     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, 1991, 1992, 1993 Free Software Foundation, Inc. Contributed by Cygnus Support.  Written by John Gilmore.

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).

This documents the internals of the GNU debugger, GDB.  It is a collection of miscellaneous information with little form at this point. Mostly, it is a repository into which you can put information about GDB as you discover it (or as you design changes to GDB).

The README File
***************

Check the README file, it often has useful information that does not appear anywhere else in the directory.

Getting Started Working on GDB
******************************

GDB 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 GDB Internals manual, has information which applies generally to many parts of GDB.

     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 GDB; feel free to submit a bug report, with a suggested comment if you can figure out what the comment should say (see Submitting Patches).  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 has a list of macros (see Host Conditionals, see Target Conditionals, see Native Conditionals, and see Obsolete Conditionals) with some documentation.

     Start with the header files.  Once you some idea of how GDB's internal symbol tables are stored (see symtab.h, 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 GDB, 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 GDB to start with, you can find more specifically the part you are looking for by stepping through each function with the next command.  Do not use 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.

     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 GDB user, you know that the step command invokes single-stepping.  The command is invoked via command tables (see command.h); by convention the function which actually performs the command is formed by taking the name of the command and adding _command, or in the case of an info subcommand, _info.  For example, the step command invokes the step_command function and the info display command invokes display_info.  When this convention is not followed, you might have to use grep or M-x tags-search in emacs, or run GDB on itself and set a breakpoint in execute_command.

     If all of the above fail, it may be appropriate to ask for information on bug-gdb.  But never post a generic question like ``I was wondering if anyone could give me some tips about understanding GDB''---if we had some magic secret we would put it in this manual. Suggestions for improving the manual are always welcome, of course.

Good luck!

Debugging GDB with itself
*************************

If gdb 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 4.0, a program can't be running in one process while it is being debugged in another.  Rather than typing the command ./gdb ./gdb, which works on Suns and such, you can copy gdb to gdb2 and then type ./gdb ./gdb2.

When you run gdb in the gdb source directory, it will read a .gdbinit file that sets up some simple things to make debugging gdb easier.  The info command, when executed without a subcommand in a gdb being debugged by gdb, will pop you back up to the top level gdb.  See .gdbinit for details.

If you use emacs, you will probably want to do a 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 M-.

Also, make sure that you've either compiled gdb with your local cc, or have run fixincludes if you are compiling with gcc.

Defining a New Host or Target Architecture
******************************************

When building support for a new host and/or target, much of the work you need to do is handled by specifying configuration files; see Adding a New Configuration.  Further work can be divided into ``host-dependent'' (see Adding a New Host) and ``target-dependent'' (see Adding a New Target).  The following discussion is meant to explain the difference between hosts and targets.

What is considered ``host-dependent'' versus ``target-dependent''?
==================================================================

Host refers to attributes of the system where GDB runs. 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 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 upage, running 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 #include files that are only available on the host system. Core file handling and setjmp handling are two common cases.

When you want to make GDB work ``native'' on a particular machine, you have to include all three kinds of information.

The dependent information in GDB is organized into files by naming conventions.

Host-Dependent Files

config/*/*.mh
     Sets Makefile parameters

config/*/xm-*.h
     Global #include's and #define's and definitions

*-xdep.c
     Global variables and functions

Native-Dependent Files

config/*/*.mh
     Sets Makefile parameters (for both host and native)

config/*/nm-*.h
     #include's and #define's and definitions.  This file is only included by the small number of modules that need it, so beware of doing feature-test #define's from its macros.

*-nat.c
     global variables and functions

Target-Dependent Files

config/*/*.mt
     Sets Makefile parameters

config/*/tm-*.h
     Global #include's and #define's and definitions

*-tdep.c
     Global variables and functions

At this writing, most supported hosts have had their host and native dependencies sorted out properly.  There are a few stragglers, which can be recognized by the absence of NATDEPFILES lines in their config/*/*.mh.

Adding a New Configuration
**************************

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 XXX (e.g. sun4), and its full three-part configuration name is XARCH-XVEND-XOS (e.g.  sparc-sun-sunos4).  In particular:

In the top level directory, edit config.sub and add XARCH, XVEND, and XOS to the lists of supported architectures, vendors, and operating systems near the bottom of the file.  Also, add XXX as an alias that maps to XARCH-XVEND-XOS.  You can test your changes by running

     ./config.sub XXX

and

     ./config.sub XARCH-XVEND-XOS

which should both respond with XARCH-XVEND-XOS and no error messages.

Now, go to the bfd directory and create a new file bfd/hosts/h-XXX.h.  Examine the other h-*.h files as templates, and create one that brings in the right include files for your system, and defines any host-specific macros needed by BFD, the Binutils, GNU LD, or the Opcodes directories. (They all share the bfd hosts directory and the configure.host file.)

Then edit bfd/configure.host.  Add a line to recognize your XARCH-XVEND-XOS configuration, and set my_host to XXX when you recognize it.  This will cause your file h-XXX.h to be linked to sysdep.h at configuration time.  When creating the line that recognizes your configuration, only match the fields that you really need to match; e.g. don't match match the architecture or manufacturer if the OS is sufficient to distinguish the configuration that your h-XXX.h file supports. Don't match the manufacturer name unless you really need to. This should make future ports easier.

Also, if this host requires any changes to the Makefile, create a file bfd/config/XXX.mh, which includes the required lines.

It's possible that the libiberty and readline directories won't need any changes for your configuration, but if they do, you can change the configure.in file there to recognize your system and map to an mh-XXX file.  Then add mh-XXX to the config/ subdirectory, to set any makefile variables you need.  The only current options in there are things like -DSYSV. (This mh-XXX naming convention differs from elsewhere in GDB, by historical accident.  It should be cleaned up so that all such files are called XXX.mh.)

Aha!  Now to configure GDB itself!  Edit gdb/configure.in to recognize your system and set gdb_host to XXX, and (unless your desired target is already available) also set gdb_target to something appropriate (for instance, XXX).  To handle new hosts, modify the segment after the comment # per-host; to handle new targets, modify after # per-target.

Finally, you'll need to specify and define GDB's host-, native-, and target-dependent .h and .c files used for your configuration; the next two chapters discuss those.

Adding a New Host
*****************

Once you have specified a new configuration for your host (see Adding a New Configuration), there are three remaining pieces to making GDB work on a new machine.  First, you have to make it host on the new machine (compile there, handle that machine's terminals properly, etc).  If you will be cross-debugging to some other kind of system that's already supported, you are done.

