2 @setfilename gdbint.info
7 * Gdb-Internals: (gdbint). The GNU debugger's internals.
13 This file documents the internals of the GNU debugger @value{GDBN}.
15 Copyright 1990-1999 Free Software Foundation, Inc.
16 Contributed by Cygnus Solutions. Written by John Gilmore.
17 Second Edition by Stan Shebs.
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.
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).
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).
35 @setchapternewpage off
36 @settitle @value{GDBN} Internals
39 @title @value{GDBN} Internals
40 @subtitle{A guide to the internals of the GNU debugger}
42 @author Cygnus Solutions
43 @author Second Edition:
45 @author Cygnus Solutions
48 \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
49 \xdef\manvers{\$Revision$} % For use in headers, footers too
51 \hfill Cygnus Solutions\par
53 \hfill \TeX{}info \texinfoversion\par
57 @vskip 0pt plus 1filll
58 Copyright @copyright{} 1990-1999 Free Software Foundation, Inc.
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.
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
71 This document documents the internals of the GNU debugger, @value{GDBN}. It
72 includes description of @value{GDBN}'s key algorithms and operations, as well
73 as the mechanisms that adapt @value{GDBN} to specific hosts and targets.
83 * Target Architecture Definition::
84 * Target Vector Definition::
97 Before diving into the internals, you should understand the formal
98 requirements and other expectations for @value{GDBN}. Although some of these may
99 seem obvious, there have been proposals for @value{GDBN} that have run counter to
102 First of all, @value{GDBN} 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.
106 @value{GDBN} is an interactive tool. Although a batch mode is available, @value{GDBN}'s
107 primary role is to interact with a human programmer.
109 @value{GDBN} 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
114 @value{GDBN} 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
120 @value{GDBN} 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.
124 @value{GDBN} should be able to run everywhere. No other debugger is available
125 for even half as many configurations as @value{GDBN} supports.
128 @node Overall Structure
130 @chapter Overall Structure
132 @value{GDBN} consists of three major subsystems: user interface, symbol handling
133 (the ``symbol side''), and target system handling (the ``target side'').
135 Ther user interface consists of several actual interfaces, plus
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.
142 The target side consists of execution control, stack frame analysis, and
143 physical target manipulation.
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
152 @section The Symbol Side
154 The symbolic side of @value{GDBN} can be thought of as ``everything you can do in
155 @value{GDBN} without having a live program running''. For instance, you can look
156 at the types of variables, and evaluate many kinds of expressions.
158 @section The Target Side
160 The target side of @value{GDBN} 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.
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, @value{GDBN} will use symbolic info to present addresses
168 relative to symbols rather than as raw numbers, but it will work either
171 @section Configurations
173 @dfn{Host} refers to attributes of the system where @value{GDBN} 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.
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
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
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.
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.
199 When you want to make @value{GDBN} work ``native'' on a particular machine, you
200 have to include all three kinds of information.
207 @value{GDBN} 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.
214 A frame is a construct that @value{GDBN} uses to keep track of calling and called
217 @code{FRAME_FP} in the machine description has no meaning to the
218 machine-independent part of @value{GDBN}, except that it is used when setting up
219 a new frame from scratch, as follows:
222 create_new_frame (read_register (FP_REGNUM), read_pc ()));
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.)
232 Given a @value{GDBN} frame, define @code{FRAME_CHAIN} to determine the address of
233 the calling function's frame. This will be used to create a new @value{GDBN}
234 frame struct, and then @code{INIT_EXTRA_FRAME_INFO} and
235 @code{INIT_FRAME_PC} will be called for the new frame.
237 @section Breakpoint Handling
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
243 There are two main ways to implement breakpoints; either as ``hardware''
244 breakpoints or as ``software'' breakpoints.
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 @value{GDBN}. 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 @value{GDBN}'s point of view
257 they work the same; @value{GDBN} need not do nothing more than set the breakpoint
258 and wait for something to happen.
260 Since they depend on hardware resources, hardware breakpoints may be
261 limited in number; when the user asks for more, @value{GDBN} will start trying to
262 set software breakpoints.
264 Software breakpoints require @value{GDBN} to do somewhat more work. The basic
265 theory is that @value{GDBN} 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, @value{GDBN} will take the exception and stop the
268 program. When the user says to continue, @value{GDBN} will restore the original
269 instruction, single-step, re-insert the trap, and continue on.
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.
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
287 The basic definition of the software breakpoint is the macro
290 Basic breakpoint object handling is in @file{breakpoint.c}. However,
291 much of the interesting breakpoint action is in @file{infrun.c}.
293 @section Single Stepping
295 @section Signal Handling
297 @section Thread Handling
299 @section Inferior Function Calls
301 @section Longjmp Support
303 @value{GDBN} 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.
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.
317 @chapter User Interface
319 @value{GDBN} has several user interfaces. Although the command-line interface
320 is the most common and most familiar, there are others.
322 @section Command Interpreter
324 The command interpreter in @value{GDBN} 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.
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}.
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.
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.
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.
350 @section Console Printing
356 @code{libgdb} was an abortive project of years ago. The theory was to
357 provide an API to @value{GDBN}'s functionality.
359 @node Symbol Handling
361 @chapter Symbol Handling
363 Symbols are a key part of @value{GDBN}'s operation. Symbols include variables,
364 functions, and types.
366 @section Symbol Reading
368 @value{GDBN} reads symbols from ``symbol files''. The usual symbol file is the
369 file containing the program which @value{GDBN} is debugging. @value{GDBN} 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.
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.
379 Symbol reading modules identify themselves to @value{GDBN} 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
387 The functions supplied by each module are:
390 @item @var{xyz}_symfile_init(struct sym_fns *sf)
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.
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.
406 There is no result from @code{@var{xyz}_symfile_init}, but it can call
407 @code{error} if it detects an unavoidable problem.
409 @item @var{xyz}_new_init()
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 @value{GDBN} 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.
419 @item @var{xyz}_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)
421 Called from @code{symbol_file_add} to actually read the symbols from a
422 symbol-file into a set of psymtabs or symtabs.
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
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 @value{GDBN} symbol-handling code.
438 @item @var{xyz}_psymtab_to_symtab (struct partial_symtab *pst)
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.
448 @section Partial Symbol Tables
450 @value{GDBN} has three types of symbol tables.
454 @item full symbol tables (symtabs). These contain the main information
455 about symbols and addresses.
457 @item partial symbol tables (psymtabs). These contain enough
458 information to know when to read the corresponding part of the full
461 @item minimal symbol tables (msymtabs). These contain information
462 gleaned from non-debugging symbols.
466 This section describes partial symbol tables.
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 @value{GDBN} 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
476 @c (@xref{Symbol Reading}.)
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.
483 The psymtab also contains the range of instruction addresses that the
484 full symbol table would represent.
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:
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
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.
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
518 It is a bug for @value{GDBN} 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.
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.
533 Fundamental Types (e.g., FT_VOID, FT_BOOLEAN).
535 These are the fundamental types that @value{GDBN} 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 @value{GDBN} knows about.
540 Type Codes (e.g., TYPE_CODE_PTR, TYPE_CODE_ARRAY).
542 Each time @value{GDBN} 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.
549 Builtin Types (e.g., builtin_type_void, builtin_type_char).
551 These are instances of type structs that roughly correspond to
552 fundamental types and are created as global types for @value{GDBN} 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.
561 @section Object File Formats
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.
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.
575 The basic @file{a.out} reader is in @file{dbxread.c}.
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.
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
588 The COFF reader is in @file{coffread.c}.
592 ECOFF is an extended COFF originally introduced for Mips and Alpha
595 The basic ECOFF reader is in @file{mipsread.c}.
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}.
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).
614 Windows 95 and NT use the PE (Portable Executable) format for their
615 executables. PE is basically COFF with additional headers.
617 While BFD includes special PE support, @value{GDBN} needs only the basic
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.
626 The basic ELF reader is in @file{elfread.c}.
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).
633 The SOM reader is in @file{hpread.c}.
635 @subsection Other File Formats
637 Other file formats that have been supported by @value{GDBN} include Netware
638 Loadable Modules (@file{nlmread.c}.
640 @section Debugging File Formats
642 This section describes characteristics of debugging information that
643 are independent of the object file format.
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.
651 While @file{dbxread.c} does some of the basic stab processing,
652 including for encapsulated versions, @file{stabsread.c} does
657 The basic COFF definition includes debugging information. The level
658 of support is minimal and non-extensible, and is not often used.
