gdbint.texinfo

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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.
(@xref{New Architectures,,Defining a New Host or Target Architecture},
for more info about this.)

If your system uses @file{/proc} to control processes, and uses ELF
format core files, then you may be able to use the same routines
for reading the registers out of processes and out of core files.

@node Target
@chapter Adding a New Target

For a new target called @var{ttt}, first specify the configuration as
described in @ref{Config,,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:

@table @file
@item gdb/config/@var{ttt}.mt
Contains a Makefile fragment specific to this target.
Specifies what object files are needed for target @var{ttt}, by
defining @samp{TDEPFILES=@dots{}}.
Also specifies the header file which describes @var{ttt}, by defining
@samp{TM_FILE= tm-@var{ttt}.h}.  You can also define @samp{TM_CFLAGS},
@samp{TM_CLIBS}, @samp{TM_CDEPS},
and other Makefile variables here; see @file{Makefile.in}.

@item gdb/tm-@var{ttt}.h
(@file{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 @file{tm-*.h} files when building a new one.

@item gdb/@var{ttt}-tdep.c
Contains any miscellaneous code required for this target machine.
On some machines it doesn't exist at all.  Sometimes the macros
in @file{tm-@var{ttt}.h} become very complicated, so they are
implemented as functions here instead, and the macro is simply
defined to call the function.

@item 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.

@item gdb/@var{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 @file{@var{arch}-pinsn.c} rather
than @file{@var{ttt}-pinsn.c}.

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

@item gdb/tm-@var{arch}.h
This often exists to describe the basic layout of the target machine's
processor chip (registers, stack, etc).
If used, it is included by @file{tm-@var{xxx}.h}.  It can
be shared among many targets that use the same processor.

@item gdb/@var{arch}-tdep.c
Similarly, there are often common subroutines that are shared by all
target machines that use this particular architecture.
@end table

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 @file{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 are beyond the scope
of this document right now.  Look at the structure of the a.out
and COFF support, build a transfer vector (@code{xvec}) for your new format,
and start populating it with routines.  Add it to the list in
@file{bfd/targets.c}.

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


@node Languages
@chapter Adding a Source Language to GDB

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

@table @emph
@item Create the expression parser.

This should reside in a file @file{@var{lang}-exp.y}.  Routines for building
parsed expressions into a @samp{union exp_element} list are in @file{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
@emph{must} be included at the top of the YACC parser, to prevent
the various parsers from defining the same global names:

@example
#define yyparse 	@var{lang}_parse
#define yylex 	@var{lang}_lex
#define yyerror 	@var{lang}_error
#define yylval 	@var{lang}_lval
#define yychar 	@var{lang}_char
#define yydebug 	@var{lang}_debug
#define yypact  	@var{lang}_pact 
#define yyr1		@var{lang}_r1   
#define yyr2		@var{lang}_r2   
#define yydef		@var{lang}_def  
#define yychk		@var{lang}_chk  
#define yypgo		@var{lang}_pgo  
#define yyact  	@var{lang}_act  
#define yyexca  	@var{lang}_exca
#define yyerrflag  	@var{lang}_errflag
#define yynerrs  	@var{lang}_nerrs
@end example

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

@item Add any evaluation routines, if necessary

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

@item Update some existing code

Add an enumerated identifier for your language to the enumerated type
@code{enum language} in @file{defs.h}.

Update the routines in @file{language.c} so your language is included.  These
routines include type predicates and such, which (in some cases) are
language dependent.  If your language does not appear in the switch
statement, an error is reported.

Also included in @file{language.c} is the code that updates the variable
@code{current_language}, and the routines that translate the
@code{language_@var{lang}} enumerated identifier into a printable
string.

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

Update @code{allocate_symtab} in @file{symfile.c} and/or symbol-reading
code so that the language of each symtab (source file) is set properly.
This is used to determine the language to use at each stack frame level.
Currently, the language is set based upon the extension of the source
file.  If the language can be better inferred from the symbol
information, please set the language of the symtab in the symbol-reading
code.

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

@item Add a place of call

Add a call to @code{@var{lang}_parse()} and @code{@var{lang}_error} in
@code{parse.c:parse_exp_1()}.

@item 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
@var{lang}, then every file dependent on @file{language.h} will have the
macro @code{_LANG_@var{lang}} defined in it.  Use @code{#ifdef}s to
leave out large routines that the user won't need if he or she is not
using your language.

Note that you do not need to do this in your YACC parser, since if GDB
is not build for @var{lang}, then @file{@var{lang}-exp.tab.o} (the
compiled form of your parser) is not linked into GDB at all.

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

@item Edit @file{Makefile.in}

Add dependencies in @file{Makefile.in}.  Make sure you update the macro
variables such as @code{HFILES} and @code{OBJS}, otherwise your code may
not get linked in, or, worse yet, it may not get @code{tar}red into the
distribution!
@end table


@node Releases
@chapter Configuring GDB for Release

From the top level directory (containing @file{gdb}, @file{bfd},
@file{libiberty}, and so on):
@example
make -f Makefile.in gdb.tar.Z
@end example

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

This procedure requires:
@itemize @bullet
@item symbolic links
@item @code{makeinfo} (texinfo2 level)
@item @TeX{}
@item @code{dvips}
@item @code{yacc} or @code{bison}
@end itemize
@noindent
@dots{} and the usual slew of utilities (@code{sed}, @code{tar}, etc.).

@subheading TEMPORARY RELEASE PROCEDURE FOR DOCUMENTATION

@file{gdb.texinfo} is currently marked up using the texinfo-2 macros,
which are not yet a default for anything (but we have to start using
them sometime).  