If you want to use GDB to debug programs that run on the new machine, you have to get it to understand the machine's object files, symbol files, and interfaces to processes; see Adding a New Target and see Adding a New Native Configuration

Several files control GDB's configuration for host systems:

gdb/config/ARCH/XXX.mh
     Specifies Makefile fragments needed when hosting on machine XXX. In particular, this lists the required machine-dependent object files, by defining XDEPFILES=....  Also specifies the header file which describes host XXX, by defining XM_FILE= xm-XXX.h.  You can also define CC, REGEX and REGEX1, SYSV_DEFINE, XM_CFLAGS, XM_ADD_FILES, XM_CLIBS, XM_CDEPS, etc.; see Makefile.in.

gdb/config/ARCH/xm-XXX.h
     (xm.h is a link to this file, created by configure). Contains C macro definitions describing the host system environment, such as byte order, host C compiler and library, ptrace support, and core file structure.  Crib from existing xm-*.h files to create a new one.

gdb/XXX-xdep.c
     Contains any miscellaneous C code required for this machine as a host.  On many machines it doesn't exist at all.  If it does exist, put XXX-xdep.o into the XDEPFILES line in gdb/config/mh-XXX.

Generic Host Support Files
--------------------------

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 xm-XXX.h file.  If these routines work for the XXX host, you can just include the generic file's name (with .o, not .c) in 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 XXX-xdep.c, and put XXX-xdep.o into XDEPFILES.

ser-bsd.c
     This contains serial line support for Berkeley-derived Unix systems.

ser-go32.c
     This contains serial line support for 32-bit programs running under DOS using the GO32 execution environment.

ser-termios.c
     This contains serial line support for System V-derived Unix systems.

Now, you are now ready to try configuring GDB to compile using your system as its host.  From the top level (above bfd, gdb, etc), do:

     ./configure XXX +target=vxworks960

This will configure your system to cross-compile for VxWorks on the Intel 960, which is probably not what you really want, but it's a test case that works at this stage.  (You haven't set up to be able to debug programs that run on XXX yet.)

If this succeeds, you can try building it all with:

     make

Repeat until the program configures, compiles, links, and runs. When run, it won't be able to do much (unless you have a VxWorks/960 board on your network) but you will know that the host support is pretty well done.

Good luck!  Comments and suggestions about this section are particularly welcome; send them to bug-gdb@prep.ai.mit.edu.

Adding a New Native Configuration
*********************************

If you are making GDB run native on the XXX machine, you have plenty more work to do.  Several files control GDB's configuration for native support:

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

gdb/config/ARCH/nm-XXX.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. Crib from existing nm-*.h files to create a new one.

gdb/XXX-nat.c
     Contains any miscellaneous C code required for this native support of this machine.  On some machines it doesn't exist at all.

Generic Native Support Files
----------------------------

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-XXX.h file.  If these routines work for the XXX 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 XXX-nat.c, and put XXX-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.

coredep.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 coredep.c, and should just provide fetch_core_registers in XXX-nat.c (or REGISTER_U_ADDR in nm-XXX.h).

coredep.c::register_addr()
     If your nm-XXX.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, coredep.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 XXX-nat.c file, and be sure XXX-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 coredep.c; if not, it's in your XXX-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. (see Defining a New Host or Target Architecture, for more info about this.)

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.

Adding a New Target
*******************

For a new target called TTT, first specify the configuration as described in Adding a New Configuration.  If your new target is the same as your new host, you've probably already done that.

A variety of files specify attributes of the GDB target environment:

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, and other Makefile variables here; see Makefile.in.

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. Crib from existing tm-*.h files when building a new one.

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.

gdb/exec.c
     Defines functions for accessing files that are executable on the target system.  These functions open and examine an exec file, extract data from one, write data to one, print information about one, etc.  Now that executable files are handled with BFD, every target should be able to use the generic exec.c rather than its own custom code.

gdb/ARCH-pinsn.c
     Prints (disassembles) the target machine's instructions. This file is usually shared with other target machines which use the same processor, which is why it is ARCH-pinsn.c rather than TTT-pinsn.c.

gdb/ARCH-opcode.h
     Contains some large initialized data structures describing the target machine's instructions. This is a bit strange for a .h file, but it's OK since it is only included in one place.  ARCH-opcode.h is shared between the debugger and the assembler, if the GNU assembler has been ported to the target machine.

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-XXX.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.

When adding support for a new target machine, there are various areas of support that might need change, or might be OK.

If you are using an existing object file format (a.out or COFF), there is probably little to be done.  See bfd/doc/bfd.texinfo for more information on writing new a.out or COFF versions.

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 right now.  Basically you must build a transfer vector (of type bfd_target), which will mean writing all the required routines, and add it to the list in bfd/targets.c.

You must then arrange for the BFD code to provide access to the debugging symbols.  Generally GDB will have to call swapping routines from BFD and a few other BFD internal routines to locate the debugging information.  As much as possible, GDB 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 bfd/libxxx.h, which is included by GDB.

If you are adding a new operating system for an existing CPU chip, add a tm-XOS.h file that describes the operating system facilities that are unusual (extra symbol table info; the breakpoint instruction needed; etc).  Then write a tm-XARCH-XOS.h that just #includes tm-XARCH.h and tm-XOS.h.  (Now that we have three-part configuration names, this will probably get revised to separate the XOS configuration from the XARCH configuration.)

Adding a Source Language to GDB
*******************************

To add other languages to GDB's expression parser, follow the following steps:

Create the expression parser.

     This should reside in a file LANG-exp.y.  Routines for building parsed expressions into a union exp_element list are in parse.c.

     Since we can't depend upon everyone having Bison, and YACC produces parsers that define a bunch of global names, the following lines must be included at the top of the YACC parser, to prevent the various parsers from defining the same global names:

          #define yyparse 	LANG_parse
          #define yylex 	LANG_lex
          #define yyerror 	LANG_error
          #define yylval 	LANG_lval
          #define yychar 	LANG_char
          #define yydebug 	LANG_debug
          #define yypact  	LANG_pact
          #define yyr1		LANG_r1
          #define yyr2		LANG_r2
          #define yydef		LANG_def
          #define yychk		LANG_chk
          #define yypgo		LANG_pgo
          #define yyact  	LANG_act
          #define yyexca  	LANG_exca
          #define yyerrflag  	LANG_errflag
          #define yynerrs  	LANG_nerrs

     At the bottom of your parser, define a struct language_defn and initialize it with the right values for your language.  Define an initialize_LANG routine and have it call add_language(LANG_language_defn) to tell the rest of GDB that your language exists.  You'll need some other supporting variables and functions, which will be used via pointers from your LANG_language_defn.  See the declaration of struct language_defn in language.h, and the other *-exp.y files, for more information.

Add any evaluation routines, if necessary

     If you need new opcodes (that represent the operations of the language), add them to the enumerated type in expression.h.  Add support code for these operations in eval.c:evaluate_subexp().  Add cases for new opcodes in two functions from parse.c: prefixify_subexp() and length_of_subexp().  These compute the number of exp_elements that a given operation takes up.

