\input texinfo @c -*- texinfo -*- @setfilename gdbint.info @include gdb-cfg.texi @dircategory Programming & development tools. @direntry START-INFO-DIR-ENTRY * Gdb-Internals: (gdbint). The GNU debugger's internals. END-INFO-DIR-ENTRY @end direntry @ifinfo This file documents the internals of the GNU debugger @value{GDBN}. Copyright 1990,1991,1992,1993,1994,1996,1998,1999,2000,2001 Free Software Foundation, Inc. Contributed by Cygnus Solutions. Written by John Gilmore. Second Edition by Stan Shebs. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being ``Algorithms'' and ``Porting GDB'', with the Front-Cover texts being ``A GNU Manual,'' and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.'' @end ifinfo @setchapternewpage off @settitle @value{GDBN} Internals @syncodeindex fn cp @syncodeindex vr cp @titlepage @title @value{GDBN} Internals @subtitle{A guide to the internals of the GNU debugger} @author John Gilmore @author Cygnus Solutions @author Second Edition: @author Stan Shebs @author Cygnus Solutions @page @tex \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$ \xdef\manvers{\$Revision$} % For use in headers, footers too {\parskip=0pt \hfill Cygnus Solutions\par \hfill \manvers\par \hfill \TeX{}info \texinfoversion\par } @end tex @vskip 0pt plus 1filll Copyright @copyright{} 1990,1991,1992,1993,1994,1996,1998,1999,2000,2001 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being ``Algorithms'' and ``Porting GDB'', with the Front-Cover texts being ``A GNU Manual,'' and with the Back-Cover Texts as in (a) below. (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.'' @end titlepage @c TeX can handle the contents at the start but makeinfo 3.12 can not @iftex @contents @end iftex @node Top @c Perhaps this should be the title of the document (but only for info, @c not for TeX). Existing GNU manuals seem inconsistent on this point. @top Scope of this Document This document documents the internals of the GNU debugger, @value{GDBN}. It includes description of @value{GDBN}'s key algorithms and operations, as well as the mechanisms that adapt @value{GDBN} to specific hosts and targets. @menu * Requirements:: * Overall Structure:: * Algorithms:: * User Interface:: * Symbol Handling:: * Language Support:: * Host Definition:: * Target Architecture Definition:: * Target Vector Definition:: * Native Debugging:: * Support Libraries:: * Coding:: * Porting GDB:: * Testsuite:: * Hints:: * Index:: @end menu @node Requirements @chapter Requirements @cindex requirements for @value{GDBN} Before diving into the internals, you should understand the formal requirements and other expectations for @value{GDBN}. Although some of these may seem obvious, there have been proposals for @value{GDBN} that have run counter to these requirements. First of all, @value{GDBN} is a debugger. It's not designed to be a front panel for embedded systems. It's not a text editor. It's not a shell. It's not a programming environment. @value{GDBN} is an interactive tool. Although a batch mode is available, @value{GDBN}'s primary role is to interact with a human programmer. @value{GDBN} should be responsive to the user. A programmer hot on the trail of a nasty bug, and operating under a looming deadline, is going to be very impatient of everything, including the response time to debugger commands. @value{GDBN} should be relatively permissive, such as for expressions. While the compiler should be picky (or have the option to be made picky), since source code lives for a long time usuazlly, the programmer doing debugging shouldn't be spending time figuring out to mollify the debugger. @value{GDBN} will be called upon to deal with really large programs. Executable sizes of 50 to 100 megabytes occur regularly, and we've heard reports of programs approaching 1 gigabyte in size. @value{GDBN} should be able to run everywhere. No other debugger is available for even half as many configurations as @value{GDBN} supports. @node Overall Structure @chapter Overall Structure @value{GDBN} consists of three major subsystems: user interface, symbol handling (the @dfn{symbol side}), and target system handling (the @dfn{target side}). The user interface consists of several actual interfaces, plus supporting code. The symbol side consists of object file readers, debugging info interpreters, symbol table management, source language expression parsing, type and value printing. The target side consists of execution control, stack frame analysis, and physical target manipulation. The target side/symbol side division is not formal, and there are a number of exceptions. For instance, core file support involves symbolic elements (the basic core file reader is in BFD) and target elements (it supplies the contents of memory and the values of registers). Instead, this division is useful for understanding how the minor subsystems should fit together. @section The Symbol Side The symbolic side of @value{GDBN} can be thought of as ``everything you can do in @value{GDBN} without having a live program running''. For instance, you can look at the types of variables, and evaluate many kinds of expressions. @section The Target Side The target side of @value{GDBN} is the ``bits and bytes manipulator''. Although it may make reference to symbolic info here and there, most of the target side will run with only a stripped executable available---or even no executable at all, in remote debugging cases. Operations such as disassembly, stack frame crawls, and register display, are able to work with no symbolic info at all. In some cases, such as disassembly, @value{GDBN} will use symbolic info to present addresses relative to symbols rather than as raw numbers, but it will work either way. @section Configurations @cindex host @cindex target @dfn{Host} refers to attributes of the system where @value{GDBN} runs. @dfn{Target} refers to the system where the program being debugged executes. In most cases they are the same machine, in which case a third type of @dfn{Native} attributes come into play. Defines and include files needed to build on the host are host support. Examples are tty support, system defined types, host byte order, host float format. Defines and information needed to handle the target format are target dependent. Examples are the stack frame format, instruction set, breakpoint instruction, registers, and how to set up and tear down the stack to call a function. Information that is only needed when the host and target are the same, is native dependent. One example is Unix child process support; if the host and target are not the same, doing a fork to start the target process is a bad idea. The various macros needed for finding the registers in the @code{upage}, running @code{ptrace}, and such are all in the native-dependent files. Another example of native-dependent code is support for features that are really part of the target environment, but which require @code{#include} files that are only available on the host system. Core file handling and @code{setjmp} handling are two common cases. When you want to make @value{GDBN} work ``native'' on a particular machine, you have to include all three kinds of information. @node Algorithms @chapter Algorithms @cindex algorithms @value{GDBN} uses a number of debugging-specific algorithms. They are often not very complicated, but get lost in the thicket of special cases and real-world issues. This chapter describes the basic algorithms and mentions some of the specific target definitions that they use. @section Frames @cindex frame @cindex call stack frame A frame is a construct that @value{GDBN} uses to keep track of calling and called functions. @findex create_new_frame @vindex FRAME_FP @code{FRAME_FP} in the machine description has no meaning to the machine-independent part of @value{GDBN}, except that it is used when setting up a new frame from scratch, as follows: @example create_new_frame (read_register (FP_REGNUM), read_pc ())); @end example @cindex frame pointer register Other than that, all the meaning imparted to @code{FP_REGNUM} is imparted by the machine-dependent code. So, @code{FP_REGNUM} can have any value that is convenient for the code that creates new frames. (@code{create_new_frame} calls @code{INIT_EXTRA_FRAME_INFO} if it is defined; that is where you should use the @code{FP_REGNUM} value, if your frames are nonstandard.) @cindex frame chain Given a @value{GDBN} frame, define @code{FRAME_CHAIN} to determine the address of the calling function's frame. This will be used to create a new @value{GDBN} frame struct, and then @code{INIT_EXTRA_FRAME_INFO} and @code{INIT_FRAME_PC} will be called for the new frame. @section Breakpoint Handling @cindex breakpoints In general, a breakpoint is a user-designated location in the program where the user wants to regain control if program execution ever reaches that location. There are two main ways to implement breakpoints; either as ``hardware'' breakpoints or as ``software'' breakpoints. @cindex hardware breakpoints @cindex program counter Hardware breakpoints are sometimes available as a builtin debugging features with some chips. Typically these work by having dedicated register into which the breakpoint address may be stored. If the PC (shorthand for @dfn{program counter}) ever matches a value in a breakpoint registers, the CPU raises an exception and reports it to @value{GDBN}. Another possibility is when an emulator is in use; many emulators include circuitry that watches the address lines coming out from the processor, and force it to stop if the address matches a breakpoint's address. A third possibility is that the target already has the ability to do breakpoints somehow; for instance, a ROM monitor may do its own software breakpoints. So although these are not literally ``hardware breakpoints'', from @value{GDBN}'s point of view they work the same; @value{GDBN} need not do nothing more than set the breakpoint and wait for something to happen. Since they depend on hardware resources, hardware breakpoints may be limited in number; when the user asks for more, @value{GDBN} will start trying to set software breakpoints. (On some architectures, notably the 32-bit x86 platforms, @value{GDBN} cannot alsways know whether there's enough hardware resources to insert all the hardware breakpoints and watchpoints. On those platforms, @value{GDBN} prints an error message only when the program being debugged is continued.) @cindex software breakpoints Software breakpoints require @value{GDBN} to do somewhat more work. The basic theory is that @value{GDBN} will replace a program instruction with a trap, illegal divide, or some other instruction that will cause an exception, and then when it's encountered, @value{GDBN} will take the exception and stop the program. When the user says to continue, @value{GDBN} will restore the original instruction, single-step, re-insert the trap, and continue on. Since it literally overwrites the program being tested, the program area must be writeable, so this technique won't work on programs in ROM. It can also distort the behavior of programs that examine themselves, although such a situation would be highly unusual. Also, the software breakpoint instruction should be the smallest size of instruction, so it doesn't overwrite an instruction that might be a jump target, and cause disaster when the program jumps into the middle of the breakpoint instruction. (Strictly speaking, the breakpoint must be no larger than the smallest interval between instructions that may be jump targets; perhaps there is an architecture where only even-numbered instructions may jumped to.) Note that it's possible for an instruction set not to have any instructions usable for a software breakpoint, although in practice only the ARC has failed to define such an instruction. @findex BREAKPOINT The basic definition of the software breakpoint is the macro @code{BREAKPOINT}. Basic breakpoint object handling is in @file{breakpoint.c}. However, much of the interesting breakpoint action is in @file{infrun.c}. @section Single Stepping @section Signal Handling @section Thread Handling @section Inferior Function Calls @section Longjmp Support @cindex @code{longjmp} debugging @value{GDBN} has support for figuring out that the target is doing a @code{longjmp} and for stopping at the target of the jump, if we are stepping. This is done with a few specialized internal breakpoints, which are visible in the output of the @samp{maint info breakpoint} command. @findex GET_LONGJMP_TARGET To make this work, you need to define a macro called @code{GET_LONGJMP_TARGET}, which will examine the @code{jmp_buf} structure and extract the longjmp target address. Since @code{jmp_buf} is target specific, you will need to define it in the appropriate @file{tm-@var{target}.h} file. Look in @file{tm-sun4os4.h} and @file{sparc-tdep.c} for examples of how to do this. @section Watchpoints @cindex watchpoints Watchpoints are a special kind of breakpoints (@pxref{Algorithms, breakpoints}) which break when data is accessed rather than when some instruction is executed. When you have data which changes without your knowing what code does that, watchpoints are the silver bullet to hunt down and kill such bugs. @cindex hardware watchpoints @cindex software watchpoints Watchpoints can be either hardware-assisted or not; the latter type is known as ``software watchpoints.'' @value{GDBN} always uses hardware-assisted watchpoints if they are available, and falls back on software watchpoints otherwise. Typical situations where @value{GDBN} will use software watchpoints are: @itemize @bullet @item The watched memory region is too large for the underlying hardware watchpoint support. For example, each x86 debug register can watch up to 4 bytes of memory, so trying to watch data structures whose size is more than 16 bytes will cause @value{GDBN} to use software watchpoints. @item The value of the expression to be watched depends on data held in registers (as opposed to memory). @item Too many different watchpoints requested. (On some architectures, this situation is impossible to detect until the debugged program is resumed.) Note that x86 debug registers are used both for hardware breakpoints and for watchpoints, so setting too many hardware breakpoints might cause watchpoint insertion to fail. @item No hardware-assisted watchpoints provided by the target implementation. @end itemize Software watchpoints are very slow, since @value{GDBN} needs to single-step the program being debugged and test the value of the watched expression(s) after each instruction. The rest of this section is mostly irrelevant for software watchpoints. @value{GDBN} uses several macros and primitives to support hardware watchpoints: @table @code @findex TARGET_HAS_HARDWARE_WATCHPOINTS @item TARGET_HAS_HARDWARE_WATCHPOINTS If defined, the target supports hardware watchpoints. @findex TARGET_CAN_USE_HARDWARE_WATCHPOINT @item TARGET_CAN_USE_HARDWARE_WATCHPOINT (@var{type}, @var{count}, @var{other}) Return the number of hardware watchpoints of type @var{type} that are possible to be set. The value is positive if @var{count} watchpoints of this type can be set, zero if setting watchpoints of this type is not supported, and negative if @var{count} is more than the maximum number of watchpoints of type @var{type} that can be set. @var{other} is non-zero if other types of watchpoints are currently enabled (there are architectures which cannot set watchpoints of different types at the same time). @findex TARGET_REGION_OK_FOR_HW_WATCHPOINT @item TARGET_REGION_OK_FOR_HW_WATCHPOINT (@var{addr}, @var{len}) Return non-zero if hardware watchpoints can be used to watch a region whose address is @var{addr} and whose length in bytes is @var{len}. @findex TARGET_REGION_SIZE_OK_FOR_HW_WATCHPOINT @item TARGET_REGION_SIZE_OK_FOR_HW_WATCHPOINT (@var{size}) Return non-zero if hardware watchpoints can be used to watch a region whose size is @var{size}. @value{GDBN} only uses this macro as a fall-back, in case @code{TARGET_REGION_OK_FOR_HW_WATCHPOINT} is not defined. @findex TARGET_DISABLE_HW_WATCHPOINTS @item TARGET_DISABLE_HW_WATCHPOINTS (@var{pid}) Disables watchpoints in the process identified by @var{pid}. This is used, e.g., on HP-UX which provides operations to disable and enable the page-level memory protection that implements hardware watchpoints on that platform. @findex TARGET_ENABLE_HW_WATCHPOINTS @item TARGET_ENABLE_HW_WATCHPOINTS (@var{pid}) Enables watchpoints in the process identified by @var{pid}. This is used, e.g., on HP-UX which provides operations to disable and enable the page-level memory protection that implements hardware watchpoints on that platform. @findex TARGET_RANGE_PROFITABLE_FOR_HW_WATCHPOINT @item TARGET_RANGE_PROFITABLE_FOR_HW_WATCHPOINT (@var{pid},@var{start},@var{len}) Some addresses may not be profitable to use hardware to watch, or may be difficult to understand when the addressed object is out of scope, and hence should not be watched with hardware watchpoints. On some targets, this may have severe performance penalties, such that we might as well use regular watchpoints, and save (possibly precious) hardware watchpoints for other locations. @findex target_insert_watchpoint @findex target_remove_watchpoint @item target_insert_watchpoint (@var{addr}, @var{len}, @var{type}) @itemx target_remove_watchpoint (@var{addr}, @var{len}, @var{type}) Insert or remove a hardware watchpoint starting at @var{addr}, for @var{len} bytes. @var{type} is the watchpoint type, one of the possible values of the enumerated data type @code{target_hw_bp_type}, defined by @file{breakpoint.h} as follows: @example enum target_hw_bp_type @{ hw_write = 0, /* Common (write) HW watchpoint */ hw_read = 1, /* Read HW watchpoint */ hw_access = 2, /* Access (read or write) HW watchpoint */ hw_execute = 3 /* Execute HW breakpoint */ @}; @end example @noindent These two macros should return 0 for success, non-zero for failure. @cindex insert or remove hardware breakpoint @findex target_remove_hw_breakpoint @findex target_insert_hw_breakpoint @item target_remove_hw_breakpoint (@var{addr}, @var{shadow}) @itemx target_insert_hw_breakpoint (@var{addr}, @var{shadow}) Insert or remove a hardware-assisted breakpoint at address @var{addr}. Returns zero for success, non-zero for failure. @var{shadow} is the real contents of the byte where the breakpoint has been inserted; it is generally not valid when hardware breakpoints are used, but since no other code touches these values, the implementations of the above two macros can use them for their internal purposes. @findex target_stopped_data_address @item target_stopped_data_address () If the inferior has some watchpoint that triggered, return the address associated with that watchpoint. Otherwise, return zero. @findex DECR_PC_AFTER_HW_BREAK @item DECR_PC_AFTER_HW_BREAK If defined, @value{GDBN} decrements the program counter by the value of @code{DECR_PC_AFTER_HW_BREAK} after a hardware break-point. This overrides the value of @code{DECR_PC_AFTER_BREAK} when a breakpoint that breaks is a hardware-assisted breakpoint. @findex HAVE_STEPPABLE_WATCHPOINT @item HAVE_STEPPABLE_WATCHPOINT If defined to a non-zero value, it is not necessary to disable a watchpoint to step over it. @findex HAVE_NONSTEPPABLE_WATCHPOINT @item HAVE_NONSTEPPABLE_WATCHPOINT If defined to a non-zero value, @value{GDBN} should disable a watchpoint to step the inferior over it. @findex HAVE_CONTINUABLE_WATCHPOINT @item HAVE_CONTINUABLE_WATCHPOINT If defined to a non-zero value, it is possible to continue the inferior after a watchpoint has been hit. @findex CANNOT_STEP_HW_WATCHPOINTS @item CANNOT_STEP_HW_WATCHPOINTS If this is defined to a non-zero value, @value{GDBN} will remove all watchpoints before stepping the inferior. @findex STOPPED_BY_WATCHPOINT @item STOPPED_BY_WATCHPOINT (@var{wait_status}) Return non-zero if stopped by a watchpoint. @var{wait_status} is of the type @code{struct target_waitstatus}, defined by @file{target.h}. @end table @subsection x86 Watchpoints @cindex x86 debug registers @cindex watchpoints, on x86 The 32-bit Intel x86 (a.k.a.@: ia32) processors feature special debug registers designed to facilitate debugging. @value{GDBN} provides a generic library of functions that x86-based ports can use to implement support for watchpoints and hardware-assisted breakpoints. This subsection documents the x86 watchpoint facilities in @value{GDBN}. To use the generic x86 watchpoint support, a port should do the following: @itemize @bullet @findex I386_USE_GENERIC_WATCHPOINTS @item Define the macro @code{I386_USE_GENERIC_WATCHPOINTS} somewhere in the target-dependent headers. @item Include the @file{config/i386/nm-i386.h} header file @emph{after} defining @code{I386_USE_GENERIC_WATCHPOINTS}. @item Add @file{i386-nat.o} to the value of the Make variable @code{NATDEPFILES} (@pxref{Native Debugging, NATDEPFILES}) or @code{TDEPFILES} (@pxref{Target Architecture Definition, TDEPFILES}). @item Provide implementations for the @code{I386_DR_LOW_*} macros described below. Typically, each macro should call a target-specific function which does the real work. @end itemize The x86 watchpoint support works by maintaining mirror images of the debug registers. Values are copied between the mirror images and the real debug registers via a set of macros which each target needs to provide: @table @code @findex I386_DR_LOW_SET_CONTROL @item I386_DR_LOW_SET_CONTROL (@var{val}) Set the Debug Control (DR7) register to the value @var{val}. @findex I386_DR_LOW_SET_ADDR @item I386_DR_LOW_SET_ADDR (@var{idx}, @var{addr}) Put the address @var{addr} into the debug register number @var{idx}. @findex I386_DR_LOW_RESET_ADDR @item I386_DR_LOW_RESET_ADDR (@var{idx}) Reset (i.e.