{cc1plus}. It can also specify how to translate options you give to GCC into options for GCC to pass to the @code{cc1plus}. Do not define this macro if it does not need to do anything. Note that everything defined in CC1_SPEC is already passed to @code{cc1plus} so there is no need to duplicate the contents of CC1_SPEC in CC1PLUS_SPEC@. @findex ASM_SPEC @item ASM_SPEC A C string constant that tells the GCC driver program options to pass to the assembler. It can also specify how to translate options you give to GCC into options for GCC to pass to the assembler. See the file @file{sun3.h} for an example of this. Do not define this macro if it does not need to do anything. @findex ASM_FINAL_SPEC @item ASM_FINAL_SPEC A C string constant that tells the GCC driver program how to run any programs which cleanup after the normal assembler. Normally, this is not needed. See the file @file{mips.h} for an example of this. Do not define this macro if it does not need to do anything. @findex LINK_SPEC @item LINK_SPEC A C string constant that tells the GCC driver program options to pass to the linker. It can also specify how to translate options you give to GCC into options for GCC to pass to the linker. Do not define this macro if it does not need to do anything. @findex LIB_SPEC @item LIB_SPEC Another C string constant used much like @code{LINK_SPEC}. The difference between the two is that @code{LIB_SPEC} is used at the end of the command given to the linker. If this macro is not defined, a default is provided that loads the standard C library from the usual place. See @file{gcc.c}. @findex LIBGCC_SPEC @item LIBGCC_SPEC Another C string constant that tells the GCC driver program how and when to place a reference to @file{libgcc.a} into the linker command line. This constant is placed both before and after the value of @code{LIB_SPEC}. If this macro is not defined, the GCC driver provides a default that passes the string @option{-lgcc} to the linker. @findex STARTFILE_SPEC @item STARTFILE_SPEC Another C string constant used much like @code{LINK_SPEC}. The difference between the two is that @code{STARTFILE_SPEC} is used at the very beginning of the command given to the linker. If this macro is not defined, a default is provided that loads the standard C startup file from the usual place. See @file{gcc.c}. @findex ENDFILE_SPEC @item ENDFILE_SPEC Another C string constant used much like @code{LINK_SPEC}. The difference between the two is that @code{ENDFILE_SPEC} is used at the very end of the command given to the linker. Do not define this macro if it does not need to do anything. @findex THREAD_MODEL_SPEC @item THREAD_MODEL_SPEC GCC @code{-v} will print the thread model GCC was configured to use. However, this doesn't work on platforms that are multilibbed on thread models, such as AIX 4.3. On such platforms, define @code{THREAD_MODEL_SPEC} such that it evaluates to a string without blanks that names one of the recognized thread models. @code{%*}, the default value of this macro, will expand to the value of @code{thread_file} set in @file{config.gcc}. @findex EXTRA_SPECS @item EXTRA_SPECS Define this macro to provide additional specifications to put in the @file{specs} file that can be used in various specifications like @code{CC1_SPEC}. The definition should be an initializer for an array of structures, containing a string constant, that defines the specification name, and a string constant that provides the specification. Do not define this macro if it does not need to do anything. @code{EXTRA_SPECS} is useful when an architecture contains several related targets, which have various @code{@dots{}_SPECS} which are similar to each other, and the maintainer would like one central place to keep these definitions. For example, the PowerPC System V.4 targets use @code{EXTRA_SPECS} to define either @code{_CALL_SYSV} when the System V calling sequence is used or @code{_CALL_AIX} when the older AIX-based calling sequence is used. The @file{config/rs6000/rs6000.h} target file defines: @example #define EXTRA_SPECS \ @{ "cpp_sysv_default", CPP_SYSV_DEFAULT @}, #define CPP_SYS_DEFAULT "" @end example The @file{config/rs6000/sysv.h} target file defines: @smallexample #undef CPP_SPEC #define CPP_SPEC \ "%@{posix: -D_POSIX_SOURCE @} \ %@{mcall-sysv: -D_CALL_SYSV @} %@{mcall-aix: -D_CALL_AIX @} \ %@{!mcall-sysv: %@{!mcall-aix: %(cpp_sysv_default) @}@} \ %@{msoft-float: -D_SOFT_FLOAT@} %@{mcpu=403: -D_SOFT_FLOAT@}" #undef CPP_SYSV_DEFAULT #define CPP_SYSV_DEFAULT "-D_CALL_SYSV" @end smallexample while the @file{config/rs6000/eabiaix.h} target file defines @code{CPP_SYSV_DEFAULT} as: @smallexample #undef CPP_SYSV_DEFAULT #define CPP_SYSV_DEFAULT "-D_CALL_AIX" @end smallexample @findex LINK_LIBGCC_SPECIAL @item LINK_LIBGCC_SPECIAL Define this macro if the driver program should find the library @file{libgcc.a} itself and should not pass @option{-L} options to the linker. If you do not define this macro, the driver program will pass the argument @option{-lgcc} to tell the linker to do the search and will pass @option{-L} options to it. @findex LINK_LIBGCC_SPECIAL_1 @item LINK_LIBGCC_SPECIAL_1 Define this macro if the driver program should find the library @file{libgcc.a}. If you do not define this macro, the driver program will pass the argument @option{-lgcc} to tell the linker to do the search. This macro is similar to @code{LINK_LIBGCC_SPECIAL}, except that it does not affect @option{-L} options. @findex LINK_GCC_C_SEQUENCE_SPEC @item LINK_GCC_C_SEQUENCE_SPEC The sequence in which libgcc and libc are specified to the linker. By default this is @code{%G %L %G}. @findex LINK_COMMAND_SPEC @item LINK_COMMAND_SPEC A C string constant giving the complete command line need to execute the linker. When you do this, you will need to update your port each time a change is made to the link command line within @file{gcc.c}. Therefore, define this macro only if you need to completely redefine the command line for invoking the linker and there is no other way to accomplish the effect you need. Overriding this macro may be avoidable by overriding @code{LINK_GCC_C_SEQUENCE_SPEC} instead. @findex LINK_ELIMINATE_DUPLICATE_LDIRECTORIES @item LINK_ELIMINATE_DUPLICATE_LDIRECTORIES A nonzero value causes @command{collect2} to remove duplicate @option{-L@var{directory}} search directories from linking commands. Do not give it a nonzero value if removing duplicate search directories changes the linker's semantics. @findex MULTILIB_DEFAULTS @item MULTILIB_DEFAULTS Define this macro as a C expression for the initializer of an array of string to tell the driver program which options are defaults for this target and thus do not need to be handled specially when using @code{MULTILIB_OPTIONS}. Do not define this macro if @code{MULTILIB_OPTIONS} is not defined in the target makefile fragment or if none of the options listed in @code{MULTILIB_OPTIONS} are set by default. @xref{Target Fragment}. @findex RELATIVE_PREFIX_NOT_LINKDIR @item RELATIVE_PREFIX_NOT_LINKDIR Define this macro to tell @code{gcc} that it should only translate a @option{-B} prefix into a @option{-L} linker option if the prefix indicates an absolute file name. @findex STANDARD_EXEC_PREFIX @item STANDARD_EXEC_PREFIX Define this macro as a C string constant if you wish to override the standard choice of @file{/usr/local/lib/gcc-lib/} as the default prefix to try when searching for the executable files of the compiler. @findex MD_EXEC_PREFIX @item MD_EXEC_PREFIX If defined, this macro is an additional prefix to try after @code{STANDARD_EXEC_PREFIX}. @code{MD_EXEC_PREFIX} is not searched when the @option{-b} option is used, or the compiler is built as a cross compiler. If you define @code{MD_EXEC_PREFIX}, then be sure to add it to the list of directories used to find the assembler in @file{configure.in}. @findex STANDARD_STARTFILE_PREFIX @item STANDARD_STARTFILE_PREFIX Define this macro as a C string constant if you wish to override the standard choice of @file{/usr/local/lib/} as the default prefix to try when searching for startup files such as @file{crt0.o}. @findex MD_STARTFILE_PREFIX @item MD_STARTFILE_PREFIX If defined, this macro supplies an additional prefix to try after the standard prefixes. @code{MD_EXEC_PREFIX} is not searched when the @option{-b} option is used, or when the compiler is built as a cross compiler. @findex MD_STARTFILE_PREFIX_1 @item MD_STARTFILE_PREFIX_1 If defined, this macro supplies yet another prefix to try after the standard prefixes. It is not searched when the @option{-b} option is used, or when the compiler is built as a cross compiler. @findex INIT_ENVIRONMENT @item INIT_ENVIRONMENT Define this macro as a C string constant if you wish to set environment variables for programs called by the driver, such as the assembler and loader. The driver passes the value of this macro to @code{putenv} to initialize the necessary environment variables. @findex LOCAL_INCLUDE_DIR @item LOCAL_INCLUDE_DIR Define this macro as a C string constant if you wish to override the standard choice of @file{/usr/local/include} as the default prefix to try when searching for local header files. @code{LOCAL_INCLUDE_DIR} comes before @code{SYSTEM_INCLUDE_DIR} in the search order. Cross compilers do not search either @file{/usr/local/include} or its replacement. @findex MODIFY_TARGET_NAME @item MODIFY_TARGET_NAME Define this macro if you with to define command-line switches that modify the default target name For each switch, you can include a string to be appended to the first part of the configuration name or a string to be deleted from the configuration name, if present. The definition should be an initializer for an array of structures. Each array element should have three elements: the switch name (a string constant, including the initial dash), one of the enumeration codes @code{ADD} or @code{DELETE} to indicate whether the string should be inserted or deleted, and the string to be inserted or deleted (a string constant). For example, on a machine where @samp{64} at the end of the configuration name denotes a 64-bit target and you want the @option{-32} and @option{-64} switches to select between 32- and 64-bit targets, you would code @smallexample #define MODIFY_TARGET_NAME \ @{ @{ "-32", DELETE, "64"@}, \ @{"-64", ADD, "64"@}@} @end smallexample @findex SYSTEM_INCLUDE_DIR @item SYSTEM_INCLUDE_DIR Define this macro as a C string constant if you wish to specify a system-specific directory to search for header files before the standard directory. @code{SYSTEM_INCLUDE_DIR} comes before @code{STANDARD_INCLUDE_DIR} in the search order. Cross compilers do not use this macro and do not search the directory specified. @findex STANDARD_INCLUDE_DIR @item STANDARD_INCLUDE_DIR Define this macro as a C string constant if you wish to override the standard choice of @file{/usr/include} as the default prefix to try when searching for header files. Cross compilers do not use this macro and do not search either @file{/usr/include} or its replacement. @findex STANDARD_INCLUDE_COMPONENT @item STANDARD_INCLUDE_COMPONENT The ``component'' corresponding to @code{STANDARD_INCLUDE_DIR}. See @code{INCLUDE_DEFAULTS}, below, for the description of components. If you do not define this macro, no component is used. @findex INCLUDE_DEFAULTS @item INCLUDE_DEFAULTS Define this macro if you wish to override the entire default search path for include files. For a native compiler, the default search path usually consists of @code{GCC_INCLUDE_DIR}, @code{LOCAL_INCLUDE_DIR}, @code{SYSTEM_INCLUDE_DIR}, @code{GPLUSPLUS_INCLUDE_DIR}, and @code{STANDARD_INCLUDE_DIR}. In addition, @code{GPLUSPLUS_INCLUDE_DIR} and @code{GCC_INCLUDE_DIR} are defined automatically by @file{Makefile}, and specify private search areas for GCC@. The directory @code{GPLUSPLUS_INCLUDE_DIR} is used only for C++ programs. The definition should be an initializer for an array of structures. Each array element should have four elements: the directory name (a string constant), the component name (also a string constant), a flag for C++-only directories, and a flag showing that the includes in the directory don't need to be wrapped in @code{extern @samp{C}} when compiling C++. Mark the end of the array with a null element. The component name denotes what GNU package the include file is part of, if any, in all upper-case letters. For example, it might be @samp{GCC} or @samp{BINUTILS}. If the package is part of a vendor-supplied operating system, code the component name as @samp{0}. For example, here is the definition used for VAX/VMS: @example #define INCLUDE_DEFAULTS \ @{ \ @{ "GNU_GXX_INCLUDE:", "G++", 1, 1@}, \ @{ "GNU_CC_INCLUDE:", "GCC", 0, 0@}, \ @{ "SYS$SYSROOT:[SYSLIB.]", 0, 0, 0@}, \ @{ ".", 0, 0, 0@}, \ @{ 0, 0, 0, 0@} \ @} @end example @end table Here is the order of prefixes tried for exec files: @enumerate @item Any prefixes specified by the user with @option{-B}. @item The environment variable @code{GCC_EXEC_PREFIX}, if any. @item The directories specified by the environment variable @code{COMPILER_PATH}. @item The macro @code{STANDARD_EXEC_PREFIX}. @item @file{/usr/lib/gcc/}. @item The macro @code{MD_EXEC_PREFIX}, if any. @end enumerate Here is the order of prefixes tried for startfiles: @enumerate @item Any prefixes specified by the user with @option{-B}. @item The environment variable @code{GCC_EXEC_PREFIX}, if any. @item The directories specified by the environment variable @code{LIBRARY_PATH} (or port-specific name; native only, cross compilers do not use this). @item The macro @code{STANDARD_EXEC_PREFIX}. @item @file{/usr/lib/gcc/}. @item The macro @code{MD_EXEC_PREFIX}, if any. @item The macro @code{MD_STARTFILE_PREFIX}, if any. @item The macro @code{STANDARD_STARTFILE_PREFIX}. @item @file{/lib/}. @item @file{/usr/lib/}. @end enumerate @node Run-time Target @section Run-time Target Specification @cindex run-time target specification @cindex predefined macros @cindex target specifications @c prevent bad page break with this line Here are run-time target specifications. @table @code @findex TARGET_CPU_CPP_BUILTINS @item TARGET_CPU_CPP_BUILTINS() This function-like macro expands to a block of code that defines built-in preprocessor macros and assertions for the target cpu, using the functions @code{builtin_define}, @code{builtin_define_std} and @code{builtin_assert} defined in @file{c-common.c}. When the front end calls this macro it provides a trailing semicolon, and since it has finished command line option processing your code can use those results freely. @code{builtin_assert} takes a string in the form you pass to the command-line option @option{-A}, such as @code{cpu=mips}, and creates the assertion. @code{builtin_define} takes a string in the form accepted by option @option{-D} and unconditionally defines the macro. @code{builtin_define_std} takes a string representing the name of an object-like macro. If it doesn't lie in the user's namespace, @code{builtin_define_std} defines it unconditionally. Otherwise, it defines a version with two leading underscores, and another version with two leading and trailing underscores, and defines the original only if an ISO standard was not requested on the command line. For example, passing @code{unix} defines @code{__unix}, @code{__unix__} and possibly @code{unix}; passing @code{_mips} defines @code{__mips}, @code{__mips__} and possibly @code{_mips}, and passing @code{_ABI64} defines only @code{_ABI64}. You can also test for the C dialect being compiled. The variable @code{c_language} is set to one of @code{clk_c}, @code{clk_cplusplus} or @code{clk_objective_c}. Note that if we are preprocessing assembler, this variable will be @code{clk_c} but the function-like macro @code{preprocessing_asm_p()} will return true, so you might want to check for that first. If you need to check for strict ANSI, the variable @code{flag_iso} can be used. The function-like macro @code{preprocessing_trad_p()} can be used to check for traditional preprocessing. With @code{TARGET_OS_CPP_BUILTINS} this macro obsoletes the @code{CPP_PREDEFINES} target macro. @findex TARGET_OS_CPP_BUILTINS @item TARGET_OS_CPP_BUILTINS() Similarly to @code{TARGET_CPU_CPP_BUILTINS} but this macro is optional and is used for the target operating system instead. With @code{TARGET_CPU_CPP_BUILTINS} this macro obsoletes the @code{CPP_PREDEFINES} target macro. @findex CPP_PREDEFINES @item CPP_PREDEFINES Define this to be a string constant containing @option{-D} options to define the predefined macros that identify this machine and system. These macros will be predefined unless the @option{-ansi} option (or a @option{-std} option for strict ISO C conformance) is specified. In addition, a parallel set of macros are predefined, whose names are made by appending @samp{__} at the beginning and at the end. These @samp{__} macros are permitted by the ISO standard, so they are predefined regardless of whether @option{-ansi} or a @option{-std} option is specified. For example, on the Sun, one can use the following value: @smallexample "-Dmc68000 -Dsun -Dunix" @end smallexample The result is to define the macros @code{__mc68000__}, @code{__sun__} and @code{__unix__} unconditionally, and the macros @code{mc68000}, @code{sun} and @code{unix} provided @option{-ansi} is not specified. @findex extern int target_flags @item extern int target_flags; This declaration should be present. @cindex optional hardware or system features @cindex features, optional, in system conventions @item TARGET_@dots{} This series of macros is to allow compiler command arguments to enable or disable the use of optional features of the target machine. For example, one machine description serves both the 68000 and the 68020; a command argument tells the compiler whether it should use 68020-only instructions or not. This command argument works by means of a macro @code{TARGET_68020} that tests a bit in @code{target_flags}. Define a macro @code{TARGET_@var{featurename}} for each such option. Its definition should test a bit in @code{target_flags}. It is recommended that a helper macro @code{TARGET_MASK_@var{featurename}} is defined for each bit-value to test, and used in @code{TARGET_@var{featurename}} and @code{TARGET_SWITCHES}. For example: @smallexample #define TARGET_MASK_68020 1 #define TARGET_68020 (target_flags & TARGET_MASK_68020) @end smallexample One place where these macros are used is in the condition-expressions of instruction patterns. Note how @code{TARGET_68020} appears frequently in the 68000 machine description file, @file{m68k.md}. Another place they are used is in the definitions of the other macros in the @file{@var{machine}.h} file. @findex TARGET_SWITCHES @item TARGET_SWITCHES This macro defines names of command options to set and clear bits in @code{target_flags}. Its definition is an initializer with a subgrouping for each command option. Each subgrouping contains a string constant, that defines the option name, a number, which contains the bits to set in @code{target_flags}, and a second string which is the description displayed by @option{--help}. If the number is negative then the bits specified by the number are cleared instead of being set. If the description string is present but empty, then no help information will be displayed for that option, but it will not count as an undocumented option. The actual option name is made by appending @samp{-m} to the specified name. Non-empty description strings should be marked with @code{N_(@dots{})} for @command{xgettext}. Please do not mark empty strings because the empty string is reserved by GNU gettext. @code{gettext("")} returns the header entry of the message catalog with meta information, not the empty string. In addition to the description for @option{--help}, more detailed documentation for each option should be added to @file{invoke.texi}. One of the subgroupings should have a null string. The number in this grouping is the default value for @code{target_flags}. Any target options act starting with that value. Here is an example which defines @option{-m68000} and @option{-m68020} with opposite meanings, and picks the latter as the default: @smallexample #define TARGET_SWITCHES \ @{ @{ "68020", TARGET_MASK_68020, "" @}, \ @{ "68000", -TARGET_MASK_68020, \ N_("Compile for the 68000") @}, \ @{ "", TARGET_MASK_68020, "" @}@} @end smallexample @findex TARGET_OPTIONS @item TARGET_OPTIONS This macro is similar to @code{TARGET_SWITCHES} but defines names of command options that have values. Its definition is an initializer with a subgrouping for each command option. Each subgrouping contains a string constant, that defines the fixed part of the option name, the address of a variable, and a description string. Non-empty description strings should be marked with @code{N_(@dots{})} for @command{xgettext}. Please do not mark empty strings because the empty string is reserved by GNU gettext. @code{gettext("")} returns the header entry of the message catalog with meta information, not the empty string. The variable, type @code{char *}, is set to the variable part of the given option if the fixed part matches. The actual option name is made by appending @samp{-m} to the specified name. Again, each option should also be documented in @file{invoke.texi}. Here is an example which defines @option{-mshort-data-@var{number}}. If the given option is @option{-mshort-data-512}, the variable @code{m88k_short_data} will be set to the string @code{"512"}. @smallexample extern char *m88k_short_data; #define TARGET_OPTIONS \ @{ @{ "short-data-", &m88k_short_data, \ N_("Specify the size of the short data section") @} @} @end smallexample @findex TARGET_VERSION @item TARGET_VERSION This macro is a C statement to print on @code{stderr} a string describing the particular machine description choice. Every machine description should define @code{TARGET_VERSION}. For example: @smallexample #ifdef MOTOROLA #define TARGET_VERSION \ fprintf (stderr, " (68k, Motorola syntax)"); #else #define TARGET_VERSION \ fprintf (stderr, " (68k, MIT syntax)"); #endif @end smallexample @findex OVERRIDE_OPTIONS @item OVERRIDE_OPTIONS Sometimes certain combinations of command options do not make sense on a particular target machine. You can define a macro @code{OVERRIDE_OPTIONS} to take account of this. This macro, if defined, is executed once just after all the command options have been parsed. Don't use this macro to turn on various extra optimizations for @option{-O}. That is what @code{OPTIMIZATION_OPTIONS} is for. @findex OPTIMIZATION_OPTIONS @item OPTIMIZATION_OPTIONS (@var{level}, @var{size}) Some machines may desire to change what optimizations are performed for various optimization levels. This macro, if defined, is executed once just after the optimization level is determined and before the remainder of the command options have been parsed. Values set in this macro are used as the default values for the other command line options. @var{level} is the optimization level specified; 2 if @option{-O2} is specified, 1 if @option{-O} is specified, and 0 if neither is specified. @var{size} is nonzero if @option{-Os} is specified and zero otherwise. You should not use this macro to change options that are not machine-specific. These should uniformly selected by the same optimization level on all supported machines. Use this macro to enable machine-specific optimizations. @strong{Do not examine @code{write_symbols} in this macro!} The debugging options are not supposed to alter the generated code. @findex CAN_DEBUG_WITHOUT_FP @item CAN_DEBUG_WITHOUT_FP Define this macro if debugging can be performed even without a frame pointer. If this macro is defined, GCC will turn on the @option{-fomit-frame-pointer} option whenever @option{-O} is specified. @end table @node Per-Function Data @section Defining data structures for per-function information. @cindex per-function data @cindex data structures If the target needs to store information on a per-function basis, GCC provides a macro and a couple of variables to allow this. Note, just using statics to store the information is a bad idea, since GCC supports nested functions, so you can be halfway through encoding one function when another one comes along. GCC defines a data structure called @code{struct function} which contains all of the data specific to an individual function. This structure contains a field called @code{machine} whose type is @code{struct machine_function *}, which can be used by targets to point to their own specific data. If a target needs per-function specific data it should define the type @code{struct machine_function} and also the macro @code{INIT_EXPANDERS}. This macro should be used to initialize the function pointer @code{init_machine_status}. This pointer is explained below. One typical use of per-function, target specific data is to create an RTX to hold the register containing the function's return address. This RTX can then be used to implement the @code{__builtin_return_address} function, for level 0. Note---earlier implementations of GCC used a single data area to hold all of the per-function information. Thus when processing of a nested function began the old per-function data had to be pushed onto a stack, and when the processing was finished, it had to be popped off the stack. GCC used to provide function pointers called @code{save_machine_status} and @code{restore_machine_status} to handle the saving and restoring of the target specific information. Since the single data area approach is no longer used, these pointers are no longer supported. The macro and function pointers are described below. @table @code @findex INIT_EXPANDERS @item INIT_EXPANDERS Macro called to initialize any target specific information. This macro is called once per function, before generation of any RTL has begun. The intention of this macro is to allow the initialization of the function pointers below. @findex init_machine_status @item init_machine_status This is a @code{void (*)(struct function *)} function pointer. If this pointer is non-@code{NULL} it will be called once per function, before function compilation starts, in order to allow the target to perform any target specific initialization of the @code{struct function} structure. It is intended that this would be used to initialize the @code{machine} of that structure. @code{struct machine_function} structures are expected to be freed by GC. Generally, any memory that they reference must be allocated by using @code{ggc_alloc}, including the structure itself. @end table @node Storage Layout @section Storage Layout @cindex storage layout Note that the definitions of the macros in this table which are sizes or alignments measured in bits do not need to be constant. They can be C expressions that refer to static variables, such as the @code{target_flags}. @xref{Run-time Target}. @table @code @findex BITS_BIG_ENDIAN @item BITS_BIG_ENDIAN Define this macro to have the value 1 if the most significant bit in a byte has the lowest number; otherwise define it to have the value zero. This means that bit-field instructions count from the most significant bit. If the machine has no bit-field instructions, then this must still be defined, but it doesn't matter which value it is defined to. This macro need not be a constant. This macro does not affect the way structure fields are packed into bytes or words; that is controlled by @code{BYTES_BIG_ENDIAN}. @findex BYTES_BIG_ENDIAN @item BYTES_BIG_ENDIAN Define this macro to have the value 1 if the most significant byte in a word has the lowest number. This macro need not be a constant. @findex WORDS_BIG_ENDIAN @item WORDS_BIG_ENDIAN Define this macro to have the value 1 if, in a multiword object, the most significant word has the lowest number. This applies to both memory locations and registers; GCC fundamentally assumes that the order of words in memory is the same as the order in registers. This macro need not be a constant. @findex LIBGCC2_WORDS_BIG_ENDIAN @item LIBGCC2_WORDS_BIG_ENDIAN Define this macro if @code{WORDS_BIG_ENDIAN} is not constant. This must be a constant value with the same meaning as @code{WORDS_BIG_ENDIAN}, which will be used only when compiling @file{libgcc2.c}. Typically the value will be set based on preprocessor defines. @findex FLOAT_WORDS_BIG_ENDIAN @item FLOAT_WORDS_BIG_ENDIAN Define this macro to have the value 1 if @code{DFmode}, @code{XFmode} or @code{TFmode} floating point numbers are stored in memory with the word containing the sign bit at the lowest address; otherwise define it to have the value 0. This macro need not be a constant. You need not define this macro if the ordering is the same as for multi-word integers. @findex BITS_PER_UNIT @item BITS_PER_UNIT Define this macro to be the number of bits in an addressable storage unit (byte). If you do not define this macro the default is 8. @findex BITS_PER_WORD @item BITS_PER_WORD Number of bits in a word. If you do not define this macro, the default is @code{BITS_PER_UNIT * UNITS_PER_WORD}. @findex MAX_BITS_PER_WORD @item MAX_BITS_PER_WORD Maximum number of bits in a word. If this is undefined, the default is @code{BITS_PER_WORD}. Otherwise, it is the constant value that is the largest value that @code{BITS_PER_WORD} can have at run-time. @findex UNITS_PER_WORD @item UNITS_PER_WORD Number of storage units in a word; normally 4. @findex MIN_UNITS_PER_WORD @item MIN_UNITS_PER_WORD Minimum number of units in a word. If this is undefined, the default is @code{UNITS_PER_WORD}. Otherwise, it is the constant value that is the smallest value that @code{UNITS_PER_WORD} can have at run-time. @findex POINTER_SIZE @item POINTER_SIZE Width of a pointer, in bits. You must specify a value no wider than the width of @code{Pmode}. If it is not equal to the width of @code{Pmode}, you must define @code{POINTERS_EXTEND_UNSIGNED}. If you do not specify a value the default is @code{BITS_PER_WORD}. @findex POINTERS_EXTEND_UNSIGNED @item POINTERS_EXTEND_UNSIGNED A C expression whose value is greater than zero if pointers that need to be extended from being @code{POINTER_SIZE} bits wide to @code{Pmode} are to be zero-extended and zero if they are to be sign-extended. If the value is less then zero then there must be an "ptr_extend" instruction that extends a pointer from @code{POINTER_SIZE} to @code{Pmode}. You need not define this macro if the @code{POINTER_SIZE} is equal to the width of @code{Pmode}. @findex PROMOTE_MODE @item PROMOTE_MODE (@var{m}, @var{unsignedp}, @var{type}) A macro to update @var{m} and @var{unsignedp} when an object whose type is @var{type} and which has the specified mode and signedness is to be stored in a register. This macro is only called when @var{type} is a scalar type. On most RISC machines, which only have operations that operate on a full register, define this macro to set @var{m} to @code{word_mode} if @var{m} is an integer mode narrower than @code{BITS_PER_WORD}. In most cases, only integer modes should be widened because wider-precision floating-point operations are usually more expensive than their narrower counterparts. For most machines, the macro definition does not change @var{unsignedp}. However, some machines, have instructions that preferentially handle either signed or unsigned quantities of certain modes. For example, on the DEC Alpha, 32-bit loads from memory and 32-bit add instructions sign-extend the result to 64 bits. On such machines, set @var{unsignedp} according to which kind of extension is more efficient. Do not define this macro if it would never modify @var{m}. @findex PROMOTE_FUNCTION_ARGS @item PROMOTE_FUNCTION_ARGS Define this macro if the promotion described by @code{PROMOTE_MODE} should also be done for outgoing function arguments. @findex PROMOTE_FUNCTION_RETURN @item PROMOTE_FUNCTION_RETURN Define this macro if the promotion described by @code{PROMOTE_MODE} should also be done for the return value of functions. If this macro is defined, @code{FUNCTION_VALUE} must perform the same promotions done by @code{PROMOTE_MODE}. @findex PROMOTE_FOR_CALL_ONLY @item PROMOTE_FOR_CALL_ONLY Define this macro if the promotion described by @code{PROMOTE_MODE} should @emph{only} be performed for outgoing function arguments or function return values, as specified by @code{PROMOTE_FUNCTION_ARGS} and @code{PROMOTE_FUNCTION_RETURN}, respectively. @findex PARM_BOUNDARY @item PARM_BOUNDARY Normal alignment required for function parameters on the stack, in bits. All stack parameters receive at least this much alignment regardless of data type. On most machines, this is the same as the size of an integer. @findex STACK_BOUNDARY @item STACK_BOUNDARY Define this macro to the minimum alignment enforced by hardware for the stack pointer on this machine. The definition is a C expression for the desired alignment (measured in bits). This value is used as a default if @code{PREFERRED_STACK_BOUNDARY} is not defined. On most machines, this should be the same as @code{PARM_BOUNDARY}. @findex PREFERRED_STACK_BOUNDARY @item PREFERRED_STACK_BOUNDARY Define this macro if you wish to preserve a certain alignment for the stack pointer, greater than what the hardware enforces. The definition is a C expression for the desired alignment (measured in bits). This macro must evaluate to a value equal to or larger than @code{STACK_BOUNDARY}. @findex FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN @item FORCE_PREFERRED_STACK_BOUNDARY_IN_MAIN A C expression that evaluates true if @code{PREFERRED_STACK_BOUNDARY} is not guaranteed by the runtime and we should emit code to align the stack at the beginning of @code{main}. @cindex @code{PUSH_ROUNDING}, interaction with @code{PREFERRED_STACK_BOUNDARY} If @code{PUSH_ROUNDING} is not defined, the stack will always be aligned to the specified boundary. If @code{PUSH_ROUNDING} is defined and specifies a less strict alignment than @code{PREFERRED_STACK_BOUNDARY}, the stack may be momentarily unaligned while pushing arguments. @findex FUNCTION_BOUNDARY @item FUNCTION_BOUNDARY Alignment required for a function entry point, in bits. @findex BIGGEST_ALIGNMENT @item BIGGEST_ALIGNMENT Biggest alignment that any data type can require on this machine, in bits. @findex MINIMUM_ATOMIC_ALIGNMENT @item MINIMUM_ATOMIC_ALIGNMENT If defined, the smallest alignment, in bits, that can be given to an object that can be referenced in one operation, without disturbing any nearby object. Normally, this is @code{BITS_PER_UNIT}, but may be larger on machines that don't have byte or half-word store operations. @findex BIGGEST_FIELD_ALIGNMENT @item BIGGEST_FIELD_ALIGNMENT Biggest alignment that any structure or union field can require on this machine, in bits. If defined, this overrides @code{BIGGEST_ALIGNMENT} for structure and union fields only, unless the field alignment has been set by the @code{__attribute__ ((aligned (@var{n})))} construct. @findex ADJUST_FIELD_ALIGN @item ADJUST_FIELD_ALIGN (@var{field}, @var{computed}) An expression for the alignment of a structure field @var{field} if the alignment computed in the usual way (including applying of @code{BIGGEST_ALIGNMENT} and @code{BIGGEST_FIELD_ALIGNMENT} to the alignment) is @var{computed}. It overrides alignment only if the field alignment has not been set by the @code{__attribute__ ((aligned (@var{n})))} construct. @findex MAX_OFILE_ALIGNMENT @item MAX_OFILE_ALIGNMENT Biggest alignment supported by the object file format of this machine. Use this macro to limit the alignment which can be specified using the @code{__attribute__ ((aligned (@var{n})))} construct. If not defined, the default value is @code{BIGGEST_ALIGNMENT}. @findex DATA_ALIGNMENT @item DATA_ALIGNMENT (@var{type}, @var{basic-align}) If defined, a C expression to compute the alignment for a variable in the static store. @var{type} is the data type, and @var{basic-align} is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. If this macro is not defined, then @var{basic-align} is used. @findex strcpy One use of this macro is to increase alignment of medium-size data to make it all fit in fewer cache lines. Another is to cause character arrays to be word-aligned so that @code{strcpy} calls that copy constants to character arrays can be done inline. @findex CONSTANT_ALIGNMENT @item CONSTANT_ALIGNMENT (@var{constant}, @var{basic-align}) If defined, a C expression to compute the alignment given to a constant that is being placed in memory. @var{constant} is the constant and @var{basic-align} is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. If this macro is not defined, then @var{basic-align} is used. The typical use of this macro is to increase alignment for string constants to be word aligned so that @code{strcpy} calls that copy constants can be done inline. @findex LOCAL_ALIGNMENT @item LOCAL_ALIGNMENT (@var{type}, @var{basic-align}) If defined, a C expression to compute the alignment for a variable in the local store. @var{type} is the data type, and @var{basic-align} is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. If this macro is not defined, then @var{basic-align} is used. One use of this macro is to increase alignment of medium-size data to make it all fit in fewer cache lines. @findex EMPTY_FIELD_BOUNDARY @item EMPTY_FIELD_BOUNDARY Alignment in bits to be given to a structure bit-field that follows an empty field such as @code{int : 0;}. Note that @code{PCC_BITFIELD_TYPE_MATTERS} also affects the alignment that results from an empty field. @findex STRUCTURE_SIZE_BOUNDARY @item STRUCTURE_SIZE_BOUNDARY Number of bits which any structure or union's size must be a multiple of. Each structure or union's size is rounded up to a multiple of this. If you do not define this macro, the default is the same as @code{BITS_PER_UNIT}. @findex STRICT_ALIGNMENT @item STRICT_ALIGNMENT Define this macro to be the value 1 if instructions will fail to work if given data not on the nominal alignment. If instructions will merely go slower in that case, define this macro as 0. @findex PCC_BITFIELD_TYPE_MATTERS @item PCC_BITFIELD_TYPE_MATTERS Define this if you wish to imitate the way many other C compilers handle alignment of bit-fields and the structures that contain them. The behavior is that the type written for a bit-field (@code{int}, @code{short}, or other integer type) imposes an alignment for the entire structure, as if the structure really did contain an ordinary field of that type. In addition, the bit-field is placed within the structure so that it would fit within such a field, not crossing a boundary for it. Thus, on most machines, a bit-field whose type is written as @code{int} would not cross a four-byte boundary, and would force four-byte alignment for the whole structure. (The alignment used may not be four bytes; it is controlled by the other alignment parameters.) If the macro is defined, its definition should be a C expression; a nonzero value for the expression enables this behavior. Note that if this macro is not defined, or its value is zero, some bit-fields may cross more than one alignment boundary. The compiler can support such references if there are @samp{insv}, @samp{extv}, and @samp{extzv} insns that can directly reference memory. The other known way of making bit-fields work is to define @code{STRUCTURE_SIZE_BOUNDARY} as large as @code{BIGGEST_ALIGNMENT}. Then every structure can be accessed with fullwords. Unless the machine has bit-field instructions or you define @code{STRUCTURE_SIZE_BOUNDARY} that way, you must define @code{PCC_BITFIELD_TYPE_MATTERS} to have a nonzero value. If your aim is to make GCC use the same conventions for laying out bit-fields as are used by another compiler, here is how to investigate what the other compiler does. Compile and run this program: @example struct foo1 @{ char x; char :0; char y; @}; struct foo2 @{ char x; int :0; char y; @}; main () @{ printf ("Size of foo1 is %d\n", sizeof (struct foo1)); printf ("Size of foo2 is %d\n", sizeof (struct foo2)); exit (0); @} @end example If this prints 2 and 5, then the compiler's behavior is what you would get from @code{PCC_BITFIELD_TYPE_MATTERS}. @findex BITFIELD_NBYTES_LIMITED @item BITFIELD_NBYTES_LIMITED Like @code{PCC_BITFIELD_TYPE_MATTERS} except that its effect is limited to aligning a bit-field within the structure. @findex MEMBER_TYPE_FORCES_BLK @item MEMBER_TYPE_FORCES_BLK (@var{field}, @var{mode}) Return 1 if a structure or array containing @var{field} should be accessed using @code{BLKMODE}. If @var{field} is the only field in the structure, @var{mode} is its mode, otherwise @var{mode} is VOIDmode. @var{mode} is provided in the case where structures of one field would require the structure's mode to retain the field's mode. Normally, this is not needed. See the file @file{c4x.h} for an example of how to use this macro to prevent a structure having a floating point field from being accessed in an integer mode. @findex ROUND_TYPE_SIZE @item ROUND_TYPE_SIZE (@var{type}, @var{computed}, @var{specified}) Define this macro as an expression for the overall size of a type (given by @var{type} as a tree node) when the size computed in the usual way is @var{computed} and the alignment is @var{specified}. The default is to round @var{computed} up to a multiple of @var{specified}. @findex ROUND_TYPE_SIZE_UNIT @item ROUND_TYPE_SIZE_UNIT (@var{type}, @var{computed}, @var{specified}) Similar to @code{ROUND_TYPE_SIZE}, but sizes and alignments are specified in units (bytes). If you define @code{ROUND_TYPE_SIZE}, you must also define this macro and they must be defined consistently with each other. @findex ROUND_TYPE_ALIGN @item ROUND_TYPE_ALIGN (@var{type}, @var{computed}, @var{specified}) Define this macro as an expression for the alignment of a type (given by @var{type} as a tree node) if the alignment computed in the usual way is @var{computed} and the alignment explicitly specified was @var{specified}. The default is to use @var{specified} if it is larger; otherwise, use the smaller of @var{computed} and @code{BIGGEST_ALIGNMENT} @findex MAX_FIXED_MODE_SIZE @item MAX_FIXED_MODE_SIZE An integer expression for the size in bits of the largest integer machine mode that should actually be used. All integer machine modes of this size or smaller can be used for structures and unions with the appropriate sizes. If this macro is undefined, @code{GET_MODE_BITSIZE (DImode)} is assumed. @findex VECTOR_MODE_SUPPORTED_P @item VECTOR_MODE_SUPPORTED_P(@var{mode}) Define this macro to be nonzero if the port is prepared to handle insns involving vector mode @var{mode}. At the very least, it must have move patterns for this mode. @findex STACK_SAVEAREA_MODE @item STACK_SAVEAREA_MODE (@var{save_level}) If defined, an expression of type @code{enum machine_mode} that specifies the mode of the save area operand of a @code{save_stack_@var{level}} named pattern (@pxref{Standard Names}). @var{save_level} is one of @code{SAVE_BLOCK}, @code{SAVE_FUNCTION}, or @code{SAVE_NONLOCAL} and selects which of the three named patterns is having its mode specified. You need not define this macro if it always returns @code{Pmode}. You would most commonly define this macro if the @code{save_stack_@var{level}} patterns need to support both a 32- and a 64-bit mode. @findex STACK_SIZE_MODE @item STACK_SIZE_MODE If defined, an expression of type @code{enum machine_mode} that specifies the mode of the size increment operand of an @code{allocate_stack} named pattern (@pxref{Standard Names}). You need not define this macro if it always returns @code{word_mode}. You would most commonly define this macro if the @code{allocate_stack} pattern needs to support both a 32- and a 64-bit mode. @findex TARGET_FLOAT_FORMAT @item TARGET_FLOAT_FORMAT A code distinguishing the floating point format of the target machine. There are five defined values: @table @code @findex IEEE_FLOAT_FORMAT @item IEEE_FLOAT_FORMAT This code indicates IEEE floating point. It is the default; there is no need to define this macro when the format is IEEE@. @findex VAX_FLOAT_FORMAT @item VAX_FLOAT_FORMAT This code indicates the ``F float'' (for @code{float}) and ``D float'' or ``G float'' formats (for @code{double}) used on the VAX and PDP-11@. @findex IBM_FLOAT_FORMAT @item IBM_FLOAT_FORMAT This code indicates the format used on the IBM System/370. @findex C4X_FLOAT_FORMAT @item C4X_FLOAT_FORMAT This code indicates the format used on the TMS320C3x/C4x. @findex UNKNOWN_FLOAT_FORMAT @item UNKNOWN_FLOAT_FORMAT This code indicates any other format. @end table If any other formats are actually in use on supported machines, new codes should be defined for them. The ordering of the component words of floating point values stored in memory is controlled by @code{FLOAT_WORDS_BIG_ENDIAN}. @findex MODE_HAS_NANS @item MODE_HAS_NANS (@var{mode}) When defined, this macro should be true if @var{mode} has a NaN representation. The compiler assumes that NaNs are not equal to anything (including themselves) and that addition, subtraction, multiplication and division all return NaNs when one operand is NaN@. By default, this macro is true if @var{mode} is a floating-point mode and the target floating-point format is IEEE@. @findex MODE_HAS_INFINITIES @item MODE_HAS_INFINITIES (@var{mode}) This macro should be true if @var{mode} can represent infinity. At present, the compiler uses this macro to decide whether @samp{x - x} is always defined. By default, the macro is true when @var{mode} is a floating-point mode and the target format is IEEE@. @findex MODE_HAS_SIGNED_ZEROS @item MODE_HAS_SIGNED_ZEROS (@var{mode}) True if @var{mode} distinguishes between positive and negative zero. The rules are expected to follow the IEEE standard: @itemize @bullet @item @samp{x + x} has the same sign as @samp{x}. @item If the sum of two values with opposite sign is zero, the result is positive for all rounding modes expect towards @minus{}infinity, for which it is negative. @item The sign of a product or quotient is negative when exactly one of the operands is negative. @end itemize The default definition is true if @var{mode} is a floating-point mode and the target format is IEEE@. @findex MODE_HAS_SIGN_DEPENDENT_ROUNDING @item MODE_HAS_SIGN_DEPENDENT_ROUNDING (@var{mode}) If defined, this macro should be true for @var{mode} if it has at least one rounding mode in which @samp{x} and @samp{-x} can be rounded to numbers of different magnitude. Two such modes are towards @minus{}infinity and towards +infinity. The default definition of this macro is true if @var{mode} is a floating-point mode and the target format is IEEE@. @findex ROUND_TOWARDS_ZERO @item ROUND_TOWARDS_ZERO If defined, this macro should be true if the prevailing rounding mode is towards zero. A true value has the following effects: @itemize @bullet @item @code{MODE_HAS_SIGN_DEPENDENT_ROUNDING} will be false for all modes. @item @file{libgcc.a}'s floating-point emulator will round towards zero rather than towards nearest. @item The compiler's floating-point emulator will round towards zero after doing arithmetic, and when converting from the internal float format to the target format. @end itemize The macro does not affect the parsing of string literals. When the primary rounding mode is towards zero, library functions like @code{strtod} might still round towards nearest, and the compiler's parser should behave like the target's @code{strtod} where possible. Not defining this macro is equivalent to returning zero. @findex LARGEST_EXPONENT_IS_NORMAL @item LARGEST_EXPONENT_IS_NORMAL (@var{size}) This macro should return true if floats with @var{size} bits do not have a NaN or infinity representation, but use the largest exponent for normal numbers instead. Defining this macro to true for @var{size} causes @code{MODE_HAS_NANS} and @code{MODE_HAS_INFINITIES} to be false for @var{size}-bit modes. It also affects the way @file{libgcc.a} and @file{real.c} emulate floating-point arithmetic. The default definition of this macro returns false for all sizes. @end table @deftypefn {Target Hook} bool TARGET_MS_BITFIELD_LAYOUT_P (tree @var{record_type}) This target hook returns @code{true} if bit-fields in the given @var{record_type} are to be laid out following the rules of Microsoft Visual C/C++, namely: (i) a bit-field won't share the same storage unit with the previous bit-field if their underlying types have different sizes, and the bit-field