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\input texinfo
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@setfilename gdbint.info
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4
@ifinfo
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@format
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START-INFO-DIR-ENTRY
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* Gdb-Internals: (gdbint).      The GNU debugger's internals.
8
END-INFO-DIR-ENTRY
9
@end format
10
@end ifinfo
11
 
12
@ifinfo
13
This file documents the internals of the GNU debugger GDB.
14
 
15
Copyright 1990-1999 Free Software Foundation, Inc.
16
Contributed by Cygnus Solutions.  Written by John Gilmore.
17
Second Edition by Stan Shebs.
18
 
19
Permission is granted to make and distribute verbatim copies of this
20
manual provided the copyright notice and this permission notice are
21
preserved on all copies.
22
 
23
@ignore
24
Permission is granted to process this file through Tex and print the
25
results, provided the printed document carries copying permission notice
26
identical to this one except for the removal of this paragraph (this
27
paragraph not being relevant to the printed manual).
28
 
29
@end ignore
30
Permission is granted to copy or distribute modified versions of this
31
manual under the terms of the GPL (for which purpose this text may be
32
regarded as a program in the language TeX).
33
@end ifinfo
34
 
35
@setchapternewpage off
36
@settitle GDB Internals
37
 
38
@titlepage
39
@title{GDB Internals}
40
@subtitle{A guide to the internals of the GNU debugger}
41
@author John Gilmore
42
@author Cygnus Solutions
43
@author Second Edition:
44
@author Stan Shebs
45
@author Cygnus Solutions
46
@page
47
@tex
48
\def\$#1${{#1}}  % Kluge: collect RCS revision info without $...$
49
\xdef\manvers{\$Revision: 1.1.1.1 $}  % For use in headers, footers too
50
{\parskip=0pt
51
\hfill Cygnus Solutions\par
52
\hfill \manvers\par
53
\hfill \TeX{}info \texinfoversion\par
54
}
55
@end tex
56
 
57
@vskip 0pt plus 1filll
58
Copyright @copyright{} 1990-1999 Free Software Foundation, Inc.
59
 
60
Permission is granted to make and distribute verbatim copies of
61
this manual provided the copyright notice and this permission notice
62
are preserved on all copies.
63
 
64
@end titlepage
65
 
66
@node Top
67
@c Perhaps this should be the title of the document (but only for info,
68
@c not for TeX).  Existing GNU manuals seem inconsistent on this point.
69
@top Scope of this Document
70
 
71
This document documents the internals of the GNU debugger, GDB.  It
72
includes description of GDB's key algorithms and operations, as well
73
as the mechanisms that adapt GDB to specific hosts and targets.
74
 
75
@menu
76
* Requirements::
77
* Overall Structure::
78
* Algorithms::
79
* User Interface::
80
* Symbol Handling::
81
* Language Support::
82
* Host Definition::
83
* Target Architecture Definition::
84
* Target Vector Definition::
85
* Native Debugging::
86
* Support Libraries::
87
* Coding::
88
* Porting GDB::
89
* Testsuite::
90
* Hints::
91
@end menu
92
 
93
@node Requirements
94
 
95
@chapter Requirements
96
 
97
Before diving into the internals, you should understand the formal
98
requirements and other expectations for GDB.  Although some of these may
99
seem obvious, there have been proposals for GDB that have run counter to
100
these requirements.
101
 
102
First of all, GDB is a debugger.  It's not designed to be a front panel
103
for embedded systems.  It's not a text editor.  It's not a shell.  It's
104
not a programming environment.
105
 
106
GDB is an interactive tool.  Although a batch mode is available, GDB's
107
primary role is to interact with a human programmer.
108
 
109
GDB should be responsive to the user.  A programmer hot on the trail of
110
a nasty bug, and operating under a looming deadline, is going to be very
111
impatient of everything, including the response time to debugger
112
commands.
113
 
114
GDB should be relatively permissive, such as for expressions.  While the
115
compiler should be picky (or have the option to be made picky), since
116
source code lives for a long time usually, the programmer doing
117
debugging shouldn't be spending time figuring out to mollify the
118
debugger.
119
 
120
GDB will be called upon to deal with really large programs.  Executable
121
sizes of 50 to 100 megabytes occur regularly, and we've heard reports of
122
programs approaching 1 gigabyte in size.
123
 
124
GDB should be able to run everywhere.  No other debugger is available
125
for even half as many configurations as GDB supports.
126
 
127
 
128
@node Overall Structure
129
 
130
@chapter Overall Structure
131
 
132
GDB consists of three major subsystems: user interface, symbol handling
133
(the ``symbol side''), and target system handling (the ``target side'').
134
 
135
Ther user interface consists of several actual interfaces, plus
136
supporting code.
137
 
138
The symbol side consists of object file readers, debugging info
139
interpreters, symbol table management, source language expression
140
parsing, type and value printing.
141
 
142
The target side consists of execution control, stack frame analysis, and
143
physical target manipulation.
144
 
145
The target side/symbol side division is not formal, and there are a
146
number of exceptions.  For instance, core file support involves symbolic
147
elements (the basic core file reader is in BFD) and target elements (it
148
supplies the contents of memory and the values of registers).  Instead,
149
this division is useful for understanding how the minor subsystems
150
should fit together.
151
 
152
@section The Symbol Side
153
 
154
The symbolic side of GDB can be thought of as ``everything you can do in
155
GDB without having a live program running''.  For instance, you can look
156
at the types of variables, and evaluate many kinds of expressions.
157
 
158
@section The Target Side
159
 
160
The target side of GDB is the ``bits and bytes manipulator''.  Although
161
it may make reference to symbolic info here and there, most of the
162
target side will run with only a stripped executable available -- or
163
even no executable at all, in remote debugging cases.
164
 
165
Operations such as disassembly, stack frame crawls, and register
166
display, are able to work with no symbolic info at all.  In some cases,
167
such as disassembly, GDB will use symbolic info to present addresses
168
relative to symbols rather than as raw numbers, but it will work either
169
way.
170
 
171
@section Configurations
172
 
173
@dfn{Host} refers to attributes of the system where GDB runs.
174
@dfn{Target} refers to the system where the program being debugged
175
executes.  In most cases they are the same machine, in which case a
176
third type of @dfn{Native} attributes come into play.
177
 
178
Defines and include files needed to build on the host are host support.
179
Examples are tty support, system defined types, host byte order, host
180
float format.
181
 
182
Defines and information needed to handle the target format are target
183
dependent.  Examples are the stack frame format, instruction set,
184
breakpoint instruction, registers, and how to set up and tear down the stack
185
to call a function.
186
 
187
Information that is only needed when the host and target are the same,
188
is native dependent.  One example is Unix child process support; if the
189
host and target are not the same, doing a fork to start the target
190
process is a bad idea.  The various macros needed for finding the
191
registers in the @code{upage}, running @code{ptrace}, and such are all
192
in the native-dependent files.
193
 
194
Another example of native-dependent code is support for features that
195
are really part of the target environment, but which require
196
@code{#include} files that are only available on the host system.  Core
197
file handling and @code{setjmp} handling are two common cases.
198
 
199
When you want to make GDB work ``native'' on a particular machine, you
200
have to include all three kinds of information.
201
 
202
 
203
@node Algorithms
204
 
205
@chapter Algorithms
206
 
207
GDB uses a number of debugging-specific algorithms.  They are often not
208
very complicated, but get lost in the thicket of special cases and
209
real-world issues.  This chapter describes the basic algorithms and
210
mentions some of the specific target definitions that they use.
211
 
212
@section Frames
213
 
214
A frame is a construct that GDB uses to keep track of calling and called
215
functions.
216
 
217
@code{FRAME_FP} in the machine description has no meaning to the
218
machine-independent part of GDB, except that it is used when setting up
219
a new frame from scratch, as follows:
220
 
221
@example
222
      create_new_frame (read_register (FP_REGNUM), read_pc ()));
223
@end example
224
 
225
Other than that, all the meaning imparted to @code{FP_REGNUM} is
226
imparted by the machine-dependent code.  So, @code{FP_REGNUM} can have
227
any value that is convenient for the code that creates new frames.
228
(@code{create_new_frame} calls @code{INIT_EXTRA_FRAME_INFO} if it is
229
defined; that is where you should use the @code{FP_REGNUM} value, if
230
your frames are nonstandard.)
231
 
232
Given a GDB frame, define @code{FRAME_CHAIN} to determine the address of
233
the calling function's frame.  This will be used to create a new GDB
234
frame struct, and then @code{INIT_EXTRA_FRAME_INFO} and
235
@code{INIT_FRAME_PC} will be called for the new frame.
236
 
237
@section Breakpoint Handling
238
 
239
In general, a breakpoint is a user-designated location in the program
240
where the user wants to regain control if program execution ever reaches
241
that location.
242
 
243
There are two main ways to implement breakpoints; either as ``hardware''
244
breakpoints or as ``software'' breakpoints.
245
 
246
Hardware breakpoints are sometimes available as a builtin debugging
247
features with some chips.  Typically these work by having dedicated
248
register into which the breakpoint address may be stored.  If the PC
249
ever matches a value in a breakpoint registers, the CPU raises an
250
exception and reports it to GDB.  Another possibility is when an
251
emulator is in use; many emulators include circuitry that watches the
252
address lines coming out from the processor, and force it to stop if the
253
address matches a breakpoint's address.  A third possibility is that the
254
target already has the ability to do breakpoints somehow; for instance,
255
a ROM monitor may do its own software breakpoints.  So although these
256
are not literally ``hardware breakpoints'', from GDB's point of view
257
they work the same; GDB need not do nothing more than set the breakpoint
258
and wait for something to happen.
259
 
260
Since they depend on hardware resources, hardware breakpoints may be
261
limited in number; when the user asks for more, GDB will start trying to
262
set software breakpoints.
263
 
264
Software breakpoints require GDB to do somewhat more work.  The basic
265
theory is that GDB will replace a program instruction with a trap,
266
illegal divide, or some other instruction that will cause an exception,
267
and then when it's encountered, GDB will take the exception and stop the
268
program. When the user says to continue, GDB will restore the original
269
instruction, single-step, re-insert the trap, and continue on.
270
 
271
Since it literally overwrites the program being tested, the program area
272
must be writeable, so this technique won't work on programs in ROM.  It
273
can also distort the behavior of programs that examine themselves,
274
although the situation would be highly unusual.
275
 
276
Also, the software breakpoint instruction should be the smallest size of
277
instruction, so it doesn't overwrite an instruction that might be a jump
278
target, and cause disaster when the program jumps into the middle of the
279
breakpoint instruction.  (Strictly speaking, the breakpoint must be no
280
larger than the smallest interval between instructions that may be jump
281
targets; perhaps there is an architecture where only even-numbered
282
instructions may jumped to.)  Note that it's possible for an instruction
283
set not to have any instructions usable for a software breakpoint,
284
although in practice only the ARC has failed to define such an
285
instruction.
286
 
287
The basic definition of the software breakpoint is the macro
288
@code{BREAKPOINT}.
289
 
290
Basic breakpoint object handling is in @file{breakpoint.c}.  However,
291
much of the interesting breakpoint action is in @file{infrun.c}.
292
 
293
@section Single Stepping
294
 
295
@section Signal Handling
296
 
297
@section Thread Handling
298
 
299
@section Inferior Function Calls
300
 
301
@section Longjmp Support
302
 
303
GDB has support for figuring out that the target is doing a
304
@code{longjmp} and for stopping at the target of the jump, if we are
305
stepping.  This is done with a few specialized internal breakpoints,
306
which are visible in the @code{maint info breakpoint} command.
307
 
308
To make this work, you need to define a macro called
309
@code{GET_LONGJMP_TARGET}, which will examine the @code{jmp_buf}
310
structure and extract the longjmp target address.  Since @code{jmp_buf}
311
is target specific, you will need to define it in the appropriate
312
@file{tm-@var{xyz}.h} file.  Look in @file{tm-sun4os4.h} and
313
@file{sparc-tdep.c} for examples of how to do this.
314
 
315
@node User Interface
316
 
317
@chapter User Interface
318
 
319
GDB has several user interfaces.  Although the command-line interface
320
is the most common and most familiar, there are others.
321
 
322
@section Command Interpreter
323
 
324
The command interpreter in GDB is fairly simple.  It is designed to
325
allow for the set of commands to be augmented dynamically, and also
326
has a recursive subcommand capability, where the first argument to
327
a command may itself direct a lookup on a different command list.
328
 
329
For instance, the @code{set} command just starts a lookup on the
330
@code{setlist} command list, while @code{set thread} recurses
331
to the @code{set_thread_cmd_list}.
332
 
333
To add commands in general, use @code{add_cmd}.  @code{add_com} adds to
334
the main command list, and should be used for those commands.  The usual
335
place to add commands is in the @code{_initialize_@var{xyz}} routines at
336
the ends of most source files.
337
 
338
Before removing commands from the command set it is a good idea to
339
deprecate them for some time.  Use @code{deprecate_cmd} on commands or
340
aliases to set the deprecated flag.  @code{deprecate_cmd} takes a
341
@code{struct cmd_list_element} as it's first argument.  You can use the
342
return value from @code{add_com} or @code{add_cmd} to deprecate the
343
command immediately after it is created.
344
 
345
The first time a comamnd is used the user will be warned and offered a
346
replacement (if one exists). Note that the replacement string passed to
347
@code{deprecate_cmd} should be the full name of the command, i.e. the
348
entire string the user should type at the command line.
349
 
350
@section Console Printing
351
 
352
@section TUI
353
 
354
@section libgdb
355
 
356
@code{libgdb} was an abortive project of years ago.  The theory was to
357
provide an API to GDB's functionality.
358
 
359
@node Symbol Handling
360
 
361
@chapter Symbol Handling
362
 
363
Symbols are a key part of GDB's operation.  Symbols include variables,
364
functions, and types.
365
 
366
@section Symbol Reading
367
 
368
GDB reads symbols from ``symbol files''.  The usual symbol file is the
369
file containing the program which GDB is debugging.  GDB can be directed
370
to use a different file for symbols (with the @code{symbol-file}
371
command), and it can also read more symbols via the ``add-file'' and
372
``load'' commands, or while reading symbols from shared libraries.
373
 
374
Symbol files are initially opened by code in @file{symfile.c} using the
375
BFD library.  BFD identifies the type of the file by examining its
376
header.  @code{find_sym_fns} then uses this identification to locate a
377
set of symbol-reading functions.
378
 
379
Symbol reading modules identify themselves to GDB by calling
380
@code{add_symtab_fns} during their module initialization.  The argument
381
to @code{add_symtab_fns} is a @code{struct sym_fns} which contains the
382
name (or name prefix) of the symbol format, the length of the prefix,
383
and pointers to four functions.  These functions are called at various
384
times to process symbol-files whose identification matches the specified
385
prefix.
386
 
387
The functions supplied by each module are:
388
 
389
@table @code
390
@item @var{xyz}_symfile_init(struct sym_fns *sf)
391
 
392
Called from @code{symbol_file_add} when we are about to read a new
393
symbol file.  This function should clean up any internal state (possibly
394
resulting from half-read previous files, for example) and prepare to
395
read a new symbol file. Note that the symbol file which we are reading
396
might be a new "main" symbol file, or might be a secondary symbol file
397
whose symbols are being added to the existing symbol table.
398
 
399
The argument to @code{@var{xyz}_symfile_init} is a newly allocated
400
@code{struct sym_fns} whose @code{bfd} field contains the BFD for the
401
new symbol file being read.  Its @code{private} field has been zeroed,
402
and can be modified as desired.  Typically, a struct of private
403
information will be @code{malloc}'d, and a pointer to it will be placed
404
in the @code{private} field.
405
 
406
There is no result from @code{@var{xyz}_symfile_init}, but it can call
407
@code{error} if it detects an unavoidable problem.
408
 
409
@item @var{xyz}_new_init()
410
 
411
Called from @code{symbol_file_add} when discarding existing symbols.
412
This function need only handle the symbol-reading module's internal
413
state; the symbol table data structures visible to the rest of GDB will
414
be discarded by @code{symbol_file_add}.  It has no arguments and no
415
result.  It may be called after @code{@var{xyz}_symfile_init}, if a new
416
symbol table is being read, or may be called alone if all symbols are
417
simply being discarded.
418
 
419
@item @var{xyz}_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)
420
 
421
Called from @code{symbol_file_add} to actually read the symbols from a
422
symbol-file into a set of psymtabs or symtabs.
423
 
424
@code{sf} points to the struct sym_fns originally passed to
425
@code{@var{xyz}_sym_init} for possible initialization.  @code{addr} is
426
the offset between the file's specified start address and its true
427
address in memory.  @code{mainline} is 1 if this is the main symbol
428
table being read, and 0 if a secondary symbol file (e.g. shared library
429
or dynamically loaded file) is being read.@refill
430
@end table
431
 
432
In addition, if a symbol-reading module creates psymtabs when
433
@var{xyz}_symfile_read is called, these psymtabs will contain a pointer
434
to a function @code{@var{xyz}_psymtab_to_symtab}, which can be called
435
from any point in the GDB symbol-handling code.
436
 
437
@table @code
438
@item @var{xyz}_psymtab_to_symtab (struct partial_symtab *pst)
439
 