660 @subsection Mips debug (Third Eye)
662 ECOFF includes a definition of a special debug format.
664 The file @file{mdebugread.c} implements reading for this format.
668 DWARF 1 is a debugging format that was originally designed to be
669 used with ELF in SVR4 systems.
675 @c If defined, these are the producer strings in a DWARF 1 file. All of
676 @c these have reasonable defaults already.
678 The DWARF 1 reader is in @file{dwarfread.c}.
682 DWARF 2 is an improved but incompatible version of DWARF 1.
684 The DWARF 2 reader is in @file{dwarf2read.c}.
688 Like COFF, the SOM definition includes debugging information.
690 @section Adding a New Symbol Reader to @value{GDBN}
692 If you are using an existing object file format (a.out, COFF, ELF, etc),
693 there is probably little to be done.
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.
698 You must then arrange for the BFD code to provide access to the
699 debugging symbols. Generally @value{GDBN} 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, @value{GDBN} should not depend on the BFD
702 internal data structures.
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 @value{GDBN}.
712 @node Language Support
714 @chapter Language Support
716 @value{GDBN}'s language support is mainly driven by the symbol reader, although
717 it is possible for the user to set the source language manually.
719 @value{GDBN} 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.
724 @section Adding a Source Language to @value{GDBN}
726 To add other languages to @value{GDBN}'s expression parser, follow the following
730 @item Create the expression parser.
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
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:
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
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 @value{GDBN}
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.
770 @item Add any evaluation routines, if necessary
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.
779 @item Update some existing code
781 Add an enumerated identifier for your language to the enumerated type
782 @code{enum language} in @file{defs.h}.
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.
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
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 @value{GDBN} is built for.
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
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}.
810 @item Add a place of call
812 Add a call to @code{@var{lang}_parse()} and @code{@var{lang}_error} in
813 @code{parse.c:parse_exp_1()}.
815 @item Use macros to trim code
817 The user has the option of building @value{GDBN} for some or all of the
818 languages. If the user decides to build @value{GDBN} 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
824 Note that you do not need to do this in your YACC parser, since if @value{GDBN}
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 @value{GDBN} at all.
828 See the file @file{configure.in} for how @value{GDBN} is configured for different
831 @item Edit @file{Makefile.in}
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
841 @node Host Definition
843 @chapter Host Definition
845 With the advent of autoconf, it's rarely necessary to have host
846 definition machinery anymore.
848 @section Adding a New Host
850 Most of @value{GDBN}'s host configuration support happens via autoconf. It
851 should be rare to need new host-specific definitions. @value{GDBN} still uses
852 the host-specific definitions and files listed below, but these mostly
853 exist for historical reasons, and should eventually disappear.
855 Several files control @value{GDBN}'s configuration for host systems:
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}.
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.
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}.
881 @subheading Generic Host Support Files
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}.
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}.
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.
902 This contains serial line support for 32-bit programs running under DOS,
903 using the GO32 execution environment.
906 This contains generic TCP support using sockets.
910 @section Host Conditionals
912 When @value{GDBN} 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
920 @item @value{GDBN}INIT_FILENAME
921 The default name of @value{GDBN}'s initialization file (normally @file{.gdbinit}).
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}.
929 This macro is deprecated.
932 Define this if your system does not have a @code{<sys/file.h>}.
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.
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}.
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.
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"}.
956 The default value of the prompt string (normally @code{"(gdb) "}).
959 The name of the generic TTY device, defaults to @code{"/dev/tty"}.
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
967 Define this if binary files are opened the same way as text files.
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
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.
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.
983 Define this if the host system has @code{termio.h}.
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}.
994 Values for host-side constants.
997 Substitute for isatty, if not available.
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}.
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.
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.
1012 @item HAVE_LONG_DOUBLE
1013 Define this if the host C compiler supports ``long double''. This is
1014 set by the configure script.
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
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.
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.
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
1036 @item MALLOC_INCOMPATIBLE
1037 Define this if the system's prototype for @code{malloc} differs from the
1038 @sc{ANSI} definition.
1040 @item MMAP_BASE_ADDRESS
1041 When using HAVE_MMAP, the first mapping should go at this address.
1043 @item MMAP_INCREMENT
1044 when using HAVE_MMAP, this is the increment between mappings.
1046 @item NEED_POSIX_SETPGID
1047 Define this to use the POSIX version of @code{setpgid} to determine
1048 whether job control is available.
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.
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
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.
1068 @value{GDBN} 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.
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
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
1096 @item NO_SIGINTERRUPT
1097 Define this to indicate that siginterrupt() is not available.
1100 Define if this is not in a system .h file.
1104 Define these to appropriate value for the system lseek(), if not already
1108 This is the signal for stopping @value{GDBN}. Defaults to SIGTSTP. (Only
1109 redefined for the Convex.)
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
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
1123 Define this to help placate lint in some situations.
1126 Define this to override the defaults of @code{__volatile__} or
1132 @node Target Architecture Definition
1134 @chapter Target Architecture Definition
1136 @value{GDBN}'s target architecture defines what sort of machine-language programs
1137 @value{GDBN} can work with, and how it works with them.
1139 At present, the target architecture definition consists of a number of C
1142 @section Registers and Memory
1144 @value{GDBN}'s model of the target machine is rather simple. @value{GDBN} assumes the
1145 machine includes a bank of registers and a block of memory. Each
1146 register may have a different size.
1148 @value{GDBN} 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.
1154 @value{GDBN} can handle big-endian, little-endian, and bi-endian architectures.
1156 @section Pointers Are Not Always Addresses
1157 @cindex pointer representation
1158 @cindex address representation
1159 @cindex word-addressed machines
1160 @cindex separate data and code address spaces
1161 @cindex spaces, separate data and code address
1162 @cindex address spaces, separate data and code
1163 @cindex code pointers, word-addressed
1164 @cindex converting between pointers and addresses
1165 @cindex D10V addresses
1167 On almost all 32-bit architectures, the representation of a pointer is
1168 indistinguishable from the representation of some fixed-length number
1169 whose value is the byte address of the object pointed to. On such
1170 machines, the words `pointer' and `address' can be used interchangeably.
1171 However, architectures with smaller word sizes are often cramped for
1172 address space, so they may choose a pointer representation that breaks this
1173 identity, and allows a larger code address space.
1175 For example, the Mitsubishi D10V is a 16-bit VLIW processor whose
1176 instructions are 32 bits long@footnote{Some D10V instructions are
1177 actually pairs of 16-bit sub-instructions. However, since you can't
1178 jump into the middle of such a pair, code addresses can only refer to
1179 full 32 bit instructions, which is what matters in this explanation.}.
1180 If the D10V used ordinary byte addresses to refer to code locations,
1181 then the processor would only be able to address 64kb of instructions.
1182 However, since instructions must be aligned on four-byte boundaries, the
1183 low two bits of any valid instruction's byte address are always zero ---
1184 byte addresses waste two bits. So instead of byte addresses, the D10V
1185 uses word addresses --- byte addresses shifted right two bits --- to
1186 refer to code. Thus, the D10V can use 16-bit words to address 256kb of
1189 However, this means that code pointers and data pointers have different
1190 forms on the D10V. The 16-bit word @code{0xC020} refers to byte address
1191 @code{0xC020} when used as a data address, but refers to byte address
1192 @code{0x30080} when used as a code address.
1194 (The D10V also uses separate code and data address spaces, which also
1195 affects the correspondence between pointers and addresses, but we're
1196 going to ignore that here; this example is already too long.)
1198 To cope with architectures like this --- the D10V is not the only one!
1199 --- @value{GDBN} tries to distinguish between @dfn{addresses}, which are
1200 byte numbers, and @dfn{pointers}, which are the target's representation
1201 of an address of a particular type of data. In the example above,
1202 @code{0xC020} is the pointer, which refers to one of the addresses
1203 @code{0xC020} or @code{0x30080}, depending on the type imposed upon it.
1204 @value{GDBN} provides functions for turning a pointer into an address
1205 and vice versa, in the appropriate way for the current architecture.
1207 Unfortunately, since addresses and pointers are identical on almost all
1208 processors, this distinction tends to bit-rot pretty quickly. Thus,
1209 each time you port @value{GDBN} to an architecture which does
1210 distinguish between pointers and addresses, you'll probably need to
1211 clean up some architecture-independent code.
