path: root/gdb/doc/gdbint.info-2

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START-INFO-DIR-ENTRY
* Gdb-Internals: (gdbint).	The GNU debugger's internals.
END-INFO-DIR-ENTRY

   This file documents the internals of the GNU debugger GDB.

   Copyright 1990-1999 Free Software Foundation, Inc.  Contributed by
Cygnus Solutions.  Written by John Gilmore.  Second Edition by Stan
Shebs.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy or distribute modified versions of this
manual under the terms of the GPL (for which purpose this text may be
regarded as a program in the language TeX).


File: gdbint.info,  Node: Target Architecture Definition,  Next: Target Vector Definition,  Prev: Host Definition,  Up: Top

Target Architecture Definition
******************************

   GDB's target architecture defines what sort of machine-language
programs GDB can work with, and how it works with them.

   At present, the target architecture definition consists of a number
of C macros.

Registers and Memory
====================

   GDB's model of the target machine is rather simple.  GDB assumes the
machine includes a bank of registers and a block of memory.  Each
register may have a different size.

   GDB 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 `REGISTER_NAME' and related macros.

   GDB can handle big-endian, little-endian, and bi-endian
architectures.

Frame Interpretation
====================

Inferior Call Setup
===================

Compiler Characteristics
========================

Target Conditionals
===================

   This section describes the macros that you can use to define the
target machine.

`ADDITIONAL_OPTIONS'

`ADDITIONAL_OPTION_CASES'

`ADDITIONAL_OPTION_HANDLER'

`ADDITIONAL_OPTION_HELP'
     These are a set of macros that allow the addition of additional
     command line options to GDB.  They are currently used only for the
     unsupported i960 Nindy target, and should not be used in any other
     configuration.

`ADDR_BITS_REMOVE (addr)'
     If a raw machine address includes any bits that are not really
     part of the address, then define this macro to expand into an
     expression that zeros those bits in ADDR.  For example, the two
     low-order bits of a Motorola 88K address may be used by some
     kernels for their own purposes, since addresses must always be
     4-byte aligned, and so are of no use for addressing.  Those bits
     should be filtered out with an expression such as `((addr) & ~3)'.

`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, GDB will probably not
     compile, let alone run correctly.  This is currently used only for
     the unsupported i960 Nindy target, and should not be used in any
     other configuration.

`BELIEVE_PCC_PROMOTION'
     Define if the compiler promotes a short or char parameter to an
     int, but still reports the parameter as its original type, rather
     than the promoted type.

`BELIEVE_PCC_PROMOTION_TYPE'
     Define this if GDB should believe the type of a short argument when
     compiled by pcc, but look within a full int space to get its value.
     Only defined for Sun-3 at present.

`BITS_BIG_ENDIAN'
     Define this if the numbering of bits in the targets does *not*
     match the endianness of the target byte order.  A value of 1 means
     that the bits are numbered in a big-endian order, 0 means
     little-endian.

`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.

`BIG_BREAKPOINT'

`LITTLE_BREAKPOINT'
     Similar to BREAKPOINT, but used for bi-endian targets.

`REMOTE_BREAKPOINT'

`LITTLE_REMOTE_BREAKPOINT'

`BIG_REMOTE_BREAKPOINT'
     Similar to BREAKPOINT, but used for remote targets.

`BREAKPOINT_FROM_PC (pcptr, lenptr)'
     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 *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 BREAKPOINTs.

`CALL_DUMMY'
     valops.c

`CALL_DUMMY_LOCATION'
     inferior.h

`CALL_DUMMY_STACK_ADJUST'
     valops.c

`CANNOT_FETCH_REGISTER (regno)'
     A C expression that should be nonzero if REGNO cannot be fetched
     from an inferior process.  This is only relevant if
     `FETCH_INFERIOR_REGISTERS' is not defined.

`CANNOT_STORE_REGISTER (regno)'
     A C expression that should be nonzero if 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, GDB will assume that all registers may be written.

`DO_DEFERRED_STORES'

`CLEAR_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?

`CPLUS_MARKER'
     Define this to expand into the character that G++ uses to
     distinguish compiler-generated identifiers from
     programmer-specified identifiers.  By default, this expands into
     `'$''.  Most System V targets should define this to `'.''.

`DBX_PARM_SYMBOL_CLASS'
     Hook for the `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.

`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 BREAKPOINT, though not always.  For most targets this
     value will be 0.

`DECR_PC_AFTER_HW_BREAK'
     Similarly, for hardware breakpoints.