440
Called from @code{psymtab_to_symtab} (or the PSYMTAB_TO_SYMTAB macro) if
441
the psymtab has not already been read in and had its @code{pst->symtab}
442
pointer set.  The argument is the psymtab to be fleshed-out into a
443
symtab.  Upon return, pst->readin should have been set to 1, and
444
pst->symtab should contain a pointer to the new corresponding symtab, or
445
zero if there were no symbols in that part of the symbol file.
446
@end table
447
 
448
@section Partial Symbol Tables
449
 
450
GDB has three types of symbol tables.
451
 
452
@itemize @bullet
453
 
454
@item full symbol tables (symtabs).  These contain the main information
455
about symbols and addresses.
456
 
457
@item partial symbol tables (psymtabs).  These contain enough
458
information to know when to read the corresponding part of the full
459
symbol table.
460
 
461
@item minimal symbol tables (msymtabs).  These contain information
462
gleaned from non-debugging symbols.
463
 
464
@end itemize
465
 
466
This section describes partial symbol tables.
467
 
468
A psymtab is constructed by doing a very quick pass over an executable
469
file's debugging information.  Small amounts of information are
470
extracted -- enough to identify which parts of the symbol table will
471
need to be re-read and fully digested later, when the user needs the
472
information.  The speed of this pass causes GDB to start up very
473
quickly.  Later, as the detailed rereading occurs, it occurs in small
474
pieces, at various times, and the delay therefrom is mostly invisible to
475
the user.
476
@c (@xref{Symbol Reading}.)
477
 
478
The symbols that show up in a file's psymtab should be, roughly, those
479
visible to the debugger's user when the program is not running code from
480
that file.  These include external symbols and types, static symbols and
481
types, and enum values declared at file scope.
482
 
483
The psymtab also contains the range of instruction addresses that the
484
full symbol table would represent.
485
 
486
The idea is that there are only two ways for the user (or much of the
487
code in the debugger) to reference a symbol:
488
 
489
@itemize @bullet
490
 
491
@item by its address
492
(e.g. execution stops at some address which is inside a function in this
493
file).  The address will be noticed to be in the range of this psymtab,
494
and the full symtab will be read in.  @code{find_pc_function},
495
@code{find_pc_line}, and other @code{find_pc_@dots{}} functions handle
496
this.
497
 
498
@item by its name
499
(e.g. the user asks to print a variable, or set a breakpoint on a
500
function).  Global names and file-scope names will be found in the
501
psymtab, which will cause the symtab to be pulled in.  Local names will
502
have to be qualified by a global name, or a file-scope name, in which
503
case we will have already read in the symtab as we evaluated the
504
qualifier.  Or, a local symbol can be referenced when we are "in" a
505
local scope, in which case the first case applies.  @code{lookup_symbol}
506
does most of the work here.
507
 
508
@end itemize
509
 
510
The only reason that psymtabs exist is to cause a symtab to be read in
511
at the right moment.  Any symbol that can be elided from a psymtab,
512
while still causing that to happen, should not appear in it.  Since
513
psymtabs don't have the idea of scope, you can't put local symbols in
514
them anyway.  Psymtabs don't have the idea of the type of a symbol,
515
either, so types need not appear, unless they will be referenced by
516
name.
517
 
518
It is a bug for GDB to behave one way when only a psymtab has been read,
519
and another way if the corresponding symtab has been read in.  Such bugs
520
are typically caused by a psymtab that does not contain all the visible
521
symbols, or which has the wrong instruction address ranges.
522
 
523
The psymtab for a particular section of a symbol-file (objfile) could be
524
thrown away after the symtab has been read in.  The symtab should always
525
be searched before the psymtab, so the psymtab will never be used (in a
526
bug-free environment).  Currently, psymtabs are allocated on an obstack,
527
and all the psymbols themselves are allocated in a pair of large arrays
528
on an obstack, so there is little to be gained by trying to free them
529
unless you want to do a lot more work.
530
 
531
@section Types
532
 
533
Fundamental Types (e.g., FT_VOID, FT_BOOLEAN).
534
 
535
These are the fundamental types that GDB uses internally.  Fundamental
536
types from the various debugging formats (stabs, ELF, etc) are mapped
537
into one of these.  They are basically a union of all fundamental types
538
that gdb knows about for all the languages that GDB knows about.
539
 
540
Type Codes (e.g., TYPE_CODE_PTR, TYPE_CODE_ARRAY).
541
 
542
Each time GDB builds an internal type, it marks it with one of these
543
types.  The type may be a fundamental type, such as TYPE_CODE_INT, or a
544
derived type, such as TYPE_CODE_PTR which is a pointer to another type.
545
Typically, several FT_* types map to one TYPE_CODE_* type, and are
546
distinguished by other members of the type struct, such as whether the
547
type is signed or unsigned, and how many bits it uses.
548
 
549
Builtin Types (e.g., builtin_type_void, builtin_type_char).
550
 
551
These are instances of type structs that roughly correspond to
552
fundamental types and are created as global types for GDB to use for
553
various ugly historical reasons.  We eventually want to eliminate these.
554
Note for example that builtin_type_int initialized in gdbtypes.c is
555
basically the same as a TYPE_CODE_INT type that is initialized in
556
c-lang.c for an FT_INTEGER fundamental type.  The difference is that the
557
builtin_type is not associated with any particular objfile, and only one
558
instance exists, while c-lang.c builds as many TYPE_CODE_INT types as
559
needed, with each one associated with some particular objfile.
560
 
561
@section Object File Formats
562
 
563
@subsection a.out
564
 
565
The @file{a.out} format is the original file format for Unix.  It
566
consists of three sections: text, data, and bss, which are for program
567
code, initialized data, and uninitialized data, respectively.
568
 
569
The @file{a.out} format is so simple that it doesn't have any reserved
570
place for debugging information.  (Hey, the original Unix hackers used
571
@file{adb}, which is a machine-language debugger.)  The only debugging
572
format for @file{a.out} is stabs, which is encoded as a set of normal
573
symbols with distinctive attributes.
574
 
575
The basic @file{a.out} reader is in @file{dbxread.c}.
576
 
577
@subsection COFF
578
 
579
The COFF format was introduced with System V Release 3 (SVR3) Unix.
580
COFF files may have multiple sections, each prefixed by a header.  The
581
number of sections is limited.
582
 
583
The COFF specification includes support for debugging.  Although this
584
was a step forward, the debugging information was woefully limited.  For
585
instance, it was not possible to represent code that came from an
586
included file.
587
 
588
The COFF reader is in @file{coffread.c}.
589
 
590
@subsection ECOFF
591
 
592
ECOFF is an extended COFF originally introduced for Mips and Alpha
593
workstations.
594
 
595
The basic ECOFF reader is in @file{mipsread.c}.
596
 
597
@subsection XCOFF
598
 
599
The IBM RS/6000 running AIX uses an object file format called XCOFF.
600
The COFF sections, symbols, and line numbers are used, but debugging
601
symbols are dbx-style stabs whose strings are located in the
602
@samp{.debug} section (rather than the string table).  For more
603
information, see @xref{Top,,,stabs,The Stabs Debugging Format}.
604
 
605
The shared library scheme has a clean interface for figuring out what
606
shared libraries are in use, but the catch is that everything which
607
refers to addresses (symbol tables and breakpoints at least) needs to be
608
relocated for both shared libraries and the main executable.  At least
609
using the standard mechanism this can only be done once the program has
610
been run (or the core file has been read).
611
 
612
@subsection PE
613
 
614
Windows 95 and NT use the PE (Portable Executable) format for their
615
executables.  PE is basically COFF with additional headers.
616
 
617
While BFD includes special PE support, GDB needs only the basic
618
COFF reader.
619
 
620
@subsection ELF
621
 
622
The ELF format came with System V Release 4 (SVR4) Unix.  ELF is similar
623
to COFF in being organized into a number of sections, but it removes
624
many of COFF's limitations.
625
 
626
The basic ELF reader is in @file{elfread.c}.
627
 
628
@subsection SOM
629
 
630
SOM is HP's object file and debug format (not to be confused with IBM's
631
SOM, which is a cross-language ABI).
632
 
633
The SOM reader is in @file{hpread.c}.
634
 
635
@subsection Other File Formats
636
 
637
Other file formats that have been supported by GDB include Netware
638
Loadable Modules (@file{nlmread.c}.
639
 
640
@section Debugging File Formats
641
 
642
This section describes characteristics of debugging information that
643
are independent of the object file format.
644
 
645
@subsection stabs
646
 
647
@code{stabs} started out as special symbols within the @code{a.out}
648
format.  Since then, it has been encapsulated into other file
649
formats, such as COFF and ELF.
650
 
651
While @file{dbxread.c} does some of the basic stab processing,
652
including for encapsulated versions, @file{stabsread.c} does
653
the real work.
654
 
655
@subsection COFF
656
 
657
The basic COFF definition includes debugging information.  The level
658
of support is minimal and non-extensible, and is not often used.
659
 
660
@subsection Mips debug (Third Eye)
661
 
662
ECOFF includes a definition of a special debug format.
663
 
664
The file @file{mdebugread.c} implements reading for this format.
665
 
666
@subsection DWARF 1
667
 
668
DWARF 1 is a debugging format that was originally designed to be
669
used with ELF in SVR4 systems.
670
 
671
@c CHILL_PRODUCER
672
@c GCC_PRODUCER
673
@c GPLUS_PRODUCER
674
@c LCC_PRODUCER
675
@c If defined, these are the producer strings in a DWARF 1 file.  All of
676
@c these have reasonable defaults already.
677
 
678
The DWARF 1 reader is in @file{dwarfread.c}.
679
 
680
@subsection DWARF 2
681
 
682
DWARF 2 is an improved but incompatible version of DWARF 1.
683
 
684
The DWARF 2 reader is in @file{dwarf2read.c}.
685
 
686
@subsection SOM
687
 
688
Like COFF, the SOM definition includes debugging information.
689
 
690
@section Adding a New Symbol Reader to GDB
691
 
692
If you are using an existing object file format (a.out, COFF, ELF, etc),
693
there is probably little to be done.
694
 
695
If you need to add a new object file format, you must first add it to
696
BFD.  This is beyond the scope of this document.
697
 
698
You must then arrange for the BFD code to provide access to the
699
debugging symbols.  Generally GDB will have to call swapping routines
700
from BFD and a few other BFD internal routines to locate the debugging
701
information.  As much as possible, GDB should not depend on the BFD
702
internal data structures.
703
 
704
For some targets (e.g., COFF), there is a special transfer vector used
705
to call swapping routines, since the external data structures on various
706
platforms have different sizes and layouts.  Specialized routines that
707
will only ever be implemented by one object file format may be called
708
directly.  This interface should be described in a file
709
@file{bfd/libxyz.h}, which is included by GDB.
710
 
711
 
712
@node Language Support
713
 
714
@chapter Language Support
715
 
716
GDB's language support is mainly driven by the symbol reader, although
717
it is possible for the user to set the source language manually.
718
 
719
GDB chooses the source language by looking at the extension of the file
720
recorded in the debug info; @code{.c} means C, @code{.f} means Fortran,
721
etc.  It may also use a special-purpose language identifier if the debug
722
format supports it, such as DWARF.
723
 
724
@section Adding a Source Language to GDB
725
 
726
To add other languages to GDB's expression parser, follow the following
727
steps:
728
 
729
@table @emph
730
@item Create the expression parser.
731
 
732
This should reside in a file @file{@var{lang}-exp.y}.  Routines for
733
building parsed expressions into a @samp{union exp_element} list are in
734
@file{parse.c}.
735
 
736
Since we can't depend upon everyone having Bison, and YACC produces
737
parsers that define a bunch of global names, the following lines
738
@emph{must} be included at the top of the YACC parser, to prevent the
739
various parsers from defining the same global names:
740
 
741
@example
742
#define yyparse         @var{lang}_parse
743
#define yylex   @var{lang}_lex
744
#define yyerror         @var{lang}_error
745
#define yylval  @var{lang}_lval
746
#define yychar  @var{lang}_char
747
#define yydebug         @var{lang}_debug
748
#define yypact          @var{lang}_pact
749
#define yyr1            @var{lang}_r1
750
#define yyr2            @var{lang}_r2
751
#define yydef           @var{lang}_def
752
#define yychk           @var{lang}_chk
753
#define yypgo           @var{lang}_pgo
754
#define yyact   @var{lang}_act
755
#define yyexca          @var{lang}_exca
756
#define yyerrflag       @var{lang}_errflag
757
#define yynerrs         @var{lang}_nerrs
758
@end example
759
 
760
At the bottom of your parser, define a @code{struct language_defn} and
761
initialize it with the right values for your language.  Define an
762
@code{initialize_@var{lang}} routine and have it call
763
@samp{add_language(@var{lang}_language_defn)} to tell the rest of GDB
764
that your language exists.  You'll need some other supporting variables
765
and functions, which will be used via pointers from your
766
@code{@var{lang}_language_defn}.  See the declaration of @code{struct
767
language_defn} in @file{language.h}, and the other @file{*-exp.y} files,
768
for more information.
769
 
770
@item Add any evaluation routines, if necessary
771
 
772
If you need new opcodes (that represent the operations of the language),
773
add them to the enumerated type in @file{expression.h}.  Add support
774
code for these operations in @code{eval.c:evaluate_subexp()}.  Add cases
775
for new opcodes in two functions from @file{parse.c}:
776
@code{prefixify_subexp()} and @code{length_of_subexp()}.  These compute
777
the number of @code{exp_element}s that a given operation takes up.
778
 
779
@item Update some existing code
780
 
781
Add an enumerated identifier for your language to the enumerated type
782
@code{enum language} in @file{defs.h}.
783
 
784
Update the routines in @file{language.c} so your language is included.
785
These routines include type predicates and such, which (in some cases)
786
are language dependent.  If your language does not appear in the switch
787
statement, an error is reported.
788
 
789
Also included in @file{language.c} is the code that updates the variable
790
@code{current_language}, and the routines that translate the
791
@code{language_@var{lang}} enumerated identifier into a printable
792
string.
793
 
794
Update the function @code{_initialize_language} to include your
795
language.  This function picks the default language upon startup, so is
796
dependent upon which languages that GDB is built for.
797
 
798
Update @code{allocate_symtab} in @file{symfile.c} and/or symbol-reading
799
code so that the language of each symtab (source file) is set properly.
800
This is used to determine the language to use at each stack frame level.
801
Currently, the language is set based upon the extension of the source
802
file.  If the language can be better inferred from the symbol
803
information, please set the language of the symtab in the symbol-reading
804
code.
805
 
806
Add helper code to @code{expprint.c:print_subexp()} to handle any new
807
expression opcodes you have added to @file{expression.h}.  Also, add the
808
printed representations of your operators to @code{op_print_tab}.
809
 
810
@item Add a place of call
811
 
812
Add a call to @code{@var{lang}_parse()} and @code{@var{lang}_error} in
813
@code{parse.c:parse_exp_1()}.
814
 
815
@item Use macros to trim code
816
 
817
The user has the option of building GDB for some or all of the
818
languages.  If the user decides to build GDB for the language
819
@var{lang}, then every file dependent on @file{language.h} will have the
820
macro @code{_LANG_@var{lang}} defined in it.  Use @code{#ifdef}s to
821
leave out large routines that the user won't need if he or she is not
822
using your language.
823
 
824
Note that you do not need to do this in your YACC parser, since if GDB
825
is not build for @var{lang}, then @file{@var{lang}-exp.tab.o} (the
826
compiled form of your parser) is not linked into GDB at all.
827
 
828
See the file @file{configure.in} for how GDB is configured for different
829
languages.
830
 
831
@item Edit @file{Makefile.in}
832
 
833
Add dependencies in @file{Makefile.in}.  Make sure you update the macro
834
variables such as @code{HFILES} and @code{OBJS}, otherwise your code may
835
not get linked in, or, worse yet, it may not get @code{tar}red into the
836
distribution!
837
 
838
@end table
839
 
840
 
841
@node Host Definition
842
 
843
@chapter Host Definition
844
 
845
With the advent of autoconf, it's rarely necessary to have host
846
definition machinery anymore.
847
 
848
@section Adding a New Host
849
 
850
Most of GDB's host configuration support happens via autoconf.  It
851
should be rare to need new host-specific definitions.  GDB still uses
852
the host-specific definitions and files listed below, but these mostly
853
exist for historical reasons, and should eventually disappear.
854
 
855
Several files control GDB's configuration for host systems:
856
 
857
@table @file
858
 
859
@item gdb/config/@var{arch}/@var{xyz}.mh
860
Specifies Makefile fragments needed when hosting on machine @var{xyz}.
861
In particular, this lists the required machine-dependent object files,
862
by defining @samp{XDEPFILES=@dots{}}.  Also specifies the header file
863
which describes host @var{xyz}, by defining @code{XM_FILE=
864
xm-@var{xyz}.h}.  You can also define @code{CC}, @code{SYSV_DEFINE},
865
@code{XM_CFLAGS}, @code{XM_ADD_FILES}, @code{XM_CLIBS}, @code{XM_CDEPS},
866
etc.; see @file{Makefile.in}.
867
 