Update some existing code

     Add an enumerated identifier for your language to the enumerated type enum language in defs.h.

     Update the routines in 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.

     Also included in language.c is the code that updates the variable current_language, and the routines that translate the language_LANG enumerated identifier into a printable string.

     Update the function _initialize_language to include your language.  This function picks the default language upon startup, so is dependent upon which languages that GDB is built for.

     Update allocate_symtab in 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.

     Add helper code to expprint.c:print_subexp() to handle any new expression opcodes you have added to expression.h.  Also, add the printed representations of your operators to op_print_tab.

Add a place of call

     Add a call to LANG_parse() and LANG_error in parse.c:parse_exp_1().

Use macros to trim code

     The user has the option of building GDB for some or all of the languages.  If the user decides to build GDB for the language LANG, then every file dependent on language.h will have the macro _LANG_LANG defined in it.  Use #ifdefs 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 GDB is not build for LANG, then LANG-exp.tab.o (the compiled form of your parser) is not linked into GDB at all.

     See the file configure.in for how GDB is configured for different languages.

Edit Makefile.in

     Add dependencies in Makefile.in.  Make sure you update the macro variables such as HFILES and OBJS, otherwise your code may not get linked in, or, worse yet, it may not get tarred into the distribution!

Configuring GDB for Release
***************************

From the top level directory (containing gdb, bfd, libiberty, and so on):

     make -f Makefile.in gdb.tar.Z

This will properly configure, clean, rebuild any files that are distributed pre-built (e.g. c-exp.tab.c or refcard.ps), and will then make a tarfile.  (If the top level directory has already beenn configured, you can just do make gdb.tar.Z instead.)

This procedure requires:

  * symbolic links

  * makeinfo (texinfo2 level)

  * TeX

  * dvips

  * yacc or bison

... and the usual slew of utilities (sed, tar, etc.).

TEMPORARY RELEASE PROCEDURE FOR DOCUMENTATION
---------------------------------------------

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 texinfo.tex needs to be included in the distribution.

For making info files, however, rather than duplicating the texinfo2 distribution, generate gdb-all.texinfo locally, and include the files gdb.info* in the distribution.  Note the plural; makeinfo will split the document into one overall file and five or so included files.

Partial Symbol Tables
*********************

GDB has three types of symbol tables.

  * full symbol tables (symtabs).  These contain the main information about symbols and addresses.

  * partial symbol tables (psymtabs).  These contain enough information to know when to read the corresponding part of the full symbol table.

  * minimal symbol tables (msymtabs).  These contain information gleaned from non-debugging symbols.

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 GDB 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.  (see 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 enum values declared at file scope.

The psymtab also contains the range of instruction addresses that the full symbol table would represent.

The idea is that there are only two ways for the user (or much of the code in the debugger) to reference a symbol:

  * 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. find_pc_function, find_pc_line, and other find_pc_... functions handle this.

  * 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. lookup_symbol does most of the work here.

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 GDB 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.

Types
*****

Fundamental Types (e.g., FT_VOID, FT_BOOLEAN).

These are the fundamental types that gdb 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 gdb knows about for all the languages that gdb knows about.

Type Codes (e.g., TYPE_CODE_PTR, TYPE_CODE_ARRAY).

Each time gdb builds an internal type, it marks it with one of these types.  The type may be a fundamental type, such as TYPE_CODE_INT, or a derived type, such as TYPE_CODE_PTR which is a pointer to another type.  Typically, several FT_* types map to one 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.

Builtin Types (e.g., builtin_type_void, builtin_type_char).

These are instances of type structs that roughly correspond to fundamental types and are created as global types for gdb to use for various ugly historical reasons.  We eventually want to eliminate these.  Note for example that builtin_type_int initialized in gdbtypes.c is basically the same as a TYPE_CODE_INT type that is initialized in c-lang.c for an FT_INTEGER fundamental type.  The difference is that the builtin_type is not associated with any particular objfile, and only one instance exists, while c-lang.c builds as many TYPE_CODE_INT types as needed, with each one associated with some particular objfile.

Binary File Descriptor Library Support for GDB
**********************************************

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.

Symbol Reading
**************

GDB reads symbols from "symbol files".  The usual symbol file is the file containing the program which gdb is debugging.  GDB can be directed to use a different file for symbols (with the ``symbol-file'' command), and it can also read more symbols via the ``add-file'' and ``load'' commands, or while reading symbols from shared libraries.

Symbol files are initially opened by symfile.c using the BFD library.  BFD identifies the type of the file by examining its header. symfile_init then uses this identification to locate a set of symbol-reading functions.

Symbol reading modules identify themselves to GDB by calling add_symtab_fns during their module initialization.  The argument to add_symtab_fns is a 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:

XXX_symfile_init(struct sym_fns *sf)

     Called from 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 XXX_symfile_init is a newly allocated struct sym_fns whose bfd field contains the BFD for the new symbol file being read.  Its private field has been zeroed, and can be modified as desired.  Typically, a struct of private information will be malloc'd, and a pointer to it will be placed in the private field.

     There is no result from XXX_symfile_init, but it can call error if it detects an unavoidable problem.

XXX_new_init()

     Called from symbol_file_add when discarding existing symbols. This function need only handle the symbol-reading module's internal state; the symbol table data structures visible to the rest of GDB will be discarded by symbol_file_add.  It has no arguments and no result. It may be called after XXX_symfile_init, if a new symbol table is being read, or may be called alone if all symbols are simply being discarded.

XXX_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)

     Called from symbol_file_add to actually read the symbols from a symbol-file into a set of psymtabs or symtabs.

     sf points to the struct sym_fns originally passed to XXX_sym_init for possible initialization.  addr is the offset between the file's specified start address and its true address in memory.  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.

In addition, if a symbol-reading module creates psymtabs when XXX_symfile_read is called, these psymtabs will contain a pointer to a function XXX_psymtab_to_symtab, which can be called from any point in the GDB symbol-handling code.

XXX_psymtab_to_symtab (struct partial_symtab *pst)

     Called from psymtab_to_symtab (or the PSYMTAB_TO_SYMTAB macro) if the psymtab has not already been read in and had its pst->symtab pointer set.  The argument is the psymtab to be fleshed-out into a symtab.  Upon return, pst->readin should have been set to 1, and 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.

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.

Frames
******

A frame is a construct that GDB uses to keep track of calling and called functions.

FRAME_FP
     in the machine description has no meaning to the machine-independent part of GDB, except that it is used when setting up a new frame from scratch, as follows:

                create_new_frame (read_register (FP_REGNUM), read_pc ()));

     Other than that, all the meaning imparted to FP_REGNUM is imparted by the machine-dependent code.  So, FP_REGNUM can have any value that is convenient for the code that creates new frames.  (create_new_frame calls INIT_EXTRA_FRAME_INFO if it is defined; that is where you should use the FP_REGNUM value, if your frames are nonstandard.)