For making paper, the only thing this implies is the right generation of
@file{texinfo.tex} needs to be included in the distribution.

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


@node Partial Symbol Tables
@chapter Partial Symbol Tables

GDB has three types of symbol tables.

@itemize @bullet
@item	full symbol tables (symtabs).  These contain the main
information about symbols and addresses.
@item	partial symbol tables (psymtabs).  These contain enough
information to know when to read the corresponding
part of the full symbol table.
@item	minimal symbol tables (msymtabs).  These contain information
gleaned from non-debugging symbols.
@end itemize

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.  (@xref{Symbol Reading}.)

The symbols that show up in a file's psymtab should be, roughly, those
visible to the debugger's user when the program is not running code from
that file.  These include external symbols and types, static
symbols and types, and 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:

@itemize @bullet

@item by its address
(e.g. execution stops at some address which is inside a function
in this file).  The address will be noticed to be in the
range of this psymtab, and the full symtab will be read in.
@code{find_pc_function}, @code{find_pc_line}, and other @code{find_pc_@dots{}}
functions handle this.

@item by its name
(e.g. the user asks to print a variable, or set a breakpoint on a
function).  Global names and file-scope names will be found in the
psymtab, which will cause the symtab to be pulled in.  Local names will
have to be qualified by a global name, or a file-scope name, in which
case we will have already read in the symtab as we evaluated the
qualifier.  Or, a local symbol can be referenced when
we are "in" a local scope, in which case the first case applies.
@code{lookup_symbol} does most of the work here.

@end itemize

The only reason that psymtabs exist is to cause a symtab to be read in
at the right moment.  Any symbol that can be elided from a psymtab,
while still causing that to happen, should not appear in it.  Since
psymtabs don't have the idea of scope, you can't put local symbols in
them anyway.  Psymtabs don't have the idea of the type of a symbol,
either, so types need not appear, unless they will be referenced by
name.

It is a bug for 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.

@node BFD support for GDB
@chapter Binary File Descriptor Library Support for GDB

BFD provides support for GDB in several ways:

@table @emph
@item	identifying executable and core files
BFD will identify a variety of file types, including a.out, coff, and
several variants thereof, as well as several kinds of core files.

@item	access to sections of files
BFD parses the file headers to determine the names, virtual addresses,
sizes, and file locations of all the various named sections in files
(such as the text section or the data section).  GDB simply calls
BFD to read or write section X at byte offset Y for length Z.

@item	specialized core file support
BFD provides routines to determine the failing command name stored
in a core file, the signal with which the program failed, and whether
a core file matches (i.e. could be a core dump of) a particular executable
file.

@item	locating the symbol information
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.
@end table

@c The interface for symbol reading is described in @ref{Symbol
@c Reading,,Symbol Reading}.


@node Symbol Reading
@chapter 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 @file{symfile.c} using the BFD
library.  BFD identifies the type of the file by examining its header.
@code{symfile_init} then uses this identification to locate a
set of symbol-reading functions.

Symbol reading modules identify themselves to GDB by calling
@code{add_symtab_fns} during their module initialization.  The argument
to @code{add_symtab_fns} is a @code{struct sym_fns} which contains
the name (or name prefix) of the symbol format, the length of the prefix,
and pointers to four functions.  These functions are called at various
times to process symbol-files whose identification matches the specified
prefix.

The functions supplied by each module are:

@table @code
@item @var{xxx}_symfile_init(struct sym_fns *sf)

Called from @code{symbol_file_add} when we are about to read a new
symbol file.  This function should clean up any internal state
(possibly resulting from half-read previous files, for example)
and prepare to read a new symbol file. Note that the symbol file
which we are reading might be a new "main" symbol file, or might
be a secondary symbol file whose symbols are being added to the
existing symbol table.

The argument to @code{@var{xxx}_symfile_init} is a newly allocated
@code{struct sym_fns} whose @code{bfd} field contains the BFD
for the new symbol file being read.  Its @code{private} field
has been zeroed, and can be modified as desired.  Typically,
a struct of private information will be @code{malloc}'d, and
a pointer to it will be placed in the @code{private} field.

There is no result from @code{@var{xxx}_symfile_init}, but it can call
@code{error} if it detects an unavoidable problem.

@item @var{xxx}_new_init()

Called from @code{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
@code{symbol_file_add}.  It has no arguments and no result.
It may be called after @code{@var{xxx}_symfile_init}, if a new symbol
table is being read, or may be called alone if all symbols are
simply being discarded.

@item @var{xxx}_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)

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

@code{sf} points to the struct sym_fns originally passed to
@code{@var{xxx}_sym_init} for possible initialization.  @code{addr} is the
offset between the file's specified start address and its true address
in memory.  @code{mainline} is 1 if this is the main symbol table being
read, and 0 if a secondary symbol file (e.g. shared library or
dynamically loaded file) is being read.@refill
@end table

In addition, if a symbol-reading module creates psymtabs when
@var{xxx}_symfile_read is called, these psymtabs will contain a pointer to
a function @code{@var{xxx}_psymtab_to_symtab}, which can be called from
any point in the GDB symbol-handling code.

@table @code
@item @var{xxx}_psymtab_to_symtab (struct partial_symtab *pst)

Called from @code{psymtab_to_symtab} (or the PSYMTAB_TO_SYMTAB
macro) if the psymtab has not already been read in and had its
@code{pst->symtab} pointer set.  The argument is the psymtab
to be fleshed-out into a symtab.  Upon return, 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.
@end table


@node Cleanups
@chapter Cleanups

Cleanups are a structured way to deal with things that need to be done