868
@item gdb/config/@var{arch}/xm-@var{xyz}.h
869
(@file{xm.h} is a link to this file, created by configure).  Contains C
870
macro definitions describing the host system environment, such as byte
871
order, host C compiler and library.
872
 
873
@item gdb/@var{xyz}-xdep.c
874
Contains any miscellaneous C code required for this machine as a host.
875
On most machines it doesn't exist at all.  If it does exist, put
876
@file{@var{xyz}-xdep.o} into the @code{XDEPFILES} line in
877
@file{gdb/config/@var{arch}/@var{xyz}.mh}.
878
 
879
@end table
880
 
881
@subheading Generic Host Support Files
882
 
883
There are some ``generic'' versions of routines that can be used by
884
various systems.  These can be customized in various ways by macros
885
defined in your @file{xm-@var{xyz}.h} file.  If these routines work for
886
the @var{xyz} host, you can just include the generic file's name (with
887
@samp{.o}, not @samp{.c}) in @code{XDEPFILES}.
888
 
889
Otherwise, if your machine needs custom support routines, you will need
890
to write routines that perform the same functions as the generic file.
891
Put them into @code{@var{xyz}-xdep.c}, and put @code{@var{xyz}-xdep.o}
892
into @code{XDEPFILES}.
893
 
894
@table @file
895
 
896
@item ser-unix.c
897
This contains serial line support for Unix systems.  This is always
898
included, via the makefile variable @code{SER_HARDWIRE}; override this
899
variable in the @file{.mh} file to avoid it.
900
 
901
@item ser-go32.c
902
This contains serial line support for 32-bit programs running under DOS,
903
using the GO32 execution environment.
904
 
905
@item ser-tcp.c
906
This contains generic TCP support using sockets.
907
 
908
@end table
909
 
910
@section Host Conditionals
911
 
912
When GDB is configured and compiled, various macros are defined or left
913
undefined, to control compilation based on the attributes of the host
914
system.  These macros and their meanings (or if the meaning is not
915
documented here, then one of the source files where they are used is
916
indicated) are:
917
 
918
@table @code
919
 
920
@item GDBINIT_FILENAME
921
The default name of GDB's initialization file (normally @file{.gdbinit}).
922
 
923
@item MEM_FNS_DECLARED
924
Your host config file defines this if it includes declarations of
925
@code{memcpy} and @code{memset}.  Define this to avoid conflicts between
926
the native include files and the declarations in @file{defs.h}.
927
 
928
@item NO_STD_REGS
929
This macro is deprecated.
930
 
931
@item NO_SYS_FILE
932
Define this if your system does not have a @code{<sys/file.h>}.
933
 
934
@item SIGWINCH_HANDLER
935
If your host defines @code{SIGWINCH}, you can define this to be the name
936
of a function to be called if @code{SIGWINCH} is received.
937
 
938
@item SIGWINCH_HANDLER_BODY
939
Define this to expand into code that will define the function named by
940
the expansion of @code{SIGWINCH_HANDLER}.
941
 
942
@item ALIGN_STACK_ON_STARTUP
943
Define this if your system is of a sort that will crash in
944
@code{tgetent} if the stack happens not to be longword-aligned when
945
@code{main} is called.  This is a rare situation, but is known to occur
946
on several different types of systems.
947
 
948
@item CRLF_SOURCE_FILES
949
Define this if host files use @code{\r\n} rather than @code{\n} as a
950
line terminator.  This will cause source file listings to omit @code{\r}
951
characters when printing and it will allow \r\n line endings of files
952
which are "sourced" by gdb.  It must be possible to open files in binary
953
mode using @code{O_BINARY} or, for fopen, @code{"rb"}.
954
 
955
@item DEFAULT_PROMPT
956
The default value of the prompt string (normally @code{"(gdb) "}).
957
 
958
@item DEV_TTY
959
The name of the generic TTY device, defaults to @code{"/dev/tty"}.
960
 
961
@item FCLOSE_PROVIDED
962
Define this if the system declares @code{fclose} in the headers included
963
in @code{defs.h}.  This isn't needed unless your compiler is unusually
964
anal.
965
 
966
@item FOPEN_RB
967
Define this if binary files are opened the same way as text files.
968
 
969
@item GETENV_PROVIDED
970
Define this if the system declares @code{getenv} in its headers included
971
in @code{defs.h}. This isn't needed unless your compiler is unusually
972
anal.
973
 
974
@item HAVE_MMAP
975
In some cases, use the system call @code{mmap} for reading symbol
976
tables.  For some machines this allows for sharing and quick updates.
977
 
978
@item HAVE_SIGSETMASK
979
Define this if the host system has job control, but does not define
980
@code{sigsetmask()}.  Currently, this is only true of the RS/6000.
981
 
982
@item HAVE_TERMIO
983
Define this if the host system has @code{termio.h}.
984
 
985
@item HOST_BYTE_ORDER
986
The ordering of bytes in the host.  This must be defined to be either
987
@code{BIG_ENDIAN} or @code{LITTLE_ENDIAN}.
988
 
989
@item INT_MAX
990
@item INT_MIN
991
@item LONG_MAX
992
@item UINT_MAX
993
@item ULONG_MAX
994
Values for host-side constants.
995
 
996
@item ISATTY
997
Substitute for isatty, if not available.
998
 
999
@item LONGEST
1000
This is the longest integer type available on the host.  If not defined,
1001
it will default to @code{long long} or @code{long}, depending on
1002
@code{CC_HAS_LONG_LONG}.
1003
 
1004
@item CC_HAS_LONG_LONG
1005
Define this if the host C compiler supports ``long long''.  This is set
1006
by the configure script.
1007
 
1008
@item PRINTF_HAS_LONG_LONG
1009
Define this if the host can handle printing of long long integers via
1010
the printf format directive ``ll''. This is set by the configure script.
1011
 
1012
@item HAVE_LONG_DOUBLE
1013
Define this if the host C compiler supports ``long double''.  This is
1014
set by the configure script.
1015
 
1016
@item PRINTF_HAS_LONG_DOUBLE
1017
Define this if the host can handle printing of long double float-point
1018
numbers via the printf format directive ``Lg''. This is set by the
1019
configure script.
1020
 
1021
@item SCANF_HAS_LONG_DOUBLE
1022
Define this if the host can handle the parsing of long double
1023
float-point numbers via the scanf format directive directive
1024
``Lg''. This is set by the configure script.
1025
 
1026
@item LSEEK_NOT_LINEAR
1027
Define this if @code{lseek (n)} does not necessarily move to byte number
1028
@code{n} in the file.  This is only used when reading source files.  It
1029
is normally faster to define @code{CRLF_SOURCE_FILES} when possible.
1030
 
1031
@item L_SET
1032
This macro is used as the argument to lseek (or, most commonly,
1033
bfd_seek).  FIXME, should be replaced by SEEK_SET instead, which is the
1034
POSIX equivalent.
1035
 
1036
@item MALLOC_INCOMPATIBLE
1037
Define this if the system's prototype for @code{malloc} differs from the
1038
@sc{ANSI} definition.
1039
 
1040
@item MMAP_BASE_ADDRESS
1041
When using HAVE_MMAP, the first mapping should go at this address.
1042
 
1043
@item MMAP_INCREMENT
1044
when using HAVE_MMAP, this is the increment between mappings.
1045
 
1046
@item NEED_POSIX_SETPGID
1047
Define this to use the POSIX version of @code{setpgid} to determine
1048
whether job control is available.
1049
 
1050
@item NORETURN
1051
If defined, this should be one or more tokens, such as @code{volatile},
1052
that can be used in both the declaration and definition of functions to
1053
indicate that they never return.  The default is already set correctly
1054
if compiling with GCC.  This will almost never need to be defined.
1055
 
1056
@item ATTR_NORETURN
1057
If defined, this should be one or more tokens, such as
1058
@code{__attribute__ ((noreturn))}, that can be used in the declarations
1059
of functions to indicate that they never return.  The default is already
1060
set correctly if compiling with GCC.  This will almost never need to be
1061
defined.
1062
 
1063
@item USE_GENERIC_DUMMY_FRAMES
1064
Define this to 1 if the target is using the generic inferior function
1065
call code.  See @code{blockframe.c} for more information.
1066
 
1067
@item USE_MMALLOC
1068
GDB will use the @code{mmalloc} library for memory allocation for symbol
1069
reading if this symbol is defined.  Be careful defining it since there
1070
are systems on which @code{mmalloc} does not work for some reason.  One
1071
example is the DECstation, where its RPC library can't cope with our
1072
redefinition of @code{malloc} to call @code{mmalloc}.  When defining
1073
@code{USE_MMALLOC}, you will also have to set @code{MMALLOC} in the
1074
Makefile, to point to the mmalloc library.  This define is set when you
1075
configure with --with-mmalloc.
1076
 
1077
@item NO_MMCHECK
1078
Define this if you are using @code{mmalloc}, but don't want the overhead
1079
of checking the heap with @code{mmcheck}.  Note that on some systems,
1080
the C runtime makes calls to malloc prior to calling @code{main}, and if
1081
@code{free} is ever called with these pointers after calling
1082
@code{mmcheck} to enable checking, a memory corruption abort is certain
1083
to occur.  These systems can still use mmalloc, but must define
1084
NO_MMCHECK.
1085
 
1086
@item MMCHECK_FORCE
1087
Define this to 1 if the C runtime allocates memory prior to
1088
@code{mmcheck} being called, but that memory is never freed so we don't
1089
have to worry about it triggering a memory corruption abort.  The
1090
default is 0, which means that @code{mmcheck} will only install the heap
1091
checking functions if there has not yet been any memory allocation
1092
calls, and if it fails to install the functions, gdb will issue a
1093
warning.  This is currently defined if you configure using
1094
--with-mmalloc.
1095
 
1096
@item NO_SIGINTERRUPT
1097
Define this to indicate that siginterrupt() is not available.
1098
 
1099
@item R_OK
1100
Define if this is not in a system .h file.
1101
 
1102
@item SEEK_CUR
1103
@item SEEK_SET
1104
Define these to appropriate value for the system lseek(), if not already
1105
defined.
1106
 
1107
@item STOP_SIGNAL
1108
This is the signal for stopping GDB.  Defaults to SIGTSTP.  (Only
1109
redefined for the Convex.)
1110
 
1111
@item USE_O_NOCTTY
1112
Define this if the interior's tty should be opened with the O_NOCTTY
1113
flag.  (FIXME: This should be a native-only flag, but @file{inflow.c} is
1114
always linked in.)
1115
 
1116
@item USG
1117
Means that System V (prior to SVR4) include files are in use.  (FIXME:
1118
This symbol is abused in @file{infrun.c}, @file{regex.c},
1119
@file{remote-nindy.c}, and @file{utils.c} for other things, at the
1120
moment.)
1121
 
1122
@item lint
1123
Define this to help placate lint in some situations.
1124
 
1125
@item volatile
1126
Define this to override the defaults of @code{__volatile__} or
1127
@code{/**/}.
1128
 
1129
@end table
1130
 
1131
 
1132
@node Target Architecture Definition
1133
 
1134
@chapter Target Architecture Definition
1135
 
1136
GDB's target architecture defines what sort of machine-language programs
1137
GDB can work with, and how it works with them.
1138
 
1139
At present, the target architecture definition consists of a number of C
1140
macros.
1141
 
1142
@section Registers and Memory
1143
 
1144
GDB's model of the target machine is rather simple.  GDB assumes the
1145
machine includes a bank of registers and a block of memory.  Each
1146
register may have a different size.
1147
 
1148
GDB does not have a magical way to match up with the compiler's idea of
1149
which registers are which; however, it is critical that they do match up
1150
accurately.  The only way to make this work is to get accurate
1151
information about the order that the compiler uses, and to reflect that
1152
in the @code{REGISTER_NAME} and related macros.
1153
 
1154
GDB can handle big-endian, little-endian, and bi-endian architectures.
1155
 
1156
@section Using Different Register and Memory Data Representations
1157
@cindex raw representation
1158
@cindex virtual representation
1159
@cindex representations, raw and virtual
1160
@cindex register data formats, converting
1161
@cindex @code{struct value}, converting register contents to
1162
 
1163
Some architectures use one representation for a value when it lives in a
1164
register, but use a different representation when it lives in memory.
1165
In GDB's terminology, the @dfn{raw} representation is the one used in
1166
the target registers, and the @dfn{virtual} representation is the one
1167
used in memory, and within GDB @code{struct value} objects.
1168
 
1169
For almost all data types on almost all architectures, the virtual and
1170
raw representations are identical, and no special handling is needed.
1171
However, they do occasionally differ.  For example:
1172
 
1173
@itemize @bullet
1174
 
1175
@item
1176
The x86 architecture supports an 80-bit long double type.  However, when
1177
we store those values in memory, they occupy twelve bytes: the
1178
floating-point number occupies the first ten, and the final two bytes
1179
are unused.  This keeps the values aligned on four-byte boundaries,
1180
allowing more efficient access.  Thus, the x86 80-bit floating-point
1181
type is the raw representation, and the twelve-byte loosely-packed
1182
arrangement is the virtual representation.
1183
 
1184
@item
1185
Some 64-bit MIPS targets present 32-bit registers to GDB as 64-bit
1186
registers, with garbage in their upper bits.  GDB ignores the top 32
1187
bits.  Thus, the 64-bit form, with garbage in the upper 32 bits, is the
1188
raw representation, and the trimmed 32-bit representation is the
1189
virtual representation.
1190
 
1191
@end itemize
1192
 
1193
In general, the raw representation is determined by the architecture, or
1194
GDB's interface to the architecture, while the virtual representation
1195
can be chosen for GDB's convenience.  GDB's register file,
1196
@code{registers}, holds the register contents in raw format, and the GDB
1197
remote protocol transmits register values in raw format.
1198
 
1199
Your architecture may define the following macros to request raw /
1200
virtual conversions:
1201
 
1202
@deftypefn {Target Macro} int REGISTER_CONVERTIBLE (int @var{reg})
1203
Return non-zero if register number @var{reg}'s value needs different raw
1204
and virtual formats.
1205
@end deftypefn
1206
 
1207
@deftypefn {Target Macro} int REGISTER_RAW_SIZE (int @var{reg})
1208
The size of register number @var{reg}'s raw value.  This is the number
1209
of bytes the register will occupy in @code{registers}, or in a GDB
1210
remote protocol packet.
1211
@end deftypefn
1212
 
1213
@deftypefn {Target Macro} int REGISTER_VIRTUAL_SIZE (int @var{reg})
1214
The size of register number @var{reg}'s value, in its virtual format.
1215
This is the size a @code{struct value}'s buffer will have, holding that
1216
register's value.
1217
@end deftypefn
1218
 
1219
@deftypefn {Target Macro} struct type *REGISTER_VIRTUAL_TYPE (int @var{reg})
1220
This is the type of the virtual representation of register number
1221
@var{reg}.  Note that there is no need for a macro giving a type for the
1222
register's raw form; once the register's value has been obtained, GDB
1223
always uses the virtual form.
1224
@end deftypefn
1225
 
1226
@deftypefn {Target Macro} void REGISTER_CONVERT_TO_VIRTUAL (int @var{reg}, struct type *@var{type}, char *@var{from}, char *@var{to})
1227
Convert the value of register number @var{reg} to @var{type}, which
1228
should always be @code{REGISTER_VIRTUAL_TYPE (@var{reg})}.  The buffer
1229
at @var{from} holds the register's value in raw format; the macro should
1230
convert the value to virtual format, and place it at @var{to}.
1231
 
1232
Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW take
1233
their @var{reg} and @var{type} arguments in different orders.
1234
@end deftypefn
1235
 
1236
@deftypefn {Target Macro} void REGISTER_CONVERT_TO_RAW (struct type *@var{type}, int @var{reg}, char *@var{from}, char *@var{to})
1237
Convert the value of register number @var{reg} to @var{type}, which
1238
should always be @code{REGISTER_VIRTUAL_TYPE (@var{reg})}.  The buffer
1239
at @var{from} holds the register's value in raw format; the macro should
1240
convert the value to virtual format, and place it at @var{to}.
1241
 
1242
Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW take
1243
their @var{reg} and @var{type} arguments in different orders.
1244
@end deftypefn
1245
 
1246
 
1247
@section Frame Interpretation
1248
 
1249
@section Inferior Call Setup
1250
 
1251
@section Compiler Characteristics
1252
 
1253
@section Target Conditionals
1254
 
1255
This section describes the macros that you can use to define the target
1256
machine.
1257
 
1258
@table @code
1259
 
1260
@item ADDITIONAL_OPTIONS
1261
@item ADDITIONAL_OPTION_CASES
1262
@item ADDITIONAL_OPTION_HANDLER
1263
@item ADDITIONAL_OPTION_HELP
1264
These are a set of macros that allow the addition of additional command
1265
line options to GDB.  They are currently used only for the unsupported
1266
i960 Nindy target, and should not be used in any other configuration.
1267
 
1268
@item ADDR_BITS_REMOVE (addr)
1269
If a raw machine instruction address includes any bits that are not
1270
really part of the address, then define this macro to expand into an
1271
expression that zeros those bits in @var{addr}.  This is only used for
1272
addresses of instructions, and even then not in all contexts.
1273
 