FRAME_CHAIN
     Given a GDB frame, determine the address of the calling function's frame.  This will be used to create a new GDB frame struct, and then INIT_EXTRA_FRAME_INFO and INIT_FRAME_PC will be called for the new frame.

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.

Longjmp Support
***************

GDB has support for figuring out that the target is doing a 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 maint info breakpoint command.

To make this work, you need to define a macro called GET_LONGJMP_TARGET, which will examine the jmp_buf structure and extract the longjmp target address.  Since jmp_buf is target specific, you will need to define it in the appropriate tm-xxx.h file.  Look in tm-sun4os4.h and sparc-tdep.c for examples of how to do this.

Coding Style
************

GDB is generally written using the GNU coding standards, as described in standards.texi, which is available for anonymous FTP from GNU archive sites.  There are some additional considerations for GDB maintainers that reflect the unique environment and style of GDB maintenance.  If you follow these guidelines, GDB will be more consistent and easier to maintain.

GDB's policy on the use of prototypes is that prototypes are used to declare functions but never to define them.  Simple macros are used in the declarations, so that a non-ANSI compiler can compile GDB without trouble.  The simple macro calls are used like this:

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

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:

     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.  All static functions should have such a declaration near the top of their source file.

We don't have a gcc option that will properly check that these rules have been followed, but it's GDB policy, and we periodically check it using the tools available (plus manual labor), and clean up any remnants.

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.  In particular:

     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.

     Do write code that doesn't 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.  In short, follow good programming practices for writing portable C code.

Submitting Patches
******************

Thanks for thinking of offering your changes back to the community of GDB 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 two main problems with getting your patches in are,

     The GDB maintainers will only install ``cleanly designed'' patches. You may not always agree on what is clean design. see Coding Style, see Clean Design.

     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.

I don't know how to get past these problems except by continuing to try.

There are two issues here -- technical and legal.

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 document for doing this by sending mail to gnu@prep.ai.mit.edu and asking for it.  I 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 GDB, but GAS, Emacs, GCC, etc) can be contributed with only one piece of legalese pushed through the bureacracy and filed with the FSF.  I can't start merging changes until this paperwork is received by the FSF (their rules, which I follow since I 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 "patch". Each message sent to me should include the changes to C code and header files for a single feature, plus ChangeLog entries for each directory where files were modified, and diffs for any changes needed to the manuals (gdb/doc/gdb.texi or gdb/doc/gdbint.texi).  If there are a lot of changes for a single feature, they can be split down into multiple messages.

In this way, if I read and like the feature, I can add it to the sources with a single patch command, do some testing, and check it in. If you leave out the ChangeLog, I have to write one.  If you leave out the doc, I have to puzzle out what needs documenting.  Etc.

The reason to send each change in a separate message is that I will not install some of the changes.  They'll be returned to you with questions or comments.  If I'm doing my job, my 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 other changes (which I am willing to accept) can be installed while one or more changes are being reworked.  If multiple features are sent in a single message, I 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 I get a lot of bug reports and a lot of patches, and most of them don't get installed because I 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 if and when I scan back over the queue -- which can literally take months sometimes.  It's in both our interests to make patch installation easy -- you get your changes installed, and I make some forward progress on GDB in a normal 12-hour day (instead of them having to wait until I have a 14-hour or 16-hour day to spend cleaning up patches before I can install them).

Please send patches to bug-gdb@prep.ai.mit.edu, if they are less than about 25,000 characters.  If longer than that, either make them available somehow (e.g. anonymous FTP), and announce it on bug-gdb, or send them directly to the GDB maintainers at gdb-patches@cygnus.com.

Host Conditionals
*****************

When GDB 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 are:

NOTE:  For now, both host and target conditionals are here. Eliminate target conditionals from this list as they are identified.

ALIGN_SIZE
     alloca.c

BLOCK_ADDRESS_FUNCTION_RELATIVE
     dbxread.c

GDBINIT_FILENAME
     main.c

KERNELDEBUG
     tm-hppa.h

MEM_FNS_DECLARED
     Your host config file defines this if it includes declarations of memcpy and memset.  Define this to avoid conflicts between the native include files and the declarations in defs.h.

NO_SYS_FILE
     dbxread.c

PYRAMID_CONTROL_FRAME_DEBUGGING
     pyr-xdep.c

SIGWINCH_HANDLER_BODY
     utils.c

1
     buildsym.c

1
     dbxread.c

1
     dbxread.c

1
     buildsym.c

1
     dwarfread.c

1
     valops.c

1
     valops.c

1
     pyr-xdep.c

ADDITIONAL_OPTIONS
     main.c

ADDITIONAL_OPTION_CASES
     main.c

ADDITIONAL_OPTION_HANDLER
     main.c

ADDITIONAL_OPTION_HELP
     main.c

ADDR_BITS_REMOVE
     defs.h

AIX_BUGGY_PTRACE_CONTINUE
     infptrace.c

ALIGN_STACK_ON_STARTUP
     main.c

ALTOS
     altos-xdep.c

ALTOS_AS
     xm-altos.h

ASCII_COFF
     remote-adapt.c

BADMAG
     coffread.c

BCS
     tm-delta88.h

BEFORE_MAIN_LOOP_HOOK
     main.c

BELIEVE_PCC_PROMOTION
     coffread.c

BELIEVE_PCC_PROMOTION_TYPE
     stabsread.c

BIG_ENDIAN
     defs.h

BITS_BIG_ENDIAN
     defs.h

BKPT_AT_MAIN
     solib.c

BLOCK_ADDRESS_ABSOLUTE
     dbxread.c

BPT_VECTOR
     tm-m68k.h

BREAKPOINT
     tm-m68k.h

BREAKPOINT_DEBUG
     breakpoint.c

BROKEN_LARGE_ALLOCA
     Avoid large alloca's.  For example, on sun's, Large alloca's fail because the attempt to increase the stack limit in main() fails because shared libraries are allocated just below the initial stack limit.  The SunOS kernel will not allow the stack to grow into the area occupied by the shared libraries.