`DISABLE_UNSETTABLE_BREAK addr'
     If defined, this should evaluate to 1 if ADDR is in a shared
     library in which breakpoints cannot be set and so should be
     disabled.

`DO_REGISTERS_INFO'
     If defined, use this to print the value of a register or all
     registers.

`END_OF_TEXT_DEFAULT'
     This is an expression that should designate the end of the text
     section (? FIXME ?)

`EXTRACT_RETURN_VALUE(type,regbuf,valbuf)'
     Define this to extract a function's return value of type TYPE from
     the raw register state REGBUF and copy that, in virtual format,
     into VALBUF.

`EXTRACT_STRUCT_VALUE_ADDRESS(regbuf)'
     Define this to extract from an array REGBUF containing the (raw)
     register state, the address in which a function should return its
     structure value, as a CORE_ADDR (or an expression that can be used
     as one).

`FLOAT_INFO'
     If defined, then the `info float' command will print information
     about the processor's floating point unit.

`FP_REGNUM'
     The number of the frame pointer register.

`FRAMELESS_FUNCTION_INVOCATION(fi, frameless)'
     Define this to set the variable FRAMELESS to 1 if the function
     invocation represented by FI does not have a stack frame
     associated with it.  Otherwise set it to 0.

`FRAME_ARGS_ADDRESS_CORRECT'
     stack.c

`FRAME_CHAIN(frame)'
     Given FRAME, return a pointer to the calling frame.

`FRAME_CHAIN_COMBINE(chain,frame)'
     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.

`FRAME_CHAIN_VALID(chain,thisframe)'
     Define this to be an expression that returns zero if the given
     frame is an outermost frame, with no caller, and nonzero
     otherwise.  Three common definitions are available.
     `default_frame_chain_valid' (the default) is nonzero if the chain
     pointer is nonzero and given frame's PC is not inside the startup
     file (such as `crt0.o').  `alternate_frame_chain_valid' is nonzero
     if the chain pointer is nonzero and the given frame's PC is not in
     `main()' or a known entry point function (such as `_start()').

`FRAME_INIT_SAVED_REGS(frame)'
     See `frame.h'.  Determines the address of all registers in the
     current stack frame storing each in `frame->saved_regs'.  Space for
     `frame->saved_regs' shall be allocated by `FRAME_INIT_SAVED_REGS'
     using either `frame_saved_regs_zalloc' or `frame_obstack_alloc'.

     FRAME_FIND_SAVED_REGS and EXTRA_FRAME_INFO are deprecated.

`FRAME_NUM_ARGS (val, fi)'
     For the frame described by FI, set VAL to the number of arguments
     that are being passed.

`FRAME_SAVED_PC(frame)'
     Given FRAME, return the pc saved there.  That is, the return
     address.

`FUNCTION_EPILOGUE_SIZE'
     For some COFF targets, the `x_sym.x_misc.x_fsize' field of the
     function end symbol is 0.  For such targets, you must define
     `FUNCTION_EPILOGUE_SIZE' to expand into the standard size of a
     function's epilogue.

`GCC_COMPILED_FLAG_SYMBOL'

`GCC2_COMPILED_FLAG_SYMBOL'
     If defined, these are the names of the symbols that GDB will look
     for to detect that GCC compiled the file.  The default symbols are
     `gcc_compiled.' and `gcc2_compiled.', respectively. (Currently
     only defined for the Delta 68.)

`GDB_TARGET_IS_HPPA'
     This determines whether horrible kludge code in dbxread.c and
     partial-stab.h is used to mangle multiple-symbol-table files from
     HPPA's.  This should all be ripped out, and a scheme like elfread.c
     used.

`GDB_TARGET_IS_MACH386'

`GDB_TARGET_IS_SUN3'

`GDB_TARGET_IS_SUN386'
     Kludges that should go away.

`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 <setjmp.h> is needed to define it.

     This macro determines the target PC address that longjmp() will
     jump to, assuming that we have just stopped at a longjmp
     breakpoint.  It takes a CORE_ADDR * as argument, and stores the
     target PC value through this pointer.  It examines the current
     state of the machine as needed.

`GET_SAVED_REGISTER'
     Define this if you need to supply your own definition for the
     function `get_saved_register'.  Currently this is only done for
     the a29k.

`HAVE_REGISTER_WINDOWS'
     Define this if the target has register windows.

`REGISTER_IN_WINDOW_P (regnum)'
     Define this to be an expression that is 1 if the given register is
     in the window.

`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 haste and we are
     repenting at leisure.

`IEEE_FLOAT'
     Define this if the target system uses IEEE-format floating point
     numbers.