1274
For example, the two low-order bits of the PC on the Hewlett-Packard PA
1275
2.0 architecture contain the privilege level of the corresponding
1276
instruction.  Since instructions must always be aligned on four-byte
1277
boundaries, the processor masks out these bits to generate the actual
1278
address of the instruction.  ADDR_BITS_REMOVE should filter out these
1279
bits with an expression such as @code{((addr) & ~3)}.
1280
 
1281
@item BEFORE_MAIN_LOOP_HOOK
1282
Define this to expand into any code that you want to execute before the
1283
main loop starts.  Although this is not, strictly speaking, a target
1284
conditional, that is how it is currently being used.  Note that if a
1285
configuration were to define it one way for a host and a different way
1286
for the target, GDB will probably not compile, let alone run correctly.
1287
This is currently used only for the unsupported i960 Nindy target, and
1288
should not be used in any other configuration.
1289
 
1290
@item BELIEVE_PCC_PROMOTION
1291
Define if the compiler promotes a short or char parameter to an int, but
1292
still reports the parameter as its original type, rather than the
1293
promoted type.
1294
 
1295
@item BELIEVE_PCC_PROMOTION_TYPE
1296
Define this if GDB should believe the type of a short argument when
1297
compiled by pcc, but look within a full int space to get its value.
1298
Only defined for Sun-3 at present.
1299
 
1300
@item BITS_BIG_ENDIAN
1301
Define this if the numbering of bits in the targets does *not* match the
1302
endianness of the target byte order.  A value of 1 means that the bits
1303
are numbered in a big-endian order, 0 means little-endian.
1304
 
1305
@item BREAKPOINT
1306
This is the character array initializer for the bit pattern to put into
1307
memory where a breakpoint is set.  Although it's common to use a trap
1308
instruction for a breakpoint, it's not required; for instance, the bit
1309
pattern could be an invalid instruction.  The breakpoint must be no
1310
longer than the shortest instruction of the architecture.
1311
 
1312
@var{BREAKPOINT} has been deprecated in favour of
1313
@var{BREAKPOINT_FROM_PC}.
1314
 
1315
@item BIG_BREAKPOINT
1316
@item LITTLE_BREAKPOINT
1317
Similar to BREAKPOINT, but used for bi-endian targets.
1318
 
1319
@var{BIG_BREAKPOINT} and @var{LITTLE_BREAKPOINT} have been deprecated in
1320
favour of @var{BREAKPOINT_FROM_PC}.
1321
 
1322
@item REMOTE_BREAKPOINT
1323
@item LITTLE_REMOTE_BREAKPOINT
1324
@item BIG_REMOTE_BREAKPOINT
1325
Similar to BREAKPOINT, but used for remote targets.
1326
 
1327
@var{BIG_REMOTE_BREAKPOINT} and @var{LITTLE_REMOTE_BREAKPOINT} have been
1328
deprecated in favour of @var{BREAKPOINT_FROM_PC}.
1329
 
1330
@item BREAKPOINT_FROM_PC (pcptr, lenptr)
1331
 
1332
Use the program counter to determine the contents and size of a
1333
breakpoint instruction.  It returns a pointer to a string of bytes that
1334
encode a breakpoint instruction, stores the length of the string to
1335
*lenptr, and adjusts pc (if necessary) to point to the actual memory
1336
location where the breakpoint should be inserted.
1337
 
1338
Although it is common to use a trap instruction for a breakpoint, it's
1339
not required; for instance, the bit pattern could be an invalid
1340
instruction.  The breakpoint must be no longer than the shortest
1341
instruction of the architecture.
1342
 
1343
Replaces all the other @var{BREAKPOINT} macros.
1344
 
1345
@item MEMORY_INSERT_BREAKPOINT (addr, contents_cache)
1346
@item MEMORY_REMOVE_BREAKPOINT (addr, contents_cache)
1347
 
1348
Insert or remove memory based breakpoints.  Reasonable defaults
1349
(@code{default_memory_insert_breakpoint} and
1350
@code{default_memory_remove_breakpoint} respectively) have been
1351
provided so that it is not necessary to define these for most
1352
architectures.  Architectures which may want to define
1353
@var{MEMORY_INSERT_BREAKPOINT} and @var{MEMORY_REMOVE_BREAKPOINT} will
1354
likely have instructions that are oddly sized or are not stored in a
1355
conventional manner.
1356
 
1357
It may also be desirable (from an efficiency standpoint) to define
1358
custom breakpoint insertion and removal routines if
1359
@var{BREAKPOINT_FROM_PC} needs to read the target's memory for some
1360
reason.
1361
 
1362
@item CALL_DUMMY_P
1363
A C expresson that is non-zero when the target suports inferior function
1364
calls.
1365
 
1366
@item CALL_DUMMY_WORDS
1367
Pointer to an array of @var{LONGEST} words of data containing
1368
host-byte-ordered @var{REGISTER_BYTES} sized values that partially
1369
specify the sequence of instructions needed for an inferior function
1370
call.
1371
 
1372
Should be deprecated in favour of a macro that uses target-byte-ordered
1373
data.
1374
 
1375
@item SIZEOF_CALL_DUMMY_WORDS
1376
The size of @var{CALL_DUMMY_WORDS}.  When @var{CALL_DUMMY_P} this must
1377
return a positive value.  See also @var{CALL_DUMMY_LENGTH}.
1378
 
1379
@item CALL_DUMMY
1380
A static initializer for @var{CALL_DUMMY_WORDS}.  Deprecated.
1381
 
1382
@item CALL_DUMMY_LOCATION
1383
inferior.h
1384
 
1385
@item CALL_DUMMY_STACK_ADJUST
1386
Stack adjustment needed when performing an inferior function call.
1387
 
1388
Should be deprecated in favor of something like @var{STACK_ALIGN}.
1389
 
1390
@item CALL_DUMMY_STACK_ADJUST_P
1391
Predicate for use of @var{CALL_DUMMY_STACK_ADJUST}.
1392
 
1393
Should be deprecated in favor of something like @var{STACK_ALIGN}.
1394
 
1395
@item CANNOT_FETCH_REGISTER (regno)
1396
A C expression that should be nonzero if @var{regno} cannot be fetched
1397
from an inferior process.  This is only relevant if
1398
@code{FETCH_INFERIOR_REGISTERS} is not defined.
1399
 
1400
@item CANNOT_STORE_REGISTER (regno)
1401
A C expression that should be nonzero if @var{regno} should not be
1402
written to the target.  This is often the case for program counters,
1403
status words, and other special registers.  If this is not defined, GDB
1404
will assume that all registers may be written.
1405
 
1406
@item DO_DEFERRED_STORES
1407
@item CLEAR_DEFERRED_STORES
1408
Define this to execute any deferred stores of registers into the inferior,
1409
and to cancel any deferred stores.
1410
 
1411
Currently only implemented correctly for native Sparc configurations?
1412
 
1413
@item COERCE_FLOAT_TO_DOUBLE (@var{formal}, @var{actual})
1414
If we are calling a function by hand, and the function was declared
1415
(according to the debug info) without a prototype, should we
1416
automatically promote floats to doubles?  This macro must evaluate to
1417
non-zero if we should, or zero if we should leave the value alone.
1418
 
1419
The argument @var{actual} is the type of the value we want to pass to
1420
the function.  The argument @var{formal} is the type of this argument,
1421
as it appears in the function's definition.  Note that @var{formal} may
1422
be zero if we have no debugging information for the function, or if
1423
we're passing more arguments than are officially declared (for example,
1424
varargs).  This macro is never invoked if the function definitely has a
1425
prototype.
1426
 
1427
The default behavior is to promote only when we have no type information
1428
for the formal parameter.  This is different from the obvious behavior,
1429
which would be to promote whenever we have no prototype, just as the
1430
compiler does.  It's annoying, but some older targets rely on this.  If
1431
you want GDB to follow the typical compiler behavior --- to always
1432
promote when there is no prototype in scope --- your gdbarch init
1433
function can call @code{set_gdbarch_coerce_float_to_double} and select
1434
the @code{standard_coerce_float_to_double} function.
1435
 
1436
@item CPLUS_MARKER
1437
Define this to expand into the character that G++ uses to distinguish
1438
compiler-generated identifiers from programmer-specified identifiers.
1439
By default, this expands into @code{'$'}.  Most System V targets should
1440
define this to @code{'.'}.
1441
 
1442
@item DBX_PARM_SYMBOL_CLASS
1443
Hook for the @code{SYMBOL_CLASS} of a parameter when decoding DBX symbol
1444
information.  In the i960, parameters can be stored as locals or as
1445
args, depending on the type of the debug record.
1446
 
1447
@item DECR_PC_AFTER_BREAK
1448
Define this to be the amount by which to decrement the PC after the
1449
program encounters a breakpoint.  This is often the number of bytes in
1450
BREAKPOINT, though not always.  For most targets this value will be 0.
1451
 
1452
@item DECR_PC_AFTER_HW_BREAK
1453
Similarly, for hardware breakpoints.
1454
 
1455
@item DISABLE_UNSETTABLE_BREAK addr
1456
If defined, this should evaluate to 1 if @var{addr} is in a shared
1457
library in which breakpoints cannot be set and so should be disabled.
1458
 
1459
@item DO_REGISTERS_INFO
1460
If defined, use this to print the value of a register or all registers.
1461
 
1462
@item END_OF_TEXT_DEFAULT
1463
This is an expression that should designate the end of the text section
1464
(? FIXME ?)
1465
 
1466
@item EXTRACT_RETURN_VALUE(type,regbuf,valbuf)
1467
Define this to extract a function's return value of type @var{type} from
1468
the raw register state @var{regbuf} and copy that, in virtual format,
1469
into @var{valbuf}.
1470
 
1471
@item EXTRACT_STRUCT_VALUE_ADDRESS(regbuf)
1472
When @var{EXTRACT_STRUCT_VALUE_ADDRESS_P} this is used to to extract
1473
from an array @var{regbuf} (containing the raw register state) the
1474
address in which a function should return its structure value, as a
1475
CORE_ADDR (or an expression that can be used as one).
1476
 
1477
@item EXTRACT_STRUCT_VALUE_ADDRESS_P
1478
Predicate for @var{EXTRACT_STRUCT_VALUE_ADDRESS}.
1479
 
1480
@item FLOAT_INFO
1481
If defined, then the `info float' command will print information about
1482
the processor's floating point unit.
1483
 
1484
@item FP_REGNUM
1485
If the virtual frame pointer is kept in a register, then define this
1486
macro to be the number (greater than or equal to zero) of that register.
1487
 
1488
This should only need to be defined if @code{TARGET_READ_FP} and
1489
@code{TARGET_WRITE_FP} are not defined.
1490
 
1491
@item FRAMELESS_FUNCTION_INVOCATION(fi)
1492
Define this to an expression that returns 1 if the function invocation
1493
represented by @var{fi} does not have a stack frame associated with it.
1494
Otherwise return 0.
1495
 
1496
@item FRAME_ARGS_ADDRESS_CORRECT
1497
stack.c
1498
 
1499
@item FRAME_CHAIN(frame)
1500
Given @var{frame}, return a pointer to the calling frame.
1501
 
1502
@item FRAME_CHAIN_COMBINE(chain,frame)
1503
Define this to take the frame chain pointer and the frame's nominal
1504
address and produce the nominal address of the caller's frame.
1505
Presently only defined for HP PA.
1506
 
1507
@item FRAME_CHAIN_VALID(chain,thisframe)
1508
 
1509
Define this to be an expression that returns zero if the given frame is
1510
an outermost frame, with no caller, and nonzero otherwise.  Several
1511
common definitions are available.
1512
 
1513
@code{file_frame_chain_valid} is nonzero if the chain pointer is nonzero
1514
and given frame's PC is not inside the startup file (such as
1515
@file{crt0.o}).  @code{func_frame_chain_valid} is nonzero if the chain
1516
pointer is nonzero and the given frame's PC is not in @code{main()} or a
1517
known entry point function (such as @code{_start()}).
1518
@code{generic_file_frame_chain_valid} and
1519
@code{generic_func_frame_chain_valid} are equivalent implementations for
1520
targets using generic dummy frames.
1521
 
1522
@item FRAME_INIT_SAVED_REGS(frame)
1523
See @file{frame.h}.  Determines the address of all registers in the
1524
current stack frame storing each in @code{frame->saved_regs}.  Space for
1525
@code{frame->saved_regs} shall be allocated by
1526
@code{FRAME_INIT_SAVED_REGS} using either
1527
@code{frame_saved_regs_zalloc} or @code{frame_obstack_alloc}.
1528
 
1529
@var{FRAME_FIND_SAVED_REGS} and @var{EXTRA_FRAME_INFO} are deprecated.
1530
 
1531
@item FRAME_NUM_ARGS (fi)
1532
For the frame described by @var{fi} return the number of arguments that
1533
are being passed.  If the number of arguments is not known, return
1534
@code{-1}.
1535
 
1536
@item FRAME_SAVED_PC(frame)
1537
Given @var{frame}, return the pc saved there.  That is, the return
1538
address.
1539
 
1540
@item FUNCTION_EPILOGUE_SIZE
1541
For some COFF targets, the @code{x_sym.x_misc.x_fsize} field of the
1542
function end symbol is 0.  For such targets, you must define
1543
@code{FUNCTION_EPILOGUE_SIZE} to expand into the standard size of a
1544
function's epilogue.
1545
 
1546
@item FUNCTION_START_OFFSET
1547
An integer, giving the offset in bytes from a function's address (as
1548
used in the values of symbols, function pointers, etc.), and the
1549
function's first genuine instruction.
1550
 
1551
This is zero on almost all machines: the function's address is usually
1552
the address of its first instruction.  However, on the VAX, for example,
1553
each function starts with two bytes containing a bitmask indicating
1554
which registers to save upon entry to the function.  The VAX @code{call}
1555
instructions check this value, and save the appropriate registers
1556
automatically.  Thus, since the offset from the function's address to
1557
its first instruction is two bytes, @code{FUNCTION_START_OFFSET} would
1558
be 2 on the VAX.
1559
 
1560
@item GCC_COMPILED_FLAG_SYMBOL
1561
@item GCC2_COMPILED_FLAG_SYMBOL
1562
If defined, these are the names of the symbols that GDB will look for to
1563
detect that GCC compiled the file.  The default symbols are
1564
@code{gcc_compiled.} and @code{gcc2_compiled.}, respectively. (Currently
1565
only defined for the Delta 68.)
1566
 
1567
@item GDB_MULTI_ARCH
1568
If defined and non-zero, enables suport for multiple architectures
1569
within GDB.
1570
 
1571
The support can be enabled at two levels.  At level one, only
1572
definitions for previously undefined macros are provided; at level two,
1573
a multi-arch definition of all architecture dependant macros will be
1574
defined.
1575
 
1576
@item GDB_TARGET_IS_HPPA
1577
This determines whether horrible kludge code in dbxread.c and
1578
partial-stab.h is used to mangle multiple-symbol-table files from
1579
HPPA's.  This should all be ripped out, and a scheme like elfread.c
1580
used.
1581
 
1582
@item GET_LONGJMP_TARGET
1583
For most machines, this is a target-dependent parameter.  On the
1584
DECstation and the Iris, this is a native-dependent parameter, since
1585
<setjmp.h> is needed to define it.
1586
 
1587
This macro determines the target PC address that longjmp() will jump to,
1588
assuming that we have just stopped at a longjmp breakpoint.  It takes a
1589
CORE_ADDR * as argument, and stores the target PC value through this
1590
pointer.  It examines the current state of the machine as needed.
1591
 
1592
@item GET_SAVED_REGISTER
1593
Define this if you need to supply your own definition for the function
1594
@code{get_saved_register}.
1595
 
1596
@item HAVE_REGISTER_WINDOWS
1597
Define this if the target has register windows.
1598
@item REGISTER_IN_WINDOW_P (regnum)
1599
Define this to be an expression that is 1 if the given register is in
1600
the window.
1601
 
1602
@item IBM6000_TARGET
1603
Shows that we are configured for an IBM RS/6000 target.  This
1604
conditional should be eliminated (FIXME) and replaced by
1605
feature-specific macros.  It was introduced in haste and we are
1606
repenting at leisure.
1607
 
1608
@item SYMBOLS_CAN_START_WITH_DOLLAR
1609
Some systems have routines whose names start with @samp{$}.  Giving this
1610
macro a non-zero value tells GDB's expression parser to check for such
1611
routines when parsing tokens that begin with @samp{$}.
1612
 
1613
On HP-UX, certain system routines (millicode) have names beginning with
1614
@samp{$} or @samp{$$}.  For example, @code{$$dyncall} is a millicode
1615
routine that handles inter-space procedure calls on PA-RISC.
1616
 
1617
@item IEEE_FLOAT
1618
Define this if the target system uses IEEE-format floating point numbers.
1619
 
1620
@item INIT_EXTRA_FRAME_INFO (fromleaf, frame)
1621
If additional information about the frame is required this should be
1622
stored in @code{frame->extra_info}.  Space for @code{frame->extra_info}
1623
is allocated using @code{frame_obstack_alloc}.
1624
 