BSTRING
     regex.c

CALL_DUMMY
     valops.c

CALL_DUMMY_LOCATION
     inferior.h

CALL_DUMMY_STACK_ADJUST
     valops.c

CANNOT_FETCH_REGISTER
     hppabsd-xdep.c

CANNOT_STORE_REGISTER
     findvar.c

CFRONT_PRODUCER
     dwarfread.c

CHILD_PREPARE_TO_STORE
     inftarg.c

CLEAR_DEFERRED_STORES
     inflow.c

CLEAR_SOLIB
     objfiles.c

COFF_ENCAPSULATE
     hppabsd-tdep.c

COFF_FORMAT
     symm-tdep.c

CORE_NEEDS_RELOCATION
     stack.c

CPLUS_MARKER
     cplus-dem.c

CREATE_INFERIOR_HOOK
     infrun.c

C_ALLOCA
     regex.c

C_GLBLREG
     coffread.c

DBXREAD_ONLY
     partial-stab.h

DBX_PARM_SYMBOL_CLASS
     stabsread.c

DEBUG
     remote-adapt.c

DEBUG_INFO
     partial-stab.h

DEBUG_PTRACE
     hppabsd-xdep.c

DECR_PC_AFTER_BREAK
     breakpoint.c

DEFAULT_PROMPT
     main.c

DELTA88
     m88k-xdep.c

DEV_TTY
     symmisc.c

DGUX
     m88k-xdep.c

DISABLE_UNSETTABLE_BREAK
     breakpoint.c

DONT_USE_REMOTE
     remote.c

DO_DEFERRED_STORES
     infrun.c

DO_REGISTERS_INFO
     infcmd.c

END_OF_TEXT_DEFAULT
     dbxread.c

EXTERN
     buildsym.h

EXTRACT_RETURN_VALUE
     tm-m68k.h

EXTRACT_STRUCT_VALUE_ADDRESS
     values.c

EXTRA_FRAME_INFO
     frame.h

EXTRA_SYMTAB_INFO
     symtab.h

FILES_INFO_HOOK
     target.c

FIXME
     coffread.c

FLOAT_INFO
     infcmd.c

FOPEN_RB
     defs.h

FP0_REGNUM
     a68v-xdep.c

FPC_REGNUM
     mach386-xdep.c

FP_REGNUM
     parse.c

FRAMELESS_FUNCTION_INVOCATION
     blockframe.c

FRAME_ARGS_ADDRESS_CORRECT
     stack.c

FRAME_CHAIN_COMBINE
     blockframe.c

FRAME_CHAIN_VALID
     frame.h

FRAME_CHAIN_VALID_ALTERNATE
     frame.h

FRAME_FIND_SAVED_REGS
     stack.c

FRAME_GET_BASEREG_VALUE
     frame.h

FRAME_NUM_ARGS
     tm-m68k.h

FRAME_SPECIFICATION_DYADIC
     stack.c

FUNCTION_EPILOGUE_SIZE
     coffread.c

F_OK
     xm-ultra3.h

GCC2_COMPILED_FLAG_SYMBOL
     dbxread.c

GCC_COMPILED_FLAG_SYMBOL
     dbxread.c

GCC_MANGLE_BUG
     symtab.c

GCC_PRODUCER
     dwarfread.c

GET_SAVED_REGISTER
     findvar.c

GPLUS_PRODUCER
     dwarfread.c

GR64_REGNUM
     remote-adapt.c

GR64_REGNUM
     remote-mm.c

HANDLE_RBRAC
     partial-stab.h

HAVE_68881
     m68k-tdep.c

HAVE_MMAP
     In some cases, use the system call mmap for reading symbol tables.  For some machines this allows for sharing and quick updates.

HAVE_REGISTER_WINDOWS
     findvar.c

HAVE_SIGSETMASK
     main.c

HAVE_TERMIO
     inflow.c

HEADER_SEEK_FD
     arm-tdep.c

HOSTING_ONLY
     xm-rtbsd.h

HOST_BYTE_ORDER
     ieee-float.c

HPUX_ASM
     xm-hp300hpux.h

HPUX_VERSION_5
     hp300ux-xdep.c

HP_OS_BUG
     infrun.c

I80960
     remote-vx.c

IEEE_DEBUG
     ieee-float.c

IEEE_FLOAT
     valprint.c

IGNORE_SYMBOL
     dbxread.c

INIT_EXTRA_FRAME_INFO
     blockframe.c

INIT_EXTRA_SYMTAB_INFO
     symfile.c

INIT_FRAME_PC
     blockframe.c

INNER_THAN
     valops.c

INT_MAX
     defs.h

INT_MIN
     defs.h

IN_GDB
     i960-pinsn.c

IN_SIGTRAMP
     infrun.c

IN_SOLIB_TRAMPOLINE
     infrun.c

ISATTY
     main.c

IS_TRAPPED_INTERNALVAR
     values.c

KERNELDEBUG
     dbxread.c

KERNEL_DEBUGGING
     tm-ultra3.h

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.

LCC_PRODUCER
     dwarfread.c

LITTLE_ENDIAN
     defs.h

LOG_FILE
     remote-adapt.c

LONGERNAMES
     cplus-dem.c

LONGEST
     defs.h

LONG_LONG
     defs.h

LONG_MAX
     defs.h

LSEEK_NOT_LINEAR
     source.c

L_LNNO32
     coffread.c

L_SET
     This macro is used as the argument to lseek (or, most commonly, bfd_seek). FIXME, it should be replaced by SEEK_SET instead, which is the POSIX equivalent.

MACHKERNELDEBUG
     hppabsd-tdep.c

MAIN
     cplus-dem.c

MAINTENANCE
     dwarfread.c

MAINTENANCE_CMDS
     breakpoint.c

MAINTENANCE_CMDS
     maint.c

MALLOC_INCOMPATIBLE
     Define this if the system's prototype for malloc differs from the ANSI definition.

MIPSEL
     mips-tdep.c

MMAP_BASE_ADDRESS
     When using HAVE_MMAP, the first mapping should go at this address.

MMAP_INCREMENT
     when using HAVE_MMAP, this is the increment between mappings.

MONO
     ser-go32.c

MOTOROLA
     xm-altos.h

NBPG
     altos-xdep.c

NEED_POSIX_SETPGID
     infrun.c

NEED_TEXT_START_END
     exec.c

NFAILURES
     regex.c

NNPC_REGNUM
     infrun.c

NORETURN
     defs.h

NOTDEF
     regex.c

NOTDEF
     remote-adapt.c

NOTDEF
     remote-mm.c

NOTICE_SIGNAL_HANDLING_CHANGE
     infrun.c

NO_HIF_SUPPORT
     remote-mm.c

NO_JOB_CONTROL
     signals.h

NO_MMALLOC
     GDB will use the mmalloc library for memory allocation for symbol reading, unless this symbol is defined.  Define it on systems on which mmalloc does not work for some reason.  One example is the DECstation, where its RPC library can't cope with our redefinition of malloc to call mmalloc.  When defining NO_MMALLOC, you will also have to override the setting of MMALLOC_LIB to empty, in the Makefile. Therefore, this define is usually set on the command line by overriding MMALLOC_DISABLE in config/*/*.mh, rather than by defining it in xm-*.h.