`INIT_EXTRA_FRAME_INFO (fromleaf, frame)'
     If additional information about the frame is required this should
     be stored in `frame->extra_info'.  Space for `frame->extra_info'
     is allocated using `frame_obstack_alloc'.

`INIT_FRAME_PC (fromleaf, prev)'
     This is a C statement that sets the pc of the frame pointed to by
     PREV.  [By default...]

`INNER_THAN (lhs,rhs)'
     Returns non-zero if stack address LHS is inner than (nearer to the
     stack top) stack address RHS. Define this as `lhs < rhs' if the
     target's stack grows downward in memory, or `lhs > rsh' if the
     stack grows upward.

`IN_SIGTRAMP (pc, name)'
     Define this to return true if the given PC and/or NAME indicates
     that the current function is a sigtramp.

`SIGTRAMP_START (pc)'

`SIGTRAMP_END (pc)'
     Define these to be the start and end address of the sigtramp for
     the given PC.  On machines where the address is just a compile time
     constant, the macro expansion will typically just ignore the
     supplied PC.

`IN_SOLIB_CALL_TRAMPOLINE pc name'
     Define this to evaluate to nonzero if the program is stopped in the
     trampoline that connects to a shared library.

`IN_SOLIB_RETURN_TRAMPOLINE pc name'
     Define this to evaluate to nonzero if the program is stopped in the
     trampoline that returns from a shared library.

`IS_TRAPPED_INTERNALVAR (name)'
     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 GDB.  Currently only used by the h8500.  Note
     that this could be either a host or target conditional.

`NEED_TEXT_START_END'
     Define this if GDB should determine the start and end addresses of
     the text section.  (Seems dubious.)

`NO_HIF_SUPPORT'
     (Specific to the a29k.)

`SOFTWARE_SINGLE_STEP_P'
     Define this as 1 if the target does not have a hardware single-step
     mechanism. The macro `SOFTWARE_SINGLE_STEP' must also be defined.

`SOFTWARE_SINGLE_STEP(signal,insert_breapoints_p)'
     A function that inserts or removes (dependant on
     INSERT_BREAPOINTS_P) breakpoints at each possible destinations of
     the next instruction. See `sparc-tdep.c' and `rs6000-tdep.c' for
     examples.

`PCC_SOL_BROKEN'
     (Used only in the Convex target.)

`PC_IN_CALL_DUMMY'
     inferior.h

`PC_LOAD_SEGMENT'
     If defined, print information about the load segment for the
     program counter.  (Defined only for the RS/6000.)

`PC_REGNUM'
     If the program counter is kept in a register, then define this
     macro to be the number of that register.  This need be defined
     only if `TARGET_WRITE_PC' is not defined.

`NPC_REGNUM'
     The number of the "next program counter" register, if defined.

`NNPC_REGNUM'
     The number of the "next next program counter" register, if defined.
     Currently, this is only defined for the Motorola 88K.

`PRINT_REGISTER_HOOK (regno)'
     If defined, this must be a function that prints the contents of the
     given register to standard output.

`PRINT_TYPELESS_INTEGER'
     This is an obscure substitute for `print_longest' that seems to
     have been defined for the Convex target.

`PROCESS_LINENUMBER_HOOK'
     A hook defined for XCOFF reading.

`PROLOGUE_FIRSTLINE_OVERLAP'
     (Only used in unsupported Convex configuration.)

`PS_REGNUM'
     If defined, this is the number of the processor status register.
     (This definition is only used in generic code when parsing "$ps".)

`POP_FRAME'
     Used in `call_function_by_hand' to remove an artificial stack
     frame.

`PUSH_ARGUMENTS (nargs, args, sp, struct_return, struct_addr)'
     Define this to push arguments onto the stack for inferior function
     call.

`PUSH_DUMMY_FRAME'
     Used in `call_function_by_hand' to create an artificial stack
     frame.

`REGISTER_BYTES'
     The total amount of space needed to store GDB's copy of the
     machine's register state.

`REGISTER_NAME(i)'
     Return the name of register I as a string.  May return NULL or NUL
     to indicate that register I is not valid.

`REG_STRUCT_HAS_ADDR (gcc_p, type)'
     Define this to return 1 if the given type will be passed by pointer
     rather than directly.

`SDB_REG_TO_REGNUM'
     Define this to convert sdb register numbers into GDB regnums.  If
     not defined, no conversion will be done.

`SHIFT_INST_REGS'
     (Only used for m88k targets.)