1213 Here are functions which convert between pointers and addresses:
1215 @deftypefun CORE_ADDR extract_typed_address (void *@var{buf}, struct type *@var{type})
1216 Treat the bytes at @var{buf} as a pointer or reference of type
1217 @var{type}, and return the address it represents, in a manner
1218 appropriate for the current architecture. This yields an address
1219 @value{GDBN} can use to read target memory, disassemble, etc. Note that
1220 @var{buf} refers to a buffer in @value{GDBN}'s memory, not the
1223 For example, if the current architecture is the Intel x86, this function
1224 extracts a little-endian integer of the appropriate length from
1225 @var{buf} and returns it. However, if the current architecture is the
1226 D10V, this function will return a 16-bit integer extracted from
1227 @var{buf}, multiplied by four if @var{type} is a pointer to a function.
1229 If @var{type} is not a pointer or reference type, then this function
1230 will signal an internal error.
1233 @deftypefun CORE_ADDR store_typed_address (void *@var{buf}, struct type *@var{type}, CORE_ADDR @var{addr})
1234 Store the address @var{addr} in @var{buf}, in the proper format for a
1235 pointer of type @var{type} in the current architecture. Note that
1236 @var{buf} refers to a buffer in @value{GDBN}'s memory, not the
1239 For example, if the current architecture is the Intel x86, this function
1240 stores @var{addr} unmodified as a little-endian integer of the
1241 appropriate length in @var{buf}. However, if the current architecture
1242 is the D10V, this function divides @var{addr} by four if @var{type} is
1243 a pointer to a function, and then stores it in @var{buf}.
1245 If @var{type} is not a pointer or reference type, then this function
1246 will signal an internal error.
1249 @deftypefun CORE_ADDR value_as_pointer (value_ptr @var{val})
1250 Assuming that @var{val} is a pointer, return the address it represents,
1251 as appropriate for the current architecture.
1253 This function actually works on integral values, as well as pointers.
1254 For pointers, it performs architecture-specific conversions as
1255 described above for @code{extract_typed_address}.
1258 @deftypefun CORE_ADDR value_from_pointer (struct type *@var{type}, CORE_ADDR @var{addr})
1259 Create and return a value representing a pointer of type @var{type} to
1260 the address @var{addr}, as appropriate for the current architecture.
1261 This function performs architecture-specific conversions as described
1262 above for @code{store_typed_address}.
1266 @value{GDBN} also provides functions that do the same tasks, but assume
1267 that pointers are simply byte addresses; they aren't sensitive to the
1268 current architecture, beyond knowing the appropriate endianness.
1270 @deftypefun CORE_ADDR extract_address (void *@var{addr}, int len)
1271 Extract a @var{len}-byte number from @var{addr} in the appropriate
1272 endianness for the current architecture, and return it. Note that
1273 @var{addr} refers to @value{GDBN}'s memory, not the inferior's.
1275 This function should only be used in architecture-specific code; it
1276 doesn't have enough information to turn bits into a true address in the
1277 appropriate way for the current architecture. If you can, use
1278 @code{extract_typed_address} instead.
1281 @deftypefun void store_address (void *@var{addr}, int @var{len}, LONGEST @var{val})
1282 Store @var{val} at @var{addr} as a @var{len}-byte integer, in the
1283 appropriate endianness for the current architecture. Note that
1284 @var{addr} refers to a buffer in @value{GDBN}'s memory, not the
1287 This function should only be used in architecture-specific code; it
1288 doesn't have enough information to turn a true address into bits in the
1289 appropriate way for the current architecture. If you can, use
1290 @code{store_typed_address} instead.
1294 Here are some macros which architectures can define to indicate the
1295 relationship between pointers and addresses. These have default
1296 definitions, appropriate for architectures on which all pointers are
1297 simple byte addresses.
1299 @deftypefn {Target Macro} CORE_ADDR POINTER_TO_ADDRESS (struct type *@var{type}, char *@var{buf})
1300 Assume that @var{buf} holds a pointer of type @var{type}, in the
1301 appropriate format for the current architecture. Return the byte
1302 address the pointer refers to.
1304 This function may safely assume that @var{type} is either a pointer or a
1308 @deftypefn {Target Macro} void ADDRESS_TO_POINTER (struct type *@var{type}, char *@var{buf}, CORE_ADDR @var{addr})
1309 Store in @var{buf} a pointer of type @var{type} representing the address
1310 @var{addr}, in the appropriate format for the current architecture.
1312 This function may safely assume that @var{type} is either a pointer or a
1317 @section Using Different Register and Memory Data Representations
1318 @cindex raw representation
1319 @cindex virtual representation
1320 @cindex representations, raw and virtual
1321 @cindex register data formats, converting
1322 @cindex @code{struct value}, converting register contents to
1324 Some architectures use one representation for a value when it lives in a
1325 register, but use a different representation when it lives in memory.
1326 In @value{GDBN}'s terminology, the @dfn{raw} representation is the one used in
1327 the target registers, and the @dfn{virtual} representation is the one
1328 used in memory, and within @value{GDBN} @code{struct value} objects.
1330 For almost all data types on almost all architectures, the virtual and
1331 raw representations are identical, and no special handling is needed.
1332 However, they do occasionally differ. For example:
1337 The x86 architecture supports an 80-bit long double type. However, when
1338 we store those values in memory, they occupy twelve bytes: the
1339 floating-point number occupies the first ten, and the final two bytes
1340 are unused. This keeps the values aligned on four-byte boundaries,
1341 allowing more efficient access. Thus, the x86 80-bit floating-point
1342 type is the raw representation, and the twelve-byte loosely-packed
1343 arrangement is the virtual representation.
1346 Some 64-bit MIPS targets present 32-bit registers to @value{GDBN} as 64-bit
1347 registers, with garbage in their upper bits. @value{GDBN} ignores the top 32
1348 bits. Thus, the 64-bit form, with garbage in the upper 32 bits, is the
1349 raw representation, and the trimmed 32-bit representation is the
1350 virtual representation.
1354 In general, the raw representation is determined by the architecture, or
1355 @value{GDBN}'s interface to the architecture, while the virtual representation
1356 can be chosen for @value{GDBN}'s convenience. @value{GDBN}'s register file,
1357 @code{registers}, holds the register contents in raw format, and the @value{GDBN}
1358 remote protocol transmits register values in raw format.
1360 Your architecture may define the following macros to request raw /
1361 virtual conversions:
1363 @deftypefn {Target Macro} int REGISTER_CONVERTIBLE (int @var{reg})
1364 Return non-zero if register number @var{reg}'s value needs different raw
1365 and virtual formats.
1368 @deftypefn {Target Macro} int REGISTER_RAW_SIZE (int @var{reg})
1369 The size of register number @var{reg}'s raw value. This is the number
1370 of bytes the register will occupy in @code{registers}, or in a @value{GDBN}
1371 remote protocol packet.
1374 @deftypefn {Target Macro} int REGISTER_VIRTUAL_SIZE (int @var{reg})
1375 The size of register number @var{reg}'s value, in its virtual format.
1376 This is the size a @code{struct value}'s buffer will have, holding that
1380 @deftypefn {Target Macro} struct type *REGISTER_VIRTUAL_TYPE (int @var{reg})
1381 This is the type of the virtual representation of register number
1382 @var{reg}. Note that there is no need for a macro giving a type for the
1383 register's raw form; once the register's value has been obtained, @value{GDBN}
1384 always uses the virtual form.
1387 @deftypefn {Target Macro} void REGISTER_CONVERT_TO_VIRTUAL (int @var{reg}, struct type *@var{type}, char *@var{from}, char *@var{to})
1388 Convert the value of register number @var{reg} to @var{type}, which
1389 should always be @code{REGISTER_VIRTUAL_TYPE (@var{reg})}. The buffer
1390 at @var{from} holds the register's value in raw format; the macro should
1391 convert the value to virtual format, and place it at @var{to}.
1393 Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW take
1394 their @var{reg} and @var{type} arguments in different orders.
1397 @deftypefn {Target Macro} void REGISTER_CONVERT_TO_RAW (struct type *@var{type}, int @var{reg}, char *@var{from}, char *@var{to})
1398 Convert the value of register number @var{reg} to @var{type}, which
1399 should always be @code{REGISTER_VIRTUAL_TYPE (@var{reg})}. The buffer
1400 at @var{from} holds the register's value in raw format; the macro should
1401 convert the value to virtual format, and place it at @var{to}.
1403 Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAW take
1404 their @var{reg} and @var{type} arguments in different orders.