@: zero out) the address stored in the debug register number @var{idx}. @findex I386_DR_LOW_GET_STATUS @item I386_DR_LOW_GET_STATUS Return the value of the Debug Status (DR6) register. This value is used immediately after it is returned by @code{I386_DR_LOW_GET_STATUS}, so as to support per-thread status register values. @end table For each one of the 4 debug registers (whose indices are from 0 to 3) that store addresses, a reference count is maintained by @value{GDBN}, to allow sharing of debug registers by several watchpoints. This allows users to define several watchpoints that watch the same expression, but with different conditions and/or commands, without wasting debug registers which are in short supply. @value{GDBN} maintains the reference counts internally, targets don't have to do anything to use this feature. The x86 debug registers can each watch a region that is 1, 2, or 4 bytes long. The ia32 architecture requires that each watched region be appropriately aligned: 2-byte region on 2-byte boundary, 4-byte region on 4-byte boundary. However, the x86 watchpoint support in @value{GDBN} can watch unaligned regions and regions larger than 4 bytes (up to 16 bytes) by allocating several debug registers to watch a single region. This allocation of several registers per a watched region is also done automatically without target code intervention. The generic x86 watchpoint support provides the following API for the @value{GDBN}'s application code: @table @code @findex i386_region_ok_for_watchpoint @item i386_region_ok_for_watchpoint (@var{addr}, @var{len}) The macro @code{TARGET_REGION_OK_FOR_HW_WATCHPOINT} is set to call this function. It counts the number of debug registers required to watch a given region, and returns a non-zero value if that number is less than 4, the number of debug registers available to x86 processors. @findex i386_stopped_data_address @item i386_stopped_data_address (void) The macros @code{STOPPED_BY_WATCHPOINT} and @code{target_stopped_data_address} are set to call this function. The argument passed to @code{STOPPED_BY_WATCHPOINT} is ignored. This function examines the breakpoint condition bits in the DR6 Debug Status register, as returned by the @code{I386_DR_LOW_GET_STATUS} macro, and returns the address associated with the first bit that is set in DR6. @findex i386_insert_watchpoint @findex i386_remove_watchpoint @item i386_insert_watchpoint (@var{addr}, @var{len}, @var{type}) @itemx i386_remove_watchpoint (@var{addr}, @var{len}, @var{type}) Insert or remove a watchpoint. The macros @code{target_insert_watchpoint} and @code{target_remove_watchpoint} are set to call these functions. @code{i386_insert_watchpoint} first looks for a debug register which is already set to watch the same region for the same access types; if found, it just increments the reference count of that debug register, thus implementing debug register sharing between watchpoints. If no such register is found, the function looks for a vacant debug register, sets its mirrorred value to @var{addr}, sets the mirrorred value of DR7 Debug Control register as appropriate for the @var{len} and @var{type} parameters, and then passes the new values of the debug register and DR7 to the inferior by calling @code{I386_DR_LOW_SET_ADDR} and @code{I386_DR_LOW_SET_CONTROL}. If more than one debug register is required to cover the given region, the above process is repeated for each debug register. @code{i386_remove_watchpoint} does the opposite: it resets the address in the mirrorred value of the debug register and its read/write and length bits in the mirrorred value of DR7, then passes these new values to the inferior via @code{I386_DR_LOW_RESET_ADDR} and @code{I386_DR_LOW_SET_CONTROL}. If a register is shared by several watchpoints, each time a @code{i386_remove_watchpoint} is called, it decrements the reference count, and only calls @code{I386_DR_LOW_RESET_ADDR} and @code{I386_DR_LOW_SET_CONTROL} when the count goes to zero. @findex i386_insert_hw_breakpoint @findex i386_remove_hw_breakpoint @item i386_insert_hw_breakpoint (@var{addr}, @var{shadow} @itemx i386_remove_hw_breakpoint (@var{addr}, @var{shadow}) These functions insert and remove hardware-assisted breakpoints. The macros @code{target_insert_hw_breakpoint} and @code{target_remove_hw_breakpoint} are set to call these functions. These functions work like @code{i386_insert_watchpoint} and @code{i386_remove_watchpoint}, respectively, except that they set up the debug registers to watch instruction execution, and each hardware-assisted breakpoint always requires exactly one debug register. @findex i386_stopped_by_hwbp @item i386_stopped_by_hwbp (void) This function returns non-zero if the inferior has some watchpoint or hardware breakpoint that triggered. It works like @code{i386_stopped_data_address}, except that it doesn't return the address whose watchpoint triggered. @findex i386_cleanup_dregs @item i386_cleanup_dregs (void) This function clears all the reference counts, addresses, and control bits in the mirror images of the debug registers. It doesn't affect the actual debug registers in the inferior process. @end table @noindent @strong{Notes:} @enumerate 1 @item x86 processors support setting watchpoints on I/O reads or writes. However, since no target supports this (as of March 2001), and since @code{enum target_hw_bp_type} doesn't even have an enumeration for I/O watchpoints, this feature is not yet available to @value{GDBN} running on x86. @item x86 processors can enable watchpoints locally, for the current task only, or globally, for all the tasks. For each debug register, there's a bit in the DR7 Debug Control register that determines whether the associated address is watched locally or globally. The current implementation of x86 watchpoint support in @value{GDBN} always sets watchpoints to be locally enabled, since global watchpoints might interfere with the underlying OS and are probably unavailable in many platforms. @end enumerate @node User Interface @chapter User Interface @value{GDBN} has several user interfaces. Although the command-line interface is the most common and most familiar, there are others. @section Command Interpreter @cindex command interpreter @cindex CLI The command interpreter in @value{GDBN} is fairly simple. It is designed to allow for the set of commands to be augmented dynamically, and also has a recursive subcommand capability, where the first argument to a command may itself direct a lookup on a different command list. For instance, the @samp{set} command just starts a lookup on the @code{setlist} command list, while @samp{set thread} recurses to the @code{set_thread_cmd_list}. @findex add_cmd @findex add_com To add commands in general, use @code{add_cmd}. @code{add_com} adds to the main command list, and should be used for those commands. The usual place to add commands is in the @code{_initialize_@var{xyz}} routines at the ends of most source files. @cindex deprecating commands @findex deprecate_cmd Before removing commands from the command set it is a good idea to deprecate them for some time. Use @code{deprecate_cmd} on commands or aliases to set the deprecated flag. @code{deprecate_cmd} takes a @code{struct cmd_list_element} as it's first argument. You can use the return value from @code{add_com} or @code{add_cmd} to deprecate the command immediately after it is created. The first time a comamnd is used the user will be warned and offered a replacement (if one exists). Note that the replacement string passed to @code{deprecate_cmd} should be the full name of the command, i.e. the entire string the user should type at the command line. @section UI-Independent Output---the @code{ui_out} Functions @c This section is based on the documentation written by Fernando @c Nasser . @cindex @code{ui_out} functions The @code{ui_out} functions present an abstraction level for the @value{GDBN} output code. They hide the specifics of different user interfaces supported by @value{GDBN}, and thus free the programmer from the need to write several versions of the same code, one each for every UI, to produce output. @subsection Overview and Terminology In general, execution of each @value{GDBN} command produces some sort of output, and can even generate an input request. Output can be generated for the following purposes: @itemize @bullet @item to display a @emph{result} of an operation; @item to convey @emph{info} or produce side-effects of a requested operation; @item to provide a @emph{notification} of an asynchronous event (including progress indication of a prolonged asynchronous operation); @item to display @emph{error messages} (including warnings); @item to show @emph{debug data}; @item to @emph{query} or prompt a user for input (a special case). @end itemize @noindent This section mainly concentrates on how to build result output, although some of it also applies to other kinds of output. Generation of output that displays the results of an operation involves one or more of the following: @itemize @bullet @item output of the actual data @item formatting the output as appropriate for console output, to make it easily readable by humans @item machine oriented formatting--a more terse formatting to allow for easy parsing by programs which read @value{GDBN}'s output @item annotation, whose purpose is to help a GUI (such as GDBTK or Emacs) to identify interesting parts in the output @end itemize The @code{ui_out} routines take care of the first three aspects. Annotations are provided by separate annotation routines. Note that use of annotations for an interface between a GUI and @value{GDBN} is deprecated. Output can be in the form of a single item, which we call a @dfn{field}; a @dfn{list} of fields; or a @dfn{table}, which is a list of fields with a header. In a BNF-like form: @example ::= any single item of data kept by gdb ;; ::= @{ @} ;; ::=
@{ @} ;;
::= @{ @} ;; ::= ;; @end example @subsection General Conventions All @code{ui_out} routines currently are of type @code{void}, except for @code{ui_out_stream_new} which returns a pointer to the newly created object. The first parameter is always the @code{ui_out} vector object, a pointer to a @code{struct ui_out}. The @var{format} parameter is like in @code{printf} family of functions. When it is present, there is usually also a variable list of arguments used to satisfy the @code{%} specifiers in the supplied format. When a character string argument is not used in a @code{ui_out} function call, a @code{NULL} pointer has to be supplied instead. @subsection Table and List Functions @cindex list output functions @cindex table output functions This section introduces @code{ui_out} routines for building lists and tables. The routines to output the actual data items (fields) are presented in the next section. To recap: A @dfn{list} is a sequence of @dfn{fields} with information about an object; a @dfn{table} is a list of lists, each on a separate line, prefixed by a @dfn{header} line with the column @dfn{titles}. Use the table functions if your output is composed of a list of fields for several objects and the console output should have a header. Use this even when you are listing just one object but you still want the header. Use the list functions for the output of each object of a table or if your output consists of a single list of fields. You can nest a list into a table, but not the other way around. @cindex nesting level in @code{ui_out} functions Lists can also be nested: some of your fields may be lists or @dfn{tuples}--@code{@{@var{name},@var{value}@}} pairs. The maximum nesting level is currently 4. The overall structure of the table output code is something like this: @example ui_out_table_begin ui_out_table_header ... ui_out_table_body ui_out_list_begin ui_out_field_* ... ui_out_list_end ... ui_out_table_end @end example Here's the description of table- and list-related @code{ui_out} functions: @deftypefun void ui_out_table_begin (struct ui_out *@var{uiout}, int @var{nbrofcols}, char *@var{tblid}) The function @code{ui_out_table_begin} marks the beginning of the output of a table. It should always be called before any other @code{ui_out} function for a given table. @var{nbrofcols} is the number of columns in the table, and @var{tblid} is an optional string identifying the table. The string pointed to by @var{tblid} is copied by the implementation of @code{ui_out_table_begin}, so the application can free the string if it was @code{malloc}ed. The companion function @code{ui_out_table_end}, described below, marks the end of the table's output. @end deftypefun @deftypefun void ui_out_table_header (struct ui_out *@var{uiout}, int @var{width}, enum ui_align @var{alignment}, char *@var{colhdr}) @code{ui_out_table_header} provides the header information for a single table column. You call this function several times, one each for every column of the table, after @code{ui_out_table_begin}, but before @code{ui_out_table_body}. The value of @var{width} gives the column width in characters. The value of @var{alignment} is one of @code{left}, @code{center}, and @code{right}, and it specifies how to align the header: left-justify, center, or right-justify it. @var{colhdr} points to a string that specifies the column header; the implementation copies that string, so column header strings in @code{malloc}ed storage can be freed after the call. @end deftypefun @deftypefun void ui_out_table_body (struct ui_out *@var{uiout}) This function marks the end of header information and the beginning of table body output. It doesn't by itself produce any data output; that is done by the list and field output functions described below. @end deftypefun @deftypefun void ui_out_table_end (struct ui_out *@var{uiout}) This function signals the end of a table's output. It should be called after the table body has been produced by the list and field output functions. There should be exactly one call to @code{ui_out_table_end} for each call to @code{ui_out_table_begin}, otherwise the @code{ui_out} functions will signal an internal error. @end deftypefun The output of the lists that represent the table rows must follow the call to @code{ui_out_table_body} and precede the call to @code{ui_out_table_end}. You produce the lists by calling @code{ui_out_list_begin} and @code{ui_out_list_end}, with suitable calls to functions which actually output fields between them. @deftypefun void ui_out_list_begin (struct ui_out *@var{uiout}, char *@var{lstid}) This function marks the beginning or a list output. @var{lstid} points to an optional string that identifies the list; it is copied by the implementation, and so strings in @code{malloc}ed storage can be freed after the call. @end deftypefun @deftypefun void ui_out_list_end (struct ui_out *@var{uiout}) This function signals an end of a list output. There should be exactly one call to @code{ui_out_list_end} for each call to @code{ui_out_list_begin}, otherwise an internal @value{GDBN} error will be signaled. @end deftypefun @subsection Item Output Functions @cindex item output functions @cindex field output functions @cindex data output The functions described below produce output for the actual data items, or fields, which contain information about the object. Choose the appropriate function accordingly to your particular needs. @deftypefun void ui_out_field_fmt (struct ui_out *@var{uiout}, char *@var{fldname}, char *@var{format}, ...) This is the most general output function. It produces the representation of the data in the variable-length argument list according to formatting specifications in @var{format}, a @code{printf}-like format string. The optional argument @var{fldname} supplies the name of the field. The data items themselves are supplied as additional arguments after @var{format}. This generic function should be used only when it is not possible to use one of the specialized versions (see below). @end deftypefun @deftypefun void ui_out_field_int (struct ui_out *@var{uiout}, char *@var{fldname}, int @var{value}) This function outputs a value of an @code{int} variable. It uses the @code{"%d"} output conversion specification. @var{fldname} specifies the name of the field. @end deftypefun @deftypefun void ui_out_field_core_addr (struct ui_out *@var{uiout}, char *@var{fldname}, CORE_ADDR @var{address}) This function outputs an address. @end deftypefun @deftypefun void ui_out_field_string (struct ui_out *@var{uiout}, char *@var{fldname}, const char *@var{string}) This function outputs a string using the @code{"%s"} conversion specification. @end deftypefun Sometimes, there's a need to compose your output piece by piece using functions that operate on a stream, such as @code{value_print} or @code{fprintf_symbol_filtered}. These functions accept an argument of the type @code{struct ui_file *}, a pointer to a @code{ui_file} object used to store the data stream used for the output. When you use one of these functions, you need a way to pass their results stored in a @code{ui_file} object to the @code{ui_out} functions. To this end, you first create a @code{ui_stream} object by calling @code{ui_out_stream_new}, pass the @code{stream} member of that @code{ui_stream} object to @code{value_print} and similar functions, and finally call @code{ui_out_field_stream} to output the field you constructed. When the @code{ui_stream} object is no longer needed, you should destroy it and free its memory by calling @code{ui_out_stream_delete}. @deftypefun struct ui_stream *ui_out_stream_new (struct ui_out *@var{uiout}) This function creates a new @code{ui_stream} object which uses the same output methods as the @code{ui_out} object whose pointer is passed in @var{uiout}. It returns a pointer to the newly created @code{ui_stream} object. @end deftypefun @deftypefun void ui_out_stream_delete (struct ui_stream *@var{streambuf}) This functions destroys a @code{ui_stream} object specified by @var{streambuf}. @end deftypefun @deftypefun void ui_out_field_stream (struct ui_out *@var{uiout}, char *@var{fieldname}, struct ui_stream *@var{streambuf}) This function consumes all the data accumulated in @code{streambuf->stream} and outputs it like @code{ui_out_field_string} does. After a call to @code{ui_out_field_stream}, the accumulated data no longer exists, but the stream is still valid and may be used for producing more fields. @end deftypefun @strong{Important:} If there is any chance that your code could bail out before completing output generation and reaching the point where @code{ui_out_stream_delete} is called, it is necessary to set up a cleanup, to avoid leaking memory and other resources. Here's a skeleton code to do that: @smallexample struct ui_stream *mybuf = ui_out_stream_new (uiout); struct cleanup *old = make_cleanup (ui_out_stream_delete, mybuf); ... do_cleanups (old); @end smallexample If the function already has the old cleanup chain set (for other kinds of cleanups), you just have to add your cleanup to it: @smallexample mybuf = ui_out_stream_new (uiout); make_cleanup (ui_out_stream_delete, mybuf); @end smallexample Note that with cleanups in place, you should not call @code{ui_out_stream_delete} directly, or you would attempt to free the same buffer twice. @subsection Utility Output Functions @deftypefun void ui_out_field_skip (struct ui_out *@var{uiout}, char *@var{fldname}) This function skips a field in a table. Use it if you have to leave an empty field without disrupting the table alignment. The argument @var{fldname} specifies a name for the (missing) filed. @end deftypefun @deftypefun void ui_out_text (struct ui_out *@var{uiout}, char *@var{string}) This function outputs the text in @var{string} in a way that makes it easy to be read by humans. For example, the console implementation of this method filters the text through a built-in pager, to prevent it from scrolling off the visible portion of the screen. Use this function for printing relatively long chunks of text around the actual field data: the text it produces is not aligned according to the table's format. Use @code{ui_out_field_string} to output a string field, and use @code{ui_out_message}, described below, to output short messages. @end deftypefun @deftypefun void ui_out_spaces (struct ui_out *@var{uiout}, int @var{nspaces}) This function outputs @var{nspaces} spaces. It is handy to align the text produced by @code{ui_out_text} with the rest of the table or list. @end deftypefun @deftypefun void ui_out_message (struct ui_out *@var{uiout}, int @var{verbosity}, char *@var{format}, ...) This function produces a formatted message, provided that the current verbosity level is at least as large as given by @var{verbosity}. The current verbosity level is specified by the user with the @samp{set verbositylevel} command.@footnote{As of this writing (April 2001), setting verbosity level is not yet implemented, and is always returned as zero. So calling @code{ui_out_message} with a @var{verbosity} argument more than zero will cause the message to never be printed.} @end deftypefun @deftypefun void ui_out_wrap_hint (struct ui_out *@var{uiout}, char *@var{indent}) This function gives the console output filter (a paging filter) a hint of where to break lines which are too long. Ignored for all other output consumers. @var{indent}, if non-@code{NULL}, is the string to be printed to indent the wrapped text on the next line; it must remain accessible until the next call to @code{ui_out_wrap_hint}, or until an explicit newline is produced by one of the other functions. If @var{indent} is @code{NULL}, the wrapped text will not be indented. @end deftypefun @deftypefun void ui_out_flush (struct ui_out *@var{uiout}) This function flushes whatever output has been accumulated so far, if the UI buffers output. @end deftypefun @subsection Examples of Use of @code{ui_out} functions @cindex using @code{ui_out} functions @cindex @code{ui_out} functions, usage examples This section gives some practical examples of using the @code{ui_out} functions to generalize the old console-oriented code in @value{GDBN}. The examples all come from functions defined on the @file{breakpoints.c} file. This example, from the @code{breakpoint_1} function, shows how to produce a table. The original code was: @example if (!found_a_breakpoint++) @{ annotate_breakpoints_headers (); annotate_field (0); printf_filtered ("Num "); annotate_field (1); printf_filtered ("Type "); annotate_field (2); printf_filtered ("Disp "); annotate_field (3); printf_filtered ("Enb "); if (addressprint) @{ annotate_field (4); printf_filtered ("Address "); @} annotate_field (5); printf_filtered ("What\n"); annotate_breakpoints_table (); @} @end example Here's the new version: @example if (!found_a_breakpoint++) @{ annotate_breakpoints_headers (); if (addressprint) ui_out_table_begin (ui, 6); else ui_out_table_begin (ui, 5); annotate_field (0); ui_out_table_header (ui, 4, left, "Num"); annotate_field (1); ui_out_table_header (ui, 15, left, "Type"); annotate_field (2); ui_out_table_header (ui, 5, left, "Disp"); annotate_field (3); ui_out_table_header (ui, 4, left, "Enb"); if (addressprint) @{ annotate_field (4); ui_out_table_header (ui, 11, left, "Address"); @} annotate_field (5); ui_out_table_header (ui, 40, left, "What"); ui_out_table_body (ui); annotate_breakpoints_table (); @} @end example This example, from the @code{print_one_breakpoint} function, shows how to produce the actual data for the table whose structure was defined in the above example. The original code was: @example annotate_record (); annotate_field (0); printf_filtered ("%-3d ", b->number); annotate_field (1); if ((int)b->type > (sizeof(bptypes)/sizeof(bptypes[0])) || ((int) b->type != bptypes[(int) b->type].type)) internal_error ("bptypes table does not describe type #%d.", (int)b->type); printf_filtered ("%-14s ", bptypes[(int)b->type].description); annotate_field (2); printf_filtered ("%-4s ", bpdisps[(int)b->disposition]); annotate_field (3); printf_filtered ("%-3c ", bpenables[(int)b->enable]); @end example This is the new version: @example annotate_record (); ui_out_list_begin (uiout, "bkpt"); annotate_field (0); ui_out_field_int (uiout, "number", b->number); annotate_field (1); if (((int) b->type > (sizeof (bptypes) / sizeof (bptypes[0]))) || ((int) b->type != bptypes[(int) b->type].type)) internal_error ("bptypes table does not describe type #%d.", (int) b->type); ui_out_field_string (uiout, "type", bptypes[(int)b->type].description); annotate_field (2); ui_out_field_string (uiout, "disp", bpdisps[(int)b->disposition]); annotate_field (3); ui_out_field_fmt (uiout, "enabled", "%c", bpenables[(int)b->enable]); @end example This example, also from @code{print_one_breakpoint}, shows how to produce a complicated output field using the @code{print_expression} functions which requires a stream to be passed. It also shows how to automate stream destruction with cleanups. The original code was: @example annotate_field (5); print_expression (b->exp, gdb_stdout); @end example The new version is: @example struct ui_stream *stb = ui_out_stream_new (uiout); struct cleanup *old_chain = make_cleanup_ui_out_stream_delete (stb); ... annotate_field (5); print_expression (b->exp, stb->stream); ui_out_field_stream (uiout, "what", local_stream); @end example This example, also from @code{print_one_breakpoint}, shows how to use @code{ui_out_text} and @code{ui_out_field_string}. The original code was: @example annotate_field (5); if (b->dll_pathname == NULL) printf_filtered ("<any library> "); else printf_filtered ("library \"%s\" ", b->dll_pathname); @end example It became: @example annotate_field (5); if (b->dll_pathname == NULL) @{ ui_out_field_string (uiout, "what", "<any library>"); ui_out_spaces (uiout, 1); @} else @{ ui_out_text (uiout, "library \""); ui_out_field_string (uiout, "what", b->dll_pathname); ui_out_text (uiout, "\" "); @} @end example The following example from @code{print_one_breakpoint} shows how to use @code{ui_out_field_int} and @code{ui_out_spaces}. The original code was: @example annotate_field (5); if (b->forked_inferior_pid != 0) printf_filtered ("process %d ", b->forked_inferior_pid); @end example It became: @example annotate_field (5); if (b->forked_inferior_pid != 0) @{ ui_out_text (uiout, "process "); ui_out_field_int (uiout, "what", b->forked_inferior_pid); ui_out_spaces (uiout, 1); @} @end example Here's an example of using @code{ui_out_field_string}. The original code was: @example annotate_field (5); if (b->exec_pathname != NULL) printf_filtered ("program \"%s\" ", b->exec_pathname); @end example It became: @example annotate_field (5); if (b->exec_pathname != NULL) @{ ui_out_text (uiout, "program \""); ui_out_field_string (uiout, "what", b->exec_pathname); ui_out_text (uiout, "\" "); @} @end example Finally, here's an example of printing an address. The original code: @example annotate_field (4); printf_filtered ("%s ", local_hex_string_custom ((unsigned long) b->address, "08l")); @end example It became: @example annotate_field (4); ui_out_field_core_addr (uiout, "Address", b->address); @end example @section Console Printing @section TUI @section libgdb @cindex @code{libgdb} @code{libgdb} was an abortive project of years ago. The theory was to provide an API to @value{GDBN}'s functionality. @node Symbol Handling @chapter Symbol Handling Symbols are a key part of @value{GDBN}'s operation. Symbols include variables, functions, and types. @section Symbol Reading @cindex symbol reading @cindex reading of symbols @cindex symbol files @value{GDBN} reads symbols from @dfn{symbol files}. The usual symbol file is the file containing the program which @value{GDBN} is debugging. @value{GDBN} can be directed to use a different file for symbols (with the @samp{symbol-file} command), and it can also read more symbols via the @samp{add-file} and @samp{load} commands, or while reading symbols from shared libraries. @findex find_sym_fns Symbol files are initially opened by code in @file{symfile.c} using the BFD library (@pxref{Support Libraries}). BFD identifies the type of the file by examining its header. @code{find_sym_fns} then uses this identification to locate a set of symbol-reading functions. @findex add_symtab_fns @cindex @code{sym_fns} structure @cindex adding a symbol-reading module Symbol-reading modules identify themselves to @value{GDBN} by calling @code{add_symtab_fns} during their module initialization. The argument to @code{add_symtab_fns} is a @code{struct sym_fns} which contains the name (or name prefix) of the symbol format, the length of the prefix, and pointers to four functions. These functions are called at various times to process symbol files whose identification matches the specified prefix. The functions supplied by each module are: @table @code @item @var{xyz}_symfile_init(struct sym_fns *sf) @cindex secondary symbol file Called from @code{symbol_file_add} when we are about to read a new symbol file. This function should clean up any internal state (possibly resulting from half-read previous files, for example) and prepare to read a new symbol file. Note that the symbol file which we are reading might be a new ``main'' symbol file, or might be a secondary symbol file whose symbols are being added to the existing symbol table. The argument to @code{@var{xyz}_symfile_init} is a newly allocated @code{struct sym_fns} whose @code{bfd} field contains the BFD for the new symbol file being read. Its @code{private} field has been zeroed, and can be modified as desired. Typically, a struct of private information will be @code{malloc}'d, and a pointer to it will be placed in the @code{private} field. There is no result from @code{@var{xyz}_symfile_init}, but it can call @code{error} if it detects an unavoidable problem. @item @var{xyz}_new_init() Called from @code{symbol_file_add} when discarding existing symbols. This function needs only handle the symbol-reading module's internal state; the symbol table data structures visible to the rest of @value{GDBN} will be discarded by @code{symbol_file_add}. It has no arguments and no result. It may be called after @code{@var{xyz}_symfile_init}, if a new symbol table is being read, or may be called alone if all symbols are simply being discarded. @item @var{xyz}_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline) Called from @code{symbol_file_add} to actually read the symbols from a symbol-file into a set of psymtabs or symtabs. @code{sf} points to the @code{struct sym_fns} originally passed to @code{@var{xyz}_sym_init} for possible initialization. @code{addr} is the offset between the file's specified start address and its true address in memory. @code{mainline} is 1 if this is the main symbol table being read, and 0 if a secondary symbol file (e.g. shared library or dynamically loaded file) is being read.@refill @end table In addition, if a symbol-reading module creates psymtabs when @var{xyz}_symfile_read is called, these psymtabs will contain a pointer to a function @code{@var{xyz}_psymtab_to_symtab}, which can be called from any point in the @value{GDBN} symbol-handling code. @table @code @item @var{xyz}_psymtab_to_symtab (struct partial_symtab *pst) Called from @code{psymtab_to_symtab} (or the @code{PSYMTAB_TO_SYMTAB} macro) if the psymtab has not already been read in and had its @code{pst->symtab} pointer set. The argument is the psymtab to be fleshed-out into a symtab. Upon return, @code{pst->readin} should have been set to 1, and @code{pst->symtab} should contain a pointer to the new corresponding symtab, or zero if there were no symbols in that part of the symbol file. @end table @section Partial Symbol Tables @value{GDBN} has three types of symbol tables: @itemize @bullet @cindex full symbol table @cindex symtabs @item Full symbol tables (@dfn{symtabs}). These contain the main information about symbols and addresses. @cindex psymtabs @item Partial symbol tables (@dfn{psymtabs}). These contain enough information to know when to read the corresponding part of the full symbol table. @cindex minimal symbol table @cindex minsymtabs @item Minimal symbol tables (@dfn{msymtabs}). These contain information gleaned from non-debugging symbols. @end itemize @cindex partial symbol table This section describes partial symbol tables. A psymtab is constructed by doing a very quick pass over an executable file's debugging information. Small amounts of information are extracted---enough to identify which parts of the symbol table will need to be re-read and fully digested later, when the user needs the information. The speed of this pass causes @value{GDBN} to start up very quickly. Later, as the detailed rereading occurs, it occurs in small pieces, at various times, and the delay therefrom is mostly invisible to the user. @c (@xref{Symbol Reading}.) The symbols that show up in a file's psymtab should be, roughly, those visible to the debugger's user when the program is not running code from that file. These include external symbols and types, static symbols and types, and @code{enum} values declared at file scope. The psymtab also contains the range of instruction addresses that the full symbol table would represent. @cindex finding a symbol @cindex symbol lookup The idea is that there are only two ways for the user (or much of the code in the debugger) to reference a symbol: @itemize @bullet @findex find_pc_function @findex find_pc_line @item By its address (e.g. execution stops at some address which is inside a function in this file). The address will be noticed to be in the range of this psymtab, and the full symtab will be read in. @code{find_pc_function}, @code{find_pc_line}, and other @code{find_pc_@dots{}} functions handle this. @cindex lookup_symbol @item By its name (e.g. the user asks to print a variable, or set a breakpoint on a function). Global names and file-scope names will be found in the psymtab, which will cause the symtab to be pulled in. Local names will have to be qualified by a global name, or a file-scope name, in which case we will have already read in the symtab as we evaluated the qualifier. Or, a local symbol can be referenced when we are ``in'' a local scope, in which case the first case applies. @code{lookup_symbol} does most of the work here. @end itemize The only reason that psymtabs exist is to cause a symtab to be read in at the right moment. Any symbol that can be elided from a psymtab, while still causing that to happen, should not appear in it. Since psymtabs don't have the idea of scope, you can't put local symbols in them anyway. Psymtabs don't have the idea of the type of a symbol, either, so types need not appear, unless they will be referenced by name. It is a bug for @value{GDBN} to behave one way when only a psymtab has been read, and another way if the corresponding symtab has been read in. Such bugs are typically caused by a psymtab that does not contain all the visible symbols, or which has the wrong instruction address ranges. The psymtab for a particular section of a symbol file (objfile) could be thrown away after the symtab has been read in. The symtab should always be searched before the psymtab, so the psymtab will never be used (in a bug-free environment). Currently, psymtabs are allocated on an obstack, and all the psymbols themselves are allocated in a pair of large arrays on an obstack, so there is little to be gained by trying to free them unless you want to do a lot more work. @section Types @unnumberedsubsec Fundamental Types (e.g., @code{FT_VOID}, @code{FT_BOOLEAN}). @cindex fundamental types These are the fundamental types that @value{GDBN} uses internally. Fundamental types from the various debugging formats (stabs, ELF, etc) are mapped into one of these. They are basically a union of all fundamental types that @value{GDBN} knows about for all the languages that @value{GDBN} knows about. @unnumberedsubsec Type Codes (e.g., @code{TYPE_CODE_PTR}, @code{TYPE_CODE_ARRAY}). @cindex type codes Each time @value{GDBN} builds an internal type, it marks it with one of these types. The type may be a fundamental type, such as @code{TYPE_CODE_INT}, or a derived type, such as @code{TYPE_CODE_PTR} which is a pointer to another type. Typically, several @code{FT_*} types map to one @code{TYPE_CODE_*} type, and are distinguished by other members of the type struct, such as whether the type is signed or unsigned, and how many bits it uses. @unnumberedsubsec Builtin Types (e.g., @code{builtin_type_void}, @code{builtin_type_char}). These are instances of type structs that roughly correspond to fundamental types and are created as global types for @value{GDBN} to use for various ugly historical reasons. We eventually want to eliminate these. Note for example that @code{builtin_type_int} initialized in @file{gdbtypes.c} is basically the same as a @code{TYPE_CODE_INT} type that is initialized in @file{c-lang.c} for an @code{FT_INTEGER} fundamental type. The difference is that the @code{builtin_type} is not associated with any particular objfile, and only one instance exists, while @file{c-lang.c} builds as many @code{TYPE_CODE_INT} types as needed, with each one associated with some particular objfile. @section Object File Formats @cindex object file formats @subsection a.out @cindex @code{a.out} format The @code{a.out} format is the original file format for Unix. It consists of three sections: @code{text}, @code{data}, and @code{bss}, which are for program code, initialized data, and uninitialized data, respectively. The @code{a.out} format is so simple that it doesn't have any reserved place for debugging information. (Hey, the original Unix hackers used @samp{adb}, which is a machine-language debugger!) The only debugging format for @code{a.out} is stabs, which is encoded as a set of normal symbols with distinctive attributes. The basic @code{a.out} reader is in @file{dbxread.c}. @subsection COFF @cindex COFF format The COFF format was introduced with System V Release 3 (SVR3) Unix. COFF files may have multiple sections, each prefixed by a header. The number of sections is limited. The COFF specification includes support for debugging. Although this was a step forward, the debugging information was woefully limited. For instance, it was not possible to represent code that came from an included file. The COFF reader is in @file{coffread.c}. @subsection ECOFF @cindex ECOFF format ECOFF is an extended COFF originally introduced for Mips and Alpha workstations. The basic ECOFF reader is in @file{mipsread.c}. @subsection XCOFF @cindex XCOFF format The IBM RS/6000 running AIX uses an object file format called XCOFF. The COFF sections, symbols, and line numbers are used, but debugging symbols are @code{dbx}-style stabs whose strings are located in the @code{.debug} section (rather than the string table). For more information, see @ref{Top,,,stabs,The Stabs Debugging Format}. The shared library scheme has a clean interface for figuring out what shared libraries are in use, but the catch is that everything which refers to addresses (symbol tables and breakpoints at least) needs to be relocated for both shared libraries and the main executable. At least using the standard mechanism this can only be done once the program has been run (or the core file has been read). @subsection PE @cindex PE-COFF format Windows 95 and NT use the PE (@dfn{Portable Executable}) format for their executables. PE is basically COFF with additional headers. While BFD includes special PE support, @value{GDBN} needs only the basic COFF reader. @subsection ELF @cindex ELF format The ELF format came with System V Release 4 (SVR4) Unix. ELF is similar to COFF in being organized into a number of sections, but it removes many of COFF's limitations. The basic ELF reader is in @file{elfread.c}. @subsection SOM @cindex SOM format SOM is HP's object file and debug format (not to be confused with IBM's SOM, which is a cross-language ABI). The SOM reader is in @file{hpread.c}. @subsection Other File Formats @cindex Netware Loadable Module format Other file formats that have been supported by @value{GDBN} include Netware Loadable Modules (@file{nlmread.c}). @section Debugging File Formats This section describes characteristics of debugging information that are independent of the object file format. @subsection stabs @cindex stabs debugging info @code{stabs} started out as special symbols within the @code{a.out} format. Since then, it has been encapsulated into other file formats, such as COFF and ELF. While @file{dbxread.c} does some of the basic stab processing, including for encapsulated versions, @file{stabsread.c} does the real work. @subsection COFF @cindex COFF debugging info The basic COFF definition includes debugging information. The level of support is minimal and non-extensible, and is not often used. @subsection Mips debug (Third Eye) @cindex ECOFF debugging info ECOFF includes a definition of a special debug format. The file @file{mdebugread.c} implements reading for this format. @subsection DWARF 1 @cindex DWARF 1 debugging info DWARF 1 is a debugging format that was originally designed to be used with ELF in SVR4 systems. @c CHILL_PRODUCER @c GCC_PRODUCER @c GPLUS_PRODUCER @c LCC_PRODUCER @c If defined, these are the producer strings in a DWARF 1 file. All of @c these have reasonable defaults already. The DWARF 1 reader is in @file{dwarfread.c}. @subsection DWARF 2 @cindex DWARF 2 debugging info DWARF 2 is an improved but incompatible version of DWARF 1. The DWARF 2 reader is in @file{dwarf2read.c}. @subsection SOM @cindex SOM debugging info Like COFF, the SOM definition includes debugging information. @section Adding a New Symbol Reader to @value{GDBN} @cindex adding debugging info reader If you are using an existing object file format (@code{a.out}, COFF, ELF, etc), there is probably little to be done. If you need to add a new object file format, you must first add it to BFD. This is beyond the scope of this document. You must then arrange for the BFD code to provide access to the debugging symbols. Generally @value{GDBN} will have to call swapping routines from BFD and a few other BFD internal routines to locate the debugging information. As much as possible, @value{GDBN} should not depend on the BFD internal data structures. For some targets (e.g., COFF), there is a special transfer vector used to call swapping routines, since the external data structures on various platforms have different sizes and layouts. Specialized routines that will only ever be implemented by one object file format may be called directly. This interface should be described in a file @file{bfd/lib@var{xyz}.h}, which is included by @value{GDBN}. @node Language Support @chapter Language Support @cindex language support @value{GDBN}'s language support is mainly driven by the symbol reader, although it is possible for the user to set the source language manually. @value{GDBN} chooses the source language by looking at the extension of the file recorded in the debug info; @file{.c} means C, @file{.f} means Fortran, etc. It may also use a special-purpose language identifier if the debug format supports it, like with DWARF. @section Adding a Source Language to @value{GDBN} @cindex adding source language To add other languages to @value{GDBN}'s expression parser, follow the following steps: @table @emph @item Create the expression parser. @cindex expression parser This should reside in a file @file{@var{lang}-exp.y}. Routines for building parsed expressions into a @code{union exp_element} list are in @file{parse.c}. @cindex language parser Since we can't depend upon everyone having Bison, and YACC produces parsers that define a bunch of global names, the following lines @strong{must} be included at the top of the YACC parser, to prevent the various parsers from defining the same global names: @example #define yyparse @var{lang}_parse #define yylex @var{lang}_lex #define yyerror @var{lang}_error #define yylval @var{lang}_lval #define yychar @var{lang}_char #define yydebug @var{lang}_debug #define yypact @var{lang}_pact #define yyr1 @var{lang}_r1 #define yyr2 @var{lang}_r2 #define yydef @var{lang}_def #define yychk @var{lang}_chk #define yypgo @var{lang}_pgo #define yyact @var{lang}_act #define yyexca @var{lang}_exca #define yyerrflag @var{lang}_errflag #define yynerrs @var{lang}_nerrs @end example At the bottom of your parser, define a @code{struct language_defn} and initialize it with the right values for your language. Define an @code{initialize_@var{lang}} routine and have it call @samp{add_language(@var{lang}_language_defn)} to tell the rest of @value{GDBN} that your language exists. You'll need some other supporting variables and functions, which will be used via pointers from your @code{@var{lang}_language_defn}. See the declaration of @code{struct language_defn} in @file{language.h}, and the other @file{*-exp.y} files, for more information. @item Add any evaluation routines, if necessary @cindex expression evaluation routines @findex evaluate_subexp @findex prefixify_subexp @findex length_of_subexp If you need new opcodes (that represent the operations of the language), add them to the enumerated type in @file{expression.h}. Add support code for these operations in the @code{evaluate_subexp} function defined in the file @file{eval.c}. Add cases for new opcodes in two functions from @file{parse.c}: @code{prefixify_subexp} and @code{length_of_subexp}. These compute the number of @code{exp_element}s that a given operation takes up. @item Update some existing code Add an enumerated identifier for your language to the enumerated type @code{enum language} in @file{defs.h}. Update the routines in @file{language.c} so your language is included. These routines include type predicates and such, which (in some cases) are language dependent. If your language does not appear in the switch statement, an error is reported. @vindex current_language Also included in @file{language.c} is the code that updates the variable @code{current_language}, and the routines that translate the @code{language_@var{lang}} enumerated identifier into a printable string. @findex _initialize_language Update the function @code{_initialize_language} to include your language. This function picks the default language upon startup, so is dependent upon which languages that @value{GDBN} is built for. @findex allocate_symtab Update @code{allocate_symtab} in @file{symfile.c} and/or symbol-reading code so that the language of each symtab (source file) is set properly. This is used to determine the language to use at each stack frame level. Currently, the language is set based upon the extension of the source file. If the language can be better inferred from the symbol information, please set the language of the symtab in the symbol-reading code. @findex print_subexp @findex op_print_tab Add helper code to @code{print_subexp} (in @file{expprint.c}) to handle any new expression opcodes you have added to @file{expression.h}. Also, add the printed representations of your operators to @code{op_print_tab}. @item Add a place of call @findex parse_exp_1 Add a call to @code{@var{lang}_parse()} and @code{@var{lang}_error} in @code{parse_exp_1} (defined in @file{parse.c}). @item Use macros to trim code @cindex trimming language-dependent code The user has the option of building @value{GDBN} for some or all of the languages. If the user decides to build @value{GDBN} for the language @var{lang}, then every file dependent on @file{language.h} will have the macro @code{_LANG_@var{lang}} defined in it. Use @code{#ifdef}s to leave out large routines that the user won't need if he or she is not using your language. Note that you do not need to do this in your YACC parser, since if @value{GDBN} is not build for @var{lang}, then @file{@var{lang}-exp.tab.o} (the compiled form of your parser) is not linked into @value{GDBN} at all. See the file @file{configure.in} for how @value{GDBN} is configured for different languages. @item Edit @file{Makefile.in} Add dependencies in @file{Makefile.in}. Make sure you update the macro variables such as @code{HFILES} and @code{OBJS}, otherwise your code may not get linked in, or, worse yet, it may not get @code{tar}red into the distribution! @end table @node Host Definition @chapter Host Definition @emph{Maintainer's note: In theory, new targets no longer need to use the host framework described below. Instead it should be possible to handle everything using autoconf. Patches eliminating this framework welcome.