`SKIP_PROLOGUE (pc)'
     A C statement that advances the PC across any function entry
     prologue instructions so as to reach "real" code.

`SKIP_PROLOGUE_FRAMELESS_P'
     A C statement that should behave similarly, but that can stop as
     soon as the function is known to have a frame.  If not defined,
     `SKIP_PROLOGUE' will be used instead.

`SKIP_TRAMPOLINE_CODE (pc)'
     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.

`SP_REGNUM'
     Define this to be the number of the register that serves as the
     stack pointer.

`STAB_REG_TO_REGNUM'
     Define this to convert stab register numbers (as gotten from `r'
     declarations) into GDB regnums.  If not defined, no conversion
     will be done.

`STACK_ALIGN (addr)'
     Define this to adjust the address to the alignment required for the
     processor's stack.

`STEP_SKIPS_DELAY (addr)'
     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, GDB will single-step over that
     instruction before resuming normally.  Currently only defined for
     the Mips.

`STORE_RETURN_VALUE (type, valbuf)'
     A C expression that stores a function return value of type TYPE,
     where VALBUF is the address of the value to be stored.

`SUN_FIXED_LBRAC_BUG'
     (Used only for Sun-3 and Sun-4 targets.)

`SYMBOL_RELOADING_DEFAULT'
     The default value of the `symbol-reloading' variable.  (Never
     defined in current sources.)

`TARGET_BYTE_ORDER_DEFAULT'
     The ordering of bytes in the target.  This must be either
     `BIG_ENDIAN' or `LITTLE_ENDIAN'.  This macro replaces
     TARGET_BYTE_ORDER which is deprecated.

`TARGET_BYTE_ORDER_SELECTABLE_P'
     Non-zero if the target has both `BIG_ENDIAN' and `LITTLE_ENDIAN'
     variants.  This macro replaces TARGET_BYTE_ORDER_SELECTABLE which
     is deprecated.

`TARGET_CHAR_BIT'
     Number of bits in a char; defaults to 8.

`TARGET_COMPLEX_BIT'
     Number of bits in a complex number; defaults to `2 *
     TARGET_FLOAT_BIT'.

`TARGET_DOUBLE_BIT'
     Number of bits in a double float; defaults to `8 *
     TARGET_CHAR_BIT'.

`TARGET_DOUBLE_COMPLEX_BIT'
     Number of bits in a double complex; defaults to `2 *
     TARGET_DOUBLE_BIT'.

`TARGET_FLOAT_BIT'
     Number of bits in a float; defaults to `4 * TARGET_CHAR_BIT'.

`TARGET_INT_BIT'
     Number of bits in an integer; defaults to `4 * TARGET_CHAR_BIT'.

`TARGET_LONG_BIT'
     Number of bits in a long integer; defaults to `4 *
     TARGET_CHAR_BIT'.

`TARGET_LONG_DOUBLE_BIT'
     Number of bits in a long double float; defaults to `2 *
     TARGET_DOUBLE_BIT'.

`TARGET_LONG_LONG_BIT'
     Number of bits in a long long integer; defaults to `2 *
     TARGET_LONG_BIT'.

`TARGET_PTR_BIT'
     Number of bits in a pointer; defaults to `TARGET_INT_BIT'.

`TARGET_SHORT_BIT'
     Number of bits in a short integer; defaults to `2 *
     TARGET_CHAR_BIT'.

`TARGET_READ_PC'

`TARGET_WRITE_PC (val, pid)'

`TARGET_READ_SP'

`TARGET_WRITE_SP'

`TARGET_READ_FP'

`TARGET_WRITE_FP'
     These change the behavior of `read_pc', `write_pc', `read_sp',
     `write_sp', `read_fp' and `write_fp'.  For most targets, these may
     be left undefined.  GDB will call the read and write register
     functions with the relevant `_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.

`TARGET_VIRTUAL_FRAME_POINTER(pc,regp,offsetp)'
     Returns a `(register, offset)' pair representing the virtual frame
     pointer in use at the code address `"pc"'.  If virtual frame
     pointers are not used, a default definition simply returns
     `FP_REGNUM', with an offset of zero.

`USE_STRUCT_CONVENTION (gcc_p, type)'
     If defined, this must be an expression that is nonzero if a value
     of the given TYPE being returned from a function must have space
     allocated for it on the stack.  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.

`VARIABLES_INSIDE_BLOCK (desc, gcc_p)'
     For dbx-style debugging information, if the compiler puts variable
     declarations inside LBRAC/RBRAC blocks, this should be defined to
     be nonzero.  DESC is the value of `n_desc' from the `N_RBRAC'
     symbol, and GCC_P is true if GDB has noticed the presence of
     either the `GCC_COMPILED_SYMBOL' or the `GCC2_COMPILED_SYMBOL'.
     By default, this is 0.