1408 @section Frame Interpretation
1410 @section Inferior Call Setup
1412 @section Compiler Characteristics
1414 @section Target Conditionals
1416 This section describes the macros that you can use to define the target
1421 @item ADDITIONAL_OPTIONS
1422 @item ADDITIONAL_OPTION_CASES
1423 @item ADDITIONAL_OPTION_HANDLER
1424 @item ADDITIONAL_OPTION_HELP
1425 These are a set of macros that allow the addition of additional command
1426 line options to @value{GDBN}. They are currently used only for the unsupported
1427 i960 Nindy target, and should not be used in any other configuration.
1429 @item ADDR_BITS_REMOVE (addr)
1430 If a raw machine instruction address includes any bits that are not
1431 really part of the address, then define this macro to expand into an
1432 expression that zeros those bits in @var{addr}. This is only used for
1433 addresses of instructions, and even then not in all contexts.
1435 For example, the two low-order bits of the PC on the Hewlett-Packard PA
1436 2.0 architecture contain the privilege level of the corresponding
1437 instruction. Since instructions must always be aligned on four-byte
1438 boundaries, the processor masks out these bits to generate the actual
1439 address of the instruction. ADDR_BITS_REMOVE should filter out these
1440 bits with an expression such as @code{((addr) & ~3)}.
1442 @item ADDRESS_TO_POINTER (@var{type}, @var{buf}, @var{addr})
1443 Store in @var{buf} a pointer of type @var{type} representing the address
1444 @var{addr}, in the appropriate format for the current architecture.
1445 This macro may safely assume that @var{type} is either a pointer or a
1447 @xref{Target Architecture Definition, , Pointers Are Not Always Addresses}.
1449 @item BEFORE_MAIN_LOOP_HOOK
1450 Define this to expand into any code that you want to execute before the
1451 main loop starts. Although this is not, strictly speaking, a target
1452 conditional, that is how it is currently being used. Note that if a
1453 configuration were to define it one way for a host and a different way
1454 for the target, @value{GDBN} will probably not compile, let alone run correctly.
1455 This is currently used only for the unsupported i960 Nindy target, and
1456 should not be used in any other configuration.
1458 @item BELIEVE_PCC_PROMOTION
1459 Define if the compiler promotes a short or char parameter to an int, but
1460 still reports the parameter as its original type, rather than the
1463 @item BELIEVE_PCC_PROMOTION_TYPE
1464 Define this if @value{GDBN} should believe the type of a short argument when
1465 compiled by pcc, but look within a full int space to get its value.
1466 Only defined for Sun-3 at present.
1468 @item BITS_BIG_ENDIAN
1469 Define this if the numbering of bits in the targets does *not* match the
1470 endianness of the target byte order. A value of 1 means that the bits
1471 are numbered in a big-endian order, 0 means little-endian.
1474 This is the character array initializer for the bit pattern to put into
1475 memory where a breakpoint is set. Although it's common to use a trap
1476 instruction for a breakpoint, it's not required; for instance, the bit
1477 pattern could be an invalid instruction. The breakpoint must be no
1478 longer than the shortest instruction of the architecture.
1480 @var{BREAKPOINT} has been deprecated in favour of
1481 @var{BREAKPOINT_FROM_PC}.
1483 @item BIG_BREAKPOINT
1484 @item LITTLE_BREAKPOINT
1485 Similar to BREAKPOINT, but used for bi-endian targets.
1487 @var{BIG_BREAKPOINT} and @var{LITTLE_BREAKPOINT} have been deprecated in
1488 favour of @var{BREAKPOINT_FROM_PC}.
1490 @item REMOTE_BREAKPOINT
1491 @item LITTLE_REMOTE_BREAKPOINT
1492 @item BIG_REMOTE_BREAKPOINT
1493 Similar to BREAKPOINT, but used for remote targets.
1495 @var{BIG_REMOTE_BREAKPOINT} and @var{LITTLE_REMOTE_BREAKPOINT} have been
1496 deprecated in favour of @var{BREAKPOINT_FROM_PC}.
1498 @item BREAKPOINT_FROM_PC (pcptr, lenptr)
1500 Use the program counter to determine the contents and size of a
1501 breakpoint instruction. It returns a pointer to a string of bytes that
1502 encode a breakpoint instruction, stores the length of the string to
1503 *lenptr, and adjusts pc (if necessary) to point to the actual memory
1504 location where the breakpoint should be inserted.
1506 Although it is common to use a trap instruction for a breakpoint, it's
1507 not required; for instance, the bit pattern could be an invalid
1508 instruction. The breakpoint must be no longer than the shortest
1509 instruction of the architecture.
1511 Replaces all the other @var{BREAKPOINT} macros.
1513 @item MEMORY_INSERT_BREAKPOINT (addr, contents_cache)
1514 @item MEMORY_REMOVE_BREAKPOINT (addr, contents_cache)
1516 Insert or remove memory based breakpoints. Reasonable defaults
1517 (@code{default_memory_insert_breakpoint} and
1518 @code{default_memory_remove_breakpoint} respectively) have been
1519 provided so that it is not necessary to define these for most
1520 architectures. Architectures which may want to define
1521 @var{MEMORY_INSERT_BREAKPOINT} and @var{MEMORY_REMOVE_BREAKPOINT} will
1522 likely have instructions that are oddly sized or are not stored in a
1523 conventional manner.
1525 It may also be desirable (from an efficiency standpoint) to define
1526 custom breakpoint insertion and removal routines if
1527 @var{BREAKPOINT_FROM_PC} needs to read the target's memory for some
1531 A C expresson that is non-zero when the target suports inferior function
1534 @item CALL_DUMMY_WORDS
1535 Pointer to an array of @var{LONGEST} words of data containing
1536 host-byte-ordered @var{REGISTER_BYTES} sized values that partially
1537 specify the sequence of instructions needed for an inferior function
1540 Should be deprecated in favour of a macro that uses target-byte-ordered
1543 @item SIZEOF_CALL_DUMMY_WORDS
1544 The size of @var{CALL_DUMMY_WORDS}. When @var{CALL_DUMMY_P} this must
1545 return a positive value. See also @var{CALL_DUMMY_LENGTH}.
1548 A static initializer for @var{CALL_DUMMY_WORDS}. Deprecated.
1550 @item CALL_DUMMY_LOCATION
1553 @item CALL_DUMMY_STACK_ADJUST
1554 Stack adjustment needed when performing an inferior function call.
1556 Should be deprecated in favor of something like @var{STACK_ALIGN}.
1558 @item CALL_DUMMY_STACK_ADJUST_P
1559 Predicate for use of @var{CALL_DUMMY_STACK_ADJUST}.
1561 Should be deprecated in favor of something like @var{STACK_ALIGN}.
1563 @item CANNOT_FETCH_REGISTER (regno)
1564 A C expression that should be nonzero if @var{regno} cannot be fetched
1565 from an inferior process. This is only relevant if
1566 @code{FETCH_INFERIOR_REGISTERS} is not defined.
1568 @item CANNOT_STORE_REGISTER (regno)
1569 A C expression that should be nonzero if @var{regno} should not be
1570 written to the target. This is often the case for program counters,
1571 status words, and other special registers. If this is not defined, @value{GDBN}
1572 will assume that all registers may be written.
1574 @item DO_DEFERRED_STORES
1575 @item CLEAR_DEFERRED_STORES
1576 Define this to execute any deferred stores of registers into the inferior,
1577 and to cancel any deferred stores.
1579 Currently only implemented correctly for native Sparc configurations?
1581 @item COERCE_FLOAT_TO_DOUBLE (@var{formal}, @var{actual})
1582 If we are calling a function by hand, and the function was declared
1583 (according to the debug info) without a prototype, should we
1584 automatically promote floats to doubles? This macro must evaluate to
1585 non-zero if we should, or zero if we should leave the value alone.
1587 The argument @var{actual} is the type of the value we want to pass to
1588 the function. The argument @var{formal} is the type of this argument,
1589 as it appears in the function's definition. Note that @var{formal} may
1590 be zero if we have no debugging information for the function, or if
1591 we're passing more arguments than are officially declared (for example,
1592 varargs). This macro is never invoked if the function definitely has a
1595 The default behavior is to promote only when we have no type information
1596 for the formal parameter. This is different from the obvious behavior,
1597 which would be to promote whenever we have no prototype, just as the
1598 compiler does. It's annoying, but some older targets rely on this. If
1599 you want @value{GDBN} to follow the typical compiler behavior --- to always
1600 promote when there is no prototype in scope --- your gdbarch init
1601 function can call @code{set_gdbarch_coerce_float_to_double} and select
1602 the @code{standard_coerce_float_to_double} function.