} With the advent of Autoconf, it's rarely necessary to have host definition machinery anymore. @section Adding a New Host @cindex adding a new host @cindex host, adding Most of @value{GDBN}'s host configuration support happens via Autoconf. New host-specific definitions should be rarely needed. @value{GDBN} still uses the host-specific definitions and files listed below, but these mostly exist for historical reasons, and should eventually disappear. Several files control @value{GDBN}'s configuration for host systems: @table @file @vindex XDEPFILES @item gdb/config/@var{arch}/@var{xyz}.mh Specifies Makefile fragments needed when hosting on machine @var{xyz}. In particular, this lists the required machine-dependent object files, by defining @samp{XDEPFILES=@dots{}}. Also specifies the header file which describes host @var{xyz}, by defining @code{XM_FILE= xm-@var{xyz}.h}. You can also define @code{CC}, @code{SYSV_DEFINE}, @code{XM_CFLAGS}, @code{XM_ADD_FILES}, @code{XM_CLIBS}, @code{XM_CDEPS}, etc.; see @file{Makefile.in}. @item gdb/config/@var{arch}/xm-@var{xyz}.h (@file{xm.h} is a link to this file, created by @code{configure}). Contains C macro definitions describing the host system environment, such as byte order, host C compiler and library. @item gdb/@var{xyz}-xdep.c Contains any miscellaneous C code required for this machine as a host. On most machines it doesn't exist at all. If it does exist, put @file{@var{xyz}-xdep.o} into the @code{XDEPFILES} line in @file{gdb/config/@var{arch}/@var{xyz}.mh}. @end table @subheading Generic Host Support Files @cindex generic host support There are some ``generic'' versions of routines that can be used by various systems. These can be customized in various ways by macros defined in your @file{xm-@var{xyz}.h} file. If these routines work for the @var{xyz} host, you can just include the generic file's name (with @samp{.o}, not @samp{.c}) in @code{XDEPFILES}. Otherwise, if your machine needs custom support routines, you will need to write routines that perform the same functions as the generic file. Put them into @code{@var{xyz}-xdep.c}, and put @code{@var{xyz}-xdep.o} into @code{XDEPFILES}. @table @file @cindex remote debugging support @cindex serial line support @item ser-unix.c This contains serial line support for Unix systems. This is always included, via the makefile variable @code{SER_HARDWIRE}; override this variable in the @file{.mh} file to avoid it. @item ser-go32.c This contains serial line support for 32-bit programs running under DOS, using the DJGPP (a.k.a.@: GO32) execution environment. @cindex TCP remote support @item ser-tcp.c This contains generic TCP support using sockets. @end table @section Host Conditionals When @value{GDBN} is configured and compiled, various macros are defined or left undefined, to control compilation based on the attributes of the host system. These macros and their meanings (or if the meaning is not documented here, then one of the source files where they are used is indicated) are: @ftable @code @item @value{GDBN}INIT_FILENAME The default name of @value{GDBN}'s initialization file (normally @file{.gdbinit}). @item MEM_FNS_DECLARED Your host config file defines this if it includes declarations of @code{memcpy} and @code{memset}. Define this to avoid conflicts between the native include files and the declarations in @file{defs.h}. @item NO_STD_REGS This macro is deprecated. @item NO_SYS_FILE Define this if your system does not have a @code{<sys/file.h>}. @item SIGWINCH_HANDLER If your host defines @code{SIGWINCH}, you can define this to be the name of a function to be called if @code{SIGWINCH} is received. @item SIGWINCH_HANDLER_BODY Define this to expand into code that will define the function named by the expansion of @code{SIGWINCH_HANDLER}. @item ALIGN_STACK_ON_STARTUP @cindex stack alignment Define this if your system is of a sort that will crash in @code{tgetent} if the stack happens not to be longword-aligned when @code{main} is called. This is a rare situation, but is known to occur on several different types of systems. @item CRLF_SOURCE_FILES @cindex DOS text files Define this if host files use @code{\r\n} rather than @code{\n} as a line terminator. This will cause source file listings to omit @code{\r} characters when printing and it will allow @code{\r\n} line endings of files which are ``sourced'' by gdb. It must be possible to open files in binary mode using @code{O_BINARY} or, for fopen, @code{"rb"}. @item DEFAULT_PROMPT @cindex prompt The default value of the prompt string (normally @code{"(gdb) "}). @item DEV_TTY @cindex terminal device The name of the generic TTY device, defaults to @code{"/dev/tty"}. @item FCLOSE_PROVIDED Define this if the system declares @code{fclose} in the headers included in @code{defs.h}. This isn't needed unless your compiler is unusually anal. @item FOPEN_RB Define this if binary files are opened the same way as text files. @item GETENV_PROVIDED Define this if the system declares @code{getenv} in its headers included in @code{defs.h}. This isn't needed unless your compiler is unusually anal. @item HAVE_MMAP @findex mmap In some cases, use the system call @code{mmap} for reading symbol tables. For some machines this allows for sharing and quick updates. @item HAVE_SIGSETMASK @findex sigsetmask Define this if the host system has job control, but does not define @code{sigsetmask}. Currently, this is only true of the RS/6000. @item HAVE_TERMIO Define this if the host system has @code{termio.h}. @item HOST_BYTE_ORDER @cindex byte order The ordering of bytes in the host. This must be defined to be either @code{BIG_ENDIAN} or @code{LITTLE_ENDIAN}. @item INT_MAX @itemx INT_MIN @itemx LONG_MAX @itemx UINT_MAX @itemx ULONG_MAX Values for host-side constants. @item ISATTY Substitute for isatty, if not available. @item LONGEST This is the longest integer type available on the host. If not defined, it will default to @code{long long} or @code{long}, depending on @code{CC_HAS_LONG_LONG}. @item CC_HAS_LONG_LONG @cindex @code{long long} data type Define this if the host C compiler supports @code{long long}. This is set by the @code{configure} script. @item PRINTF_HAS_LONG_LONG Define this if the host can handle printing of long long integers via the printf format conversion specifier @code{ll}. This is set by the @code{configure} script. @item HAVE_LONG_DOUBLE Define this if the host C compiler supports @code{long double}. This is set by the @code{configure} script. @item PRINTF_HAS_LONG_DOUBLE Define this if the host can handle printing of long double float-point numbers via the printf format conversion specifier @code{Lg}. This is set by the @code{configure} script. @item SCANF_HAS_LONG_DOUBLE Define this if the host can handle the parsing of long double float-point numbers via the scanf format conversion specifier @code{Lg}. This is set by the @code{configure} script. @item LSEEK_NOT_LINEAR Define this if @code{lseek (n)} does not necessarily move to byte number @code{n} in the file. This is only used when reading source files. It is normally faster to define @code{CRLF_SOURCE_FILES} when possible. @item L_SET This macro is used as the argument to @code{lseek} (or, most commonly, @code{bfd_seek}). FIXME, should be replaced by SEEK_SET instead, which is the POSIX equivalent. @item MALLOC_INCOMPATIBLE Define this if the system's prototype for @code{malloc} differs from the @sc{ansi} definition. @item MMAP_BASE_ADDRESS When using HAVE_MMAP, the first mapping should go at this address. @item MMAP_INCREMENT when using HAVE_MMAP, this is the increment between mappings. @item NEED_POSIX_SETPGID @findex setpgid Define this to use the POSIX version of @code{setpgid} to determine whether job control is available. @item NORETURN If defined, this should be one or more tokens, such as @code{volatile}, that can be used in both the declaration and definition of functions to indicate that they never return. The default is already set correctly if compiling with GCC. This will almost never need to be defined. @item ATTR_NORETURN If defined, this should be one or more tokens, such as @code{__attribute__ ((noreturn))}, that can be used in the declarations of functions to indicate that they never return. The default is already set correctly if compiling with GCC. This will almost never need to be defined. @item USE_GENERIC_DUMMY_FRAMES @cindex generic dummy frames Define this to 1 if the target is using the generic inferior function call code. See @code{blockframe.c} for more information. @item USE_MMALLOC @findex mmalloc @value{GDBN} will use the @code{mmalloc} library for memory allocation for symbol reading if this symbol is defined. Be careful defining it since there are systems on which @code{mmalloc} does not work for some reason. One example is the DECstation, where its RPC library can't cope with our redefinition of @code{malloc} to call @code{mmalloc}. When defining @code{USE_MMALLOC}, you will also have to set @code{MMALLOC} in the Makefile, to point to the @code{mmalloc} library. This define is set when you configure with @samp{--with-mmalloc}. @item NO_MMCHECK @findex mmcheck Define this if you are using @code{mmalloc}, but don't want the overhead of checking the heap with @code{mmcheck}. Note that on some systems, the C runtime makes calls to @code{malloc} prior to calling @code{main}, and if @code{free} is ever called with these pointers after calling @code{mmcheck} to enable checking, a memory corruption abort is certain to occur. These systems can still use @code{mmalloc}, but must define @code{NO_MMCHECK}. @item MMCHECK_FORCE Define this to 1 if the C runtime allocates memory prior to @code{mmcheck} being called, but that memory is never freed so we don't have to worry about it triggering a memory corruption abort. The default is 0, which means that @code{mmcheck} will only install the heap checking functions if there has not yet been any memory allocation calls, and if it fails to install the functions, @value{GDBN} will issue a warning. This is currently defined if you configure using @samp{--with-mmalloc}. @item NO_SIGINTERRUPT @findex siginterrupt Define this to indicate that @code{siginterrupt} is not available. @item R_OK Define if this is not in a system header file (typically, @file{unistd.h}). @item SEEK_CUR @itemx SEEK_SET Define these to appropriate value for the system @code{lseek}, if not already defined. @item STOP_SIGNAL This is the signal for stopping @value{GDBN}. Defaults to @code{SIGTSTP}. (Only redefined for the Convex.) @item USE_O_NOCTTY Define this if the interior's tty should be opened with the @code{O_NOCTTY} flag. (FIXME: This should be a native-only flag, but @file{inflow.c} is always linked in.) @item USG Means that System V (prior to SVR4) include files are in use. (FIXME: This symbol is abused in @file{infrun.c}, @file{regex.c}, @file{remote-nindy.c}, and @file{utils.c} for other things, at the moment.) @item lint Define this to help placate @code{lint} in some situations. @item volatile Define this to override the defaults of @code{__volatile__} or @code{/**/}. @end ftable @node Target Architecture Definition @chapter Target Architecture Definition @cindex target architecture definition @value{GDBN}'s target architecture defines what sort of machine-language programs @value{GDBN} can work with, and how it works with them. The target architecture object is implemented as the C structure @code{struct gdbarch *}. The structure, and its methods, are generated using the Bourn shell script @file{gdbarch.sh}. @section Registers and Memory @value{GDBN}'s model of the target machine is rather simple. @value{GDBN} assumes the machine includes a bank of registers and a block of memory. Each register may have a different size. @value{GDBN} does not have a magical way to match up with the compiler's idea of which registers are which; however, it is critical that they do match up accurately. The only way to make this work is to get accurate information about the order that the compiler uses, and to reflect that in the @code{REGISTER_NAME} and related macros. @value{GDBN} can handle big-endian, little-endian, and bi-endian architectures. @section Pointers Are Not Always Addresses @cindex pointer representation @cindex address representation @cindex word-addressed machines @cindex separate data and code address spaces @cindex spaces, separate data and code address @cindex address spaces, separate data and code @cindex code pointers, word-addressed @cindex converting between pointers and addresses @cindex D10V addresses On almost all 32-bit architectures, the representation of a pointer is indistinguishable from the representation of some fixed-length number whose value is the byte address of the object pointed to. On such machines, the words ``pointer'' and ``address'' can be used interchangeably. However, architectures with smaller word sizes are often cramped for address space, so they may choose a pointer representation that breaks this identity, and allows a larger code address space. For example, the Mitsubishi D10V is a 16-bit VLIW processor whose instructions are 32 bits long@footnote{Some D10V instructions are actually pairs of 16-bit sub-instructions. However, since you can't jump into the middle of such a pair, code addresses can only refer to full 32 bit instructions, which is what matters in this explanation.}. If the D10V used ordinary byte addresses to refer to code locations, then the processor would only be able to address 64kb of instructions. However, since instructions must be aligned on four-byte boundaries, the low two bits of any valid instruction's byte address are always zero---byte addresses waste two bits. So instead of byte addresses, the D10V uses word addresses---byte addresses shifted right two bits---to refer to code. Thus, the D10V can use 16-bit words to address 256kb of code space. However, this means that code pointers and data pointers have different forms on the D10V. The 16-bit word @code{0xC020} refers to byte address @code{0xC020} when used as a data address, but refers to byte address @code{0x30080} when used as a code address. (The D10V also uses separate code and data address spaces, which also affects the correspondence between pointers and addresses, but we're going to ignore that here; this example is already too long.) To cope with architectures like this---the D10V is not the only one!---@value{GDBN} tries to distinguish between @dfn{addresses}, which are byte numbers, and @dfn{pointers}, which are the target's representation of an address of a particular type of data. In the example above, @code{0xC020} is the pointer, which refers to one of the addresses @code{0xC020} or @code{0x30080}, depending on the type imposed upon it. @value{GDBN} provides functions for turning a pointer into an address and vice versa, in the appropriate way for the current architecture. Unfortunately, since addresses and pointers are identical on almost all processors, this distinction tends to bit-rot pretty quickly. Thus, each time you port @value{GDBN} to an architecture which does distinguish between pointers and addresses, you'll probably need to clean up some architecture-independent code. Here are functions which convert between pointers and addresses: @deftypefun CORE_ADDR extract_typed_address (void *@var{buf}, struct type *@var{type}) Treat the bytes at @var{buf} as a pointer or reference of type @var{type}, and return the address it represents, in a manner appropriate for the current architecture. This yields an address @value{GDBN} can use to read target memory, disassemble, etc. Note that @var{buf} refers to a buffer in @value{GDBN}'s memory, not the inferior's. For example, if the current architecture is the Intel x86, this function extracts a little-endian integer of the appropriate length from @var{buf} and returns it. However, if the current architecture is the D10V, this function will return a 16-bit integer extracted from @var{buf}, multiplied by four if @var{type} is a pointer to a function. If @var{type} is not a pointer or reference type, then this function will signal an internal error. @end deftypefun @deftypefun CORE_ADDR store_typed_address (void *@var{buf}, struct type *@var{type}, CORE_ADDR @var{addr}) Store the address @var{addr} in @var{buf}, in the proper format for a pointer of type @var{type} in the current architecture. Note that @var{buf} refers to a buffer in @value{GDBN}'s memory, not the inferior's. For example, if the current architecture is the Intel x86, this function stores @var{addr} unmodified as a little-endian integer of the appropriate length in @var{buf}. However, if the current architecture is the D10V, this function divides @var{addr} by four if @var{type} is a pointer to a function, and then stores it in @var{buf}. If @var{type} is not a pointer or reference type, then this function will signal an internal error. @end deftypefun @deftypefun CORE_ADDR value_as_pointer (value_ptr @var{val}) Assuming that @var{val} is a pointer, return the address it represents, as appropriate for the current architecture. This function actually works on integral values, as well as pointers. For pointers, it performs architecture-specific conversions as described above for @code{extract_typed_address}. @end deftypefun @deftypefun CORE_ADDR value_from_pointer (struct type *@var{type}, CORE_ADDR @var{addr}) Create and return a value representing a pointer of type @var{type} to the address @var{addr}, as appropriate for the current architecture. This function performs architecture-specific conversions as described above for @code{store_typed_address}. @end deftypefun @value{GDBN} also provides functions that do the same tasks, but assume that pointers are simply byte addresses; they aren't sensitive to the current architecture, beyond knowing the appropriate endianness. @deftypefun CORE_ADDR extract_address (void *@var{addr}, int len) Extract a @var{len}-byte number from @var{addr} in the appropriate endianness for the current architecture, and return it. Note that @var{addr} refers to @value{GDBN}'s memory, not the inferior's. This function should only be used in architecture-specific code; it doesn't have enough information to turn bits into a true address in the appropriate way for the current architecture. If you can, use @code{extract_typed_address} instead. @end deftypefun @deftypefun void store_address (void *@var{addr}, int @var{len}, LONGEST @var{val}) Store @var{val} at @var{addr} as a @var{len}-byte integer, in the appropriate endianness for the current architecture. Note that @var{addr} refers to a buffer in @value{GDBN}'s memory, not the inferior's. This function should only be used in architecture-specific code; it doesn't have enough information to turn a true address into bits in the appropriate way for the current architecture. If you can, use @code{store_typed_address} instead. @end deftypefun Here are some macros which architectures can define to indicate the relationship between pointers and addresses. These have default definitions, appropriate for architectures on which all pointers are simple byte addresses. @deftypefn {Target Macro} CORE_ADDR POINTER_TO_ADDRESS (struct type *@var{type}, char *@var{buf}) Assume that @var{buf} holds a pointer of type @var{type}, in the appropriate format for the current architecture. Return the byte address the pointer refers to. This function may safely assume that @var{type} is either a pointer or a C@t{++} reference type. @end deftypefn @deftypefn {Target Macro} void ADDRESS_TO_POINTER (struct type *@var{type}, char *@var{buf}, CORE_ADDR @var{addr}) Store in @var{buf} a pointer of type @var{type} representing the address @var{addr}, in the appropriate format for the current architecture. This function may safely assume that @var{type} is either a pointer or a C@t{++} reference type. @end deftypefn @section Using Different Register and Memory Data Representations @cindex raw representation @cindex virtual representation @cindex representations, raw and virtual @cindex register data formats, converting @cindex @code{struct value}, converting register contents to @emph{Maintainer's note: The way GDB manipulates registers is undergoing significant change. Many of the macros and functions refered to in the sections below are likely to be made obsolete. See the file @file{TODO} for more up-to-date information.} Some architectures use one representation for a value when it lives in a register, but use a different representation when it lives in memory. In @value{GDBN}'s terminology, the @dfn{raw} representation is the one used in the target registers, and the @dfn{virtual} representation is the one used in memory, and within @value{GDBN} @code{struct value} objects. For almost all data types on almost all architectures, the virtual and raw representations are identical, and no special handling is needed. However, they do occasionally differ. For example: @itemize @bullet @item The x86 architecture supports an 80-bit @code{long double} type. However, when we store those values in memory, they occupy twelve bytes: the floating-point number occupies the first ten, and the final two bytes are unused. This keeps the values aligned on four-byte boundaries, allowing more efficient access. Thus, the x86 80-bit floating-point type is the raw representation, and the twelve-byte loosely-packed arrangement is the virtual representation. @item Some 64-bit MIPS targets present 32-bit registers to @value{GDBN} as 64-bit registers, with garbage in their upper bits. @value{GDBN} ignores the top 32 bits. Thus, the 64-bit form, with garbage in the upper 32 bits, is the raw representation, and the trimmed 32-bit representation is the virtual representation. @end itemize In general, the raw representation is determined by the architecture, or @value{GDBN}'s interface to the architecture, while the virtual representation can be chosen for @value{GDBN}'s convenience. @value{GDBN}'s register file, @code{registers}, holds the register contents in raw format, and the @value{GDBN} remote protocol transmits register values in raw format. Your architecture may define the following macros to request conversions between the raw and virtual format: @deftypefn {Target Macro} int REGISTER_CONVERTIBLE (int @var{reg}) Return non-zero if register number @var{reg}'s value needs different raw and virtual formats. You should not use @code{REGISTER_CONVERT_TO_VIRTUAL} for a register unless this macro returns a non-zero value for that register. @end deftypefn @deftypefn {Target Macro} int REGISTER_RAW_SIZE (int @var{reg}) The size of register number @var{reg}'s raw value. This is the number of bytes the register will occupy in @code{registers}, or in a @value{GDBN} remote protocol packet. @end deftypefn @deftypefn {Target Macro} int REGISTER_VIRTUAL_SIZE (int @var{reg}) The size of register number @var{reg}'s value, in its virtual format. This is the size a @code{struct value}'s buffer will have, holding that register's value. @end deftypefn @deftypefn {Target Macro} struct type *REGISTER_VIRTUAL_TYPE (int @var{reg}) This is the type of the virtual representation of register number @var{reg}. Note that there is no need for a macro giving a type for the register's raw form; once the register's value has been obtained, @value{GDBN} always uses the virtual form. @end deftypefn @deftypefn {Target Macro} void REGISTER_CONVERT_TO_VIRTUAL (int @var{reg}, struct type *@var{type}, char *@var{from}, char *@var{to}) Convert the value of register number @var{reg} to @var{type}, which should always be @code{REGISTER_VIRTUAL_TYPE (@var{reg})}. The buffer at @var{from} holds the register's value in raw format; the macro should convert the value to virtual format, and place it at @var{to}. Note that @code{REGISTER_CONVERT_TO_VIRTUAL} and @code{REGISTER_CONVERT_TO_RAW} take their @var{reg} and @var{type} arguments in different orders. You should only use @code{REGISTER_CONVERT_TO_VIRTUAL} with registers for which the @code{REGISTER_CONVERTIBLE} macro returns a non-zero value. @end deftypefn @deftypefn {Target Macro} void REGISTER_CONVERT_TO_RAW (struct type *@var{type}, int @var{reg}, char *@var{from}, char *@var{to}) Convert the value of register number @var{reg} to @var{type}, which should always be @code{REGISTER_VIRTUAL_TYPE (@var{reg})}. The buffer at @var{from} holds the register's value in raw format; the macro should convert the value to virtual format, and place it at @var{to}. Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW take their @var{reg} and @var{type} arguments in different orders. @end deftypefn @section Frame Interpretation @section Inferior Call Setup @section Compiler Characteristics @section Target Conditionals This section describes the macros that you can use to define the target machine. @table @code @item ADDITIONAL_OPTIONS @itemx ADDITIONAL_OPTION_CASES @itemx ADDITIONAL_OPTION_HANDLER @itemx ADDITIONAL_OPTION_HELP @findex ADDITIONAL_OPTION_HELP @findex ADDITIONAL_OPTION_HANDLER @findex ADDITIONAL_OPTION_CASES @findex ADDITIONAL_OPTIONS These are a set of macros that allow the addition of additional command line options to @value{GDBN}. They are currently used only for the unsupported i960 Nindy target, and should not be used in any other configuration. @item ADDR_BITS_REMOVE (addr) @findex ADDR_BITS_REMOVE If a raw machine instruction address includes any bits that are not really part of the address, then define this macro to expand into an expression that zeroes those bits in @var{addr}. This is only used for addresses of instructions, and even then not in all contexts. For example, the two low-order bits of the PC on the Hewlett-Packard PA 2.0 architecture contain the privilege level of the corresponding instruction. Since instructions must always be aligned on four-byte boundaries, the processor masks out these bits to generate the actual address of the instruction. ADDR_BITS_REMOVE should filter out these bits with an expression such as @code{((addr) & ~3)}. @item ADDRESS_TO_POINTER (@var{type}, @var{buf}, @var{addr}) @findex ADDRESS_TO_POINTER Store in @var{buf} a pointer of type @var{type} representing the address @var{addr}, in the appropriate format for the current architecture. This macro may safely assume that @var{type} is either a pointer or a C@t{++} reference type. @xref{Target Architecture Definition, , Pointers Are Not Always Addresses}. @item BEFORE_MAIN_LOOP_HOOK @findex BEFORE_MAIN_LOOP_HOOK Define this to expand into any code that you want to execute before the main loop starts. Although this is not, strictly speaking, a target conditional, that is how it is currently being used. Note that if a configuration were to define it one way for a host and a different way for the target, @value{GDBN} will probably not compile, let alone run correctly. This macro is currently used only for the unsupported i960 Nindy target, and should not be used in any other configuration. @item BELIEVE_PCC_PROMOTION @findex BELIEVE_PCC_PROMOTION Define if the compiler promotes a @code{short} or @code{char} parameter to an @code{int}, but still reports the parameter as its original type, rather than the promoted type. @item BELIEVE_PCC_PROMOTION_TYPE @findex BELIEVE_PCC_PROMOTION_TYPE Define this if @value{GDBN} should believe the type of a @code{short} argument when compiled by @code{pcc}, but look within a full int space to get its value. Only defined for Sun-3 at present. @item BITS_BIG_ENDIAN @findex BITS_BIG_ENDIAN Define this if the numbering of bits in the targets does @strong{not} match the endianness of the target byte order. A value of 1 means that the bits are numbered in a big-endian bit order, 0 means little-endian. @item BREAKPOINT @findex BREAKPOINT This is the character array initializer for the bit pattern to put into memory where a breakpoint is set. Although it's common to use a trap instruction for a breakpoint, it's not required; for instance, the bit pattern could be an invalid instruction. The breakpoint must be no longer than the shortest instruction of the architecture. @code{BREAKPOINT} has been deprecated in favor of @code{BREAKPOINT_FROM_PC}. @item BIG_BREAKPOINT @itemx LITTLE_BREAKPOINT @findex LITTLE_BREAKPOINT @findex BIG_BREAKPOINT Similar to BREAKPOINT, but used for bi-endian targets. @code{BIG_BREAKPOINT} and @code{LITTLE_BREAKPOINT} have been deprecated in favor of @code{BREAKPOINT_FROM_PC}. @item REMOTE_BREAKPOINT @itemx LITTLE_REMOTE_BREAKPOINT @itemx BIG_REMOTE_BREAKPOINT @findex BIG_REMOTE_BREAKPOINT @findex LITTLE_REMOTE_BREAKPOINT @findex REMOTE_BREAKPOINT Similar to BREAKPOINT, but used for remote targets. @code{BIG_REMOTE_BREAKPOINT} and @code{LITTLE_REMOTE_BREAKPOINT} have been deprecated in favor of @code{BREAKPOINT_FROM_PC}. @item BREAKPOINT_FROM_PC (@var{pcptr}, @var{lenptr}) @findex BREAKPOINT_FROM_PC Use the program counter to determine the contents and size of a breakpoint instruction. It returns a pointer to a string of bytes that encode a breakpoint instruction, stores the length of the string to *@var{lenptr}, and adjusts pc (if necessary) to point to the actual memory location where the breakpoint should be inserted. Although it is common to use a trap instruction for a breakpoint, it's not required; for instance, the bit pattern could be an invalid instruction. The breakpoint must be no longer than the shortest instruction of the architecture. Replaces all the other @var{BREAKPOINT} macros. @item MEMORY_INSERT_BREAKPOINT (@var{addr}, @var{contents_cache}) @itemx MEMORY_REMOVE_BREAKPOINT (@var{addr}, @var{contents_cache}) @findex MEMORY_REMOVE_BREAKPOINT @findex MEMORY_INSERT_BREAKPOINT Insert or remove memory based breakpoints. Reasonable defaults (@code{default_memory_insert_breakpoint} and @code{default_memory_remove_breakpoint} respectively) have been provided so that it is not necessary to define these for most architectures. Architectures which may want to define @code{MEMORY_INSERT_BREAKPOINT} and @code{MEMORY_REMOVE_BREAKPOINT} will likely have instructions that are oddly sized or are not stored in a conventional manner. It may also be desirable (from an efficiency standpoint) to define custom breakpoint insertion and removal routines if @code{BREAKPOINT_FROM_PC} needs to read the target's memory for some reason. @item CALL_DUMMY_P @findex CALL_DUMMY_P A C expresson that is non-zero when the target suports inferior function calls. @item CALL_DUMMY_WORDS @findex CALL_DUMMY_WORDS Pointer to an array of @code{LONGEST} words of data containing host-byte-ordered @code{REGISTER_BYTES} sized values that partially specify the sequence of instructions needed for an inferior function call. Should be deprecated in favor of a macro that uses target-byte-ordered data. @item SIZEOF_CALL_DUMMY_WORDS @findex SIZEOF_CALL_DUMMY_WORDS The size of @code{CALL_DUMMY_WORDS}. When @code{CALL_DUMMY_P} this must return a positive value. See also @code{CALL_DUMMY_LENGTH}. @item CALL_DUMMY @findex CALL_DUMMY A static initializer for @code{CALL_DUMMY_WORDS}. Deprecated. @item CALL_DUMMY_LOCATION @findex CALL_DUMMY_LOCATION See the file @file{inferior.h}. @item CALL_DUMMY_STACK_ADJUST @findex CALL_DUMMY_STACK_ADJUST Stack adjustment needed when performing an inferior function call. Should be deprecated in favor of something like @code{STACK_ALIGN}. @item CALL_DUMMY_STACK_ADJUST_P @findex CALL_DUMMY_STACK_ADJUST_P Predicate for use of @code{CALL_DUMMY_STACK_ADJUST}. Should be deprecated in favor of something like @code{STACK_ALIGN}. @item CANNOT_FETCH_REGISTER (@var{regno}) @findex CANNOT_FETCH_REGISTER A C expression that should be nonzero if @var{regno} cannot be fetched from an inferior process. This is only relevant if @code{FETCH_INFERIOR_REGISTERS} is not defined. @item CANNOT_STORE_REGISTER (@var{regno}) @findex CANNOT_STORE_REGISTER A C expression that should be nonzero if @var{regno} should not be written to the target. This is often the case for program counters, status words, and other special registers. If this is not defined, @value{GDBN} will assume that all registers may be written. @item DO_DEFERRED_STORES @itemx CLEAR_DEFERRED_STORES @findex CLEAR_DEFERRED_STORES @findex DO_DEFERRED_STORES Define this to execute any deferred stores of registers into the inferior, and to cancel any deferred stores. Currently only implemented correctly for native Sparc configurations? @item COERCE_FLOAT_TO_DOUBLE (@var{formal}, @var{actual}) @findex COERCE_FLOAT_TO_DOUBLE @cindex promotion to @code{double} If we are calling a function by hand, and the function was declared (according to the debug info) without a prototype, should we automatically promote @code{float}s to @code{double}s? This macro must evaluate to non-zero if we should, or zero if we should leave the value alone. The argument @var{actual} is the type of the value we want to pass to the function. The argument @var{formal} is the type of this argument, as it appears in the function's definition. Note that @var{formal} may be zero if we have no debugging information for the function, or if we're passing more arguments than are officially declared (for example, varargs). This macro is never invoked if the function definitely has a prototype. @findex set_gdbarch_coerce_float_to_double @findex standard_coerce_float_to_double The default behavior is to promote only when we have no type information for the formal parameter. This is different from the obvious behavior, which would be to promote whenever we have no prototype, just as the compiler does. It's annoying, but some older targets rely on this. If you want @value{GDBN} to follow the typical compiler behavior---to always promote when there is no prototype in scope---your gdbarch @code{init} function can call @code{set_gdbarch_coerce_float_to_double} and select the @code{standard_coerce_float_to_double} function. @item CPLUS_MARKER @findex CPLUS_MARKERz Define this to expand into the character that G@t{++} uses to distinguish compiler-generated identifiers from programmer-specified identifiers. By default, this expands into @code{'$'}. Most System V targets should define this to @code{'.'}. @item DBX_PARM_SYMBOL_CLASS @findex DBX_PARM_SYMBOL_CLASS Hook for the @code{SYMBOL_CLASS} of a parameter when decoding DBX symbol information. In the i960, parameters can be stored as locals or as args, depending on the type of the debug record. @item DECR_PC_AFTER_BREAK @findex DECR_PC_AFTER_BREAK Define this to be the amount by which to decrement the PC after the program encounters a breakpoint. This is often the number of bytes in @code{BREAKPOINT}, though not always. For most targets this value will be 0. @item DECR_PC_AFTER_HW_BREAK @findex DECR_PC_AFTER_HW_BREAK Similarly, for hardware breakpoints. @item DISABLE_UNSETTABLE_BREAK (@var{addr}) @findex DISABLE_UNSETTABLE_BREAK If defined, this should evaluate to 1 if @var{addr} is in a shared library in which breakpoints cannot be set and so should be disabled. @item DO_REGISTERS_INFO @findex DO_REGISTERS_INFO If defined, use this to print the value of a register or all registers. @item DWARF_REG_TO_REGNUM @findex DWARF_REG_TO_REGNUM Convert DWARF register number into @value{GDBN} regnum. If not defined, no conversion will be performed. @item DWARF2_REG_TO_REGNUM @findex DWARF2_REG_TO_REGNUM Convert DWARF2 register number into @value{GDBN} regnum. If not defined, no conversion will be performed. @item ECOFF_REG_TO_REGNUM @findex ECOFF_REG_TO_REGNUM Convert ECOFF register number into @value{GDBN} regnum. If not defined, no conversion will be performed. @item END_OF_TEXT_DEFAULT @findex END_OF_TEXT_DEFAULT This is an expression that should designate the end of the text section. @c (? FIXME ?) @item EXTRACT_RETURN_VALUE(@var{type}, @var{regbuf}, @var{valbuf}) @findex EXTRACT_RETURN_VALUE Define this to extract a function's return value of type @var{type} from the raw register state @var{regbuf} and copy that, in virtual format, into @var{valbuf}. @item EXTRACT_STRUCT_VALUE_ADDRESS(@var{regbuf}) @findex EXTRACT_STRUCT_VALUE_ADDRESS When defined, extract from the array @var{regbuf} (containing the raw register state) the @code{CORE_ADDR} at which a function should return its structure value. If not defined, @code{EXTRACT_RETURN_VALUE} is used. @item EXTRACT_STRUCT_VALUE_ADDRESS_P() @findex EXTRACT_STRUCT_VALUE_ADDRESS_P Predicate for @code{EXTRACT_STRUCT_VALUE_ADDRESS}. @item FLOAT_INFO @findex FLOAT_INFO If defined, then the @samp{info float} command will print information about the processor's floating point unit. @item FP_REGNUM @findex FP_REGNUM If the virtual frame pointer is kept in a register, then define this macro to be the number (greater than or equal to zero) of that register. This should only need to be defined if @code{TARGET_READ_FP} and @code{TARGET_WRITE_FP} are not defined. @item FRAMELESS_FUNCTION_INVOCATION(@var{fi}) @findex FRAMELESS_FUNCTION_INVOCATION Define this to an expression that returns 1 if the function invocation represented by @var{fi} does not have a stack frame associated with it. Otherwise return 0. @item FRAME_ARGS_ADDRESS_CORRECT @findex FRAME_ARGS_ADDRESS_CORRECT See @file{stack.c}. @item FRAME_CHAIN(@var{frame}) @findex FRAME_CHAIN Given @var{frame}, return a pointer to the calling frame. @item FRAME_CHAIN_COMBINE(@var{chain}, @var{frame}) @findex FRAME_CHAIN_COMBINE Define this to take the frame chain pointer and the frame's nominal address and produce the nominal address of the caller's frame. Presently only defined for HP PA. @item FRAME_CHAIN_VALID(@var{chain}, @var{thisframe}) @findex FRAME_CHAIN_VALID Define this to be an expression that returns zero if the given frame is an outermost frame, with no caller, and nonzero otherwise. Several common definitions are available: @itemize @bullet @item @code{file_frame_chain_valid} is nonzero if the chain pointer is nonzero and given frame's PC is not inside the startup file (such as @file{crt0.o}). @item @code{func_frame_chain_valid} is nonzero if the chain pointer is nonzero and the given frame's PC is not in @code{main} or a known entry point function (such as @code{_start}). @item @code{generic_file_frame_chain_valid} and @code{generic_func_frame_chain_valid} are equivalent implementations for targets using generic dummy frames. @end itemize @item FRAME_INIT_SAVED_REGS(@var{frame}) @findex FRAME_INIT_SAVED_REGS See @file{frame.h}. Determines the address of all registers in the current stack frame storing each in @code{frame->saved_regs}. Space for @code{frame->saved_regs} shall be allocated by @code{FRAME_INIT_SAVED_REGS} using either @code{frame_saved_regs_zalloc} or @code{frame_obstack_alloc}. @code{FRAME_FIND_SAVED_REGS} and @code{EXTRA_FRAME_INFO} are deprecated. @item FRAME_NUM_ARGS (@var{fi}) @findex FRAME_NUM_ARGS For the frame described by @var{fi} return the number of arguments that are being passed. If the number of arguments is not known, return @code{-1}. @item FRAME_SAVED_PC(@var{frame}) @findex FRAME_SAVED_PC Given @var{frame}, return the pc saved there. This is the return address. @item FUNCTION_EPILOGUE_SIZE @findex FUNCTION_EPILOGUE_SIZE For some COFF targets, the @code{x_sym.x_misc.x_fsize} field of the function end symbol is 0. For such targets, you must define @code{FUNCTION_EPILOGUE_SIZE} to expand into the standard size of a function's epilogue. @item FUNCTION_START_OFFSET @findex FUNCTION_START_OFFSET An integer, giving the offset in bytes from a function's address (as used in the values of symbols, function pointers, etc.), and the function's first genuine instruction. This is zero on almost all machines: the function's address is usually the address of its first instruction. However, on the VAX, for example, each function starts with two bytes containing a bitmask indicating which registers to save upon entry to the function. The VAX @code{call} instructions check this value, and save the appropriate registers automatically. Thus, since the offset from the function's address to its first instruction is two bytes, @code{FUNCTION_START_OFFSET} would be 2 on the VAX. @item GCC_COMPILED_FLAG_SYMBOL @itemx GCC2_COMPILED_FLAG_SYMBOL @findex GCC2_COMPILED_FLAG_SYMBOL @findex GCC_COMPILED_FLAG_SYMBOL If defined, these are the names of the symbols that @value{GDBN} will look for to detect that GCC compiled the file. The default symbols are @code{gcc_compiled.} and @code{gcc2_compiled.}, respectively. (Currently only defined for the Delta 68.) @item @value{GDBN}_MULTI_ARCH @findex @value{GDBN}_MULTI_ARCH If defined and non-zero, enables suport for multiple architectures within @value{GDBN}. This support can be enabled at two levels. At level one, only definitions for previously undefined macros are provided; at level two, a multi-arch definition of all architecture dependant macros will be defined. @item @value{GDBN}_TARGET_IS_HPPA @findex @value{GDBN}_TARGET_IS_HPPA This determines whether horrible kludge code in @file{dbxread.c} and @file{partial-stab.h} is used to mangle multiple-symbol-table files from HPPA's. This should all be ripped out, and a scheme like @file{elfread.c} used instead. @item GET_LONGJMP_TARGET @findex GET_LONGJMP_TARGET For most machines, this is a target-dependent parameter. On the DECstation and the Iris, this is a native-dependent parameter, since trhe header file @file{setjmp.h} is needed to define it. This macro determines the target PC address that @code{longjmp} will jump to, assuming that we have just stopped at a @code{longjmp} breakpoint. It takes a @code{CORE_ADDR *} as argument, and stores the target PC value through this pointer. It examines the current state of the machine as needed. @item GET_SAVED_REGISTER @findex GET_SAVED_REGISTER @findex get_saved_register Define this if you need to supply your own definition for the function @code{get_saved_register}. @item HAVE_REGISTER_WINDOWS @findex HAVE_REGISTER_WINDOWS Define this if the target has register windows. @item REGISTER_IN_WINDOW_P (@var{regnum}) @findex REGISTER_IN_WINDOW_P Define this to be an expression that is 1 if the given register is in the window. @item IBM6000_TARGET @findex IBM6000_TARGET Shows that we are configured for an IBM RS/6000 target. This conditional should be eliminated (FIXME) and replaced by feature-specific macros. It was introduced in a haste and we are repenting at leisure. @item I386_USE_GENERIC_WATCHPOINTS An x86-based target can define this to use the generic x86 watchpoint support; see @ref{Algorithms, I386_USE_GENERIC_WATCHPOINTS}. @item SYMBOLS_CAN_START_WITH_DOLLAR @findex SYMBOLS_CAN_START_WITH_DOLLAR Some systems have routines whose names start with @samp{$}. Giving this macro a non-zero value tells @value{GDBN}'s expression parser to check for such routines when parsing tokens that begin with @samp{$}. On HP-UX, certain system routines (millicode) have names beginning with @samp{$} or @samp{$$}. For example, @code{$$dyncall} is a millicode routine that handles inter-space procedure calls on PA-RISC. @item IEEE_FLOAT @findex IEEE_FLOAT Define this if the target system uses IEEE-format floating point numbers. @item INIT_EXTRA_FRAME_INFO (@var{fromleaf}, @var{frame}) @findex INIT_EXTRA_FRAME_INFO If additional information about the frame is required this should be stored in @code{frame->extra_info}. Space for @code{frame->extra_info} is allocated using @code{frame_obstack_alloc}. @item INIT_FRAME_PC (@var{fromleaf}, @var{prev}) @findex INIT_FRAME_PC This is a C statement that sets the pc of the frame pointed to by @var{prev}. [By default...] @item INNER_THAN (@var{lhs}, @var{rhs}) @findex INNER_THAN Returns non-zero if stack address @var{lhs} is inner than (nearer to the stack top) stack address @var{rhs}. Define this as @code{lhs < rhs} if the target's stack grows downward in memory, or @code{lhs > rsh} if the stack grows upward. @item IN_SIGTRAMP (@var{pc}, @var{name}) @findex IN_SIGTRAMP Define this to return non-zero if the given @var{pc} and/or @var{name} indicates that the current function is a @code{sigtramp}. @item SIGTRAMP_START (@var{pc}) @findex SIGTRAMP_START @itemx SIGTRAMP_END (@var{pc}) @findex SIGTRAMP_END Define these to be the start and end address of the @code{sigtramp} for the given @var{pc}. On machines where the address is just a compile time constant, the macro expansion will typically just ignore the supplied @var{pc}. @item IN_SOLIB_CALL_TRAMPOLINE (@var{pc}, @var{name}) @findex IN_SOLIB_CALL_TRAMPOLINE Define this to evaluate to nonzero if the program is stopped in the trampoline that connects to a shared library. @item IN_SOLIB_RETURN_TRAMPOLINE (@var{pc}, @var{name}) @findex IN_SOLIB_RETURN_TRAMPOLINE Define this to evaluate to nonzero if the program is stopped in the trampoline that returns from a shared library. @item IN_SOLIB_DYNSYM_RESOLVE_CODE (@var{pc}) @findex IN_SOLIB_DYNSYM_RESOLVE_CODE Define this to evaluate to nonzero if the program is stopped in the dynamic linker. @item SKIP_SOLIB_RESOLVER (@var{pc}) @findex SKIP_SOLIB_RESOLVER Define this to evaluate to the (nonzero) address at which execution should continue to get past the dynamic linker's symbol resolution function. A zero value indicates that it is not important or necessary to set a breakpoint to get through the dynamic linker and that single stepping will suffice. @item IS_TRAPPED_INTERNALVAR (@var{name}) @findex IS_TRAPPED_INTERNALVAR This is an ugly hook to allow the specification of special actions that should occur as a side-effect of setting the value of a variable internal to @value{GDBN}. Currently only used by the h8500. Note that this could be either a host or target conditional. @item NEED_TEXT_START_END @findex NEED_TEXT_START_END Define this if @value{GDBN} should determine the start and end addresses of the text section. (Seems dubious.) @item NO_HIF_SUPPORT @findex NO_HIF_SUPPORT (Specific to the a29k.) @item POINTER_TO_ADDRESS (@var{type}, @var{buf}) @findex POINTER_TO_ADDRESS Assume that @var{buf} holds a pointer of type @var{type}, in the appropriate format for the current architecture. Return the byte address the pointer refers to. @xref{Target Architecture Definition, , Pointers Are Not Always Addresses}. @item REGISTER_CONVERTIBLE (@var{reg}) @findex REGISTER_CONVERTIBLE Return non-zero if @var{reg} uses different raw and virtual formats. @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}. @item REGISTER_RAW_SIZE (@var{reg}) @findex REGISTER_RAW_SIZE Return the raw size of @var{reg}. @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}. @item REGISTER_VIRTUAL_SIZE (@var{reg}) @findex REGISTER_VIRTUAL_SIZE Return the virtual size of @var{reg}. @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}. @item REGISTER_VIRTUAL_TYPE (@var{reg}) @findex REGISTER_VIRTUAL_TYPE Return the virtual type of @var{reg}. @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}. @item REGISTER_CONVERT_TO_VIRTUAL(@var{reg}, @var{type}, @var{from}, @var{to}) @findex REGISTER_CONVERT_TO_VIRTUAL Convert the value of register @var{reg} from its raw form to its virtual form. @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}. @item REGISTER_CONVERT_TO_RAW(@var{type}, @var{reg}, @var{from}, @var{to}) @findex REGISTER_CONVERT_TO_RAW Convert the value of register @var{reg} from its virtual form to its raw form. @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}. @item RETURN_VALUE_ON_STACK(@var{type}) @findex RETURN_VALUE_ON_STACK @cindex returning structures by value @cindex structures, returning by value Return non-zero if values of type TYPE are returned on the stack, using the ``struct convention'' (i.e., the caller provides a pointer to a buffer in which the callee should store the return value). This controls how the @samp{finish} command finds a function's return value, and whether an inferior function call reserves space on the stack for the return value. The full logic @value{GDBN} uses here is kind of odd. @itemize @bullet @item If the type being returned by value is not a structure, union, or array, and @code{RETURN_VALUE_ON_STACK} returns zero, then @value{GDBN} concludes the value is not returned using the struct convention. @item Otherwise, @value{GDBN} calls @code{USE_STRUCT_CONVENTION} (see below). If that returns non-zero, @value{GDBN} assumes the struct convention is in use. @end itemize In other words, to indicate that a given type is returned by value using the struct convention, that type must be either a struct, union, array, or something @code{RETURN_VALUE_ON_STACK} likes, @emph{and} something that @code{USE_STRUCT_CONVENTION} likes. Note that, in C and C@t{++}, arrays are never returned by value. In those languages, these predicates will always see a pointer type, never an array type. All the references above to arrays being returned by value apply