`OS9K_VARIABLES_INSIDE_BLOCK (desc, gcc_p)'
     Similarly, for OS/9000.  Defaults to 1.

   Motorola M68K target conditionals.

`BPT_VECTOR'
     Define this to be the 4-bit location of the breakpoint trap
     vector.  If not defined, it will default to `0xf'.

`REMOTE_BPT_VECTOR'
     Defaults to `1'.

Adding a New Target
===================

   The following files define a target to GDB:

`gdb/config/ARCH/TTT.mt'
     Contains a Makefile fragment specific to this target.  Specifies
     what object files are needed for target TTT, by defining
     `TDEPFILES=...'.  Also specifies the header file which describes
     TTT, by defining `TM_FILE= tm-TTT.h'.  You can also define
     `TM_CFLAGS', `TM_CLIBS', `TM_CDEPS', but these are now deprecated
     and may go away in future versions of GDB.

`gdb/config/ARCH/tm-TTT.h'
     (`tm.h' is a link to this file, created by configure).  Contains
     macro definitions about the target machine's registers, stack frame
     format and instructions.

`gdb/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
     `tm-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.

`gdb/config/ARCH/tm-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 `tm-TTT.h'.  It can be shared among many targets that
     use the same processor.

`gdb/ARCH-tdep.c'
     Similarly, there are often common subroutines that are shared by
     all target machines that use this particular architecture.

   If you are adding a new operating system for an existing CPU chip,
add a `config/tm-OS.h' file that describes the operating system
facilities that are unusual (extra symbol table info; the breakpoint
instruction needed; etc).  Then write a `ARCH/tm-OS.h' that just
`#include's `tm-ARCH.h' and `config/tm-OS.h'.


File: gdbint.info,  Node: Target Vector Definition,  Next: Native Debugging,  Prev: Target Architecture Definition,  Up: Top

Target Vector Definition
************************

   The target vector defines the interface between GDB's abstract
handling of target systems, and the nitty-gritty code that actually
exercises control over a process or a serial port.  GDB includes some
30-40 different target vectors; however, each configuration of GDB
includes only a few of them.

File Targets
============

   Both executables and core files have target vectors.

Standard Protocol and Remote Stubs
==================================

   GDB's file `remote.c' talks a serial protocol to code that runs in
the target system.  GDB provides several sample "stubs" that can be
integrated into target programs or operating systems for this purpose;
they are named `*-stub.c'.

   The GDB 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 trap_low:

  1. %l1 and %l2 contain pc and npc respectively at the time of the trap

  2. traps are disabled

  3. you are in the correct trap window


   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 `exceptionHandler()',
which is provided by the external environment.  For instance, this could
setup 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 `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 GDB.

ROM Monitor Interface
=====================

Custom Protocols
================

Transport Layer
===============

Builtin Simulator
=================


File: gdbint.info,  Node: Native Debugging,  Next: Support Libraries,  Prev: Target Vector Definition,  Up: Top

Native Debugging
****************

   Several files control GDB's configuration for native support:

`gdb/config/ARCH/XYZ.mh'
     Specifies Makefile fragments needed when hosting *or native* on
     machine XYZ.  In particular, this lists the required
     native-dependent object files, by defining `NATDEPFILES=...'.
     Also specifies the header file which describes native support on
     XYZ, by defining `NAT_FILE= nm-XYZ.h'.  You can also define
     `NAT_CFLAGS', `NAT_ADD_FILES', `NAT_CLIBS', `NAT_CDEPS', etc.; see
     `Makefile.in'.

`gdb/config/ARCH/nm-XYZ.h'
     (`nm.h' is a link to this file, created by configure).  Contains C
     macro definitions describing the native system environment, such as
     child process control and core file support.

`gdb/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.

   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 `nm-XYZ.h' file.  If these routines work for the XYZ
host, you can just include the generic file's name (with `.o', not
`.c') in `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 `XYZ-nat.c', and put `XYZ-nat.o' into
`NATDEPFILES'.

`inftarg.c'
     This contains the *target_ops vector* that supports Unix child
     processes on systems which use ptrace and wait to control the
     child.

`procfs.c'
     This contains the *target_ops vector* that supports Unix child
     processes on systems which use /proc to control the child.

`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.

`infptrace.c'
     This is the low level interface to inferior processes for systems
     using the Unix `ptrace' call in a vanilla way.