1605 Define this to expand into the character that G++ uses to distinguish
1606 compiler-generated identifiers from programmer-specified identifiers.
1607 By default, this expands into @code{'$'}. Most System V targets should
1608 define this to @code{'.'}.
1610 @item DBX_PARM_SYMBOL_CLASS
1611 Hook for the @code{SYMBOL_CLASS} of a parameter when decoding DBX symbol
1612 information. In the i960, parameters can be stored as locals or as
1613 args, depending on the type of the debug record.
1615 @item DECR_PC_AFTER_BREAK
1616 Define this to be the amount by which to decrement the PC after the
1617 program encounters a breakpoint. This is often the number of bytes in
1618 BREAKPOINT, though not always. For most targets this value will be 0.
1620 @item DECR_PC_AFTER_HW_BREAK
1621 Similarly, for hardware breakpoints.
1623 @item DISABLE_UNSETTABLE_BREAK addr
1624 If defined, this should evaluate to 1 if @var{addr} is in a shared
1625 library in which breakpoints cannot be set and so should be disabled.
1627 @item DO_REGISTERS_INFO
1628 If defined, use this to print the value of a register or all registers.
1630 @item END_OF_TEXT_DEFAULT
1631 This is an expression that should designate the end of the text section
1634 @item EXTRACT_RETURN_VALUE(type,regbuf,valbuf)
1635 Define this to extract a function's return value of type @var{type} from
1636 the raw register state @var{regbuf} and copy that, in virtual format,
1639 @item EXTRACT_STRUCT_VALUE_ADDRESS(regbuf)
1640 When @var{EXTRACT_STRUCT_VALUE_ADDRESS_P} this is used to to extract
1641 from an array @var{regbuf} (containing the raw register state) the
1642 address in which a function should return its structure value, as a
1643 CORE_ADDR (or an expression that can be used as one).
1645 @item EXTRACT_STRUCT_VALUE_ADDRESS_P
1646 Predicate for @var{EXTRACT_STRUCT_VALUE_ADDRESS}.
1649 If defined, then the `info float' command will print information about
1650 the processor's floating point unit.
1653 If the virtual frame pointer is kept in a register, then define this
1654 macro to be the number (greater than or equal to zero) of that register.
1656 This should only need to be defined if @code{TARGET_READ_FP} and
1657 @code{TARGET_WRITE_FP} are not defined.
1659 @item FRAMELESS_FUNCTION_INVOCATION(fi)
1660 Define this to an expression that returns 1 if the function invocation
1661 represented by @var{fi} does not have a stack frame associated with it.
1664 @item FRAME_ARGS_ADDRESS_CORRECT
1667 @item FRAME_CHAIN(frame)
1668 Given @var{frame}, return a pointer to the calling frame.
1670 @item FRAME_CHAIN_COMBINE(chain,frame)
1671 Define this to take the frame chain pointer and the frame's nominal
1672 address and produce the nominal address of the caller's frame.
1673 Presently only defined for HP PA.
1675 @item FRAME_CHAIN_VALID(chain,thisframe)
1677 Define this to be an expression that returns zero if the given frame is
1678 an outermost frame, with no caller, and nonzero otherwise. Several
1679 common definitions are available.
1681 @code{file_frame_chain_valid} is nonzero if the chain pointer is nonzero
1682 and given frame's PC is not inside the startup file (such as
1683 @file{crt0.o}). @code{func_frame_chain_valid} is nonzero if the chain
1684 pointer is nonzero and the given frame's PC is not in @code{main()} or a
1685 known entry point function (such as @code{_start()}).
1686 @code{generic_file_frame_chain_valid} and
1687 @code{generic_func_frame_chain_valid} are equivalent implementations for
1688 targets using generic dummy frames.
1690 @item FRAME_INIT_SAVED_REGS(frame)
1691 See @file{frame.h}. Determines the address of all registers in the
1692 current stack frame storing each in @code{frame->saved_regs}. Space for
1693 @code{frame->saved_regs} shall be allocated by
1694 @code{FRAME_INIT_SAVED_REGS} using either
1695 @code{frame_saved_regs_zalloc} or @code{frame_obstack_alloc}.
1697 @var{FRAME_FIND_SAVED_REGS} and @var{EXTRA_FRAME_INFO} are deprecated.
1699 @item FRAME_NUM_ARGS (fi)
1700 For the frame described by @var{fi} return the number of arguments that
1701 are being passed. If the number of arguments is not known, return
1704 @item FRAME_SAVED_PC(frame)
1705 Given @var{frame}, return the pc saved there. That is, the return
1708 @item FUNCTION_EPILOGUE_SIZE
1709 For some COFF targets, the @code{x_sym.x_misc.x_fsize} field of the
1710 function end symbol is 0. For such targets, you must define
1711 @code{FUNCTION_EPILOGUE_SIZE} to expand into the standard size of a
1712 function's epilogue.
1714 @item FUNCTION_START_OFFSET
1715 An integer, giving the offset in bytes from a function's address (as
1716 used in the values of symbols, function pointers, etc.), and the
1717 function's first genuine instruction.
1719 This is zero on almost all machines: the function's address is usually
1720 the address of its first instruction. However, on the VAX, for example,
1721 each function starts with two bytes containing a bitmask indicating
1722 which registers to save upon entry to the function. The VAX @code{call}
1723 instructions check this value, and save the appropriate registers
1724 automatically. Thus, since the offset from the function's address to
1725 its first instruction is two bytes, @code{FUNCTION_START_OFFSET} would
1728 @item GCC_COMPILED_FLAG_SYMBOL
1729 @item GCC2_COMPILED_FLAG_SYMBOL
1730 If defined, these are the names of the symbols that @value{GDBN} will look for to
1731 detect that GCC compiled the file. The default symbols are
1732 @code{gcc_compiled.} and @code{gcc2_compiled.}, respectively. (Currently
1733 only defined for the Delta 68.)
1735 @item @value{GDBN}_MULTI_ARCH
1736 If defined and non-zero, enables suport for multiple architectures
1737 within @value{GDBN}.
1739 The support can be enabled at two levels. At level one, only
1740 definitions for previously undefined macros are provided; at level two,
1741 a multi-arch definition of all architecture dependant macros will be
1744 @item @value{GDBN}_TARGET_IS_HPPA
1745 This determines whether horrible kludge code in dbxread.c and
1746 partial-stab.h is used to mangle multiple-symbol-table files from
1747 HPPA's. This should all be ripped out, and a scheme like elfread.c
1750 @item GET_LONGJMP_TARGET
1751 For most machines, this is a target-dependent parameter. On the
1752 DECstation and the Iris, this is a native-dependent parameter, since
1753 <setjmp.h> is needed to define it.
1755 This macro determines the target PC address that longjmp() will jump to,
1756 assuming that we have just stopped at a longjmp breakpoint. It takes a
1757 CORE_ADDR * as argument, and stores the target PC value through this
1758 pointer. It examines the current state of the machine as needed.
1760 @item GET_SAVED_REGISTER
1761 Define this if you need to supply your own definition for the function
1762 @code{get_saved_register}.
1764 @item HAVE_REGISTER_WINDOWS
1765 Define this if the target has register windows.
1766 @item REGISTER_IN_WINDOW_P (regnum)
1767 Define this to be an expression that is 1 if the given register is in
1770 @item IBM6000_TARGET
1771 Shows that we are configured for an IBM RS/6000 target. This
1772 conditional should be eliminated (FIXME) and replaced by
1773 feature-specific macros. It was introduced in haste and we are
1774 repenting at leisure.
1776 @item SYMBOLS_CAN_START_WITH_DOLLAR
1777 Some systems have routines whose names start with @samp{$}. Giving this
1778 macro a non-zero value tells @value{GDBN}'s expression parser to check for such
1779 routines when parsing tokens that begin with @samp{$}.
1781 On HP-UX, certain system routines (millicode) have names beginning with
1782 @samp{$} or @samp{$$}. For example, @code{$$dyncall} is a millicode
1783 routine that handles inter-space procedure calls on PA-RISC.
1786 Define this if the target system uses IEEE-format floating point numbers.
1788 @item INIT_EXTRA_FRAME_INFO (fromleaf, frame)
1789 If additional information about the frame is required this should be
1790 stored in @code{frame->extra_info}. Space for @code{frame->extra_info}
1791 is allocated using @code{frame_obstack_alloc}.
