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INFO-DIR-SECTION Programming & development tools.

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* Gdb-Internals: (gdbint).      The GNU debugger's internals.

END-INFO-DIR-ENTRY

END-INFO-DIR-ENTRY

   This file documents the internals of the GNU debugger GDB.

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."

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

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 `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.

`I386_USE_GENERIC_WATCHPOINTS'

     An x86-based machine can define this to use the generic x86

     watchpoint support; see *Note I386_USE_GENERIC_WATCHPOINTS:

     Algorithms.

`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.

`PREPARE_TO_PROCEED (SELECT_IT)'

     This (ugly) macro allows a native configuration to customize the

     way the `proceed' function in `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 GDB must step over it first.

     If defined, `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 SELECT_IT is non-zero,

     it should reselect the old thread.

`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'

     See `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'

     See `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.

ISO-C

-----

   GDB assumes an ISO-C compliant compiler.

   GDB does not assume an ISO-C or POSIX compliant C library.

Memory Management

-----------------

   GDB does not use the functions `malloc', `realloc', `calloc', `free'

and `asprintf'.

   GDB uses the functions `xmalloc', `xrealloc' and `xcalloc' when

allocating memory.  Unlike `malloc' et.al.  these functions do not

return when the memory pool is empty.  Instead, they unwind the stack

using cleanups.  These functions return `NULL' when requested to

allocate a chunk of memory of size zero.

   _Pragmatics: By using these functions, the need to check every

memory allocation is removed.  These functions provide portable

behavior._

   GDB does not use the function `free'.

   GDB uses the function `xfree' to return memory to the memory pool.

Consistent with ISO-C, this function ignores a request to free a `NULL'

pointer.

   _Pragmatics: On some systems `free' fails when passed a `NULL'

pointer._

   GDB can use the non-portable function `alloca' for the allocation of

small temporary values (such as strings).

   _Pragmatics: This function is very non-portable.  Some systems

restrict the memory being allocated to no more than a few kilobytes._

   GDB uses the string function `xstrdup' and the print function

`xasprintf'.

   _Pragmatics: `asprintf' and `strdup' can fail.  Print functions such

as `sprintf' are very prone to buffer overflow errors._

Compiler Warnings

-----------------

   With few exceptions, developers should include the configuration

option `--enable-gdb-build-warnings=,-Werror' when building GDB.  The

exceptions are listed in the file `gdb/MAINTAINERS'.

   This option causes GDB (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:

`-Wimplicit'

     Since GDB 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

     `-Wstrict-prototypes'.

`-Wreturn-type'

     Such code often appears to work except on instruction set

     architectures that use register windows.

`-Wcomment'

`-Wtrigraphs'

`-Wformat'

     Since GDB uses the `format printf' attribute on all `printf' like

     functions this checks not just `printf' calls but also calls to

     functions such as `fprintf_unfiltered'.

`-Wparentheses'

     This warning includes uses of the assignment operator within an

     `if' statement.

`-Wpointer-arith'

`-Wuninitialized'

   _Pragmatics: Due to the way that GDB is implemented most functions

have unused parameters.  Consequently the warning `-Wunused-parameter'

is precluded from the list.  The macro `ATTRIBUTE_UNUSED' is not used

as it leads to false negatives -- it is not an error to have

`ATTRIBUTE_UNUSED' on a parameter that is being used.  The options

`-Wall' and `-Wunused' are also precluded because they both include

`-Wunused-parameter'._

   _Pragmatics: GDB has not simply accepted the warnings enabled by

`-Wall -Werror -W...'.  Instead it is selecting warnings when and where

their benefits can be demonstrated._

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.

     /* Declaration */

     static void foo (void);

     /* Definition */

     void

     foo (void)

     {

     }

   _Pragmatics: This simplifies scripting.  Function definitions can be

found using `^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 `diff' and `patch' utilities.

   Pointers are declared using the traditional K&R C style:

     void *foo;

and not:

     void * foo;

     void* foo;

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.

   _Macros are bad, M'kay._

   Declarations like `struct foo *' should be used in preference to

declarations like `typedef struct foo { ... } *foo_ptr'.

Function Prototypes

-------------------

   Prototypes must be used when both _declaring_ and _defining_ a

function.  Prototypes for GDB 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 `_initialize_*' functions, which must

be external so that `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.

