This is Info file gdbint.info, produced by Makeinfo version 1.68 from
the input file ../../../devo/gdb/doc/gdbint.texinfo.

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, 91, 92, 93, 94, 95, 96, 97, 1998 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).


File: gdbint.info,  Node: Top,  Next: README,  Up: (dir)

Scope of this Document
**********************

   This document documents the internals of the GNU debugger, GDB.  It
is intended to document aspects of GDB which apply across many different
parts of GDB (for example, *note Coding Style::.), or which are global
aspects of design (for example, what are the major modules and which
files document them in detail?).  Information which pertains to specific
data structures, functions, variables, etc., should be put in comments
in the source code, not here.  It is more likely to get noticed and kept
up to date there.  Some of the information in this document should
probably be moved into comments.

* Menu:

* README::			The README File
* Getting Started::		Getting started working on GDB
* Debugging GDB::		Debugging GDB with itself
* New Architectures::		Defining a New Host or Target Architecture
* Config::			Adding a New Configuration
* Host::			Adding a New Host
* Native::			Adding a New Native Configuration
* Target::			Adding a New Target
* Languages::			Defining New Source Languages
* Releases::			Configuring GDB for Release
* Partial Symbol Tables::	How GDB reads symbols quickly at startup
* Types::			How GDB keeps track of types
* BFD support for GDB::		How BFD and GDB interface
* Symbol Reading::		Defining New Symbol Readers
* Cleanups::			Cleanups
* Wrapping::			Wrapping Output Lines
* Frames::			Keeping track of function calls
* Remote Stubs::		Code that runs in targets and talks to GDB
* Longjmp Support::		Stepping through longjmp's in the target
* Coding Style::		Strunk and White for GDB maintainers
* Clean Design::		Frank Lloyd Wright for GDB maintainers
* Submitting Patches::		How to get your changes into GDB releases
* Host Conditionals::		What features exist in the host
* Target Conditionals::		What features exist in the target
* Native Conditionals::		Conditionals for when host and target are same
* Obsolete Conditionals::	Conditionals that don't exist any more
* XCOFF::			The Object file format used on IBM's RS/6000


File: gdbint.info,  Node: README,  Next: Getting Started,  Prev: Top,  Up: Top

The `README' File
*****************

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


File: gdbint.info,  Node: Getting Started,  Next: Debugging GDB,  Prev: README,  Up: Top

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 (*note 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
     (*note Host Conditionals::., *note Target Conditionals::., *note
     Native Conditionals::., and *note 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!


File: gdbint.info,  Node: Debugging GDB,  Next: New Architectures,  Prev: Getting Started,  Up: Top

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 4.2, 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.


File: gdbint.info,  Node: New Architectures,  Next: Config,  Prev: Debugging GDB,  Up: Top

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; *note
Adding a New Configuration: Config..  Further work can be divided into
"host-dependent" (*note Adding a New Host: Host.) and
"target-dependent" (*note Adding a New Target: 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'.


File: gdbint.info,  Node: Config,  Next: Host,  Prev: New Architectures,  Up: Top

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 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.


File: gdbint.info,  Node: Host,  Next: Native,  Prev: Config,  Up: Top

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

   Once you have specified a new configuration for your host (*note
Adding a New Configuration: Config.), 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; *note Adding a New Target: Target.
and *note Adding a New Native Configuration: Native.

   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'.


File: gdbint.info,  Node: Native,  Next: Target,  Prev: Host,  Up: Top

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.

`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 `XXX-nat.c' (or
     `REGISTER_U_ADDR' in `nm-XXX.h').

`core-aout.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, `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 `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
`core-aout.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.  (*Note Defining
a New Host or Target Architecture: New Architectures, 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.


File: gdbint.info,  Node: Target,  Next: Languages,  Prev: Native,  Up: Top

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

   For a new target called TTT, first specify the configuration as
described in *Note Adding a New Configuration: Config.  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/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 `#include's
`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.)


File: gdbint.info,  Node: Languages,  Next: Releases,  Prev: Target,  Up: Top

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_element's 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 `#ifdef's to leave out
     large routines that the user won't need if he or she is not using
     your language.

     Note that you do not need to do this in your YACC parser, since if
     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 `tar'red into the
     distribution!


File: gdbint.info,  Node: Releases,  Next: Partial Symbol Tables,  Prev: Languages,  Up: Top

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

   From the top level directory (containing `gdb', `bfd', `libiberty',
and so on):
     make -f Makefile.in gdb.tar.gz

   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 been
configured, you can just do `make gdb.tar.gz' 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.


File: gdbint.info,  Node: Partial Symbol Tables,  Next: Types,  Prev: Releases,  Up: Top

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.  (*Note 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.


File: gdbint.info,  Node: Types,  Next: BFD support for GDB,  Prev: Partial Symbol Tables,  Up: Top

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.


File: gdbint.info,  Node: BFD support for GDB,  Next: Symbol Reading,  Prev: Types,  Up: Top

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.


File: gdbint.info,  Node: Symbol Reading,  Next: Cleanups,  Prev: BFD support for GDB,  Up: Top

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.


File: gdbint.info,  Node: Cleanups,  Next: Wrapping,  Prev: Symbol Reading,  Up: Top

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).


File: gdbint.info,  Node: Wrapping,  Next: Frames,  Prev: Cleanups,  Up: Top

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.


File: gdbint.info,  Node: Frames,  Next: Remote Stubs,  Prev: Wrapping,  Up: Top

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.