NO_MMALLOC_CHECK
     Define this if you are using mmalloc, but don't want the overhead of checking the heap with mmcheck.

NO_SIGINTERRUPT
     remote-adapt.c

NO_SINGLE_STEP
     infptrace.c

NPC_REGNUM
     infcmd.c

NS32K_SVC_IMMED_OPERANDS
     ns32k-opcode.h

NUMERIC_REG_NAMES
     mips-tdep.c

N_SETV
     dbxread.c

N_SET_MAGIC
     hppabsd-tdep.c

NaN
     tm-umax.h

ONE_PROCESS_WRITETEXT
     breakpoint.c

O_BINARY
     exec.c

O_RDONLY
     xm-ultra3.h

PC
     convx-opcode.h

PCC_SOL_BROKEN
     dbxread.c

PC_IN_CALL_DUMMY
     inferior.h

PC_LOAD_SEGMENT
     stack.c

PC_REGNUM
     parse.c

PRINT_RANDOM_SIGNAL
     infcmd.c

PRINT_REGISTER_HOOK
     infcmd.c

PRINT_TYPELESS_INTEGER
     valprint.c

PROCESS_LINENUMBER_HOOK
     buildsym.c

PROLOGUE_FIRSTLINE_OVERLAP
     infrun.c

PSIGNAL_IN_SIGNAL_H
     defs.h

PS_REGNUM
     parse.c

PUSH_ARGUMENTS
     valops.c

PYRAMID_CONTROL_FRAME_DEBUGGING
     pyr-xdep.c

PYRAMID_CORE
     pyr-xdep.c

PYRAMID_PTRACE
     pyr-xdep.c

REGISTER_BYTES
     remote.c

REGISTER_NAMES
     tm-a29k.h

REG_STACK_SEGMENT
     exec.c

REG_STRUCT_HAS_ADDR
     findvar.c

RE_NREGS
     regex.h

R_FP
     dwarfread.c

R_OK
     xm-altos.h

SDB_REG_TO_REGNUM
     coffread.c

SEEK_END
     state.c

SEEK_SET
     state.c

SEM
     coffread.c

SET_STACK_LIMIT_HUGE
     When defined, stack limits will be raised to their maximum.  Use this if your host supports setrlimit and you have trouble with stringtab in dbxread.c.

     Also used in fork-child.c to return stack limits before child processes are forked.

SHELL_COMMAND_CONCAT
     infrun.c

SHELL_FILE
     infrun.c

SHIFT_INST_REGS
     breakpoint.c

SIGN_EXTEND_CHAR
     regex.c

SIGTRAP_STOP_AFTER_LOAD
     infrun.c

SKIP_PROLOGUE
     tm-m68k.h

SKIP_PROLOGUE_FRAMELESS_P
     blockframe.c

SKIP_TRAMPOLINE_CODE
     infrun.c

SOLIB_ADD
     core.c

SOLIB_CREATE_INFERIOR_HOOK
     infrun.c

SP_REGNUM
     parse.c

STAB_REG_TO_REGNUM
     stabsread.h

STACK_ALIGN
     valops.c

STACK_DIRECTION
     alloca.c

START_INFERIOR_TRAPS_EXPECTED
     infrun.c

STOP_SIGNAL
     main.c

STORE_RETURN_VALUE
     tm-m68k.h

SUN4_COMPILER_FEATURE
     infrun.c

SUN_FIXED_LBRAC_BUG
     dbxread.c

SVR4_SHARED_LIBS
     solib.c

SWITCH_ENUM_BUG
     regex.c

SYM1
     tm-ultra3.h

SYMBOL_RELOADING_DEFAULT
     symfile.c

SYNTAX_TABLE
     regex.c

Sword
     regex.c

TDESC
     infrun.c

TIOCGETC
     inflow.c

TIOCGLTC
     inflow.c

TIOCGPGRP
     inflow.c

TIOCLGET
     inflow.c

TIOCLSET
     inflow.c

TIOCNOTTY
     inflow.c

TM_FILE_OVERRIDE
     defs.h

T_ARG
     coffread.c

T_VOID
     coffread.c

UINT_MAX
     defs.h

UPAGES
     altos-xdep.c

USER
     m88k-tdep.c

USE_GAS
     xm-news.h

USE_O_NOCTTY
     inflow.c

USE_STRUCT_CONVENTION
     values.c

USG
     Means that System V (prior to SVR4) include files are in use. (FIXME:  This symbol is abused in infrun.c, regex.c, remote-nindy.c, and utils.c for other things, at the moment.)

USIZE
     xm-m88k.h

U_FPSTATE
     i386-xdep.c

VARIABLES_INSIDE_BLOCK
     dbxread.c

WRS_ORIG
     remote-vx.c

_LANG_c
     language.c

_LANG_m2
     language.c

__GNUC__
     news-xdep.c

__GO32__
     inflow.c

__HAVE_68881__
     m68k-stub.c

__HPUX_ASM__
     xm-hp300hpux.h

__INT_VARARGS_H
     printcmd.c

__not_on_pyr_yet
     pyr-xdep.c

alloca
     defs.h

const
     defs.h

GOULD_PN
     gould-pinsn.c

emacs
     alloca.c

hp800
     xm-hppabsd.h

hpux
     hppabsd-core.c

lint
     valarith.c

longest_to_int
     defs.h

mc68020
     m68k-stub.c

notdef
     gould-pinsn.c

ns32k_opcodeT
     ns32k-opcode.h

sgi
     mips-tdep.c

sparc
     regex.c

static
     alloca.c

sun
     m68k-tdep.c

sun386
     tm-sun386.h

test
     regex.c

ultrix
     xm-mips.h

volatile
     defs.h

x_name
     coffread.c

x_zeroes
     coffread.c

Target Conditionals
*******************

When GDB is configured and compiled, various macros are defined or left undefined, to control compilation based on the attributes of the target system.  These macros and their meanings are:

NOTE:  For now, both host and target conditionals are here. Eliminate host conditionals from this list as they are identified.

PUSH_DUMMY_FRAME
     Used in call_function_by_hand to create an artificial stack frame.

POP_FRAME
     Used in call_function_by_hand to remove an artificial stack frame.