1625
@item INIT_FRAME_PC (fromleaf, prev)
1626
This is a C statement that sets the pc of the frame pointed to by
1627
@var{prev}.  [By default...]
1628
 
1629
@item INNER_THAN (lhs,rhs)
1630
Returns non-zero if stack address @var{lhs} is inner than (nearer to the
1631
stack top) stack address @var{rhs}. Define this as @code{lhs < rhs} if
1632
the target's stack grows downward in memory, or @code{lhs > rsh} if the
1633
stack grows upward.
1634
 
1635
@item IN_SIGTRAMP (pc, name)
1636
Define this to return true if the given @var{pc} and/or @var{name}
1637
indicates that the current function is a sigtramp.
1638
 
1639
@item SIGTRAMP_START (pc)
1640
@item SIGTRAMP_END (pc)
1641
Define these to be the start and end address of the sigtramp for the
1642
given @var{pc}.  On machines where the address is just a compile time
1643
constant, the macro expansion will typically just ignore the supplied
1644
@var{pc}.
1645
 
1646
@item IN_SOLIB_CALL_TRAMPOLINE pc name
1647
Define this to evaluate to nonzero if the program is stopped in the
1648
trampoline that connects to a shared library.
1649
 
1650
@item IN_SOLIB_RETURN_TRAMPOLINE pc name
1651
Define this to evaluate to nonzero if the program is stopped in the
1652
trampoline that returns from a shared library.
1653
 
1654
@item IN_SOLIB_DYNSYM_RESOLVE_CODE pc
1655
Define this to evaluate to nonzero if the program is stopped in the
1656
dynamic linker.
1657
 
1658
@item SKIP_SOLIB_RESOLVER pc
1659
Define this to evaluate to the (nonzero) address at which execution
1660
should continue to get past the dynamic linker's symbol resolution
1661
function.  A zero value indicates that it is not important or necessary
1662
to set a breakpoint to get through the dynamic linker and that single
1663
stepping will suffice.
1664
 
1665
@item IS_TRAPPED_INTERNALVAR (name)
1666
This is an ugly hook to allow the specification of special actions that
1667
should occur as a side-effect of setting the value of a variable
1668
internal to GDB.  Currently only used by the h8500.  Note that this
1669
could be either a host or target conditional.
1670
 
1671
@item NEED_TEXT_START_END
1672
Define this if GDB should determine the start and end addresses of the
1673
text section.  (Seems dubious.)
1674
 
1675
@item NO_HIF_SUPPORT
1676
(Specific to the a29k.)
1677
 
1678
@item REGISTER_CONVERTIBLE (@var{reg})
1679
Return non-zero if @var{reg} uses different raw and virtual formats.
1680
@xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1681
 
1682
@item REGISTER_RAW_SIZE (@var{reg})
1683
Return the raw size of @var{reg}.
1684
@xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1685
 
1686
@item REGISTER_VIRTUAL_SIZE (@var{reg})
1687
Return the virtual size of @var{reg}.
1688
@xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1689
 
1690
@item REGISTER_VIRTUAL_TYPE (@var{reg})
1691
Return the virtual type of @var{reg}.
1692
@xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1693
 
1694
@item REGISTER_CONVERT_TO_VIRTUAL(@var{reg}, @var{type}, @var{from}, @var{to})
1695
Convert the value of register @var{reg} from its raw form to its virtual
1696
form.
1697
@xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1698
 
1699
@item REGISTER_CONVERT_TO_RAW(@var{type}, @var{reg}, @var{from}, @var{to})
1700
Convert the value of register @var{reg} from its virtual form to its raw
1701
form.
1702
@xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1703
 
1704
@item SOFTWARE_SINGLE_STEP_P
1705
Define this as 1 if the target does not have a hardware single-step
1706
mechanism. The macro @code{SOFTWARE_SINGLE_STEP} must also be defined.
1707
 
1708
@item SOFTWARE_SINGLE_STEP(signal,insert_breapoints_p)
1709
A function that inserts or removes (dependant on
1710
@var{insert_breapoints_p}) breakpoints at each possible destinations of
1711
the next instruction. See @code{sparc-tdep.c} and @code{rs6000-tdep.c}
1712
for examples.
1713
 
1714
@item SOFUN_ADDRESS_MAYBE_MISSING
1715
 
1716
Somebody clever observed that, the more actual addresses you have in the
1717
debug information, the more time the linker has to spend relocating
1718
them.  So whenever there's some other way the debugger could find the
1719
address it needs, you should omit it from the debug info, to make
1720
linking faster.
1721
 
1722
@code{SOFUN_ADDRESS_MAYBE_MISSING} indicates that a particular set of
1723
hacks of this sort are in use, affecting @code{N_SO} and @code{N_FUN}
1724
entries in stabs-format debugging information.  @code{N_SO} stabs mark
1725
the beginning and ending addresses of compilation units in the text
1726
segment.  @code{N_FUN} stabs mark the starts and ends of functions.
1727
 
1728
@code{SOFUN_ADDRESS_MAYBE_MISSING} means two things:
1729
@itemize @bullet
1730
 
1731
@item
1732
@code{N_FUN} stabs have an address of zero.  Instead, you should find the
1733
addresses where the function starts by taking the function name from
1734
the stab, and then looking that up in the minsyms (the linker/
1735
assembler symbol table).  In other words, the stab has the name, and
1736
the linker / assembler symbol table is the only place that carries
1737
the address.
1738
 
1739
@item
1740
@code{N_SO} stabs have an address of zero, too.  You just look at the
1741
@code{N_FUN} stabs that appear before and after the @code{N_SO} stab,
1742
and guess the starting and ending addresses of the compilation unit from
1743
them.
1744
 
1745
@end itemize
1746
 
1747
@item PCC_SOL_BROKEN
1748
(Used only in the Convex target.)
1749
 
1750
@item PC_IN_CALL_DUMMY
1751
inferior.h
1752
 
1753
@item PC_LOAD_SEGMENT
1754
If defined, print information about the load segment for the program
1755
counter.  (Defined only for the RS/6000.)
1756
 
1757
@item PC_REGNUM
1758
If the program counter is kept in a register, then define this macro to
1759
be the number (greater than or equal to zero) of that register.
1760
 
1761
This should only need to be defined if @code{TARGET_READ_PC} and
1762
@code{TARGET_WRITE_PC} are not defined.
1763
 
1764
@item NPC_REGNUM
1765
The number of the ``next program counter'' register, if defined.
1766
 
1767
@item NNPC_REGNUM
1768
The number of the ``next next program counter'' register, if defined.
1769
Currently, this is only defined for the Motorola 88K.
1770
 
1771
@item PARM_BOUNDARY
1772
If non-zero, round arguments to a boundary of this many bits before
1773
pushing them on the stack.
1774
 
1775
@item PRINT_REGISTER_HOOK (regno)
1776
If defined, this must be a function that prints the contents of the
1777
given register to standard output.
1778
 
1779
@item PRINT_TYPELESS_INTEGER
1780
This is an obscure substitute for @code{print_longest} that seems to
1781
have been defined for the Convex target.
1782
 
1783
@item PROCESS_LINENUMBER_HOOK
1784
A hook defined for XCOFF reading.
1785
 
1786
@item PROLOGUE_FIRSTLINE_OVERLAP
1787
(Only used in unsupported Convex configuration.)
1788
 
1789
@item PS_REGNUM
1790
If defined, this is the number of the processor status register.  (This
1791
definition is only used in generic code when parsing "$ps".)
1792
 
1793
@item POP_FRAME
1794
Used in @samp{call_function_by_hand} to remove an artificial stack
1795
frame.
1796
 
1797
@item PUSH_ARGUMENTS (nargs, args, sp, struct_return, struct_addr)
1798
Define this to push arguments onto the stack for inferior function
1799
call. Return the updated stack pointer value.
1800
 
1801
@item PUSH_DUMMY_FRAME
1802
Used in @samp{call_function_by_hand} to create an artificial stack frame.
1803
 
1804
@item REGISTER_BYTES
1805
The total amount of space needed to store GDB's copy of the machine's
1806
register state.
1807
 
1808
@item REGISTER_NAME(i)
1809
Return the name of register @var{i} as a string.  May return @var{NULL}
1810
or @var{NUL} to indicate that register @var{i} is not valid.
1811
 
1812
@item REGISTER_NAMES
1813
Deprecated in favor of @var{REGISTER_NAME}.
1814
 
1815
@item REG_STRUCT_HAS_ADDR (gcc_p, type)
1816
Define this to return 1 if the given type will be passed by pointer
1817
rather than directly.
1818
 
1819
@item SAVE_DUMMY_FRAME_TOS (sp)
1820
Used in @samp{call_function_by_hand} to notify the target dependent code
1821
of the top-of-stack value that will be passed to the the inferior code.
1822
This is the value of the @var{SP} after both the dummy frame and space
1823
for parameters/results have been allocated on the stack.
1824
 
1825
@item SDB_REG_TO_REGNUM
1826
Define this to convert sdb register numbers into GDB regnums.  If not
1827
defined, no conversion will be done.
1828
 
1829
@item SHIFT_INST_REGS
1830
(Only used for m88k targets.)
1831
 
1832
@item SKIP_PERMANENT_BREAKPOINT
1833
Advance the inferior's PC past a permanent breakpoint.  GDB normally
1834
steps over a breakpoint by removing it, stepping one instruction, and
1835
re-inserting the breakpoint.  However, permanent breakpoints are
1836
hardwired into the inferior, and can't be removed, so this strategy
1837
doesn't work.  Calling SKIP_PERMANENT_BREAKPOINT adjusts the processor's
1838
state so that execution will resume just after the breakpoint.  This
1839
macro does the right thing even when the breakpoint is in the delay slot
1840
of a branch or jump.
1841
 
1842
@item SKIP_PROLOGUE (pc)
1843
A C expression that returns the address of the ``real'' code beyond the
1844
function entry prologue found at @var{pc}.
1845
 
1846
@item SKIP_PROLOGUE_FRAMELESS_P
1847
A C expression that should behave similarly, but that can stop as soon
1848
as the function is known to have a frame.  If not defined,
1849
@code{SKIP_PROLOGUE} will be used instead.
1850
 
1851
@item SKIP_TRAMPOLINE_CODE (pc)
1852
If the target machine has trampoline code that sits between callers and
1853
the functions being called, then define this macro to return a new PC
1854
that is at the start of the real function.
1855
 
1856
@item SP_REGNUM
1857
If the stack-pointer is kept in a register, then define this macro to be
1858
the number (greater than or equal to zero) of that register.
1859
 
1860
This should only need to be defined if @code{TARGET_WRITE_SP} and
1861
@code{TARGET_WRITE_SP} are not defined.
1862
 
1863
@item STAB_REG_TO_REGNUM
1864
Define this to convert stab register numbers (as gotten from `r'
1865
declarations) into GDB regnums.  If not defined, no conversion will be
1866
done.
1867
 
1868
@item STACK_ALIGN (addr)
1869
Define this to adjust the address to the alignment required for the
1870
processor's stack.
1871
 
1872
@item STEP_SKIPS_DELAY (addr)
1873
Define this to return true if the address is of an instruction with a
1874
delay slot.  If a breakpoint has been placed in the instruction's delay
1875
slot, GDB will single-step over that instruction before resuming
1876
normally.  Currently only defined for the Mips.
1877
 
1878
@item STORE_RETURN_VALUE (type, valbuf)
1879
A C expression that stores a function return value of type @var{type},
1880
where @var{valbuf} is the address of the value to be stored.
1881
 
1882
@item SUN_FIXED_LBRAC_BUG
1883
(Used only for Sun-3 and Sun-4 targets.)
1884
 
1885
@item SYMBOL_RELOADING_DEFAULT
1886
The default value of the `symbol-reloading' variable.  (Never defined in
1887
current sources.)
1888
 
1889
@item TARGET_BYTE_ORDER_DEFAULT
1890
The ordering of bytes in the target.  This must be either
1891
@code{BIG_ENDIAN} or @code{LITTLE_ENDIAN}.  This macro replaces
1892
@var{TARGET_BYTE_ORDER} which is deprecated.
1893
 
1894
@item TARGET_BYTE_ORDER_SELECTABLE_P
1895
Non-zero if the target has both @code{BIG_ENDIAN} and
1896
@code{LITTLE_ENDIAN} variants.  This macro replaces
1897
@var{TARGET_BYTE_ORDER_SELECTABLE} which is deprecated.
1898
 
1899
@item TARGET_CHAR_BIT
1900
Number of bits in a char; defaults to 8.
1901
 
1902
@item TARGET_COMPLEX_BIT
1903
Number of bits in a complex number; defaults to @code{2 * TARGET_FLOAT_BIT}.
1904
 
1905
At present this macro is not used.
1906
 
1907
@item TARGET_DOUBLE_BIT
1908
Number of bits in a double float; defaults to @code{8 * TARGET_CHAR_BIT}.
1909
 
1910
@item TARGET_DOUBLE_COMPLEX_BIT
1911
Number of bits in a double complex; defaults to @code{2 * TARGET_DOUBLE_BIT}.
1912
 
1913
At present this macro is not used.
1914
 
1915
@item TARGET_FLOAT_BIT
1916
Number of bits in a float; defaults to @code{4 * TARGET_CHAR_BIT}.
1917
 
1918
@item TARGET_INT_BIT
1919
Number of bits in an integer; defaults to @code{4 * TARGET_CHAR_BIT}.
1920
 
1921
@item TARGET_LONG_BIT
1922
Number of bits in a long integer; defaults to @code{4 * TARGET_CHAR_BIT}.
1923
 
1924
@item TARGET_LONG_DOUBLE_BIT
1925
Number of bits in a long double float;
1926
defaults to @code{2 * TARGET_DOUBLE_BIT}.
1927
 
1928
@item TARGET_LONG_LONG_BIT
1929
Number of bits in a long long integer; defaults to @code{2 * TARGET_LONG_BIT}.
1930
 
1931
@item TARGET_PTR_BIT
1932
Number of bits in a pointer; defaults to @code{TARGET_INT_BIT}.
1933
 
1934
@item TARGET_SHORT_BIT
1935
Number of bits in a short integer; defaults to @code{2 * TARGET_CHAR_BIT}.
1936
 
1937
@item TARGET_READ_PC
1938
@item TARGET_WRITE_PC (val, pid)
1939
@item TARGET_READ_SP
1940
@item TARGET_WRITE_SP
1941
@item TARGET_READ_FP
1942
@item TARGET_WRITE_FP
1943
These change the behavior of @code{read_pc}, @code{write_pc},
1944
@code{read_sp}, @code{write_sp}, @code{read_fp} and @code{write_fp}.
1945
For most targets, these may be left undefined.  GDB will call the read
1946
and write register functions with the relevant @code{_REGNUM} argument.
1947
 
1948
These macros are useful when a target keeps one of these registers in a
1949
hard to get at place; for example, part in a segment register and part
1950
in an ordinary register.
1951
 
1952
@item TARGET_VIRTUAL_FRAME_POINTER(pc,regp,offsetp)
1953
Returns a @code{(register, offset)} pair representing the virtual
1954
frame pointer in use at the code address @code{"pc"}.  If virtual
1955
frame pointers are not used, a default definition simply returns
1956
@code{FP_REGNUM}, with an offset of zero.
1957
 
1958
@item USE_STRUCT_CONVENTION (gcc_p, type)
1959
If defined, this must be an expression that is nonzero if a value of the
1960
given @var{type} being returned from a function must have space
1961
allocated for it on the stack.  @var{gcc_p} is true if the function
1962
being considered is known to have been compiled by GCC; this is helpful
1963
for systems where GCC is known to use different calling convention than
1964
other compilers.
1965
 
1966
@item VARIABLES_INSIDE_BLOCK (desc, gcc_p)
1967
For dbx-style debugging information, if the compiler puts variable
1968
declarations inside LBRAC/RBRAC blocks, this should be defined to be
1969
nonzero.  @var{desc} is the value of @code{n_desc} from the
1970
@code{N_RBRAC} symbol, and @var{gcc_p} is true if GDB has noticed the
1971
presence of either the @code{GCC_COMPILED_SYMBOL} or the
1972
@code{GCC2_COMPILED_SYMBOL}.  By default, this is 0.
1973
 
1974
@item OS9K_VARIABLES_INSIDE_BLOCK (desc, gcc_p)
1975
Similarly, for OS/9000.  Defaults to 1.
1976
 
1977
@end table
1978
 
1979
Motorola M68K target conditionals.
1980
 
1981
@table @code
1982
 
1983
@item BPT_VECTOR
1984
Define this to be the 4-bit location of the breakpoint trap vector.  If
1985
not defined, it will default to @code{0xf}.
1986
 
1987
@item REMOTE_BPT_VECTOR
1988
Defaults to @code{1}.
1989
 
1990
@end table
1991
 
1992
@section Adding a New Target
1993
 
1994
The following files define a target to GDB:
1995
 
1996
@table @file
1997
 
1998
@item gdb/config/@var{arch}/@var{ttt}.mt
1999
Contains a Makefile fragment specific to this target.  Specifies what
2000
object files are needed for target @var{ttt}, by defining
2001
@samp{TDEPFILES=@dots{}} and @samp{TDEPLIBS=@dots{}}.  Also specifies
2002
the header file which describes @var{ttt}, by defining @samp{TM_FILE=
2003
tm-@var{ttt}.h}.
2004
 
