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

END-INFO-DIR-ENTRY

   This file documents the internals of the GNU debugger GDB.

   Copyright 1990-1999 Free Software Foundation, Inc.  Contributed by

Cygnus Solutions.  Written by John Gilmore.  Second Edition by Stan

Shebs.

   Permission is granted to make and distribute verbatim copies of this

manual provided the copyright notice and this permission notice are

preserved on all copies.

   Permission is granted to copy or distribute modified versions of this

manual under the terms of the GPL (for which purpose this text may be

regarded as a program in the language TeX).

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

Scope of this Document

**********************

   This document documents the internals of the GNU debugger, GDB.  It

includes description of GDB's key algorithms and operations, as well as

the mechanisms that adapt GDB to specific hosts and targets.

* Menu:

* Requirements::

* Overall Structure::

* Algorithms::

* User Interface::

* Symbol Handling::

* Language Support::

* Host Definition::

* Target Architecture Definition::

* Target Vector Definition::

* Native Debugging::

* Support Libraries::

* Coding::

* Porting GDB::

* Testsuite::

* Hints::

File: gdbint.info,  Node: Requirements,  Next: Overall Structure,  Prev: Top,  Up: Top

Requirements

************

   Before diving into the internals, you should understand the formal

requirements and other expectations for GDB.  Although some of these may

seem obvious, there have been proposals for GDB that have run counter to

these requirements.

   First of all, GDB is a debugger.  It's not designed to be a front

panel for embedded systems.  It's not a text editor.  It's not a shell.

It's not a programming environment.

   GDB is an interactive tool.  Although a batch mode is available,

GDB's primary role is to interact with a human programmer.

   GDB should be responsive to the user.  A programmer hot on the trail

of a nasty bug, and operating under a looming deadline, is going to be

very impatient of everything, including the response time to debugger

commands.

   GDB should be relatively permissive, such as for expressions.  While

the compiler should be picky (or have the option to be made picky),

since source code lives for a long time usually, the programmer doing

debugging shouldn't be spending time figuring out to mollify the

debugger.

   GDB will be called upon to deal with really large programs.

Executable sizes of 50 to 100 megabytes occur regularly, and we've

heard reports of programs approaching 1 gigabyte in size.

   GDB should be able to run everywhere.  No other debugger is available

for even half as many configurations as GDB supports.

File: gdbint.info,  Node: Overall Structure,  Next: Algorithms,  Prev: Requirements,  Up: Top

Overall Structure

*****************

   GDB consists of three major subsystems: user interface, symbol

handling (the "symbol side"), and target system handling (the "target

side").

   Ther user interface consists of several actual interfaces, plus

supporting code.

   The symbol side consists of object file readers, debugging info

interpreters, symbol table management, source language expression

parsing, type and value printing.

   The target side consists of execution control, stack frame analysis,

and physical target manipulation.

   The target side/symbol side division is not formal, and there are a

number of exceptions.  For instance, core file support involves symbolic

elements (the basic core file reader is in BFD) and target elements (it

supplies the contents of memory and the values of registers).  Instead,

this division is useful for understanding how the minor subsystems

should fit together.

The Symbol Side

===============

   The symbolic side of GDB can be thought of as "everything you can do

in GDB without having a live program running".  For instance, you can

look at the types of variables, and evaluate many kinds of expressions.

The Target Side

===============

   The target side of GDB is the "bits and bytes manipulator".  Although

it may make reference to symbolic info here and there, most of the

target side will run with only a stripped executable available - or

even no executable at all, in remote debugging cases.

   Operations such as disassembly, stack frame crawls, and register

display, are able to work with no symbolic info at all.  In some cases,

such as disassembly, GDB will use symbolic info to present addresses

relative to symbols rather than as raw numbers, but it will work either

way.

Configurations

==============

   "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.

File: gdbint.info,  Node: Algorithms,  Next: User Interface,  Prev: Overall Structure,  Up: Top

Algorithms

**********

   GDB uses a number of debugging-specific algorithms.  They are often

not very complicated, but get lost in the thicket of special cases and

real-world issues.  This chapter describes the basic algorithms and

mentions some of the specific target definitions that they use.