only to other languages. @item SOFTWARE_SINGLE_STEP_P() @findex SOFTWARE_SINGLE_STEP_P Define this as 1 if the target does not have a hardware single-step mechanism. The macro @code{SOFTWARE_SINGLE_STEP} must also be defined. @item SOFTWARE_SINGLE_STEP(@var{signal}, @var{insert_breapoints_p}) @findex SOFTWARE_SINGLE_STEP A function that inserts or removes (depending on @var{insert_breapoints_p}) breakpoints at each possible destinations of the next instruction. See @file{sparc-tdep.c} and @file{rs6000-tdep.c} for examples. @item SOFUN_ADDRESS_MAYBE_MISSING @findex SOFUN_ADDRESS_MAYBE_MISSING Somebody clever observed that, the more actual addresses you have in the debug information, the more time the linker has to spend relocating them. So whenever there's some other way the debugger could find the address it needs, you should omit it from the debug info, to make linking faster. @code{SOFUN_ADDRESS_MAYBE_MISSING} indicates that a particular set of hacks of this sort are in use, affecting @code{N_SO} and @code{N_FUN} entries in stabs-format debugging information. @code{N_SO} stabs mark the beginning and ending addresses of compilation units in the text segment. @code{N_FUN} stabs mark the starts and ends of functions. @code{SOFUN_ADDRESS_MAYBE_MISSING} means two things: @itemize @bullet @item @code{N_FUN} stabs have an address of zero. Instead, you should find the addresses where the function starts by taking the function name from the stab, and then looking that up in the minsyms (the linker/assembler symbol table). In other words, the stab has the name, and the linker/assembler symbol table is the only place that carries the address. @item @code{N_SO} stabs have an address of zero, too. You just look at the @code{N_FUN} stabs that appear before and after the @code{N_SO} stab, and guess the starting and ending addresses of the compilation unit from them. @end itemize @item PCC_SOL_BROKEN @findex PCC_SOL_BROKEN (Used only in the Convex target.) @item PC_IN_CALL_DUMMY @findex PC_IN_CALL_DUMMY See @file{inferior.h}. @item PC_LOAD_SEGMENT @findex PC_LOAD_SEGMENT If defined, print information about the load segment for the program counter. (Defined only for the RS/6000.) @item PC_REGNUM @findex PC_REGNUM If the program counter is kept in a register, then define this macro to be the number (greater than or equal to zero) of that register. This should only need to be defined if @code{TARGET_READ_PC} and @code{TARGET_WRITE_PC} are not defined. @item NPC_REGNUM @findex NPC_REGNUM The number of the ``next program counter'' register, if defined. @item NNPC_REGNUM @findex NNPC_REGNUM The number of the ``next next program counter'' register, if defined. Currently, this is only defined for the Motorola 88K. @item PARM_BOUNDARY @findex PARM_BOUNDARY If non-zero, round arguments to a boundary of this many bits before pushing them on the stack. @item PRINT_REGISTER_HOOK (@var{regno}) @findex PRINT_REGISTER_HOOK If defined, this must be a function that prints the contents of the given register to standard output. @item PRINT_TYPELESS_INTEGER @findex PRINT_TYPELESS_INTEGER This is an obscure substitute for @code{print_longest} that seems to have been defined for the Convex target. @item PROCESS_LINENUMBER_HOOK @findex PROCESS_LINENUMBER_HOOK A hook defined for XCOFF reading. @item PROLOGUE_FIRSTLINE_OVERLAP @findex PROLOGUE_FIRSTLINE_OVERLAP (Only used in unsupported Convex configuration.) @item PS_REGNUM @findex PS_REGNUM If defined, this is the number of the processor status register. (This definition is only used in generic code when parsing "$ps".) @item POP_FRAME @findex POP_FRAME @findex call_function_by_hand @findex return_command Used in @samp{call_function_by_hand} to remove an artificial stack frame and in @samp{return_command} to remove a real stack frame. @item PUSH_ARGUMENTS (@var{nargs}, @var{args}, @var{sp}, @var{struct_return}, @var{struct_addr}) @findex PUSH_ARGUMENTS Define this to push arguments onto the stack for inferior function call. Returns the updated stack pointer value. @item PUSH_DUMMY_FRAME @findex PUSH_DUMMY_FRAME Used in @samp{call_function_by_hand} to create an artificial stack frame. @item REGISTER_BYTES @findex REGISTER_BYTES The total amount of space needed to store @value{GDBN}'s copy of the machine's register state. @item REGISTER_NAME(@var{i}) @findex REGISTER_NAME Return the name of register @var{i} as a string. May return @code{NULL} or @code{NUL} to indicate that register @var{i} is not valid. @item REGISTER_NAMES @findex REGISTER_NAMES Deprecated in favor of @code{REGISTER_NAME}. @item REG_STRUCT_HAS_ADDR (@var{gcc_p}, @var{type}) @findex REG_STRUCT_HAS_ADDR Define this to return 1 if the given type will be passed by pointer rather than directly. @item SAVE_DUMMY_FRAME_TOS (@var{sp}) @findex SAVE_DUMMY_FRAME_TOS Used in @samp{call_function_by_hand} to notify the target dependent code of the top-of-stack value that will be passed to the the inferior code. This is the value of the @code{SP} after both the dummy frame and space for parameters/results have been allocated on the stack. @item SDB_REG_TO_REGNUM @findex SDB_REG_TO_REGNUM Define this to convert sdb register numbers into @value{GDBN} regnums. If not defined, no conversion will be done. @item SHIFT_INST_REGS @findex SHIFT_INST_REGS (Only used for m88k targets.) @item SKIP_PERMANENT_BREAKPOINT @findex SKIP_PERMANENT_BREAKPOINT Advance the inferior's PC past a permanent breakpoint. @value{GDBN} normally steps over a breakpoint by removing it, stepping one instruction, and re-inserting the breakpoint. However, permanent breakpoints are hardwired into the inferior, and can't be removed, so this strategy doesn't work. Calling @code{SKIP_PERMANENT_BREAKPOINT} adjusts the processor's state so that execution will resume just after the breakpoint. This macro does the right thing even when the breakpoint is in the delay slot of a branch or jump. @item SKIP_PROLOGUE (@var{pc}) @findex SKIP_PROLOGUE A C expression that returns the address of the ``real'' code beyond the function entry prologue found at @var{pc}. @item SKIP_PROLOGUE_FRAMELESS_P @findex SKIP_PROLOGUE_FRAMELESS_P A C expression that should behave similarly, but that can stop as soon as the function is known to have a frame. If not defined, @code{SKIP_PROLOGUE} will be used instead. @item SKIP_TRAMPOLINE_CODE (@var{pc}) @findex SKIP_TRAMPOLINE_CODE If the target machine has trampoline code that sits between callers and the functions being called, then define this macro to return a new PC that is at the start of the real function. @item SP_REGNUM @findex SP_REGNUM If the stack-pointer is kept in a register, then define this macro to be the number (greater than or equal to zero) of that register. This should only need to be defined if @code{TARGET_WRITE_SP} and @code{TARGET_WRITE_SP} are not defined. @item STAB_REG_TO_REGNUM @findex STAB_REG_TO_REGNUM Define this to convert stab register numbers (as gotten from `r' declarations) into @value{GDBN} regnums. If not defined, no conversion will be done. @item STACK_ALIGN (@var{addr}) @findex STACK_ALIGN Define this to adjust the address to the alignment required for the processor's stack. @item STEP_SKIPS_DELAY (@var{addr}) @findex STEP_SKIPS_DELAY Define this to return true if the address is of an instruction with a delay slot. If a breakpoint has been placed in the instruction's delay slot, @value{GDBN} will single-step over that instruction before resuming normally. Currently only defined for the Mips. @item STORE_RETURN_VALUE (@var{type}, @var{valbuf}) @findex STORE_RETURN_VALUE A C expression that stores a function return value of type @var{type}, where @var{valbuf} is the address of the value to be stored. @item SUN_FIXED_LBRAC_BUG @findex SUN_FIXED_LBRAC_BUG (Used only for Sun-3 and Sun-4 targets.) @item SYMBOL_RELOADING_DEFAULT @findex SYMBOL_RELOADING_DEFAULT The default value of the ``symbol-reloading'' variable. (Never defined in current sources.) @item TARGET_BYTE_ORDER_DEFAULT @findex TARGET_BYTE_ORDER_DEFAULT The ordering of bytes in the target. This must be either @code{BIG_ENDIAN} or @code{LITTLE_ENDIAN}. This macro replaces @code{TARGET_BYTE_ORDER} which is deprecated. @item TARGET_BYTE_ORDER_SELECTABLE_P @findex TARGET_BYTE_ORDER_SELECTABLE_P Non-zero if the target has both @code{BIG_ENDIAN} and @code{LITTLE_ENDIAN} variants. This macro replaces @code{TARGET_BYTE_ORDER_SELECTABLE} which is deprecated. @item TARGET_CHAR_BIT @findex TARGET_CHAR_BIT Number of bits in a char; defaults to 8. @item TARGET_COMPLEX_BIT @findex TARGET_COMPLEX_BIT Number of bits in a complex number; defaults to @code{2 * TARGET_FLOAT_BIT}. At present this macro is not used. @item TARGET_DOUBLE_BIT @findex TARGET_DOUBLE_BIT Number of bits in a double float; defaults to @code{8 * TARGET_CHAR_BIT}. @item TARGET_DOUBLE_COMPLEX_BIT @findex TARGET_DOUBLE_COMPLEX_BIT Number of bits in a double complex; defaults to @code{2 * TARGET_DOUBLE_BIT}. At present this macro is not used. @item TARGET_FLOAT_BIT @findex TARGET_FLOAT_BIT Number of bits in a float; defaults to @code{4 * TARGET_CHAR_BIT}. @item TARGET_INT_BIT @findex TARGET_INT_BIT Number of bits in an integer; defaults to @code{4 * TARGET_CHAR_BIT}. @item TARGET_LONG_BIT @findex TARGET_LONG_BIT Number of bits in a long integer; defaults to @code{4 * TARGET_CHAR_BIT}. @item TARGET_LONG_DOUBLE_BIT @findex TARGET_LONG_DOUBLE_BIT Number of bits in a long double float; defaults to @code{2 * TARGET_DOUBLE_BIT}. @item TARGET_LONG_LONG_BIT @findex TARGET_LONG_LONG_BIT Number of bits in a long long integer; defaults to @code{2 * TARGET_LONG_BIT}. @item TARGET_PTR_BIT @findex TARGET_PTR_BIT Number of bits in a pointer; defaults to @code{TARGET_INT_BIT}. @item TARGET_SHORT_BIT @findex TARGET_SHORT_BIT Number of bits in a short integer; defaults to @code{2 * TARGET_CHAR_BIT}. @item TARGET_READ_PC @findex TARGET_READ_PC @itemx TARGET_WRITE_PC (@var{val}, @var{pid}) @findex TARGET_WRITE_PC @itemx TARGET_READ_SP @findex TARGET_READ_SP @itemx TARGET_WRITE_SP @findex TARGET_WRITE_SP @itemx TARGET_READ_FP @findex TARGET_READ_FP @itemx TARGET_WRITE_FP @findex TARGET_WRITE_FP @findex read_pc @findex write_pc @findex read_sp @findex write_sp @findex read_fp @findex write_fp These change the behavior of @code{read_pc}, @code{write_pc}, @code{read_sp}, @code{write_sp}, @code{read_fp} and @code{write_fp}. For most targets, these may be left undefined. @value{GDBN} will call the read and write register functions with the relevant @code{_REGNUM} argument. These macros are useful when a target keeps one of these registers in a hard to get at place; for example, part in a segment register and part in an ordinary register. @item TARGET_VIRTUAL_FRAME_POINTER(@var{pc}, @var{regp}, @var{offsetp}) @findex TARGET_VIRTUAL_FRAME_POINTER Returns a @code{(register, offset)} pair representing the virtual frame pointer in use at the code address @var{pc}. If virtual frame pointers are not used, a default definition simply returns @code{FP_REGNUM}, with an offset of zero. @item TARGET_HAS_HARDWARE_WATCHPOINTS If non-zero, the target has support for hardware-assisted watchpoints. @xref{Algorithms, watchpoints}, for more details and other related macros. @item USE_STRUCT_CONVENTION (@var{gcc_p}, @var{type}) @findex USE_STRUCT_CONVENTION If defined, this must be an expression that is nonzero if a value of the given @var{type} being returned from a function must have space allocated for it on the stack. @var{gcc_p} is true if the function being considered is known to have been compiled by GCC; this is helpful for systems where GCC is known to use different calling convention than other compilers. @item VARIABLES_INSIDE_BLOCK (@var{desc}, @var{gcc_p}) @findex VARIABLES_INSIDE_BLOCK For dbx-style debugging information, if the compiler puts variable declarations inside LBRAC/RBRAC blocks, this should be defined to be nonzero. @var{desc} is the value of @code{n_desc} from the @code{N_RBRAC} symbol, and @var{gcc_p} is true if @value{GDBN} has noticed the presence of either the @code{GCC_COMPILED_SYMBOL} or the @code{GCC2_COMPILED_SYMBOL}. By default, this is 0. @item OS9K_VARIABLES_INSIDE_BLOCK (@var{desc}, @var{gcc_p}) @findex OS9K_VARIABLES_INSIDE_BLOCK Similarly, for OS/9000. Defaults to 1. @end table Motorola M68K target conditionals. @ftable @code @item BPT_VECTOR Define this to be the 4-bit location of the breakpoint trap vector. If not defined, it will default to @code{0xf}. @item REMOTE_BPT_VECTOR Defaults to @code{1}. @end ftable @section Adding a New Target @cindex adding a target The following files add a target to @value{GDBN}: @table @file @vindex TDEPFILES @item gdb/config/@var{arch}/@var{ttt}.mt Contains a Makefile fragment specific to this target. Specifies what object files are needed for target @var{ttt}, by defining @samp{TDEPFILES=@dots{}} and @samp{TDEPLIBS=@dots{}}. Also specifies the header file which describes @var{ttt}, by defining @samp{TM_FILE= tm-@var{ttt}.h}. You can also define @samp{TM_CFLAGS}, @samp{TM_CLIBS}, @samp{TM_CDEPS}, but these are now deprecated, replaced by autoconf, and may go away in future versions of @value{GDBN}. @item gdb/@var{ttt}-tdep.c Contains any miscellaneous code required for this target machine. On some machines it doesn't exist at all. Sometimes the macros in @file{tm-@var{ttt}.h} become very complicated, so they are implemented as functions here instead, and the macro is simply defined to call the function. This is vastly preferable, since it is easier to understand and debug. @item gdb/@var{arch}-tdep.c @itemx gdb/@var{arch}-tdep.h This often exists to describe the basic layout of the target machine's processor chip (registers, stack, etc.). If used, it is included by @file{@var{ttt}-tdep.h}. It can be shared among many targets that use the same processor. @item gdb/config/@var{arch}/tm-@var{ttt}.h (@file{tm.h} is a link to this file, created by @code{configure}). Contains macro definitions about the target machine's registers, stack frame format and instructions. New targets do not need this file and should not create it. @item gdb/config/@var{arch}/tm-@var{arch}.h This often exists to describe the basic layout of the target machine's processor chip (registers, stack, etc.). If used, it is included by @file{tm-@var{ttt}.h}. It can be shared among many targets that use the same processor. New targets do not need this file and should not create it. @end table If you are adding a new operating system for an existing CPU chip, add a @file{config/tm-@var{os}.h} file that describes the operating system facilities that are unusual (extra symbol table info; the breakpoint instruction needed; etc.). Then write a @file{@var{arch}/tm-@var{os}.h} that just @code{#include}s @file{tm-@var{arch}.h} and @file{config/tm-@var{os}.h}. @node Target Vector Definition @chapter Target Vector Definition @cindex target vector The target vector defines the interface between @value{GDBN}'s abstract handling of target systems, and the nitty-gritty code that actually exercises control over a process or a serial port. @value{GDBN} includes some 30-40 different target vectors; however, each configuration of @value{GDBN} includes only a few of them. @section File Targets Both executables and core files have target vectors. @section Standard Protocol and Remote Stubs @value{GDBN}'s file @file{remote.c} talks a serial protocol to code that runs in the target system. @value{GDBN} provides several sample @dfn{stubs} that can be integrated into target programs or operating systems for this purpose; they are named @file{*-stub.c}. The @value{GDBN} user's manual describes how to put such a stub into your target code. What follows is a discussion of integrating the SPARC stub into a complicated operating system (rather than a simple program), by Stu Grossman, the author of this stub. The trap handling code in the stub assumes the following upon entry to @code{trap_low}: @enumerate @item %l1 and %l2 contain pc and npc respectively at the time of the trap; @item traps are disabled; @item you are in the correct trap window. @end enumerate As long as your trap handler can guarantee those conditions, then there is no reason why you shouldn't be able to ``share'' traps with the stub. The stub has no requirement that it be jumped to directly from the hardware trap vector. That is why it calls @code{exceptionHandler()}, which is provided by the external environment. For instance, this could set up the hardware traps to actually execute code which calls the stub first, and then transfers to its own trap handler. For the most point, there probably won't be much of an issue with ``sharing'' traps, as the traps we use are usually not used by the kernel, and often indicate unrecoverable error conditions. Anyway, this is all controlled by a table, and is trivial to modify. The most important trap for us is for @code{ta 1}. Without that, we can't single step or do breakpoints. Everything else is unnecessary for the proper operation of the debugger/stub. From reading the stub, it's probably not obvious how breakpoints work. They are simply done by deposit/examine operations from @value{GDBN}. @section ROM Monitor Interface @section Custom Protocols @section Transport Layer @section Builtin Simulator @node Native Debugging @chapter Native Debugging @cindex native debugging Several files control @value{GDBN}'s configuration for native support: @table @file @vindex NATDEPFILES @item gdb/config/@var{arch}/@var{xyz}.mh Specifies Makefile fragments needed when hosting @emph{or native} on machine @var{xyz}. In particular, this lists the required native-dependent object files, by defining @samp{NATDEPFILES=@dots{}}. Also specifies the header file which describes native support on @var{xyz}, by defining @samp{NAT_FILE= nm-@var{xyz}.h}. You can also define @samp{NAT_CFLAGS}, @samp{NAT_ADD_FILES}, @samp{NAT_CLIBS}, @samp{NAT_CDEPS}, etc.; see @file{Makefile.in}. @item gdb/config/@var{arch}/nm-@var{xyz}.h (@file{nm.h} is a link to this file, created by @code{configure}). Contains C macro definitions describing the native system environment, such as child process control and core file support. @item gdb/@var{xyz}-nat.c Contains any miscellaneous C code required for this native support of this machine. On some machines it doesn't exist at all. @end table There are some ``generic'' versions of routines that can be used by various systems. These can be customized in various ways by macros defined in your @file{nm-@var{xyz}.h} file. If these routines work for the @var{xyz} host, you can just include the generic file's name (with @samp{.o}, not @samp{.c}) in @code{NATDEPFILES}. Otherwise, if your machine needs custom support routines, you will need to write routines that perform the same functions as the generic file. Put them into @file{@var{xyz}-nat.c}, and put @file{@var{xyz}-nat.o} into @code{NATDEPFILES}. @table @file @item inftarg.c This contains the @emph{target_ops vector} that supports Unix child processes on systems which use ptrace and wait to control the child. @item procfs.c This contains the @emph{target_ops vector} that supports Unix child processes on systems which use /proc to control the child. @item fork-child.c This does the low-level grunge that uses Unix system calls to do a ``fork and exec'' to start up a child process. @item infptrace.c This is the low level interface to inferior processes for systems using the Unix @code{ptrace} call in a vanilla way. @end table @section Native core file Support @cindex native core files @table @file @findex fetch_core_registers @item core-aout.c::fetch_core_registers() Support for reading registers out of a core file. This routine calls @code{register_addr()}, see below. Now that BFD is used to read core files, virtually all machines should use @code{core-aout.c}, and should just provide @code{fetch_core_registers} in @code{@var{xyz}-nat.c} (or @code{REGISTER_U_ADDR} in @code{nm-@var{xyz}.h}). @item core-aout.c::register_addr() If your @code{nm-@var{xyz}.h} file defines the macro @code{REGISTER_U_ADDR(addr, blockend, regno)}, it should be defined to set @code{addr} to the offset within the @samp{user} struct of @value{GDBN} register number @code{regno}. @code{blockend} is the offset within the ``upage'' of @code{u.u_ar0}. If @code{REGISTER_U_ADDR} is defined, @file{core-aout.c} will define the @code{register_addr()} function and use the macro in it. If you do not define @code{REGISTER_U_ADDR}, but you are using the standard @code{fetch_core_registers()}, you will need to define your own version of @code{register_addr()}, put it into your @code{@var{xyz}-nat.c} file, and be sure @code{@var{xyz}-nat.o} is in the @code{NATDEPFILES} list. If you have your own @code{fetch_core_registers()}, you may not need a separate @code{register_addr()}. Many custom @code{fetch_core_registers()} implementations simply locate the registers themselves.