2005
You can also define @samp{TM_CFLAGS}, @samp{TM_CLIBS}, @samp{TM_CDEPS},
2006
but these are now deprecated, replaced by autoconf, and may go away in
2007
future versions of GDB.
2008
 
2009
@item gdb/config/@var{arch}/tm-@var{ttt}.h
2010
(@file{tm.h} is a link to this file, created by configure).  Contains
2011
macro definitions about the target machine's registers, stack frame
2012
format and instructions.
2013
 
2014
@item gdb/@var{ttt}-tdep.c
2015
Contains any miscellaneous code required for this target machine.  On
2016
some machines it doesn't exist at all.  Sometimes the macros in
2017
@file{tm-@var{ttt}.h} become very complicated, so they are implemented
2018
as functions here instead, and the macro is simply defined to call the
2019
function.  This is vastly preferable, since it is easier to understand
2020
and debug.
2021
 
2022
@item gdb/config/@var{arch}/tm-@var{arch}.h
2023
This often exists to describe the basic layout of the target machine's
2024
processor chip (registers, stack, etc).  If used, it is included by
2025
@file{tm-@var{ttt}.h}.  It can be shared among many targets that use the
2026
same processor.
2027
 
2028
@item gdb/@var{arch}-tdep.c
2029
Similarly, there are often common subroutines that are shared by all
2030
target machines that use this particular architecture.
2031
 
2032
@end table
2033
 
2034
If you are adding a new operating system for an existing CPU chip, add a
2035
@file{config/tm-@var{os}.h} file that describes the operating system
2036
facilities that are unusual (extra symbol table info; the breakpoint
2037
instruction needed; etc).  Then write a @file{@var{arch}/tm-@var{os}.h}
2038
that just @code{#include}s @file{tm-@var{arch}.h} and
2039
@file{config/tm-@var{os}.h}.
2040
 
2041
 
2042
@node Target Vector Definition
2043
 
2044
@chapter Target Vector Definition
2045
 
2046
The target vector defines the interface between GDB's abstract handling
2047
of target systems, and the nitty-gritty code that actually exercises
2048
control over a process or a serial port.  GDB includes some 30-40
2049
different target vectors; however, each configuration of GDB includes
2050
only a few of them.
2051
 
2052
@section File Targets
2053
 
2054
Both executables and core files have target vectors.
2055
 
2056
@section Standard Protocol and Remote Stubs
2057
 
2058
GDB's file @file{remote.c} talks a serial protocol to code that runs in
2059
the target system.  GDB provides several sample ``stubs'' that can be
2060
integrated into target programs or operating systems for this purpose;
2061
they are named @file{*-stub.c}.
2062
 
2063
The GDB user's manual describes how to put such a stub into your target
2064
code.  What follows is a discussion of integrating the SPARC stub into a
2065
complicated operating system (rather than a simple program), by Stu
2066
Grossman, the author of this stub.
2067
 
2068
The trap handling code in the stub assumes the following upon entry to
2069
trap_low:
2070
 
2071
@enumerate
2072
 
2073
@item %l1 and %l2 contain pc and npc respectively at the time of the trap
2074
 
2075
@item traps are disabled
2076
 
2077
@item you are in the correct trap window
2078
 
2079
@end enumerate
2080
 
2081
As long as your trap handler can guarantee those conditions, then there
2082
is no reason why you shouldn't be able to `share' traps with the stub.
2083
The stub has no requirement that it be jumped to directly from the
2084
hardware trap vector.  That is why it calls @code{exceptionHandler()},
2085
which is provided by the external environment.  For instance, this could
2086
setup the hardware traps to actually execute code which calls the stub
2087
first, and then transfers to its own trap handler.
2088
 
2089
For the most point, there probably won't be much of an issue with
2090
`sharing' traps, as the traps we use are usually not used by the kernel,
2091
and often indicate unrecoverable error conditions.  Anyway, this is all
2092
controlled by a table, and is trivial to modify.  The most important
2093
trap for us is for @code{ta 1}.  Without that, we can't single step or
2094
do breakpoints.  Everything else is unnecessary for the proper operation
2095
of the debugger/stub.
2096
 
2097
From reading the stub, it's probably not obvious how breakpoints work.
2098
They are simply done by deposit/examine operations from GDB.
2099
 
2100
@section ROM Monitor Interface
2101
 
2102
@section Custom Protocols
2103
 
2104
@section Transport Layer
2105
 
2106
@section Builtin Simulator
2107
 
2108
 
2109
@node Native Debugging
2110
 
2111
@chapter Native Debugging
2112
 
2113
Several files control GDB's configuration for native support:
2114
 
2115
@table @file
2116
 
2117
@item gdb/config/@var{arch}/@var{xyz}.mh
2118
Specifies Makefile fragments needed when hosting @emph{or native} on
2119
machine @var{xyz}.  In particular, this lists the required
2120
native-dependent object files, by defining @samp{NATDEPFILES=@dots{}}.
2121
Also specifies the header file which describes native support on
2122
@var{xyz}, by defining @samp{NAT_FILE= nm-@var{xyz}.h}.  You can also
2123
define @samp{NAT_CFLAGS}, @samp{NAT_ADD_FILES}, @samp{NAT_CLIBS},
2124
@samp{NAT_CDEPS}, etc.; see @file{Makefile.in}.
2125
 
2126
@item gdb/config/@var{arch}/nm-@var{xyz}.h
2127
(@file{nm.h} is a link to this file, created by configure).  Contains C
2128
macro definitions describing the native system environment, such as
2129
child process control and core file support.
2130
 
2131
@item gdb/@var{xyz}-nat.c
2132
Contains any miscellaneous C code required for this native support of
2133
this machine.  On some machines it doesn't exist at all.
2134
 
2135
@end table
2136
 
2137
There are some ``generic'' versions of routines that can be used by
2138
various systems.  These can be customized in various ways by macros
2139
defined in your @file{nm-@var{xyz}.h} file.  If these routines work for
2140
the @var{xyz} host, you can just include the generic file's name (with
2141
@samp{.o}, not @samp{.c}) in @code{NATDEPFILES}.
2142
 
2143
Otherwise, if your machine needs custom support routines, you will need
2144
to write routines that perform the same functions as the generic file.
2145
Put them into @code{@var{xyz}-nat.c}, and put @code{@var{xyz}-nat.o}
2146
into @code{NATDEPFILES}.
2147
 
2148
@table @file
2149
 
2150
@item inftarg.c
2151
This contains the @emph{target_ops vector} that supports Unix child
2152
processes on systems which use ptrace and wait to control the child.
2153
 
2154
@item procfs.c
2155
This contains the @emph{target_ops vector} that supports Unix child
2156
processes on systems which use /proc to control the child.
2157
 
2158
@item fork-child.c
2159
This does the low-level grunge that uses Unix system calls to do a "fork
2160
and exec" to start up a child process.
2161
 
2162
@item infptrace.c
2163
This is the low level interface to inferior processes for systems using
2164
the Unix @code{ptrace} call in a vanilla way.
2165
 
2166
@end table
2167
 
2168
@section Native core file Support
2169
 
2170
@table @file
2171
 
2172
@item core-aout.c::fetch_core_registers()
2173
Support for reading registers out of a core file.  This routine calls
2174
@code{register_addr()}, see below.  Now that BFD is used to read core
2175
files, virtually all machines should use @code{core-aout.c}, and should
2176
just provide @code{fetch_core_registers} in @code{@var{xyz}-nat.c} (or
2177
@code{REGISTER_U_ADDR} in @code{nm-@var{xyz}.h}).
2178
 
2179
@item core-aout.c::register_addr()
2180
If your @code{nm-@var{xyz}.h} file defines the macro
2181
@code{REGISTER_U_ADDR(addr, blockend, regno)}, it should be defined to
2182
set @code{addr} to the offset within the @samp{user} struct of GDB
2183
register number @code{regno}.  @code{blockend} is the offset within the
2184
``upage'' of @code{u.u_ar0}.  If @code{REGISTER_U_ADDR} is defined,
2185
@file{core-aout.c} will define the @code{register_addr()} function and
2186
use the macro in it.  If you do not define @code{REGISTER_U_ADDR}, but
2187
you are using the standard @code{fetch_core_registers()}, you will need
2188
to define your own version of @code{register_addr()}, put it into your
2189
@code{@var{xyz}-nat.c} file, and be sure @code{@var{xyz}-nat.o} is in
2190
the @code{NATDEPFILES} list.  If you have your own
2191
@code{fetch_core_registers()}, you may not need a separate
2192
@code{register_addr()}.  Many custom @code{fetch_core_registers()}
2193
implementations simply locate the registers themselves.@refill
2194
 
2195
@end table
2196
 
2197
When making GDB run native on a new operating system, to make it
2198
possible to debug core files, you will need to either write specific
2199
code for parsing your OS's core files, or customize
2200
@file{bfd/trad-core.c}.  First, use whatever @code{#include} files your
2201
machine uses to define the struct of registers that is accessible
2202
(possibly in the u-area) in a core file (rather than
2203
@file{machine/reg.h}), and an include file that defines whatever header
2204
exists on a core file (e.g. the u-area or a @samp{struct core}).  Then
2205
modify @code{trad_unix_core_file_p()} to use these values to set up the
2206
section information for the data segment, stack segment, any other
2207
segments in the core file (perhaps shared library contents or control
2208
information), ``registers'' segment, and if there are two discontiguous
2209
sets of registers (e.g.  integer and float), the ``reg2'' segment.  This
2210
section information basically delimits areas in the core file in a
2211
standard way, which the section-reading routines in BFD know how to seek
2212
around in.
2213
 
2214
Then back in GDB, you need a matching routine called
2215
@code{fetch_core_registers()}.  If you can use the generic one, it's in
2216
@file{core-aout.c}; if not, it's in your @file{@var{xyz}-nat.c} file.
2217
It will be passed a char pointer to the entire ``registers'' segment,
2218
its length, and a zero; or a char pointer to the entire ``regs2''
2219
segment, its length, and a 2.  The routine should suck out the supplied
2220
register values and install them into GDB's ``registers'' array.
2221
 
2222
If your system uses @file{/proc} to control processes, and uses ELF
2223
format core files, then you may be able to use the same routines for
2224
reading the registers out of processes and out of core files.
2225
 
2226
@section ptrace
2227
 
2228
@section /proc
2229
 
2230
@section win32
2231
 
2232
@section shared libraries
2233
 
2234
@section Native Conditionals
2235
 
2236
When GDB is configured and compiled, various macros are defined or left
2237
undefined, to control compilation when the host and target systems are
2238
the same.  These macros should be defined (or left undefined) in
2239
@file{nm-@var{system}.h}.
2240
 
2241
@table @code
2242
 
2243
@item ATTACH_DETACH
2244
If defined, then GDB will include support for the @code{attach} and
2245
@code{detach} commands.
2246
 
2247
@item CHILD_PREPARE_TO_STORE
2248
If the machine stores all registers at once in the child process, then
2249
define this to ensure that all values are correct.  This usually entails
2250
a read from the child.
2251
 
2252
[Note that this is incorrectly defined in @file{xm-@var{system}.h} files
2253
currently.]
2254
 
2255
@item FETCH_INFERIOR_REGISTERS
2256
Define this if the native-dependent code will provide its own routines
2257
@code{fetch_inferior_registers} and @code{store_inferior_registers} in
2258
@file{@var{HOST}-nat.c}.  If this symbol is @emph{not} defined, and
2259
@file{infptrace.c} is included in this configuration, the default
2260
routines in @file{infptrace.c} are used for these functions.
2261
 
2262
@item FILES_INFO_HOOK
2263
(Only defined for Convex.)
2264
 
2265
@item FP0_REGNUM
2266
This macro is normally defined to be the number of the first floating
2267
point register, if the machine has such registers.  As such, it would
2268
appear only in target-specific code.  However, /proc support uses this
2269
to decide whether floats are in use on this target.
2270
 
2271
@item GET_LONGJMP_TARGET
2272
For most machines, this is a target-dependent parameter.  On the
2273
DECstation and the Iris, this is a native-dependent parameter, since
2274
<setjmp.h> is needed to define it.
2275
 
2276
This macro determines the target PC address that longjmp() will jump to,
2277
assuming that we have just stopped at a longjmp breakpoint.  It takes a
2278
CORE_ADDR * as argument, and stores the target PC value through this
2279
pointer.  It examines the current state of the machine as needed.
2280
 
2281
@item KERNEL_U_ADDR
2282
Define this to the address of the @code{u} structure (the ``user
2283
struct'', also known as the ``u-page'') in kernel virtual memory.  GDB
2284
needs to know this so that it can subtract this address from absolute
2285
addresses in the upage, that are obtained via ptrace or from core files.
2286
On systems that don't need this value, set it to zero.
2287
 
2288
@item KERNEL_U_ADDR_BSD
2289
Define this to cause GDB to determine the address of @code{u} at
2290
runtime, by using Berkeley-style @code{nlist} on the kernel's image in
2291
the root directory.
2292
 
2293
@item KERNEL_U_ADDR_HPUX
2294
Define this to cause GDB to determine the address of @code{u} at
2295
runtime, by using HP-style @code{nlist} on the kernel's image in the
2296
root directory.
2297
 
2298
@item ONE_PROCESS_WRITETEXT
2299
Define this to be able to, when a breakpoint insertion fails, warn the
2300
user that another process may be running with the same executable.
2301
 
2302
@item PREPARE_TO_PROCEED @var{select_it}
2303
This (ugly) macro allows a native configuration to customize the way the
2304
@code{proceed} function in @file{infrun.c} deals with switching between
2305
threads.
2306
 
2307
In a multi-threaded task we may select another thread and then continue
2308
or step.  But if the old thread was stopped at a breakpoint, it will
2309
immediately cause another breakpoint stop without any execution (i.e. it
2310
will report a breakpoint hit incorrectly).  So GDB must step over it
2311
first.
2312
 
2313
If defined, @code{PREPARE_TO_PROCEED} should check the current thread
2314
against the thread that reported the most recent event.  If a step-over
2315
is required, it returns TRUE.  If @var{select_it} is non-zero, it should
2316
reselect the old thread.
2317
 
2318
@item PROC_NAME_FMT
2319
Defines the format for the name of a @file{/proc} device.  Should be
2320
defined in @file{nm.h} @emph{only} in order to override the default
2321
definition in @file{procfs.c}.
2322
 
2323
@item PTRACE_FP_BUG
2324
mach386-xdep.c
2325
 
2326
@item PTRACE_ARG3_TYPE
2327
The type of the third argument to the @code{ptrace} system call, if it
2328
exists and is different from @code{int}.
2329
 
2330
@item REGISTER_U_ADDR
2331
Defines the offset of the registers in the ``u area''.
2332
 
2333
@item SHELL_COMMAND_CONCAT
2334
If defined, is a string to prefix on the shell command used to start the
2335
inferior.
2336
 
2337
@item SHELL_FILE
2338
If defined, this is the name of the shell to use to run the inferior.
2339
Defaults to @code{"/bin/sh"}.
2340
 
2341
@item SOLIB_ADD (filename, from_tty, targ)
2342
Define this to expand into an expression that will cause the symbols in
2343
@var{filename} to be added to GDB's symbol table.
2344
 
2345
@item SOLIB_CREATE_INFERIOR_HOOK
2346
Define this to expand into any shared-library-relocation code that you
2347
want to be run just after the child process has been forked.
2348
 
2349
@item START_INFERIOR_TRAPS_EXPECTED
2350
When starting an inferior, GDB normally expects to trap twice; once when
2351
the shell execs, and once when the program itself execs.  If the actual
2352
number of traps is something other than 2, then define this macro to
2353
expand into the number expected.
2354
 
2355
@item SVR4_SHARED_LIBS
2356
Define this to indicate that SVR4-style shared libraries are in use.
2357
 
2358
@item USE_PROC_FS
2359
This determines whether small routines in @file{*-tdep.c}, which
2360
translate register values between GDB's internal representation and the
2361
/proc representation, are compiled.
2362
 
2363
@item U_REGS_OFFSET
2364
This is the offset of the registers in the upage.  It need only be
2365
defined if the generic ptrace register access routines in
2366
@file{infptrace.c} are being used (that is, @file{infptrace.c} is
2367
configured in, and @code{FETCH_INFERIOR_REGISTERS} is not defined).  If
2368
the default value from @file{infptrace.c} is good enough, leave it
2369
undefined.
2370
 
2371
The default value means that u.u_ar0 @emph{points to} the location of
2372
the registers.  I'm guessing that @code{#define U_REGS_OFFSET 0} means
2373
that u.u_ar0 @emph{is} the location of the registers.
2374
 
2375
@item CLEAR_SOLIB
2376
objfiles.c
2377
 
2378
@item DEBUG_PTRACE
2379
Define this to debug ptrace calls.
2380
 
2381
@end table
2382
 
2383
 
2384
@node Support Libraries
2385
 
2386
@chapter Support Libraries
2387
 
2388
@section BFD
2389
 
2390
BFD provides support for GDB in several ways:
2391
 
2392
@table @emph
2393
 
2394
@item identifying executable and core files
2395
BFD will identify a variety of file types, including a.out, coff, and
2396
several variants thereof, as well as several kinds of core files.
2397
 