1793 @item INIT_FRAME_PC (fromleaf, prev)
1794 This is a C statement that sets the pc of the frame pointed to by
1795 @var{prev}. [By default...]
1797 @item INNER_THAN (lhs,rhs)
1798 Returns non-zero if stack address @var{lhs} is inner than (nearer to the
1799 stack top) stack address @var{rhs}. Define this as @code{lhs < rhs} if
1800 the target's stack grows downward in memory, or @code{lhs > rsh} if the
1803 @item IN_SIGTRAMP (pc, name)
1804 Define this to return true if the given @var{pc} and/or @var{name}
1805 indicates that the current function is a sigtramp.
1807 @item SIGTRAMP_START (pc)
1808 @item SIGTRAMP_END (pc)
1809 Define these to be the start and end address of the sigtramp for the
1810 given @var{pc}. On machines where the address is just a compile time
1811 constant, the macro expansion will typically just ignore the supplied
1814 @item IN_SOLIB_CALL_TRAMPOLINE pc name
1815 Define this to evaluate to nonzero if the program is stopped in the
1816 trampoline that connects to a shared library.
1818 @item IN_SOLIB_RETURN_TRAMPOLINE pc name
1819 Define this to evaluate to nonzero if the program is stopped in the
1820 trampoline that returns from a shared library.
1822 @item IN_SOLIB_DYNSYM_RESOLVE_CODE pc
1823 Define this to evaluate to nonzero if the program is stopped in the
1826 @item SKIP_SOLIB_RESOLVER pc
1827 Define this to evaluate to the (nonzero) address at which execution
1828 should continue to get past the dynamic linker's symbol resolution
1829 function. A zero value indicates that it is not important or necessary
1830 to set a breakpoint to get through the dynamic linker and that single
1831 stepping will suffice.
1833 @item IS_TRAPPED_INTERNALVAR (name)
1834 This is an ugly hook to allow the specification of special actions that
1835 should occur as a side-effect of setting the value of a variable
1836 internal to @value{GDBN}. Currently only used by the h8500. Note that this
1837 could be either a host or target conditional.
1839 @item NEED_TEXT_START_END
1840 Define this if @value{GDBN} should determine the start and end addresses of the
1841 text section. (Seems dubious.)
1843 @item NO_HIF_SUPPORT
1844 (Specific to the a29k.)
1846 @item POINTER_TO_ADDRESS (@var{type}, @var{buf})
1847 Assume that @var{buf} holds a pointer of type @var{type}, in the
1848 appropriate format for the current architecture. Return the byte
1849 address the pointer refers to.
1850 @xref{Target Architecture Definition, , Pointers Are Not Always Addresses}.
1852 @item REGISTER_CONVERTIBLE (@var{reg})
1853 Return non-zero if @var{reg} uses different raw and virtual formats.
1854 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1856 @item REGISTER_RAW_SIZE (@var{reg})
1857 Return the raw size of @var{reg}.
1858 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1860 @item REGISTER_VIRTUAL_SIZE (@var{reg})
1861 Return the virtual size of @var{reg}.
1862 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1864 @item REGISTER_VIRTUAL_TYPE (@var{reg})
1865 Return the virtual type of @var{reg}.
1866 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1868 @item REGISTER_CONVERT_TO_VIRTUAL(@var{reg}, @var{type}, @var{from}, @var{to})
1869 Convert the value of register @var{reg} from its raw form to its virtual
1871 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1873 @item REGISTER_CONVERT_TO_RAW(@var{type}, @var{reg}, @var{from}, @var{to})
1874 Convert the value of register @var{reg} from its virtual form to its raw
1876 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
1878 @item SOFTWARE_SINGLE_STEP_P
1879 Define this as 1 if the target does not have a hardware single-step
1880 mechanism. The macro @code{SOFTWARE_SINGLE_STEP} must also be defined.
1882 @item SOFTWARE_SINGLE_STEP(signal,insert_breapoints_p)
1883 A function that inserts or removes (dependant on
1884 @var{insert_breapoints_p}) breakpoints at each possible destinations of
1885 the next instruction. See @code{sparc-tdep.c} and @code{rs6000-tdep.c}
1888 @item SOFUN_ADDRESS_MAYBE_MISSING
1890 Somebody clever observed that, the more actual addresses you have in the
1891 debug information, the more time the linker has to spend relocating
1892 them. So whenever there's some other way the debugger could find the
1893 address it needs, you should omit it from the debug info, to make
1896 @code{SOFUN_ADDRESS_MAYBE_MISSING} indicates that a particular set of
1897 hacks of this sort are in use, affecting @code{N_SO} and @code{N_FUN}
1898 entries in stabs-format debugging information. @code{N_SO} stabs mark
1899 the beginning and ending addresses of compilation units in the text
1900 segment. @code{N_FUN} stabs mark the starts and ends of functions.
1902 @code{SOFUN_ADDRESS_MAYBE_MISSING} means two things:
1906 @code{N_FUN} stabs have an address of zero. Instead, you should find the
1907 addresses where the function starts by taking the function name from
1908 the stab, and then looking that up in the minsyms (the linker/
1909 assembler symbol table). In other words, the stab has the name, and
1910 the linker / assembler symbol table is the only place that carries
1914 @code{N_SO} stabs have an address of zero, too. You just look at the
1915 @code{N_FUN} stabs that appear before and after the @code{N_SO} stab,
1916 and guess the starting and ending addresses of the compilation unit from
1921 @item PCC_SOL_BROKEN
1922 (Used only in the Convex target.)
1924 @item PC_IN_CALL_DUMMY
1927 @item PC_LOAD_SEGMENT
1928 If defined, print information about the load segment for the program
1929 counter. (Defined only for the RS/6000.)
1932 If the program counter is kept in a register, then define this macro to
1933 be the number (greater than or equal to zero) of that register.
1935 This should only need to be defined if @code{TARGET_READ_PC} and
1936 @code{TARGET_WRITE_PC} are not defined.
1939 The number of the ``next program counter'' register, if defined.
1942 The number of the ``next next program counter'' register, if defined.
1943 Currently, this is only defined for the Motorola 88K.
1946 If non-zero, round arguments to a boundary of this many bits before
1947 pushing them on the stack.
1949 @item PRINT_REGISTER_HOOK (regno)
1950 If defined, this must be a function that prints the contents of the
1951 given register to standard output.
1953 @item PRINT_TYPELESS_INTEGER
1954 This is an obscure substitute for @code{print_longest} that seems to
1955 have been defined for the Convex target.
1957 @item PROCESS_LINENUMBER_HOOK
1958 A hook defined for XCOFF reading.
1960 @item PROLOGUE_FIRSTLINE_OVERLAP
1961 (Only used in unsupported Convex configuration.)
1964 If defined, this is the number of the processor status register. (This
1965 definition is only used in generic code when parsing "$ps".)
1968 Used in @samp{call_function_by_hand} to remove an artificial stack
1971 @item PUSH_ARGUMENTS (nargs, args, sp, struct_return, struct_addr)
1972 Define this to push arguments onto the stack for inferior function
1973 call. Return the updated stack pointer value.
1975 @item PUSH_DUMMY_FRAME
1976 Used in @samp{call_function_by_hand} to create an artificial stack frame.
1978 @item REGISTER_BYTES
1979 The total amount of space needed to store @value{GDBN}'s copy of the machine's
1982 @item REGISTER_NAME(i)
1983 Return the name of register @var{i} as a string. May return @var{NULL}
1984 or @var{NUL} to indicate that register @var{i} is not valid.
1986 @item REGISTER_NAMES
1987 Deprecated in favor of @var{REGISTER_NAME}.
1989 @item REG_STRUCT_HAS_ADDR (gcc_p, type)
1990 Define this to return 1 if the given type will be passed by pointer
1991 rather than directly.
1993 @item SAVE_DUMMY_FRAME_TOS (sp)
1994 Used in @samp{call_function_by_hand} to notify the target dependent code
1995 of the top-of-stack value that will be passed to the the inferior code.
1996 This is the value of the @var{SP} after both the dummy frame and space
1997 for parameters/results have been allocated on the stack.
1999 @item SDB_REG_TO_REGNUM
2000 Define this to convert sdb register numbers into @value{GDBN} regnums. If not
2001 defined, no conversion will be done.
2003 @item SHIFT_INST_REGS
2004 (Only used for m88k targets.)