Native core file Support
========================

`core-aout.c::fetch_core_registers()'
     Support for reading registers out of a core file.  This routine
     calls `register_addr()', see below.  Now that BFD is used to read
     core files, virtually all machines should use `core-aout.c', and
     should just provide `fetch_core_registers' in `XYZ-nat.c' (or
     `REGISTER_U_ADDR' in `nm-XYZ.h').

`core-aout.c::register_addr()'
     If your `nm-XYZ.h' file defines the macro `REGISTER_U_ADDR(addr,
     blockend, regno)', it should be defined to set `addr' to the
     offset within the `user' struct of GDB register number `regno'.
     `blockend' is the offset within the "upage" of `u.u_ar0'.  If
     `REGISTER_U_ADDR' is defined, `core-aout.c' will define the
     `register_addr()' function and use the macro in it.  If you do not
     define `REGISTER_U_ADDR', but you are using the standard
     `fetch_core_registers()', you will need to define your own version
     of `register_addr()', put it into your `XYZ-nat.c' file, and be
     sure `XYZ-nat.o' is in the `NATDEPFILES' list.  If you have your
     own `fetch_core_registers()', you may not need a separate
     `register_addr()'.  Many custom `fetch_core_registers()'
     implementations simply locate the registers themselves.

   When making GDB 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 `bfd/trad-core.c'.
First, use whatever `#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 `machine/reg.h'), and an include file that
defines whatever header exists on a core file (e.g. the u-area or a
`struct core').  Then modify `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 GDB, you need a matching routine called
`fetch_core_registers()'.  If you can use the generic one, it's in
`core-aout.c'; if not, it's in your `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 GDB's "registers" array.

   If your system uses `/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.

ptrace
======

/proc
=====

win32
=====

shared libraries
================

Native Conditionals
===================

   When GDB 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
`nm-SYSTEM.h'.

`ATTACH_DETACH'
     If defined, then GDB will include support for the `attach' and
     `detach' commands.

`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 `xm-SYSTEM.h' files
     currently.]

`FETCH_INFERIOR_REGISTERS'
     Define this if the native-dependent code will provide its own
     routines `fetch_inferior_registers' and `store_inferior_registers'
     in `HOST-nat.c'.  If this symbol is *not* defined, and
     `infptrace.c' is included in this configuration, the default
     routines in `infptrace.c' are used for these functions.

`FILES_INFO_HOOK'
     (Only defined for Convex.)

`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,
     /proc support uses this to decide whether floats are in use on
     this target.

`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 <setjmp.h> is needed to define it.

     This macro determines the target PC address that longjmp() will
     jump to, assuming that we have just stopped at a longjmp
     breakpoint.  It takes a CORE_ADDR * as argument, and stores the
     target PC value through this pointer.  It examines the current
     state of the machine as needed.

`KERNEL_U_ADDR'
     Define this to the address of the `u' structure (the "user
     struct", also known as the "u-page") in kernel virtual memory.  GDB
     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.

`KERNEL_U_ADDR_BSD'
     Define this to cause GDB to determine the address of `u' at
     runtime, by using Berkeley-style `nlist' on the kernel's image in
     the root directory.

`KERNEL_U_ADDR_HPUX'
     Define this to cause GDB to determine the address of `u' at
     runtime, by using HP-style `nlist' on the kernel's image in the
     root directory.

`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.

`PROC_NAME_FMT'
     Defines the format for the name of a `/proc' device.  Should be
     defined in `nm.h' *only* in order to override the default
     definition in `procfs.c'.

`PTRACE_FP_BUG'
     mach386-xdep.c

`PTRACE_ARG3_TYPE'
     The type of the third argument to the `ptrace' system call, if it
     exists and is different from `int'.

`REGISTER_U_ADDR'
     Defines the offset of the registers in the "u area".

`SHELL_COMMAND_CONCAT'
     If defined, is a string to prefix on the shell command used to
     start the inferior.

`SHELL_FILE'
     If defined, this is the name of the shell to use to run the
     inferior.  Defaults to `"/bin/sh"'.

`SOLIB_ADD (filename, from_tty, targ)'
     Define this to expand into an expression that will cause the
     symbols in FILENAME to be added to GDB's symbol table.

`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.

`START_INFERIOR_TRAPS_EXPECTED'
     When starting an inferior, GDB 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.

`SVR4_SHARED_LIBS'
     Define this to indicate that SVR4-style shared libraries are in
     use.

`USE_PROC_FS'
     This determines whether small routines in `*-tdep.c', which
     translate register values between GDB's internal representation
     and the /proc representation, are compiled.