2398
@item access to sections of files
2399
BFD parses the file headers to determine the names, virtual addresses,
2400
sizes, and file locations of all the various named sections in files
2401
(such as the text section or the data section).  GDB simply calls BFD to
2402
read or write section X at byte offset Y for length Z.
2403
 
2404
@item specialized core file support
2405
BFD provides routines to determine the failing command name stored in a
2406
core file, the signal with which the program failed, and whether a core
2407
file matches (i.e. could be a core dump of) a particular executable
2408
file.
2409
 
2410
@item locating the symbol information
2411
GDB uses an internal interface of BFD to determine where to find the
2412
symbol information in an executable file or symbol-file.  GDB itself
2413
handles the reading of symbols, since BFD does not ``understand'' debug
2414
symbols, but GDB uses BFD's cached information to find the symbols,
2415
string table, etc.
2416
 
2417
@end table
2418
 
2419
@section opcodes
2420
 
2421
The opcodes library provides GDB's disassembler.  (It's a separate
2422
library because it's also used in binutils, for @file{objdump}).
2423
 
2424
@section readline
2425
 
2426
@section mmalloc
2427
 
2428
@section libiberty
2429
 
2430
@section gnu-regex
2431
 
2432
Regex conditionals.
2433
 
2434
@table @code
2435
 
2436
@item C_ALLOCA
2437
 
2438
@item NFAILURES
2439
 
2440
@item RE_NREGS
2441
 
2442
@item SIGN_EXTEND_CHAR
2443
 
2444
@item SWITCH_ENUM_BUG
2445
 
2446
@item SYNTAX_TABLE
2447
 
2448
@item Sword
2449
 
2450
@item sparc
2451
 
2452
@end table
2453
 
2454
@section include
2455
 
2456
@node Coding
2457
 
2458
@chapter Coding
2459
 
2460
This chapter covers topics that are lower-level than the major
2461
algorithms of GDB.
2462
 
2463
@section Cleanups
2464
 
2465
Cleanups are a structured way to deal with things that need to be done
2466
later.  When your code does something (like @code{malloc} some memory,
2467
or open a file) that needs to be undone later (e.g. free the memory or
2468
close the file), it can make a cleanup.  The cleanup will be done at
2469
some future point: when the command is finished, when an error occurs,
2470
or when your code decides it's time to do cleanups.
2471
 
2472
You can also discard cleanups, that is, throw them away without doing
2473
what they say.  This is only done if you ask that it be done.
2474
 
2475
Syntax:
2476
 
2477
@table @code
2478
 
2479
@item struct cleanup *@var{old_chain};
2480
Declare a variable which will hold a cleanup chain handle.
2481
 
2482
@item @var{old_chain} = make_cleanup (@var{function}, @var{arg});
2483
Make a cleanup which will cause @var{function} to be called with
2484
@var{arg} (a @code{char *}) later.  The result, @var{old_chain}, is a
2485
handle that can be passed to @code{do_cleanups} or
2486
@code{discard_cleanups} later.  Unless you are going to call
2487
@code{do_cleanups} or @code{discard_cleanups} yourself, you can ignore
2488
the result from @code{make_cleanup}.
2489
 
2490
@item do_cleanups (@var{old_chain});
2491
Perform all cleanups done since @code{make_cleanup} returned
2492
@var{old_chain}.  E.g.:
2493
@example
2494
make_cleanup (a, 0);
2495
old = make_cleanup (b, 0);
2496
do_cleanups (old);
2497
@end example
2498
@noindent
2499
will call @code{b()} but will not call @code{a()}.  The cleanup that
2500
calls @code{a()} will remain in the cleanup chain, and will be done
2501
later unless otherwise discarded.@refill
2502
 
2503
@item discard_cleanups (@var{old_chain});
2504
Same as @code{do_cleanups} except that it just removes the cleanups from
2505
the chain and does not call the specified functions.
2506
 
2507
@end table
2508
 
2509
Some functions, e.g. @code{fputs_filtered()} or @code{error()}, specify
2510
that they ``should not be called when cleanups are not in place''.  This
2511
means that any actions you need to reverse in the case of an error or
2512
interruption must be on the cleanup chain before you call these
2513
functions, since they might never return to your code (they
2514
@samp{longjmp} instead).
2515
 
2516
@section Wrapping Output Lines
2517
 
2518
Output that goes through @code{printf_filtered} or @code{fputs_filtered}
2519
or @code{fputs_demangled} needs only to have calls to @code{wrap_here}
2520
added in places that would be good breaking points.  The utility
2521
routines will take care of actually wrapping if the line width is
2522
exceeded.
2523
 
2524
The argument to @code{wrap_here} is an indentation string which is
2525
printed @emph{only} if the line breaks there.  This argument is saved
2526
away and used later.  It must remain valid until the next call to
2527
@code{wrap_here} or until a newline has been printed through the
2528
@code{*_filtered} functions.  Don't pass in a local variable and then
2529
return!
2530
 
2531
It is usually best to call @code{wrap_here()} after printing a comma or
2532
space.  If you call it before printing a space, make sure that your
2533
indentation properly accounts for the leading space that will print if
2534
the line wraps there.
2535
 
2536
Any function or set of functions that produce filtered output must
2537
finish by printing a newline, to flush the wrap buffer, before switching
2538
to unfiltered (``@code{printf}'') output.  Symbol reading routines that
2539
print warnings are a good example.
2540
 
2541
@section GDB Coding Standards
2542
 
2543
GDB follows the GNU coding standards, as described in
2544
@file{etc/standards.texi}.  This file is also available for anonymous
2545
FTP from GNU archive sites.  GDB takes a strict interpretation of the
2546
standard; in general, when the GNU standard recommends a practice but
2547
does not require it, GDB requires it.
2548
 
2549
GDB follows an additional set of coding standards specific to GDB,
2550
as described in the following sections.
2551
 
2552
You can configure with @samp{--enable-build-warnings} to get GCC to
2553
check on a number of these rules.  GDB sources ought not to engender any
2554
complaints, unless they are caused by bogus host systems.  (The exact
2555
set of enabled warnings is currently @samp{-Wall -Wpointer-arith
2556
-Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations}.
2557
 
2558
@subsection Formatting
2559
 
2560
The standard GNU recommendations for formatting must be followed
2561
strictly.
2562
 
2563
Note that while in a definition, the function's name must be in column
2564
zero; in a function declaration, the name must be on the same line as
2565
the return type.
2566
 
2567
In addition, there must be a space between a function or macro name and
2568
the opening parenthesis of its argument list (except for macro
2569
definitions, as required by C).  There must not be a space after an open
2570
paren/bracket or before a close paren/bracket.
2571
 
2572
While additional whitespace is generally helpful for reading, do not use
2573
more than one blank line to separate blocks, and avoid adding whitespace
2574
after the end of a program line (as of 1/99, some 600 lines had whitespace
2575
after the semicolon).  Excess whitespace causes difficulties for diff and
2576
patch.
2577
 
2578
@subsection Comments
2579
 
2580
The standard GNU requirements on comments must be followed strictly.
2581
 
2582
Block comments must appear in the following form, with no `/*'- or
2583
'*/'-only lines, and no leading `*':
2584
 
2585
@example @code
2586
/* Wait for control to return from inferior to debugger.  If inferior
2587
   gets a signal, we may decide to start it up again instead of
2588
   returning.  That is why there is a loop in this function.  When
2589
   this function actually returns it means the inferior should be left
2590
   stopped and GDB should read more commands.  */
2591
@end example
2592
 
2593
(Note that this format is encouraged by Emacs; tabbing for a multi-line
2594
comment works correctly, and M-Q fills the block consistently.)
2595
 
2596
Put a blank line between the block comments preceding function or
2597
variable definitions, and the definition itself.
2598
 
2599
In general, put function-body comments on lines by themselves, rather
2600
than trying to fit them into the 20 characters left at the end of a
2601
line, since either the comment or the code will inevitably get longer
2602
than will fit, and then somebody will have to move it anyhow.
2603
 
2604
@subsection C Usage
2605
 
2606
Code must not depend on the sizes of C data types, the format of the
2607
host's floating point numbers, the alignment of anything, or the order
2608
of evaluation of expressions.
2609
 
2610
Use functions freely.  There are only a handful of compute-bound areas
2611
in GDB that might be affected by the overhead of a function call, mainly
2612
in symbol reading.  Most of GDB's performance is limited by the target
2613
interface (whether serial line or system call).
2614
 
2615
However, use functions with moderation.  A thousand one-line functions
2616
are just as hard to understand as a single thousand-line function.
2617
 
2618
@subsection Function Prototypes
2619
 
2620
Prototypes must be used to @emph{declare} functions, and may be used to
2621
@emph{define} them.  Prototypes for GDB functions must include both the
2622
argument type and name, with the name matching that used in the actual
2623
function definition.
2624
 
2625
All external functions should have a declaration in a header file that
2626
callers include, except for @code{_initialize_*} functions, which must
2627
be external so that @file{init.c} construction works, but shouldn't be
2628
visible to random source files.
2629
 
2630
All static functions must be declared in a block near the top of the
2631
source file.
2632
 
2633
@subsection Clean Design
2634
 
2635
In addition to getting the syntax right, there's the little question of
2636
semantics.  Some things are done in certain ways in GDB because long
2637
experience has shown that the more obvious ways caused various kinds of
2638
trouble.
2639
 
2640
You can't assume the byte order of anything that comes from a target
2641
(including @var{value}s, object files, and instructions).  Such things
2642
must be byte-swapped using @code{SWAP_TARGET_AND_HOST} in GDB, or one of
2643
the swap routines defined in @file{bfd.h}, such as @code{bfd_get_32}.
2644
 
2645
You can't assume that you know what interface is being used to talk to
2646
the target system.  All references to the target must go through the
2647
current @code{target_ops} vector.
2648
 
2649
You can't assume that the host and target machines are the same machine
2650
(except in the ``native'' support modules).  In particular, you can't
2651
assume that the target machine's header files will be available on the
2652
host machine.  Target code must bring along its own header files --
2653
written from scratch or explicitly donated by their owner, to avoid
2654
copyright problems.
2655
 
2656
Insertion of new @code{#ifdef}'s will be frowned upon.  It's much better
2657
to write the code portably than to conditionalize it for various
2658
systems.
2659
 
2660
New @code{#ifdef}'s which test for specific compilers or manufacturers
2661
or operating systems are unacceptable.  All @code{#ifdef}'s should test
2662
for features.  The information about which configurations contain which
2663
features should be segregated into the configuration files.  Experience
2664
has proven far too often that a feature unique to one particular system
2665
often creeps into other systems; and that a conditional based on some
2666
predefined macro for your current system will become worthless over
2667
time, as new versions of your system come out that behave differently
2668
with regard to this feature.
2669
 
2670
Adding code that handles specific architectures, operating systems,
2671
target interfaces, or hosts, is not acceptable in generic code.  If a
2672
hook is needed at that point, invent a generic hook and define it for
2673
your configuration, with something like:
2674
 
2675
@example
2676
#ifdef  WRANGLE_SIGNALS
2677
   WRANGLE_SIGNALS (signo);
2678
#endif
2679
@end example
2680
 
2681
In your host, target, or native configuration file, as appropriate,
2682
define @code{WRANGLE_SIGNALS} to do the machine-dependent thing.  Take a
2683
bit of care in defining the hook, so that it can be used by other ports
2684
in the future, if they need a hook in the same place.
2685
 
2686
If the hook is not defined, the code should do whatever "most" machines
2687
want.  Using @code{#ifdef}, as above, is the preferred way to do this,
2688
but sometimes that gets convoluted, in which case use
2689
 
2690
@example
2691
#ifndef SPECIAL_FOO_HANDLING
2692
#define SPECIAL_FOO_HANDLING(pc, sp) (0)
2693
#endif
2694
@end example
2695
 
2696
where the macro is used or in an appropriate header file.
2697
 
2698
Whether to include a @dfn{small} hook, a hook around the exact pieces of
2699
code which are system-dependent, or whether to replace a whole function
2700
with a hook depends on the case.  A good example of this dilemma can be
2701
found in @code{get_saved_register}.  All machines that GDB 2.8 ran on
2702
just needed the @code{FRAME_FIND_SAVED_REGS} hook to find the saved
2703
registers.  Then the SPARC and Pyramid came along, and
2704
@code{HAVE_REGISTER_WINDOWS} and @code{REGISTER_IN_WINDOW_P} were
2705
introduced.  Then the 29k and 88k required the @code{GET_SAVED_REGISTER}
2706
hook.  The first three are examples of small hooks; the latter replaces
2707
a whole function.  In this specific case, it is useful to have both
2708
kinds; it would be a bad idea to replace all the uses of the small hooks
2709
with @code{GET_SAVED_REGISTER}, since that would result in much
2710
duplicated code.  Other times, duplicating a few lines of code here or
2711
there is much cleaner than introducing a large number of small hooks.
2712
 
2713
Another way to generalize GDB along a particular interface is with an
2714
attribute struct.  For example, GDB has been generalized to handle
2715
multiple kinds of remote interfaces -- not by #ifdef's everywhere, but
2716
by defining the "target_ops" structure and having a current target (as
2717
well as a stack of targets below it, for memory references).  Whenever
2718
something needs to be done that depends on which remote interface we are
2719
using, a flag in the current target_ops structure is tested (e.g.
2720
`target_has_stack'), or a function is called through a pointer in the
2721
current target_ops structure.  In this way, when a new remote interface
2722
is added, only one module needs to be touched -- the one that actually
2723
implements the new remote interface.  Other examples of
2724
attribute-structs are BFD access to multiple kinds of object file
2725
formats, or GDB's access to multiple source languages.
2726
 
2727
Please avoid duplicating code.  For example, in GDB 3.x all the code
2728
interfacing between @code{ptrace} and the rest of GDB was duplicated in
2729
@file{*-dep.c}, and so changing something was very painful.  In GDB 4.x,
2730
these have all been consolidated into @file{infptrace.c}.
2731
@file{infptrace.c} can deal with variations between systems the same way
2732
any system-independent file would (hooks, #if defined, etc.), and
2733
machines which are radically different don't need to use infptrace.c at
2734
all.
2735
 
2736
Don't put debugging printfs in the code.
2737
 
2738
@node Porting GDB
2739
 
2740
@chapter Porting GDB
2741
 
2742
Most of the work in making GDB compile on a new machine is in specifying
2743
the configuration of the machine.  This is done in a dizzying variety of
2744
header files and configuration scripts, which we hope to make more
2745
sensible soon.  Let's say your new host is called an @var{xyz} (e.g.
2746
@samp{sun4}), and its full three-part configuration name is
2747
@code{@var{arch}-@var{xvend}-@var{xos}} (e.g.  @samp{sparc-sun-sunos4}).
2748
In particular:
2749
 
2750
In the top level directory, edit @file{config.sub} and add @var{arch},
2751
@var{xvend}, and @var{xos} to the lists of supported architectures,
2752
vendors, and operating systems near the bottom of the file.  Also, add
2753
@var{xyz} as an alias that maps to
2754
@code{@var{arch}-@var{xvend}-@var{xos}}.  You can test your changes by
2755
running
2756
 
2757
@example
2758
./config.sub @var{xyz}
2759
@end example
2760
@noindent
2761
and
2762
@example
2763
./config.sub @code{@var{arch}-@var{xvend}-@var{xos}}
2764
@end example
2765
@noindent
2766
which should both respond with @code{@var{arch}-@var{xvend}-@var{xos}}
2767
and no error messages.
2768
 
2769
You need to port BFD, if that hasn't been done already.  Porting BFD is
2770
beyond the scope of this manual.
2771
 
2772
To configure GDB itself, edit @file{gdb/configure.host} to recognize
2773
your system and set @code{gdb_host} to @var{xyz}, and (unless your
2774
desired target is already available) also edit @file{gdb/configure.tgt},
2775
setting @code{gdb_target} to something appropriate (for instance,
2776
@var{xyz}).
2777
 
2778
Finally, you'll need to specify and define GDB's host-, native-, and
2779
target-dependent @file{.h} and @file{.c} files used for your
2780
configuration.
2781
 
2782
@section Configuring GDB for Release
2783
 
2784
From the top level directory (containing @file{gdb}, @file{bfd},
2785
@file{libiberty}, and so on):
2786
@example
2787
make -f Makefile.in gdb.tar.gz
2788
@end example
2789
 
2790
This will properly configure, clean, rebuild any files that are
2791
distributed pre-built (e.g. @file{c-exp.tab.c} or @file{refcard.ps}),
2792
and will then make a tarfile.  (If the top level directory has already
2793
been configured, you can just do @code{make gdb.tar.gz} instead.)
2794
 
2795
This procedure requires:
2796
@itemize @bullet
2797
@item symbolic links
2798
@item @code{makeinfo} (texinfo2 level)
2799
@item @TeX{}
2800
@item @code{dvips}
2801
@item @code{yacc} or @code{bison}
2802
@end itemize
2803
@noindent
2804
@dots{} and the usual slew of utilities (@code{sed}, @code{tar}, etc.).
2805
 