ALIGN_SIZE
     alloca.c

BLOCK_ADDRESS_FUNCTION_RELATIVE
     dbxread.c

GDBINIT_FILENAME
     main.c

KERNELDEBUG
     tm-hppa.h

NO_SYS_FILE
     dbxread.c

PYRAMID_CONTROL_FRAME_DEBUGGING
     pyr-xdep.c

SIGWINCH_HANDLER_BODY
     utils.c

ADDITIONAL_OPTIONS
     main.c

ADDITIONAL_OPTION_CASES
     main.c

ADDITIONAL_OPTION_HANDLER
     main.c

ADDITIONAL_OPTION_HELP
     main.c

ADDR_BITS_REMOVE
     defs.h

ALIGN_STACK_ON_STARTUP
     main.c

ALTOS
     altos-xdep.c

ALTOS_AS
     xm-altos.h

ASCII_COFF
     remote-adapt.c

BADMAG
     coffread.c

BCS
     tm-delta88.h

BEFORE_MAIN_LOOP_HOOK
     main.c

BELIEVE_PCC_PROMOTION
     coffread.c

BELIEVE_PCC_PROMOTION_TYPE
     stabsread.c

BIG_ENDIAN
     defs.h

BITS_BIG_ENDIAN
     defs.h

BKPT_AT_MAIN
     solib.c

BLOCK_ADDRESS_ABSOLUTE
     dbxread.c

BPT_VECTOR
     tm-m68k.h

BREAKPOINT
     tm-m68k.h

BREAKPOINT_DEBUG
     breakpoint.c

BSTRING
     regex.c

CALL_DUMMY
     valops.c

CALL_DUMMY_LOCATION
     inferior.h

CALL_DUMMY_STACK_ADJUST
     valops.c

CANNOT_FETCH_REGISTER
     hppabsd-xdep.c

CANNOT_STORE_REGISTER
     findvar.c

CFRONT_PRODUCER
     dwarfread.c

CHILD_PREPARE_TO_STORE
     inftarg.c

CLEAR_DEFERRED_STORES
     inflow.c

CLEAR_SOLIB
     objfiles.c

COFF_ENCAPSULATE
     hppabsd-tdep.c

COFF_FORMAT
     symm-tdep.c

CORE_NEEDS_RELOCATION
     stack.c

CPLUS_MARKER
     cplus-dem.c

CREATE_INFERIOR_HOOK
     infrun.c

C_ALLOCA
     regex.c

C_GLBLREG
     coffread.c

DBXREAD_ONLY
     partial-stab.h

DBX_PARM_SYMBOL_CLASS
     stabsread.c

DEBUG
     remote-adapt.c

DEBUG_INFO
     partial-stab.h

DEBUG_PTRACE
     hppabsd-xdep.c

DECR_PC_AFTER_BREAK
     breakpoint.c

DEFAULT_PROMPT
     main.c

DELTA88
     m88k-xdep.c

DEV_TTY
     symmisc.c

DGUX
     m88k-xdep.c

DISABLE_UNSETTABLE_BREAK
     breakpoint.c

DONT_USE_REMOTE
     remote.c

DO_DEFERRED_STORES
     infrun.c

DO_REGISTERS_INFO
     infcmd.c

END_OF_TEXT_DEFAULT
     dbxread.c

EXTERN
     buildsym.h

EXTRACT_RETURN_VALUE
     tm-m68k.h

EXTRACT_STRUCT_VALUE_ADDRESS
     values.c

EXTRA_FRAME_INFO
     frame.h

EXTRA_SYMTAB_INFO
     symtab.h

FILES_INFO_HOOK
     target.c

FIXME
     coffread.c

FLOAT_INFO
     infcmd.c

FOPEN_RB
     defs.h

FP0_REGNUM
     a68v-xdep.c

FPC_REGNUM
     mach386-xdep.c

FP_REGNUM
     parse.c

FPU
     Unused?  6-oct-92 rich@cygnus.com.  FIXME.

FRAMELESS_FUNCTION_INVOCATION
     blockframe.c

FRAME_ARGS_ADDRESS_CORRECT
     stack.c

FRAME_CHAIN
     Given FRAME, return a pointer to the calling frame.

FRAME_CHAIN_COMBINE
     blockframe.c

FRAME_CHAIN_VALID
     frame.h

FRAME_CHAIN_VALID_ALTERNATE
     frame.h

FRAME_FIND_SAVED_REGS
     stack.c

FRAME_GET_BASEREG_VALUE
     frame.h

FRAME_NUM_ARGS
     tm-m68k.h

FRAME_SPECIFICATION_DYADIC
     stack.c

FRAME_SAVED_PC
     Given FRAME, return the pc saved there.  That is, the return address.

FUNCTION_EPILOGUE_SIZE
     coffread.c

F_OK
     xm-ultra3.h

GCC2_COMPILED_FLAG_SYMBOL
     dbxread.c

GCC_COMPILED_FLAG_SYMBOL
     dbxread.c

GCC_MANGLE_BUG
     symtab.c

GCC_PRODUCER
     dwarfread.c

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
     mach386-xdep.c

GDB_TARGET_IS_SUN3
     a68v-xdep.c

GDB_TARGET_IS_SUN386
     sun386-xdep.c

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
     findvar.c

GPLUS_PRODUCER
     dwarfread.c

GR64_REGNUM
     remote-adapt.c

GR64_REGNUM
     remote-mm.c

HANDLE_RBRAC
     partial-stab.h

HAVE_68881
     m68k-tdep.c

HAVE_REGISTER_WINDOWS
     findvar.c

HAVE_SIGSETMASK
     main.c

HAVE_TERMIO
     inflow.c

HEADER_SEEK_FD
     arm-tdep.c

HOSTING_ONLY
     xm-rtbsd.h

HOST_BYTE_ORDER
     ieee-float.c

HPUX_ASM
     xm-hp300hpux.h

HPUX_VERSION_5
     hp300ux-xdep.c

HP_OS_BUG
     infrun.c

I80960
     remote-vx.c

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_DEBUG
     ieee-float.c

IEEE_FLOAT
     valprint.c

IGNORE_SYMBOL
     dbxread.c

INIT_EXTRA_FRAME_INFO
     blockframe.c

INIT_EXTRA_SYMTAB_INFO
     symfile.c

INIT_FRAME_PC
     blockframe.c

INNER_THAN
     valops.c

INT_MAX
     defs.h

INT_MIN
     defs.h

IN_GDB
     i960-pinsn.c

IN_SIGTRAMP
     infrun.c

IN_SOLIB_TRAMPOLINE
     infrun.c

ISATTY
     main.c

IS_TRAPPED_INTERNALVAR
     values.c

KERNELDEBUG
     dbxread.c

KERNEL_DEBUGGING
     tm-ultra3.h

LCC_PRODUCER
     dwarfread.c

LITTLE_ENDIAN
     defs.h

LOG_FILE
     remote-adapt.c

LONGERNAMES
     cplus-dem.c

LONGEST
     defs.h

LONG_LONG
     defs.h

LONG_MAX
     defs.h

L_LNNO32
     coffread.c

MACHKERNELDEBUG
     hppabsd-tdep.c

MAIN
     cplus-dem.c

MAINTENANCE
     dwarfread.c

MAINTENANCE_CMDS
     breakpoint.c

MAINTENANCE_CMDS
     maint.c

MIPSEL
     mips-tdep.c

MOTOROLA
     xm-altos.h

NBPG
     altos-xdep.c

NEED_POSIX_SETPGID
     infrun.c

NEED_TEXT_START_END
     exec.c

NFAILURES
     regex.c

NNPC_REGNUM
     infrun.c

NORETURN
     defs.h

NOTDEF
     regex.c

NOTDEF
     remote-adapt.c

NOTDEF
     remote-mm.c

NOTICE_SIGNAL_HANDLING_CHANGE
     infrun.c

NO_HIF_SUPPORT
     remote-mm.c

NO_SIGINTERRUPT
     remote-adapt.c

NO_SINGLE_STEP
     infptrace.c

NO_TYPEDEFS
     xcoffread.c--This causes types not to be read, to save memory and speed things up.