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.)

   Given a GDB frame, define `FRAME_CHAIN' to 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.

Breakpoint Handling

===================

   In general, a breakpoint is a user-designated location in the program

where the user wants to regain control if program execution ever reaches

that location.

   There are two main ways to implement breakpoints; either as

"hardware" breakpoints or as "software" breakpoints.

   Hardware breakpoints are sometimes available as a builtin debugging

features with some chips.  Typically these work by having dedicated

register into which the breakpoint address may be stored.  If the PC

ever matches a value in a breakpoint registers, the CPU raises an

exception and reports it to GDB.  Another possibility is when an

emulator is in use; many emulators include circuitry that watches the

address lines coming out from the processor, and force it to stop if the

address matches a breakpoint's address.  A third possibility is that the

target already has the ability to do breakpoints somehow; for instance,

a ROM monitor may do its own software breakpoints.  So although these

are not literally "hardware breakpoints", from GDB's point of view they

work the same; GDB need not do nothing more than set the breakpoint and

wait for something to happen.

   Since they depend on hardware resources, hardware breakpoints may be

limited in number; when the user asks for more, GDB will start trying to

set software breakpoints.

   Software breakpoints require GDB to do somewhat more work.  The basic

theory is that GDB will replace a program instruction with a trap,

illegal divide, or some other instruction that will cause an exception,

and then when it's encountered, GDB will take the exception and stop the

program. When the user says to continue, GDB will restore the original

instruction, single-step, re-insert the trap, and continue on.

   Since it literally overwrites the program being tested, the program

area must be writeable, so this technique won't work on programs in

ROM.  It can also distort the behavior of programs that examine

themselves, although the situation would be highly unusual.

   Also, the software breakpoint instruction should be the smallest

size of instruction, so it doesn't overwrite an instruction that might

be a jump target, and cause disaster when the program jumps into the

middle of the breakpoint instruction.  (Strictly speaking, the

breakpoint must be no larger than the smallest interval between

instructions that may be jump targets; perhaps there is an architecture

where only even-numbered instructions may jumped to.)  Note that it's

possible for an instruction set not to have any instructions usable for

a software breakpoint, although in practice only the ARC has failed to

define such an instruction.

   The basic definition of the software breakpoint is the macro

`BREAKPOINT'.

   Basic breakpoint object handling is in `breakpoint.c'.  However,

much of the interesting breakpoint action is in `infrun.c'.

Single Stepping

===============

Signal Handling

===============

Thread Handling

===============

Inferior Function Calls

=======================

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-XYZ.h'

file.  Look in `tm-sun4os4.h' and `sparc-tdep.c' for examples of how to

do this.

File: gdbint.info,  Node: User Interface,  Next: Symbol Handling,  Prev: Algorithms,  Up: Top

User Interface

**************

   GDB has several user interfaces.  Although the command-line interface

is the most common and most familiar, there are others.

Command Interpreter

===================

   The command interpreter in GDB is fairly simple.  It is designed to

allow for the set of commands to be augmented dynamically, and also has

a recursive subcommand capability, where the first argument to a

command may itself direct a lookup on a different command list.

   For instance, the `set' command just starts a lookup on the

`setlist' command list, while `set thread' recurses to the

`set_thread_cmd_list'.

   To add commands in general, use `add_cmd'.  `add_com' adds to the

main command list, and should be used for those commands.  The usual

place to add commands is in the `_initialize_XYZ' routines at the ends

of most source files.

   Before removing commands from the command set it is a good idea to

deprecate them for some time.  Use `deprecate_cmd' on commands or

aliases to set the deprecated flag.  `deprecate_cmd' takes a `struct

cmd_list_element' as it's first argument.  You can use the return value

from `add_com' or `add_cmd' to deprecate the command immediately after

it is created.

   The first time a comamnd is used the user will be warned and offered

a replacement (if one exists). Note that the replacement string passed

to `deprecate_cmd' should be the full name of the command, i.e. the

entire string the user should type at the command line.

Console Printing

================

TUI

===

libgdb

======

   `libgdb' was an abortive project of years ago.  The theory was to

provide an API to GDB's functionality.