2006 @item SKIP_PERMANENT_BREAKPOINT
2007 Advance the inferior's PC past a permanent breakpoint. @value{GDBN} normally
2008 steps over a breakpoint by removing it, stepping one instruction, and
2009 re-inserting the breakpoint. However, permanent breakpoints are
2010 hardwired into the inferior, and can't be removed, so this strategy
2011 doesn't work. Calling SKIP_PERMANENT_BREAKPOINT adjusts the processor's
2012 state so that execution will resume just after the breakpoint. This
2013 macro does the right thing even when the breakpoint is in the delay slot
2014 of a branch or jump.
2016 @item SKIP_PROLOGUE (pc)
2017 A C expression that returns the address of the ``real'' code beyond the
2018 function entry prologue found at @var{pc}.
2020 @item SKIP_PROLOGUE_FRAMELESS_P
2021 A C expression that should behave similarly, but that can stop as soon
2022 as the function is known to have a frame. If not defined,
2023 @code{SKIP_PROLOGUE} will be used instead.
2025 @item SKIP_TRAMPOLINE_CODE (pc)
2026 If the target machine has trampoline code that sits between callers and
2027 the functions being called, then define this macro to return a new PC
2028 that is at the start of the real function.
2031 If the stack-pointer is kept in a register, then define this macro to be
2032 the number (greater than or equal to zero) of that register.
2034 This should only need to be defined if @code{TARGET_WRITE_SP} and
2035 @code{TARGET_WRITE_SP} are not defined.
2037 @item STAB_REG_TO_REGNUM
2038 Define this to convert stab register numbers (as gotten from `r'
2039 declarations) into @value{GDBN} regnums. If not defined, no conversion will be
2042 @item STACK_ALIGN (addr)
2043 Define this to adjust the address to the alignment required for the
2046 @item STEP_SKIPS_DELAY (addr)
2047 Define this to return true if the address is of an instruction with a
2048 delay slot. If a breakpoint has been placed in the instruction's delay
2049 slot, @value{GDBN} will single-step over that instruction before resuming
2050 normally. Currently only defined for the Mips.
2052 @item STORE_RETURN_VALUE (type, valbuf)
2053 A C expression that stores a function return value of type @var{type},
2054 where @var{valbuf} is the address of the value to be stored.
2056 @item SUN_FIXED_LBRAC_BUG
2057 (Used only for Sun-3 and Sun-4 targets.)
2059 @item SYMBOL_RELOADING_DEFAULT
2060 The default value of the `symbol-reloading' variable. (Never defined in
2063 @item TARGET_BYTE_ORDER_DEFAULT
2064 The ordering of bytes in the target. This must be either
2065 @code{BIG_ENDIAN} or @code{LITTLE_ENDIAN}. This macro replaces
2066 @var{TARGET_BYTE_ORDER} which is deprecated.
2068 @item TARGET_BYTE_ORDER_SELECTABLE_P
2069 Non-zero if the target has both @code{BIG_ENDIAN} and
2070 @code{LITTLE_ENDIAN} variants. This macro replaces
2071 @var{TARGET_BYTE_ORDER_SELECTABLE} which is deprecated.
2073 @item TARGET_CHAR_BIT
2074 Number of bits in a char; defaults to 8.
2076 @item TARGET_COMPLEX_BIT
2077 Number of bits in a complex number; defaults to @code{2 * TARGET_FLOAT_BIT}.
2079 At present this macro is not used.
2081 @item TARGET_DOUBLE_BIT
2082 Number of bits in a double float; defaults to @code{8 * TARGET_CHAR_BIT}.
2084 @item TARGET_DOUBLE_COMPLEX_BIT
2085 Number of bits in a double complex; defaults to @code{2 * TARGET_DOUBLE_BIT}.
2087 At present this macro is not used.
2089 @item TARGET_FLOAT_BIT
2090 Number of bits in a float; defaults to @code{4 * TARGET_CHAR_BIT}.
2092 @item TARGET_INT_BIT
2093 Number of bits in an integer; defaults to @code{4 * TARGET_CHAR_BIT}.
2095 @item TARGET_LONG_BIT
2096 Number of bits in a long integer; defaults to @code{4 * TARGET_CHAR_BIT}.
2098 @item TARGET_LONG_DOUBLE_BIT
2099 Number of bits in a long double float;
2100 defaults to @code{2 * TARGET_DOUBLE_BIT}.
2102 @item TARGET_LONG_LONG_BIT
2103 Number of bits in a long long integer; defaults to @code{2 * TARGET_LONG_BIT}.
2105 @item TARGET_PTR_BIT
2106 Number of bits in a pointer; defaults to @code{TARGET_INT_BIT}.
2108 @item TARGET_SHORT_BIT
2109 Number of bits in a short integer; defaults to @code{2 * TARGET_CHAR_BIT}.
2111 @item TARGET_READ_PC
2112 @item TARGET_WRITE_PC (val, pid)
2113 @item TARGET_READ_SP
2114 @item TARGET_WRITE_SP
2115 @item TARGET_READ_FP
2116 @item TARGET_WRITE_FP
2117 These change the behavior of @code{read_pc}, @code{write_pc},
2118 @code{read_sp}, @code{write_sp}, @code{read_fp} and @code{write_fp}.
2119 For most targets, these may be left undefined. @value{GDBN} will call the read
2120 and write register functions with the relevant @code{_REGNUM} argument.
2122 These macros are useful when a target keeps one of these registers in a
2123 hard to get at place; for example, part in a segment register and part
2124 in an ordinary register.
2126 @item TARGET_VIRTUAL_FRAME_POINTER(pc,regp,offsetp)
2127 Returns a @code{(register, offset)} pair representing the virtual
2128 frame pointer in use at the code address @code{"pc"}. If virtual
2129 frame pointers are not used, a default definition simply returns
2130 @code{FP_REGNUM}, with an offset of zero.
2132 @item USE_STRUCT_CONVENTION (gcc_p, type)
2133 If defined, this must be an expression that is nonzero if a value of the
2134 given @var{type} being returned from a function must have space
2135 allocated for it on the stack. @var{gcc_p} is true if the function
2136 being considered is known to have been compiled by GCC; this is helpful
2137 for systems where GCC is known to use different calling convention than
2140 @item VARIABLES_INSIDE_BLOCK (desc, gcc_p)
2141 For dbx-style debugging information, if the compiler puts variable
2142 declarations inside LBRAC/RBRAC blocks, this should be defined to be
2143 nonzero. @var{desc} is the value of @code{n_desc} from the
2144 @code{N_RBRAC} symbol, and @var{gcc_p} is true if @value{GDBN} has noticed the
2145 presence of either the @code{GCC_COMPILED_SYMBOL} or the
2146 @code{GCC2_COMPILED_SYMBOL}. By default, this is 0.
2148 @item OS9K_VARIABLES_INSIDE_BLOCK (desc, gcc_p)
2149 Similarly, for OS/9000. Defaults to 1.
2153 Motorola M68K target conditionals.
2158 Define this to be the 4-bit location of the breakpoint trap vector. If
2159 not defined, it will default to @code{0xf}.
2161 @item REMOTE_BPT_VECTOR
2162 Defaults to @code{1}.
2166 @section Adding a New Target
2168 The following files define a target to @value{GDBN}:
2172 @item gdb/config/@var{arch}/@var{ttt}.mt
2173 Contains a Makefile fragment specific to this target. Specifies what
2174 object files are needed for target @var{ttt}, by defining
2175 @samp{TDEPFILES=@dots{}} and @samp{TDEPLIBS=@dots{}}. Also specifies
2176 the header file which describes @var{ttt}, by defining @samp{TM_FILE=
2179 You can also define @samp{TM_CFLAGS}, @samp{TM_CLIBS}, @samp{TM_CDEPS},
2180 but these are now deprecated, replaced by autoconf, and may go away in
2181 future versions of @value{GDBN}.
2183 @item gdb/config/@var{arch}/tm-@var{ttt}.h
2184 (@file{tm.h} is a link to this file, created by configure). Contains
2185 macro definitions about the target machine's registers, stack frame
2186 format and instructions.
2188 @item gdb/@var{ttt}-tdep.c
2189 Contains any miscellaneous code required for this target machine. On
2190 some machines it doesn't exist at all. Sometimes the macros in
2191 @file{tm-@var{ttt}.h} become very complicated, so they are implemented
2192 as functions here instead, and the macro is simply defined to call the
2193 function. This is vastly preferable, since it is easier to understand
2196 @item gdb/config/@var{arch}/tm-@var{arch}.h
2197 This often exists to describe the basic layout of the target machine's
2198 processor chip (registers, stack, etc). If used, it is included by
2199 @file{tm-@var{ttt}.h}. It can be shared among many targets that use the
2202 @item gdb/@var{arch}-tdep.c
2203 Similarly, there are often common subroutines that are shared by all
2204 target machines that use this particular architecture.