`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
     `infptrace.c' are being used (that is, `infptrace.c' is configured
     in, and `FETCH_INFERIOR_REGISTERS' is not defined).  If the
     default value from `infptrace.c' is good enough, leave it
     undefined.

     The default value means that u.u_ar0 *points to* the location of
     the registers.  I'm guessing that `#define U_REGS_OFFSET 0' means
     that u.u_ar0 *is* the location of the registers.

`CLEAR_SOLIB'
     objfiles.c

`DEBUG_PTRACE'
     Define this to debug ptrace calls.


File: gdbint.info,  Node: Support Libraries,  Next: Coding,  Prev: Native Debugging,  Up: Top

Support Libraries
*****************

BFD
===

   BFD provides support for GDB in several ways:

*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.

*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).
     GDB simply calls BFD to read or write section X at byte offset Y
     for length Z.

*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.

*locating the symbol information*
     GDB uses an internal interface of BFD to determine where to find
     the symbol information in an executable file or symbol-file.  GDB
     itself handles the reading of symbols, since BFD does not
     "understand" debug symbols, but GDB uses BFD's cached information
     to find the symbols, string table, etc.

opcodes
=======

   The opcodes library provides GDB's disassembler.  (It's a separate
library because it's also used in binutils, for `objdump').

readline
========

mmalloc
=======

libiberty
=========

gnu-regex
=========

   Regex conditionals.

`C_ALLOCA'

`NFAILURES'

`RE_NREGS'

`SIGN_EXTEND_CHAR'

`SWITCH_ENUM_BUG'

`SYNTAX_TABLE'

`Sword'

`sparc'
include
=======


File: gdbint.info,  Node: Coding,  Next: Porting GDB,  Prev: Support Libraries,  Up: Top

Coding
******

   This chapter covers topics that are lower-level than the major
algorithms of GDB.

Cleanups
========

   Cleanups are a structured way to deal with things that need to be
done later.  When your code does something (like `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:

`struct cleanup *OLD_CHAIN;'
     Declare a variable which will hold a cleanup chain handle.

`OLD_CHAIN = make_cleanup (FUNCTION, ARG);'
     Make a cleanup which will cause FUNCTION to be called with ARG (a
     `char *') later.  The result, OLD_CHAIN, is a handle that can be
     passed to `do_cleanups' or `discard_cleanups' later.  Unless you
     are going to call `do_cleanups' or `discard_cleanups' yourself,
     you can ignore the result from `make_cleanup'.

`do_cleanups (OLD_CHAIN);'
     Perform all cleanups done since `make_cleanup' returned OLD_CHAIN.
     E.g.:
          make_cleanup (a, 0);
          old = make_cleanup (b, 0);
          do_cleanups (old);

     will call `b()' but will not call `a()'.  The cleanup that calls
     `a()' will remain in the cleanup chain, and will be done later
     unless otherwise discarded.

`discard_cleanups (OLD_CHAIN);'
     Same as `do_cleanups' except that it just removes the cleanups from
     the chain and does not call the specified functions.

   Some functions, e.g. `fputs_filtered()' or `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 `longjmp'
instead).

Wrapping Output Lines
=====================

   Output that goes through `printf_filtered' or `fputs_filtered' or
`fputs_demangled' needs only to have calls to `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 `wrap_here' is an indentation string which is
printed *only* if the line breaks there.  This argument is saved away
and used later.  It must remain valid until the next call to
`wrap_here' or until a newline has been printed through the
`*_filtered' functions.  Don't pass in a local variable and then return!

   It is usually best to call `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 ("`printf'") output.  Symbol reading routines that print
warnings are a good example.

GDB Coding Standards
====================

   GDB follows the GNU coding standards, as described in
`etc/standards.texi'.  This file is also available for anonymous FTP
from GNU archive sites.  GDB takes a strict interpretation of the
standard; in general, when the GNU standard recommends a practice but
does not require it, GDB requires it.

   GDB follows an additional set of coding standards specific to GDB,
as described in the following sections.

   You can configure with `--enable-build-warnings' to get GCC to check
on a number of these rules.  GDB sources ought not to engender any
complaints, unless they are caused by bogus host systems.  (The exact
set of enabled warnings is currently `-Wall -Wpointer-arith
-Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations'.

Formatting
----------

   The standard GNU recommendations for formatting must be followed
strictly.

   Note that while in a definition, the function's name must be in
column zero; in a function declaration, the name must be on the same
line as the return type.