NPC_REGNUM
     infcmd.c

NS32K_SVC_IMMED_OPERANDS
     ns32k-opcode.h

NUMERIC_REG_NAMES
     mips-tdep.c

N_SETV
     dbxread.c

N_SET_MAGIC
     hppabsd-tdep.c

NaN
     tm-umax.h

ONE_PROCESS_WRITETEXT
     breakpoint.c

PC
     convx-opcode.h

PCC_SOL_BROKEN
     dbxread.c

PC_IN_CALL_DUMMY
     inferior.h

PC_LOAD_SEGMENT
     stack.c

PC_REGNUM
     parse.c

PRINT_RANDOM_SIGNAL
     infcmd.c

PRINT_REGISTER_HOOK
     infcmd.c

PRINT_TYPELESS_INTEGER
     valprint.c

PROCESS_LINENUMBER_HOOK
     buildsym.c

PROLOGUE_FIRSTLINE_OVERLAP
     infrun.c

PSIGNAL_IN_SIGNAL_H
     defs.h

PS_REGNUM
     parse.c

PUSH_ARGUMENTS
     valops.c

REGISTER_BYTES
     remote.c

REGISTER_NAMES
     tm-a29k.h

REG_STACK_SEGMENT
     exec.c

REG_STRUCT_HAS_ADDR
     findvar.c

RE_NREGS
     regex.h

R_FP
     dwarfread.c

R_OK
     xm-altos.h

SDB_REG_TO_REGNUM
     coffread.c

SEEK_END
     state.c

SEEK_SET
     state.c

SEM
     coffread.c

SHELL_COMMAND_CONCAT
     infrun.c

SHELL_FILE
     infrun.c

SHIFT_INST_REGS
     breakpoint.c

SIGN_EXTEND_CHAR
     regex.c

SIGTRAP_STOP_AFTER_LOAD
     infrun.c

SKIP_PROLOGUE
     tm-m68k.h

SKIP_PROLOGUE_FRAMELESS_P
     blockframe.c

SKIP_TRAMPOLINE_CODE
     infrun.c

SOLIB_ADD
     core.c

SOLIB_CREATE_INFERIOR_HOOK
     infrun.c

SP_REGNUM
     parse.c

STAB_REG_TO_REGNUM
     stabsread.h

STACK_ALIGN
     valops.c

STACK_DIRECTION
     alloca.c

START_INFERIOR_TRAPS_EXPECTED
     infrun.c

STOP_SIGNAL
     main.c

STORE_RETURN_VALUE
     tm-m68k.h

SUN4_COMPILER_FEATURE
     infrun.c

SUN_FIXED_LBRAC_BUG
     dbxread.c

SVR4_SHARED_LIBS
     solib.c

SWITCH_ENUM_BUG
     regex.c

SYM1
     tm-ultra3.h

SYMBOL_RELOADING_DEFAULT
     symfile.c

SYNTAX_TABLE
     regex.c

Sword
     regex.c

TARGET_BYTE_ORDER
     defs.h

TARGET_CHAR_BIT
     defs.h

TARGET_COMPLEX_BIT
     defs.h

TARGET_DOUBLE_BIT
     defs.h

TARGET_DOUBLE_COMPLEX_BIT
     defs.h

TARGET_FLOAT_BIT
     defs.h

TARGET_INT_BIT
     defs.h

TARGET_LONG_BIT
     defs.h

TARGET_LONG_DOUBLE_BIT
     defs.h

TARGET_LONG_LONG_BIT
     defs.h

TARGET_PTR_BIT
     defs.h

TARGET_SHORT_BIT
     defs.h

TDESC
     infrun.c

TM_FILE_OVERRIDE
     defs.h

T_ARG
     coffread.c

T_VOID
     coffread.c

UINT_MAX
     defs.h

USER
     m88k-tdep.c

USE_GAS
     xm-news.h

USE_STRUCT_CONVENTION
     values.c

USIZE
     xm-m88k.h

U_FPSTATE
     i386-xdep.c

VARIABLES_INSIDE_BLOCK
     dbxread.c

WRS_ORIG
     remote-vx.c

_LANG_c
     language.c

_LANG_m2
     language.c

__GO32__
     inflow.c

__HAVE_68881__
     m68k-stub.c

__HPUX_ASM__
     xm-hp300hpux.h

__INT_VARARGS_H
     printcmd.c

__not_on_pyr_yet
     pyr-xdep.c

GOULD_PN
     gould-pinsn.c

emacs
     alloca.c

hp800
     xm-hppabsd.h

hpux
     hppabsd-core.c

longest_to_int
     defs.h

mc68020
     m68k-stub.c

ns32k_opcodeT
     ns32k-opcode.h

sgi
     mips-tdep.c

sparc
     regex.c

static
     alloca.c

sun
     m68k-tdep.c

sun386
     tm-sun386.h

test
     regex.c

x_name
     coffread.c

x_zeroes
     coffread.c

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.

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.

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.

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''; see Host.

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.

Obsolete Conditionals
*********************

Fragments of old code in GDB 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.

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 GDB gets the info portably from there.  The values in GDB's configuration files should be moved into BFD configuration files (if needed there), and deleted from all of GDB's config files.

     Any 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!

The XCOFF Object File Format
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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 dbx-style stabs whose strings are located in the .debug section (rather than the string table).  Files are indicated with a C_FILE symbol (.file) which is analogous to N_SO; include files are delimited with C_BINCL (.bi) and C_EINCL (.ei) which correspond to N_SOL rather than Sun's N_BINCL (that is, they don't nest and there is no equivalent to N_EXCL).  The values of the C_BINCL and C_EINCL symbols are offsets into the executable file which point to the beginning and the end of the portion of the linetable which correspond to this include file (warning: C_EINCL is inclusive not exclusive like most end of something pointers).  Other differences from standard stabs include the use of negative type numbers for builtin types.

The shared library scheme has a nice 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).