File: gdbint.info,  Node: Symbol Handling,  Next: Language Support,  Prev: User Interface,  Up: Top

Symbol Handling

***************

   Symbols are a key part of GDB's operation.  Symbols include

variables, functions, and types.

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 code in `symfile.c' using the

BFD library.  BFD identifies the type of the file by examining its

header.  `find_sym_fns' 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:

`XYZ_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 `XYZ_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 `XYZ_symfile_init', but it can call

     `error' if it detects an unavoidable problem.

`XYZ_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 `XYZ_symfile_init', if a new

     symbol table is being read, or may be called alone if all symbols

     are simply being discarded.

`XYZ_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

     `XYZ_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

XYZ_symfile_read is called, these psymtabs will contain a pointer to a

function `XYZ_psymtab_to_symtab', which can be called from any point in

the GDB symbol-handling code.

`XYZ_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.

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.

   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.

Object File Formats

===================

a.out

-----

   The `a.out' format is the original file format for Unix.  It

consists of three sections: text, data, and bss, which are for program

code, initialized data, and uninitialized data, respectively.

   The `a.out' format is so simple that it doesn't have any reserved

place for debugging information.  (Hey, the original Unix hackers used

`adb', which is a machine-language debugger.)  The only debugging

format for `a.out' is stabs, which is encoded as a set of normal

symbols with distinctive attributes.

   The basic `a.out' reader is in `dbxread.c'.

COFF

----

   The COFF format was introduced with System V Release 3 (SVR3) Unix.

COFF files may have multiple sections, each prefixed by a header.  The

number of sections is limited.

   The COFF specification includes support for debugging.  Although this

was a step forward, the debugging information was woefully limited.  For

instance, it was not possible to represent code that came from an

included file.

   The COFF reader is in `coffread.c'.

ECOFF

-----

   ECOFF is an extended COFF originally introduced for Mips and Alpha

workstations.

   The basic ECOFF reader is in `mipsread.c'.

XCOFF

-----

   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).  For more information, see

*Note Top: (stabs)Top.

   The shared library scheme has a 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).

PE

--

   Windows 95 and NT use the PE (Portable Executable) format for their

executables.  PE is basically COFF with additional headers.

   While BFD includes special PE support, GDB needs only the basic COFF

reader.

ELF

---

   The ELF format came with System V Release 4 (SVR4) Unix.  ELF is

similar to COFF in being organized into a number of sections, but it

removes many of COFF's limitations.

   The basic ELF reader is in `elfread.c'.

SOM

---

   SOM is HP's object file and debug format (not to be confused with

IBM's SOM, which is a cross-language ABI).

   The SOM reader is in `hpread.c'.

Other File Formats

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

   Other file formats that have been supported by GDB include Netware

Loadable Modules (`nlmread.c'.

Debugging File Formats

======================

   This section describes characteristics of debugging information that

are independent of the object file format.

stabs

-----

   `stabs' started out as special symbols within the `a.out' format.

Since then, it has been encapsulated into other file formats, such as

COFF and ELF.

   While `dbxread.c' does some of the basic stab processing, including

for encapsulated versions, `stabsread.c' does the real work.

COFF

----

   The basic COFF definition includes debugging information.  The level

of support is minimal and non-extensible, and is not often used.

Mips debug (Third Eye)

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

   ECOFF includes a definition of a special debug format.

   The file `mdebugread.c' implements reading for this format.

DWARF 1

-------

   DWARF 1 is a debugging format that was originally designed to be

used with ELF in SVR4 systems.

   The DWARF 1 reader is in `dwarfread.c'.

DWARF 2

-------

   DWARF 2 is an improved but incompatible version of DWARF 1.

   The DWARF 2 reader is in `dwarf2read.c'.

SOM

---

   Like COFF, the SOM definition includes debugging information.

Adding a New Symbol Reader to GDB

=================================

   If you are using an existing object file format (a.out, COFF, ELF,

etc), there is probably little to be done.

   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.

   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/libxyz.h', which is included by GDB.

File: gdbint.info,  Node: Language Support,  Next: Host Definition,  Prev: Symbol Handling,  Up: Top

Language Support

****************

   GDB's language support is mainly driven by the symbol reader,

although it is possible for the user to set the source language

manually.