will be aligned to the highest alignment of the underlying types of itself and of the previous bit-field; (ii) a zero-sized bit-field will affect the alignment of the whole enclosing structure, even if it is unnamed; except that (iii) a zero-sized bit-field will be disregarded unless it follows another bit-field of non-zero size. If this hook returns @code{true}, other macros that control bit-field layout are ignored. When a bit-field is inserted into a packed record, the whole size of the underlying type is used by one or more same-size adjacent bit-fields (that is, if its long:3, 32 bits is used in the record, and any additional adjacent long bit-fields are packed into the same chunk of 32 bits. However, if the size changes, a new field of that size is allocated). In an unpacked record, this is the same as using alignment, but not equivalent when packing. If both MS bit-fields and @samp{__attribute__((packed))} are used, the latter will take precedence. If @samp{__attribute__((packed))} is used on a single field when MS bit-fields are in use, it will take precedence for that field, but the alignment of the rest of the structure may affect its placement. @end deftypefn @node Type Layout @section Layout of Source Language Data Types These macros define the sizes and other characteristics of the standard basic data types used in programs being compiled. Unlike the macros in the previous section, these apply to specific features of C and related languages, rather than to fundamental aspects of storage layout. @table @code @findex INT_TYPE_SIZE @item INT_TYPE_SIZE A C expression for the size in bits of the type @code{int} on the target machine. If you don't define this, the default is one word. @findex SHORT_TYPE_SIZE @item SHORT_TYPE_SIZE A C expression for the size in bits of the type @code{short} on the target machine. If you don't define this, the default is half a word. (If this would be less than one storage unit, it is rounded up to one unit.) @findex LONG_TYPE_SIZE @item LONG_TYPE_SIZE A C expression for the size in bits of the type @code{long} on the target machine. If you don't define this, the default is one word. @findex ADA_LONG_TYPE_SIZE @item ADA_LONG_TYPE_SIZE On some machines, the size used for the Ada equivalent of the type @code{long} by a native Ada compiler differs from that used by C. In that situation, define this macro to be a C expression to be used for the size of that type. If you don't define this, the default is the value of @code{LONG_TYPE_SIZE}. @findex MAX_LONG_TYPE_SIZE @item MAX_LONG_TYPE_SIZE Maximum number for the size in bits of the type @code{long} on the target machine. If this is undefined, the default is @code{LONG_TYPE_SIZE}. Otherwise, it is the constant value that is the largest value that @code{LONG_TYPE_SIZE} can have at run-time. This is used in @code{cpp}. @findex LONG_LONG_TYPE_SIZE @item LONG_LONG_TYPE_SIZE A C expression for the size in bits of the type @code{long long} on the target machine. If you don't define this, the default is two words. If you want to support GNU Ada on your machine, the value of this macro must be at least 64. @findex CHAR_TYPE_SIZE @item CHAR_TYPE_SIZE A C expression for the size in bits of the type @code{char} on the target machine. If you don't define this, the default is @code{BITS_PER_UNIT}. @findex BOOL_TYPE_SIZE @item BOOL_TYPE_SIZE A C expression for the size in bits of the C++ type @code{bool} and C99 type @code{_Bool} on the target machine. If you don't define this, and you probably shouldn't, the default is @code{CHAR_TYPE_SIZE}. @findex FLOAT_TYPE_SIZE @item FLOAT_TYPE_SIZE A C expression for the size in bits of the type @code{float} on the target machine. If you don't define this, the default is one word. @findex DOUBLE_TYPE_SIZE @item DOUBLE_TYPE_SIZE A C expression for the size in bits of the type @code{double} on the target machine. If you don't define this, the default is two words. @findex LONG_DOUBLE_TYPE_SIZE @item LONG_DOUBLE_TYPE_SIZE A C expression for the size in bits of the type @code{long double} on the target machine. If you don't define this, the default is two words. @findex MAX_LONG_DOUBLE_TYPE_SIZE Maximum number for the size in bits of the type @code{long double} on the target machine. If this is undefined, the default is @code{LONG_DOUBLE_TYPE_SIZE}. Otherwise, it is the constant value that is the largest value that @code{LONG_DOUBLE_TYPE_SIZE} can have at run-time. This is used in @code{cpp}. @findex TARGET_FLT_EVAL_METHOD @item TARGET_FLT_EVAL_METHOD A C expression for the value for @code{FLT_EVAL_METHOD} in @file{float.h}, assuming, if applicable, that the floating-point control word is in its default state. If you do not define this macro the value of @code{FLT_EVAL_METHOD} will be zero. @findex WIDEST_HARDWARE_FP_SIZE @item WIDEST_HARDWARE_FP_SIZE A C expression for the size in bits of the widest floating-point format supported by the hardware. If you define this macro, you must specify a value less than or equal to the value of @code{LONG_DOUBLE_TYPE_SIZE}. If you do not define this macro, the value of @code{LONG_DOUBLE_TYPE_SIZE} is the default. @findex DEFAULT_SIGNED_CHAR @item DEFAULT_SIGNED_CHAR An expression whose value is 1 or 0, according to whether the type @code{char} should be signed or unsigned by default. The user can always override this default with the options @option{-fsigned-char} and @option{-funsigned-char}. @findex DEFAULT_SHORT_ENUMS @item DEFAULT_SHORT_ENUMS A C expression to determine whether to give an @code{enum} type only as many bytes as it takes to represent the range of possible values of that type. A nonzero value means to do that; a zero value means all @code{enum} types should be allocated like @code{int}. If you don't define the macro, the default is 0. @findex SIZE_TYPE @item SIZE_TYPE A C expression for a string describing the name of the data type to use for size values. The typedef name @code{size_t} is defined using the contents of the string. The string can contain more than one keyword. If so, separate them with spaces, and write first any length keyword, then @code{unsigned} if appropriate, and finally @code{int}. The string must exactly match one of the data type names defined in the function @code{init_decl_processing} in the file @file{c-decl.c}. You may not omit @code{int} or change the order---that would cause the compiler to crash on startup. If you don't define this macro, the default is @code{"long unsigned int"}. @findex PTRDIFF_TYPE @item PTRDIFF_TYPE A C expression for a string describing the name of the data type to use for the result of subtracting two pointers. The typedef name @code{ptrdiff_t} is defined using the contents of the string. See @code{SIZE_TYPE} above for more information. If you don't define this macro, the default is @code{"long int"}. @findex WCHAR_TYPE @item WCHAR_TYPE A C expression for a string describing the name of the data type to use for wide characters. The typedef name @code{wchar_t} is defined using the contents of the string. See @code{SIZE_TYPE} above for more information. If you don't define this macro, the default is @code{"int"}. @findex WCHAR_TYPE_SIZE @item WCHAR_TYPE_SIZE A C expression for the size in bits of the data type for wide characters. This is used in @code{cpp}, which cannot make use of @code{WCHAR_TYPE}. @findex MAX_WCHAR_TYPE_SIZE @item MAX_WCHAR_TYPE_SIZE Maximum number for the size in bits of the data type for wide characters. If this is undefined, the default is @code{WCHAR_TYPE_SIZE}. Otherwise, it is the constant value that is the largest value that @code{WCHAR_TYPE_SIZE} can have at run-time. This is used in @code{cpp}. @findex GCOV_TYPE_SIZE @item GCOV_TYPE_SIZE A C expression for the size in bits of the type used for gcov counters on the target machine. If you don't define this, the default is one @code{LONG_TYPE_SIZE} in case it is greater or equal to 64-bit and @code{LONG_LONG_TYPE_SIZE} otherwise. You may want to re-define the type to ensure atomicity for counters in multithreaded programs. @findex WINT_TYPE @item WINT_TYPE A C expression for a string describing the name of the data type to use for wide characters passed to @code{printf} and returned from @code{getwc}. The typedef name @code{wint_t} is defined using the contents of the string. See @code{SIZE_TYPE} above for more information. If you don't define this macro, the default is @code{"unsigned int"}. @findex INTMAX_TYPE @item INTMAX_TYPE A C expression for a string describing the name of the data type that can represent any value of any standard or extended signed integer type. The typedef name @code{intmax_t} is defined using the contents of the string. See @code{SIZE_TYPE} above for more information. If you don't define this macro, the default is the first of @code{"int"}, @code{"long int"}, or @code{"long long int"} that has as much precision as @code{long long int}. @findex UINTMAX_TYPE @item UINTMAX_TYPE A C expression for a string describing the name of the data type that can represent any value of any standard or extended unsigned integer type. The typedef name @code{uintmax_t} is defined using the contents of the string. See @code{SIZE_TYPE} above for more information. If you don't define this macro, the default is the first of @code{"unsigned int"}, @code{"long unsigned int"}, or @code{"long long unsigned int"} that has as much precision as @code{long long unsigned int}. @findex TARGET_PTRMEMFUNC_VBIT_LOCATION @item TARGET_PTRMEMFUNC_VBIT_LOCATION The C++ compiler represents a pointer-to-member-function with a struct that looks like: @example struct @{ union @{ void (*fn)(); ptrdiff_t vtable_index; @}; ptrdiff_t delta; @}; @end example @noindent The C++ compiler must use one bit to indicate whether the function that will be called through a pointer-to-member-function is virtual. Normally, we assume that the low-order bit of a function pointer must always be zero. Then, by ensuring that the vtable_index is odd, we can distinguish which variant of the union is in use. But, on some platforms function pointers can be odd, and so this doesn't work. In that case, we use the low-order bit of the @code{delta} field, and shift the remainder of the @code{delta} field to the left. GCC will automatically make the right selection about where to store this bit using the @code{FUNCTION_BOUNDARY} setting for your platform. However, some platforms such as ARM/Thumb have @code{FUNCTION_BOUNDARY} set such that functions always start at even addresses, but the lowest bit of pointers to functions indicate whether the function at that address is in ARM or Thumb mode. If this is the case of your architecture, you should define this macro to @code{ptrmemfunc_vbit_in_delta}. In general, you should not have to define this macro. On architectures in which function addresses are always even, according to @code{FUNCTION_BOUNDARY}, GCC will automatically define this macro to @code{ptrmemfunc_vbit_in_pfn}. @findex TARGET_VTABLE_USES_DESCRIPTORS @item TARGET_VTABLE_USES_DESCRIPTORS Normally, the C++ compiler uses function pointers in vtables. This macro allows the target to change to use ``function descriptors'' instead. Function descriptors are found on targets for whom a function pointer is actually a small data structure. Normally the data structure consists of the actual code address plus a data pointer to which the function's data is relative. If vtables are used, the value of this macro should be the number of words that the function descriptor occupies. @findex TARGET_VTABLE_ENTRY_ALIGN @item TARGET_VTABLE_ENTRY_ALIGN By default, the vtable entries are void pointers, the so the alignment is the same as pointer alignment. The value of this macro specifies the alignment of the vtable entry in bits. It should be defined only when special alignment is necessary. */ @findex TARGET_VTABLE_DATA_ENTRY_DISTANCE @item TARGET_VTABLE_DATA_ENTRY_DISTANCE There are a few non-descriptor entries in the vtable at offsets below zero. If these entries must be padded (say, to preserve the alignment specified by @code{TARGET_VTABLE_ENTRY_ALIGN}), set this to the number of words in each data entry. @end table @node Escape Sequences @section Target Character Escape Sequences @cindex escape sequences By default, GCC assumes that the C character escape sequences take on their ASCII values for the target. If this is not correct, you must explicitly define all of the macros below. @table @code @findex TARGET_BELL @item TARGET_BELL A C constant expression for the integer value for escape sequence @samp{\a}. @findex TARGET_ESC @item TARGET_ESC A C constant expression for the integer value of the target escape character. As an extension, GCC evaluates the escape sequences @samp{\e} and @samp{\E} to this. @findex TARGET_TAB @findex TARGET_BS @findex TARGET_NEWLINE @item TARGET_BS @itemx TARGET_TAB @itemx TARGET_NEWLINE C constant expressions for the integer values for escape sequences @samp{\b}, @samp{\t} and @samp{\n}. @findex TARGET_VT @findex TARGET_FF @findex TARGET_CR @item TARGET_VT @itemx TARGET_FF @itemx TARGET_CR C constant expressions for the integer values for escape sequences @samp{\v}, @samp{\f} and @samp{\r}. @end table @node Registers @section Register Usage @cindex register usage This section explains how to describe what registers the target machine has, and how (in general) they can be used. The description of which registers a specific instruction can use is done with register classes; see @ref{Register Classes}. For information on using registers to access a stack frame, see @ref{Frame Registers}. For passing values in registers, see @ref{Register Arguments}. For returning values in registers, see @ref{Scalar Return}. @menu * Register Basics:: Number and kinds of registers. * Allocation Order:: Order in which registers are allocated. * Values in Registers:: What kinds of values each reg can hold. * Leaf Functions:: Renumbering registers for leaf functions. * Stack Registers:: Handling a register stack such as 80387. @end menu @node Register Basics @subsection Basic Characteristics of Registers @c prevent bad page break with this line Registers have various characteristics. @table @code @findex FIRST_PSEUDO_REGISTER @item FIRST_PSEUDO_REGISTER Number of hardware registers known to the compiler. They receive numbers 0 through @code{FIRST_PSEUDO_REGISTER-1}; thus, the first pseudo register's number really is assigned the number @code{FIRST_PSEUDO_REGISTER}. @item FIXED_REGISTERS @findex FIXED_REGISTERS @cindex fixed register An initializer that says which registers are used for fixed purposes all throughout the compiled code and are therefore not available for general allocation. These would include the stack pointer, the frame pointer (except on machines where that can be used as a general register when no frame pointer is needed), the program counter on machines where that is considered one of the addressable registers, and any other numbered register with a standard use. This information is expressed as a sequence of numbers, separated by commas and surrounded by braces. The @var{n}th number is 1 if register @var{n} is fixed, 0 otherwise. The table initialized from this macro, and the table initialized by the following one, may be overridden at run time either automatically, by the actions of the macro @code{CONDITIONAL_REGISTER_USAGE}, or by the user with the command options @option{-ffixed-@var{reg}}, @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}}. @findex CALL_USED_REGISTERS @item CALL_USED_REGISTERS @cindex call-used register @cindex call-clobbered register @cindex call-saved register Like @code{FIXED_REGISTERS} but has 1 for each register that is clobbered (in general) by function calls as well as for fixed registers. This macro therefore identifies the registers that are not available for general allocation of values that must live across function calls. If a register has 0 in @code{CALL_USED_REGISTERS}, the compiler automatically saves it on function entry and restores it on function exit, if the register is used within the function. @findex CALL_REALLY_USED_REGISTERS @item CALL_REALLY_USED_REGISTERS @cindex call-used register @cindex call-clobbered register @cindex call-saved register Like @code{CALL_USED_REGISTERS} except this macro doesn't require that the entire set of @code{FIXED_REGISTERS} be included. (@code{CALL_USED_REGISTERS} must be a superset of @code{FIXED_REGISTERS}). This macro is optional. If not specified, it defaults to the value of @code{CALL_USED_REGISTERS}. @findex HARD_REGNO_CALL_PART_CLOBBERED @item HARD_REGNO_CALL_PART_CLOBBERED (@var{regno}, @var{mode}) @cindex call-used register @cindex call-clobbered register @cindex call-saved register A C expression that is nonzero if it is not permissible to store a value of mode @var{mode} in hard register number @var{regno} across a call without some part of it being clobbered. For most machines this macro need not be defined. It is only required for machines that do not preserve the entire contents of a register across a call. @findex CONDITIONAL_REGISTER_USAGE @findex fixed_regs @findex call_used_regs @item CONDITIONAL_REGISTER_USAGE Zero or more C statements that may conditionally modify five variables @code{fixed_regs}, @code{call_used_regs}, @code{global_regs}, @code{reg_names}, and @code{reg_class_contents}, to take into account any dependence of these register sets on target flags. The first three of these are of type @code{char []} (interpreted as Boolean vectors). @code{global_regs} is a @code{const char *[]}, and @code{reg_class_contents} is a @code{HARD_REG_SET}. Before the macro is called, @code{fixed_regs}, @code{call_used_regs}, @code{reg_class_contents}, and @code{reg_names} have been initialized from @code{FIXED_REGISTERS}, @code{CALL_USED_REGISTERS}, @code{REG_CLASS_CONTENTS}, and @code{REGISTER_NAMES}, respectively. @code{global_regs} has been cleared, and any @option{-ffixed-@var{reg}}, @option{-fcall-used-@var{reg}} and @option{-fcall-saved-@var{reg}} command options have been applied. You need not define this macro if it has no work to do. @cindex disabling certain registers @cindex controlling register usage If the usage of an entire class of registers depends on the target flags, you may indicate this to GCC by using this macro to modify @code{fixed_regs} and @code{call_used_regs} to 1 for each of the registers in the classes which should not be used by GCC@. Also define the macro @code{REG_CLASS_FROM_LETTER} to return @code{NO_REGS} if it is called with a letter for a class that shouldn't be used. (However, if this class is not included in @code{GENERAL_REGS} and all of the insn patterns whose constraints permit this class are controlled by target switches, then GCC will automatically avoid using these registers when the target switches are opposed to them.) @findex NON_SAVING_SETJMP @item NON_SAVING_SETJMP If this macro is defined and has a nonzero value, it means that @code{setjmp} and related functions fail to save the registers, or that @code{longjmp} fails to restore them. To compensate, the compiler avoids putting variables in registers in functions that use @code{setjmp}. @findex INCOMING_REGNO @item INCOMING_REGNO (@var{out}) Define this macro if the target machine has register windows. This C expression returns the register number as seen by the called function corresponding to the register number @var{out} as seen by the calling function. Return @var{out} if register number @var{out} is not an outbound register. @findex OUTGOING_REGNO @item OUTGOING_REGNO (@var{in}) Define this macro if the target machine has register windows. This C expression returns the register number as seen by the calling function corresponding to the register number @var{in} as seen by the called function. Return @var{in} if register number @var{in} is not an inbound register. @findex LOCAL_REGNO @item LOCAL_REGNO (@var{regno}) Define this macro if the target machine has register windows. This C expression returns true if the register is call-saved but is in the register window. Unlike most call-saved registers, such registers need not be explicitly restored on function exit or during non-local gotos. @ignore @findex PC_REGNUM @item PC_REGNUM If the program counter has a register number, define this as that register number. Otherwise, do not define it. @end ignore @end table @node Allocation Order @subsection Order of Allocation of Registers @cindex order of register allocation @cindex register allocation order @c prevent bad page break with this line Registers are allocated in order. @table @code @findex REG_ALLOC_ORDER @item REG_ALLOC_ORDER If defined, an initializer for a vector of integers, containing the numbers of hard registers in the order in which GCC should prefer to use them (from most preferred to least). If this macro is not defined, registers are used lowest numbered first (all else being equal). One use of this macro is on machines where the highest numbered registers must always be saved and the save-multiple-registers instruction supports only sequences of consecutive registers. On such machines, define @code{REG_ALLOC_ORDER} to be an initializer that lists the highest numbered allocable register first. @findex ORDER_REGS_FOR_LOCAL_ALLOC @item ORDER_REGS_FOR_LOCAL_ALLOC A C statement (sans semicolon) to choose the order in which to allocate hard registers for pseudo-registers local to a basic block. Store the desired register order in the array @code{reg_alloc_order}. Element 0 should be the register to allocate first; element 1, the next register; and so on. The macro body should not assume anything about the contents of @code{reg_alloc_order} before execution of the macro. On most machines, it is not necessary to define this macro. @end table @node Values in Registers @subsection How Values Fit in Registers This section discusses the macros that describe which kinds of values (specifically, which machine modes) each register can hold, and how many consecutive registers are needed for a given mode. @table @code @findex HARD_REGNO_NREGS @item HARD_REGNO_NREGS (@var{regno}, @var{mode}) A C expression for the number of consecutive hard registers, starting at register number @var{regno}, required to hold a value of mode @var{mode}. On a machine where all registers are exactly one word, a suitable definition of this macro is @smallexample #define HARD_REGNO_NREGS(REGNO, MODE) \ ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ / UNITS_PER_WORD) @end smallexample @findex HARD_REGNO_MODE_OK @item HARD_REGNO_MODE_OK (@var{regno}, @var{mode}) A C expression that is nonzero if it is permissible to store a value of mode @var{mode} in hard register number @var{regno} (or in several registers starting with that one). For a machine where all registers are equivalent, a suitable definition is @smallexample #define HARD_REGNO_MODE_OK(REGNO, MODE) 1 @end smallexample You need not include code to check for the numbers of fixed registers, because the allocation mechanism considers them to be always occupied. @cindex register pairs On some machines, double-precision values must be kept in even/odd register pairs. You can implement that by defining this macro to reject odd register numbers for such modes. The minimum requirement for a mode to be OK in a register is that the @samp{mov@var{mode}} instruction pattern support moves between the register and other hard register in the same class and that moving a value into the register and back out not alter it. Since the same instruction used to move @code{word_mode} will work for all narrower integer modes, it is not necessary on any machine for @code{HARD_REGNO_MODE_OK} to distinguish between these modes, provided you define patterns @samp{movhi}, etc., to take advantage of this. This is useful because of the interaction between @code{HARD_REGNO_MODE_OK} and @code{MODES_TIEABLE_P}; it is very desirable for all integer modes to be tieable. Many machines have special registers for floating point arithmetic. Often people assume that floating point machine modes are allowed only in floating point registers. This is not true. Any registers that can hold integers can safely @emph{hold} a floating point machine mode, whether or not floating arithmetic can be done on it in those registers. Integer move instructions can be used to move the values. On some machines, though, the converse is true: fixed-point machine modes may not go in floating registers. This is true if the floating registers normalize any value stored in them, because storing a non-floating value there would garble it. In this case, @code{HARD_REGNO_MODE_OK} should reject fixed-point machine modes in floating registers. But if the floating registers do not automatically normalize, if you can store any bit pattern in one and retrieve it unchanged without a trap, then any machine mode may go in a floating register, so you can define this macro to say so. The primary significance of special floating registers is rather that they are the registers acceptable in floating point arithmetic instructions. However, this is of no concern to @code{HARD_REGNO_MODE_OK}. You handle it by writing the proper constraints for those instructions. On some machines, the floating registers are especially slow to access, so that it is better to store a value in a stack frame than in such a register if floating point arithmetic is not being done. As long as the floating registers are not in class @code{GENERAL_REGS}, they will not be used unless some pattern's constraint asks for one. @findex MODES_TIEABLE_P @item MODES_TIEABLE_P (@var{mode1}, @var{mode2}) A C expression that is nonzero if a value of mode @var{mode1} is accessible in mode @var{mode2} without copying. If @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode1})} and @code{HARD_REGNO_MODE_OK (@var{r}, @var{mode2})} are always the same for any @var{r}, then @code{MODES_TIEABLE_P (@var{mode1}, @var{mode2})} should be nonzero. If they differ for any @var{r}, you should define this macro to return zero unless some other mechanism ensures the accessibility of the value in a narrower mode. You should define this macro to return nonzero in as many cases as possible since doing so will allow GCC to perform better register allocation. @findex AVOID_CCMODE_COPIES @item AVOID_CCMODE_COPIES Define this macro if the compiler should avoid copies to/from @code{CCmode} registers. You should only define this macro if support for copying to/from @code{CCmode} is incomplete. @end table @node Leaf Functions @subsection Handling Leaf Functions @cindex leaf functions @cindex functions, leaf On some machines, a leaf function (i.e., one which makes no calls) can run more efficiently if it does not make its own register window. Often this means it is required to receive its arguments in the registers where they are passed by the caller, instead of the registers where they would normally arrive. The special treatment for leaf functions generally applies only when other conditions are met; for example, often they may use only those registers for its own variables and temporaries. We use the term ``leaf function'' to mean a function that is suitable for this special handling, so that functions with no calls are not necessarily ``leaf functions''. GCC assigns register numbers before it knows whether the function is suitable for leaf function treatment. So it needs to renumber the registers in order to output a leaf function. The following macros accomplish this. @table @code @findex LEAF_REGISTERS @item LEAF_REGISTERS Name of a char vector, indexed by hard register number, which contains 1 for a register that is allowable in a candidate for leaf function treatment. If leaf function treatment involves renumbering the registers, then the registers marked here should be the ones before renumbering---those that GCC would ordinarily allocate. The registers which will actually be used in the assembler code, after renumbering, should not be marked with 1 in this vector. Define this macro only if the target machine offers a way to optimize the treatment of leaf functions. @findex LEAF_REG_REMAP @item LEAF_REG_REMAP (@var{regno}) A C expression whose value is the register number to which @var{regno} should be renumbered, when a function is treated as a leaf function. If @var{regno} is a register number which should not appear in a leaf function before renumbering, then the expression should yield @minus{}1, which will cause the compiler to abort. Define this macro only if the target machine offers a way to optimize the treatment of leaf functions, and registers need to be renumbered to do this. @end table @findex current_function_is_leaf @findex current_function_uses_only_leaf_regs @code{TARGET_ASM_FUNCTION_PROLOGUE} and @code{TARGET_ASM_FUNCTION_EPILOGUE} must usually treat leaf functions specially. They can test the C variable @code{current_function_is_leaf} which is nonzero for leaf functions. @code{current_function_is_leaf} is set prior to local register allocation and is valid for the remaining compiler passes. They can also test the C variable @code{current_function_uses_only_leaf_regs} which is nonzero for leaf functions which only use leaf registers. @code{current_function_uses_only_leaf_regs} is valid after reload and is only useful if @code{LEAF_REGISTERS} is defined. @c changed this to fix overfull. ALSO: why the "it" at the beginning @c of the next paragraph?! --mew 2feb93 @node Stack Registers @subsection Registers That Form a Stack There are special features to handle computers where some of the ``registers'' form a stack, as in the 80387 coprocessor for the 80386. Stack registers are normally written by pushing onto the stack, and are numbered relative to the top of the stack. Currently, GCC can only handle one group of stack-like registers, and they must be consecutively numbered. @table @code @findex STACK_REGS @item STACK_REGS Define this if the machine has any stack-like registers. @findex FIRST_STACK_REG @item FIRST_STACK_REG The number of the first stack-like register. This one is the top of the stack. @findex LAST_STACK_REG @item LAST_STACK_REG The number of the last stack-like register. This one is the bottom of the stack. @end table @node Register Classes @section Register Classes @cindex register class definitions @cindex class definitions, register On many machines, the numbered registers are not all equivalent. For example, certain registers may not be allowed for indexed addressing; certain registers may not be allowed in some instructions. These machine restrictions are described to the compiler using @dfn{register classes}. You define a number of register classes, giving each one a name and saying which of the registers belong to it. Then you can specify register classes that are allowed as operands to particular instruction patterns. @findex ALL_REGS @findex NO_REGS In general, each register will belong to several classes. In fact, one class must be named @code{ALL_REGS} and contain all the registers. Another class must be named @code{NO_REGS} and contain no registers. Often the union of two classes will be another class; however, this is not required. @findex GENERAL_REGS One of the classes must be named @code{GENERAL_REGS}. There is nothing terribly special about the name, but the operand constraint letters @samp{r} and @samp{g} specify this class. If @code{GENERAL_REGS} is the same as @code{ALL_REGS}, just define it as a macro which expands to @code{ALL_REGS}. Order the classes so that if class @var{x} is contained in class @var{y} then @var{x} has a lower class number than @var{y}. The way classes other than @code{GENERAL_REGS} are specified in operand constraints is through machine-dependent operand constraint letters. You can define such letters to correspond to various classes, then use them in operand constraints. You should define a class for the union of two classes whenever some instruction allows both classes. For example, if an instruction allows either a floating point (coprocessor) register or a general register for a certain operand, you should define a class @code{FLOAT_OR_GENERAL_REGS} which includes both of them. Otherwise you will get suboptimal code. You must also specify certain redundant information about the register classes: for each class, which classes contain it and which ones are contained in it; for each pair of classes, the largest class contained in their union. When a value occupying several consecutive registers is expected in a certain class, all the registers used must belong to that class. Therefore, register classes cannot be used to enforce a requirement for a register pair to start with an even-numbered register. The way to specify this requirement is with @code{HARD_REGNO_MODE_OK}. Register classes used for input-operands of bitwise-and or shift instructions have a special requirement: each such class must have, for each fixed-point machine mode, a subclass whose registers can transfer that mode to or from memory. For example, on some machines, the operations for single-byte values (@code{QImode}) are limited to certain registers. When this is so, each register class that is used in a bitwise-and or shift instruction must have a subclass consisting of registers from which single-byte values can be loaded or stored. This is so that @code{PREFERRED_RELOAD_CLASS} can always have a possible value to return. @table @code @findex enum reg_class @item enum reg_class An enumeral type that must be defined with all the register class names as enumeral values. @code{NO_REGS} must be first. @code{ALL_REGS} must be the last register class, followed by one more enumeral value, @code{LIM_REG_CLASSES}, which is not a register class but rather tells how many classes there are. Each register class has a number, which is the value of casting the class name to type @code{int}. The number serves as an index in many of the tables described below. @findex N_REG_CLASSES @item N_REG_CLASSES The number of distinct register classes, defined as follows: @example #define N_REG_CLASSES (int) LIM_REG_CLASSES @end example @findex REG_CLASS_NAMES @item REG_CLASS_NAMES An initializer containing the names of the register classes as C string constants. These names are used in writing some of the debugging dumps. @findex REG_CLASS_CONTENTS @item REG_CLASS_CONTENTS An initializer containing the contents of the register classes, as integers which are bit masks. The @var{n}th integer specifies the contents of class @var{n}. The way the integer @var{mask} is interpreted is that register @var{r} is in the class if @code{@var{mask} & (1 << @var{r})} is 1. When the machine has more than 32 registers, an integer does not suffice. Then the integers are replaced by sub-initializers, braced groupings containing several integers. Each sub-initializer must be suitable as an initializer for the type @code{HARD_REG_SET} which is defined in @file{hard-reg-set.h}. In this situation, the first integer in each sub-initializer corresponds to registers 0 through 31, the second integer to registers 32 through 63, and so on. @findex REGNO_REG_CLASS @item REGNO_REG_CLASS (@var{regno}) A C expression whose value is a register class containing hard register @var{regno}. In general there is more than one such class; choose a class which is @dfn{minimal}, meaning that no smaller class also contains the register. @findex BASE_REG_CLASS @item BASE_REG_CLASS A macro whose definition is the name of the class to which a valid base register must belong. A base register is one used in an address which is the register value plus a displacement. @findex MODE_BASE_REG_CLASS @item MODE_BASE_REG_CLASS (@var{mode}) This is a variation of the @code{BASE_REG_CLASS} macro which allows the selection of a base register in a mode depenedent manner. If @var{mode} is VOIDmode then it should return the same value as @code{BASE_REG_CLASS}. @findex INDEX_REG_CLASS @item INDEX_REG_CLASS A macro whose definition is the name of the class to which a valid index register must belong. An index register is one used in an address where its value is either multiplied by a scale factor or added to another register (as well as added to a displacement). @findex REG_CLASS_FROM_LETTER @item REG_CLASS_FROM_LETTER (@var{char}) A C expression which defines the machine-dependent operand constraint letters for register classes. If @var{char} is such a letter, the value should be the register class corresponding to it. Otherwise, the value should be @code{NO_REGS}. The register letter @samp{r}, corresponding to class @code{GENERAL_REGS}, will not be passed to this macro; you do not need to handle it. @findex REGNO_OK_FOR_BASE_P @item REGNO_OK_FOR_BASE_P (@var{num}) A C expression which is nonzero if register number @var{num} is suitable for use as a base register in operand addresses. It may be either a suitable hard register or a pseudo register that has been allocated such a hard register. @findex REGNO_MODE_OK_FOR_BASE_P @item REGNO_MODE_OK_FOR_BASE_P (@var{num}, @var{mode}) A C expression that is just like @code{REGNO_OK_FOR_BASE_P}, except that that expression may examine the mode of the memory reference in @var{mode}. You should define this macro if the mode of the memory reference affects whether a register may be used as a base register. If you define this macro, the compiler will use it instead of @code{REGNO_OK_FOR_BASE_P}. @findex REGNO_OK_FOR_INDEX_P @item REGNO_OK_FOR_INDEX_P (@var{num}) A C expression which is nonzero if register number @var{num} is suitable for use as an index register in operand addresses. It may be either a suitable hard register or a pseudo register that has been allocated such a hard register. The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two registers, neither one of them scaled, then either one may be labeled the ``base'' and the other the ``index''; but whichever labeling is used must fit the machine's constraints of which registers may serve in each capacity. The compiler will try both labelings, looking for one that is valid, and will reload one or both registers only if neither labeling works. @findex PREFERRED_RELOAD_CLASS @item PREFERRED_RELOAD_CLASS (@var{x}, @var{class}) A C expression that places additional restrictions on the register class to use when it is necessary to copy value @var{x} into a register in class @var{class}. The value is a register class; perhaps @var{class}, or perhaps another, smaller class. On many machines, the following definition is safe: @example #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS @end example Sometimes returning a more restrictive class makes better code. For example, on the 68000, when @var{x} is an integer constant that is in range for a @samp{moveq} instruction, the value of this macro is always @code{DATA_REGS} as long as @var{class} includes the data registers. Requiring a data register guarantees that a @samp{moveq} will be used. If @var{x} is a @code{const_double}, by returning @code{NO_REGS} you can force @var{x} into a memory constant. This is useful on certain machines where immediate floating values cannot be loaded into certain kinds of registers. @findex PREFERRED_OUTPUT_RELOAD_CLASS @item PREFERRED_OUTPUT_RELOAD_CLASS (@var{x}, @var{class}) Like @code{PREFERRED_RELOAD_CLASS}, but for output reloads instead of input reloads. If you don't define this macro, the default is to use @var{class}, unchanged. @findex LIMIT_RELOAD_CLASS @item LIMIT_RELOAD_CLASS (@var{mode}, @var{class}) A C expression that places additional restrictions on the register class to use when it is necessary to be able to hold a value of mode @var{mode} in a reload register for which class @var{class} would ordinarily be used. Unlike @code{PREFERRED_RELOAD_CLASS}, this macro should be used when there are certain modes that simply can't go in certain reload classes. The value is a register class; perhaps @var{class}, or perhaps another, smaller class. Don't define this macro unless the target machine has limitations which require the macro to do something nontrivial. @findex SECONDARY_RELOAD_CLASS @findex SECONDARY_INPUT_RELOAD_CLASS @findex SECONDARY_OUTPUT_RELOAD_CLASS @item SECONDARY_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) @itemx SECONDARY_INPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) @itemx SECONDARY_OUTPUT_RELOAD_CLASS (@var{class}, @var{mode}, @var{x}) Many machines have some registers that cannot be copied directly to or from memory or even from other types of registers. An example is the @samp{MQ} register, which on most machines, can only be copied to or from general registers, but not memory. Some machines allow copying all registers to and from memory, but require a scratch register for stores to some memory locations (e.g., those with symbolic address on the RT, and those with certain symbolic address on the SPARC when compiling PIC)@. In some cases, both an intermediate and a scratch register are required. You should define these macros to indicate to the reload phase that it may need to allocate at least one register for a reload in addition to the register to contain the data. Specifically, if copying @var{x} to a register @var{class} in @var{mode} requires an intermediate register, you should define @code{SECONDARY_INPUT_RELOAD_CLASS} to return the largest register class all of whose registers can be used as intermediate registers or scratch registers. If copying a register @var{class} in @var{mode} to @var{x} requires an intermediate or scratch register, @code{SECONDARY_OUTPUT_RELOAD_CLASS} should be defined to return the largest register class required. If the requirements for input and output reloads are the same, the macro @code{SECONDARY_RELOAD_CLASS} should be used instead of defining both macros identically. The values returned by these macros are often @code{GENERAL_REGS}. Return @code{NO_REGS} if no spare register is needed; i.e., if @var{x} can be directly copied to or from a register of @var{class} in @var{mode} without requiring a scratch register. Do not define this macro if it would always return @code{NO_REGS}. If a scratch register is required (either with or without an intermediate register), you should define patterns for @samp{reload_in@var{m}} or @samp{reload_out@var{m}}, as required (@pxref{Standard Names}. These patterns, which will normally be implemented with a @code{define_expand}, should be similar to the @samp{mov@var{m}} patterns, except that operand 2 is the scratch register. Define constraints for the reload register and scratch register that contain a single register class. If the original reload register (whose class is @var{class}) can meet the constraint given in the pattern, the value returned by these macros is used for the class of the scratch register. Otherwise, two additional reload registers are required. Their classes are obtained from the constraints in the insn pattern. @var{x} might be a pseudo-register or a @code{subreg} of a pseudo-register, which could either be in a hard register or in memory. Use @code{true_regnum} to find out; it will return @minus{}1 if the pseudo is in memory and the hard register number if it is in a register. These macros should not be used in the case where a particular class of registers can only be copied to memory and not to another class of registers. In that case, secondary reload registers are not needed and would not be helpful. Instead, a stack location must be used to perform the copy and the @code{mov@var{m}} pattern should use memory as an intermediate storage. This case often occurs between floating-point and general registers. @findex SECONDARY_MEMORY_NEEDED @item SECONDARY_MEMORY_NEEDED (@var{class1}, @var{class2}, @var{m}) Certain machines have the property that some registers cannot be copied to some other registers without using memory. Define this macro on those machines to be a C expression that is nonzero if objects of mode @var{m} in registers of @var{class1} can only be copied to registers of class @var{class2} by storing a register of @var{class1} into memory and loading that memory location into a register of @var{class2}. Do not define this macro if its value would always be zero. @findex SECONDARY_MEMORY_NEEDED_RTX @item SECONDARY_MEMORY_NEEDED_RTX (@var{mode}) Normally when @code{SECONDARY_MEMORY_NEEDED} is defined, the compiler allocates a stack slot for a memory location needed for register copies. If this macro is defined, the compiler instead uses the memory location defined by this macro. Do not define this macro if you do not define @code{SECONDARY_MEMORY_NEEDED}. @findex SECONDARY_MEMORY_NEEDED_MODE @item SECONDARY_MEMORY_NEEDED_MODE (@var{mode}) When the compiler needs a secondary memory location to copy between two registers of mode @var{mode}, it normally allocates sufficient memory to hold a quantity of @code{BITS_PER_WORD} bits and performs the store and load operations in a mode that many bits wide and whose class is the same as that of @var{mode}. This is right thing to do on most machines because it ensures that all bits of the register are copied and prevents accesses to the registers in a narrower mode, which some machines prohibit for floating-point registers. However, this default behavior is not correct on some machines, such as the DEC Alpha, that store short integers in floating-point registers differently than in integer registers. On those machines, the default widening will not work correctly and you must define this macro to suppress that widening in some cases. See the file @file{alpha.h} for details. Do not define this macro if you do not define @code{SECONDARY_MEMORY_NEEDED} or if widening @var{mode} to a mode that is @code{BITS_PER_WORD} bits wide is correct for your machine. @findex SMALL_REGISTER_CLASSES @item SMALL_REGISTER_CLASSES On some machines, it is risky to let hard registers live across arbitrary insns. Typically, these machines have instructions that require values to be in specific registers (like an accumulator), and reload will fail if the required hard register is used for another purpose across such an insn. Define @code{SMALL_REGISTER_CLASSES} to be an expression with a nonzero value on these machines. When this macro has a nonzero value, the compiler will try to minimize the lifetime of hard registers. It is always safe to define this macro with a nonzero value, but if you unnecessarily define it, you will reduce the amount of optimizations that can be performed in some cases. If you do not define this macro with a nonzero value when it is required, the compiler will run out of spill registers and print a fatal error message. For most machines, you should not define this macro at all. @findex CLASS_LIKELY_SPILLED_P @item CLASS_LIKELY_SPILLED_P (@var{class}) A C expression whose value is nonzero if pseudos that have been assigned to registers of class @var{class} would likely be spilled because registers of @var{class} are needed for spill registers. The default value of this macro returns 1 if @var{class} has exactly one register and zero otherwise. On most machines, this default should be used. Only define this macro to some other expression if pseudos allocated by @file{local-alloc.c} end up in memory because their hard registers were needed for spill registers. If this macro returns nonzero for those classes, those pseudos will only be allocated by @file{global.c}, which knows how to reallocate the pseudo to another register. If there would not be another register available for reallocation, you should not change the definition of this macro since the only effect of such a definition would be to slow down register allocation. @findex CLASS_MAX_NREGS @item CLASS_MAX_NREGS (@var{class}, @var{mode}) A C expression for the maximum number of consecutive registers of class @var{class} needed to hold a value of mode @var{mode}. This is closely related to the macro @code{HARD_REGNO_NREGS}. In fact, the value of the macro @code{CLASS_MAX_NREGS (@var{class}, @var{mode})} should be the maximum value of @code{HARD_REGNO_NREGS (@var{regno}, @var{mode})} for all @var{regno} values in the class @var{class}. This macro helps control the handling of multiple-word values in the reload pass. @item CLASS_CANNOT_CHANGE_MODE If defined, a C expression for a class that contains registers for which the compiler may not change modes arbitrarily. @item CLASS_CANNOT_CHANGE_MODE_P(@var{from}, @var{to}) A C expression