@refill @end table When making @value{GDBN} run native on a new operating system, to make it possible to debug core files, you will need to either write specific code for parsing your OS's core files, or customize @file{bfd/trad-core.c}. First, use whatever @code{#include} files your machine uses to define the struct of registers that is accessible (possibly in the u-area) in a core file (rather than @file{machine/reg.h}), and an include file that defines whatever header exists on a core file (e.g. the u-area or a @code{struct core}). Then modify @code{trad_unix_core_file_p} to use these values to set up the section information for the data segment, stack segment, any other segments in the core file (perhaps shared library contents or control information), ``registers'' segment, and if there are two discontiguous sets of registers (e.g. integer and float), the ``reg2'' segment. This section information basically delimits areas in the core file in a standard way, which the section-reading routines in BFD know how to seek around in. Then back in @value{GDBN}, you need a matching routine called @code{fetch_core_registers}. If you can use the generic one, it's in @file{core-aout.c}; if not, it's in your @file{@var{xyz}-nat.c} file. It will be passed a char pointer to the entire ``registers'' segment, its length, and a zero; or a char pointer to the entire ``regs2'' segment, its length, and a 2. The routine should suck out the supplied register values and install them into @value{GDBN}'s ``registers'' array. If your system uses @file{/proc} to control processes, and uses ELF format core files, then you may be able to use the same routines for reading the registers out of processes and out of core files. @section ptrace @section /proc @section win32 @section shared libraries @section Native Conditionals @cindex native conditionals When @value{GDBN} is configured and compiled, various macros are defined or left undefined, to control compilation when the host and target systems are the same. These macros should be defined (or left undefined) in @file{nm-@var{system}.h}. @table @code @item ATTACH_DETACH @findex ATTACH_DETACH If defined, then @value{GDBN} will include support for the @code{attach} and @code{detach} commands. @item CHILD_PREPARE_TO_STORE @findex CHILD_PREPARE_TO_STORE If the machine stores all registers at once in the child process, then define this to ensure that all values are correct. This usually entails a read from the child. [Note that this is incorrectly defined in @file{xm-@var{system}.h} files currently.] @item FETCH_INFERIOR_REGISTERS @findex FETCH_INFERIOR_REGISTERS Define this if the native-dependent code will provide its own routines @code{fetch_inferior_registers} and @code{store_inferior_registers} in @file{@var{host}-nat.c}. If this symbol is @emph{not} defined, and @file{infptrace.c} is included in this configuration, the default routines in @file{infptrace.c} are used for these functions. @item FILES_INFO_HOOK @findex FILES_INFO_HOOK (Only defined for Convex.) @item FP0_REGNUM @findex FP0_REGNUM This macro is normally defined to be the number of the first floating point register, if the machine has such registers. As such, it would appear only in target-specific code. However, @file{/proc} support uses this to decide whether floats are in use on this target. @item GET_LONGJMP_TARGET @findex GET_LONGJMP_TARGET For most machines, this is a target-dependent parameter. On the DECstation and the Iris, this is a native-dependent parameter, since @file{setjmp.h} is needed to define it. This macro determines the target PC address that @code{longjmp} will jump to, assuming that we have just stopped at a longjmp breakpoint. It takes a @code{CORE_ADDR *} as argument, and stores the target PC value through this pointer. It examines the current state of the machine as needed. @item I386_USE_GENERIC_WATCHPOINTS An x86-based machine can define this to use the generic x86 watchpoint support; see @ref{Algorithms, I386_USE_GENERIC_WATCHPOINTS}. @item KERNEL_U_ADDR @findex KERNEL_U_ADDR Define this to the address of the @code{u} structure (the ``user struct'', also known as the ``u-page'') in kernel virtual memory. @value{GDBN} needs to know this so that it can subtract this address from absolute addresses in the upage, that are obtained via ptrace or from core files. On systems that don't need this value, set it to zero. @item KERNEL_U_ADDR_BSD @findex KERNEL_U_ADDR_BSD Define this to cause @value{GDBN} to determine the address of @code{u} at runtime, by using Berkeley-style @code{nlist} on the kernel's image in the root directory. @item KERNEL_U_ADDR_HPUX @findex KERNEL_U_ADDR_HPUX Define this to cause @value{GDBN} to determine the address of @code{u} at runtime, by using HP-style @code{nlist} on the kernel's image in the root directory. @item ONE_PROCESS_WRITETEXT @findex ONE_PROCESS_WRITETEXT Define this to be able to, when a breakpoint insertion fails, warn the user that another process may be running with the same executable. @item PREPARE_TO_PROCEED (@var{select_it}) @findex PREPARE_TO_PROCEED This (ugly) macro allows a native configuration to customize the way the @code{proceed} function in @file{infrun.c} deals with switching between threads. In a multi-threaded task we may select another thread and then continue or step. But if the old thread was stopped at a breakpoint, it will immediately cause another breakpoint stop without any execution (i.e. it will report a breakpoint hit incorrectly). So @value{GDBN} must step over it first. If defined, @code{PREPARE_TO_PROCEED} should check the current thread against the thread that reported the most recent event. If a step-over is required, it returns TRUE. If @var{select_it} is non-zero, it should reselect the old thread. @item PROC_NAME_FMT @findex PROC_NAME_FMT Defines the format for the name of a @file{/proc} device. Should be defined in @file{nm.h} @emph{only} in order to override the default definition in @file{procfs.c}. @item PTRACE_FP_BUG @findex PTRACE_FP_BUG See @file{mach386-xdep.c}. @item PTRACE_ARG3_TYPE @findex PTRACE_ARG3_TYPE The type of the third argument to the @code{ptrace} system call, if it exists and is different from @code{int}. @item REGISTER_U_ADDR @findex REGISTER_U_ADDR Defines the offset of the registers in the ``u area''. @item SHELL_COMMAND_CONCAT @findex SHELL_COMMAND_CONCAT If defined, is a string to prefix on the shell command used to start the inferior. @item SHELL_FILE @findex SHELL_FILE If defined, this is the name of the shell to use to run the inferior. Defaults to @code{"/bin/sh"}. @item SOLIB_ADD (@var{filename}, @var{from_tty}, @var{targ}) @findex SOLIB_ADD Define this to expand into an expression that will cause the symbols in @var{filename} to be added to @value{GDBN}'s symbol table. @item SOLIB_CREATE_INFERIOR_HOOK @findex SOLIB_CREATE_INFERIOR_HOOK Define this to expand into any shared-library-relocation code that you want to be run just after the child process has been forked. @item START_INFERIOR_TRAPS_EXPECTED @findex START_INFERIOR_TRAPS_EXPECTED When starting an inferior, @value{GDBN} normally expects to trap twice; once when the shell execs, and once when the program itself execs. If the actual number of traps is something other than 2, then define this macro to expand into the number expected. @item SVR4_SHARED_LIBS @findex SVR4_SHARED_LIBS Define this to indicate that SVR4-style shared libraries are in use. @item USE_PROC_FS @findex USE_PROC_FS This determines whether small routines in @file{*-tdep.c}, which translate register values between @value{GDBN}'s internal representation and the @file{/proc} representation, are compiled. @item U_REGS_OFFSET @findex U_REGS_OFFSET This is the offset of the registers in the upage. It need only be defined if the generic ptrace register access routines in @file{infptrace.c} are being used (that is, @file{infptrace.c} is configured in, and @code{FETCH_INFERIOR_REGISTERS} is not defined). If the default value from @file{infptrace.c} is good enough, leave it undefined. The default value means that u.u_ar0 @emph{points to} the location of the registers. I'm guessing that @code{#define U_REGS_OFFSET 0} means that @code{u.u_ar0} @emph{is} the location of the registers. @item CLEAR_SOLIB @findex CLEAR_SOLIB See @file{objfiles.c}. @item DEBUG_PTRACE @findex DEBUG_PTRACE Define this to debug @code{ptrace} calls. @end table @node Support Libraries @chapter Support Libraries @section BFD @cindex BFD library BFD provides support for @value{GDBN} in several ways: @table @emph @item identifying executable and core files BFD will identify a variety of file types, including a.out, coff, and several variants thereof, as well as several kinds of core files. @item access to sections of files BFD parses the file headers to determine the names, virtual addresses, sizes, and file locations of all the various named sections in files (such as the text section or the data section). @value{GDBN} simply calls BFD to read or write section @var{x} at byte offset @var{y} for length @var{z}. @item specialized core file support BFD provides routines to determine the failing command name stored in a core file, the signal with which the program failed, and whether a core file matches (i.e.@: could be a core dump of) a particular executable file. @item locating the symbol information @value{GDBN} uses an internal interface of BFD to determine where to find the symbol information in an executable file or symbol-file. @value{GDBN} itself handles the reading of symbols, since BFD does not ``understand'' debug symbols, but @value{GDBN} uses BFD's cached information to find the symbols, string table, etc. @end table @section opcodes @cindex opcodes library The opcodes library provides @value{GDBN}'s disassembler. (It's a separate library because it's also used in binutils, for @file{objdump}). @section readline @section mmalloc @section libiberty @section gnu-regex @cindex regular expressions library Regex conditionals. @table @code @item C_ALLOCA @item NFAILURES @item RE_NREGS @item SIGN_EXTEND_CHAR @item SWITCH_ENUM_BUG @item SYNTAX_TABLE @item Sword @item sparc @end table @section include @node Coding @chapter Coding This chapter covers topics that are lower-level than the major algorithms of @value{GDBN}. @section Cleanups @cindex cleanups Cleanups are a structured way to deal with things that need to be done later. When your code does something (like @code{malloc} some memory, or open a file) that needs to be undone later (e.g., free the memory or close the file), it can make a cleanup. The cleanup will be done at some future point: when the command is finished, when an error occurs, or when your code decides it's time to do cleanups. You can also discard cleanups, that is, throw them away without doing what they say. This is only done if you ask that it be done. Syntax: @table @code @item struct cleanup *@var{old_chain}; Declare a variable which will hold a cleanup chain handle. @findex make_cleanup @item @var{old_chain} = make_cleanup (@var{function}, @var{arg}); Make a cleanup which will cause @var{function} to be called with @var{arg} (a @code{char *}) later. The result, @var{old_chain}, is a handle that can be passed to @code{do_cleanups} or @code{discard_cleanups} later. Unless you are going to call @code{do_cleanups} or @code{discard_cleanups} yourself, you can ignore the result from @code{make_cleanup}. @findex do_cleanups @item do_cleanups (@var{old_chain}); Perform all cleanups done since @code{make_cleanup} returned @var{old_chain}. E.g.: @example make_cleanup (a, 0); old = make_cleanup (b, 0); do_cleanups (old); @end example @noindent will call @code{b()} but will not call @code{a()}. The cleanup that calls @code{a()} will remain in the cleanup chain, and will be done later unless otherwise discarded.@refill @findex discard_cleanups @item discard_cleanups (@var{old_chain}); Same as @code{do_cleanups} except that it just removes the cleanups from the chain and does not call the specified functions. @end table Some functions, e.g. @code{fputs_filtered()} or @code{error()}, specify that they ``should not be called when cleanups are not in place''. This means that any actions you need to reverse in the case of an error or interruption must be on the cleanup chain before you call these functions, since they might never return to your code (they @samp{longjmp} instead). @section Wrapping Output Lines @cindex line wrap in output @findex wrap_here Output that goes through @code{printf_filtered} or @code{fputs_filtered} or @code{fputs_demangled} needs only to have calls to @code{wrap_here} added in places that would be good breaking points. The utility routines will take care of actually wrapping if the line width is exceeded. The argument to @code{wrap_here} is an indentation string which is printed @emph{only} if the line breaks there. This argument is saved away and used later. It must remain valid until the next call to @code{wrap_here} or until a newline has been printed through the @code{*_filtered} functions. Don't pass in a local variable and then return! It is usually best to call @code{wrap_here} after printing a comma or space. If you call it before printing a space, make sure that your indentation properly accounts for the leading space that will print if the line wraps there. Any function or set of functions that produce filtered output must finish by printing a newline, to flush the wrap buffer, before switching to unfiltered (@code{printf}) output. Symbol reading routines that print warnings are a good example. @section @value{GDBN} Coding Standards @cindex coding standards @value{GDBN} follows the GNU coding standards, as described in @file{etc/standards.texi}. This file is also available for anonymous FTP from GNU archive sites. @value{GDBN} takes a strict interpretation of the standard; in general, when the GNU standard recommends a practice but does not require it, @value{GDBN} requires it. @value{GDBN} follows an additional set of coding standards specific to @value{GDBN}, as described in the following sections. @subsection ISO-C @value{GDBN} assumes an ISO-C compliant compiler. @value{GDBN} does not assume an ISO-C or POSIX compliant C library. @subsection Memory Management @value{GDBN} does not use the functions @code{malloc}, @code{realloc}, @code{calloc}, @code{free} and @code{asprintf}. @value{GDBN} uses the functions @code{xmalloc}, @code{xrealloc} and @code{xcalloc} when allocating memory. Unlike @code{malloc} et.al.@: these functions do not return when the memory pool is empty. Instead, they unwind the stack using cleanups. These functions return @code{NULL} when requested to allocate a chunk of memory of size zero. @emph{Pragmatics: By using these functions, the need to check every memory allocation is removed. These functions provide portable behavior.} @value{GDBN} does not use the function @code{free}. @value{GDBN} uses the function @code{xfree} to return memory to the memory pool. Consistent with ISO-C, this function ignores a request to free a @code{NULL} pointer. @emph{Pragmatics: On some systems @code{free} fails when passed a @code{NULL} pointer.} @value{GDBN} can use the non-portable function @code{alloca} for the allocation of small temporary values (such as strings). @emph{Pragmatics: This function is very non-portable. Some systems restrict the memory being allocated to no more than a few kilobytes.} @value{GDBN} uses the string function @code{xstrdup} and the print function @code{xasprintf}. @emph{Pragmatics: @code{asprintf} and @code{strdup} can fail. Print functions such as @code{sprintf} are very prone to buffer overflow errors.} @subsection Compiler Warnings @cindex compiler warnings With few exceptions, developers should include the configuration option @samp{--enable-gdb-build-warnings=,-Werror} when building @value{GDBN}. The exceptions are listed in the file @file{gdb/MAINTAINERS}. This option causes @value{GDBN} (when built using GCC) to be compiled with a carefully selected list of compiler warning flags. Any warnings from those flags being treated as errors. The current list of warning flags includes: @table @samp @item -Wimplicit Since @value{GDBN} coding standard requires all functions to be declared using a prototype, the flag has the side effect of ensuring that prototyped functions are always visible with out resorting to @samp{-Wstrict-prototypes}. @item -Wreturn-type Such code often appears to work except on instruction set architectures that use register windows. @item -Wcomment @item -Wtrigraphs @item -Wformat Since @value{GDBN} uses the @code{format printf} attribute on all @code{printf} like functions this checks not just @code{printf} calls but also calls to functions such as @code{fprintf_unfiltered}. @item -Wparentheses This warning includes uses of the assignment operator within an @code{if} statement. @item -Wpointer-arith @item -Wuninitialized @end table @emph{Pragmatics: Due to the way that @value{GDBN} is implemented most functions have unused parameters. Consequently the warning @samp{-Wunused-parameter} is precluded from the list. The macro @code{ATTRIBUTE_UNUSED} is not used as it leads to false negatives --- it is not an error to have @code{ATTRIBUTE_UNUSED} on a parameter that is being used. The options @samp{-Wall} and @samp{-Wunused} are also precluded because they both include @samp{-Wunused-parameter}.} @emph{Pragmatics: @value{GDBN} has not simply accepted the warnings enabled by @samp{-Wall -Werror -W...}. Instead it is selecting warnings when and where their benefits can be demonstrated.} @subsection Formatting @cindex source code formatting The standard GNU recommendations for formatting must be followed strictly. A function declaration should not have its name in column zero. A function definition should have its name in column zero. @example /* Declaration */ static void foo (void); /* Definition */ void foo (void) @{ @} @end example @emph{Pragmatics: This simplifies scripting. Function definitions can be found using @samp{^function-name}.} There must be a space between a function or macro name and the opening parenthesis of its argument list (except for macro definitions, as required by C). There must not be a space after an open paren/bracket or before a close paren/bracket. While additional whitespace is generally helpful for reading, do not use more than one blank line to separate blocks, and avoid adding whitespace after the end of a program line (as of 1/99, some 600 lines had whitespace after the semicolon). Excess whitespace causes difficulties for @code{diff} and @code{patch} utilities. Pointers are declared using the traditional K&R C style: @example void *foo; @end example @noindent and not: @example void * foo; void* foo; @end example @subsection Comments @cindex comment formatting The standard GNU requirements on comments must be followed strictly. Block comments must appear in the following form, with no @code{/*}- or @code{*/}-only lines, and no leading @code{*}: @example /* Wait for control to return from inferior to debugger. If inferior gets a signal, we may decide to start it up again instead of returning. That is why there is a loop in this function. When this function actually returns it means the inferior should be left stopped and @value{GDBN} should read more commands. */ @end example (Note that this format is encouraged by Emacs; tabbing for a multi-line comment works correctly, and @kbd{M-q} fills the block consistently.) Put a blank line between the block comments preceding function or variable definitions, and the definition itself. In general, put function-body comments on lines by themselves, rather than trying to fit them into the 20 characters left at the end of a line, since either the comment or the code will inevitably get longer than will fit, and then somebody will have to move it anyhow. @subsection C Usage @cindex C data types Code must not depend on the sizes of C data types, the format of the host's floating point numbers, the alignment of anything, or the order of evaluation of expressions. @cindex function usage Use functions freely. There are only a handful of compute-bound areas in @value{GDBN} that might be affected by the overhead of a function call, mainly in symbol reading. Most of @value{GDBN}'s performance is limited by the target interface (whether serial line or system call). However, use functions with moderation. A thousand one-line functions are just as hard to understand as a single thousand-line function. @emph{Macros are bad, M'kay.} @cindex types Declarations like @samp{struct foo *} should be used in preference to declarations like @samp{typedef struct foo @{ @dots{} @} *foo_ptr}. @subsection Function Prototypes @cindex function prototypes Prototypes must be used when both @emph{declaring} and @emph{defining} a function. Prototypes for @value{GDBN} functions must include both the argument type and name, with the name matching that used in the actual function definition. All external functions should have a declaration in a header file that callers include, except for @code{_initialize_*} functions, which must be external so that @file{init.c} construction works, but shouldn't be visible to random source files. Where a source file needs a forward declaration of a static function, that declaration must appear in a block near the top of the source file. @subsection Internal Error Recovery During its execution, @value{GDBN} can encounter two types of errors. User errors and internal errors. User errors include not only a user entering an incorrect command but also problems arising from corrupt object files and system errors when interacting with the target. Internal errors include situtations where @value{GDBN} has detected, at run time, a corrupt or erroneous situtation. When reporting an internal error, @value{GDBN} uses @code{internal_error} and @code{gdb_assert}. @value{GDBN} must not call @code{abort} or @code{assert}. @emph{Pragmatics: There is no @code{internal_warning} function. Either the code detected a user error, recovered from it and issued a @code{warning} or the code failed to correctly recover from the user error and issued an @code{internal_error}.} @subsection File Names Any file used when building the core of @value{GDBN} must be in lower case. Any file used when building the core of @value{GDBN} must be 8.3 unique. These requirements apply to both source and generated files. @emph{Pragmatics: The core of @value{GDBN} must be buildable on many platforms including DJGPP and MacOS/HFS. Every time an unfriendly file is introduced to the build process both @file{Makefile.in} and @file{configure.in} need to be modified accordingly. Compare the convoluted conversion process needed to transform @file{COPYING} into @file{copying.c} with the conversion needed to transform @file{version.in} into @file{version.c}.} Any file non 8.3 compliant file (that is not used when building the core of @value{GDBN}) must be added to @file{gdb/config/djgpp/fnchange.lst}. @emph{Pragmatics: This is clearly a compromise.} When @value{GDBN} has a local version of a system header file (ex @file{string.h}) the file name based on the POSIX header prefixed with @file{gdb_} (@file{gdb_string.h}). For other files @samp{-} is used as the separator. @subsection Include Files All @file{.c} files should include @file{defs.h} first. All @file{.c} files should explicitly include the headers for any declarations they refer to. They should not rely on files being included indirectly. With the exception of the global definitions supplied by @file{defs.h}, a header file should explictily include the header declaring any @code{typedefs} et.al.