2806
@subheading TEMPORARY RELEASE PROCEDURE FOR DOCUMENTATION
2807
 
2808
@file{gdb.texinfo} is currently marked up using the texinfo-2 macros,
2809
which are not yet a default for anything (but we have to start using
2810
them sometime).
2811
 
2812
For making paper, the only thing this implies is the right generation of
2813
@file{texinfo.tex} needs to be included in the distribution.
2814
 
2815
For making info files, however, rather than duplicating the texinfo2
2816
distribution, generate @file{gdb-all.texinfo} locally, and include the
2817
files @file{gdb.info*} in the distribution.  Note the plural;
2818
@code{makeinfo} will split the document into one overall file and five
2819
or so included files.
2820
 
2821
@node Testsuite
2822
 
2823
@chapter Testsuite
2824
 
2825
The testsuite is an important component of the GDB package.  While it is
2826
always worthwhile to encourage user testing, in practice this is rarely
2827
sufficient; users typically use only a small subset of the available
2828
commands, and it has proven all too common for a change to cause a
2829
significant regression that went unnoticed for some time.
2830
 
2831
The GDB testsuite uses the DejaGNU testing framework.  DejaGNU is built
2832
using tcl and expect.  The tests themselves are calls to various tcl
2833
procs; the framework runs all the procs and summarizes the passes and
2834
fails.
2835
 
2836
@section Using the Testsuite
2837
 
2838
To run the testsuite, simply go to the GDB object directory (or to the
2839
testsuite's objdir) and type @code{make check}.  This just sets up some
2840
environment variables and invokes DejaGNU's @code{runtest} script.  While
2841
the testsuite is running, you'll get mentions of which test file is in use,
2842
and a mention of any unexpected passes or fails.  When the testsuite is
2843
finished, you'll get a summary that looks like this:
2844
@example
2845
                === gdb Summary ===
2846
 
2847
# of expected passes            6016
2848
# of unexpected failures        58
2849
# of unexpected successes       5
2850
# of expected failures          183
2851
# of unresolved testcases       3
2852
# of untested testcases         5
2853
@end example
2854
The ideal test run consists of expected passes only; however, reality
2855
conspires to keep us from this ideal.  Unexpected failures indicate
2856
real problems, whether in GDB or in the testsuite.  Expected failures
2857
are still failures, but ones which have been decided are too hard to
2858
deal with at the time; for instance, a test case might work everywhere
2859
except on AIX, and there is no prospect of the AIX case being fixed in
2860
the near future.  Expected failures should not be added lightly, since
2861
you may be masking serious bugs in GDB.  Unexpected successes are expected
2862
fails that are passing for some reason, while unresolved and untested
2863
cases often indicate some minor catastrophe, such as the compiler being
2864
unable to deal with a test program.
2865
 
2866
When making any significant change to GDB, you should run the testsuite
2867
before and after the change, to confirm that there are no regressions.
2868
Note that truly complete testing would require that you run the
2869
testsuite with all supported configurations and a variety of compilers;
2870
however this is more than really necessary.  In many cases testing with
2871
a single configuration is sufficient.  Other useful options are to test
2872
one big-endian (Sparc) and one little-endian (x86) host, a cross config
2873
with a builtin simulator (powerpc-eabi, mips-elf), or a 64-bit host
2874
(Alpha).
2875
 
2876
If you add new functionality to GDB, please consider adding tests for it
2877
as well; this way future GDB hackers can detect and fix their changes
2878
that break the functionality you added.  Similarly, if you fix a bug
2879
that was not previously reported as a test failure, please add a test
2880
case for it.  Some cases are extremely difficult to test, such as code
2881
that handles host OS failures or bugs in particular versions of
2882
compilers, and it's OK not to try to write tests for all of those.
2883
 
2884
@section Testsuite Organization
2885
 
2886
The testsuite is entirely contained in @file{gdb/testsuite}.  While the
2887
testsuite includes some makefiles and configury, these are very minimal,
2888
and used for little besides cleaning up, since the tests themselves
2889
handle the compilation of the programs that GDB will run.  The file
2890
@file{testsuite/lib/gdb.exp} contains common utility procs useful for
2891
all GDB tests, while the directory @file{testsuite/config} contains
2892
configuration-specific files, typically used for special-purpose
2893
definitions of procs like @code{gdb_load} and @code{gdb_start}.
2894
 
2895
The tests themselves are to be found in @file{testsuite/gdb.*} and
2896
subdirectories of those.  The names of the test files must always end
2897
with @file{.exp}.  DejaGNU collects the test files by wildcarding
2898
in the test directories, so both subdirectories and individual files
2899
get chosen and run in alphabetical order.
2900
 
2901
The following table lists the main types of subdirectories and what they
2902
are for.  Since DejaGNU finds test files no matter where they are
2903
located, and since each test file sets up its own compilation and
2904
execution environment, this organization is simply for convenience and
2905
intelligibility.
2906
 
2907
@table @code
2908
 
2909
@item gdb.base
2910
 
2911
This is the base testsuite.  The tests in it should apply to all
2912
configurations of GDB (but generic native-only tests may live here).
2913
The test programs should be in the subset of C that is valid K&R,
2914
ANSI/ISO, and C++ (ifdefs are allowed if necessary, for instance
2915
for prototypes).
2916
 
2917
@item gdb.@var{lang}
2918
 
2919
Language-specific tests for all languages besides C.  Examples are
2920
@file{gdb.c++} and @file{gdb.java}.
2921
 
2922
@item gdb.@var{platform}
2923
 
2924
Non-portable tests.  The tests are specific to a specific configuration
2925
(host or target), such as HP-UX or eCos.  Example is @file{gdb.hp}, for
2926
HP-UX.
2927
 
2928
@item gdb.@var{compiler}
2929
 
2930
Tests specific to a particular compiler.  As of this writing (June
2931
1999), there aren't currently any groups of tests in this category that
2932
couldn't just as sensibly be made platform-specific, but one could
2933
imagine a gdb.gcc, for tests of GDB's handling of GCC extensions.
2934
 
2935
@item gdb.@var{subsystem}
2936
 
2937
Tests that exercise a specific GDB subsystem in more depth.  For
2938
instance, @file{gdb.disasm} exercises various disassemblers, while
2939
@file{gdb.stabs} tests pathways through the stabs symbol reader.
2940
 
2941
@end table
2942
 
2943
@section Writing Tests
2944
 
2945
In many areas, the GDB tests are already quite comprehensive; you
2946
should be able to copy existing tests to handle new cases.
2947
 
2948
You should try to use @code{gdb_test} whenever possible, since it
2949
includes cases to handle all the unexpected errors that might happen.
2950
However, it doesn't cost anything to add new test procedures; for
2951
instance, @file{gdb.base/exprs.exp} defines a @code{test_expr} that
2952
calls @code{gdb_test} multiple times.
2953
 
2954
Only use @code{send_gdb} and @code{gdb_expect} when absolutely
2955
necessary, such as when GDB has several valid responses to a command.
2956
 
2957
The source language programs do @emph{not} need to be in a consistent
2958
style.  Since GDB is used to debug programs written in many different
2959
styles, it's worth having a mix of styles in the testsuite; for
2960
instance, some GDB bugs involving the display of source lines would
2961
never manifest themselves if the programs used GNU coding style
2962
uniformly.
2963
 
2964
@node Hints
2965
 
2966
@chapter Hints
2967
 
2968
Check the @file{README} file, it often has useful information that does not
2969
appear anywhere else in the directory.
2970
 
2971
@menu
2972
* Getting Started::             Getting started working on GDB
2973
* Debugging GDB::               Debugging GDB with itself
2974
@end menu
2975
 
2976
@node Getting Started,,, Hints
2977
 
2978
@section Getting Started
2979
 
2980
GDB is a large and complicated program, and if you first starting to
2981
work on it, it can be hard to know where to start.  Fortunately, if you
2982
know how to go about it, there are ways to figure out what is going on.
2983
 
2984
This manual, the GDB Internals manual, has information which applies
2985
generally to many parts of GDB.
2986
 
2987
Information about particular functions or data structures are located in
2988
comments with those functions or data structures.  If you run across a
2989
function or a global variable which does not have a comment correctly
2990
explaining what is does, this can be thought of as a bug in GDB; feel
2991
free to submit a bug report, with a suggested comment if you can figure
2992
out what the comment should say.  If you find a comment which is
2993
actually wrong, be especially sure to report that.
2994
 
2995
Comments explaining the function of macros defined in host, target, or
2996
native dependent files can be in several places.  Sometimes they are
2997
repeated every place the macro is defined.  Sometimes they are where the
2998
macro is used.  Sometimes there is a header file which supplies a
2999
default definition of the macro, and the comment is there.  This manual
3000
also documents all the available macros.
3001
@c (@pxref{Host Conditionals}, @pxref{Target
3002
@c Conditionals}, @pxref{Native Conditionals}, and @pxref{Obsolete
3003
@c Conditionals})
3004
 
3005
Start with the header files.  Once you have some idea of how GDB's internal
3006
symbol tables are stored (see @file{symtab.h}, @file{gdbtypes.h}), you
3007
will find it much easier to understand the code which uses and creates
3008
those symbol tables.
3009
 
3010
You may wish to process the information you are getting somehow, to
3011
enhance your understanding of it.  Summarize it, translate it to another
3012
language, add some (perhaps trivial or non-useful) feature to GDB, use
3013
the code to predict what a test case would do and write the test case
3014
and verify your prediction, etc.  If you are reading code and your eyes
3015
are starting to glaze over, this is a sign you need to use a more active
3016
approach.
3017
 
3018
Once you have a part of GDB to start with, you can find more
3019
specifically the part you are looking for by stepping through each
3020
function with the @code{next} command.  Do not use @code{step} or you
3021
will quickly get distracted; when the function you are stepping through
3022
calls another function try only to get a big-picture understanding
3023
(perhaps using the comment at the beginning of the function being
3024
called) of what it does.  This way you can identify which of the
3025
functions being called by the function you are stepping through is the
3026
one which you are interested in.  You may need to examine the data
3027
structures generated at each stage, with reference to the comments in
3028
the header files explaining what the data structures are supposed to
3029
look like.
3030
 
3031
Of course, this same technique can be used if you are just reading the
3032
code, rather than actually stepping through it.  The same general
3033
principle applies---when the code you are looking at calls something
3034
else, just try to understand generally what the code being called does,
3035
rather than worrying about all its details.
3036
 
3037
A good place to start when tracking down some particular area is with a
3038
command which invokes that feature.  Suppose you want to know how
3039
single-stepping works.  As a GDB user, you know that the @code{step}
3040
command invokes single-stepping.  The command is invoked via command
3041
tables (see @file{command.h}); by convention the function which actually
3042
performs the command is formed by taking the name of the command and
3043
adding @samp{_command}, or in the case of an @code{info} subcommand,
3044
@samp{_info}.  For example, the @code{step} command invokes the
3045
@code{step_command} function and the @code{info display} command invokes
3046
@code{display_info}.  When this convention is not followed, you might
3047
have to use @code{grep} or @kbd{M-x tags-search} in emacs, or run GDB on
3048
itself and set a breakpoint in @code{execute_command}.
3049
 
3050
If all of the above fail, it may be appropriate to ask for information
3051
on @code{bug-gdb}.  But @emph{never} post a generic question like ``I was
3052
wondering if anyone could give me some tips about understanding
3053
GDB''---if we had some magic secret we would put it in this manual.
3054
Suggestions for improving the manual are always welcome, of course.
3055
 
3056
@node Debugging GDB,,,Hints
3057
 
3058
@section Debugging GDB with itself
3059
 
3060
If GDB is limping on your machine, this is the preferred way to get it
3061
fully functional.  Be warned that in some ancient Unix systems, like
3062
Ultrix 4.2, a program can't be running in one process while it is being
3063
debugged in another.  Rather than typing the command @code{@w{./gdb
3064
./gdb}}, which works on Suns and such, you can copy @file{gdb} to
3065
@file{gdb2} and then type @code{@w{./gdb ./gdb2}}.
3066
 
3067
When you run GDB in the GDB source directory, it will read a
3068
@file{.gdbinit} file that sets up some simple things to make debugging
3069
gdb easier.  The @code{info} command, when executed without a subcommand
3070
in a GDB being debugged by gdb, will pop you back up to the top level
3071
gdb.  See @file{.gdbinit} for details.
3072
 
3073
If you use emacs, you will probably want to do a @code{make TAGS} after
3074
you configure your distribution; this will put the machine dependent
3075
routines for your local machine where they will be accessed first by
3076
@kbd{M-.}
3077
 
3078
Also, make sure that you've either compiled GDB with your local cc, or
3079
have run @code{fixincludes} if you are compiling with gcc.
3080
 
3081
@section Submitting Patches
3082
 
3083
Thanks for thinking of offering your changes back to the community of
3084
GDB users.  In general we like to get well designed enhancements.
3085
Thanks also for checking in advance about the best way to transfer the
3086
changes.
3087
 
3088
The GDB maintainers will only install ``cleanly designed'' patches.
3089
This manual summarizes what we believe to be clean design for GDB.
3090
 
3091
If the maintainers don't have time to put the patch in when it arrives,
3092
or if there is any question about a patch, it goes into a large queue
3093
with everyone else's patches and bug reports.
3094
 
3095
The legal issue is that to incorporate substantial changes requires a
3096
copyright assignment from you and/or your employer, granting ownership
3097
of the changes to the Free Software Foundation.  You can get the
3098
standard documents for doing this by sending mail to @code{gnu@@gnu.org}
3099
and asking for it.  We recommend that people write in "All programs
3100
owned by the Free Software Foundation" as "NAME OF PROGRAM", so that
3101
changes in many programs (not just GDB, but GAS, Emacs, GCC, etc) can be
3102
contributed with only one piece of legalese pushed through the
3103
bureacracy and filed with the FSF.  We can't start merging changes until
3104
this paperwork is received by the FSF (their rules, which we follow
3105
since we maintain it for them).
3106
 
3107
Technically, the easiest way to receive changes is to receive each
3108
feature as a small context diff or unidiff, suitable for "patch".  Each
3109
message sent to me should include the changes to C code and header files
3110
for a single feature, plus ChangeLog entries for each directory where
3111
files were modified, and diffs for any changes needed to the manuals
3112
(gdb/doc/gdb.texinfo or gdb/doc/gdbint.texinfo).  If there are a lot of
3113
changes for a single feature, they can be split down into multiple
3114
messages.
3115
 
3116
In this way, if we read and like the feature, we can add it to the
3117
sources with a single patch command, do some testing, and check it in.
3118
If you leave out the ChangeLog, we have to write one.  If you leave
3119
out the doc, we have to puzzle out what needs documenting.  Etc.
3120
 
3121
The reason to send each change in a separate message is that we will not
3122
install some of the changes.  They'll be returned to you with questions
3123
or comments.  If we're doing our job correctly, the message back to you
3124
will say what you have to fix in order to make the change acceptable.
3125
The reason to have separate messages for separate features is so that
3126
the acceptable changes can be installed while one or more changes are
3127
being reworked.  If multiple features are sent in a single message, we
3128
tend to not put in the effort to sort out the acceptable changes from
3129
the unacceptable, so none of the features get installed until all are
3130
acceptable.
3131
 
3132
If this sounds painful or authoritarian, well, it is.  But we get a lot
3133
of bug reports and a lot of patches, and many of them don't get
3134
installed because we don't have the time to finish the job that the bug
3135
reporter or the contributor could have done.  Patches that arrive
3136
complete, working, and well designed, tend to get installed on the day
3137
they arrive.  The others go into a queue and get installed as time
3138
permits, which, since the maintainers have many demands to meet, may not
3139
be for quite some time.
3140
 
3141
Please send patches directly to the GDB maintainers at
3142
@code{gdb-patches@@sourceware.cygnus.com}.
3143
 
3144
@section Obsolete Conditionals
3145
 
3146
Fragments of old code in GDB sometimes reference or set the following
3147
configuration macros.  They should not be used by new code, and old uses
3148
should be removed as those parts of the debugger are otherwise touched.
3149
 
3150
@table @code
3151
 
3152
@item STACK_END_ADDR
3153
This macro used to define where the end of the stack appeared, for use
3154
in interpreting core file formats that don't record this address in the
3155
core file itself.  This information is now configured in BFD, and GDB
3156
gets the info portably from there.  The values in GDB's configuration
3157
files should be moved into BFD configuration files (if needed there),
3158
and deleted from all of GDB's config files.
3159
 
3160
Any @file{@var{foo}-xdep.c} file that references STACK_END_ADDR
3161
is so old that it has never been converted to use BFD.  Now that's old!
3162
 
3163
@item PYRAMID_CONTROL_FRAME_DEBUGGING
3164
pyr-xdep.c
3165
@item PYRAMID_CORE
3166
pyr-xdep.c
3167
@item PYRAMID_PTRACE
3168
pyr-xdep.c
3169
 
3170
@item REG_STACK_SEGMENT
3171
exec.c
3172
 
3173
@end table
3174
 
3175
 
3176
@contents
3177
@bye

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