that is true if, for a register in @code{CLASS_CANNOT_CHANGE_MODE}, the requested mode punning is invalid. For the example, loading 32-bit integer or floating-point objects into floating-point registers on the Alpha extends them to 64 bits. Therefore loading a 64-bit object and then storing it as a 32-bit object does not store the low-order 32 bits, as would be the case for a normal register. Therefore, @file{alpha.h} defines @code{CLASS_CANNOT_CHANGE_MODE} as @code{FLOAT_REGS} and @code{CLASS_CANNOT_CHANGE_MODE_P} restricts mode changes to same-size modes. Compare this to IA-64, which extends floating-point values to 82-bits, and stores 64-bit integers in a different format than 64-bit doubles. Therefore @code{CLASS_CANNOT_CHANGE_MODE_P} is always true. @end table Three other special macros describe which operands fit which constraint letters. @table @code @findex CONST_OK_FOR_LETTER_P @item CONST_OK_FOR_LETTER_P (@var{value}, @var{c}) A C expression that defines the machine-dependent operand constraint letters (@samp{I}, @samp{J}, @samp{K}, @dots{} @samp{P}) that specify particular ranges of integer values. If @var{c} is one of those letters, the expression should check that @var{value}, an integer, is in the appropriate range and return 1 if so, 0 otherwise. If @var{c} is not one of those letters, the value should be 0 regardless of @var{value}. @findex CONST_DOUBLE_OK_FOR_LETTER_P @item CONST_DOUBLE_OK_FOR_LETTER_P (@var{value}, @var{c}) A C expression that defines the machine-dependent operand constraint letters that specify particular ranges of @code{const_double} values (@samp{G} or @samp{H}). If @var{c} is one of those letters, the expression should check that @var{value}, an RTX of code @code{const_double}, is in the appropriate range and return 1 if so, 0 otherwise. If @var{c} is not one of those letters, the value should be 0 regardless of @var{value}. @code{const_double} is used for all floating-point constants and for @code{DImode} fixed-point constants. A given letter can accept either or both kinds of values. It can use @code{GET_MODE} to distinguish between these kinds. @findex EXTRA_CONSTRAINT @item EXTRA_CONSTRAINT (@var{value}, @var{c}) A C expression that defines the optional machine-dependent constraint letters that can be used to segregate specific types of operands, usually memory references, for the target machine. Any letter that is not elsewhere defined and not matched by @code{REG_CLASS_FROM_LETTER} may be used. Normally this macro will not be defined. If it is required for a particular target machine, it should return 1 if @var{value} corresponds to the operand type represented by the constraint letter @var{c}. If @var{c} is not defined as an extra constraint, the value returned should be 0 regardless of @var{value}. For example, on the ROMP, load instructions cannot have their output in r0 if the memory reference contains a symbolic address. Constraint letter @samp{Q} is defined as representing a memory address that does @emph{not} contain a symbolic address. An alternative is specified with a @samp{Q} constraint on the input and @samp{r} on the output. The next alternative specifies @samp{m} on the input and a register class that does not include r0 on the output. @findex EXTRA_MEMORY_CONSTRAINT @item EXTRA_MEMORY_CONSTRAINT (@var{c}) A C expression that defines the optional machine-dependent constraint letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should be treated like memory constraints by the reload pass. It should return 1 if the operand type represented by the constraint letter @var{c} comprises a subset of all memory references including all those whose address is simply a base register. This allows the reload pass to reload an operand, if it does not directly correspond to the operand type of @var{c}, by copying its address into a base register. For example, on the S/390, some instructions do not accept arbitrary memory references, but only those that do not make use of an index register. The constraint letter @samp{Q} is defined via @code{EXTRA_CONSTRAINT} as representing a memory address of this type. If the letter @samp{Q} is marked as @code{EXTRA_MEMORY_CONSTRAINT}, a @samp{Q} constraint can handle any memory operand, because the reload pass knows it can be reloaded by copying the memory address into a base register if required. This is analogous to the way a @samp{o} constraint can handle any memory operand. @findex EXTRA_ADDRESS_CONSTRAINT @item EXTRA_ADDRESS_CONSTRAINT (@var{c}) A C expression that defines the optional machine-dependent constraint letters, amongst those accepted by @code{EXTRA_CONSTRAINT}, that should be treated like address constraints by the reload pass. It should return 1 if the operand type represented by the constraint letter @var{c} comprises a subset of all memory addresses including all those that consist of just a base register. This allows the reload pass to reload an operand, if it does not directly correspond to the operand type of @var{c}, by copying it into a base register. Any constraint marked as @code{EXTRA_ADDRESS_CONSTRAINT} can only be used with the @code{address_operand} predicate. It is treated analogously to the @samp{p} constraint. @end table @node Stack and Calling @section Stack Layout and Calling Conventions @cindex calling conventions @c prevent bad page break with this line This describes the stack layout and calling conventions. @menu * Frame Layout:: * Exception Handling:: * Stack Checking:: * Frame Registers:: * Elimination:: * Stack Arguments:: * Register Arguments:: * Scalar Return:: * Aggregate Return:: * Caller Saves:: * Function Entry:: * Profiling:: * Tail Calls:: @end menu @node Frame Layout @subsection Basic Stack Layout @cindex stack frame layout @cindex frame layout @c prevent bad page break with this line Here is the basic stack layout. @table @code @findex STACK_GROWS_DOWNWARD @item STACK_GROWS_DOWNWARD Define this macro if pushing a word onto the stack moves the stack pointer to a smaller address. When we say, ``define this macro if @dots{},'' it means that the compiler checks this macro only with @code{#ifdef} so the precise definition used does not matter. @findex STACK_PUSH_CODE @item STACK_PUSH_CODE This macro defines the operation used when something is pushed on the stack. In RTL, a push operation will be @code{(set (mem (STACK_PUSH_CODE (reg sp))) @dots{})} The choices are @code{PRE_DEC}, @code{POST_DEC}, @code{PRE_INC}, and @code{POST_INC}. Which of these is correct depends on the stack direction and on whether the stack pointer points to the last item on the stack or whether it points to the space for the next item on the stack. The default is @code{PRE_DEC} when @code{STACK_GROWS_DOWNWARD} is defined, which is almost always right, and @code{PRE_INC} otherwise, which is often wrong. @findex FRAME_GROWS_DOWNWARD @item FRAME_GROWS_DOWNWARD Define this macro if the addresses of local variable slots are at negative offsets from the frame pointer. @findex ARGS_GROW_DOWNWARD @item ARGS_GROW_DOWNWARD Define this macro if successive arguments to a function occupy decreasing addresses on the stack. @findex STARTING_FRAME_OFFSET @item STARTING_FRAME_OFFSET Offset from the frame pointer to the first local variable slot to be allocated. If @code{FRAME_GROWS_DOWNWARD}, find the next slot's offset by subtracting the first slot's length from @code{STARTING_FRAME_OFFSET}. Otherwise, it is found by adding the length of the first slot to the value @code{STARTING_FRAME_OFFSET}. @c i'm not sure if the above is still correct.. had to change it to get @c rid of an overfull. --mew 2feb93 @findex STACK_POINTER_OFFSET @item STACK_POINTER_OFFSET Offset from the stack pointer register to the first location at which outgoing arguments are placed. If not specified, the default value of zero is used. This is the proper value for most machines. If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above the first location at which outgoing arguments are placed. @findex FIRST_PARM_OFFSET @item FIRST_PARM_OFFSET (@var{fundecl}) Offset from the argument pointer register to the first argument's address. On some machines it may depend on the data type of the function. If @code{ARGS_GROW_DOWNWARD}, this is the offset to the location above the first argument's address. @findex STACK_DYNAMIC_OFFSET @item STACK_DYNAMIC_OFFSET (@var{fundecl}) Offset from the stack pointer register to an item dynamically allocated on the stack, e.g., by @code{alloca}. The default value for this macro is @code{STACK_POINTER_OFFSET} plus the length of the outgoing arguments. The default is correct for most machines. See @file{function.c} for details. @findex DYNAMIC_CHAIN_ADDRESS @item DYNAMIC_CHAIN_ADDRESS (@var{frameaddr}) A C expression whose value is RTL representing the address in a stack frame where the pointer to the caller's frame is stored. Assume that @var{frameaddr} is an RTL expression for the address of the stack frame itself. If you don't define this macro, the default is to return the value of @var{frameaddr}---that is, the stack frame address is also the address of the stack word that points to the previous frame. @findex SETUP_FRAME_ADDRESSES @item SETUP_FRAME_ADDRESSES If defined, a C expression that produces the machine-specific code to setup the stack so that arbitrary frames can be accessed. For example, on the SPARC, we must flush all of the register windows to the stack before we can access arbitrary stack frames. You will seldom need to define this macro. @findex BUILTIN_SETJMP_FRAME_VALUE @item BUILTIN_SETJMP_FRAME_VALUE If defined, a C expression that contains an rtx that is used to store the address of the current frame into the built in @code{setjmp} buffer. The default value, @code{virtual_stack_vars_rtx}, is correct for most machines. One reason you may need to define this macro is if @code{hard_frame_pointer_rtx} is the appropriate value on your machine. @findex RETURN_ADDR_RTX @item RETURN_ADDR_RTX (@var{count}, @var{frameaddr}) A C expression whose value is RTL representing the value of the return address for the frame @var{count} steps up from the current frame, after the prologue. @var{frameaddr} is the frame pointer of the @var{count} frame, or the frame pointer of the @var{count} @minus{} 1 frame if @code{RETURN_ADDR_IN_PREVIOUS_FRAME} is defined. The value of the expression must always be the correct address when @var{count} is zero, but may be @code{NULL_RTX} if there is not way to determine the return address of other frames. @findex RETURN_ADDR_IN_PREVIOUS_FRAME @item RETURN_ADDR_IN_PREVIOUS_FRAME Define this if the return address of a particular stack frame is accessed from the frame pointer of the previous stack frame. @findex INCOMING_RETURN_ADDR_RTX @item INCOMING_RETURN_ADDR_RTX A C expression whose value is RTL representing the location of the incoming return address at the beginning of any function, before the prologue. This RTL is either a @code{REG}, indicating that the return value is saved in @samp{REG}, or a @code{MEM} representing a location in the stack. You only need to define this macro if you want to support call frame debugging information like that provided by DWARF 2. If this RTL is a @code{REG}, you should also define @code{DWARF_FRAME_RETURN_COLUMN} to @code{DWARF_FRAME_REGNUM (REGNO)}. @findex INCOMING_FRAME_SP_OFFSET @item INCOMING_FRAME_SP_OFFSET A C expression whose value is an integer giving the offset, in bytes, from the value of the stack pointer register to the top of the stack frame at the beginning of any function, before the prologue. The top of the frame is defined to be the value of the stack pointer in the previous frame, just before the call instruction. You only need to define this macro if you want to support call frame debugging information like that provided by DWARF 2. @findex ARG_POINTER_CFA_OFFSET @item ARG_POINTER_CFA_OFFSET (@var{fundecl}) A C expression whose value is an integer giving the offset, in bytes, from the argument pointer to the canonical frame address (cfa). The final value should coincide with that calculated by @code{INCOMING_FRAME_SP_OFFSET}. Which is unfortunately not usable during virtual register instantiation. The default value for this macro is @code{FIRST_PARM_OFFSET (fundecl)}, which is correct for most machines; in general, the arguments are found immediately before the stack frame. Note that this is not the case on some targets that save registers into the caller's frame, such as SPARC and rs6000, and so such targets need to define this macro. You only need to define this macro if the default is incorrect, and you want to support call frame debugging information like that provided by DWARF 2. @findex SMALL_STACK @item SMALL_STACK Define this macro if the stack size for the target is very small. This has the effect of disabling gcc's built-in @samp{alloca}, though @samp{__builtin_alloca} is not affected. @end table @node Exception Handling @subsection Exception Handling Support @cindex exception handling @table @code @findex EH_RETURN_DATA_REGNO @item EH_RETURN_DATA_REGNO (@var{N}) A C expression whose value is the @var{N}th register number used for data by exception handlers, or @code{INVALID_REGNUM} if fewer than @var{N} registers are usable. The exception handling library routines communicate with the exception handlers via a set of agreed upon registers. Ideally these registers should be call-clobbered; it is possible to use call-saved registers, but may negatively impact code size. The target must support at least 2 data registers, but should define 4 if there are enough free registers. You must define this macro if you want to support call frame exception handling like that provided by DWARF 2. @findex EH_RETURN_STACKADJ_RTX @item EH_RETURN_STACKADJ_RTX A C expression whose value is RTL representing a location in which to store a stack adjustment to be applied before function return. This is used to unwind the stack to an exception handler's call frame. It will be assigned zero on code paths that return normally. Typically this is a call-clobbered hard register that is otherwise untouched by the epilogue, but could also be a stack slot. You must define this macro if you want to support call frame exception handling like that provided by DWARF 2. @findex EH_RETURN_HANDLER_RTX @item EH_RETURN_HANDLER_RTX A C expression whose value is RTL representing a location in which to store the address of an exception handler to which we should return. It will not be assigned on code paths that return normally. Typically this is the location in the call frame at which the normal return address is stored. For targets that return by popping an address off the stack, this might be a memory address just below the @emph{target} call frame rather than inside the current call frame. @code{EH_RETURN_STACKADJ_RTX} will have already been assigned, so it may be used to calculate the location of the target call frame. Some targets have more complex requirements than storing to an address calculable during initial code generation. In that case the @code{eh_return} instruction pattern should be used instead. If you want to support call frame exception handling, you must define either this macro or the @code{eh_return} instruction pattern. @findex ASM_PREFERRED_EH_DATA_FORMAT @item ASM_PREFERRED_EH_DATA_FORMAT(@var{code}, @var{global}) This macro chooses the encoding of pointers embedded in the exception handling sections. If at all possible, this should be defined such that the exception handling section will not require dynamic relocations, and so may be read-only. @var{code} is 0 for data, 1 for code labels, 2 for function pointers. @var{global} is true if the symbol may be affected by dynamic relocations. The macro should return a combination of the @code{DW_EH_PE_*} defines as found in @file{dwarf2.h}. If this macro is not defined, pointers will not be encoded but represented directly. @findex ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX @item ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX(@var{file}, @var{encoding}, @var{size}, @var{addr}, @var{done}) This macro allows the target to emit whatever special magic is required to represent the encoding chosen by @code{ASM_PREFERRED_EH_DATA_FORMAT}. Generic code takes care of pc-relative and indirect encodings; this must be defined if the target uses text-relative or data-relative encodings. This is a C statement that branches to @var{done} if the format was handled. @var{encoding} is the format chosen, @var{size} is the number of bytes that the format occupies, @var{addr} is the @code{SYMBOL_REF} to be emitted. @findex MD_FALLBACK_FRAME_STATE_FOR @item MD_FALLBACK_FRAME_STATE_FOR(@var{context}, @var{fs}, @var{success}) This macro allows the target to add cpu and operating system specific code to the call-frame unwinder for use when there is no unwind data available. The most common reason to implement this macro is to unwind through signal frames. This macro is called from @code{uw_frame_state_for} in @file{unwind-dw2.c} and @file{unwind-ia64.c}. @var{context} is an @code{_Unwind_Context}; @var{fs} is an @code{_Unwind_FrameState}. Examine @code{context->ra} for the address of the code being executed and @code{context->cfa} for the stack pointer value. If the frame can be decoded, the register save addresses should be updated in @var{fs} and the macro should branch to @var{success}. If the frame cannot be decoded, the macro should do nothing. @end table @node Stack Checking @subsection Specifying How Stack Checking is Done GCC will check that stack references are within the boundaries of the stack, if the @option{-fstack-check} is specified, in one of three ways: @enumerate @item If the value of the @code{STACK_CHECK_BUILTIN} macro is nonzero, GCC will assume that you have arranged for stack checking to be done at appropriate places in the configuration files, e.g., in @code{TARGET_ASM_FUNCTION_PROLOGUE}. GCC will do not other special processing. @item If @code{STACK_CHECK_BUILTIN} is zero and you defined a named pattern called @code{check_stack} in your @file{md} file, GCC will call that pattern with one argument which is the address to compare the stack value against. You must arrange for this pattern to report an error if the stack pointer is out of range. @item If neither of the above are true, GCC will generate code to periodically ``probe'' the stack pointer using the values of the macros defined below. @end enumerate Normally, you will use the default values of these macros, so GCC will use the third approach. @table @code @findex STACK_CHECK_BUILTIN @item STACK_CHECK_BUILTIN A nonzero value if stack checking is done by the configuration files in a machine-dependent manner. You should define this macro if stack checking is require by the ABI of your machine or if you would like to have to stack checking in some more efficient way than GCC's portable approach. The default value of this macro is zero. @findex STACK_CHECK_PROBE_INTERVAL @item STACK_CHECK_PROBE_INTERVAL An integer representing the interval at which GCC must generate stack probe instructions. You will normally define this macro to be no larger than the size of the ``guard pages'' at the end of a stack area. The default value of 4096 is suitable for most systems. @findex STACK_CHECK_PROBE_LOAD @item STACK_CHECK_PROBE_LOAD A integer which is nonzero if GCC should perform the stack probe as a load instruction and zero if GCC should use a store instruction. The default is zero, which is the most efficient choice on most systems. @findex STACK_CHECK_PROTECT @item STACK_CHECK_PROTECT The number of bytes of stack needed to recover from a stack overflow, for languages where such a recovery is supported. The default value of 75 words should be adequate for most machines. @findex STACK_CHECK_MAX_FRAME_SIZE @item STACK_CHECK_MAX_FRAME_SIZE The maximum size of a stack frame, in bytes. GCC will generate probe instructions in non-leaf functions to ensure at least this many bytes of stack are available. If a stack frame is larger than this size, stack checking will not be reliable and GCC will issue a warning. The default is chosen so that GCC only generates one instruction on most systems. You should normally not change the default value of this macro. @findex STACK_CHECK_FIXED_FRAME_SIZE @item STACK_CHECK_FIXED_FRAME_SIZE GCC uses this value to generate the above warning message. It represents the amount of fixed frame used by a function, not including space for any callee-saved registers, temporaries and user variables. You need only specify an upper bound for this amount and will normally use the default of four words. @findex STACK_CHECK_MAX_VAR_SIZE @item STACK_CHECK_MAX_VAR_SIZE The maximum size, in bytes, of an object that GCC will place in the fixed area of the stack frame when the user specifies @option{-fstack-check}. GCC computed the default from the values of the above macros and you will normally not need to override that default. @end table @need 2000 @node Frame Registers @subsection Registers That Address the Stack Frame @c prevent bad page break with this line This discusses registers that address the stack frame. @table @code @findex STACK_POINTER_REGNUM @item STACK_POINTER_REGNUM The register number of the stack pointer register, which must also be a fixed register according to @code{FIXED_REGISTERS}. On most machines, the hardware determines which register this is. @findex FRAME_POINTER_REGNUM @item FRAME_POINTER_REGNUM The register number of the frame pointer register, which is used to access automatic variables in the stack frame. On some machines, the hardware determines which register this is. On other machines, you can choose any register you wish for this purpose. @findex HARD_FRAME_POINTER_REGNUM @item HARD_FRAME_POINTER_REGNUM On some machines the offset between the frame pointer and starting offset of the automatic variables is not known until after register allocation has been done (for example, because the saved registers are between these two locations). On those machines, define @code{FRAME_POINTER_REGNUM} the number of a special, fixed register to be used internally until the offset is known, and define @code{HARD_FRAME_POINTER_REGNUM} to be the actual hard register number used for the frame pointer. You should define this macro only in the very rare circumstances when it is not possible to calculate the offset between the frame pointer and the automatic variables until after register allocation has been completed. When this macro is defined, you must also indicate in your definition of @code{ELIMINABLE_REGS} how to eliminate @code{FRAME_POINTER_REGNUM} into either @code{HARD_FRAME_POINTER_REGNUM} or @code{STACK_POINTER_REGNUM}. Do not define this macro if it would be the same as @code{FRAME_POINTER_REGNUM}. @findex ARG_POINTER_REGNUM @item ARG_POINTER_REGNUM The register number of the arg pointer register, which is used to access the function's argument list. On some machines, this is the same as the frame pointer register. On some machines, the hardware determines which register this is. On other machines, you can choose any register you wish for this purpose. If this is not the same register as the frame pointer register, then you must mark it as a fixed register according to @code{FIXED_REGISTERS}, or arrange to be able to eliminate it (@pxref{Elimination}). @findex RETURN_ADDRESS_POINTER_REGNUM @item RETURN_ADDRESS_POINTER_REGNUM The register number of the return address pointer register, which is used to access the current function's return address from the stack. On some machines, the return address is not at a fixed offset from the frame pointer or stack pointer or argument pointer. This register can be defined to point to the return address on the stack, and then be converted by @code{ELIMINABLE_REGS} into either the frame pointer or stack pointer. Do not define this macro unless there is no other way to get the return address from the stack. @findex STATIC_CHAIN_REGNUM @findex STATIC_CHAIN_INCOMING_REGNUM @item STATIC_CHAIN_REGNUM @itemx STATIC_CHAIN_INCOMING_REGNUM Register numbers used for passing a function's static chain pointer. If register windows are used, the register number as seen by the called function is @code{STATIC_CHAIN_INCOMING_REGNUM}, while the register number as seen by the calling function is @code{STATIC_CHAIN_REGNUM}. If these registers are the same, @code{STATIC_CHAIN_INCOMING_REGNUM} need not be defined. The static chain register need not be a fixed register. If the static chain is passed in memory, these macros should not be defined; instead, the next two macros should be defined. @findex STATIC_CHAIN @findex STATIC_CHAIN_INCOMING @item STATIC_CHAIN @itemx STATIC_CHAIN_INCOMING If the static chain is passed in memory, these macros provide rtx giving @code{mem} expressions that denote where they are stored. @code{STATIC_CHAIN} and @code{STATIC_CHAIN_INCOMING} give the locations as seen by the calling and called functions, respectively. Often the former will be at an offset from the stack pointer and the latter at an offset from the frame pointer. @findex stack_pointer_rtx @findex frame_pointer_rtx @findex arg_pointer_rtx The variables @code{stack_pointer_rtx}, @code{frame_pointer_rtx}, and @code{arg_pointer_rtx} will have been initialized prior to the use of these macros and should be used to refer to those items. If the static chain is passed in a register, the two previous macros should be defined instead. @findex DWARF_FRAME_REGISTERS @item DWARF_FRAME_REGISTERS This macro specifies the maximum number of hard registers that can be saved in a call frame. This is used to size data structures used in DWARF2 exception handling. Prior to GCC 3.0, this macro was needed in order to establish a stable exception handling ABI in the face of adding new hard registers for ISA extensions. In GCC 3.0 and later, the EH ABI is insulated from changes in the number of hard registers. Nevertheless, this macro can still be used to reduce the runtime memory requirements of the exception handling routines, which can be substantial if the ISA contains a lot of registers that are not call-saved. If this macro is not defined, it defaults to @code{FIRST_PSEUDO_REGISTER}. @findex PRE_GCC3_DWARF_FRAME_REGISTERS @item PRE_GCC3_DWARF_FRAME_REGISTERS This macro is similar to @code{DWARF_FRAME_REGISTERS}, but is provided for backward compatibility in pre GCC 3.0 compiled code. If this macro is not defined, it defaults to @code{DWARF_FRAME_REGISTERS}. @end table @node Elimination @subsection Eliminating Frame Pointer and Arg Pointer @c prevent bad page break with this line This is about eliminating the frame pointer and arg pointer. @table @code @findex FRAME_POINTER_REQUIRED @item FRAME_POINTER_REQUIRED A C expression which is nonzero if a function must have and use a frame pointer. This expression is evaluated in the reload pass. If its value is nonzero the function will have a frame pointer. The expression can in principle examine the current function and decide according to the facts, but on most machines the constant 0 or the constant 1 suffices. Use 0 when the machine allows code to be generated with no frame pointer, and doing so saves some time or space. Use 1 when there is no possible advantage to avoiding a frame pointer. In certain cases, the compiler does not know how to produce valid code without a frame pointer. The compiler recognizes those cases and automatically gives the function a frame pointer regardless of what @code{FRAME_POINTER_REQUIRED} says. You don't need to worry about them. In a function that does not require a frame pointer, the frame pointer register can be allocated for ordinary usage, unless you mark it as a fixed register. See @code{FIXED_REGISTERS} for more information. @findex INITIAL_FRAME_POINTER_OFFSET @findex get_frame_size @item INITIAL_FRAME_POINTER_OFFSET (@var{depth-var}) A C statement to store in the variable @var{depth-var} the difference between the frame pointer and the stack pointer values immediately after the function prologue. The value would be computed from information such as the result of @code{get_frame_size ()} and the tables of registers @code{regs_ever_live} and @code{call_used_regs}. If @code{ELIMINABLE_REGS} is defined, this macro will be not be used and need not be defined. Otherwise, it must be defined even if @code{FRAME_POINTER_REQUIRED} is defined to always be true; in that case, you may set @var{depth-var} to anything. @findex ELIMINABLE_REGS @item ELIMINABLE_REGS If defined, this macro specifies a table of register pairs used to eliminate unneeded registers that point into the stack frame. If it is not defined, the only elimination attempted by the compiler is to replace references to the frame pointer with references to the stack pointer. The definition of this macro is a list of structure initializations, each of which specifies an original and replacement register. On some machines, the position of the argument pointer is not known until the compilation is completed. In such a case, a separate hard register must be used for the argument pointer. This register can be eliminated by replacing it with either the frame pointer or the argument pointer, depending on whether or not the frame pointer has been eliminated. In this case, you might specify: @example #define ELIMINABLE_REGS \ @{@{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM@}, \ @{ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM@}, \ @{FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM@}@} @end example Note that the elimination of the argument pointer with the stack pointer is specified first since that is the preferred elimination. @findex CAN_ELIMINATE @item CAN_ELIMINATE (@var{from-reg}, @var{to-reg}) A C expression that returns nonzero if the compiler is allowed to try to replace register number @var{from-reg} with register number @var{to-reg}. This macro need only be defined if @code{ELIMINABLE_REGS} is defined, and will usually be the constant 1, since most of the cases preventing register elimination are things that the compiler already knows about. @findex INITIAL_ELIMINATION_OFFSET @item INITIAL_ELIMINATION_OFFSET (@var{from-reg}, @var{to-reg}, @var{offset-var}) This macro is similar to @code{INITIAL_FRAME_POINTER_OFFSET}. It specifies the initial difference between the specified pair of registers. This macro must be defined if @code{ELIMINABLE_REGS} is defined. @end table @node Stack Arguments @subsection Passing Function Arguments on the Stack @cindex arguments on stack @cindex stack arguments The macros in this section control how arguments are passed on the stack. See the following section for other macros that control passing certain arguments in registers. @table @code @findex PROMOTE_PROTOTYPES @item PROMOTE_PROTOTYPES A C expression whose value is nonzero if an argument declared in a prototype as an integral type smaller than @code{int} should actually be passed as an @code{int}. In addition to avoiding errors in certain cases of mismatch, it also makes for better code on certain machines. If the macro is not defined in target header files, it defaults to 0. @findex PUSH_ARGS @item PUSH_ARGS A C expression. If nonzero, push insns will be used to pass outgoing arguments. If the target machine does not have a push instruction, set it to zero. That directs GCC to use an alternate strategy: to allocate the entire argument block and then store the arguments into it. When @code{PUSH_ARGS} is nonzero, @code{PUSH_ROUNDING} must be defined too. On some machines, the definition @findex PUSH_ROUNDING @item PUSH_ROUNDING (@var{npushed}) A C expression that is the number of bytes actually pushed onto the stack when an instruction attempts to push @var{npushed} bytes. On some machines, the definition @example #define PUSH_ROUNDING(BYTES) (BYTES) @end example @noindent will suffice. But on other machines, instructions that appear to push one byte actually push two bytes in an attempt to maintain alignment. Then the definition should be @example #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) @end example @findex ACCUMULATE_OUTGOING_ARGS @findex current_function_outgoing_args_size @item ACCUMULATE_OUTGOING_ARGS A C expression. If nonzero, the maximum amount of space required for outgoing arguments will be computed and placed into the variable @code{current_function_outgoing_args_size}. No space will be pushed onto the stack for each call; instead, the function prologue should increase the stack frame size by this amount. Setting both @code{PUSH_ARGS} and @code{ACCUMULATE_OUTGOING_ARGS} is not proper. @findex REG_PARM_STACK_SPACE @item REG_PARM_STACK_SPACE (@var{fndecl}) Define this macro if functions should assume that stack space has been allocated for arguments even when their values are passed in registers. The value of this macro is the size, in bytes, of the area reserved for arguments passed in registers for the function represented by @var{fndecl}, which can be zero if GCC is calling a library function. This space can be allocated by the caller, or be a part of the machine-dependent stack frame: @code{OUTGOING_REG_PARM_STACK_SPACE} says which. @c above is overfull. not sure what to do. --mew 5feb93 did @c something, not sure if it looks good. --mew 10feb93 @findex MAYBE_REG_PARM_STACK_SPACE @findex FINAL_REG_PARM_STACK_SPACE @item MAYBE_REG_PARM_STACK_SPACE @itemx FINAL_REG_PARM_STACK_SPACE (@var{const_size}, @var{var_size}) Define these macros in addition to the one above if functions might allocate stack space for arguments even when their values are passed in registers. These should be used when the stack space allocated for arguments in registers is not a simple constant independent of the function declaration. The value of the first macro is the size, in bytes, of the area that we should initially assume would be reserved for arguments passed in registers. The value of the second macro is the actual size, in bytes, of the area that will be reserved for arguments passed in registers. This takes two arguments: an integer representing the number of bytes of fixed sized arguments on the stack, and a tree representing the number of bytes of variable sized arguments on the stack. When these macros are defined, @code{REG_PARM_STACK_SPACE} will only be called for libcall functions, the current function, or for a function being called when it is known that such stack space must be allocated. In each case this value can be easily computed. When deciding whether a called function needs such stack space, and how much space to reserve, GCC uses these two macros instead of @code{REG_PARM_STACK_SPACE}. @findex OUTGOING_REG_PARM_STACK_SPACE @item OUTGOING_REG_PARM_STACK_SPACE Define this if it is the responsibility of the caller to allocate the area reserved for arguments passed in registers. If @code{ACCUMULATE_OUTGOING_ARGS} is defined, this macro controls whether the space for these arguments counts in the value of @code{current_function_outgoing_args_size}. @findex STACK_PARMS_IN_REG_PARM_AREA @item STACK_PARMS_IN_REG_PARM_AREA Define this macro if @code{REG_PARM_STACK_SPACE} is defined, but the stack parameters don't skip the area specified by it. @c i changed this, makes more sens and it should have taken care of the @c overfull.. not as specific, tho. --mew 5feb93 Normally, when a parameter is not passed in registers, it is placed on the stack beyond the @code{REG_PARM_STACK_SPACE} area. Defining this macro suppresses this behavior and causes the parameter to be passed on the stack in its natural location. @findex RETURN_POPS_ARGS @item RETURN_POPS_ARGS (@var{fundecl}, @var{funtype}, @var{stack-size}) A C expression that should indicate the number of bytes of its own arguments that a function pops on returning, or 0 if the function pops no arguments and the caller must therefore pop them all after the function returns. @var{fundecl} is a C variable whose value is a tree node that describes the function in question. Normally it is a node of type @code{FUNCTION_DECL} that describes the declaration of the function. From this you can obtain the @code{DECL_ATTRIBUTES} of the function. @var{funtype} is a C variable whose value is a tree node that describes the function in question. Normally it is a node of type @code{FUNCTION_TYPE} that describes the data type of the function. From this it is possible to obtain the data types of the value and arguments (if known). When a call to a library function is being considered, @var{fundecl} will contain an identifier node for the library function. Thus, if you need to distinguish among various library functions, you can do so by their names. Note that ``library function'' in this context means a function used to perform arithmetic, whose name is known specially in the compiler and was not mentioned in the C code being compiled. @var{stack-size} is the number of bytes of arguments passed on the stack. If a variable number of bytes is passed, it is zero, and argument popping will always be the responsibility of the calling function. On the VAX, all functions always pop their arguments, so the definition of this macro is @var{stack-size}. On the 68000, using the standard calling convention, no functions pop their arguments, so the value of the macro is always 0 in this case. But an alternative calling convention is available in which functions that take a fixed number of arguments pop them but other functions (such as @code{printf}) pop nothing (the caller pops all). When this convention is in use, @var{funtype} is examined to determine whether a function takes a fixed number of arguments. @findex CALL_POPS_ARGS @item CALL_POPS_ARGS (@var{cum}) A C expression that should indicate the number of bytes a call sequence pops off the stack. It is added to the value of @code{RETURN_POPS_ARGS} when compiling a function call. @var{cum} is the variable in which all arguments to the called function have been accumulated. On certain architectures, such as the SH5, a call trampoline is used that pops certain registers off the stack, depending on the arguments that have been passed to the function. Since this is a property of the call site, not of the called function, @code{RETURN_POPS_ARGS} is not appropriate. @end table @node Register Arguments @subsection Passing Arguments in Registers @cindex arguments in registers @cindex registers arguments This section describes the macros which let you control how various types of arguments are passed in registers or how they are arranged in the stack. @table @code @findex FUNCTION_ARG @item FUNCTION_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) A C expression that controls whether a function argument is passed in a register, and which register. The arguments are @var{cum}, which summarizes all the previous arguments; @var{mode}, the machine mode of the argument; @var{type}, the data type of the argument as a tree node or 0 if that is not known (which happens for C support library functions); and @var{named}, which is 1 for an ordinary argument and 0 for nameless arguments that correspond to @samp{@dots{}} in the called function's prototype. @var{type} can be an incomplete type if a syntax error has previously occurred. The value of the expression is usually either a @code{reg} RTX for the hard register in which to pass the argument, or zero to pass the argument on the stack. For machines like the VAX and 68000, where normally all arguments are pushed, zero suffices as a definition. The value of the expression can also be a @code{parallel} RTX@. This is used when an argument is passed in multiple locations. The mode of the of the @code{parallel} should be the mode of the entire argument. The @code{parallel} holds any number of @code{expr_list} pairs; each one describes where part of the argument is passed. In each @code{expr_list} the first operand must be a @code{reg} RTX for the hard register in which to pass this part of the argument, and the mode of the register RTX indicates how large this part of the argument is. The second operand of the @code{expr_list} is a @code{const_int} which gives the offset in bytes into the entire argument of where this part starts. As a special exception the first @code{expr_list} in the @code{parallel} RTX may have a first operand of zero. This indicates that the entire argument is also stored on the stack. The last time this macro is called, it is called with @code{MODE == VOIDmode}, and its result is passed to the @code{call} or @code{call_value} pattern as operands 2 and 3 respectively. @cindex @file{stdarg.h} and register arguments The usual way to make the ISO library @file{stdarg.h} work on a machine where some arguments are usually passed in registers, is to cause nameless arguments to be passed on the stack instead. This is done by making @code{FUNCTION_ARG} return 0 whenever @var{named} is 0. @cindex @code{MUST_PASS_IN_STACK}, and @code{FUNCTION_ARG} @cindex @code{REG_PARM_STACK_SPACE}, and @code{FUNCTION_ARG} You may use the macro @code{MUST_PASS_IN_STACK (@var{mode}, @var{type})} in the definition of this macro to determine if this argument is of a type that must be passed in the stack. If @code{REG_PARM_STACK_SPACE} is not defined and @code{FUNCTION_ARG} returns nonzero for such an argument, the compiler will abort. If @code{REG_PARM_STACK_SPACE} is defined, the argument will be computed in the stack and then loaded into a register. @findex MUST_PASS_IN_STACK @item MUST_PASS_IN_STACK (@var{mode}, @var{type}) Define as a C expression that evaluates to nonzero if we do not know how to pass TYPE solely in registers. The file @file{expr.h} defines a definition that is usually appropriate, refer to @file{expr.h} for additional documentation. @findex FUNCTION_INCOMING_ARG @item FUNCTION_INCOMING_ARG (@var{cum}, @var{mode}, @var{type}, @var{named}) Define this macro if the target machine has ``register windows'', so that the register in which a function sees an arguments is not necessarily the same as the one in which the caller passed the argument. For such machines, @code{FUNCTION_ARG} computes the register in which the caller passes the value, and @code{FUNCTION_INCOMING_ARG} should be defined in a similar fashion to tell the function being called where the arguments will arrive. If @code{FUNCTION_INCOMING_ARG} is not defined, @code{FUNCTION_ARG} serves both purposes. @findex FUNCTION_ARG_PARTIAL_NREGS @item FUNCTION_ARG_PARTIAL_NREGS (@var{cum}, @var{mode}, @var{type}, @var{named}) A C expression for the number of words, at the beginning of an argument, that must be put in registers. The value must be zero for arguments that are passed entirely in registers or that are entirely pushed on the stack. On some machines, certain arguments must be passed partially in registers and partially in memory. On these machines, typically the first @var{n} words of arguments are passed in registers, and the rest on the stack. If a multi-word argument (a @code{double} or a structure) crosses that boundary, its first few words must be passed in registers and the rest must be pushed. This macro tells the compiler when this occurs, and how many of the words should go in registers. @code{FUNCTION_ARG} for these arguments should return the first register to be used by the caller for this argument; likewise @code{FUNCTION_INCOMING_ARG}, for the called function. @findex FUNCTION_ARG_PASS_BY_REFERENCE @item FUNCTION_ARG_PASS_BY_REFERENCE (@var{cum}, @var{mode}, @var{type}, @var{named}) A C expression that indicates when an argument must be passed by reference. If nonzero for an argument, a copy of that argument is made in memory and a pointer to the argument is passed instead of the argument itself. The pointer is passed in whatever way is appropriate for passing a pointer to that type. On machines where @code{REG_PARM_STACK_SPACE} is not defined, a suitable definition of this macro might be @smallexample #define FUNCTION_ARG_PASS_BY_REFERENCE\ (CUM, MODE, TYPE, NAMED) \ MUST_PASS_IN_STACK (MODE, TYPE) @end smallexample @c this is *still* too long. --mew 5feb93 @findex FUNCTION_ARG_CALLEE_COPIES @item FUNCTION_ARG_CALLEE_COPIES (@var{cum}, @var{mode}, @var{type}, @var{named}) If defined, a C expression that indicates when it is the called function's responsibility to make a copy of arguments passed by invisible reference. Normally, the caller makes a copy and passes the address of the copy to the routine being called. When @code{FUNCTION_ARG_CALLEE_COPIES} is defined and is nonzero, the caller does not make a copy. Instead, it passes a pointer to the ``live'' value. The called function must not modify this value. If it can be determined that the value won't be modified, it need not make a copy; otherwise a copy must be made. @findex FUNCTION_ARG_REG_LITTLE_ENDIAN @item FUNCTION_ARG_REG_LITTLE_ENDIAN If defined TRUE on a big-endian system then structure arguments passed (and returned) in registers are passed in a little-endian manner instead of the big-endian manner. On the HP-UX IA64 and PA64 platforms structures are aligned differently then integral values and setting this value to true will allow for the special handling of structure arguments and return values. @findex CUMULATIVE_ARGS @item CUMULATIVE_ARGS A C type for declaring a variable that is used as the first argument of @code{FUNCTION_ARG} and other related values. For some target machines, the type @code{int} suffices and can hold the number of bytes of argument so far. There is no need to record in @code{CUMULATIVE_ARGS} anything about the arguments that have been passed on the stack. The compiler has other variables to keep track of that. For target machines on which all arguments are passed on the stack, there is no need to store anything in @code{CUMULATIVE_ARGS}; however, the data structure must exist and should not be empty, so use @code{int}. @findex INIT_CUMULATIVE_ARGS @item INIT_CUMULATIVE_ARGS (@var{cum}, @var{fntype}, @var{libname}, @var{indirect}) A C statement (sans semicolon) for initializing the variable @var{cum} for the state at the beginning of the argument list. The variable has type @code{CUMULATIVE_ARGS}. The value of @var{fntype} is the tree node for the data type of the function which will receive the args, or 0 if the args are to a compiler support library function. The value of @var{indirect} is nonzero when processing an indirect call, for example a call through a function pointer. The value of @var{indirect} is zero for a call to an explicitly named function, a library function call, or when @code{INIT_CUMULATIVE_ARGS} is used to find arguments for the function being compiled. When processing a call to a compiler support library function, @var{libname} identifies which one. It is a @code{symbol_ref} rtx which contains the name of the function, as a string. @var{libname} is 0 when an ordinary C function call is being processed. Thus, each time this macro is called, either @var{libname} or @var{fntype} is nonzero, but never both of them at once. @findex INIT_CUMULATIVE_LIBCALL_ARGS @item INIT_CUMULATIVE_LIBCALL_ARGS (@var{cum}, @var{mode}, @var{libname}) Like @code{INIT_CUMULATIVE_ARGS} but only used for outgoing libcalls, it gets a @code{MODE} argument instead of @var{fntype}, that would be @code{NULL}. @var{indirect} would always be zero, too. If this macro is not defined, @code{INIT_CUMULATIVE_ARGS (cum, NULL_RTX, libname, 0)} is used instead. @findex INIT_CUMULATIVE_INCOMING_ARGS @item INIT_CUMULATIVE_INCOMING_ARGS (@var{cum}, @var{fntype}, @var{libname}) Like @code{INIT_CUMULATIVE_ARGS} but overrides it for the purposes of finding the arguments for the function being compiled. If this macro is undefined, @code{INIT_CUMULATIVE_ARGS} is used instead. The value passed for @var{libname} is always 0, since library routines with special calling conventions are never compiled with GCC@. The argument @var{libname} exists for symmetry with @code{INIT_CUMULATIVE_ARGS}. @c could use "this macro" in place of @code{INIT_CUMULATIVE_ARGS}, maybe. @c --mew 5feb93 i switched the order of the sentences. --mew 10feb93 @findex FUNCTION_ARG_ADVANCE @item FUNCTION_ARG_ADVANCE (@var{cum}, @var{mode}, @var{type}, @var{named}) A C statement (sans semicolon) to update the summarizer variable @var{cum} to advance past an argument in the argument list. The values @var{mode}, @var{type} and @var{named} describe that argument. Once this is done, the variable @var{cum} is suitable for analyzing the @emph{following} argument with @code{FUNCTION_ARG}, etc. This macro need not do anything if the argument in question was passed on the stack. The compiler knows how to track the amount of stack space used for arguments without any special help. @findex FUNCTION_ARG_PADDING @item FUNCTION_ARG_PADDING (@var{mode}, @var{type}) If defined, a C expression which determines whether, and in which direction, to pad out an argument with extra space. The value should be of type @code{enum direction}: either @code{upward} to pad above the argument, @code{downward} to pad below, or @code{none} to inhibit padding. The @emph{amount} of padding is always just enough to reach the next multiple of @code{FUNCTION_ARG_BOUNDARY}; this macro does not control it. This macro has a default definition which is right for most systems. For little-endian machines, the default is to pad upward. For big-endian machines, the default is to pad downward for an argument of constant size shorter than an @code{int}, and upward otherwise. @findex PAD_VARARGS_DOWN @item PAD_VARARGS_DOWN If defined, a C expression which determines whether the default implementation of va_arg will attempt to pad down before reading the next argument, if that argument is smaller than its aligned space as controlled by @code{PARM_BOUNDARY}. If this macro is not defined, all such arguments are padded down if @code{BYTES_BIG_ENDIAN} is true. @findex FUNCTION_ARG_BOUNDARY @item FUNCTION_ARG_BOUNDARY (@var{mode}, @var{type}) If defined, a C expression that gives the alignment boundary, in bits, of an argument with the specified mode and type. If it is not defined, @code{PARM_BOUNDARY} is used for all arguments. @findex FUNCTION_ARG_REGNO_P @item FUNCTION_ARG_REGNO_P (@var{regno}) A C expression that is nonzero if @var{regno} is the number of a hard register in which function arguments are sometimes passed. This does @emph{not} include implicit arguments such as the static chain and the structure-value address. On many machines, no registers can be used for this purpose since all function arguments are pushed on the stack. @findex LOAD_ARGS_REVERSED @item LOAD_ARGS_REVERSED If defined, the order in which arguments are loaded into their respective argument registers is reversed so that the last argument is loaded first. This macro only affects arguments passed in registers. @end table @node Scalar Return @subsection How Scalar Function Values Are Returned @cindex return values in registers @cindex values, returned by functions @cindex scalars, returned as values This section discusses the macros that control returning scalars as values---values that can fit in registers. @table @code @findex FUNCTION_VALUE @item FUNCTION_VALUE (@var{valtype}, @var{func}) A C expression to create an RTX representing the place where a function returns a value of data type @var{valtype}. @var{valtype} is a tree node representing a data type. Write @code{TYPE_MODE (@var{valtype})} to get the machine mode used to represent that type. On many machines, only the mode is relevant. (Actually, on most machines, scalar values are returned in the same place regardless of mode). The value of the expression is usually a @code{reg} RTX for the hard register where the return value is stored. The value can also be a @code{parallel} RTX, if the return value is in multiple places. See @code{FUNCTION_ARG} for an explanation of the @code{parallel} form. If @code{PROMOTE_FUNCTION_RETURN} is defined, you must apply the same promotion rules specified in @code{PROMOTE_MODE} if @var{valtype} is a scalar type. If the precise function being called is known, @var{func} is a tree node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null pointer. This makes it possible to use a different value-returning convention for specific functions when all their calls are known. @code{FUNCTION_VALUE} is not used for return vales with aggregate data types, because these are returned in another way. See @code{STRUCT_VALUE_REGNUM} and related macros, below. @findex FUNCTION_OUTGOING_VALUE @item FUNCTION_OUTGOING_VALUE (@var{valtype}, @var{func}) Define this macro if the target machine has ``register windows'' so that the register in which a function returns its value is not the same as the one in which the caller sees the value. For such machines, @code{FUNCTION_VALUE} computes the register in which the caller will see the value. @code{FUNCTION_OUTGOING_VALUE} should be defined in a similar fashion to tell the function where to put the value. If @code{FUNCTION_OUTGOING_VALUE} is not defined, @code{FUNCTION_VALUE} serves both purposes. @code{FUNCTION_OUTGOING_VALUE} is not used for return vales with aggregate data types, because these are returned in another way. See @code{STRUCT_VALUE_REGNUM} and related macros, below. @findex LIBCALL_VALUE @item LIBCALL_VALUE (@var{mode}) A C expression to create an RTX representing the place where a library function returns a value of mode @var{mode}. If the precise function being called is known, @var{func} is a tree node (@code{FUNCTION_DECL}) for it; otherwise, @var{func} is a null pointer. This makes it possible to use a different value-returning convention for specific functions when all their calls are known. Note that ``library function'' in this context means a compiler support routine, used to perform arithmetic, whose name is known specially by the compiler and was not mentioned in the C code being compiled. The definition of @code{LIBRARY_VALUE} need not be concerned aggregate data types, because none of the library functions returns such types. @findex FUNCTION_VALUE_REGNO_P @item FUNCTION_VALUE_REGNO_P (@var{regno}) A C expression that is nonzero if @var{regno} is the number of a hard register in which the values of called function may come back. A register whose use for returning values is limited to serving as the second of a pair (for a value of type @code{double}, say) need not be recognized by this macro. So for most machines, this definition suffices: @example #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) @end example If the machine has register windows, so that the caller and the called function use different registers for the return value, this macro should recognize only the caller's register numbers. @findex APPLY_RESULT_SIZE @item APPLY_RESULT_SIZE Define this macro if @samp{untyped_call} and @samp{untyped_return} need more space than is implied by @code{FUNCTION_VALUE_REGNO_P} for saving and restoring an arbitrary return value. @end table @node Aggregate Return @subsection How Large Values Are Returned @cindex aggregates as return values @cindex large return values @cindex returning aggregate values @cindex structure value address When a function value's mode is @code{BLKmode} (and in some other cases), the value is not returned according to @code{FUNCTION_VALUE} (@pxref{Scalar Return}). Instead, the caller passes the address of a block of memory in which the value should be stored. This address is called the @dfn{structure value address}. This section describes how to control returning structure values in memory. @table @code @findex RETURN_IN_MEMORY @item RETURN_IN_MEMORY (@var{type}) A C expression which can inhibit the returning of certain function values in registers, based on the type of value. A nonzero value says to return the function value in memory, just as large structures are always returned. Here @var{type} will be a C expression of type @code{tree}, representing the data type of the value. Note that values of mode @code{BLKmode} must be explicitly handled by this macro. Also, the option @option{-fpcc-struct-return} takes effect regardless of this macro. On most systems, it is possible to leave the macro undefined; this causes a default definition to be used, whose value is the constant 1 for @code{BLKmode} values, and 0 otherwise. Do not use this macro to indicate that structures and unions should always be returned in memory. You should instead use @code{DEFAULT_PCC_STRUCT_RETURN} to indicate this. @findex DEFAULT_PCC_STRUCT_RETURN @item DEFAULT_PCC_STRUCT_RETURN Define this macro to be 1 if all structure and union return values must be in memory. Since this results in slower code, this should be defined only if needed for compatibility with other compilers or with an ABI@. If you define this macro to be 0, then the conventions used for structure and union return values are decided by the @code{RETURN_IN_MEMORY} macro. If not defined, this defaults to the value 1. @findex STRUCT_VALUE_REGNUM @item STRUCT_VALUE_REGNUM If the structure value address is passed in a register, then @code{STRUCT_VALUE_REGNUM} should be the number of that register. @findex STRUCT_VALUE @item STRUCT_VALUE If the structure value address is not passed in a register, define @code{STRUCT_VALUE} as an expression returning an RTX for the place where the address is passed. If it returns 0, the address is passed as an ``invisible'' first argument. @findex STRUCT_VALUE_INCOMING_REGNUM @item STRUCT_VALUE_INCOMING_REGNUM On some architectures the place where the structure value address is found by the called function is not the same place that the caller put it. This can be due to register windows, or it could be because the function prologue moves it to a different place. If the incoming location of the structure value address is in a register, define this macro as the register number. @findex STRUCT_VALUE_INCOMING @item STRUCT_VALUE_INCOMING If the incoming location is not a register, then you should define @code{STRUCT_VALUE_INCOMING} as an expression for an RTX for where the called function should find the value. If it should find the value on the stack, define this to create a @code{mem} which refers to the frame pointer. A definition of 0 means that the address is passed as an ``invisible'' first argument. @findex PCC_STATIC_STRUCT_RETURN @item PCC_STATIC_STRUCT_RETURN Define this macro if the usual system convention on the target machine for returning structures and unions is for the called function to return the address of a static variable containing the value. Do not define this if the usual system convention is for the caller to pass an address to the subroutine. This macro has effect in @option{-fpcc-struct-return} mode, but it does nothing when you use @option{-freg-struct-return} mode. @end table @node Caller Saves @subsection Caller-Saves Register Allocation If you enable it, GCC can save registers around function calls. This makes it possible to use call-clobbered registers to hold variables that must live across calls. @table @code @findex DEFAULT_CALLER_SAVES @item DEFAULT_CALLER_SAVES Define this macro if function calls on the target machine do not preserve any registers; in other words, if @code{CALL_USED_REGISTERS} has 1 for all registers. When defined, this macro enables @option{-fcaller-saves} by default for all optimization levels. It has no effect for optimization levels 2 and higher, where @option{-fcaller-saves} is the default. @findex CALLER_SAVE_PROFITABLE @item CALLER_SAVE_PROFITABLE (@var{refs}, @var{calls}) A C expression to determine whether it is worthwhile to consider placing a pseudo-register in a call-clobbered hard register and saving and restoring it around each function call. The expression should be 1 when this is worth doing, and 0 otherwise. If you don't define this macro, a default is used which is good on most machines: @code{4 * @var{calls} < @var{refs}}. @findex HARD_REGNO_CALLER_SAVE_MODE @item HARD_REGNO_CALLER_SAVE_MODE (@var{regno}, @var{nregs}) A C expression specifying which mode is required for saving @var{nregs} of a pseudo-register in call-clobbered hard register @var{regno}. If @var{regno} is unsuitable for caller save, @code{VOIDmode} should be returned. For most machines this macro need not be defined since GCC will select the smallest suitable mode. @end table @node Function Entry @subsection Function Entry and Exit @cindex function entry and exit @cindex prologue @cindex epilogue This section describes the macros that output function entry (@dfn{prologue}) and exit (@dfn{epilogue}) code. @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_PROLOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) If defined, a function that outputs the assembler code for entry to a function. The prologue is responsible for setting up the stack frame, initializing the frame pointer register, saving registers that must be saved, and allocating @var{size} additional bytes of storage for the local variables. @var{size} is an integer. @var{file} is a stdio stream to which the assembler code should be output. The label for the beginning of the function need not be output by this macro. That has already been done when the macro is run. @findex regs_ever_live To determine which registers to save, the macro can refer to the array @code{regs_ever_live}: element @var{r} is nonzero if hard register @var{r} is used anywhere within the function. This implies the function prologue should save register @var{r}, provided it is not one of the call-used registers. (@code{TARGET_ASM_FUNCTION_EPILOGUE} must likewise use @code{regs_ever_live}.) On machines that have ``register windows'', the function entry code does not save on the stack the registers that are in the windows, even if they are supposed to be preserved by function calls; instead it takes appropriate steps to ``push'' the register stack, if any non-call-used registers are used in the function. @findex frame_pointer_needed On machines where functions may or may not have frame-pointers, the function entry code must vary accordingly; it must set up the frame pointer if one is wanted, and not otherwise. To determine whether a frame pointer is in wanted, the macro can refer to the variable @code{frame_pointer_needed}. The variable's value will be 1 at run time in a function that needs a frame pointer. @xref{Elimination}. The function entry code is responsible for allocating any stack space required for the function. This stack space consists of the regions listed below. In most cases, these regions are allocated in the order listed, with the last listed region closest to the top of the stack (the lowest address if @code{STACK_GROWS_DOWNWARD} is defined, and the highest address if it is not defined). You can use a different order for a machine if doing so is more convenient or required for compatibility reasons. Except in cases where required by standard or by a debugger, there is no reason why the stack layout used by GCC need agree with that used by other compilers for a machine. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_END_PROLOGUE (FILE *@var{file}) If defined, a function that outputs assembler code at the end of a prologue. This should be used when the function prologue is being emitted as RTL, and you have some extra assembler that needs to be emitted. @xref{prologue instruction pattern}. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_BEGIN_EPILOGUE (FILE *@var{file}) If defined, a function that outputs assembler code at the start of an epilogue. This should be used when the function epilogue is being emitted as RTL, and you have some extra assembler that needs to be emitted. @xref{epilogue instruction pattern}. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_FUNCTION_EPILOGUE (FILE *@var{file}, HOST_WIDE_INT @var{size}) If defined, a function that outputs the assembler code for exit from a function. The epilogue is responsible for restoring the saved registers and stack pointer to their values when the function was called, and returning control to the caller. This macro takes the same arguments as the macro @code{TARGET_ASM_FUNCTION_PROLOGUE}, and the registers to restore are determined from @code{regs_ever_live} and @code{CALL_USED_REGISTERS} in the same way. On some machines, there is a single instruction that does all the work of returning from the function. On these machines, give that instruction the name @samp{return} and do not define the macro @code{TARGET_ASM_FUNCTION_EPILOGUE} at all. Do not define a pattern named @samp{return} if you want the @code{TARGET_ASM_FUNCTION_EPILOGUE} to be used. If you want the target switches to control whether return instructions or epilogues are used, define a @samp{return} pattern with a validity condition that tests the target switches appropriately. If the @samp{return} pattern's validity condition is false, epilogues will be used. On machines where functions may or may not have frame-pointers, the function exit code must vary accordingly. Sometimes the code for these two cases is completely different. To determine whether a frame pointer is wanted, the macro can refer to the variable @code{frame_pointer_needed}. The variable's value will be 1 when compiling a function that needs a frame pointer. Normally, @code{TARGET_ASM_FUNCTION_PROLOGUE} and @code{TARGET_ASM_FUNCTION_EPILOGUE} must treat leaf functions specially. The C variable @code{current_function_is_leaf} is nonzero for such a function. @xref{Leaf Functions}. On some machines, some functions pop their arguments on exit while others leave that for the caller to do. For example, the 68020 when given @option{-mrtd} pops arguments in functions that take a fixed number of arguments. @findex current_function_pops_args Your definition of the macro @code{RETURN_POPS_ARGS} decides which functions pop their own arguments. @code{TARGET_ASM_FUNCTION_EPILOGUE} needs to know what was decided. The variable that is called @code{current_function_pops_args} is the number of bytes of its arguments that a function should pop. @xref{Scalar Return}. @c what is the "its arguments" in the above sentence referring to, pray @c tell? --mew 5feb93 @end deftypefn @table @code @itemize @bullet @item @findex current_function_pretend_args_size A region of @code{current_function_pretend_args_size} bytes of uninitialized space just underneath the first argument arriving on the stack. (This may not be at the very start of the allocated stack region if the calling sequence has pushed anything else since pushing the stack arguments. But usually, on such machines, nothing else has been pushed yet, because the function prologue itself does all the pushing.) This region is used on machines where an argument may be passed partly in registers and partly in memory, and, in some cases to support the features in @code{}. @item An area of memory used to save certain registers used by the function. The size of this area, which may also include space for such things as the return address and pointers to previous stack frames, is machine-specific and usually depends on which registers have been used in the function. Machines with register windows often do not require a save area. @item A region of at least @var{size} bytes, possibly rounded up to an allocation boundary, to contain the local variables of the function. On some machines, this region and the save area may occur in the opposite order, with the save area closer to the top of the stack. @item @cindex @code{ACCUMULATE_OUTGOING_ARGS} and stack frames Optionally, when @code{ACCUMULATE_OUTGOING_ARGS} is defined, a region of @code{current_function_outgoing_args_size} bytes to be used for outgoing argument lists of the function. @xref{Stack Arguments}. @end itemize Normally, it is necessary for the macros @code{TARGET_ASM_FUNCTION_PROLOGUE} and @code{TARGET_ASM_FUNCTION_EPILOGUE} to treat leaf functions specially. The C variable @code{current_function_is_leaf} is nonzero for such a function. @findex EXIT_IGNORE_STACK @item EXIT_IGNORE_STACK Define this macro as a C expression that is nonzero if the return instruction or the function epilogue ignores the value of the stack pointer; in other words, if it is safe to delete an instruction to adjust the stack pointer before a return from the function. Note that this macro's value is relevant only for functions for which frame pointers are maintained. It is never safe to delete a final stack adjustment in a function that has no frame pointer, and the compiler knows this regardless of @code{EXIT_IGNORE_STACK}. @findex EPILOGUE_USES @item EPILOGUE_USES (@var{regno}) Define this macro as a C expression that is nonzero for registers that are used by the epilogue or the @samp{return} pattern. The stack and frame pointer registers are already be assumed to be used as needed. @findex EH_USES @item EH_USES (@var{regno}) Define this macro as a C expression that is nonzero for registers that are used by the exception handling mechanism, and so should be considered live on entry to an exception edge. @findex DELAY_SLOTS_FOR_EPILOGUE @item DELAY_SLOTS_FOR_EPILOGUE Define this macro if the function epilogue contains delay slots to which instructions from the rest of the function can be ``moved''. The definition should be a C expression whose value is an integer representing the number of delay slots there. @findex ELIGIBLE_FOR_EPILOGUE_DELAY @item ELIGIBLE_FOR_EPILOGUE_DELAY (@var{insn}, @var{n}) A C expression that returns 1 if @var{insn} can be placed in delay slot number @var{n} of the epilogue. The argument @var{n} is an integer which identifies the delay slot now being considered (since different slots may have different rules of eligibility). It is never negative and is always less than the number of epilogue delay slots (what @code{DELAY_SLOTS_FOR_EPILOGUE} returns). If you reject a particular insn for a given delay slot, in principle, it may be reconsidered for a subsequent delay slot. Also, other insns may (at least in principle) be considered for the so far unfilled delay slot. @findex current_function_epilogue_delay_list @findex final_scan_insn The insns accepted to fill the epilogue delay slots are put in an RTL list made with @code{insn_list} objects, stored in the variable @code{current_function_epilogue_delay_list}. The insn for the first delay slot comes first in the list. Your definition of the macro @code{TARGET_ASM_FUNCTION_EPILOGUE} should fill the delay slots by outputting the insns in this list, usually by calling @code{final_scan_insn}. You need not define this macro if you did not define @code{DELAY_SLOTS_FOR_EPILOGUE}. @findex ASM_OUTPUT_MI_THUNK @item ASM_OUTPUT_MI_THUNK (@var{file}, @var{thunk_fndecl}, @var{delta}, @var{function}) A C compound statement that outputs the assembler code for a thunk function, used to implement C++ virtual function calls with multiple inheritance. The thunk acts as a wrapper around a virtual function, adjusting the implicit object parameter before handing control off to the real function. First, emit code to add the integer @var{delta} to the location that contains the incoming first argument. Assume that this argument contains a pointer, and is the one used to pass the @code{this} pointer in C++. This is the incoming argument @emph{before} the function prologue, e.g.@: @samp{%o0} on a sparc. The addition must preserve the values of all other incoming arguments. After the addition, emit code to jump to @var{function}, which is a @code{FUNCTION_DECL}. This is a direct pure jump, not a call, and does not touch the return address. Hence returning from @var{FUNCTION} will return to whoever called the current @samp{thunk}. The effect must be as if @var{function} had been called directly with the adjusted first argument. This macro is responsible for emitting all of the code for a thunk function; @code{TARGET_ASM_FUNCTION_PROLOGUE} and @code{TARGET_ASM_FUNCTION_EPILOGUE} are not invoked. The @var{thunk_fndecl} is redundant. (@var{delta} and @var{function} have already been extracted from it.) It might possibly be useful on some targets, but probably not. If you do not define this macro, the target-independent code in the C++ front end will generate a less efficient heavyweight thunk that calls @var{function} instead of jumping to it. The generic approach does not support varargs. @end table @node Profiling @subsection Generating Code for Profiling @cindex profiling, code generation These macros will help you generate code for profiling. @table @code @findex FUNCTION_PROFILER @item FUNCTION_PROFILER (@var{file}, @var{labelno}) A C statement or compound statement to output to @var{file} some assembler code to call the profiling subroutine @code{mcount}. @findex mcount The details of how @code{mcount} expects to be called are determined by your operating system environment, not by GCC@. To figure them out, compile a small program for profiling using the system's installed C compiler and look at the assembler code that results. Older implementations of @code{mcount} expect the address of a counter variable to be loaded into some register. The name of this variable is @samp{LP} followed by the number @var{labelno}, so you would generate the name using @samp{LP%d} in a @code{fprintf}. @findex PROFILE_HOOK @item PROFILE_HOOK A C statement or compound statement to output to @var{file} some assembly code to call the profiling subroutine @code{mcount} even the target does not support profiling. @findex NO_PROFILE_COUNTERS @item NO_PROFILE_COUNTERS Define this macro if the @code{mcount} subroutine on your system does not need a counter variable allocated for each function. This is true for almost all modern implementations. If you define this macro, you must not use the @var{labelno} argument to @code{FUNCTION_PROFILER}. @findex PROFILE_BEFORE_PROLOGUE @item PROFILE_BEFORE_PROLOGUE Define this macro if the code for function profiling should come before the function prologue. Normally, the profiling code comes after. @end table @node Tail Calls @subsection Permitting tail calls @cindex tail calls @table @code @findex FUNCTION_OK_FOR_SIBCALL @item FUNCTION_OK_FOR_SIBCALL (@var{decl}) A C expression that evaluates to true if it is ok to perform a sibling call to @var{decl} from the current function. It is not uncommon for limitations of calling conventions to prevent tail calls to functions outside the current unit of translation, or during PIC compilation. Use this macro to enforce these restrictions, as the @code{sibcall} md pattern can not fail, or fall over to a ``normal'' call. @end table @node Varargs @section Implementing the Varargs Macros @cindex varargs implementation GCC comes with an implementation of @code{} and @code{} that work without change on machines that pass arguments on the stack. Other machines require their own implementations of varargs, and the two machine independent header files must have conditionals to include it. ISO @code{} differs from traditional @code{} mainly in the calling convention for @code{va_start}. The traditional implementation takes just one argument, which is the variable in which to store the argument pointer. The ISO implementation of @code{va_start} takes an additional second argument. The user is supposed to write the last named argument of the function here. However, @code{va_start} should not use this argument. The way to find the end of the named arguments is with the built-in functions described below. @table @code @findex __builtin_saveregs @item __builtin_saveregs () Use this built-in function to save the argument registers in memory so that the varargs mechanism can access them. Both ISO and traditional versions of @code{va_start} must use @code{__builtin_saveregs}, unless you use @code{SETUP_INCOMING_VARARGS} (see below) instead. On some machines, @code{__builtin_saveregs} is open-coded under the control of the macro @code{EXPAND_BUILTIN_SAVEREGS}. On other machines, it calls a routine written in assembler language, found in @file{libgcc2.c}. Code generated for the call to @code{__builtin_saveregs} appears at the beginning of the function, as opposed to where the call to @code{__builtin_saveregs} is written, regardless of what the code is. This is because the registers must be saved before the function starts to use them for its own purposes. @c i rewrote the first sentence above to fix an overfull hbox. --mew @c 10feb93 @findex __builtin_args_info @item __builtin_args_info (@var{category}) Use this built-in function to find the first anonymous arguments in registers. In general, a machine may have several categories of registers used for arguments, each for a particular category of data types. (For example, on some machines, floating-point registers are used for floating-point arguments while other arguments are passed in the general registers.) To make non-varargs functions use the proper calling convention, you have defined the @code{CUMULATIVE_ARGS} data type to record how many registers in each category have been used so far @code{__builtin_args_info} accesses the same data structure of type @code{CUMULATIVE_ARGS} after the ordinary argument layout is finished with it, with @var{category} specifying which word to access. Thus, the value indicates the first unused register in a given category. Normally, you would use @code{__builtin_args_info} in the implementation of @code{va_start}, accessing each category just once and storing the value in the @code{va_list} object. This is because @code{va_list} will have to update the values, and there is no way to alter the values accessed by @code{__builtin_args_info}. @findex __builtin_next_arg @item __builtin_next_arg (@var{lastarg}) This is the equivalent of @code{__builtin_args_info}, for stack arguments. It returns the address of the first anonymous stack argument, as type @code{void *}. If @code{ARGS_GROW_DOWNWARD}, it returns the address of the location above the first anonymous stack argument. Use it in @code{va_start} to initialize the pointer for fetching arguments from the stack. Also use it in @code{va_start} to verify that the second parameter @var{lastarg} is the last named argument of the current function. @findex __builtin_classify_type @item __builtin_classify_type (@var{object}) Since each machine has its own conventions for which data types are passed in which kind of register, your implementation of @code{va_arg} has to embody these conventions. The easiest way to categorize the specified data type is to use @code{__builtin_classify_type} together with @code{sizeof} and @code{__alignof__}. @code{__builtin_classify_type} ignores the value of @var{object}, considering only its data type. It returns an integer describing what kind of type that is---integer, floating, pointer, structure, and so on. The file @file{typeclass.h} defines an enumeration that you can use to interpret the values of @code{__builtin_classify_type}. @end table These machine description macros help implement varargs: @table @code @findex EXPAND_BUILTIN_SAVEREGS @item EXPAND_BUILTIN_SAVEREGS () If defined, is a C expression that produces the machine-specific code for a call to @code{__builtin_saveregs}. This code will be moved to the very beginning of the function, before any parameter access are made. The return value of this function should be an RTX that contains the value to use as the return of @code{__builtin_saveregs}. @findex SETUP_INCOMING_VARARGS @item SETUP_INCOMING_VARARGS (@var{args_so_far}, @var{mode}, @var{type}, @var{pretend_args_size}, @var{second_time}) This macro offers an alternative to using @code{__builtin_saveregs} and defining the macro @code{EXPAND_BUILTIN_SAVEREGS}. Use it to store the anonymous register arguments into the stack so that all the arguments appear to have been passed consecutively on the stack. Once this is done, you can use the standard implementation of varargs that works for machines that pass all their arguments on the stack. The argument @var{args_so_far} is the @code{CUMULATIVE_ARGS} data structure, containing the values that are obtained after processing the named arguments. The arguments @var{mode} and @var{type} describe the last named argument---its machine mode and its data type as a tree node. The macro implementation should do two things: first, push onto the stack all the argument registers @emph{not} used for the named arguments, and second, store the size of the data thus pushed into the @code{int}-valued variable whose name is supplied as the argument @var{pretend_args_size}. The value that you store here will serve as additional offset for setting up the stack frame. Because you must generate code to push the anonymous arguments at compile time without knowing their data types, @code{SETUP_INCOMING_VARARGS} is only useful on machines that have just a single category of argument register and use it uniformly for all data types. If the argument @var{second_time} is nonzero, it means that the arguments of the function are being analyzed for the second time. This happens for an inline function, which is not actually compiled until the end of the source file. The macro @code{SETUP_INCOMING_VARARGS} should not generate any instructions in this case. @findex STRICT_ARGUMENT_NAMING @item STRICT_ARGUMENT_NAMING Define this macro to be a nonzero value if the location where a function argument is passed depends on whether or not it is a named argument. This macro controls how the @var{named} argument to @code{FUNCTION_ARG} is set for varargs and stdarg functions. If this macro returns a nonzero value, the @var{named} argument is always true for named arguments, and false for unnamed arguments. If it returns a value of zero, but @code{SETUP_INCOMING_VARARGS} is defined, then all arguments are treated as named. Otherwise, all named arguments except the last are treated as named. You need not define this macro if it always returns zero. @findex PRETEND_OUTGOING_VARARGS_NAMED @item PRETEND_OUTGOING_VARARGS_NAMED If you need to conditionally change ABIs so that one works with @code{SETUP_INCOMING_VARARGS}, but the other works like neither @code{SETUP_INCOMING_VARARGS} nor @code{STRICT_ARGUMENT_NAMING} was defined, then define this macro to return nonzero if @code{SETUP_INCOMING_VARARGS} is used, zero otherwise. Otherwise, you should not define this macro. @end table @node Trampolines @section Trampolines for Nested Functions @cindex trampolines for nested functions @cindex nested functions, trampolines for A @dfn{trampoline} is a small piece of code that is created at run time when the address of a nested function is taken. It normally resides on the stack, in the stack frame of the containing function. These macros tell GCC how to generate code to allocate and initialize a trampoline. The instructions in the trampoline must do two things: load a constant address into the static chain register, and jump to the real address of the nested function. On CISC machines such as the m68k, this requires two instructions, a move immediate and a jump. Then the two addresses exist in the trampoline as word-long immediate operands. On RISC machines, it is often necessary to load each address into a register in two parts. Then pieces of each address form separate immediate operands. The code generated to initialize the trampoline must store the variable parts---the static chain value and the function address---into the immediate operands of the instructions. On a CISC machine, this is simply a matter of copying each address to a memory reference at the proper offset from the start of the trampoline. On a RISC machine, it may be necessary to take out pieces of the address and store them separately. @table @code @findex TRAMPOLINE_TEMPLATE @item TRAMPOLINE_TEMPLATE (@var{file}) A C statement to output, on the stream @var{file}, assembler code for a block of data that contains the constant parts of a trampoline. This code should not include a label---the label is taken care of automatically. If you do not define this macro, it means no template is needed for the target. Do not define this macro on systems where the block move code to copy the trampoline into place would be larger than the code to generate it on the spot. @findex TRAMPOLINE_SECTION @item TRAMPOLINE_SECTION The name of a subroutine to switch to the section in which the trampoline template is to be placed (@pxref{Sections}). The default is a value of @samp{readonly_data_section}, which places the trampoline in the section containing read-only data. @findex TRAMPOLINE_SIZE @item TRAMPOLINE_SIZE A C expression for the size in bytes of the trampoline, as an integer. @findex TRAMPOLINE_ALIGNMENT @item TRAMPOLINE_ALIGNMENT Alignment required for trampolines, in bits. If you don't define this macro, the value of @code{BIGGEST_ALIGNMENT} is used for aligning trampolines. @findex INITIALIZE_TRAMPOLINE @item INITIALIZE_TRAMPOLINE (@var{addr}, @var{fnaddr}, @var{static_chain}) A C statement to initialize the variable parts of a trampoline. @var{addr} is an RTX for the address of the trampoline; @var{fnaddr} is an RTX for the address of the nested function; @var{static_chain} is an RTX for the static chain value that should be passed to the function when it is called. @findex TRAMPOLINE_ADJUST_ADDRESS @item TRAMPOLINE_ADJUST_ADDRESS (@var{addr}) A C statement that should perform any machine-specific adjustment in the address of the trampoline. Its argument contains the address that was passed to @code{INITIALIZE_TRAMPOLINE}. In case the address to be used for a function call should be different from the address in which the template was stored, the different address should be assigned to @var{addr}. If this macro is not defined, @var{addr} will be used for function calls. @findex ALLOCATE_TRAMPOLINE @item ALLOCATE_TRAMPOLINE (@var{fp}) A C expression to allocate run-time space for a trampoline. The expression value should be an RTX representing a memory reference to the space for the trampoline. @cindex @code{TARGET_ASM_FUNCTION_EPILOGUE} and trampolines @cindex @code{TARGET_ASM_FUNCTION_PROLOGUE} and trampolines If this macro is not defined, by default the trampoline is allocated as a stack slot. This default is right for most machines. The exceptions are machines where it is impossible to execute instructions in the stack area. On such machines, you may have to implement a separate stack, using this macro in conjunction with @code{TARGET_ASM_FUNCTION_PROLOGUE} and @code{TARGET_ASM_FUNCTION_EPILOGUE}. @var{fp} points to a data structure, a @code{struct function}, which describes the compilation status of the immediate containing function of the function which the trampoline is for. Normally (when @code{ALLOCATE_TRAMPOLINE} is not defined), the stack slot for the trampoline is in the stack frame of this containing function. Other allocation strategies probably must do something analogous with this information. @end table Implementing trampolines is difficult on many machines because they have separate instruction and data caches. Writing into a stack location fails to clear the memory in the instruction cache, so when the program jumps to that location, it executes the old contents. Here are two possible solutions. One is to clear the relevant parts of the instruction cache whenever a trampoline is set up. The other is to make all trampolines identical, by having them jump to a standard subroutine. The former technique makes trampoline execution faster; the latter makes initialization faster. To clear the instruction cache when a trampoline is initialized, define the following macros which describe the shape of the cache. @table @code @findex INSN_CACHE_SIZE @item INSN_CACHE_SIZE The total size in bytes of the cache. @findex INSN_CACHE_LINE_WIDTH @item INSN_CACHE_LINE_WIDTH The length in bytes of each cache line. The cache is divided into cache lines which are disjoint slots, each holding a contiguous chunk of data fetched from memory. Each time data is brought into the cache, an entire line is read at once. The data loaded into a cache line is always aligned on a boundary equal to the line size. @findex INSN_CACHE_DEPTH @item INSN_CACHE_DEPTH The number of alternative cache lines that can hold any particular memory location. @end table Alternatively, if the machine has system calls or instructions to clear the instruction cache directly, you can define the following macro. @table @code @findex CLEAR_INSN_CACHE @item CLEAR_INSN_CACHE (@var{beg}, @var{end}) If defined, expands to a C expression clearing the @emph{instruction cache} in the specified interval. If it is not defined, and the macro @code{INSN_CACHE_SIZE} is defined, some generic code is generated to clear the cache. The definition of this macro would typically be a series of @code{asm} statements. Both @var{beg} and @var{end} are both pointer expressions. @end table To use a standard subroutine, define the following macro. In addition, you must make sure that the instructions in a trampoline fill an entire cache line with identical instructions, or else ensure that the beginning of the trampoline code is always aligned at the same point in its cache line. Look in @file{m68k.h} as a guide. @table @code @findex TRANSFER_FROM_TRAMPOLINE @item TRANSFER_FROM_TRAMPOLINE Define this macro if trampolines need a special subroutine to do their work. The macro should expand to a series of @code{asm} statements which will be compiled with GCC@. They go in a library function named @code{__transfer_from_trampoline}. If you need to avoid executing the ordinary prologue code of a compiled C function when you jump to the subroutine, you can do so by placing a special label of your own in the assembler code. Use one @code{asm} statement to generate an assembler label, and another to make the label global. Then trampolines can use that label to jump directly to your special assembler code. @end table @node Library Calls @section Implicit Calls to Library Routines @cindex library subroutine names @cindex @file{libgcc.a} @c prevent bad page break with this line Here is an explanation of implicit calls to library routines. @table @code @findex MULSI3_LIBCALL @item MULSI3_LIBCALL A C string constant giving the name of the function to call for multiplication of one signed full-word by another. If you do not define this macro, the default name is used, which is @code{__mulsi3}, a function defined in @file{libgcc.a}. @findex DIVSI3_LIBCALL @item DIVSI3_LIBCALL A C string constant giving the name of the function to call for division of one signed full-word by another. If you do not define this macro, the default name is used, which is @code{__divsi3}, a function defined in @file{libgcc.a}. @findex UDIVSI3_LIBCALL @item UDIVSI3_LIBCALL A C string constant giving the name of the function to call for division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is @code{__udivsi3}, a function defined in @file{libgcc.a}. @findex MODSI3_LIBCALL @item MODSI3_LIBCALL A C string constant giving the name of the function to call for the remainder in division of one signed full-word by another. If you do not define this macro, the default name is used, which is @code{__modsi3}, a function defined in @file{libgcc.a}. @findex UMODSI3_LIBCALL @item UMODSI3_LIBCALL A C string constant giving the name of the function to call for the remainder in division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is @code{__umodsi3}, a function defined in @file{libgcc.a}. @findex MULDI3_LIBCALL @item MULDI3_LIBCALL A C string constant giving the name of the function to call for multiplication of one signed double-word by another. If you do not define this macro, the default name is used, which is @code{__muldi3}, a function defined in @file{libgcc.a}. @findex DIVDI3_LIBCALL @item DIVDI3_LIBCALL A C string constant giving the name of the function to call for division of one signed double-word by another. If you do not define this macro, the default name is used, which is @code{__divdi3}, a function defined in @file{libgcc.a}. @findex UDIVDI3_LIBCALL @item UDIVDI3_LIBCALL A C string constant giving the name of the function to call for division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is @code{__udivdi3}, a function defined in @file{libgcc.a}. @findex MODDI3_LIBCALL @item MODDI3_LIBCALL A C string constant giving the name of the function to call for the remainder in division of one signed double-word by another. If you do not define this macro, the default name is used, which is @code{__moddi3}, a function defined in @file{libgcc.a}. @findex UMODDI3_LIBCALL @item UMODDI3_LIBCALL A C string constant giving the name of the function to call for the remainder in division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is @code{__umoddi3}, a function defined in @file{libgcc.a}. @findex DECLARE_LIBRARY_RENAMES @item DECLARE_LIBRARY_RENAMES This macro, if defined, should expand to a piece of C code that will get expanded when compiling functions for libgcc.a. It can be used to provide alternate names for gcc's internal library functions if there are ABI-mandated names that the compiler should provide. @findex INIT_TARGET_OPTABS @item INIT_TARGET_OPTABS Define this macro as a C statement that declares additional library routines renames existing ones. @code{init_optabs} calls this macro after initializing all the normal library routines. @findex FLOAT_LIB_COMPARE_RETURNS_BOOL (@var{mode}, @var{comparison}) @item FLOAT_LIB_COMPARE_RETURNS_BOOL Define this macro as a C statement that returns nonzero if a call to the floating point comparison library function will return a boolean value that indicates the result of the comparison. It should return zero if one of gcc's own libgcc functions is called. Most ports don't need to define this macro. @findex TARGET_EDOM @cindex @code{EDOM}, implicit usage @item TARGET_EDOM The value of @code{EDOM} on the target machine, as a C integer constant expression. If you don't define this macro, GCC does not attempt to deposit the value of @code{EDOM} into @code{errno} directly. Look in @file{/usr/include/errno.h} to find the value of @code{EDOM} on your system. If you do not define @code{TARGET_EDOM}, then compiled code reports domain errors by calling the library function and letting it report the error. If mathematical functions on your system use @code{matherr} when there is an error, then you should leave @code{TARGET_EDOM} undefined so that @code{matherr} is used normally. @findex GEN_ERRNO_RTX @cindex @code{errno}, implicit usage @item GEN_ERRNO_RTX Define this macro as a C expression to create an rtl expression that refers to the global ``variable'' @code{errno}. (On certain systems, @code{errno} may not actually be a variable.) If you don't define this macro, a reasonable default is used. @findex TARGET_MEM_FUNCTIONS @cindex @code{bcopy}, implicit usage @cindex @code{memcpy}, implicit usage @cindex @code{memmove}, implicit usage @cindex @code{bzero}, implicit usage @cindex @code{memset}, implicit usage @item TARGET_MEM_FUNCTIONS Define this macro if GCC should generate calls to the ISO C (and System V) library functions @code{memcpy}, @code{memmove} and @code{memset} rather than the BSD functions @code{bcopy} and @code{bzero}. @findex LIBGCC_NEEDS_DOUBLE @item LIBGCC_NEEDS_DOUBLE Define this macro if @code{float} arguments cannot be passed to library routines (so they must be converted to @code{double}). This macro affects both how library calls are generated and how the library routines in @file{libgcc.a} accept their arguments. It is useful on machines where floating and fixed point arguments are passed differently, such as the i860. @findex NEXT_OBJC_RUNTIME @item NEXT_OBJC_RUNTIME Define this macro to generate code for Objective-C message sending using the calling convention of the NeXT system. This calling convention involves passing the object, the selector and the method arguments all at once to the method-lookup library function. The default calling convention passes just the object and the selector to the lookup function, which returns a pointer to the method. @end table @node Addressing Modes @section Addressing Modes @cindex addressing modes @c prevent bad page break with this line This is about addressing modes. @table @code @findex HAVE_PRE_INCREMENT @findex HAVE_PRE_DECREMENT @findex HAVE_POST_INCREMENT @findex HAVE_POST_DECREMENT @item HAVE_PRE_INCREMENT @itemx HAVE_PRE_DECREMENT @itemx HAVE_POST_INCREMENT @itemx HAVE_POST_DECREMENT A C expression that is nonzero if the machine supports pre-increment, pre-decrement, post-increment, or post-decrement addressing respectively. @findex HAVE_POST_MODIFY_DISP @findex HAVE_PRE_MODIFY_DISP @item HAVE_PRE_MODIFY_DISP @itemx HAVE_POST_MODIFY_DISP A C expression that is nonzero if the machine supports pre- or post-address side-effect generation involving constants other than the size of the memory operand. @findex HAVE_POST_MODIFY_REG @findex