   In addition, 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 diff and patch.

Comments
--------

   The standard GNU requirements on comments must be followed strictly.

   Block comments must appear in the following form, with no `/*'- or
'*/'-only lines, and no leading `*':

     /* 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 GDB should read more commands.  */

   (Note that this format is encouraged by Emacs; tabbing for a
multi-line comment works correctly, and 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.

C Usage
-------

   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.

   Use functions freely.  There are only a handful of compute-bound
areas in GDB that might be affected by the overhead of a function call,
mainly in symbol reading.  Most of GDB'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.

Function Prototypes
-------------------

   Prototypes must be used to *declare* functions but never to *define*
them.  Prototypes for GDB functions must include both the argument type
and name, with the name matching that used in the actual function
definition.

   For the sake of compatibility with pre-ANSI compilers, define
prototypes with the `PARAMS' macro:

     extern int memory_remove_breakpoint PARAMS ((CORE_ADDR addr,
                                                  char *contents_cache));

   Note the double parentheses around the parameter types.  This allows
an arbitrary number of parameters to be described, without freaking out
the C preprocessor.  When the function has no parameters, it should be
described like:

     extern void noprocess PARAMS ((void));

   The `PARAMS' macro expands to its argument in ANSI C, or to a simple
`()' in traditional C.

   All external functions should have a `PARAMS' declaration in a
header file that callers include, except for `_initialize_*' functions,
which must be external so that `init.c' construction works, but
shouldn't be visible to random source files.

   All static functions must be declared in a block near the top of the
source file.

Clean Design
------------

   In addition to getting the syntax right, there's the little question
of semantics.  Some things are done in certain ways in GDB because long
experience has shown that the more obvious ways caused various kinds of
trouble.

   You can't assume the byte order of anything that comes from a target
(including VALUEs, object files, and instructions).  Such things must
be byte-swapped using `SWAP_TARGET_AND_HOST' in GDB, or one of the swap
routines defined in `bfd.h', such as `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 `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.

   Insertion of new `#ifdef''s will be frowned upon.  It's much better
to write the code portably than to conditionalize it for various
systems.

   New `#ifdef''s which test for specific compilers or manufacturers or
operating systems are unacceptable.  All `#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.  If a
hook is needed at that point, invent a generic hook and define it for
your configuration, with something like:

     #ifdef	WRANGLE_SIGNALS
        WRANGLE_SIGNALS (signo);
     #endif

   In your host, target, or native configuration file, as appropriate,
define `WRANGLE_SIGNALS' to do the machine-dependent thing.  Take a bit
of care in defining the hook, so that it can be used by other ports in
the future, if they need a hook in the same place.

   If the hook is not defined, the code should do whatever "most"
machines want.  Using `#ifdef', as above, is the preferred way to do
this, but sometimes that gets convoluted, in which case use

     #ifndef SPECIAL_FOO_HANDLING
     #define SPECIAL_FOO_HANDLING(pc, sp) (0)
     #endif

   where the macro is used or in an appropriate header file.

   Whether to include a "small" hook, a hook around the exact pieces of
code which are system-dependent, or whether to replace a whole function
with a hook depends on the case.  A good example of this dilemma can be
found in `get_saved_register'.  All machines that GDB 2.8 ran on just
needed the `FRAME_FIND_SAVED_REGS' hook to find the saved registers.
Then the SPARC and Pyramid came along, and `HAVE_REGISTER_WINDOWS' and
`REGISTER_IN_WINDOW_P' were introduced.  Then the 29k and 88k required
the `GET_SAVED_REGISTER' hook.  The first three are examples of small
hooks; the latter replaces a whole function.  In this specific case, it
is useful to have both kinds; it would be a bad idea to replace all the
uses of the small hooks with `GET_SAVED_REGISTER', since that would
result in much duplicated code.  Other times, duplicating a few lines
of code here or there is much cleaner than introducing a large number
of small hooks.

   Another way to generalize GDB along a particular interface is with an
attribute struct.  For example, GDB has been generalized to handle
multiple kinds of remote interfaces - not by #ifdef's everywhere, but
by defining the "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.
`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 GDB's access to multiple source languages.

   Please avoid duplicating code.  For example, in GDB 3.x all the code
interfacing between `ptrace' and the rest of GDB was duplicated in
`*-dep.c', and so changing something was very painful.  In GDB 4.x,
these have all been consolidated into `infptrace.c'.  `infptrace.c' can
deal with variations between systems the same way any
system-independent file would (hooks, #if defined, etc.), and machines
which are radically different don't need to use infptrace.c at all.