   GDB chooses the source language by looking at the extension of the

file recorded in the debug info; `.c' means C, `.f' means Fortran, etc.

It may also use a special-purpose language identifier if the debug

format supports it, such as DWARF.

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: Host Definition,  Next: Target Architecture Definition,  Prev: Language Support,  Up: Top

Host Definition

***************

   With the advent of autoconf, it's rarely necessary to have host

definition machinery anymore.

Adding a New Host

=================

   Most of GDB's host configuration support happens via autoconf.  It

should be rare to need new host-specific definitions.  GDB still uses

the host-specific definitions and files listed below, but these mostly

exist for historical reasons, and should eventually disappear.

   Several files control GDB's configuration for host systems:

`gdb/config/ARCH/XYZ.mh'

     Specifies Makefile fragments needed when hosting on machine XYZ.

     In particular, this lists the required machine-dependent object

     files, by defining `XDEPFILES=...'.  Also specifies the header file

     which describes host XYZ, by defining `XM_FILE= xm-XYZ.h'.  You

     can also define `CC', `SYSV_DEFINE', `XM_CFLAGS', `XM_ADD_FILES',

     `XM_CLIBS', `XM_CDEPS', etc.; see `Makefile.in'.

`gdb/config/ARCH/xm-XYZ.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.

`gdb/XYZ-xdep.c'

     Contains any miscellaneous C code required for this machine as a

     host.  On most machines it doesn't exist at all.  If it does

     exist, put `XYZ-xdep.o' into the `XDEPFILES' line in

     `gdb/config/ARCH/XYZ.mh'.

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-XYZ.h' file.  If these routines work for the XYZ

host, you can just include the generic file's name (with `.o', not

`.c') in `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 `XYZ-xdep.c', and put `XYZ-xdep.o' into

`XDEPFILES'.

`ser-unix.c'

     This contains serial line support for Unix systems.  This is always

     included, via the makefile variable `SER_HARDWIRE'; override this

     variable in the `.mh' file to avoid it.

`ser-go32.c'

     This contains serial line support for 32-bit programs running

     under DOS, using the GO32 execution environment.

`ser-tcp.c'

     This contains generic TCP support using sockets.

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 (or if the meaning is not

documented here, then one of the source files where they are used is

indicated) are:

`GDBINIT_FILENAME'

     The default name of GDB's initialization file (normally

     `.gdbinit').

`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_STD_REGS'

     This macro is deprecated.

`NO_SYS_FILE'

     Define this if your system does not have a `'.

`SIGWINCH_HANDLER'

     If your host defines `SIGWINCH', you can define this to be the name

     of a function to be called if `SIGWINCH' is received.

`SIGWINCH_HANDLER_BODY'

     Define this to expand into code that will define the function

     named by the expansion of `SIGWINCH_HANDLER'.

`ALIGN_STACK_ON_STARTUP'

     Define this if your system is of a sort that will crash in

     `tgetent' if the stack happens not to be longword-aligned when

     `main' is called.  This is a rare situation, but is known to occur

     on several different types of systems.

`CRLF_SOURCE_FILES'

     Define this if host files use `\r\n' rather than `\n' as a line

     terminator.  This will cause source file listings to omit `\r'

     characters when printing and it will allow \r\n line endings of

     files which are "sourced" by gdb.  It must be possible to open

     files in binary mode using `O_BINARY' or, for fopen, `"rb"'.

`DEFAULT_PROMPT'

     The default value of the prompt string (normally `"(gdb) "').

`DEV_TTY'

     The name of the generic TTY device, defaults to `"/dev/tty"'.

`FCLOSE_PROVIDED'

     Define this if the system declares `fclose' in the headers included

     in `defs.h'.  This isn't needed unless your compiler is unusually

     anal.

`FOPEN_RB'

     Define this if binary files are opened the same way as text files.

`GETENV_PROVIDED'

     Define this if the system declares `getenv' in its headers included

     in `defs.h'. This isn't needed unless your compiler is unusually

     anal.

`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_SIGSETMASK'