HAVE_PRE_MODIFY_REG @item HAVE_PRE_MODIFY_REG @itemx HAVE_POST_MODIFY_REG A C expression that is nonzero if the machine supports pre- or post-address side-effect generation involving a register displacement. @findex CONSTANT_ADDRESS_P @item CONSTANT_ADDRESS_P (@var{x}) A C expression that is 1 if the RTX @var{x} is a constant which is a valid address. On most machines, this can be defined as @code{CONSTANT_P (@var{x})}, but a few machines are more restrictive in which constant addresses are supported. @findex CONSTANT_P @code{CONSTANT_P} accepts integer-values expressions whose values are not explicitly known, such as @code{symbol_ref}, @code{label_ref}, and @code{high} expressions and @code{const} arithmetic expressions, in addition to @code{const_int} and @code{const_double} expressions. @findex MAX_REGS_PER_ADDRESS @item MAX_REGS_PER_ADDRESS A number, the maximum number of registers that can appear in a valid memory address. Note that it is up to you to specify a value equal to the maximum number that @code{GO_IF_LEGITIMATE_ADDRESS} would ever accept. @findex GO_IF_LEGITIMATE_ADDRESS @item GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{label}) A C compound statement with a conditional @code{goto @var{label};} executed if @var{x} (an RTX) is a legitimate memory address on the target machine for a memory operand of mode @var{mode}. It usually pays to define several simpler macros to serve as subroutines for this one. Otherwise it may be too complicated to understand. This macro must exist in two variants: a strict variant and a non-strict one. The strict variant is used in the reload pass. It must be defined so that any pseudo-register that has not been allocated a hard register is considered a memory reference. In contexts where some kind of register is required, a pseudo-register with no hard register must be rejected. The non-strict variant is used in other passes. It must be defined to accept all pseudo-registers in every context where some kind of register is required. @findex REG_OK_STRICT Compiler source files that want to use the strict variant of this macro define the macro @code{REG_OK_STRICT}. You should use an @code{#ifdef REG_OK_STRICT} conditional to define the strict variant in that case and the non-strict variant otherwise. Subroutines to check for acceptable registers for various purposes (one for base registers, one for index registers, and so on) are typically among the subroutines used to define @code{GO_IF_LEGITIMATE_ADDRESS}. Then only these subroutine macros need have two variants; the higher levels of macros may be the same whether strict or not. Normally, constant addresses which are the sum of a @code{symbol_ref} and an integer are stored inside a @code{const} RTX to mark them as constant. Therefore, there is no need to recognize such sums specifically as legitimate addresses. Normally you would simply recognize any @code{const} as legitimate. Usually @code{PRINT_OPERAND_ADDRESS} is not prepared to handle constant sums that are not marked with @code{const}. It assumes that a naked @code{plus} indicates indexing. If so, then you @emph{must} reject such naked constant sums as illegitimate addresses, so that none of them will be given to @code{PRINT_OPERAND_ADDRESS}. @cindex @code{TARGET_ENCODE_SECTION_INFO} and address validation On some machines, whether a symbolic address is legitimate depends on the section that the address refers to. On these machines, define the target hook @code{TARGET_ENCODE_SECTION_INFO} to store the information into the @code{symbol_ref}, and then check for it here. When you see a @code{const}, you will have to look inside it to find the @code{symbol_ref} in order to determine the section. @xref{Assembler Format}. @findex saveable_obstack The best way to modify the name string is by adding text to the beginning, with suitable punctuation to prevent any ambiguity. Allocate the new name in @code{saveable_obstack}. You will have to modify @code{ASM_OUTPUT_LABELREF} to remove and decode the added text and output the name accordingly, and define @code{TARGET_STRIP_NAME_ENCODING} to access the original name string. You can check the information stored here into the @code{symbol_ref} in the definitions of the macros @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}. @findex REG_OK_FOR_BASE_P @item REG_OK_FOR_BASE_P (@var{x}) A C expression that is nonzero if @var{x} (assumed to be a @code{reg} RTX) is valid for use as a base register. For hard registers, it should always accept those which the hardware permits and reject the others. Whether the macro accepts or rejects pseudo registers must be controlled by @code{REG_OK_STRICT} as described above. This usually requires two variant definitions, of which @code{REG_OK_STRICT} controls the one actually used. @findex REG_MODE_OK_FOR_BASE_P @item REG_MODE_OK_FOR_BASE_P (@var{x}, @var{mode}) A C expression that is just like @code{REG_OK_FOR_BASE_P}, except that that expression may examine the mode of the memory reference in @var{mode}. You should define this macro if the mode of the memory reference affects whether a register may be used as a base register. If you define this macro, the compiler will use it instead of @code{REG_OK_FOR_BASE_P}. @findex REG_OK_FOR_INDEX_P @item REG_OK_FOR_INDEX_P (@var{x}) A C expression that is nonzero if @var{x} (assumed to be a @code{reg} RTX) is valid for use as an index register. The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two registers, neither one of them scaled, then either one may be labeled the ``base'' and the other the ``index''; but whichever labeling is used must fit the machine's constraints of which registers may serve in each capacity. The compiler will try both labelings, looking for one that is valid, and will reload one or both registers only if neither labeling works. @findex FIND_BASE_TERM @item FIND_BASE_TERM (@var{x}) A C expression to determine the base term of address @var{x}. This macro is used in only one place: `find_base_term' in alias.c. It is always safe for this macro to not be defined. It exists so that alias analysis can understand machine-dependent addresses. The typical use of this macro is to handle addresses containing a label_ref or symbol_ref within an UNSPEC@. @findex LEGITIMIZE_ADDRESS @item LEGITIMIZE_ADDRESS (@var{x}, @var{oldx}, @var{mode}, @var{win}) A C compound statement that attempts to replace @var{x} with a valid memory address for an operand of mode @var{mode}. @var{win} will be a C statement label elsewhere in the code; the macro definition may use @example GO_IF_LEGITIMATE_ADDRESS (@var{mode}, @var{x}, @var{win}); @end example @noindent to avoid further processing if the address has become legitimate. @findex break_out_memory_refs @var{x} will always be the result of a call to @code{break_out_memory_refs}, and @var{oldx} will be the operand that was given to that function to produce @var{x}. The code generated by this macro should not alter the substructure of @var{x}. If it transforms @var{x} into a more legitimate form, it should assign @var{x} (which will always be a C variable) a new value. It is not necessary for this macro to come up with a legitimate address. The compiler has standard ways of doing so in all cases. In fact, it is safe for this macro to do nothing. But often a machine-dependent strategy can generate better code. @findex LEGITIMIZE_RELOAD_ADDRESS @item LEGITIMIZE_RELOAD_ADDRESS (@var{x}, @var{mode}, @var{opnum}, @var{type}, @var{ind_levels}, @var{win}) A C compound statement that attempts to replace @var{x}, which is an address that needs reloading, with a valid memory address for an operand of mode @var{mode}. @var{win} will be a C statement label elsewhere in the code. It is not necessary to define this macro, but it might be useful for performance reasons. For example, on the i386, it is sometimes possible to use a single reload register instead of two by reloading a sum of two pseudo registers into a register. On the other hand, for number of RISC processors offsets are limited so that often an intermediate address needs to be generated in order to address a stack slot. By defining @code{LEGITIMIZE_RELOAD_ADDRESS} appropriately, the intermediate addresses generated for adjacent some stack slots can be made identical, and thus be shared. @emph{Note}: This macro should be used with caution. It is necessary to know something of how reload works in order to effectively use this, and it is quite easy to produce macros that build in too much knowledge of reload internals. @emph{Note}: This macro must be able to reload an address created by a previous invocation of this macro. If it fails to handle such addresses then the compiler may generate incorrect code or abort. @findex push_reload The macro definition should use @code{push_reload} to indicate parts that need reloading; @var{opnum}, @var{type} and @var{ind_levels} are usually suitable to be passed unaltered to @code{push_reload}. The code generated by this macro must not alter the substructure of @var{x}. If it transforms @var{x} into a more legitimate form, it should assign @var{x} (which will always be a C variable) a new value. This also applies to parts that you change indirectly by calling @code{push_reload}. @findex strict_memory_address_p The macro definition may use @code{strict_memory_address_p} to test if the address has become legitimate. @findex copy_rtx If you want to change only a part of @var{x}, one standard way of doing this is to use @code{copy_rtx}. Note, however, that is unshares only a single level of rtl. Thus, if the part to be changed is not at the top level, you'll need to replace first the top level. It is not necessary for this macro to come up with a legitimate address; but often a machine-dependent strategy can generate better code. @findex GO_IF_MODE_DEPENDENT_ADDRESS @item GO_IF_MODE_DEPENDENT_ADDRESS (@var{addr}, @var{label}) A C statement or compound statement with a conditional @code{goto @var{label};} executed if memory address @var{x} (an RTX) can have different meanings depending on the machine mode of the memory reference it is used for or if the address is valid for some modes but not others. Autoincrement and autodecrement addresses typically have mode-dependent effects because the amount of the increment or decrement is the size of the operand being addressed. Some machines have other mode-dependent addresses. Many RISC machines have no mode-dependent addresses. You may assume that @var{addr} is a valid address for the machine. @findex LEGITIMATE_CONSTANT_P @item LEGITIMATE_CONSTANT_P (@var{x}) A C expression that is nonzero if @var{x} is a legitimate constant for an immediate operand on the target machine. You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not check this. In fact, @samp{1} is a suitable definition for this macro on machines where anything @code{CONSTANT_P} is valid. @end table @node Condition Code @section Condition Code Status @cindex condition code status @c prevent bad page break with this line This describes the condition code status. @findex cc_status The file @file{conditions.h} defines a variable @code{cc_status} to describe how the condition code was computed (in case the interpretation of the condition code depends on the instruction that it was set by). This variable contains the RTL expressions on which the condition code is currently based, and several standard flags. Sometimes additional machine-specific flags must be defined in the machine description header file. It can also add additional machine-specific information by defining @code{CC_STATUS_MDEP}. @table @code @findex CC_STATUS_MDEP @item CC_STATUS_MDEP C code for a data type which is used for declaring the @code{mdep} component of @code{cc_status}. It defaults to @code{int}. This macro is not used on machines that do not use @code{cc0}. @findex CC_STATUS_MDEP_INIT @item CC_STATUS_MDEP_INIT A C expression to initialize the @code{mdep} field to ``empty''. The default definition does nothing, since most machines don't use the field anyway. If you want to use the field, you should probably define this macro to initialize it. This macro is not used on machines that do not use @code{cc0}. @findex NOTICE_UPDATE_CC @item NOTICE_UPDATE_CC (@var{exp}, @var{insn}) A C compound statement to set the components of @code{cc_status} appropriately for an insn @var{insn} whose body is @var{exp}. It is this macro's responsibility to recognize insns that set the condition code as a byproduct of other activity as well as those that explicitly set @code{(cc0)}. This macro is not used on machines that do not use @code{cc0}. If there are insns that do not set the condition code but do alter other machine registers, this macro must check to see whether they invalidate the expressions that the condition code is recorded as reflecting. For example, on the 68000, insns that store in address registers do not set the condition code, which means that usually @code{NOTICE_UPDATE_CC} can leave @code{cc_status} unaltered for such insns. But suppose that the previous insn set the condition code based on location @samp{a4@@(102)} and the current insn stores a new value in @samp{a4}. Although the condition code is not changed by this, it will no longer be true that it reflects the contents of @samp{a4@@(102)}. Therefore, @code{NOTICE_UPDATE_CC} must alter @code{cc_status} in this case to say that nothing is known about the condition code value. The definition of @code{NOTICE_UPDATE_CC} must be prepared to deal with the results of peephole optimization: insns whose patterns are @code{parallel} RTXs containing various @code{reg}, @code{mem} or constants which are just the operands. The RTL structure of these insns is not sufficient to indicate what the insns actually do. What @code{NOTICE_UPDATE_CC} should do when it sees one is just to run @code{CC_STATUS_INIT}. A possible definition of @code{NOTICE_UPDATE_CC} is to call a function that looks at an attribute (@pxref{Insn Attributes}) named, for example, @samp{cc}. This avoids having detailed information about patterns in two places, the @file{md} file and in @code{NOTICE_UPDATE_CC}. @findex EXTRA_CC_MODES @item EXTRA_CC_MODES Condition codes are represented in registers by machine modes of class @code{MODE_CC}. By default, there is just one mode, @code{CCmode}, with this class. If you need more such modes, create a file named @file{@var{machine}-modes.def} in your @file{config/@var{machine}} directory (@pxref{Back End, , Anatomy of a Target Back End}), containing a list of these modes. Each entry in the list should be a call to the macro @code{CC}. This macro takes one argument, which is the name of the mode: it should begin with @samp{CC}. Do not put quotation marks around the name, or include the trailing @samp{mode}; these are automatically added. There should not be anything else in the file except comments. A sample @file{@var{machine}-modes.def} file might look like this: @smallexample CC (CC_NOOV) /* @r{Comparison only valid if there was no overflow.} */ CC (CCFP) /* @r{Floating point comparison that cannot trap.} */ CC (CCFPE) /* @r{Floating point comparison that may trap.} */ @end smallexample When you create this file, the macro @code{EXTRA_CC_MODES} is automatically defined by @command{configure}, with value @samp{1}. @findex SELECT_CC_MODE @item SELECT_CC_MODE (@var{op}, @var{x}, @var{y}) Returns a mode from class @code{MODE_CC} to be used when comparison operation code @var{op} is applied to rtx @var{x} and @var{y}. For example, on the SPARC, @code{SELECT_CC_MODE} is defined as (see @pxref{Jump Patterns} for a description of the reason for this definition) @smallexample #define SELECT_CC_MODE(OP,X,Y) \ (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ || GET_CODE (X) == NEG) \ ? CC_NOOVmode : CCmode)) @end smallexample You need not define this macro if @code{EXTRA_CC_MODES} is not defined. @findex CANONICALIZE_COMPARISON @item CANONICALIZE_COMPARISON (@var{code}, @var{op0}, @var{op1}) On some machines not all possible comparisons are defined, but you can convert an invalid comparison into a valid one. For example, the Alpha does not have a @code{GT} comparison, but you can use an @code{LT} comparison instead and swap the order of the operands. On such machines, define this macro to be a C statement to do any required conversions. @var{code} is the initial comparison code and @var{op0} and @var{op1} are the left and right operands of the comparison, respectively. You should modify @var{code}, @var{op0}, and @var{op1} as required. GCC will not assume that the comparison resulting from this macro is valid but will see if the resulting insn matches a pattern in the @file{md} file. You need not define this macro if it would never change the comparison code or operands. @findex REVERSIBLE_CC_MODE @item REVERSIBLE_CC_MODE (@var{mode}) A C expression whose value is one if it is always safe to reverse a comparison whose mode is @var{mode}. If @code{SELECT_CC_MODE} can ever return @var{mode} for a floating-point inequality comparison, then @code{REVERSIBLE_CC_MODE (@var{mode})} must be zero. You need not define this macro if it would always returns zero or if the floating-point format is anything other than @code{IEEE_FLOAT_FORMAT}. For example, here is the definition used on the SPARC, where floating-point inequality comparisons are always given @code{CCFPEmode}: @smallexample #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) @end smallexample @findex REVERSE_CONDITION (@var{code}, @var{mode}) A C expression whose value is reversed condition code of the @var{code} for comparison done in CC_MODE @var{mode}. The macro is used only in case @code{REVERSIBLE_CC_MODE (@var{mode})} is nonzero. Define this macro in case machine has some non-standard way how to reverse certain conditionals. For instance in case all floating point conditions are non-trapping, compiler may freely convert unordered compares to ordered one. Then definition may look like: @smallexample #define REVERSE_CONDITION(CODE, MODE) \ ((MODE) != CCFPmode ? reverse_condition (CODE) \ : reverse_condition_maybe_unordered (CODE)) @end smallexample @findex REVERSE_CONDEXEC_PREDICATES_P @item REVERSE_CONDEXEC_PREDICATES_P (@var{code1}, @var{code2}) A C expression that returns true if the conditional execution predicate @var{code1} is the inverse of @var{code2} and vice versa. Define this to return 0 if the target has conditional execution predicates that cannot be reversed safely. If no expansion is specified, this macro is defined as follows: @smallexample #define REVERSE_CONDEXEC_PREDICATES_P (x, y) \ ((x) == reverse_condition (y)) @end smallexample @end table @node Costs @section Describing Relative Costs of Operations @cindex costs of instructions @cindex relative costs @cindex speed of instructions These macros let you describe the relative speed of various operations on the target machine. @table @code @findex CONST_COSTS @item CONST_COSTS (@var{x}, @var{code}, @var{outer_code}) A part of a C @code{switch} statement that describes the relative costs of constant RTL expressions. It must contain @code{case} labels for expression codes @code{const_int}, @code{const}, @code{symbol_ref}, @code{label_ref} and @code{const_double}. Each case must ultimately reach a @code{return} statement to return the relative cost of the use of that kind of constant value in an expression. The cost may depend on the precise value of the constant, which is available for examination in @var{x}, and the rtx code of the expression in which it is contained, found in @var{outer_code}. @var{code} is the expression code---redundant, since it can be obtained with @code{GET_CODE (@var{x})}. @findex RTX_COSTS @findex COSTS_N_INSNS @item RTX_COSTS (@var{x}, @var{code}, @var{outer_code}) Like @code{CONST_COSTS} but applies to nonconstant RTL expressions. This can be used, for example, to indicate how costly a multiply instruction is. In writing this macro, you can use the construct @code{COSTS_N_INSNS (@var{n})} to specify a cost equal to @var{n} fast instructions. @var{outer_code} is the code of the expression in which @var{x} is contained. This macro is optional; do not define it if the default cost assumptions are adequate for the target machine. @findex DEFAULT_RTX_COSTS @item DEFAULT_RTX_COSTS (@var{x}, @var{code}, @var{outer_code}) This macro, if defined, is called for any case not handled by the @code{RTX_COSTS} or @code{CONST_COSTS} macros. This eliminates the need to put case labels into the macro, but the code, or any functions it calls, must assume that the RTL in @var{x} could be of any type that has not already been handled. The arguments are the same as for @code{RTX_COSTS}, and the macro should execute a return statement giving the cost of any RTL expressions that it can handle. The default cost calculation is used for any RTL for which this macro does not return a value. This macro is optional; do not define it if the default cost assumptions are adequate for the target machine. @findex ADDRESS_COST @item ADDRESS_COST (@var{address}) An expression giving the cost of an addressing mode that contains @var{address}. If not defined, the cost is computed from the @var{address} expression and the @code{CONST_COSTS} values. For most CISC machines, the default cost is a good approximation of the true cost of the addressing mode. However, on RISC machines, all instructions normally have the same length and execution time. Hence all addresses will have equal costs. In cases where more than one form of an address is known, the form with the lowest cost will be used. If multiple forms have the same, lowest, cost, the one that is the most complex will be used. For example, suppose an address that is equal to the sum of a register and a constant is used twice in the same basic block. When this macro is not defined, the address will be computed in a register and memory references will be indirect through that register. On machines where the cost of the addressing mode containing the sum is no higher than that of a simple indirect reference, this will produce an additional instruction and possibly require an additional register. Proper specification of this macro eliminates this overhead for such machines. Similar use of this macro is made in strength reduction of loops. @var{address} need not be valid as an address. In such a case, the cost is not relevant and can be any value; invalid addresses need not be assigned a different cost. On machines where an address involving more than one register is as cheap as an address computation involving only one register, defining @code{ADDRESS_COST} to reflect this can cause two registers to be live over a region of code where only one would have been if @code{ADDRESS_COST} were not defined in that manner. This effect should be considered in the definition of this macro. Equivalent costs should probably only be given to addresses with different numbers of registers on machines with lots of registers. This macro will normally either not be defined or be defined as a constant. @findex REGISTER_MOVE_COST @item REGISTER_MOVE_COST (@var{mode}, @var{from}, @var{to}) A C expression for the cost of moving data of mode @var{mode} from a register in class @var{from} to one in class @var{to}. The classes are expressed using the enumeration values such as @code{GENERAL_REGS}. A value of 2 is the default; other values are interpreted relative to that. It is not required that the cost always equal 2 when @var{from} is the same as @var{to}; on some machines it is expensive to move between registers if they are not general registers. If reload sees an insn consisting of a single @code{set} between two hard registers, and if @code{REGISTER_MOVE_COST} applied to their classes returns a value of 2, reload does not check to ensure that the constraints of the insn are met. Setting a cost of other than 2 will allow reload to verify that the constraints are met. You should do this if the @samp{mov@var{m}} pattern's constraints do not allow such copying. @findex MEMORY_MOVE_COST @item MEMORY_MOVE_COST (@var{mode}, @var{class}, @var{in}) A C expression for the cost of moving data of mode @var{mode} between a register of class @var{class} and memory; @var{in} is zero if the value is to be written to memory, nonzero if it is to be read in. This cost is relative to those in @code{REGISTER_MOVE_COST}. If moving between registers and memory is more expensive than between two registers, you should define this macro to express the relative cost. If you do not define this macro, GCC uses a default cost of 4 plus the cost of copying via a secondary reload register, if one is needed. If your machine requires a secondary reload register to copy between memory and a register of @var{class} but the reload mechanism is more complex than copying via an intermediate, define this macro to reflect the actual cost of the move. GCC defines the function @code{memory_move_secondary_cost} if secondary reloads are needed. It computes the costs due to copying via a secondary register. If your machine copies from memory using a secondary register in the conventional way but the default base value of 4 is not correct for your machine, define this macro to add some other value to the result of that function. The arguments to that function are the same as to this macro. @findex BRANCH_COST @item BRANCH_COST A C expression for the cost of a branch instruction. A value of 1 is the default; other values are interpreted relative to that. @end table Here are additional macros which do not specify precise relative costs, but only that certain actions are more expensive than GCC would ordinarily expect. @table @code @findex SLOW_BYTE_ACCESS @item SLOW_BYTE_ACCESS Define this macro as a C expression which is nonzero if accessing less than a word of memory (i.e.@: a @code{char} or a @code{short}) is no faster than accessing a word of memory, i.e., if such access require more than one instruction or if there is no difference in cost between byte and (aligned) word loads. When this macro is not defined, the compiler will access a field by finding the smallest containing object; when it is defined, a fullword load will be used if alignment permits. Unless bytes accesses are faster than word accesses, using word accesses is preferable since it may eliminate subsequent memory access if subsequent accesses occur to other fields in the same word of the structure, but to different bytes. @findex SLOW_UNALIGNED_ACCESS @item SLOW_UNALIGNED_ACCESS (@var{mode}, @var{alignment}) Define this macro to be the value 1 if memory accesses described by the @var{mode} and @var{alignment} parameters have a cost many times greater than aligned accesses, for example if they are emulated in a trap handler. When this macro is nonzero, the compiler will act as if @code{STRICT_ALIGNMENT} were nonzero when generating code for block moves. This can cause significantly more instructions to be produced. Therefore, do not set this macro nonzero if unaligned accesses only add a cycle or two to the time for a memory access. If the value of this macro is always zero, it need not be defined. If this macro is defined, it should produce a nonzero value when @code{STRICT_ALIGNMENT} is nonzero. @findex DONT_REDUCE_ADDR @item DONT_REDUCE_ADDR Define this macro to inhibit strength reduction of memory addresses. (On some machines, such strength reduction seems to do harm rather than good.) @findex MOVE_RATIO @item MOVE_RATIO The threshold of number of scalar memory-to-memory move insns, @emph{below} which a sequence of insns should be generated instead of a string move insn or a library call. Increasing the value will always make code faster, but eventually incurs high cost in increased code size. Note that on machines where the corresponding move insn is a @code{define_expand} that emits a sequence of insns, this macro counts the number of such sequences. If you don't define this, a reasonable default is used. @findex MOVE_BY_PIECES_P @item MOVE_BY_PIECES_P (@var{size}, @var{alignment}) A C expression used to determine whether @code{move_by_pieces} will be used to copy a chunk of memory, or whether some other block move mechanism will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less than @code{MOVE_RATIO}. @findex MOVE_MAX_PIECES @item MOVE_MAX_PIECES A C expression used by @code{move_by_pieces} to determine the largest unit a load or store used to copy memory is. Defaults to @code{MOVE_MAX}. @findex CLEAR_RATIO @item CLEAR_RATIO The threshold of number of scalar move insns, @emph{below} which a sequence of insns should be generated to clear memory instead of a string clear insn or a library call. Increasing the value will always make code faster, but eventually incurs high cost in increased code size. If you don't define this, a reasonable default is used. @findex CLEAR_BY_PIECES_P @item CLEAR_BY_PIECES_P (@var{size}, @var{alignment}) A C expression used to determine whether @code{clear_by_pieces} will be used to clear a chunk of memory, or whether some other block clear mechanism will be used. Defaults to 1 if @code{move_by_pieces_ninsns} returns less than @code{CLEAR_RATIO}. @findex USE_LOAD_POST_INCREMENT @item USE_LOAD_POST_INCREMENT (@var{mode}) A C expression used to determine whether a load postincrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_POST_INCREMENT}. @findex USE_LOAD_POST_DECREMENT @item USE_LOAD_POST_DECREMENT (@var{mode}) A C expression used to determine whether a load postdecrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_POST_DECREMENT}. @findex USE_LOAD_PRE_INCREMENT @item USE_LOAD_PRE_INCREMENT (@var{mode}) A C expression used to determine whether a load preincrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_PRE_INCREMENT}. @findex USE_LOAD_PRE_DECREMENT @item USE_LOAD_PRE_DECREMENT (@var{mode}) A C expression used to determine whether a load predecrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_PRE_DECREMENT}. @findex USE_STORE_POST_INCREMENT @item USE_STORE_POST_INCREMENT (@var{mode}) A C expression used to determine whether a store postincrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_POST_INCREMENT}. @findex USE_STORE_POST_DECREMENT @item USE_STORE_POST_DECREMENT (@var{mode}) A C expression used to determine whether a store postdecrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_POST_DECREMENT}. @findex USE_STORE_PRE_INCREMENT @item USE_STORE_PRE_INCREMENT (@var{mode}) This macro is used to determine whether a store preincrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_PRE_INCREMENT}. @findex USE_STORE_PRE_DECREMENT @item USE_STORE_PRE_DECREMENT (@var{mode}) This macro is used to determine whether a store predecrement is a good thing to use for a given mode. Defaults to the value of @code{HAVE_PRE_DECREMENT}. @findex NO_FUNCTION_CSE @item NO_FUNCTION_CSE Define this macro if it is as good or better to call a constant function address than to call an address kept in a register. @findex NO_RECURSIVE_FUNCTION_CSE @item NO_RECURSIVE_FUNCTION_CSE Define this macro if it is as good or better for a function to call itself with an explicit address than to call an address kept in a register. @end table @node Scheduling @section Adjusting the Instruction Scheduler The instruction scheduler may need a fair amount of machine-specific adjustment in order to produce good code. GCC provides several target hooks for this purpose. It is usually enough to define just a few of them: try the first ones in this list first. @deftypefn {Target Hook} int TARGET_SCHED_ISSUE_RATE (void) This hook returns the maximum number of instructions that can ever issue at the same time on the target machine. The default is one. Although the insn scheduler can define itself the possibility of issue an insn on the same cycle, the value can serve as an additional constraint to issue insns on the same simulated processor cycle (see hooks @samp{TARGET_SCHED_REORDER} and @samp{TARGET_SCHED_REORDER2}). This value must be constant over the entire compilation. If you need it to vary depending on what the instructions are, you must use @samp{TARGET_SCHED_VARIABLE_ISSUE}. For the automaton based pipeline interface, you could define this hook to return the value of the macro @code{MAX_DFA_ISSUE_RATE}. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_VARIABLE_ISSUE (FILE *@var{file}, int @var{verbose}, rtx @var{insn}, int @var{more}) This hook is executed by the scheduler after it has scheduled an insn from the ready list. It should return the number of insns which can still be issued in the current cycle. Normally this is @samp{@w{@var{more} - 1}}. You should define this hook if some insns take more machine resources than others, so that fewer insns can follow them in the same cycle. @var{file} is either a null pointer, or a stdio stream to write any debug output to. @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. @var{insn} is the instruction that was scheduled. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_COST (rtx @var{insn}, rtx @var{link}, rtx @var{dep_insn}, int @var{cost}) This function corrects the value of @var{cost} based on the relationship between @var{insn} and @var{dep_insn} through the dependence @var{link}. It should return the new value. The default is to make no adjustment to @var{cost}. This can be used for example to specify to the scheduler using the traditional pipeline description that an output- or anti-dependence does not incur the same cost as a data-dependence. If the scheduler using the automaton based pipeline description, the cost of anti-dependence is zero and the cost of output-dependence is maximum of one and the difference of latency times of the first and the second insns. If these values are not acceptable, you could use the hook to modify them too. See also @pxref{Automaton pipeline description}. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_ADJUST_PRIORITY (rtx @var{insn}, int @var{priority}) This hook adjusts the integer scheduling priority @var{priority} of @var{insn}. It should return the new priority. Reduce the priority to execute @var{insn} earlier, increase the priority to execute @var{insn} later. Do not define this hook if you do not need to adjust the scheduling priorities of insns. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_REORDER (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_readyp}, int @var{clock}) This hook is executed by the scheduler after it has scheduled the ready list, to allow the machine description to reorder it (for example to combine two small instructions together on @samp{VLIW} machines). @var{file} is either a null pointer, or a stdio stream to write any debug output to. @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. @var{ready} is a pointer to the ready list of instructions that are ready to be scheduled. @var{n_readyp} is a pointer to the number of elements in the ready list. The scheduler reads the ready list in reverse order, starting with @var{ready}[@var{*n_readyp}-1] and going to @var{ready}[0]. @var{clock} is the timer tick of the scheduler. You may modify the ready list and the number of ready insns. The return value is the number of insns that can issue this cycle; normally this is just @code{issue_rate}. See also @samp{TARGET_SCHED_REORDER2}. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_REORDER2 (FILE *@var{file}, int @var{verbose}, rtx *@var{ready}, int *@var{n_ready}, @var{clock}) Like @samp{TARGET_SCHED_REORDER}, but called at a different time. That function is called whenever the scheduler starts a new cycle. This one is called once per iteration over a cycle, immediately after @samp{TARGET_SCHED_VARIABLE_ISSUE}; it can reorder the ready list and return the number of insns to be scheduled in the same cycle. Defining this hook can be useful if there are frequent situations where scheduling one insn causes other insns to become ready in the same cycle. These other insns can then be taken into account properly. @end deftypefn @deftypefn {Target Hook} void TARGET_SCHED_INIT (FILE *@var{file}, int @var{verbose}, int @var{max_ready}) This hook is executed by the scheduler at the beginning of each block of instructions that are to be scheduled. @var{file} is either a null pointer, or a stdio stream to write any debug output to. @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. @var{max_ready} is the maximum number of insns in the current scheduling region that can be live at the same time. This can be used to allocate scratch space if it is needed, e.g. by @samp{TARGET_SCHED_REORDER}. @end deftypefn @deftypefn {Target Hook} void TARGET_SCHED_FINISH (FILE *@var{file}, int @var{verbose}) This hook is executed by the scheduler at the end of each block of instructions that are to be scheduled. It can be used to perform cleanup of any actions done by the other scheduling hooks. @var{file} is either a null pointer, or a stdio stream to write any debug output to. @var{verbose} is the verbose level provided by @option{-fsched-verbose-@var{n}}. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_USE_DFA_PIPELINE_INTERFACE (void) This hook is called many times during insn scheduling. If the hook returns nonzero, the automaton based pipeline description is used for insn scheduling. Otherwise the traditional pipeline description is used. The default is usage of the traditional pipeline description. You should also remember that to simplify the insn scheduler sources an empty traditional pipeline description interface is generated even if there is no a traditional pipeline description in the @file{.md} file. The same is true for the automaton based pipeline description. That means that you should be accurate in defining the hook. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_DFA_PRE_CYCLE_INSN (void) The hook returns an RTL insn. The automaton state used in the pipeline hazard recognizer is changed as if the insn were scheduled when the new simulated processor cycle starts. Usage of the hook may simplify the automaton pipeline description for some @acronym{VLIW} processors. If the hook is defined, it is used only for the automaton based pipeline description. The default is not to change the state when the new simulated processor cycle starts. @end deftypefn @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN (void) The hook can be used to initialize data used by the previous hook. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_DFA_POST_CYCLE_INSN (void) The hook is analogous to @samp{TARGET_SCHED_DFA_PRE_CYCLE_INSN} but used to changed the state as if the insn were scheduled when the new simulated processor cycle finishes. @end deftypefn @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_POST_CYCLE_INSN (void) The hook is analogous to @samp{TARGET_SCHED_INIT_DFA_PRE_CYCLE_INSN} but used to initialize data used by the previous hook. @end deftypefn @deftypefn {Target Hook} int TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD (void) This hook controls better choosing an insn from the ready insn queue for the @acronym{DFA}-based insn scheduler. Usually the scheduler chooses the first insn from the queue. If the hook returns a positive value, an additional scheduler code tries all permutations of @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD ()} subsequent ready insns to choose an insn whose issue will result in maximal number of issued insns on the same cycle. For the @acronym{VLIW} processor, the code could actually solve the problem of packing simple insns into the @acronym{VLIW} insn. Of course, if the rules of @acronym{VLIW} packing are described in the automaton. This code also could be used for superscalar @acronym{RISC} processors. Let us consider a superscalar @acronym{RISC} processor with 3 pipelines. Some insns can be executed in pipelines @var{A} or @var{B}, some insns can be executed only in pipelines @var{B} or @var{C}, and one insn can be executed in pipeline @var{B}. The processor may issue the 1st insn into @var{A} and the 2nd one into @var{B}. In this case, the 3rd insn will wait for freeing @var{B} until the next cycle. If the scheduler issues the 3rd insn the first, the processor could issue all 3 insns per cycle. Actually this code demonstrates advantages of the automaton based pipeline hazard recognizer. We try quickly and easy many insn schedules to choose the best one. The default is no multipass scheduling. @end deftypefn @deftypefn {Target Hook} void TARGET_SCHED_INIT_DFA_BUBBLES (void) The @acronym{DFA}-based scheduler could take the insertion of nop operations for better insn scheduling into account. It can be done only if the multi-pass insn scheduling works (see hook @samp{TARGET_SCHED_FIRST_CYCLE_MULTIPASS_DFA_LOOKAHEAD}). Let us consider a @acronym{VLIW} processor insn with 3 slots. Each insn can be placed only in one of the three slots. We have 3 ready insns @var{A}, @var{B}, and @var{C}. @var{A} and @var{C} can be placed only in the 1st slot, @var{B} can be placed only in the 3rd slot. We described the automaton which does not permit empty slot gaps between insns (usually such description is simpler). Without this code the scheduler would place each insn in 3 separate @acronym{VLIW} insns. If the scheduler places a nop insn into the 2nd slot, it could place the 3 insns into 2 @acronym{VLIW} insns. What is the nop insn is returned by hook @samp{TARGET_SCHED_DFA_BUBBLE}. Hook @samp{TARGET_SCHED_INIT_DFA_BUBBLES} can be used to initialize or create the nop insns. You should remember that the scheduler does not insert the nop insns. It is not wise because of the following optimizations. The scheduler only considers such possibility to improve the result schedule. The nop insns should be inserted lately, e.g. on the final phase. @end deftypefn @deftypefn {Target Hook} rtx TARGET_SCHED_DFA_BUBBLE (int @var{index}) This hook @samp{FIRST_CYCLE_MULTIPASS_SCHEDULING} is used to insert nop operations for better insn scheduling when @acronym{DFA}-based scheduler makes multipass insn scheduling (see also description of hook @samp{TARGET_SCHED_INIT_DFA_BUBBLES}). This hook returns a nop insn with given @var{index}. The indexes start with zero. The hook should return @code{NULL} if there are no more nop insns with indexes greater than given index. @end deftypefn Macros in the following table are generated by the program @file{genattr} and can be useful for writing the hooks. @table @code @findex TRADITIONAL_PIPELINE_INTERFACE @item TRADITIONAL_PIPELINE_INTERFACE The macro definition is generated if there is a traditional pipeline description in @file{.md} file. You should also remember that to simplify the insn scheduler sources an empty traditional pipeline description interface is generated even if there is no a traditional pipeline description in the @file{.md} file. The macro can be used to distinguish the two types of the traditional interface. @findex DFA_PIPELINE_INTERFACE @item DFA_PIPELINE_INTERFACE The macro definition is generated if there is an automaton pipeline description in @file{.md} file. You should also remember that to simplify the insn scheduler sources an empty automaton pipeline description interface is generated even if there is no an automaton pipeline description in the @file{.md} file. The macro can be used to distinguish the two types of the automaton interface. @findex MAX_DFA_ISSUE_RATE @item MAX_DFA_ISSUE_RATE The macro definition is generated in the automaton based pipeline description interface. Its value is calculated from the automaton based pipeline description and is equal to maximal number of all insns described in constructions @samp{define_insn_reservation} which can be issued on the same processor cycle. @end table @node Sections @section Dividing the Output into Sections (Texts, Data, @dots{}) @c the above section title is WAY too long. maybe cut the part between @c the (...)? --mew 10feb93 An object file is divided into sections containing different types of data. In the most common case, there are three sections: the @dfn{text section}, which holds instructions and read-only data; the @dfn{data section}, which holds initialized writable data; and the @dfn{bss section}, which holds uninitialized data. Some systems have other kinds of sections. The compiler must tell the assembler when to switch sections. These macros control what commands to output to tell the assembler this. You can also define additional sections. @table @code @findex TEXT_SECTION_ASM_OP @item TEXT_SECTION_ASM_OP A C expression whose value is a string, including spacing, containing the assembler operation that should precede instructions and read-only data. Normally @code{"\t.text"} is right. @findex TEXT_SECTION @item TEXT_SECTION A C statement that switches to the default section containing instructions. Normally this is not needed, as simply defining @code{TEXT_SECTION_ASM_OP} is enough. The MIPS port uses this to sort all functions after all data declarations. @findex HOT_TEXT_SECTION_NAME @item HOT_TEXT_SECTION_NAME If defined, a C string constant for the name of the section containing most frequently executed functions of the program. If not defined, GCC will provide a default definition if the target supports named sections. @findex UNLIKELY_EXECUTED_TEXT_SECTION_NAME @item UNLIKELY_EXECUTED_TEXT_SECTION_NAME If defined, a C string constant for the name of the section containing unlikely executed functions in the program. @findex DATA_SECTION_ASM_OP @item DATA_SECTION_ASM_OP A C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as writable initialized data. Normally @code{"\t.data"} is right. @findex READONLY_DATA_SECTION_ASM_OP @item READONLY_DATA_SECTION_ASM_OP A C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as read-only initialized data. @findex READONLY_DATA_SECTION @item READONLY_DATA_SECTION A macro naming a function to call to switch to the proper section for read-only data. The default is to use @code{READONLY_DATA_SECTION_ASM_OP} if defined, else fall back to @code{text_section}. The most common definition will be @code{data_section}, if the target does not have a special read-only data section, and does not put data in the text section. @findex SHARED_SECTION_ASM_OP @item SHARED_SECTION_ASM_OP If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as shared data. If not defined, @code{DATA_SECTION_ASM_OP} will be used. @findex BSS_SECTION_ASM_OP @item BSS_SECTION_ASM_OP If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as uninitialized global data. If not defined, and neither @code{ASM_OUTPUT_BSS} nor @code{ASM_OUTPUT_ALIGNED_BSS} are defined, uninitialized global data will be output in the data section if @option{-fno-common} is passed, otherwise @code{ASM_OUTPUT_COMMON} will be used. @findex SHARED_BSS_SECTION_ASM_OP @item SHARED_BSS_SECTION_ASM_OP If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as uninitialized global shared data. If not defined, and @code{BSS_SECTION_ASM_OP} is, the latter will be used. @findex INIT_SECTION_ASM_OP @item INIT_SECTION_ASM_OP If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as initialization code. If not defined, GCC will assume such a section does not exist. @findex FINI_SECTION_ASM_OP @item FINI_SECTION_ASM_OP If defined, a C expression whose value is a string, including spacing, containing the assembler operation to identify the following data as finalization code. If not defined, GCC will assume such a section does not exist. @findex CRT_CALL_STATIC_FUNCTION @item CRT_CALL_STATIC_FUNCTION (@var{section_op}, @var{function}) If defined, an ASM statement that switches to a different section via @var{section_op}, calls @var{function}, and switches back to the text section. This is used in @file{crtstuff.c} if @code{INIT_SECTION_ASM_OP} or @code{FINI_SECTION_ASM_OP} to calls to initialization and finalization functions from the init and fini sections. By default, this macro uses a simple function call. Some ports need hand-crafted assembly code to avoid dependencies on registers initialized in the function prologue or to ensure that constant pools don't end up too far way in the text section. @findex FORCE_CODE_SECTION_ALIGN @item FORCE_CODE_SECTION_ALIGN If defined, an ASM statement that aligns a code section to some arbitrary boundary. This is used to force all fragments of the @code{.init} and @code{.fini} sections to have to same alignment and thus prevent the linker from having to add any padding. @findex EXTRA_SECTIONS @findex in_text @findex in_data @item EXTRA_SECTIONS A list of names for sections other than the standard two, which are @code{in_text} and @code{in_data}. You need not define this macro on a system with no other sections (that GCC needs to use). @findex EXTRA_SECTION_FUNCTIONS @findex text_section @findex data_section @item EXTRA_SECTION_FUNCTIONS One or more functions to be defined in @file{varasm.c}. These functions should do jobs analogous to those of @code{text_section} and @code{data_section}, for your additional sections. Do not define this macro if you do not define @code{EXTRA_SECTIONS}. @findex JUMP_TABLES_IN_TEXT_SECTION @item JUMP_TABLES_IN_TEXT_SECTION Define this macro to be an expression with a nonzero value if jump tables (for @code{tablejump} insns) should be output in the text section, along with the assembler instructions. Otherwise, the readonly data section is used. This macro is irrelevant if there is no separate readonly data section. @end table @deftypefn {Target Hook} void TARGET_ASM_SELECT_SECTION (tree @var{exp}, int @var{reloc}, unsigned HOST_WIDE_INT @var{align}) Switches to the appropriate section for output of @var{exp}. You can assume that @var{exp} is either a @code{VAR_DECL} node or a constant of some sort. @var{reloc} indicates whether the initial value of @var{exp} requires link-time relocations. Bit 0 is set when variable contains local relocations only, while bit 1 is set for global relocations. Select the section by calling @code{data_section} or one of the alternatives for other sections. @var{align} is the constant alignment in bits. The default version of this function takes care of putting read-only variables in @code{readonly_data_section}. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_UNIQUE_SECTION (tree @var{decl}, int @var{reloc}) Build up a unique section name, expressed as a @code{STRING_CST} node, and assign it to @samp{DECL_SECTION_NAME (@var{decl})}. As with @code{TARGET_ASM_SELECT_SECTION}, @var{reloc} indicates whether the initial value of @var{exp} requires link-time relocations. The default version of this function appends the symbol name to the ELF section name that would normally be used for the symbol. For example, the function @code{foo} would be placed in @code{.text.foo}. Whatever the actual target object format, this is often good enough. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_SELECT_RTX_SECTION (enum machine_mode @var{mode}, rtx @var{x}, unsigned HOST_WIDE_INT @var{align}) Switches to the appropriate section for output of constant pool entry @var{x} in @var{mode}. You can assume that @var{x} is some kind of constant in RTL@. The argument @var{mode} is redundant except in the case of a @code{const_int} rtx. Select the section by calling @code{readonly_data_section} or one of the alternatives for other sections. @var{align} is the constant alignment in bits. The default version of this function takes care of putting symbolic constants in @code{flag_pic} mode in @code{data_section} and everything else in @code{readonly_data_section}. @end deftypefn @deftypefn {Target Hook} void TARGET_ENCODE_SECTION_INFO (tree @var{decl}, int @var{new_decl_p}) Define this hook if references to a symbol or a constant must be treated differently depending on something about the variable or function named by the symbol (such as what section it is in). The hook is executed under two circumstances. One is immediately after the rtl for @var{decl} that represents a variable or a function has been created and stored in @code{DECL_RTL(@var{decl})}. The value of the rtl will be a @code{mem} whose address is a @code{symbol_ref}. The other is immediately after the rtl for @var{decl} that represents a constant has been created and stored in @code{TREE_CST_RTL (@var{decl})}. The macro is called once for each distinct constant in a source file. The @var{new_decl_p} argument will be true if this is the first time that @code{ENCODE_SECTION_INFO} has been invoked on this decl. It will be false for subsequent invocations, which will happen for duplicate declarations. Whether or not anything must be done for the duplicate declaration depends on whether the hook examines @code{DECL_ATTRIBUTES}. @cindex @code{SYMBOL_REF_FLAG}, in @code{TARGET_ENCODE_SECTION_INFO} The usual thing for this hook to do is to record a flag in the @code{symbol_ref} (such as @code{SYMBOL_REF_FLAG}) or to store a modified name string in the @code{symbol_ref} (if one bit is not enough information). @end deftypefn @deftypefn {Target Hook} const char *TARGET_STRIP_NAME_ENCODING (const char *name) Decode @var{name} and return the real name part, sans the characters that @code{TARGET_ENCODE_SECTION_INFO} may have added. @end deftypefn @deftypefn {Target Hook} bool TARGET_IN_SMALL_DATA_P (tree @var{exp}) Returns true if @var{exp} should be placed into a ``small data'' section. The default version of this hook always returns false. @end deftypefn @deftypevar {Target Hook} bool TARGET_HAVE_SRODATA_SECTION Contains the value true if the target places read-only ``small data'' into a separate section. The default value is false. @end deftypevar @deftypefn {Target Hook} bool TARGET_BINDS_LOCAL_P (tree @var{exp}) Returns true if @var{exp} names an object for which name resolution rules must resolve to the current ``module'' (dynamic shared library or executable image). The default version of this hook implements the name resolution rules for ELF, which has a looser model of global name binding than other currently supported object file formats. @end deftypefn @deftypevar {Target Hook} bool TARGET_HAVE_TLS Contains the value true if the target supports thread-local storage. The default value is false. @end deftypevar @node PIC @section Position Independent Code @cindex position independent code @cindex PIC This section describes macros that help implement generation of position independent code. Simply defining these macros is not enough to generate valid PIC; you must also add support to the macros @code{GO_IF_LEGITIMATE_ADDRESS} and @code{PRINT_OPERAND_ADDRESS}, as well as @code{LEGITIMIZE_ADDRESS}. You must modify the definition of @samp{movsi} to do something appropriate when the source operand contains a symbolic address. You may also need to alter the handling of switch statements so that they use relative addresses. @c i rearranged the order of the macros above to try to force one of @c them to the next line, to eliminate an overfull hbox. --mew 10feb93 @table @code @findex PIC_OFFSET_TABLE_REGNUM @item PIC_OFFSET_TABLE_REGNUM The register number of the register used to address a table of static data addresses in memory. In some cases this register is defined by a processor's ``application binary interface'' (ABI)@. When this macro is defined, RTL is generated for this register once, as with the stack pointer and frame pointer registers. If this macro is not defined, it is up to the machine-dependent files to allocate such a register (if necessary). Note that this register must be fixed when in use (e.g.@: when @code{flag_pic} is true). @findex PIC_OFFSET_TABLE_REG_CALL_CLOBBERED @item PIC_OFFSET_TABLE_REG_CALL_CLOBBERED Define this macro if the register defined by @code{PIC_OFFSET_TABLE_REGNUM} is clobbered by calls. Do not define this macro if @code{PIC_OFFSET_TABLE_REGNUM} is not defined. @findex FINALIZE_PIC @item FINALIZE_PIC By generating position-independent code, when two different programs (A and B) share a common library (libC.a), the text of the library can be shared whether or not the library is linked at the same address for both programs. In some of these environments, position-independent code requires not only the use of different addressing modes, but also special code to enable the use of these addressing modes. The @code{FINALIZE_PIC} macro serves as a hook to emit these special codes once the function is being compiled into assembly code, but not before. (It is not done before, because in the case of compiling an inline function, it would lead to multiple PIC prologues being included in functions which used inline functions and were compiled to assembly language.) @findex LEGITIMATE_PIC_OPERAND_P @item LEGITIMATE_PIC_OPERAND_P (@var{x}) A C expression that is nonzero if @var{x} is a legitimate immediate operand on the target machine when generating position independent code. You can assume that @var{x} satisfies @code{CONSTANT_P}, so you need not check this. You can also assume @var{flag_pic} is true, so you need not check it either. You need not define this macro if all constants (including @code{SYMBOL_REF}) can be immediate operands when generating position independent code. @end table @node Assembler Format @section Defining the Output Assembler Language This section describes macros whose principal purpose is to describe how to write instructions in assembler language---rather than what the instructions do. @menu * File Framework:: Structural information for the assembler file. * Data Output:: Output of constants (numbers, strings, addresses). * Uninitialized Data:: Output of uninitialized variables. * Label Output:: Output and generation of labels. * Initialization:: General principles of initialization and termination routines. * Macros for Initialization:: Specific macros that control the handling of initialization and termination routines. * Instruction Output:: Output of actual instructions. * Dispatch Tables:: Output of jump tables. * Exception Region Output:: Output of exception region code. * Alignment Output:: Pseudo ops for alignment and skipping data. @end menu @node File Framework @subsection The Overall Framework of an Assembler File @cindex assembler format @cindex output of assembler code @c prevent bad page break with this line This describes the overall framework of an assembler file. @table @code @findex ASM_FILE_START @item ASM_FILE_START (@var{stream}) A C expression which outputs to the stdio stream @var{stream} some appropriate text to go at the start of an assembler file. Normally this macro is defined to output a line containing @samp{#NO_APP}, which is a comment that has no effect on most assemblers but tells the GNU assembler that it can save time by not checking for certain assembler constructs. On systems that use SDB, it is necessary to output certain commands; see @file{attasm.h}. @findex ASM_FILE_END @item ASM_FILE_END (@var{stream}) A C expression which outputs to the stdio stream @var{stream} some appropriate text to go at the end of an assembler file. If this macro is not defined, the default is to output nothing special at the end of the file. Most systems don't require any definition. On systems that use SDB, it is necessary to output certain commands; see @file{attasm.h}. @findex ASM_COMMENT_START @item ASM_COMMENT_START A C string constant describing how to begin a comment in the target assembler language. The compiler assumes that the comment will end at the end of the line. @findex ASM_APP_ON @item ASM_APP_ON A C string constant for text to be output before each @code{asm} statement or group of consecutive ones. Normally this is @code{"#APP"}, which is a comment that has no effect on most assemblers but tells the GNU assembler that it must check the lines that follow for all valid assembler constructs. @findex ASM_APP_OFF @item ASM_APP_OFF A C string constant for text to be output after each @code{asm} statement or group of consecutive ones. Normally this is @code{"#NO_APP"}, which tells the GNU assembler to resume making the time-saving assumptions that are valid for ordinary compiler output. @findex ASM_OUTPUT_SOURCE_FILENAME @item ASM_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) A C statement to output COFF information or DWARF debugging information which indicates that filename @var{name} is the current source file to the stdio stream @var{stream}. This macro need not be defined if the standard form of output for the file format in use is appropriate. @findex OUTPUT_QUOTED_STRING @item OUTPUT_QUOTED_STRING (@var{stream}, @var{string}) A C statement to output the string @var{string} to the stdio stream @var{stream}. If you do not call the function @code{output_quoted_string} in your config files, GCC will only call it to output filenames to the assembler source. So you can use it to canonicalize the format of the filename using this macro. @findex ASM_OUTPUT_SOURCE_LINE @item ASM_OUTPUT_SOURCE_LINE (@var{stream}, @var{line}) A C statement to output DBX or SDB debugging information before code for line number @var{line} of the current source file to the stdio stream @var{stream}. This macro need not be defined if the standard form of debugging information for the debugger in use is appropriate. @findex ASM_OUTPUT_IDENT @item ASM_OUTPUT_IDENT (@var{stream}, @var{string}) A C statement to output something to the assembler file to handle a @samp{#ident} directive containing the text @var{string}. If this macro is not defined, nothing is output for a @samp{#ident} directive. @findex OBJC_PROLOGUE @item OBJC_PROLOGUE A C statement to output any assembler statements which are required to precede any Objective-C object definitions or message sending. The statement is executed only when compiling an Objective-C program. @end table @deftypefn {Target Hook} void TARGET_ASM_NAMED_SECTION (const char *@var{name}, unsigned int @var{flags}, unsigned int @var{align}) Output assembly directives to switch to section @var{name}. The section should have attributes as specified by @var{flags}, which is a bit mask of the @code{SECTION_*} flags defined in @file{output.h}. If @var{align} is nonzero, it contains an alignment in bytes to be used for the section, otherwise some target default should be used. Only targets that must specify an alignment within the section directive need pay attention to @var{align} -- we will still use @code{ASM_OUTPUT_ALIGN}. @end deftypefn @deftypefn {Target Hook} bool TARGET_HAVE_NAMED_SECTIONS This flag is true if the target supports @code{TARGET_ASM_NAMED_SECTION}. @end deftypefn @deftypefn {Target Hook} {unsigned int} TARGET_SECTION_TYPE_FLAGS (tree @var{decl}, const char *@var{name}, int @var{reloc}) Choose a set of section attributes for use by @code{TARGET_ASM_NAMED_SECTION} based on a variable or function decl, a section name, and whether or not the declaration's initializer may contain runtime relocations. @var{decl} may be null, in which case read-write data should be assumed. The default version if this function handles choosing code vs data, read-only vs read-write data, and @code{flag_pic}. You should only need to override this if your target has special flags that might be set via @code{__attribute__}. @end deftypefn @need 2000 @node Data Output @subsection Output of Data @deftypevr {Target Hook} {const char *} TARGET_ASM_BYTE_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_HI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_SI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_DI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_ALIGNED_TI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_HI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_SI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_DI_OP @deftypevrx {Target Hook} {const char *} TARGET_ASM_UNALIGNED_TI_OP These hooks specify assembly directives for creating certain kinds of integer object. The @code{TARGET_ASM_BYTE_OP} directive creates a byte-sized object, the @code{TARGET_ASM_ALIGNED_HI_OP} one creates an aligned two-byte object, and so on. Any of the hooks may be @code{NULL}, indicating that no suitable directive is available. The compiler will print these strings at the start of a new line, followed immediately by the object's initial value. In most cases, the string should contain a tab, a pseudo-op, and then another tab. @end deftypevr @deftypefn {Target Hook} bool TARGET_ASM_INTEGER (rtx @var{x}, unsigned int @var{size}, int @var{aligned_p}) The @code{assemble_integer} function uses this hook to output an integer object. @var{x} is the object's value, @var{size} is its size in bytes and @var{aligned_p} indicates whether it is aligned. The function should return @code{true} if it was able to output the object. If it returns false, @code{assemble_integer} will try to split the object into smaller parts. The default implementation of this hook will use the @code{TARGET_ASM_BYTE_OP} family of strings, returning @code{false} when the relevant string is @code{NULL}. @end deftypefn @table @code @findex OUTPUT_ADDR_CONST_EXTRA @item OUTPUT_ADDR_CONST_EXTRA (@var{stream}, @var{x}, @var{fail}) A C statement to recognize @var{rtx} patterns that @code{output_addr_const} can't deal with, and output assembly code to @var{stream} corresponding to the pattern @var{x}. This may be used to allow machine-dependent @code{UNSPEC}s to appear within constants. If @code{OUTPUT_ADDR_CONST_EXTRA} fails to recognize a pattern, it must @code{goto fail}, so that a standard error message is printed. If it prints an error message itself, by calling, for example, @code{output_operand_lossage}, it may just complete normally. @findex ASM_OUTPUT_ASCII @item ASM_OUTPUT_ASCII (@var{stream}, @var{ptr}, @var{len}) A C statement to output to the stdio stream @var{stream} an assembler instruction to assemble a string constant containing the @var{len} bytes at @var{ptr}. @var{ptr} will be a C expression of type @code{char *} and @var{len} a C expression of type @code{int}. If the assembler has a @code{.ascii} pseudo-op as found in the Berkeley Unix assembler, do not define the macro @code{ASM_OUTPUT_ASCII}. @findex ASM_OUTPUT_FDESC @item ASM_OUTPUT_FDESC (@var{stream}, @var{decl}, @var{n}) A C statement to output word @var{n} of a function descriptor for @var{decl}. This must be defined if @code{TARGET_VTABLE_USES_DESCRIPTORS} is defined, and is otherwise unused. @findex CONSTANT_POOL_BEFORE_FUNCTION @item CONSTANT_POOL_BEFORE_FUNCTION You may define this macro as a C expression. You should define the expression to have a nonzero value if GCC should output the constant pool for a function before the code for the function, or a zero value if GCC should output the constant pool after the function. If you do not define this macro, the usual case, GCC will output the constant pool before the function. @findex ASM_OUTPUT_POOL_PROLOGUE @item ASM_OUTPUT_POOL_PROLOGUE (@var{file}, @var{funname}, @var{fundecl}, @var{size}) A C statement to output assembler commands to define the start of the constant pool for a function. @var{funname} is a string giving the name of the function. Should the return type of the function be required, it can be obtained via @var{fundecl}. @var{size} is the size, in bytes, of the constant pool that will be written immediately after this call. If no constant-pool prefix is required, the usual case, this macro need not be defined. @findex ASM_OUTPUT_SPECIAL_POOL_ENTRY @item ASM_OUTPUT_SPECIAL_POOL_ENTRY (@var{file}, @var{x}, @var{mode}, @var{align}, @var{labelno}, @var{jumpto}) A C statement (with or without semicolon) to output a constant in the constant pool, if it needs special treatment. (This macro need not do anything for RTL expressions that can be output normally.) The argument @var{file} is the standard I/O stream to output the assembler code on. @var{x} is the RTL expression for the constant to output, and @var{mode} is the machine mode (in case @var{x} is a @samp{const_int}). @var{align} is the required alignment for the value @var{x}; you should output an assembler directive to force this much alignment. The argument @var{labelno} is a number to use in an internal label for the address of this pool entry. The definition of this macro is responsible for outputting the label definition at the proper place. Here is how to do this: @example ASM_OUTPUT_INTERNAL_LABEL (@var{file}, "LC", @var{labelno}); @end example When you output a pool entry specially, you should end with a @code{goto} to the label @var{jumpto}. This will prevent the same pool entry from being output a second time in the usual manner. You need not define this macro if it would do nothing. @findex CONSTANT_AFTER_FUNCTION_P @item CONSTANT_AFTER_FUNCTION_P (@var{exp}) Define this macro as a C expression which is nonzero if the constant @var{exp}, of type @code{tree}, should be output after the code for a function. The compiler will normally output all constants before the function; you need not define this macro if this is OK@. @findex ASM_OUTPUT_POOL_EPILOGUE @item ASM_OUTPUT_POOL_EPILOGUE (@var{file} @var{funname} @var{fundecl} @var{size}) A C statement to output assembler commands to at the end of the constant pool for a function. @var{funname} is a string giving the name of the function. Should the return type of the function be required, you can obtain it via @var{fundecl}. @var{size} is the size, in bytes, of the constant pool that GCC wrote immediately before this call. If no constant-pool epilogue is required, the usual case, you need not define this macro. @findex IS_ASM_LOGICAL_LINE_SEPARATOR @item IS_ASM_LOGICAL_LINE_SEPARATOR (@var{C}) Define this macro as a C expression which is nonzero if @var{C} is used as a logical line separator by the assembler. If you do not define this macro, the default is that only the character @samp{;} is treated as a logical line separator. @end table @deftypevr {Target Hook} {const char *} TARGET_ASM_OPEN_PAREN @deftypevrx {Target Hook} {const char *} TARGET_ASM_CLOSE_PAREN These target hooks are C string constants, describing the syntax in the assembler for grouping arithmetic expressions. If not overridden, they default to normal parentheses, which is correct for most assemblers. @end deftypevr These macros are provided by @file{real.h} for writing the definitions of @code{ASM_OUTPUT_DOUBLE} and the like: @table @code @item REAL_VALUE_TO_TARGET_SINGLE (@var{x}, @var{l}) @itemx REAL_VALUE_TO_TARGET_DOUBLE (@var{x}, @var{l}) @itemx REAL_VALUE_TO_TARGET_LONG_DOUBLE (@var{x}, @var{l}) @findex REAL_VALUE_TO_TARGET_SINGLE @findex REAL_VALUE_TO_TARGET_DOUBLE @findex REAL_VALUE_TO_TARGET_LONG_DOUBLE These translate @var{x}, of type @code{REAL_VALUE_TYPE}, to the target's floating point representation, and store its bit pattern in the variable @var{l}. For @code{REAL_VALUE_TO_TARGET_SINGLE}, this variable should be a simple @code{long int}. For the others, it should be an array of @code{long int}. The number of elements in this array is determined by the size of the desired target floating point data type: 32 bits of it go in each @code{long int} array element. Each array element holds 32 bits of the result, even if @code{long int} is wider than 32 bits on the host machine. The array element values are designed so that you can print them out using @code{fprintf} in the order they should appear in the target machine's memory. @item REAL_VALUE_TO_DECIMAL (@var{x}, @var{string}, @var{digits}) @findex REAL_VALUE_TO_DECIMAL This macro converts @var{x}, of type @code{REAL_VALUE_TYPE}, to a decimal number and stores it as a string into @var{string}. You must pass, as @var{string}, the address of a long enough block of space to hold the result. The argument @var{digits} is the number of decimal digits to print, or @minus{}1 to indicate ``enough'', i.e. @code{DECIMAL_DIG} for for the target. @end table @node Uninitialized Data @subsection Output of Uninitialized Variables Each of the macros in this section is used to do the whole job of outputting a single uninitialized variable. @table @code @findex ASM_OUTPUT_COMMON @item ASM_OUTPUT_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) A C statement (sans semicolon) to output to the stdio stream @var{stream} the assembler definition of a common-label named @var{name} whose size is @var{size} bytes. The variable @var{rounded} is the size rounded up to whatever alignment the caller wants. Use the expression @code{assemble_name (@var{stream}, @var{name})} to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. This macro controls how the assembler definitions of uninitialized common global variables are output. @findex ASM_OUTPUT_ALIGNED_COMMON @item ASM_OUTPUT_ALIGNED_COMMON (@var{stream}, @var{name}, @var{size}, @var{alignment}) Like @code{ASM_OUTPUT_COMMON} except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of @code{ASM_OUTPUT_COMMON}, and gives you more flexibility in handling the required alignment of the variable. The alignment is specified as the number of bits. @findex ASM_OUTPUT_ALIGNED_DECL_COMMON @item ASM_OUTPUT_ALIGNED_DECL_COMMON (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) Like @code{ASM_OUTPUT_ALIGNED_COMMON} except that @var{decl} of the variable to be output, if there is one, or @code{NULL_TREE} if there is no corresponding variable. If you define this macro, GCC will use it in place of both @code{ASM_OUTPUT_COMMON} and @code{ASM_OUTPUT_ALIGNED_COMMON}. Define this macro when you need to see the variable's decl in order to chose what to output. @findex ASM_OUTPUT_SHARED_COMMON @item ASM_OUTPUT_SHARED_COMMON (@var{stream}, @var{name}, @var{size}, @var{rounded}) If defined, it is similar to @code{ASM_OUTPUT_COMMON}, except that it is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_COMMON} will be used. @findex ASM_OUTPUT_BSS @item ASM_OUTPUT_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) A C statement (sans semicolon) to output to the stdio stream @var{stream} the assembler definition of uninitialized global @var{decl} named @var{name} whose size is @var{size} bytes. The variable @var{rounded} is the size rounded up to whatever alignment the caller wants. Try to use function @code{asm_output_bss} defined in @file{varasm.c} when defining this macro. If unable, use the expression @code{assemble_name (@var{stream}, @var{name})} to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. This macro controls how the assembler definitions of uninitialized global variables are output. This macro exists to properly support languages like C++ which do not have @code{common} data. However, this macro currently is not defined for all targets. If this macro and @code{ASM_OUTPUT_ALIGNED_BSS} are not defined then @code{ASM_OUTPUT_COMMON} or @code{ASM_OUTPUT_ALIGNED_COMMON} or @code{ASM_OUTPUT_ALIGNED_DECL_COMMON} is used. @findex ASM_OUTPUT_ALIGNED_BSS @item ASM_OUTPUT_ALIGNED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) Like @code{ASM_OUTPUT_BSS} except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of @code{ASM_OUTPUT_BSS}, and gives you more flexibility in handling the required alignment of the variable. The alignment is specified as the number of bits. Try to use function @code{asm_output_aligned_bss} defined in file @file{varasm.c} when defining this macro. @findex ASM_OUTPUT_SHARED_BSS @item ASM_OUTPUT_SHARED_BSS (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{rounded}) If defined, it is similar to @code{ASM_OUTPUT_BSS}, except that it is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_BSS} will be used. @findex ASM_OUTPUT_LOCAL @item ASM_OUTPUT_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) A C statement (sans semicolon) to output to the stdio stream @var{stream} the assembler definition of a local-common-label named @var{name} whose size is @var{size} bytes. The variable @var{rounded} is the size rounded up to whatever alignment the caller wants. Use the expression @code{assemble_name (@var{stream}, @var{name})} to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. This macro controls how the assembler definitions of uninitialized static variables are output. @findex ASM_OUTPUT_ALIGNED_LOCAL @item ASM_OUTPUT_ALIGNED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{alignment}) Like @code{ASM_OUTPUT_LOCAL} except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of @code{ASM_OUTPUT_LOCAL}, and gives you more flexibility in handling the required alignment of the variable. The alignment is specified as the number of bits. @findex ASM_OUTPUT_ALIGNED_DECL_LOCAL @item ASM_OUTPUT_ALIGNED_DECL_LOCAL (@var{stream}, @var{decl}, @var{name}, @var{size}, @var{alignment}) Like @code{ASM_OUTPUT_ALIGNED_DECL} except that @var{decl} of the variable to be output, if there is one, or @code{NULL_TREE} if there is no corresponding variable. If you define this macro, GCC will use it in place of both @code{ASM_OUTPUT_DECL} and @code{ASM_OUTPUT_ALIGNED_DECL}. Define this macro when you need to see the variable's decl in order to chose what to output. @findex ASM_OUTPUT_SHARED_LOCAL @item ASM_OUTPUT_SHARED_LOCAL (@var{stream}, @var{name}, @var{size}, @var{rounded}) If defined, it is similar to @code{ASM_OUTPUT_LOCAL}, except that it is used when @var{name} is shared. If not defined, @code{ASM_OUTPUT_LOCAL} will be used. @end table @node Label Output @subsection Output and Generation of Labels @c prevent bad page break with this line This is about outputting labels. @table @code @findex ASM_OUTPUT_LABEL @findex assemble_name @item ASM_OUTPUT_LABEL (@var{stream}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} the assembler definition of a label named @var{name}. Use the expression @code{assemble_name (@var{stream}, @var{name})} to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. A default definition of this macro is provided which is correct for most systems. @findex SIZE_ASM_OP @item SIZE_ASM_OP A C string containing the appropriate assembler directive to specify the size of a symbol, without any arguments. On systems that use ELF, the default (in @file{config/elfos.h}) is @samp{"\t.size\t"}; on other systems, the default is not to define this macro. Define this macro only if it is correct to use the default definitions of @code{ASM_OUTPUT_SIZE_DIRECTIVE} and @code{ASM_OUTPUT_MEASURED_SIZE} for your system. If you need your own custom definitions of those macros, or if you do not need explicit symbol sizes at all, do not define this macro. @findex ASM_OUTPUT_SIZE_DIRECTIVE @item ASM_OUTPUT_SIZE_DIRECTIVE (@var{stream}, @var{name}, @var{size}) A C statement (sans semicolon) to output to the stdio stream @var{stream} a directive telling the assembler that the size of the symbol @var{name} is @var{size}. @var{size} is a @code{HOST_WIDE_INT}. If you define @code{SIZE_ASM_OP}, a default definition of this macro is provided. @findex ASM_OUTPUT_MEASURED_SIZE @item ASM_OUTPUT_MEASURED_SIZE (@var{stream}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} a directive telling the assembler to calculate the size of the symbol @var{name} by subtracting its address from the current address. If you define @code{SIZE_ASM_OP}, a default definition of this macro is provided. The default assumes that the assembler recognizes a special @samp{.} symbol as referring to the current address, and can calculate the difference between this and another symbol. If your assembler does not recognize @samp{.} or cannot do calculations with it, you will need to redefine @code{ASM_OUTPUT_MEASURED_SIZE} to use some other technique. @findex TYPE_ASM_OP @item TYPE_ASM_OP A C string containing the appropriate assembler directive to specify the type of a symbol, without any arguments. On systems that use ELF, the default (in @file{config/elfos.h}) is @samp{"\t.type\t"}; on other systems, the default is not to define this macro. Define this macro only if it is correct to use the default definition of @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own custom definition of this macro, or if you do not need explicit symbol types at all, do not define this macro. @findex TYPE_OPERAND_FMT @item TYPE_OPERAND_FMT A C string which specifies (using @code{printf} syntax) the format of the second operand to @code{TYPE_ASM_OP}. On systems that use ELF, the default (in @file{config/elfos.h}) is @samp{"@@%s"}; on other systems, the default is not to define this macro. Define this macro only if it is correct to use the default definition of @code{ASM_OUTPUT_TYPE_DIRECTIVE} for your system. If you need your own custom definition of this macro, or if you do not need explicit symbol types at all, do not define this macro. @findex ASM_OUTPUT_TYPE_DIRECTIVE @item ASM_OUTPUT_TYPE_DIRECTIVE (@var{stream}, @var{type}) A C statement (sans semicolon) to output to the stdio stream @var{stream} a directive telling the assembler that the type of the symbol @var{name} is @var{type}. @var{type} is a C string; currently, that string is always either @samp{"function"} or @samp{"object"}, but you should not count on this. If you define @code{TYPE_ASM_OP} and @code{TYPE_OPERAND_FMT}, a default definition of this macro is provided. @findex ASM_DECLARE_FUNCTION_NAME @item ASM_DECLARE_FUNCTION_NAME (@var{stream}, @var{name}, @var{decl}) A C statement (sans semicolon) to output to the stdio stream @var{stream} any text necessary for declaring the name @var{name} of a function which is being defined. This macro is responsible for outputting the label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the @code{FUNCTION_DECL} tree node representing the function. If this macro is not defined, then the function name is defined in the usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} in the definition of this macro. @findex ASM_DECLARE_FUNCTION_SIZE @item ASM_DECLARE_FUNCTION_SIZE (@var{stream}, @var{name}, @var{decl}) A C statement (sans semicolon) to output to the stdio stream @var{stream} any text necessary for declaring the size of a function which is being defined. The argument @var{name} is the name of the function. The argument @var{decl} is the @code{FUNCTION_DECL} tree node representing the function. If this macro is not defined, then the function size is not defined. You may wish to use @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. @findex ASM_DECLARE_OBJECT_NAME @item ASM_DECLARE_OBJECT_NAME (@var{stream}, @var{name}, @var{decl}) A C statement (sans semicolon) to output to the stdio stream @var{stream} any text necessary for declaring the name @var{name} of an initialized variable which is being defined. This macro must output the label definition (perhaps using @code{ASM_OUTPUT_LABEL}). The argument @var{decl} is the @code{VAR_DECL} tree node representing the variable. If this macro is not defined, then the variable name is defined in the usual manner as a label (by means of @code{ASM_OUTPUT_LABEL}). You may wish to use @code{ASM_OUTPUT_TYPE_DIRECTIVE} and/or @code{ASM_OUTPUT_SIZE_DIRECTIVE} in the definition of this macro. @findex ASM_DECLARE_REGISTER_GLOBAL @item ASM_DECLARE_REGISTER_GLOBAL (@var{stream}, @var{decl}, @var{regno}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} any text necessary for claiming a register @var{regno} for a global variable @var{decl} with name @var{name}. If you don't define this macro, that is equivalent to defining it to do nothing. @findex ASM_FINISH_DECLARE_OBJECT @item ASM_FINISH_DECLARE_OBJECT (@var{stream}, @var{decl}, @var{toplevel}, @var{atend}) A C statement (sans semicolon) to finish up declaring a variable name once the compiler has processed its initializer fully and thus has had a chance to determine the size of an array when controlled by an initializer. This is used on systems where it's necessary to declare something about the size of the object. If you don't define this macro, that is equivalent to defining it to do nothing. You may wish to use @code{ASM_OUTPUT_SIZE_DIRECTIVE} and/or @code{ASM_OUTPUT_MEASURED_SIZE} in the definition of this macro. @end table @deftypefn {Target Hook} void TARGET_ASM_GLOBALIZE_LABEL (FILE *@var{stream}, const char *@var{name}) This target hook is a function to output to the stdio stream @var{stream} some commands that will make the label @var{name} global; that is, available for reference from other files. The default implementation relies on a proper definition of @code{GLOBAL_ASM_OP}. @end deftypefn @table @code @findex ASM_WEAKEN_LABEL @item ASM_WEAKEN_LABEL (@var{stream}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} some commands that will make the label @var{name} weak; that is, available for reference from other files but only used if no other definition is available. Use the expression @code{assemble_name (@var{stream}, @var{name})} to output the name itself; before and after that, output the additional assembler syntax for making that name weak, and a newline. If you don't define this macro or @code{ASM_WEAKEN_DECL}, GCC will not support weak symbols and you should not define the @code{SUPPORTS_WEAK} macro. @findex ASM_WEAKEN_DECL @item ASM_WEAKEN_DECL (@var{stream}, @var{decl}, @var{name}, @var{value}) Combines (and replaces) the function of @code{ASM_WEAKEN_LABEL} and @code{ASM_OUTPUT_WEAK_ALIAS}, allowing access to the associated function or variable decl. If @var{value} is not @code{NULL}, this C statement should output to the stdio stream @var{stream} assembler code which defines (equates) the weak symbol @var{name} to have the value @var{value}. If @var{value} is @code{NULL}, it should output commands to make @var{name} weak. @findex SUPPORTS_WEAK @item SUPPORTS_WEAK A C expression which evaluates to true if the target supports weak symbols. If you don't define this macro, @file{defaults.h} provides a default definition. If either @code{ASM_WEAKEN_LABEL} or @code{ASM_WEAKEN_DECL} is defined, the default definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if you want to control weak symbol support with a compiler flag such as @option{-melf}. @findex MAKE_DECL_ONE_ONLY (@var{decl}) @item MAKE_DECL_ONE_ONLY A C statement (sans semicolon) to mark @var{decl} to be emitted as a public symbol such that extra copies in multiple translation units will be discarded by the linker. Define this macro if your object file format provides support for this concept, such as the @samp{COMDAT} section flags in the Microsoft Windows PE/COFF format, and this support requires changes to @var{decl}, such as putting it in a separate section. @findex SUPPORTS_ONE_ONLY @item SUPPORTS_ONE_ONLY A C expression which evaluates to true if the target supports one-only semantics. If you don't define this macro, @file{varasm.c} provides a default definition. If @code{MAKE_DECL_ONE_ONLY} is defined, the default definition is @samp{1}; otherwise, it is @samp{0}. Define this macro if you want to control one-only symbol support with a compiler flag, or if setting the @code{DECL_ONE_ONLY} flag is enough to mark a declaration to be emitted as one-only. @deftypefn {Target Hook} void TARGET_ASM_ASSEMBLE_VISIBILITY (tree @var{decl}, const char *@var{visibility}) This target hook is a function to output to @var{asm_out_file} some commands that will make the symbol(s) associated with @var{decl} have hidden, protected or internal visibility as specified by @var{visibility}. @end deftypefn @findex ASM_OUTPUT_EXTERNAL @item ASM_OUTPUT_EXTERNAL (@var{stream}, @var{decl}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} any text necessary for declaring the name of an external symbol named @var{name} which is referenced in this compilation but not defined. The value of @var{decl} is the tree node for the declaration. This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything. @findex ASM_OUTPUT_EXTERNAL_LIBCALL @item ASM_OUTPUT_EXTERNAL_LIBCALL (@var{stream}, @var{symref}) A C statement (sans semicolon) to output on @var{stream} an assembler pseudo-op to declare a library function name external. The name of the library function is given by @var{symref}, which has type @code{rtx} and is a @code{symbol_ref}. This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything. @findex ASM_OUTPUT_LABELREF @item ASM_OUTPUT_LABELREF (@var{stream}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} a reference in assembler syntax to a label named @var{name}. This should add @samp{_} to the front of the name, if that is customary on your operating system, as it is in most Berkeley Unix systems. This macro is used in @code{assemble_name}. @findex ASM_OUTPUT_SYMBOL_REF @item ASM_OUTPUT_SYMBOL_REF (@var{stream}, @var{sym}) A C statement (sans semicolon) to output a reference to @code{SYMBOL_REF} @var{sym}. If not defined, @code{assemble_name} will be used to output the name of the symbol. This macro may be used to modify the way a symbol is referenced depending on information encoded by @code{TARGET_ENCODE_SECTION_INFO}. @findex ASM_OUTPUT_LABEL_REF @item ASM_OUTPUT_LABEL_REF (@var{stream}, @var{buf}) A C statement (sans semicolon) to output a reference to @var{buf}, the result of @code{ASM_GENERATE_INTERNAL_LABEL}. If not defined, @code{assemble_name} will be used to output the name of the symbol. This macro is not used by @code{output_asm_label}, or the @code{%l} specifier that calls it; the intention is that this macro should be set when it is necessary to output a label differently when its address is being taken. @findex ASM_OUTPUT_INTERNAL_LABEL @item ASM_OUTPUT_INTERNAL_LABEL (@var{stream}, @var{prefix}, @var{num}) A C statement to output to the stdio stream @var{stream} a label whose name is made from the string @var{prefix} and the number @var{num}. It is absolutely essential that these labels be distinct from the labels used for user-level functions and variables. Otherwise, certain programs will have name conflicts with internal labels. It is desirable to exclude internal labels from the symbol table of the object file. Most assemblers have a naming convention for labels that should be excluded; on many systems, the letter @samp{L} at the beginning of a label has this effect. You should find out what convention your system uses, and follow it. The usual definition of this macro is as follows: @example fprintf (@var{stream}, "L%s%d:\n", @var{prefix}, @var{num}) @end example @findex ASM_OUTPUT_DEBUG_LABEL @item ASM_OUTPUT_DEBUG_LABEL (@var{stream}, @var{prefix}, @var{num}) A C statement to output to the stdio stream @var{stream} a debug info label whose name is made from the string @var{prefix} and the number @var{num}. This is useful for VLIW targets, where debug info labels may need to be treated differently than branch target labels. On some systems, branch target labels must be at the beginning of instruction bundles, but debug info labels can occur in the middle of instruction bundles. If this macro is not defined, then @code{ASM_OUTPUT_INTERNAL_LABEL} will be used. @findex ASM_GENERATE_INTERNAL_LABEL @item ASM_GENERATE_INTERNAL_LABEL (@var{string}, @var{prefix}, @var{num}) A C statement to store into the string @var{string} a label whose name is made from the string @var{prefix} and the number @var{num}. This string, when output subsequently by @code{assemble_name}, should produce the output that @code{ASM_OUTPUT_INTERNAL_LABEL} would produce with the same @var{prefix} and @var{num}. If the string begins with @samp{*}, then @code{assemble_name} will output the rest of the string unchanged. It is often convenient for @code{ASM_GENERATE_INTERNAL_LABEL} to use @samp{*} in this way. If the string doesn't start with @samp{*}, then @code{ASM_OUTPUT_LABELREF} gets to output the string, and may change it. (Of course, @code{ASM_OUTPUT_LABELREF} is also part of your machine description, so you should know what it does on your machine.) @findex ASM_FORMAT_PRIVATE_NAME @item ASM_FORMAT_PRIVATE_NAME (@var{outvar}, @var{name}, @var{number}) A C expression to assign to @var{outvar} (which is a variable of type @code{char *}) a newly allocated string made from the string @var{name} and the number @var{number}, with some suitable punctuation added. Use @code{alloca} to get space for the string. The string will be used as an argument to @code{ASM_OUTPUT_LABELREF} to produce an assembler label for an internal static variable whose name is @var{name}. Therefore, the string must be such as to result in valid assembler code. The argument @var{number} is different each time this macro is executed; it prevents conflicts between similarly-named internal static variables in different scopes. Ideally this string should not be a valid C identifier, to prevent any conflict with the user's own symbols. Most assemblers allow periods or percent signs in assembler symbols; putting at least one of these between the name and the number will suffice. @findex ASM_OUTPUT_DEF @item ASM_OUTPUT_DEF (@var{stream}, @var{name}, @var{value}) A C statement to output to the stdio stream @var{stream} assembler code which defines (equates) the symbol @var{name} to have the value @var{value}. @findex SET_ASM_OP If @code{SET_ASM_OP} is defined, a default definition is provided which is correct for most systems. @findex ASM_OUTPUT_DEF_FROM_DECLS @item ASM_OUTPUT_DEF_FROM_DECLS (@var{stream}, @var{decl_of_name}, @var{decl_of_value}) A C statement to output to the stdio stream @var{stream} assembler code which defines (equates) the symbol whose tree node is @var{decl_of_name} to have the value of the tree node @var{decl_of_value}. This macro will be used in preference to @samp{ASM_OUTPUT_DEF} if it is defined and if the tree nodes are available. @findex SET_ASM_OP If @code{SET_ASM_OP} is defined, a default definition is provided which is correct for most systems. @findex ASM_OUTPUT_WEAK_ALIAS @item ASM_OUTPUT_WEAK_ALIAS (@var{stream}, @var{name}, @var{value}) A C statement to output to the stdio stream @var{stream} assembler code which defines (equates) the weak symbol @var{name} to have the value @var{value}. If @var{value} is @code{NULL}, it defines @var{name} as an undefined weak symbol. Define this macro if the target only supports weak aliases; define @code{ASM_OUTPUT_DEF} instead if possible. @findex OBJC_GEN_METHOD_LABEL @item OBJC_GEN_METHOD_LABEL (@var{buf}, @var{is_inst}, @var{class_name}, @var{cat_name}, @var{sel_name}) Define this macro to override the default assembler names used for Objective-C methods. The default name is a unique method number followed by the name of the class (e.g.@: @samp{_1_Foo}). For methods in categories, the name of the category is also included in the assembler name (e.g.