Internal Error Recovery

-----------------------

   During its execution, GDB 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 GDB has detected, at run

time, a corrupt or erroneous situtation.

   When reporting an internal error, GDB uses `internal_error' and

`gdb_assert'.

   GDB must not call `abort' or `assert'.

   _Pragmatics: There is no `internal_warning' function.  Either the

code detected a user error, recovered from it and issued a `warning' or

the code failed to correctly recover from the user error and issued an

`internal_error'._

File Names

----------

   Any file used when building the core of GDB must be in lower case.

Any file used when building the core of GDB must be 8.3 unique.  These

requirements apply to both source and generated files.

   _Pragmatics: The core of GDB must be buildable on many platforms

including DJGPP and MacOS/HFS.  Every time an unfriendly file is

introduced to the build process both `Makefile.in' and `configure.in'

need to be modified accordingly.  Compare the convoluted conversion

process needed to transform `COPYING' into `copying.c' with the

conversion needed to transform `version.in' into `version.c'._

   Any file non 8.3 compliant file (that is not used when building the

core of GDB) must be added to `gdb/config/djgpp/fnchange.lst'.

   _Pragmatics: This is clearly a compromise._

   When GDB has a local version of a system header file (ex `string.h')

the file name based on the POSIX header prefixed with `gdb_'

(`gdb_string.h').

   For other files `-' is used as the separator.

Include Files

-------------

   All `.c' files should include `defs.h' first.

   All `.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 `defs.h', a

header file should explictily include the header declaring any

`typedefs' et.al. it refers to.

   `extern' declarations should never appear in `.c' files.

   All include files should be wrapped in:

     #ifndef INCLUDE_FILE_NAME_H

     #define INCLUDE_FILE_NAME_H

     header body

     #endif

Clean Design and Portable Implementation

----------------------------------------

   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.

   One particularly notorious area where system dependencies tend to

creep in is handling of file names.  The mainline GDB code assumes

Posix semantics of file names: absolute file names begin with a forward

slash `/', 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:

`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.

`IS_DIR_SEPARATOR (C'

     Evaluates to a non-zero value if C is a directory separator

     character.  On Unix and GNU/Linux systems, only a slash `/' is

     such a character, but on Windows, both `/' and `\' will pass.

`IS_ABSOLUTE_PATH (FILE)'

     Evaluates to a non-zero value if FILE is an absolute file name.

     For Unix and GNU/Linux hosts, a name which begins with a slash `/'

     is absolute.  On DOS and Windows, `d:/foo' and `x:\bar' are also

     absolute file names.

`FILENAME_CMP (F1, F2)'

     Calls a function which compares file names F1 and F2 as

     appropriate for the underlying host filesystem.  For Posix systems,

     this simply calls `strcmp'; on case-insensitive filesystems it

     will call `strcasecmp' instead.

`DIRNAME_SEPARATOR'

     Evaluates to a character which separates directories in

     `PATH'-style lists, typically held in environment variables.  This

     character is `:' on Unix, `;' on DOS and Windows.

`SLASH_STRING'

     This evaluates to a constant string you should use to produce an

     absolute filename from leading directories and the file's basename.

     `SLASH_STRING' is `"/"' on most systems, but might be `"\\"' for

     some Windows-based ports.

   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 `dirname' and `basename'

library functions (available in `libiberty' for platforms which don't

provide them), instead of searching for a slash with `strrchr'.

   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.

   All debugging code must be controllable using the `set debug MODULE'

command.  Do not use `printf' to print trace messages.  Use

`fprintf_unfiltered(gdb_stdlog, ...'.  Do not use `#ifdef DEBUG'.

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

Porting GDB

***********

   Most of the work in making GDB 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

XYZ (e.g.,  `sun4'), and its full three-part configuration name is

`ARCH-XVEND-XOS' (e.g., `sparc-sun-sunos4').  In particular:

   * In the top level directory, edit `config.sub' and add ARCH, XVEND,

     and XOS to the lists of supported architectures, vendors, and

     operating systems near the bottom of the file.  Also, add XYZ as

     an alias that maps to `ARCH-XVEND-XOS'.  You can test your changes

     by running