@: it refers to. @code{extern} declarations should never appear in @code{.c} files. All include files should be wrapped in: @example #ifndef INCLUDE_FILE_NAME_H #define INCLUDE_FILE_NAME_H header body #endif @end example @subsection Clean Design and Portable Implementation @cindex design In addition to getting the syntax right, there's the little question of semantics. Some things are done in certain ways in @value{GDBN} because long experience has shown that the more obvious ways caused various kinds of trouble. @cindex assumptions about targets You can't assume the byte order of anything that comes from a target (including @var{value}s, object files, and instructions). Such things must be byte-swapped using @code{SWAP_TARGET_AND_HOST} in @value{GDBN}, or one of the swap routines defined in @file{bfd.h}, such as @code{bfd_get_32}. You can't assume that you know what interface is being used to talk to the target system. All references to the target must go through the current @code{target_ops} vector. You can't assume that the host and target machines are the same machine (except in the ``native'' support modules). In particular, you can't assume that the target machine's header files will be available on the host machine. Target code must bring along its own header files -- written from scratch or explicitly donated by their owner, to avoid copyright problems. @cindex portability Insertion of new @code{#ifdef}'s will be frowned upon. It's much better to write the code portably than to conditionalize it for various systems. @cindex system dependencies New @code{#ifdef}'s which test for specific compilers or manufacturers or operating systems are unacceptable. All @code{#ifdef}'s should test for features. The information about which configurations contain which features should be segregated into the configuration files. Experience has proven far too often that a feature unique to one particular system often creeps into other systems; and that a conditional based on some predefined macro for your current system will become worthless over time, as new versions of your system come out that behave differently with regard to this feature. Adding code that handles specific architectures, operating systems, target interfaces, or hosts, is not acceptable in generic code. @cindex portable file name handling @cindex file names, portability One particularly notorious area where system dependencies tend to creep in is handling of file names. The mainline @value{GDBN} code assumes Posix semantics of file names: absolute file names begin with a forward slash @file{/}, slashes are used to separate leading directories, case-sensitive file names. These assumptions are not necessarily true on non-Posix systems such as MS-Windows. To avoid system-dependent code where you need to take apart or construct a file name, use the following portable macros: @table @code @findex HAVE_DOS_BASED_FILE_SYSTEM @item HAVE_DOS_BASED_FILE_SYSTEM This preprocessing symbol is defined to a non-zero value on hosts whose filesystems belong to the MS-DOS/MS-Windows family. Use this symbol to write conditional code which should only be compiled for such hosts. @findex IS_DIR_SEPARATOR @item IS_DIR_SEPARATOR (@var{c} Evaluates to a non-zero value if @var{c} is a directory separator character. On Unix and GNU/Linux systems, only a slash @file{/} is such a character, but on Windows, both @file{/} and @file{\} will pass. @findex IS_ABSOLUTE_PATH @item IS_ABSOLUTE_PATH (@var{file}) Evaluates to a non-zero value if @var{file} is an absolute file name. For Unix and GNU/Linux hosts, a name which begins with a slash @file{/} is absolute. On DOS and Windows, @file{d:/foo} and @file{x:\bar} are also absolute file names. @findex FILENAME_CMP @item FILENAME_CMP (@var{f1}, @var{f2}) Calls a function which compares file names @var{f1} and @var{f2} as appropriate for the underlying host filesystem. For Posix systems, this simply calls @code{strcmp}; on case-insensitive filesystems it will call @code{strcasecmp} instead. @findex DIRNAME_SEPARATOR @item DIRNAME_SEPARATOR Evaluates to a character which separates directories in @code{PATH}-style lists, typically held in environment variables. This character is @samp{:} on Unix, @samp{;} on DOS and Windows. @findex SLASH_STRING @item SLASH_STRING This evaluates to a constant string you should use to produce an absolute filename from leading directories and the file's basename. @code{SLASH_STRING} is @code{"/"} on most systems, but might be @code{"\\"} for some Windows-based ports. @end table In addition to using these macros, be sure to use portable library functions whenever possible. For example, to extract a directory or a basename part from a file name, use the @code{dirname} and @code{basename} library functions (available in @code{libiberty} for platforms which don't provide them), instead of searching for a slash with @code{strrchr}. Another way to generalize @value{GDBN} along a particular interface is with an attribute struct. For example, @value{GDBN} has been generalized to handle multiple kinds of remote interfaces---not by @code{#ifdef}s everywhere, but by defining the @code{target_ops} structure and having a current target (as well as a stack of targets below it, for memory references). Whenever something needs to be done that depends on which remote interface we are using, a flag in the current target_ops structure is tested (e.g., @code{target_has_stack}), or a function is called through a pointer in the current target_ops structure. In this way, when a new remote interface is added, only one module needs to be touched---the one that actually implements the new remote interface. Other examples of attribute-structs are BFD access to multiple kinds of object file formats, or @value{GDBN}'s access to multiple source languages. Please avoid duplicating code. For example, in @value{GDBN} 3.x all the code interfacing between @code{ptrace} and the rest of @value{GDBN} was duplicated in @file{*-dep.c}, and so changing something was very painful. In @value{GDBN} 4.x, these have all been consolidated into @file{infptrace.c}. @file{infptrace.c} can deal with variations between systems the same way any system-independent file would (hooks, @code{#if defined}, etc.), and machines which are radically different don't need to use @file{infptrace.c} at all. All debugging code must be controllable using the @samp{set debug @var{module}} command. Do not use @code{printf} to print trace messages. Use @code{fprintf_unfiltered(gdb_stdlog, ...}. Do not use @code{#ifdef DEBUG}. @node Porting GDB @chapter Porting @value{GDBN} @cindex porting to new machines Most of the work in making @value{GDBN} compile on a new machine is in specifying the configuration of the machine. This is done in a dizzying variety of header files and configuration scripts, which we hope to make more sensible soon. Let's say your new host is called an @var{xyz} (e.g., @samp{sun4}), and its full three-part configuration name is @code{@var{arch}-@var{xvend}-@var{xos}} (e.g., @samp{sparc-sun-sunos4}). In particular: @itemize @bullet @item In the top level directory, edit @file{config.sub} and add @var{arch}, @var{xvend}, and @var{xos} to the lists of supported architectures, vendors, and operating systems near the bottom of the file. Also, add @var{xyz} as an alias that maps to @code{@var{arch}-@var{xvend}-@var{xos}}. You can test your changes by running @example ./config.sub @var{xyz} @end example @noindent and @example ./config.sub @code{@var{arch}-@var{xvend}-@var{xos}} @end example @noindent which should both respond with @code{@var{arch}-@var{xvend}-@var{xos}} and no error messages. @noindent You need to port BFD, if that hasn't been done already. Porting BFD is beyond the scope of this manual. @item To configure @value{GDBN} itself, edit @file{gdb/configure.host} to recognize your system and set @code{gdb_host} to @var{xyz}, and (unless your desired target is already available) also edit @file{gdb/configure.tgt}, setting @code{gdb_target} to something appropriate (for instance, @var{xyz}). @item Finally, you'll need to specify and define @value{GDBN}'s host-, native-, and target-dependent @file{.h} and @file{.c} files used for your configuration. @end itemize @section Configuring @value{GDBN} for Release @cindex preparing a release @cindex making a distribution tarball From the top level directory (containing @file{gdb}, @file{bfd}, @file{libiberty}, and so on): @example make -f Makefile.in gdb.tar.gz @end example @noindent This will properly configure, clean, rebuild any files that are distributed pre-built (e.g. @file{c-exp.tab.c} or @file{refcard.ps}), and will then make a tarfile. (If the top level directory has already been configured, you can just do @code{make gdb.tar.gz} instead.) This procedure requires: @itemize @bullet @item symbolic links; @item @code{makeinfo} (texinfo2 level); @item @TeX{}; @item @code{dvips}; @item @code{yacc} or @code{bison}. @end itemize @noindent @dots{} and the usual slew of utilities (@code{sed}, @code{tar}, etc.). @subheading TEMPORARY RELEASE PROCEDURE FOR DOCUMENTATION @file{gdb.texinfo} is currently marked up using the texinfo-2 macros, which are not yet a default for anything (but we have to start using them sometime). For making paper, the only thing this implies is the right generation of @file{texinfo.tex} needs to be included in the distribution. For making info files, however, rather than duplicating the texinfo2 distribution, generate @file{gdb-all.texinfo} locally, and include the files @file{gdb.info*} in the distribution. Note the plural; @code{makeinfo} will split the document into one overall file and five or so included files. @node Testsuite @chapter Testsuite @cindex test suite The testsuite is an important component of the @value{GDBN} package. While it is always worthwhile to encourage user testing, in practice this is rarely sufficient; users typically use only a small subset of the available commands, and it has proven all too common for a change to cause a significant regression that went unnoticed for some time. The @value{GDBN} testsuite uses the DejaGNU testing framework. DejaGNU is built using @code{Tcl} and @code{expect}. The tests themselves are calls to various @code{Tcl} procs; the framework runs all the procs and summarizes the passes and fails. @section Using the Testsuite @cindex running the test suite To run the testsuite, simply go to the @value{GDBN} object directory (or to the testsuite's objdir) and type @code{make check}. This just sets up some environment variables and invokes DejaGNU's @code{runtest} script. While the testsuite is running, you'll get mentions of which test file is in use, and a mention of any unexpected passes or fails. When the testsuite is finished, you'll get a summary that looks like this: @example === gdb Summary === # of expected passes 6016 # of unexpected failures 58 # of unexpected successes 5 # of expected failures 183 # of unresolved testcases 3 # of untested testcases 5 @end example The ideal test run consists of expected passes only; however, reality conspires to keep us from this ideal. Unexpected failures indicate real problems, whether in @value{GDBN} or in the testsuite. Expected failures are still failures, but ones which have been decided are too hard to deal with at the time; for instance, a test case might work everywhere except on AIX, and there is no prospect of the AIX case being fixed in the near future. Expected failures should not be added lightly, since you may be masking serious bugs in @value{GDBN}. Unexpected successes are expected fails that are passing for some reason, while unresolved and untested cases often indicate some minor catastrophe, such as the compiler being unable to deal with a test program. When making any significant change to @value{GDBN}, you should run the testsuite before and after the change, to confirm that there are no regressions. Note that truly complete testing would require that you run the testsuite with all supported configurations and a variety of compilers; however this is more than really necessary. In many cases testing with a single configuration is sufficient. Other useful options are to test one big-endian (Sparc) and one little-endian (x86) host, a cross config with a builtin simulator (powerpc-eabi, mips-elf), or a 64-bit host (Alpha). If you add new functionality to @value{GDBN}, please consider adding tests for it as well; this way future @value{GDBN} hackers can detect and fix their changes that break the functionality you added. Similarly, if you fix a bug that was not previously reported as a test failure, please add a test case for it. Some cases are extremely difficult to test, such as code that handles host OS failures or bugs in particular versions of compilers, and it's OK not to try to write tests for all of those. @section Testsuite Organization @cindex test suite organization The testsuite is entirely contained in @file{gdb/testsuite}. While the testsuite includes some makefiles and configury, these are very minimal, and used for little besides cleaning up, since the tests themselves handle the compilation of the programs that @value{GDBN} will run. The file @file{testsuite/lib/gdb.exp} contains common utility procs useful for all @value{GDBN} tests, while the directory @file{testsuite/config} contains configuration-specific files, typically used for special-purpose definitions of procs like @code{gdb_load} and @code{gdb_start}. The tests themselves are to be found in @file{testsuite/gdb.*} and subdirectories of those. The names of the test files must always end with @file{.exp}. DejaGNU collects the test files by wildcarding in the test directories, so both subdirectories and individual files get chosen and run in alphabetical order. The following table lists the main types of subdirectories and what they are for. Since DejaGNU finds test files no matter where they are located, and since each test file sets up its own compilation and execution environment, this organization is simply for convenience and intelligibility. @table @file @item gdb.base This is the base testsuite. The tests in it should apply to all configurations of @value{GDBN} (but generic native-only tests may live here). The test programs should be in the subset of C that is valid K&R, ANSI/ISO, and C++ (@code{#ifdef}s are allowed if necessary, for instance for prototypes). @item gdb.@var{lang} Language-specific tests for any language @var{lang} besides C. Examples are @file{gdb.c++} and @file{gdb.java}. @item gdb.@var{platform} Non-portable tests. The tests are specific to a specific configuration (host or target), such as HP-UX or eCos. Example is @file{gdb.hp}, for HP-UX. @item gdb.@var{compiler} Tests specific to a particular compiler. As of this writing (June 1999), there aren't currently any groups of tests in this category that couldn't just as sensibly be made platform-specific, but one could imagine a @file{gdb.gcc}, for tests of @value{GDBN}'s handling of GCC extensions. @item gdb.@var{subsystem} Tests that exercise a specific @value{GDBN} subsystem in more depth. For instance, @file{gdb.disasm} exercises various disassemblers, while @file{gdb.stabs} tests pathways through the stabs symbol reader. @end table @section Writing Tests @cindex writing tests In many areas, the @value{GDBN} tests are already quite comprehensive; you should be able to copy existing tests to handle new cases. You should try to use @code{gdb_test} whenever possible, since it includes cases to handle all the unexpected errors that might happen. However, it doesn't cost anything to add new test procedures; for instance, @file{gdb.base/exprs.exp} defines a @code{test_expr} that calls @code{gdb_test} multiple times. Only use @code{send_gdb} and @code{gdb_expect} when absolutely necessary, such as when @value{GDBN} has several valid responses to a command. The source language programs do @emph{not} need to be in a consistent style. Since @value{GDBN} is used to debug programs written in many different styles, it's worth having a mix of styles in the testsuite; for instance, some @value{GDBN} bugs involving the display of source lines would never manifest themselves if the programs used GNU coding style uniformly. @node Hints @chapter Hints Check the @file{README} file, it often has useful information that does not appear anywhere else in the directory. @menu * Getting Started:: Getting started working on @value{GDBN} * Debugging GDB:: Debugging @value{GDBN} with itself @end menu @node Getting Started,,, Hints @section Getting Started @value{GDBN} is a large and complicated program, and if you first starting to work on it, it can be hard to know where to start. Fortunately, if you know how to go about it, there are ways to figure out what is going on. This manual, the @value{GDBN} Internals manual, has information which applies generally to many parts of @value{GDBN}. Information about particular functions or data structures are located in comments with those functions or data structures. If you run across a function or a global variable which does not have a comment correctly explaining what is does, this can be thought of as a bug in @value{GDBN}; feel free to submit a bug report, with a suggested comment if you can figure out what the comment should say. If you find a comment which is actually wrong, be especially sure to report that. Comments explaining the function of macros defined in host, target, or native dependent files can be in several places. Sometimes they are repeated every place the macro is defined. Sometimes they are where the macro is used. Sometimes there is a header file which supplies a default definition of the macro, and the comment is there. This manual also documents all the available macros. @c (@pxref{Host Conditionals}, @pxref{Target @c Conditionals}, @pxref{Native Conditionals}, and @pxref{Obsolete @c Conditionals}) Start with the header files. Once you have some idea of how @value{GDBN}'s internal symbol tables are stored (see @file{symtab.h}, @file{gdbtypes.h}), you will find it much easier to understand the code which uses and creates those symbol tables. You may wish to process the information you are getting somehow, to enhance your understanding of it. Summarize it, translate it to another language, add some (perhaps trivial or non-useful) feature to @value{GDBN}, use the code to predict what a test case would do and write the test case and verify your prediction, etc. If you are reading code and your eyes are starting to glaze over, this is a sign you need to use a more active approach. Once you have a part of @value{GDBN} to start with, you can find more specifically the part you are looking for by stepping through each function with the @code{next} command. Do not use @code{step} or you will quickly get distracted; when the function you are stepping through calls another function try only to get a big-picture understanding (perhaps using the comment at the beginning of the function being called) of what it does. This way you can identify which of the functions being called by the function you are stepping through is the one which you are interested in. You may need to examine the data structures generated at each stage, with reference to the comments in the header files explaining what the data structures are supposed to look like. Of course, this same technique can be used if you are just reading the code, rather than actually stepping through it. The same general principle applies---when the code you are looking at calls something else, just try to understand generally what the code being called does, rather than worrying about all its details. @cindex command implementation A good place to start when tracking down some particular area is with a command which invokes that feature. Suppose you want to know how single-stepping works. As a @value{GDBN} user, you know that the @code{step} command invokes single-stepping. The command is invoked via command tables (see @file{command.h}); by convention the function which actually performs the command is formed by taking the name of the command and adding @samp{_command}, or in the case of an @code{info} subcommand, @samp{_info}. For example, the @code{step} command invokes the @code{step_command} function and the @code{info display} command invokes @code{display_info}. When this convention is not followed, you might have to use @code{grep} or @kbd{M-x tags-search} in emacs, or run @value{GDBN} on itself and set a breakpoint in @code{execute_command}. @cindex @code{bug-gdb} mailing list If all of the above fail, it may be appropriate to ask for information on @code{bug-gdb}. But @emph{never} post a generic question like ``I was wondering if anyone could give me some tips about understanding @value{GDBN}''---if we had some magic secret we would put it in this manual. Suggestions for improving the manual are always welcome, of course. @node Debugging GDB,,,Hints @section Debugging @value{GDBN} with itself @cindex debugging @value{GDBN} If @value{GDBN} is limping on your machine, this is the preferred way to get it fully functional. Be warned that in some ancient Unix systems, like Ultrix 4.2, a program can't be running in one process while it is being debugged in another. Rather than typing the command @kbd{@w{./gdb ./gdb}}, which works on Suns and such, you can copy @file{gdb} to @file{gdb2} and then type @kbd{@w{./gdb ./gdb2}}. When you run @value{GDBN} in the @value{GDBN} source directory, it will read a @file{.gdbinit} file that sets up some simple things to make debugging gdb easier. The @code{info} command, when executed without a subcommand in a @value{GDBN} being debugged by gdb, will pop you back up to the top level gdb. See @file{.gdbinit} for details. If you use emacs, you will probably want to do a @code{make TAGS} after you configure your distribution; this will put the machine dependent routines for your local machine where they will be accessed first by @kbd{M-.} Also, make sure that you've either compiled @value{GDBN} with your local cc, or have run @code{fixincludes} if you are compiling with gcc. @section Submitting Patches @cindex submitting patches Thanks for thinking of offering your changes back to the community of @value{GDBN} users. In general we like to get well designed enhancements. Thanks also for checking in advance about the best way to transfer the changes. The @value{GDBN} maintainers will only install ``cleanly designed'' patches. This manual summarizes what we believe to be clean design for @value{GDBN}. If the maintainers don't have time to put the patch in when it arrives, or if there is any question about a patch, it goes into a large queue with everyone else's patches and bug reports. @cindex legal papers for code contributions The legal issue is that to incorporate substantial changes requires a copyright assignment from you and/or your employer, granting ownership of the changes to the Free Software Foundation. You can get the standard documents for doing this by sending mail to @code{gnu@@gnu.org} and asking for it. We recommend that people write in "All programs owned by the Free Software Foundation" as "NAME OF PROGRAM", so that changes in many programs (not just @value{GDBN}, but GAS, Emacs, GCC, etc) can be contributed with only one piece of legalese pushed through the bureacracy and filed with the FSF. We can't start merging changes until this paperwork is received by the FSF (their rules, which we follow since we maintain it for them). Technically, the easiest way to receive changes is to receive each feature as a small context diff or unidiff, suitable for @code{patch}. Each message sent to me should include the changes to C code and header files for a single feature, plus @file{ChangeLog} entries for each directory where files were modified, and diffs for any changes needed to the manuals (@file{gdb/doc/gdb.texinfo} or @file{gdb/doc/gdbint.texinfo}). If there are a lot of changes for a single feature, they can be split down into multiple messages. In this way, if we read and like the feature, we can add it to the sources with a single patch command, do some testing, and check it in. If you leave out the @file{ChangeLog}, we have to write one. If you leave out the doc, we have to puzzle out what needs documenting. Etc., etc. The reason to send each change in a separate message is that we will not install some of the changes. They'll be returned to you with questions or comments. If we're doing our job correctly, the message back to you will say what you have to fix in order to make the change acceptable. The reason to have separate messages for separate features is so that the acceptable changes can be installed while one or more changes are being reworked. If multiple features are sent in a single message, we tend to not put in the effort to sort out the acceptable changes from the unacceptable, so none of the features get installed until all are acceptable. If this sounds painful or authoritarian, well, it is. But we get a lot of bug reports and a lot of patches, and many of them don't get installed because we don't have the time to finish the job that the bug reporter or the contributor could have done. Patches that arrive complete, working, and well designed, tend to get installed on the day they arrive. The others go into a queue and get installed as time permits, which, since the maintainers have many demands to meet, may not be for quite some time. Please send patches directly to @email{gdb-patches@@sourceware.cygnus.com, the @value{GDBN} maintainers}. @section Obsolete Conditionals @cindex obsolete code Fragments of old code in @value{GDBN} sometimes reference or set the following configuration macros. They should not be used by new code, and old uses should be removed as those parts of the debugger are otherwise touched. @table @code @item STACK_END_ADDR This macro used to define where the end of the stack appeared, for use in interpreting core file formats that don't record this address in the core file itself. This information is now configured in BFD, and @value{GDBN} gets the info portably from there. The values in @value{GDBN}'s configuration files should be moved into BFD configuration files (if needed there), and deleted from all of @value{GDBN}'s config files. Any @file{@var{foo}-xdep.c} file that references STACK_END_ADDR is so old that it has never been converted to use BFD. Now that's old! @item PYRAMID_CONTROL_FRAME_DEBUGGING pyr-xdep.c @item PYRAMID_CORE pyr-xdep.c @item PYRAMID_PTRACE pyr-xdep.c @item REG_STACK_SEGMENT exec.c @end table @node Index @unnumbered Index @printindex cp @c TeX can handle the contents at the start but makeinfo 3.12 can not @ifinfo @contents @end ifinfo @ifhtml @contents @end ifhtml @bye