@: @samp{_1_Foo_Bar}). These names are safe on most systems, but make debugging difficult since the method's selector is not present in the name. Therefore, particular systems define other ways of computing names. @var{buf} is an expression of type @code{char *} which gives you a buffer in which to store the name; its length is as long as @var{class_name}, @var{cat_name} and @var{sel_name} put together, plus 50 characters extra. The argument @var{is_inst} specifies whether the method is an instance method or a class method; @var{class_name} is the name of the class; @var{cat_name} is the name of the category (or @code{NULL} if the method is not in a category); and @var{sel_name} is the name of the selector. On systems where the assembler can handle quoted names, you can use this macro to provide more human-readable names. @findex ASM_DECLARE_CLASS_REFERENCE @item ASM_DECLARE_CLASS_REFERENCE (@var{stream}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} commands to declare that the label @var{name} is an Objective-C class reference. This is only needed for targets whose linkers have special support for NeXT-style runtimes. @findex ASM_DECLARE_UNRESOLVED_REFERENCE @item ASM_DECLARE_UNRESOLVED_REFERENCE (@var{stream}, @var{name}) A C statement (sans semicolon) to output to the stdio stream @var{stream} commands to declare that the label @var{name} is an unresolved Objective-C class reference. This is only needed for targets whose linkers have special support for NeXT-style runtimes. @end table @node Initialization @subsection How Initialization Functions Are Handled @cindex initialization routines @cindex termination routines @cindex constructors, output of @cindex destructors, output of The compiled code for certain languages includes @dfn{constructors} (also called @dfn{initialization routines})---functions to initialize data in the program when the program is started. These functions need to be called before the program is ``started''---that is to say, before @code{main} is called. Compiling some languages generates @dfn{destructors} (also called @dfn{termination routines}) that should be called when the program terminates. To make the initialization and termination functions work, the compiler must output something in the assembler code to cause those functions to be called at the appropriate time. When you port the compiler to a new system, you need to specify how to do this. There are two major ways that GCC currently supports the execution of initialization and termination functions. Each way has two variants. Much of the structure is common to all four variations. @findex __CTOR_LIST__ @findex __DTOR_LIST__ The linker must build two lists of these functions---a list of initialization functions, called @code{__CTOR_LIST__}, and a list of termination functions, called @code{__DTOR_LIST__}. Each list always begins with an ignored function pointer (which may hold 0, @minus{}1, or a count of the function pointers after it, depending on the environment). This is followed by a series of zero or more function pointers to constructors (or destructors), followed by a function pointer containing zero. Depending on the operating system and its executable file format, either @file{crtstuff.c} or @file{libgcc2.c} traverses these lists at startup time and exit time. Constructors are called in reverse order of the list; destructors in forward order. The best way to handle static constructors works only for object file formats which provide arbitrarily-named sections. A section is set aside for a list of constructors, and another for a list of destructors. Traditionally these are called @samp{.ctors} and @samp{.dtors}. Each object file that defines an initialization function also puts a word in the constructor section to point to that function. The linker accumulates all these words into one contiguous @samp{.ctors} section. Termination functions are handled similarly. This method will be chosen as the default by @file{target-def.h} if @code{TARGET_ASM_NAMED_SECTION} is defined. A target that does not support arbitrary sections, but does support special designated constructor and destructor sections may define @code{CTORS_SECTION_ASM_OP} and @code{DTORS_SECTION_ASM_OP} to achieve the same effect. When arbitrary sections are available, there are two variants, depending upon how the code in @file{crtstuff.c} is called. On systems that support a @dfn{.init} section which is executed at program startup, parts of @file{crtstuff.c} are compiled into that section. The program is linked by the @code{gcc} driver like this: @example ld -o @var{output_file} crti.o crtbegin.o @dots{} -lgcc crtend.o crtn.o @end example The prologue of a function (@code{__init}) appears in the @code{.init} section of @file{crti.o}; the epilogue appears in @file{crtn.o}. Likewise for the function @code{__fini} in the @dfn{.fini} section. Normally these files are provided by the operating system or by the GNU C library, but are provided by GCC for a few targets. The objects @file{crtbegin.o} and @file{crtend.o} are (for most targets) compiled from @file{crtstuff.c}. They contain, among other things, code fragments within the @code{.init} and @code{.fini} sections that branch to routines in the @code{.text} section. The linker will pull all parts of a section together, which results in a complete @code{__init} function that invokes the routines we need at startup. To use this variant, you must define the @code{INIT_SECTION_ASM_OP} macro properly. If no init section is available, when GCC compiles any function called @code{main} (or more accurately, any function designated as a program entry point by the language front end calling @code{expand_main_function}), it inserts a procedure call to @code{__main} as the first executable code after the function prologue. The @code{__main} function is defined in @file{libgcc2.c} and runs the global constructors. In file formats that don't support arbitrary sections, there are again two variants. In the simplest variant, the GNU linker (GNU @code{ld}) and an `a.out' format must be used. In this case, @code{TARGET_ASM_CONSTRUCTOR} is defined to produce a @code{.stabs} entry of type @samp{N_SETT}, referencing the name @code{__CTOR_LIST__}, and with the address of the void function containing the initialization code as its value. The GNU linker recognizes this as a request to add the value to a @dfn{set}; the values are accumulated, and are eventually placed in the executable as a vector in the format described above, with a leading (ignored) count and a trailing zero element. @code{TARGET_ASM_DESTRUCTOR} is handled similarly. Since no init section is available, the absence of @code{INIT_SECTION_ASM_OP} causes the compilation of @code{main} to call @code{__main} as above, starting the initialization process. The last variant uses neither arbitrary sections nor the GNU linker. This is preferable when you want to do dynamic linking and when using file formats which the GNU linker does not support, such as `ECOFF'@. In this case, @code{TARGET_HAVE_CTORS_DTORS} is false, initialization and termination functions are recognized simply by their names. This requires an extra program in the linkage step, called @command{collect2}. This program pretends to be the linker, for use with GCC; it does its job by running the ordinary linker, but also arranges to include the vectors of initialization and termination functions. These functions are called via @code{__main} as described above. In order to use this method, @code{use_collect2} must be defined in the target in @file{config.gcc}. @ifinfo The following section describes the specific macros that control and customize the handling of initialization and termination functions. @end ifinfo @node Macros for Initialization @subsection Macros Controlling Initialization Routines Here are the macros that control how the compiler handles initialization and termination functions: @table @code @findex INIT_SECTION_ASM_OP @item INIT_SECTION_ASM_OP If defined, a C string constant, including spacing, for the assembler operation to identify the following data as initialization code. If not defined, GCC will assume such a section does not exist. When you are using special sections for initialization and termination functions, this macro also controls how @file{crtstuff.c} and @file{libgcc2.c} arrange to run the initialization functions. @item HAS_INIT_SECTION @findex HAS_INIT_SECTION If defined, @code{main} will not call @code{__main} as described above. This macro should be defined for systems that control start-up code on a symbol-by-symbol basis, such as OSF/1, and should not be defined explicitly for systems that support @code{INIT_SECTION_ASM_OP}. @item LD_INIT_SWITCH @findex LD_INIT_SWITCH If defined, a C string constant for a switch that tells the linker that the following symbol is an initialization routine. @item LD_FINI_SWITCH @findex LD_FINI_SWITCH If defined, a C string constant for a switch that tells the linker that the following symbol is a finalization routine. @item COLLECT_SHARED_INIT_FUNC (@var{stream}, @var{func}) If defined, a C statement that will write a function that can be automatically called when a shared library is loaded. The function should call @var{func}, which takes no arguments. If not defined, and the object format requires an explicit initialization function, then a function called @code{_GLOBAL__DI} will be generated. This function and the following one are used by collect2 when linking a shared library that needs constructors or destructors, or has DWARF2 exception tables embedded in the code. @item COLLECT_SHARED_FINI_FUNC (@var{stream}, @var{func}) If defined, a C statement that will write a function that can be automatically called when a shared library is unloaded. The function should call @var{func}, which takes no arguments. If not defined, and the object format requires an explicit finalization function, then a function called @code{_GLOBAL__DD} will be generated. @item INVOKE__main @findex INVOKE__main If defined, @code{main} will call @code{__main} despite the presence of @code{INIT_SECTION_ASM_OP}. This macro should be defined for systems where the init section is not actually run automatically, but is still useful for collecting the lists of constructors and destructors. @item SUPPORTS_INIT_PRIORITY @findex SUPPORTS_INIT_PRIORITY If nonzero, the C++ @code{init_priority} attribute is supported and the compiler should emit instructions to control the order of initialization of objects. If zero, the compiler will issue an error message upon encountering an @code{init_priority} attribute. @end table @deftypefn {Target Hook} bool TARGET_HAVE_CTORS_DTORS This value is true if the target supports some ``native'' method of collecting constructors and destructors to be run at startup and exit. It is false if we must use @command{collect2}. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_CONSTRUCTOR (rtx @var{symbol}, int @var{priority}) If defined, a function that outputs assembler code to arrange to call the function referenced by @var{symbol} at initialization time. Assume that @var{symbol} is a @code{SYMBOL_REF} for a function taking no arguments and with no return value. If the target supports initialization priorities, @var{priority} is a value between 0 and @code{MAX_INIT_PRIORITY}; otherwise it must be @code{DEFAULT_INIT_PRIORITY}. If this macro is not defined by the target, a suitable default will be chosen if (1) the target supports arbitrary section names, (2) the target defines @code{CTORS_SECTION_ASM_OP}, or (3) @code{USE_COLLECT2} is not defined. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_DESTRUCTOR (rtx @var{symbol}, int @var{priority}) This is like @code{TARGET_ASM_CONSTRUCTOR} but used for termination functions rather than initialization functions. @end deftypefn If @code{TARGET_HAVE_CTORS_DTORS} is true, the initialization routine generated for the generated object file will have static linkage. If your system uses @command{collect2} as the means of processing constructors, then that program normally uses @command{nm} to scan an object file for constructor functions to be called. On certain kinds of systems, you can define these macros to make @command{collect2} work faster (and, in some cases, make it work at all): @table @code @findex OBJECT_FORMAT_COFF @item OBJECT_FORMAT_COFF Define this macro if the system uses COFF (Common Object File Format) object files, so that @command{collect2} can assume this format and scan object files directly for dynamic constructor/destructor functions. @findex OBJECT_FORMAT_ROSE @item OBJECT_FORMAT_ROSE Define this macro if the system uses ROSE format object files, so that @command{collect2} can assume this format and scan object files directly for dynamic constructor/destructor functions. These macros are effective only in a native compiler; @command{collect2} as part of a cross compiler always uses @command{nm} for the target machine. @findex REAL_NM_FILE_NAME @item REAL_NM_FILE_NAME Define this macro as a C string constant containing the file name to use to execute @command{nm}. The default is to search the path normally for @command{nm}. If your system supports shared libraries and has a program to list the dynamic dependencies of a given library or executable, you can define these macros to enable support for running initialization and termination functions in shared libraries: @findex LDD_SUFFIX @item LDD_SUFFIX Define this macro to a C string constant containing the name of the program which lists dynamic dependencies, like @command{"ldd"} under SunOS 4. @findex PARSE_LDD_OUTPUT @item PARSE_LDD_OUTPUT (@var{ptr}) Define this macro to be C code that extracts filenames from the output of the program denoted by @code{LDD_SUFFIX}. @var{ptr} is a variable of type @code{char *} that points to the beginning of a line of output from @code{LDD_SUFFIX}. If the line lists a dynamic dependency, the code must advance @var{ptr} to the beginning of the filename on that line. Otherwise, it must set @var{ptr} to @code{NULL}. @end table @node Instruction Output @subsection Output of Assembler Instructions @c prevent bad page break with this line This describes assembler instruction output. @table @code @findex REGISTER_NAMES @item REGISTER_NAMES A C initializer containing the assembler's names for the machine registers, each one as a C string constant. This is what translates register numbers in the compiler into assembler language. @findex ADDITIONAL_REGISTER_NAMES @item ADDITIONAL_REGISTER_NAMES If defined, a C initializer for an array of structures containing a name and a register number. This macro defines additional names for hard registers, thus allowing the @code{asm} option in declarations to refer to registers using alternate names. @findex ASM_OUTPUT_OPCODE @item ASM_OUTPUT_OPCODE (@var{stream}, @var{ptr}) Define this macro if you are using an unusual assembler that requires different names for the machine instructions. The definition is a C statement or statements which output an assembler instruction opcode to the stdio stream @var{stream}. The macro-operand @var{ptr} is a variable of type @code{char *} which points to the opcode name in its ``internal'' form---the form that is written in the machine description. The definition should output the opcode name to @var{stream}, performing any translation you desire, and increment the variable @var{ptr} to point at the end of the opcode so that it will not be output twice. In fact, your macro definition may process less than the entire opcode name, or more than the opcode name; but if you want to process text that includes @samp{%}-sequences to substitute operands, you must take care of the substitution yourself. Just be sure to increment @var{ptr} over whatever text should not be output normally. @findex recog_data.operand If you need to look at the operand values, they can be found as the elements of @code{recog_data.operand}. If the macro definition does nothing, the instruction is output in the usual way. @findex FINAL_PRESCAN_INSN @item FINAL_PRESCAN_INSN (@var{insn}, @var{opvec}, @var{noperands}) If defined, a C statement to be executed just prior to the output of assembler code for @var{insn}, to modify the extracted operands so they will be output differently. Here the argument @var{opvec} is the vector containing the operands extracted from @var{insn}, and @var{noperands} is the number of elements of the vector which contain meaningful data for this insn. The contents of this vector are what will be used to convert the insn template into assembler code, so you can change the assembler output by changing the contents of the vector. This macro is useful when various assembler syntaxes share a single file of instruction patterns; by defining this macro differently, you can cause a large class of instructions to be output differently (such as with rearranged operands). Naturally, variations in assembler syntax affecting individual insn patterns ought to be handled by writing conditional output routines in those patterns. If this macro is not defined, it is equivalent to a null statement. @findex FINAL_PRESCAN_LABEL @item FINAL_PRESCAN_LABEL If defined, @code{FINAL_PRESCAN_INSN} will be called on each @code{CODE_LABEL}. In that case, @var{opvec} will be a null pointer and @var{noperands} will be zero. @findex PRINT_OPERAND @item PRINT_OPERAND (@var{stream}, @var{x}, @var{code}) A C compound statement to output to stdio stream @var{stream} the assembler syntax for an instruction operand @var{x}. @var{x} is an RTL expression. @var{code} is a value that can be used to specify one of several ways of printing the operand. It is used when identical operands must be printed differently depending on the context. @var{code} comes from the @samp{%} specification that was used to request printing of the operand. If the specification was just @samp{%@var{digit}} then @var{code} is 0; if the specification was @samp{%@var{ltr} @var{digit}} then @var{code} is the ASCII code for @var{ltr}. @findex reg_names If @var{x} is a register, this macro should print the register's name. The names can be found in an array @code{reg_names} whose type is @code{char *[]}. @code{reg_names} is initialized from @code{REGISTER_NAMES}. When the machine description has a specification @samp{%@var{punct}} (a @samp{%} followed by a punctuation character), this macro is called with a null pointer for @var{x} and the punctuation character for @var{code}. @findex PRINT_OPERAND_PUNCT_VALID_P @item PRINT_OPERAND_PUNCT_VALID_P (@var{code}) A C expression which evaluates to true if @var{code} is a valid punctuation character for use in the @code{PRINT_OPERAND} macro. If @code{PRINT_OPERAND_PUNCT_VALID_P} is not defined, it means that no punctuation characters (except for the standard one, @samp{%}) are used in this way. @findex PRINT_OPERAND_ADDRESS @item PRINT_OPERAND_ADDRESS (@var{stream}, @var{x}) A C compound statement to output to stdio stream @var{stream} the assembler syntax for an instruction operand that is a memory reference whose address is @var{x}. @var{x} is an RTL expression. @cindex @code{TARGET_ENCODE_SECTION_INFO} usage On some machines, the syntax for a symbolic address depends on the section that the address refers to. On these machines, define the hook @code{TARGET_ENCODE_SECTION_INFO} to store the information into the @code{symbol_ref}, and then check for it here. @xref{Assembler Format}. @findex DBR_OUTPUT_SEQEND @findex dbr_sequence_length @item DBR_OUTPUT_SEQEND(@var{file}) A C statement, to be executed after all slot-filler instructions have been output. If necessary, call @code{dbr_sequence_length} to determine the number of slots filled in a sequence (zero if not currently outputting a sequence), to decide how many no-ops to output, or whatever. Don't define this macro if it has nothing to do, but it is helpful in reading assembly output if the extent of the delay sequence is made explicit (e.g.@: with white space). @findex final_sequence Note that output routines for instructions with delay slots must be prepared to deal with not being output as part of a sequence (i.e.@: when the scheduling pass is not run, or when no slot fillers could be found.) The variable @code{final_sequence} is null when not processing a sequence, otherwise it contains the @code{sequence} rtx being output. @findex REGISTER_PREFIX @findex LOCAL_LABEL_PREFIX @findex USER_LABEL_PREFIX @findex IMMEDIATE_PREFIX @findex asm_fprintf @item REGISTER_PREFIX @itemx LOCAL_LABEL_PREFIX @itemx USER_LABEL_PREFIX @itemx IMMEDIATE_PREFIX If defined, C string expressions to be used for the @samp{%R}, @samp{%L}, @samp{%U}, and @samp{%I} options of @code{asm_fprintf} (see @file{final.c}). These are useful when a single @file{md} file must support multiple assembler formats. In that case, the various @file{tm.h} files can define these macros differently. @item ASM_FPRINTF_EXTENSIONS(@var{file}, @var{argptr}, @var{format}) @findex ASM_FPRINTF_EXTENSIONS If defined this macro should expand to a series of @code{case} statements which will be parsed inside the @code{switch} statement of the @code{asm_fprintf} function. This allows targets to define extra printf formats which may useful when generating their assembler statements. Note that upper case letters are reserved for future generic extensions to asm_fprintf, and so are not available to target specific code. The output file is given by the parameter @var{file}. The varargs input pointer is @var{argptr} and the rest of the format string, starting the character after the one that is being switched upon, is pointed to by @var{format}. @findex ASSEMBLER_DIALECT @item ASSEMBLER_DIALECT If your target supports multiple dialects of assembler language (such as different opcodes), define this macro as a C expression that gives the numeric index of the assembler language dialect to use, with zero as the first variant. If this macro is defined, you may use constructs of the form @smallexample @samp{@{option0|option1|option2@dots{}@}} @end smallexample @noindent in the output templates of patterns (@pxref{Output Template}) or in the first argument of @code{asm_fprintf}. This construct outputs @samp{option0}, @samp{option1}, @samp{option2}, etc., if the value of @code{ASSEMBLER_DIALECT} is zero, one, two, etc. Any special characters within these strings retain their usual meaning. If there are fewer alternatives within the braces than the value of @code{ASSEMBLER_DIALECT}, the construct outputs nothing. If you do not define this macro, the characters @samp{@{}, @samp{|} and @samp{@}} do not have any special meaning when used in templates or operands to @code{asm_fprintf}. Define the macros @code{REGISTER_PREFIX}, @code{LOCAL_LABEL_PREFIX}, @code{USER_LABEL_PREFIX} and @code{IMMEDIATE_PREFIX} if you can express the variations in assembler language syntax with that mechanism. Define @code{ASSEMBLER_DIALECT} and use the @samp{@{option0|option1@}} syntax if the syntax variant are larger and involve such things as different opcodes or operand order. @findex ASM_OUTPUT_REG_PUSH @item ASM_OUTPUT_REG_PUSH (@var{stream}, @var{regno}) A C expression to output to @var{stream} some assembler code which will push hard register number @var{regno} onto the stack. The code need not be optimal, since this macro is used only when profiling. @findex ASM_OUTPUT_REG_POP @item ASM_OUTPUT_REG_POP (@var{stream}, @var{regno}) A C expression to output to @var{stream} some assembler code which will pop hard register number @var{regno} off of the stack. The code need not be optimal, since this macro is used only when profiling. @end table @node Dispatch Tables @subsection Output of Dispatch Tables @c prevent bad page break with this line This concerns dispatch tables. @table @code @cindex dispatch table @findex ASM_OUTPUT_ADDR_DIFF_ELT @item ASM_OUTPUT_ADDR_DIFF_ELT (@var{stream}, @var{body}, @var{value}, @var{rel}) A C statement to output to the stdio stream @var{stream} an assembler pseudo-instruction to generate a difference between two labels. @var{value} and @var{rel} are the numbers of two internal labels. The definitions of these labels are output using @code{ASM_OUTPUT_INTERNAL_LABEL}, and they must be printed in the same way here. For example, @example fprintf (@var{stream}, "\t.word L%d-L%d\n", @var{value}, @var{rel}) @end example You must provide this macro on machines where the addresses in a dispatch table are relative to the table's own address. If defined, GCC will also use this macro on all machines when producing PIC@. @var{body} is the body of the @code{ADDR_DIFF_VEC}; it is provided so that the mode and flags can be read. @findex ASM_OUTPUT_ADDR_VEC_ELT @item ASM_OUTPUT_ADDR_VEC_ELT (@var{stream}, @var{value}) This macro should be provided on machines where the addresses in a dispatch table are absolute. The definition should be a C statement to output to the stdio stream @var{stream} an assembler pseudo-instruction to generate a reference to a label. @var{value} is the number of an internal label whose definition is output using @code{ASM_OUTPUT_INTERNAL_LABEL}. For example, @example fprintf (@var{stream}, "\t.word L%d\n", @var{value}) @end example @findex ASM_OUTPUT_CASE_LABEL @item ASM_OUTPUT_CASE_LABEL (@var{stream}, @var{prefix}, @var{num}, @var{table}) Define this if the label before a jump-table needs to be output specially. The first three arguments are the same as for @code{ASM_OUTPUT_INTERNAL_LABEL}; the fourth argument is the jump-table which follows (a @code{jump_insn} containing an @code{addr_vec} or @code{addr_diff_vec}). This feature is used on system V to output a @code{swbeg} statement for the table. If this macro is not defined, these labels are output with @code{ASM_OUTPUT_INTERNAL_LABEL}. @findex ASM_OUTPUT_CASE_END @item ASM_OUTPUT_CASE_END (@var{stream}, @var{num}, @var{table}) Define this if something special must be output at the end of a jump-table. The definition should be a C statement to be executed after the assembler code for the table is written. It should write the appropriate code to stdio stream @var{stream}. The argument @var{table} is the jump-table insn, and @var{num} is the label-number of the preceding label. If this macro is not defined, nothing special is output at the end of the jump-table. @end table @node Exception Region Output @subsection Assembler Commands for Exception Regions @c prevent bad page break with this line This describes commands marking the start and the end of an exception region. @table @code @findex EH_FRAME_SECTION_NAME @item EH_FRAME_SECTION_NAME If defined, a C string constant for the name of the section containing exception handling frame unwind information. If not defined, GCC will provide a default definition if the target supports named sections. @file{crtstuff.c} uses this macro to switch to the appropriate section. You should define this symbol if your target supports DWARF 2 frame unwind information and the default definition does not work. @findex EH_FRAME_IN_DATA_SECTION @item EH_FRAME_IN_DATA_SECTION If defined, DWARF 2 frame unwind information will be placed in the data section even though the target supports named sections. This might be necessary, for instance, if the system linker does garbage collection and sections cannot be marked as not to be collected. Do not define this macro unless @code{TARGET_ASM_NAMED_SECTION} is also defined. @findex MASK_RETURN_ADDR @item MASK_RETURN_ADDR An rtx used to mask the return address found via @code{RETURN_ADDR_RTX}, so that it does not contain any extraneous set bits in it. @findex DWARF2_UNWIND_INFO @item DWARF2_UNWIND_INFO Define this macro to 0 if your target supports DWARF 2 frame unwind information, but it does not yet work with exception handling. Otherwise, if your target supports this information (if it defines @samp{INCOMING_RETURN_ADDR_RTX} and either @samp{UNALIGNED_INT_ASM_OP} or @samp{OBJECT_FORMAT_ELF}), GCC will provide a default definition of 1. If this macro is defined to 1, the DWARF 2 unwinder will be the default exception handling mechanism; otherwise, @code{setjmp}/@code{longjmp} will be used by default. If this macro is defined to anything, the DWARF 2 unwinder will be used instead of inline unwinders and @code{__unwind_function} in the non-@code{setjmp} case. @findex DWARF_CIE_DATA_ALIGNMENT @item DWARF_CIE_DATA_ALIGNMENT This macro need only be defined if the target might save registers in the function prologue at an offset to the stack pointer that is not aligned to @code{UNITS_PER_WORD}. The definition should be the negative minimum alignment if @code{STACK_GROWS_DOWNWARD} is defined, and the positive minimum alignment otherwise. @xref{SDB and DWARF}. Only applicable if the target supports DWARF 2 frame unwind information. @end table @deftypefn {Target Hook} void TARGET_ASM_EXCEPTION_SECTION () If defined, a function that switches to the section in which the main exception table is to be placed (@pxref{Sections}). The default is a function that switches to a section named @code{.gcc_except_table} on machines that support named sections via @code{TARGET_ASM_NAMED_SECTION}, otherwise if @option{-fpic} or @option{-fPIC} is in effect, the @code{data_section}, otherwise the @code{readonly_data_section}. @end deftypefn @deftypefn {Target Hook} void TARGET_ASM_EH_FRAME_SECTION () If defined, a function that switches to the section in which the DWARF 2 frame unwind information to be placed (@pxref{Sections}). The default is a function that outputs a standard GAS section directive, if @code{EH_FRAME_SECTION_NAME} is defined, or else a data section directive followed by a synthetic label. @end deftypefn @deftypevar {Target Hook} bool TARGET_TERMINATE_DW2_EH_FRAME_INFO Contains the value true if the target should add a zero word onto the end of a Dwarf-2 frame info section when used for exception handling. Default value is false if @code{EH_FRAME_SECTION_NAME} is defined, and true otherwise. @end deftypevar @node Alignment Output @subsection Assembler Commands for Alignment @c prevent bad page break with this line This describes commands for alignment. @table @code @findex JUMP_ALIGN @item JUMP_ALIGN (@var{label}) The alignment (log base 2) to put in front of @var{label}, which is a common destination of jumps and has no fallthru incoming edge. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. Unless it's necessary to inspect the @var{label} parameter, it is better to set the variable @var{align_jumps} in the target's @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's selection in @var{align_jumps} in a @code{JUMP_ALIGN} implementation. @findex LABEL_ALIGN_AFTER_BARRIER @item LABEL_ALIGN_AFTER_BARRIER (@var{label}) The alignment (log base 2) to put in front of @var{label}, which follows a @code{BARRIER}. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. @findex LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP @item LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP The maximum number of bytes to skip when applying @code{LABEL_ALIGN_AFTER_BARRIER}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. @findex LOOP_ALIGN @item LOOP_ALIGN (@var{label}) The alignment (log base 2) to put in front of @var{label}, which follows a @code{NOTE_INSN_LOOP_BEG} note. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. Unless it's necessary to inspect the @var{label} parameter, it is better to set the variable @code{align_loops} in the target's @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's selection in @code{align_loops} in a @code{LOOP_ALIGN} implementation. @findex LOOP_ALIGN_MAX_SKIP @item LOOP_ALIGN_MAX_SKIP The maximum number of bytes to skip when applying @code{LOOP_ALIGN}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. @findex LABEL_ALIGN @item LABEL_ALIGN (@var{label}) The alignment (log base 2) to put in front of @var{label}. If @code{LABEL_ALIGN_AFTER_BARRIER} / @code{LOOP_ALIGN} specify a different alignment, the maximum of the specified values is used. Unless it's necessary to inspect the @var{label} parameter, it is better to set the variable @code{align_labels} in the target's @code{OVERRIDE_OPTIONS}. Otherwise, you should try to honor the user's selection in @code{align_labels} in a @code{LABEL_ALIGN} implementation. @findex LABEL_ALIGN_MAX_SKIP @item LABEL_ALIGN_MAX_SKIP The maximum number of bytes to skip when applying @code{LABEL_ALIGN}. This works only if @code{ASM_OUTPUT_MAX_SKIP_ALIGN} is defined. @findex ASM_OUTPUT_SKIP @item ASM_OUTPUT_SKIP (@var{stream}, @var{nbytes}) A C statement to output to the stdio stream @var{stream} an assembler instruction to advance the location counter by @var{nbytes} bytes. Those bytes should be zero when loaded. @var{nbytes} will be a C expression of type @code{int}. @findex ASM_NO_SKIP_IN_TEXT @item ASM_NO_SKIP_IN_TEXT Define this macro if @code{ASM_OUTPUT_SKIP} should not be used in the text section because it fails to put zeros in the bytes that are skipped. This is true on many Unix systems, where the pseudo--op to skip bytes produces no-op instructions rather than zeros when used in the text section. @findex ASM_OUTPUT_ALIGN @item ASM_OUTPUT_ALIGN (@var{stream}, @var{power}) A C statement to output to the stdio stream @var{stream} an assembler command to advance the location counter to a multiple of 2 to the @var{power} bytes. @var{power} will be a C expression of type @code{int}. @findex ASM_OUTPUT_ALIGN_WITH_NOP @item ASM_OUTPUT_ALIGN_WITH_NOP (@var{stream}, @var{power}) Like @code{ASM_OUTPUT_ALIGN}, except that the ``nop'' instruction is used for padding, if necessary. @findex ASM_OUTPUT_MAX_SKIP_ALIGN @item ASM_OUTPUT_MAX_SKIP_ALIGN (@var{stream}, @var{power}, @var{max_skip}) A C statement to output to the stdio stream @var{stream} an assembler command to advance the location counter to a multiple of 2 to the @var{power} bytes, but only if @var{max_skip} or fewer bytes are needed to satisfy the alignment request. @var{power} and @var{max_skip} will be a C expression of type @code{int}. @end table @need 3000 @node Debugging Info @section Controlling Debugging Information Format @c prevent bad page break with this line This describes how to specify debugging information. @menu * All Debuggers:: Macros that affect all debugging formats uniformly. * DBX Options:: Macros enabling specific options in DBX format. * DBX Hooks:: Hook macros for varying DBX format. * File Names and DBX:: Macros controlling output of file names in DBX format. * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. * VMS Debug:: Macros for VMS debug format. @end menu @node All Debuggers @subsection Macros Affecting All Debugging Formats @c prevent bad page break with this line These macros affect all debugging formats. @table @code @findex DBX_REGISTER_NUMBER @item DBX_REGISTER_NUMBER (@var{regno}) A C expression that returns the DBX register number for the compiler register number @var{regno}. In the default macro provided, the value of this expression will be @var{regno} itself. But sometimes there are some registers that the compiler knows about and DBX does not, or vice versa. In such cases, some register may need to have one number in the compiler and another for DBX@. If two registers have consecutive numbers inside GCC, and they can be used as a pair to hold a multiword value, then they @emph{must} have consecutive numbers after renumbering with @code{DBX_REGISTER_NUMBER}. Otherwise, debuggers will be unable to access such a pair, because they expect register pairs to be consecutive in their own numbering scheme. If you find yourself defining @code{DBX_REGISTER_NUMBER} in way that does not preserve register pairs, then what you must do instead is redefine the actual register numbering scheme. @findex DEBUGGER_AUTO_OFFSET @item DEBUGGER_AUTO_OFFSET (@var{x}) A C expression that returns the integer offset value for an automatic variable having address @var{x} (an RTL expression). The default computation assumes that @var{x} is based on the frame-pointer and gives the offset from the frame-pointer. This is required for targets that produce debugging output for DBX or COFF-style debugging output for SDB and allow the frame-pointer to be eliminated when the @option{-g} options is used. @findex DEBUGGER_ARG_OFFSET @item DEBUGGER_ARG_OFFSET (@var{offset}, @var{x}) A C expression that returns the integer offset value for an argument having address @var{x} (an RTL expression). The nominal offset is @var{offset}. @findex PREFERRED_DEBUGGING_TYPE @item PREFERRED_DEBUGGING_TYPE A C expression that returns the type of debugging output GCC should produce when the user specifies just @option{-g}. Define this if you have arranged for GCC to support more than one format of debugging output. Currently, the allowable values are @code{DBX_DEBUG}, @code{SDB_DEBUG}, @code{DWARF_DEBUG}, @code{DWARF2_DEBUG}, @code{XCOFF_DEBUG}, @code{VMS_DEBUG}, and @code{VMS_AND_DWARF2_DEBUG}. When the user specifies @option{-ggdb}, GCC normally also uses the value of this macro to select the debugging output format, but with two exceptions. If @code{DWARF2_DEBUGGING_INFO} is defined and @code{LINKER_DOES_NOT_WORK_WITH_DWARF2} is not defined, GCC uses the value @code{DWARF2_DEBUG}. Otherwise, if @code{DBX_DEBUGGING_INFO} is defined, GCC uses @code{DBX_DEBUG}. The value of this macro only affects the default debugging output; the user can always get a specific type of output by using @option{-gstabs}, @option{-gcoff}, @option{-gdwarf-1}, @option{-gdwarf-2}, @option{-gxcoff}, or @option{-gvms}. @end table @node DBX Options @subsection Specific Options for DBX Output @c prevent bad page break with this line These are specific options for DBX output. @table @code @findex DBX_DEBUGGING_INFO @item DBX_DEBUGGING_INFO Define this macro if GCC should produce debugging output for DBX in response to the @option{-g} option. @findex XCOFF_DEBUGGING_INFO @item XCOFF_DEBUGGING_INFO Define this macro if GCC should produce XCOFF format debugging output in response to the @option{-g} option. This is a variant of DBX format. @findex DEFAULT_GDB_EXTENSIONS @item DEFAULT_GDB_EXTENSIONS Define this macro to control whether GCC should by default generate GDB's extended version of DBX debugging information (assuming DBX-format debugging information is enabled at all). If you don't define the macro, the default is 1: always generate the extended information if there is any occasion to. @findex DEBUG_SYMS_TEXT @item DEBUG_SYMS_TEXT Define this macro if all @code{.stabs} commands should be output while in the text section. @findex ASM_STABS_OP @item ASM_STABS_OP A C string constant, including spacing, naming the assembler pseudo op to use instead of @code{"\t.stabs\t"} to define an ordinary debugging symbol. If you don't define this macro, @code{"\t.stabs\t"} is used. This macro applies only to DBX debugging information format. @findex ASM_STABD_OP @item ASM_STABD_OP A C string constant, including spacing, naming the assembler pseudo op to use instead of @code{"\t.stabd\t"} to define a debugging symbol whose value is the current location. If you don't define this macro, @code{"\t.stabd\t"} is used. This macro applies only to DBX debugging information format. @findex ASM_STABN_OP @item ASM_STABN_OP A C string constant, including spacing, naming the assembler pseudo op to use instead of @code{"\t.stabn\t"} to define a debugging symbol with no name. If you don't define this macro, @code{"\t.stabn\t"} is used. This macro applies only to DBX debugging information format. @findex DBX_NO_XREFS @item DBX_NO_XREFS Define this macro if DBX on your system does not support the construct @samp{xs@var{tagname}}. On some systems, this construct is used to describe a forward reference to a structure named @var{tagname}. On other systems, this construct is not supported at all. @findex DBX_CONTIN_LENGTH @item DBX_CONTIN_LENGTH A symbol name in DBX-format debugging information is normally continued (split into two separate @code{.stabs} directives) when it exceeds a certain length (by default, 80 characters). On some operating systems, DBX requires this splitting; on others, splitting must not be done. You can inhibit splitting by defining this macro with the value zero. You can override the default splitting-length by defining this macro as an expression for the length you desire. @findex DBX_CONTIN_CHAR @item DBX_CONTIN_CHAR Normally continuation is indicated by adding a @samp{\} character to the end of a @code{.stabs} string when a continuation follows. To use a different character instead, define this macro as a character constant for the character you want to use. Do not define this macro if backslash is correct for your system. @findex DBX_STATIC_STAB_DATA_SECTION @item DBX_STATIC_STAB_DATA_SECTION Define this macro if it is necessary to go to the data section before outputting the @samp{.stabs} pseudo-op for a non-global static variable. @findex DBX_TYPE_DECL_STABS_CODE @item DBX_TYPE_DECL_STABS_CODE The value to use in the ``code'' field of the @code{.stabs} directive for a typedef. The default is @code{N_LSYM}. @findex DBX_STATIC_CONST_VAR_CODE @item DBX_STATIC_CONST_VAR_CODE The value to use in the ``code'' field of the @code{.stabs} directive for a static variable located in the text section. DBX format does not provide any ``right'' way to do this. The default is @code{N_FUN}. @findex DBX_REGPARM_STABS_CODE @item DBX_REGPARM_STABS_CODE The value to use in the ``code'' field of the @code{.stabs} directive for a parameter passed in registers. DBX format does not provide any ``right'' way to do this. The default is @code{N_RSYM}. @findex DBX_REGPARM_STABS_LETTER @item DBX_REGPARM_STABS_LETTER The letter to use in DBX symbol data to identify a symbol as a parameter passed in registers. DBX format does not customarily provide any way to do this. The default is @code{'P'}. @findex DBX_MEMPARM_STABS_LETTER @item DBX_MEMPARM_STABS_LETTER The letter to use in DBX symbol data to identify a symbol as a stack parameter. The default is @code{'p'}. @findex DBX_FUNCTION_FIRST @item DBX_FUNCTION_FIRST Define this macro if the DBX information for a function and its arguments should precede the assembler code for the function. Normally, in DBX format, the debugging information entirely follows the assembler code. @findex DBX_LBRAC_FIRST @item DBX_LBRAC_FIRST Define this macro if the @code{N_LBRAC} symbol for a block should precede the debugging information for variables and functions defined in that block. Normally, in DBX format, the @code{N_LBRAC} symbol comes first. @findex DBX_BLOCKS_FUNCTION_RELATIVE @item DBX_BLOCKS_FUNCTION_RELATIVE Define this macro if the value of a symbol describing the scope of a block (@code{N_LBRAC} or @code{N_RBRAC}) should be relative to the start of the enclosing function. Normally, GCC uses an absolute address. @findex DBX_USE_BINCL @item DBX_USE_BINCL Define this macro if GCC should generate @code{N_BINCL} and @code{N_EINCL} stabs for included header files, as on Sun systems. This macro also directs GCC to output a type number as a pair of a file number and a type number within the file. Normally, GCC does not generate @code{N_BINCL} or @code{N_EINCL} stabs, and it outputs a single number for a type number. @end table @node DBX Hooks @subsection Open-Ended Hooks for DBX Format @c prevent bad page break with this line These are hooks for DBX format. @table @code @findex DBX_OUTPUT_LBRAC @item DBX_OUTPUT_LBRAC (@var{stream}, @var{name}) Define this macro to say how to output to @var{stream} the debugging information for the start of a scope level for variable names. The argument @var{name} is the name of an assembler symbol (for use with @code{assemble_name}) whose value is the address where the scope begins. @findex DBX_OUTPUT_RBRAC @item DBX_OUTPUT_RBRAC (@var{stream}, @var{name}) Like @code{DBX_OUTPUT_LBRAC}, but for the end of a scope level. @findex DBX_OUTPUT_NFUN @item DBX_OUTPUT_NFUN (@var{stream}, @var{lscope_label}, @var{decl}) Define this macro if the target machine requires special handling to output an @code{N_FUN} entry for the function @var{decl}. @findex DBX_OUTPUT_ENUM @item DBX_OUTPUT_ENUM (@var{stream}, @var{type}) Define this macro if the target machine requires special handling to output an enumeration type. The definition should be a C statement (sans semicolon) to output the appropriate information to @var{stream} for the type @var{type}. @findex DBX_OUTPUT_FUNCTION_END @item DBX_OUTPUT_FUNCTION_END (@var{stream}, @var{function}) Define this macro if the target machine requires special output at the end of the debugging information for a function. The definition should be a C statement (sans semicolon) to output the appropriate information to @var{stream}. @var{function} is the @code{FUNCTION_DECL} node for the function. @findex DBX_OUTPUT_STANDARD_TYPES @item DBX_OUTPUT_STANDARD_TYPES (@var{syms}) Define this macro if you need to control the order of output of the standard data types at the beginning of compilation. The argument @var{syms} is a @code{tree} which is a chain of all the predefined global symbols, including names of data types. Normally, DBX output starts with definitions of the types for integers and characters, followed by all the other predefined types of the particular language in no particular order. On some machines, it is necessary to output different particular types first. To do this, define @code{DBX_OUTPUT_STANDARD_TYPES} to output those symbols in the necessary order. Any predefined types that you don't explicitly output will be output afterward in no particular order. Be careful not to define this macro so that it works only for C@. There are no global variables to access most of the built-in types, because another language may have another set of types. The way to output a particular type is to look through @var{syms} to see if you can find it. Here is an example: @smallexample @{ tree decl; for (decl = syms; decl; decl = TREE_CHAIN (decl)) if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)), "long int")) dbxout_symbol (decl); @dots{} @} @end smallexample @noindent This does nothing if the expected type does not exist. See the function @code{init_decl_processing} in @file{c-decl.c} to find the names to use for all the built-in C types. Here is another way of finding a particular type: @c this is still overfull. --mew 10feb93 @smallexample @{ tree decl; for (decl = syms; decl; decl = TREE_CHAIN (decl)) if (TREE_CODE (decl) == TYPE_DECL && (TREE_CODE (TREE_TYPE (decl)) == INTEGER_CST) && TYPE_PRECISION (TREE_TYPE (decl)) == 16 && TYPE_UNSIGNED (TREE_TYPE (decl))) @group /* @r{This must be @code{unsigned short}.} */ dbxout_symbol (decl); @dots{} @} @end group @end smallexample @findex NO_DBX_FUNCTION_END @item NO_DBX_FUNCTION_END Some stabs encapsulation formats (in particular ECOFF), cannot handle the @code{.stabs "",N_FUN,,0,0,Lscope-function-1} gdb dbx extension construct. On those machines, define this macro to turn this feature off without disturbing the rest of the gdb extensions. @end table @node File Names and DBX @subsection File Names in DBX Format @c prevent bad page break with this line This describes file names in DBX format. @table @code @findex DBX_WORKING_DIRECTORY @item DBX_WORKING_DIRECTORY Define this if DBX wants to have the current directory recorded in each object file. Note that the working directory is always recorded if GDB extensions are enabled. @findex DBX_OUTPUT_MAIN_SOURCE_FILENAME @item DBX_OUTPUT_MAIN_SOURCE_FILENAME (@var{stream}, @var{name}) A C statement to output DBX debugging information to the stdio stream @var{stream} which indicates that file @var{name} is the main source file---the file specified as the input file for compilation. This macro is called only once, at the beginning of compilation. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. @findex DBX_OUTPUT_MAIN_SOURCE_DIRECTORY @item DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (@var{stream}, @var{name}) A C statement to output DBX debugging information to the stdio stream @var{stream} which indicates that the current directory during compilation is named @var{name}. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. @findex DBX_OUTPUT_MAIN_SOURCE_FILE_END @item DBX_OUTPUT_MAIN_SOURCE_FILE_END (@var{stream}, @var{name}) A C statement to output DBX debugging information at the end of compilation of the main source file @var{name}. If you don't define this macro, nothing special is output at the end of compilation, which is correct for most machines. @findex DBX_OUTPUT_SOURCE_FILENAME @item DBX_OUTPUT_SOURCE_FILENAME (@var{stream}, @var{name}) A C statement to output DBX debugging information to the stdio stream @var{stream} which indicates that file @var{name} is the current source file. This output is generated each time input shifts to a different source file as a result of @samp{#include}, the end of an included file, or a @samp{#line} command. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. @end table @need 2000 @node SDB and DWARF @subsection Macros for SDB and DWARF Output @c prevent bad page break with this line Here are macros for SDB and DWARF output. @table @code @findex SDB_DEBUGGING_INFO @item SDB_DEBUGGING_INFO Define this macro if GCC should produce COFF-style debugging output for SDB in response to the @option{-g} option. @findex DWARF_DEBUGGING_INFO @item DWARF_DEBUGGING_INFO Define this macro if GCC should produce dwarf format debugging output in response to the @option{-g} option. @findex DWARF2_DEBUGGING_INFO @item DWARF2_DEBUGGING_INFO Define this macro if GCC should produce dwarf version 2 format debugging output in response to the @option{-g} option. To support optional call frame debugging information, you must also define @code{INCOMING_RETURN_ADDR_RTX} and either set @code{RTX_FRAME_RELATED_P} on the prologue insns if you use RTL for the prologue, or call @code{dwarf2out_def_cfa} and @code{dwarf2out_reg_save} as appropriate from @code{TARGET_ASM_FUNCTION_PROLOGUE} if you don't. @findex DWARF2_FRAME_INFO @item DWARF2_FRAME_INFO Define this macro to a nonzero value if GCC should always output Dwarf 2 frame information. If @code{DWARF2_UNWIND_INFO} (@pxref{Exception Region Output} is nonzero, GCC will output this information not matter how you define @code{DWARF2_FRAME_INFO}. @findex LINKER_DOES_NOT_WORK_WITH_DWARF2 @item LINKER_DOES_NOT_WORK_WITH_DWARF2 Define this macro if the linker does not work with Dwarf version 2. Normally, if the user specifies only @option{-ggdb} GCC will use Dwarf version 2 if available; this macro disables this. See the description of the @code{PREFERRED_DEBUGGING_TYPE} macro for more details. @findex DWARF2_GENERATE_TEXT_SECTION_LABEL @item DWARF2_GENERATE_TEXT_SECTION_LABEL By default, the Dwarf 2 debugging information generator will generate a label to mark the beginning of the text section. If it is better simply to use the name of the text section itself, rather than an explicit label, to indicate the beginning of the text section, define this macro to zero. @findex DWARF2_ASM_LINE_DEBUG_INFO @item DWARF2_ASM_LINE_DEBUG_INFO Define this macro to be a nonzero value if the assembler can generate Dwarf 2 line debug info sections. This will result in much more compact line number tables, and hence is desirable if it works. @findex ASM_OUTPUT_DWARF_DELTA @item ASM_OUTPUT_DWARF_DELTA (@var{stream}, @var{size}, @var{label1}, @var{label2}) A C statement to issue assembly directives that create a difference between the two given labels, using an integer of the given size. @findex ASM_OUTPUT_DWARF_OFFSET @item ASM_OUTPUT_DWARF_OFFSET (@var{stream}, @var{size}, @var{label}) A C statement to issue assembly directives that create a section-relative reference to the given label, using an integer of the given size. @findex ASM_OUTPUT_DWARF_PCREL @item ASM_OUTPUT_DWARF_PCREL (@var{stream}, @var{size}, @var{label}) A C statement to issue assembly directives that create a self-relative reference to the given label, using an integer of the given size. @findex PUT_SDB_@dots{} @item PUT_SDB_@dots{} Define these macros to override the assembler syntax for the special SDB assembler directives. See @file{sdbout.c} for a list of these macros and their arguments. If the standard syntax is used, you need not define them yourself. @findex SDB_DELIM @item SDB_DELIM Some assemblers do not support a semicolon as a delimiter, even between SDB assembler directives. In that case, define this macro to be the delimiter to use (usually @samp{\n}). It is not necessary to define a new set of @code{PUT_SDB_@var{op}} macros if this is the only change required. @findex SDB_GENERATE_FAKE @item SDB_GENERATE_FAKE Define this macro to override the usual method of constructing a dummy name for anonymous structure and union types. See @file{sdbout.c} for more information. @findex SDB_ALLOW_UNKNOWN_REFERENCES @item SDB_ALLOW_UNKNOWN_REFERENCES Define this macro to allow references to unknown structure, union, or enumeration tags to be emitted. Standard COFF does not allow handling of unknown references, MIPS ECOFF has support for it. @findex SDB_ALLOW_FORWARD_REFERENCES @item SDB_ALLOW_FORWARD_REFERENCES Define this macro to allow references to structure, union, or enumeration tags that have not yet been seen to be handled. Some assemblers choke if forward tags are used, while some require it. @end table @need 2000 @node VMS Debug @subsection Macros for VMS Debug Format @c prevent bad page break with this line Here are macros for VMS debug format. @table @code @findex VMS_DEBUGGING_INFO @item VMS_DEBUGGING_INFO Define this macro if GCC should produce debugging output for VMS in response to the @option{-g} option. The default behavior for VMS is to generate minimal debug info for a traceback in the absence of @option{-g} unless explicitly overridden with @option{-g0}. This behavior is controlled by @code{OPTIMIZATION_OPTIONS} and @code{OVERRIDE_OPTIONS}. @end table @node Floating Point @section Cross Compilation and Floating Point @cindex cross compilation and floating point @cindex floating point and cross compilation While all modern machines use twos-complement representation for integers, there are a variety of representations for floating point numbers. This means that in a cross-compiler the representation of floating point numbers in the compiled program may be different from that used in the machine doing the compilation. Because different representation systems may offer different amounts of range and precision, all floating point constants must be represented in the target machine's format. Therefore, the cross compiler cannot safely use the host machine's floating point arithmetic; it must emulate the target's arithmetic. To ensure consistency, GCC always uses emulation to work with floating point values, even when the host and target floating point formats are identical. The following macros are provided by @file{real.h} for the compiler to use. All parts of the compiler which generate or optimize floating-point calculations must use these macros. They may evaluate their operands more than once, so operands must not have side effects. @defmac REAL_VALUE_TYPE The C data type to be used to hold a floating point value in the target machine's format. Typically this is a @code{struct} containing an array of @code{HOST_WIDE_INT}, but all code should treat it as an opaque quantity. @end defmac @deftypefn Macro int REAL_VALUES_EQUAL (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) Compares for equality the two values, @var{x} and @var{y}. If the target floating point format supports negative zeroes and/or NaNs, @samp{REAL_VALUES_EQUAL (-0.0, 0.0)} is true, and @samp{REAL_VALUES_EQUAL (NaN, NaN)} is false. @end deftypefn @deftypefn Macro int REAL_VALUES_LESS (REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) Tests whether @var{x} is less than @var{y}. @end deftypefn @deftypefn Macro HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE @var{x}) Truncates @var{x} to a signed integer, rounding toward zero. @end deftypefn @deftypefn Macro {unsigned HOST_WIDE_INT} REAL_VALUE_UNSIGNED_FIX (REAL_VALUE_TYPE @var{x}) Truncates @var{x} to an unsigned integer, rounding toward zero. If @var{x} is negative, returns zero. @end deftypefn @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *@var{string}, enum machine_mode @var{mode}) Converts @var{string} into a floating point number in the target machine's representation for mode @var{mode}. This routine can handle both decimal and hexadecimal floating point constants, using the syntax defined by the C language for both. @end deftypefn @deftypefn Macro int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE @var{x}) Returns 1 if @var{x} is negative (including negative zero), 0 otherwise. @end deftypefn @deftypefn Macro int REAL_VALUE_ISINF (REAL_VALUE_TYPE @var{x}) Determines whether @var{x} represents infinity (positive or negative). @end deftypefn @deftypefn Macro int REAL_VALUE_ISNAN (REAL_VALUE_TYPE @var{x}) Determines whether @var{x} represents a ``NaN'' (not-a-number). @end deftypefn @deftypefn Macro void REAL_ARITHMETIC (REAL_VALUE_TYPE @var{output}, enum tree_code @var{code}, REAL_VALUE_TYPE @var{x}, REAL_VALUE_TYPE @var{y}) Calculates an arithmetic operation on the two floating point values @var{x} and @var{y}, storing the result in @var{output} (which must be a variable). The operation to be performed is specified by @var{code}. Only the following codes are supported: @code{PLUS_EXPR}, @code{MINUS_EXPR}, @code{MULT_EXPR}, @code{RDIV_EXPR}, @code{MAX_EXPR}, @code{MIN_EXPR}. If @code{REAL_ARITHMETIC} is asked to evaluate division by zero and the target's floating point format cannot represent infinity, it will call @code{abort}. Callers should check for this situation first, using @code{MODE_HAS_INFINITIES}. @xref{Storage Layout}. @end deftypefn @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE @var{x}) Returns the negative of the floating point value @var{x}. @end deftypefn @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE @var{x}) Returns the absolute value of @var{x}. @end deftypefn @deftypefn Macro REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE @var{mode}, enum machine_mode @var{x}) Truncates the floating point value @var{x} to fit in @var{mode}. The return value is still a full-size @code{REAL_VALUE_TYPE}, but it has an appropriate bit pattern to be output asa floating constant whose precision accords with mode @var{mode}. @end deftypefn @deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x}) Converts a floating point value @var{x} into a double-precision integer which is then stored into @var{low} and @var{high}. If the value is not integral, it is truncated. @end deftypefn @deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode}) @findex REAL_VALUE_FROM_INT Converts a double-precision integer found in @var{low} and @var{high}, into a floating point value which is then stored into @var{x}. The value is truncated to fit in mode @var{mode}. @end deftypefn @node Mode Switching @section Mode Switching Instructions @cindex mode switching The following macros control mode switching optimizations: @table @code @findex OPTIMIZE_MODE_SWITCHING @item OPTIMIZE_MODE_SWITCHING (@var{entity}) Define this macro if the port needs extra instructions inserted for mode switching in an optimizing compilation. For an example, the SH4 can perform both single and double precision floating point operations, but to perform a single precision operation, the FPSCR PR bit has to be cleared, while for a double precision operation, this bit has to be set. Changing the PR bit requires a general purpose register as a scratch register, hence these FPSCR sets have to be inserted before reload, i.e.@: you can't put this into instruction emitting or @code{MACHINE_DEPENDENT_REORG}. You can have multiple entities that are mode-switched, and select at run time which entities actually need it. @code{OPTIMIZE_MODE_SWITCHING} should return nonzero for any @var{entity} that needs mode-switching. If you define this macro, you also have to define @code{NUM_MODES_FOR_MODE_SWITCHING}, @code{MODE_NEEDED}, @code{MODE_PRIORITY_TO_MODE} and @code{EMIT_MODE_SET}. @code{NORMAL_MODE} is optional. @findex NUM_MODES_FOR_MODE_SWITCHING @item NUM_MODES_FOR_MODE_SWITCHING If you define @code{OPTIMIZE_MODE_SWITCHING}, you have to define this as initializer for an array of integers. Each initializer element N refers to an entity that needs mode switching, and specifies the number of different modes that might need to be set for this entity. The position of the initializer in the initializer - starting counting at zero - determines the integer that is used to refer to the mode-switched entity in question. In macros that take mode arguments / yield a mode result, modes are represented as numbers 0 @dots{} N @minus{} 1. N is used to specify that no mode switch is needed / supplied. @findex MODE_NEEDED @item MODE_NEEDED (@var{entity}, @var{insn}) @var{entity} is an integer specifying a mode-switched entity. If @code{OPTIMIZE_MODE_SWITCHING} is defined, you must define this macro to return an integer value not larger than the corresponding element in @code{NUM_MODES_FOR_MODE_SWITCHING}, to denote the mode that @var{entity} must be switched into prior to the execution of @var{insn}. @findex NORMAL_MODE @item NORMAL_MODE (@var{entity}) If this macro is defined, it is evaluated for every @var{entity} that needs mode switching. It should evaluate to an integer, which is a mode that @var{entity} is assumed to be switched to at function entry and exit. @findex MODE_PRIORITY_TO_MODE @item MODE_PRIORITY_TO_MODE (@var{entity}, @var{n}) This macro specifies the order in which modes for @var{entity} are processed. 0 is the highest priority, @code{NUM_MODES_FOR_MODE_SWITCHING[@var{entity}] - 1} the lowest. The value of the macro should be an integer designating a mode for @var{entity}. For any fixed @var{entity}, @code{mode_priority_to_mode} (@var{entity}, @var{n}) shall be a bijection in 0 @dots{} @code{num_modes_for_mode_switching[@var{entity}] - 1}. @findex EMIT_MODE_SET @item EMIT_MODE_SET (@var{entity}, @var{mode}, @var{hard_regs_live}) Generate one or more insns to set @var{entity} to @var{mode}. @var{hard_reg_live} is the set of hard registers live at the point where the insn(s) are to be inserted. @end table @node Target Attributes @section Defining target-specific uses of @code{__attribute__} @cindex target attributes @cindex machine attributes @cindex attributes, target-specific Target-specific attributes may be defined for functions, data and types. These are described using the following target hooks; they also need to be documented in @file{extend.texi}. @deftypevr {Target Hook} {const struct attribute_spec *} TARGET_ATTRIBUTE_TABLE If defined, this target hook points to an array of @samp{struct attribute_spec} (defined in @file{tree.h}) specifying the machine specific attributes for this target and some of the restrictions on the entities to which these attributes are applied and the arguments they take. @end deftypevr @deftypefn {Target Hook} int TARGET_COMP_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) If defined, this target hook is a function which returns zero if the attributes on @var{type1} and @var{type2} are incompatible, one if they are compatible, and two if they are nearly compatible (which causes a warning to be generated). If this is not defined, machine-specific attributes are supposed always to be compatible. @end deftypefn @deftypefn {Target Hook} void TARGET_SET_DEFAULT_TYPE_ATTRIBUTES (tree @var{type}) If defined, this target hook is a function which assigns default attributes to newly defined @var{type}. @end deftypefn @deftypefn {Target Hook} tree TARGET_MERGE_TYPE_ATTRIBUTES (tree @var{type1}, tree @var{type2}) Define this target hook if the merging of type attributes needs special handling. If defined, the result is a list of the combined @code{TYPE_ATTRIBUTES} of @var{type1} and @var{type2}. It is assumed that @code{comptypes} has already been called and returned 1. This function may call @code{merge_attributes} to handle machine-independent merging. @end deftypefn @deftypefn {Target Hook} tree TARGET_MERGE_DECL_ATTRIBUTES (tree @var{olddecl}, tree @var{newdecl}) Define this target hook if the merging of decl attributes needs special handling. If defined, the result is a list of the combined @code{DECL_ATTRIBUTES} of @var{olddecl} and @var{newdecl}. @var{newdecl} is a duplicate declaration of @var{olddecl}. Examples of when this is needed are when one attribute overrides another, or when an attribute is nullified by a subsequent definition. This function may call @code{merge_attributes} to handle machine-independent merging. @findex TARGET_DLLIMPORT_DECL_ATTRIBUTES If the only target-specific handling you require is @samp{dllimport} for Windows targets, you should define the macro @code{TARGET_DLLIMPORT_DECL_ATTRIBUTES}. This links in a function called @code{merge_dllimport_decl_attributes} which can then be defined as the expansion of @code{TARGET_MERGE_DECL_ATTRIBUTES}. This is done in @file{i386/cygwin.h} and @file{i386/i386.c}, for example. @end deftypefn @deftypefn {Target Hook} void TARGET_INSERT_ATTRIBUTES (tree @var{node}, tree *@var{attr_ptr}) Define this target hook if you want to be able to add attributes to a decl when it is being created. This is normally useful for back ends which wish to implement a pragma by using the attributes which correspond to the pragma's effect. The @var{node} argument is the decl which is being created. The @var{attr_ptr} argument is a pointer to the attribute list for this decl. The list itself should not be modified, since it may be shared with other decls, but attributes may be chained on the head of the list and @code{*@var{attr_ptr}} modified to point to the new attributes, or a copy of the list may be made if further changes are needed. @end deftypefn @deftypefn {Target Hook} bool TARGET_FUNCTION_ATTRIBUTE_INLINABLE_P (tree @var{fndecl}) @cindex inlining This target hook returns @code{true} if it is ok to inline @var{fndecl} into the current function, despite its having target-specific attributes, @code{false} otherwise. By default, if a function has a target specific attribute attached to it, it will not be inlined. @end deftypefn @node MIPS Coprocessors @section Defining coprocessor specifics for MIPS targets. @cindex MIPS coprocessor-definition macros The MIPS specification allows MIPS implementations to have as many as 4 coprocessors, each with as many as 32 private registers. gcc supports accessing these registers and transferring values between the registers and memory using asm-ized variables. For example: @smallexample register unsigned int cp0count asm ("c0r1"); unsigned int d; d = cp0count + 3; @end smallexample (``c0r1'' is the default name of register 1 in coprocessor 0; alternate names may be added as described below, or the default names may be overridden entirely in @code{SUBTARGET_CONDITIONAL_REGISTER_USAGE}.) Coprocessor registers are assumed to be epilogue-used; sets to them will be preserved even if it does not appear that the register is used again later in the function. Another note: according to the MIPS spec, coprocessor 1 (if present) is the FPU. One accesses COP1 registers through standard mips floating-point support; they are not included in this mechanism. There is one macro used in defining the MIPS coprocessor interface which you may want to override in subtargets; it is described below. @table @code @item ALL_COP_ADDITIONAL_REGISTER_NAMES @findex ALL_COP_ADDITIONAL_REGISTER_NAMES A comma-separated list (with leading comma) of pairs describing the alternate names of coprocessor registers. The format of each entry should be @smallexample @{ @var{alternatename}, @var{register_number}@} @end smallexample Default: empty. @end table @node Misc @section Miscellaneous Parameters @cindex parameters, miscellaneous @c prevent bad page break with this line Here are several miscellaneous parameters. @table @code @item PREDICATE_CODES @findex PREDICATE_CODES Define this if you have defined special-purpose predicates in the file @file{@var{machine}.c}. This macro is called within an initializer of an array of structures. The first field in the structure is the name of a predicate and the second field is an array of rtl codes. For each predicate, list all rtl codes that can be in expressions matched by the predicate. The list should have a trailing comma. Here is an example of two entries in the list for a typical RISC machine: @smallexample #define PREDICATE_CODES \ @{"gen_reg_rtx_operand", @{SUBREG, REG@}@}, \ @{"reg_or_short_cint_operand", @{SUBREG, REG, CONST_INT@}@}, @end smallexample Defining this macro does not affect the generated code (however, incorrect definitions that omit an rtl code that may be matched by the predicate can cause the compiler to malfunction). Instead, it allows the table built by @file{genrecog} to be more compact and efficient, thus speeding up the compiler. The most important predicates to include in the list specified by this macro are those used in the most insn patterns. For each predicate function named in @code{PREDICATE_CODES}, a declaration will be generated in @file{insn-codes.h}. @item SPECIAL_MODE_PREDICATES @findex SPECIAL_MODE_PREDICATES Define this if you have special predicates that know special things about modes. Genrecog will warn about certain forms of @code{match_operand} without a mode; if the operand predicate is listed in @code{SPECIAL_MODE_PREDICATES}, the warning will be suppressed. Here is an example from the IA-32 port (@code{ext_register_operand} specially checks for @code{HImode} or @code{SImode} in preparation for a byte extraction from @code{%ah} etc.). @smallexample #define SPECIAL_MODE_PREDICATES \ "ext_register_operand", @end smallexample @findex CASE_VECTOR_MODE @item CASE_VECTOR_MODE An alias for a machine mode name. This is the machine mode that elements of a jump-table should have. @findex CASE_VECTOR_SHORTEN_MODE @item CASE_VECTOR_SHORTEN_MODE (@var{min_offset}, @var{max_offset}, @var{body}) Optional: return the preferred mode for an @code{addr_diff_vec} when the minimum and maximum offset are known. If you define this, it enables extra code in branch shortening to deal with @code{addr_diff_vec}. To make this work, you also have to define @code{INSN_ALIGN} and make the alignment for @code{addr_diff_vec} explicit. The @var{body} argument is provided so that the offset_unsigned and scale flags can be updated. @findex CASE_VECTOR_PC_RELATIVE @item CASE_VECTOR_PC_RELATIVE Define this macro to be a C expression to indicate when jump-tables should contain relative addresses. If jump-tables never contain relative addresses, then you need not define this macro. @findex CASE_DROPS_THROUGH @item CASE_DROPS_THROUGH Define this if control falls through a @code{case} insn when the index value is out of range. This means the specified default-label is actually ignored by the @code{case} insn proper. @findex CASE_VALUES_THRESHOLD @item CASE_VALUES_THRESHOLD Define this to be the smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. The default is four for machines with a @code{casesi} instruction and five otherwise. This is best for most machines. @findex WORD_REGISTER_OPERATIONS @item WORD_REGISTER_OPERATIONS Define this macro if operations between registers with integral mode smaller than a word are always performed on the entire register. Most RISC machines have this property and most CISC machines do not. @findex LOAD_EXTEND_OP @item LOAD_EXTEND_OP (@var{mode}) Define this macro to be a C expression indicating when insns that read memory in @var{mode}, an integral mode narrower than a word, set the bits outside of @var{mode} to be either the sign-extension or the zero-extension of the data read. Return @code{SIGN_EXTEND} for values of @var{mode} for which the insn sign-extends, @code{ZERO_EXTEND} for which it zero-extends, and @code{NIL} for other modes. This macro is not called with @var{mode} non-integral or with a width greater than or equal to @code{BITS_PER_WORD}, so you may return any value in this case. Do not define this macro if it would always return @code{NIL}. On machines where this macro is defined, you will normally define it as the constant @code{SIGN_EXTEND} or @code{ZERO_EXTEND}. @findex SHORT_IMMEDIATES_SIGN_EXTEND @item SHORT_IMMEDIATES_SIGN_EXTEND Define this macro if loading short immediate values into registers sign extends. @findex FIXUNS_TRUNC_LIKE_FIX_TRUNC @item FIXUNS_TRUNC_LIKE_FIX_TRUNC Define this macro if the same instructions that convert a floating point number to a signed fixed point number also convert validly to an unsigned one. @findex MOVE_MAX @item MOVE_MAX The maximum number of bytes that a single instruction can move quickly between memory and registers or between two memory locations. @findex MAX_MOVE_MAX @item MAX_MOVE_MAX The maximum number of bytes that a single instruction can move quickly between memory and registers or between two memory locations. If this is undefined, the default is @code{MOVE_MAX}. Otherwise, it is the constant value that is the largest value that @code{MOVE_MAX} can have at run-time. @findex SHIFT_COUNT_TRUNCATED @item SHIFT_COUNT_TRUNCATED A C expression that is nonzero if on this machine the number of bits actually used for the count of a shift operation is equal to the number of bits needed to represent the size of the object being shifted. When this macro is nonzero, the compiler will assume that it is safe to omit a sign-extend, zero-extend, and certain bitwise `and' instructions that truncates the count of a shift operation. On machines that have instructions that act on bit-fields at variable positions, which may include `bit test' instructions, a nonzero @code{SHIFT_COUNT_TRUNCATED} also enables deletion of truncations of the values that serve as arguments to bit-field instructions. If both types of instructions truncate the count (for shifts) and position (for bit-field operations), or if no variable-position bit-field instructions exist, you should define this macro. However, on some machines, such as the 80386 and the 680x0, truncation only applies to shift operations and not the (real or pretended) bit-field operations. Define @code{SHIFT_COUNT_TRUNCATED} to be zero on such machines. Instead, add patterns to the @file{md} file that include the implied truncation of the shift instructions. You need not define this macro if it would always have the value of zero. @findex TRULY_NOOP_TRUNCATION @item TRULY_NOOP_TRUNCATION (@var{outprec}, @var{inprec}) A C expression which is nonzero if on this machine it is safe to ``convert'' an integer of @var{inprec} bits to one of @var{outprec} bits (where @var{outprec} is smaller than @var{inprec}) by merely operating on it as if it had only @var{outprec} bits. On many machines, this expression can be 1. @c rearranged this, removed the phrase "it is reported that". this was @c to fix an overfull hbox. --mew 10feb93 When @code{TRULY_NOOP_TRUNCATION} returns 1 for a pair of sizes for modes for which @code{MODES_TIEABLE_P} is 0, suboptimal code can result. If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in such cases may improve things. @findex STORE_FLAG_VALUE @item STORE_FLAG_VALUE A C expression describing the value returned by a comparison operator with an integral mode and stored by a store-flag instruction (@samp{s@var{cond}}) when the condition is true. This description must apply to @emph{all} the @samp{s@var{cond}} patterns and all the comparison operators whose results have a @code{MODE_INT} mode. A value of 1 or @minus{}1 means that the instruction implementing the comparison operator returns exactly 1 or @minus{}1 when the comparison is true and 0 when the comparison is false. Otherwise, the value indicates which bits of the result are guaranteed to be 1 when the comparison is true. This value is interpreted in the mode of the comparison operation, which is given by the mode of the first operand in the @samp{s@var{cond}} pattern. Either the low bit or the sign bit of @code{STORE_FLAG_VALUE} be on. Presently, only those bits are used by the compiler. If @code{STORE_FLAG_VALUE} is neither 1 or @minus{}1, the compiler will generate code that depends only on the specified bits. It can also replace comparison operators with equivalent operations if they cause the required bits to be set, even if the remaining bits are undefined. For example, on a machine whose comparison operators return an @code{SImode} value and where @code{STORE_FLAG_VALUE} is defined as @samp{0x80000000}, saying that just the sign bit is relevant, the expression @smallexample (ne:SI (and:SI @var{x} (const_int @var{power-of-2})) (const_int 0)) @end smallexample @noindent can be converted to @smallexample (ashift:SI @var{x} (const_int @var{n})) @end smallexample @noindent where @var{n} is the appropriate shift count to move the bit being tested into the sign bit. There is no way to describe a machine that always sets the low-order bit for a true value, but does not guarantee the value of any other bits, but we do not know of any machine that has such an instruction. If you are trying to port GCC to such a machine, include an instruction to perform a logical-and of the result with 1 in the pattern for the comparison operators and let us know at @email{gcc@@gcc.gnu.org}. Often, a machine will have multiple instructions that obtain a value from a comparison (or the condition codes). Here are rules to guide the choice of value for @code{STORE_FLAG_VALUE}, and hence the instructions to be used: @itemize @bullet @item Use the shortest sequence that yields a valid definition for @code{STORE_FLAG_VALUE}. It is more efficient for the compiler to ``normalize'' the value (convert it to, e.g., 1 or 0) than for the comparison operators to do so because there may be opportunities to combine the normalization with other operations. @item For equal-length sequences, use a value of 1 or @minus{}1, with @minus{}1 being slightly preferred on machines with expensive jumps and 1 preferred on other machines. @item As a second choice, choose a value of @samp{0x80000001} if instructions exist that set both the sign and low-order bits but do not define the others. @item Otherwise, use a value of @samp{0x80000000}. @end itemize Many machines can produce both the value chosen for @code{STORE_FLAG_VALUE} and its negation in the same number of instructions. On those machines, you should also define a pattern for those cases, e.g., one matching @smallexample (set @var{A} (neg:@var{m} (ne:@var{m} @var{B} @var{C}))) @end smallexample Some machines can also perform @code{and} or @code{plus} operations on condition code values with less instructions than the corresponding @samp{s@var{cond}} insn followed by @code{and} or @code{plus}. On those machines, define the appropriate patterns. Use the names @code{incscc} and @code{decscc}, respectively, for the patterns which perform @code{plus} or @code{minus} operations on condition code values. See @file{rs6000.md} for some examples. The GNU Superoptizer can be used to find such instruction sequences on other machines. You need not define @code{STORE_FLAG_VALUE} if the machine has no store-flag instructions. @findex FLOAT_STORE_FLAG_VALUE @item FLOAT_STORE_FLAG_VALUE (@var{mode}) A C expression that gives a nonzero @code{REAL_VALUE_TYPE} value that is returned when comparison operators with floating-point results are true. Define this macro on machine that have comparison operations that return floating-point values. If there are no such operations, do not define this macro. @findex Pmode @item Pmode An alias for the machine mode for pointers. On most machines, define this to be the integer mode corresponding to the width of a hardware pointer; @code{SImode} on 32-bit machine or @code{DImode} on 64-bit machines. On some machines you must define this to be one of the partial integer modes, such as @code{PSImode}. The width of @code{Pmode} must be at least as large as the value of @code{POINTER_SIZE}. If it is not equal, you must define the macro @code{POINTERS_EXTEND_UNSIGNED} to specify how pointers are extended to @code{Pmode}. @findex FUNCTION_MODE @item FUNCTION_MODE An alias for the machine mode used for memory references to functions being called, in @code{call} RTL expressions. On most machines this should be @code{QImode}. @findex INTEGRATE_THRESHOLD @item INTEGRATE_THRESHOLD (@var{decl}) A C expression for the maximum number of instructions above which the function @var{decl} should not be inlined. @var{decl} is a @code{FUNCTION_DECL} node. The default definition of this macro is 64 plus 8 times the number of arguments that the function accepts. Some people think a larger threshold should be used on RISC machines. @findex STDC_0_IN_SYSTEM_HEADERS @item STDC_0_IN_SYSTEM_HEADERS In normal operation, the preprocessor expands @code{__STDC__} to the constant 1, to signify that GCC conforms to ISO Standard C@. On some hosts, like Solaris, the system compiler uses a different convention, where @code{__STDC__} is normally 0, but is 1 if the user specifies strict conformance to the C Standard. Defining @code{STDC_0_IN_SYSTEM_HEADERS} makes GNU CPP follows the host convention when processing system header files, but when processing user files @code{__STDC__} will always expand to 1. @findex NO_IMPLICIT_EXTERN_C @item NO_IMPLICIT_EXTERN_C Define this macro if the system header files support C++ as well as C@. This macro inhibits the usual method of using system header files in C++, which is to pretend that the file's contents are enclosed in @samp{extern "C" @{@dots{}@}}. @findex HANDLE_PRAGMA @item HANDLE_PRAGMA (@var{getc}, @var{ungetc}, @var{name}) This macro is no longer supported. You must use @code{REGISTER_TARGET_PRAGMAS} instead. @findex REGISTER_TARGET_PRAGMAS @findex #pragma @findex pragma @item REGISTER_TARGET_PRAGMAS (@var{pfile}) Define this macro if you want to implement any target-specific pragmas. If defined, it is a C expression which makes a series of calls to @code{cpp_register_pragma} for each pragma, with @var{pfile} passed as the first argument to to these functions. The macro may also do any setup required for the pragmas. The primary reason to define this macro is to provide compatibility with other compilers for the same target. In general, we discourage definition of target-specific pragmas for GCC@. If the pragma can be implemented by attributes then you should consider defining the target hook @samp{TARGET_INSERT_ATTRIBUTES} as well. Preprocessor macros that appear on pragma lines are not expanded. All @samp{#pragma} directives that do not match any registered pragma are silently ignored, unless the user specifies @option{-Wunknown-pragmas}. @deftypefun void cpp_register_pragma (cpp_reader *@var{pfile}, const char *@var{space}, const char *@var{name}, void (*@var{callback}) (cpp_reader *)) Each call to @code{cpp_register_pragma} establishes one pragma. The @var{callback} routine will be called when the preprocessor encounters a pragma of the form @smallexample #pragma [@var{space}] @var{name} @dots{} @end smallexample @var{space} is the case-sensitive namespace of the pragma, or @code{NULL} to put the pragma in the global namespace. The callback routine receives @var{pfile} as its first argument, which can be passed on to cpplib's functions if necessary. You can lex tokens after the @var{name} by calling @code{c_lex}. Tokens that are not read by the callback will be silently ignored. The end of the line is indicated by a token of type @code{CPP_EOF}. For an example use of this routine, see @file{c4x.h} and the callback routines defined in @file{c4x-c.c}. Note that the use of @code{c_lex} is specific to the C and C++ compilers. It will not work in the Java or Fortran compilers, or any other language compilers for that matter. Thus if @code{c_lex} is going to be called from target-specific code, it must only be done so when building the C and C++ compilers. This can be done by defining the variables @code{c_target_objs} and @code{cxx_target_objs} in the target entry in the @file{config.gcc} file. These variables should name the target-specific, language-specific object file which contains the code that uses @code{c_lex}. Note it will also be necessary to add a rule to the makefile fragment pointed to by @code{tmake_file} that shows how to build this object file. @end deftypefun @findex HANDLE_SYSV_PRAGMA @findex #pragma @findex pragma @item HANDLE_SYSV_PRAGMA Define this macro (to a value of 1) if you want the System V style pragmas @samp{#pragma pack()} and @samp{#pragma weak [=]} to be supported by gcc. The pack pragma specifies the maximum alignment (in bytes) of fields within a structure, in much the same way as the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets the behavior to the default. A subtlety for Microsoft Visual C/C++ style bit-field packing (e.g. -mms-bitfields) for targets that support it: When a bit-field is inserted into a packed record, the whole size of the underlying type is used by one or more same-size adjacent bit-fields (that is, if its long:3, 32 bits is used in the record, and any additional adjacent long bit-fields are packed into the same chunk of 32 bits. However, if the size changes, a new field of that size is allocated). If both MS bit-fields and @samp{__attribute__((packed))} are used, the latter will take precedence. If @samp{__attribute__((packed))} is used on a single field when MS bit-fields are in use, it will take precedence for that field, but the alignment of the rest of the structure may affect its placement. The weak pragma only works if @code{SUPPORTS_WEAK} and @code{ASM_WEAKEN_LABEL} are defined. If enabled it allows the creation of specifically named weak labels, optionally with a value. @findex HANDLE_PRAGMA_PACK_PUSH_POP @findex #pragma @findex pragma @item HANDLE_PRAGMA_PACK_PUSH_POP Define this macro (to a value of 1) if you want to support the Win32 style pragmas @samp{#pragma pack(push,@var{n})} and @samp{#pragma pack(pop)}. The @samp{pack(push,@var{n})} pragma specifies the maximum alignment (in bytes) of fields within a structure, in much the same way as the @samp{__aligned__} and @samp{__packed__} @code{__attribute__}s do. A pack value of zero resets the behavior to the default. Successive invocations of this pragma cause the previous values to be stacked, so that invocations of @samp{#pragma pack(pop)} will return to the previous value. @findex DOLLARS_IN_IDENTIFIERS @item DOLLARS_IN_IDENTIFIERS Define this macro to control use of the character @samp{$} in identifier names. 0 means @samp{$} is not allowed by default; 1 means it is allowed. 1 is the default; there is no need to define this macro in that case. This macro controls the compiler proper; it does not affect the preprocessor. @findex NO_DOLLAR_IN_LABEL @item NO_DOLLAR_IN_LABEL Define this macro if the assembler does not accept the character @samp{$} in label names. By default constructors and destructors in G++ have @samp{$} in the identifiers. If this macro is defined, @samp{.} is used instead. @findex NO_DOT_IN_LABEL @item NO_DOT_IN_LABEL Define this macro if the assembler does not accept the character @samp{.} in label names. By default constructors and destructors in G++ have names that use @samp{.}. If this macro is defined, these names are rewritten to avoid @samp{.}. @findex DEFAULT_MAIN_RETURN @item DEFAULT_MAIN_RETURN Define this macro if the target system expects every program's @code{main} function to return a standard ``success'' value by default (if no other value is explicitly returned). The definition should be a C statement (sans semicolon) to generate the appropriate rtl instructions. It is used only when compiling the end of @code{main}. @item NEED_ATEXIT @findex NEED_ATEXIT Define this if the target system lacks the function @code{atexit} from the ISO C standard. If this macro is defined, a default definition will be provided to support C++. If @code{ON_EXIT} is not defined, a default @code{exit} function will also be provided. @item ON_EXIT @findex ON_EXIT Define this macro if the target has another way to implement atexit functionality without replacing @code{exit}. For instance, SunOS 4 has a similar @code{on_exit} library function. The definition should be a functional macro which can be used just like the @code{atexit} function. @item EXIT_BODY @findex EXIT_BODY Define this if your @code{exit} function needs to do something besides calling an external function @code{_cleanup} before terminating with @code{_exit}. The @code{EXIT_BODY} macro is only needed if @code{NEED_ATEXIT} is defined and @code{ON_EXIT} is not defined. @findex INSN_SETS_ARE_DELAYED @item INSN_SETS_ARE_DELAYED (@var{insn}) Define this macro as a C expression that is nonzero if it is safe for the delay slot scheduler to place instructions in the delay slot of @var{insn}, even if they appear to use a resource set or clobbered in @var{insn}. @var{insn} is always a @code{jump_insn} or an @code{insn}; GCC knows that every @code{call_insn} has this behavior. On machines where some @code{insn} or @code{jump_insn} is really a function call and hence has this behavior, you should define this macro. You need not define this macro if it would always return zero. @findex INSN_REFERENCES_ARE_DELAYED @item INSN_REFERENCES_ARE_DELAYED (@var{insn}) Define this macro as a C expression that is nonzero if it is safe for the delay slot scheduler to place instructions in the delay slot of @var{insn}, even if they appear to set or clobber a resource referenced in @var{insn}. @var{insn} is always a @code{jump_insn} or an @code{insn}. On machines where some @code{insn} or @code{jump_insn} is really a function call and its operands are registers whose use is actually in the subroutine it calls, you should define this macro. Doing so allows the delay slot scheduler to move instructions which copy arguments into the argument registers into the delay slot of @var{insn}. You need not define this macro if it would always return zero. @findex MACHINE_DEPENDENT_REORG @item MACHINE_DEPENDENT_REORG (@var{insn}) In rare cases, correct code generation requires extra machine dependent processing between the second jump optimization pass and delayed branch scheduling. On those machines, define this macro as a C statement to act on the code starting at @var{insn}. @findex MULTIPLE_SYMBOL_SPACES @item MULTIPLE_SYMBOL_SPACES Define this macro if in some cases global symbols from one translation unit may not be bound to undefined symbols in another translation unit without user intervention. For instance, under Microsoft Windows symbols must be explicitly imported from shared libraries (DLLs). @findex MD_ASM_CLOBBERS @item MD_ASM_CLOBBERS (@var{clobbers}) A C statement that adds to @var{clobbers} @code{STRING_CST} trees for any hard regs the port wishes to automatically clobber for all asms. @findex MAX_INTEGER_COMPUTATION_MODE @item MAX_INTEGER_COMPUTATION_MODE Define this to the largest integer machine mode which can be used for operations other than load, store and copy operations. You need only define this macro if the target holds values larger than @code{word_mode} in general purpose registers. Most targets should not define this macro. @findex MATH_LIBRARY @item MATH_LIBRARY Define this macro as a C string constant for the linker argument to link in the system math library, or @samp{""} if the target does not have a separate math library. You need only define this macro if the default of @samp{"-lm"} is wrong. @findex LIBRARY_PATH_ENV @item LIBRARY_PATH_ENV Define this macro as a C string constant for the environment variable that specifies where the linker should look for libraries. You need only define this macro if the default of @samp{"LIBRARY_PATH"} is wrong. @findex TARGET_HAS_F_SETLKW @item TARGET_HAS_F_SETLKW Define this macro if the target supports file locking with fcntl / F_SETLKW@. Note that this functionality is part of POSIX@. Defining @code{TARGET_HAS_F_SETLKW} will enable the test coverage code to use file locking when exiting a program, which avoids race conditions if the program has forked. @findex MAX_CONDITIONAL_EXECUTE @item MAX_CONDITIONAL_EXECUTE A C expression for the maximum number of instructions to execute via conditional execution instructions instead of a branch. A value of @code{BRANCH_COST}+1 is the default if the machine does not use cc0, and 1 if it does use cc0. @findex IFCVT_MODIFY_TESTS @item IFCVT_MODIFY_TESTS(@var{ce_info}, @var{true_expr}, @var{false_expr}) Used if the target needs to perform machine-dependent modifications on the conditionals used for turning basic blocks into conditionally executed code. @var{ce_info} points to a data structure, @code{struct ce_if_block}, which contains information about the currently processed blocks. @var{true_expr} and @var{false_expr} are the tests that are used for converting the then-block and the else-block, respectively. Set either @var{true_expr} or @var{false_expr} to a null pointer if the tests cannot be converted. @findex IFCVT_MODIFY_MULTIPLE_TESTS @item IFCVT_MODIFY_MULTIPLE_TESTS(@var{ce_info}, @var{bb}, @var{true_expr}, @var{false_expr}) Like @code{IFCVT_MODIFY_TESTS}, but used when converting more complicated if-statements into conditions combined by @code{and} and @code{or} operations. @var{bb} contains the basic block that contains the test that is currently being processed and about to be turned into a condition. @findex IFCVT_MODIFY_INSN @item IFCVT_MODIFY_INSN(@var{ce_info}, @var{pattern}, @var{insn}) A C expression to modify the @var{PATTERN} of an @var{INSN} that is to be converted to conditional execution format. @var{ce_info} points to a data structure, @code{struct ce_if_block}, which contains information about the currently processed blocks. @findex IFCVT_MODIFY_FINAL @item IFCVT_MODIFY_FINAL(@var{ce_info}) A C expression to perform any final machine dependent modifications in converting code to conditional execution. The involved basic blocks can be found in the @code{struct ce_if_block} structure that is pointed to by @var{ce_info}. @findex IFCVT_MODIFY_CANCEL @item IFCVT_MODIFY_CANCEL(@var{ce_info}) A C expression to cancel any machine dependent modifications in converting code to conditional execution. The involved basic blocks can be found in the @code{struct ce_if_block} structure that is pointed to by @var{ce_info}. @findex IFCVT_INIT_EXTRA_FIELDS @item IFCVT_INIT_EXTRA_FIELDS(@var{ce_info}) A C expression to initialize any extra fields in a @code{struct ce_if_block} structure, which are defined by the @code{IFCVT_EXTRA_FIELDS} macro. @findex IFCVT_EXTRA_FIELDS @item IFCVT_EXTRA_FIELDS If defined, it should expand to a set of field declarations that will be added to the @code{struct ce_if_block} structure. These should be intialized by the @code{IFCVT_INIT_EXTRA_FIELDS} macro. @end table @deftypefn {Target Hook} void TARGET_INIT_BUILTINS () Define this hook if you have any machine-specific built-in functions that need to be defined. It should be a function that performs the necessary setup. Machine specific built-in functions can be useful to expand special machine instructions that would otherwise not normally be generated because they have no equivalent in the source language (for example, SIMD vector instructions or prefetch instructions). To create a built-in function, call the function @code{builtin_function} which is defined by the language front end. You can use any type nodes set up by @code{build_common_tree_nodes} and @code{build_common_tree_nodes_2}; only language front ends that use those two functions will call @samp{TARGET_INIT_BUILTINS}. @end deftypefn @deftypefn {Target Hook} rtx TARGET_EXPAND_BUILTIN (tree @var{exp}, rtx @var{target}, rtx @var{subtarget}, enum machine_mode @var{mode}, int @var{ignore}) Expand a call to a machine specific built-in function that was set up by @samp{TARGET_INIT_BUILTINS}. @var{exp} is the expression for the function call; the result should go to @var{target} if that is convenient, and have mode @var{mode} if that is convenient. @var{subtarget} may be used as the target for computing one of @var{exp}'s operands. @var{ignore} is nonzero if the value is to be ignored. This function should return the result of the call to the built-in function. @end deftypefn @table @code @findex MD_CAN_REDIRECT_BRANCH @item MD_CAN_REDIRECT_BRANCH(@var{branch1}, @var{branch2}) Take a branch insn in @var{branch1} and another in @var{branch2}. Return true if redirecting @var{branch1} to the destination of @var{branch2} is possible. On some targets, branches may have a limited range. Optimizing the filling of delay slots can result in branches being redirected, and this may in turn cause a branch offset to overflow. @findex ALLOCATE_INITIAL_VALUE @item ALLOCATE_INITIAL_VALUE(@var{hard_reg}) When the initial value of a hard register has been copied in a pseudo register, it is often not necessary to actually allocate another register to this pseudo register, because the original hard register or a stack slot it has been saved into can be used. @code{ALLOCATE_INITIAL_VALUE}, if defined, is called at the start of register allocation once for each hard register that had its initial value copied by using @code{get_func_hard_reg_initial_val} or @code{get_hard_reg_initial_val}. Possible values are @code{NULL_RTX}, if you don't want to do any special allocation, a @code{REG} rtx---that would typically be the hard register itself, if it is known not to be clobbered---or a @code{MEM}. If you are returning a @code{MEM}, this is only a hint for the allocator; it might decide to use another register anyways. You may use @code{current_function_leaf_function} in the definition of the macro, functions that use @code{REG_N_SETS}, to determine if the hard register in question will not be clobbered. @findex TARGET_OBJECT_SUFFIX @item TARGET_OBJECT_SUFFIX Define this macro to be a C string representing the suffix for object files on your target machine. If you do not define this macro, GCC will use @samp{.o} as the suffix for object files. @findex TARGET_EXECUTABLE_SUFFIX @item TARGET_EXECUTABLE_SUFFIX Define this macro to be a C string representing the suffix to be automatically added to executable files on your target machine. If you do not define this macro, GCC will use the null string as the suffix for executable files. @findex COLLECT_EXPORT_LIST @item COLLECT_EXPORT_LIST If defined, @code{collect2} will scan the individual object files specified on its command line and create an export list for the linker. Define this macro for systems like AIX, where the linker discards object files that are not referenced from @code{main} and uses export lists. @end table @deftypefn {Target Hook} bool TARGET_CANNOT_MODIFY_JUMPS_P (void) This target hook returns @code{true} past the point in which new jump instructions could be created. On machines that require a register for every jump such as the SHmedia ISA of SH5, this point would typically be reload, so this target hook should be defined to a function such as: @smallexample static bool cannot_modify_jumps_past_reload_p () @{ return (reload_completed || reload_in_progress); @} @end smallexample @end deftypefn