2208 If you are adding a new operating system for an existing CPU chip, add a
2209 @file{config/tm-@var{os}.h} file that describes the operating system
2210 facilities that are unusual (extra symbol table info; the breakpoint
2211 instruction needed; etc). Then write a @file{@var{arch}/tm-@var{os}.h}
2212 that just @code{#include}s @file{tm-@var{arch}.h} and
2213 @file{config/tm-@var{os}.h}.
2216 @node Target Vector Definition
2218 @chapter Target Vector Definition
2220 The target vector defines the interface between @value{GDBN}'s abstract handling
2221 of target systems, and the nitty-gritty code that actually exercises
2222 control over a process or a serial port. @value{GDBN} includes some 30-40
2223 different target vectors; however, each configuration of @value{GDBN} includes
2226 @section File Targets
2228 Both executables and core files have target vectors.
2230 @section Standard Protocol and Remote Stubs
2232 @value{GDBN}'s file @file{remote.c} talks a serial protocol to code that runs in
2233 the target system. @value{GDBN} provides several sample ``stubs'' that can be
2234 integrated into target programs or operating systems for this purpose;
2235 they are named @file{*-stub.c}.
2237 The @value{GDBN} user's manual describes how to put such a stub into your target
2238 code. What follows is a discussion of integrating the SPARC stub into a
2239 complicated operating system (rather than a simple program), by Stu
2240 Grossman, the author of this stub.
2242 The trap handling code in the stub assumes the following upon entry to
2247 @item %l1 and %l2 contain pc and npc respectively at the time of the trap
2249 @item traps are disabled
2251 @item you are in the correct trap window
2255 As long as your trap handler can guarantee those conditions, then there
2256 is no reason why you shouldn't be able to `share' traps with the stub.
2257 The stub has no requirement that it be jumped to directly from the
2258 hardware trap vector. That is why it calls @code{exceptionHandler()},
2259 which is provided by the external environment. For instance, this could
2260 setup the hardware traps to actually execute code which calls the stub
2261 first, and then transfers to its own trap handler.
2263 For the most point, there probably won't be much of an issue with
2264 `sharing' traps, as the traps we use are usually not used by the kernel,
2265 and often indicate unrecoverable error conditions. Anyway, this is all
2266 controlled by a table, and is trivial to modify. The most important
2267 trap for us is for @code{ta 1}. Without that, we can't single step or
2268 do breakpoints. Everything else is unnecessary for the proper operation
2269 of the debugger/stub.
2271 From reading the stub, it's probably not obvious how breakpoints work.
2272 They are simply done by deposit/examine operations from @value{GDBN}.
2274 @section ROM Monitor Interface
2276 @section Custom Protocols
2278 @section Transport Layer
2280 @section Builtin Simulator
2283 @node Native Debugging
2285 @chapter Native Debugging
2287 Several files control @value{GDBN}'s configuration for native support:
2291 @item gdb/config/@var{arch}/@var{xyz}.mh
2292 Specifies Makefile fragments needed when hosting @emph{or native} on
2293 machine @var{xyz}. In particular, this lists the required
2294 native-dependent object files, by defining @samp{NATDEPFILES=@dots{}}.
2295 Also specifies the header file which describes native support on
2296 @var{xyz}, by defining @samp{NAT_FILE= nm-@var{xyz}.h}. You can also
2297 define @samp{NAT_CFLAGS}, @samp{NAT_ADD_FILES}, @samp{NAT_CLIBS},
2298 @samp{NAT_CDEPS}, etc.; see @file{Makefile.in}.
2300 @item gdb/config/@var{arch}/nm-@var{xyz}.h
2301 (@file{nm.h} is a link to this file, created by configure). Contains C
2302 macro definitions describing the native system environment, such as
2303 child process control and core file support.
2305 @item gdb/@var{xyz}-nat.c
2306 Contains any miscellaneous C code required for this native support of
2307 this machine. On some machines it doesn't exist at all.
2311 There are some ``generic'' versions of routines that can be used by
2312 various systems. These can be customized in various ways by macros
2313 defined in your @file{nm-@var{xyz}.h} file. If these routines work for
2314 the @var{xyz} host, you can just include the generic file's name (with
2315 @samp{.o}, not @samp{.c}) in @code{NATDEPFILES}.
2317 Otherwise, if your machine needs custom support routines, you will need
2318 to write routines that perform the same functions as the generic file.
2319 Put them into @code{@var{xyz}-nat.c}, and put @code{@var{xyz}-nat.o}
2320 into @code{NATDEPFILES}.
2325 This contains the @emph{target_ops vector} that supports Unix child
2326 processes on systems which use ptrace and wait to control the child.
2329 This contains the @emph{target_ops vector} that supports Unix child
2330 processes on systems which use /proc to control the child.
2333 This does the low-level grunge that uses Unix system calls to do a "fork
2334 and exec" to start up a child process.
2337 This is the low level interface to inferior processes for systems using
2338 the Unix @code{ptrace} call in a vanilla way.
2342 @section Native core file Support
2346 @item core-aout.c::fetch_core_registers()
2347 Support for reading registers out of a core file. This routine calls
2348 @code{register_addr()}, see below. Now that BFD is used to read core
2349 files, virtually all machines should use @code{core-aout.c}, and should
2350 just provide @code{fetch_core_registers} in @code{@var{xyz}-nat.c} (or
2351 @code{REGISTER_U_ADDR} in @code{nm-@var{xyz}.h}).
2353 @item core-aout.c::register_addr()
2354 If your @code{nm-@var{xyz}.h} file defines the macro
2355 @code{REGISTER_U_ADDR(addr, blockend, regno)}, it should be defined to
2356 set @code{addr} to the offset within the @samp{user} struct of @value{GDBN}
2357 register number @code{regno}. @code{blockend} is the offset within the
2358 ``upage'' of @code{u.u_ar0}. If @code{REGISTER_U_ADDR} is defined,
2359 @file{core-aout.c} will define the @code{register_addr()} function and
2360 use the macro in it. If you do not define @code{REGISTER_U_ADDR}, but
2361 you are using the standard @code{fetch_core_registers()}, you will need
2362 to define your own version of @code{register_addr()}, put it into your
2363 @code{@var{xyz}-nat.c} file, and be sure @code{@var{xyz}-nat.o} is in
2364 the @code{NATDEPFILES} list. If you have your own
2365 @code{fetch_core_registers()}, you may not need a separate
2366 @code{register_addr()}. Many custom @code{fetch_core_registers()}
2367 implementations simply locate the registers themselves.@refill
2371 When making @value{GDBN} run native on a new operating system, to make it
2372 possible to debug core files, you will need to either write specific
2373 code for parsing your OS's core files, or customize
2374 @file{bfd/trad-core.c}. First, use whatever @code{#include} files your
2375 machine uses to define the struct of registers that is accessible
2376 (possibly in the u-area) in a core file (rather than
2377 @file{machine/reg.h}), and an include file that defines whatever header
2378 exists on a core file (e.g. the u-area or a @samp{struct core}). Then
2379 modify @code{trad_unix_core_file_p()} to use these values to set up the
2380 section information for the data segment, stack segment, any other
2381 segments in the core file (perhaps shared library contents or control
2382 information), ``registers'' segment, and if there are two discontiguous
2383 sets of registers (e.g. integer and float), the ``reg2'' segment. This
2384 section information basically delimits areas in the core file in a
2385 standard way, which the section-reading routines in BFD know how to seek
2388 Then back in @value{GDBN}, you need a matching routine called
2389 @code{fetch_core_registers()}. If you can use the generic one, it's in
2390 @file{core-aout.c}; if not, it's in your @file{@var{xyz}-nat.c} file.
2391 It will be passed a char pointer to the entire ``registers'' segment,
2392 its length, and a zero; or a char pointer to the entire ``regs2''
2393 segment, its length, and a 2. The routine should suck out the supplied
2394 register values and install them into @value{GDBN}'s ``registers'' array.
2396 If your system uses @file{/proc} to control processes, and uses ELF
2397 format core files, then you may be able to use the same routines for
2398 reading the registers out of processes and out of core files.
2406 @section shared libraries
2408 @section Native Conditionals
2410 When @value{GDBN} is configured and compiled, various macros are defined or left
2411 undefined, to control compilation when the host and target systems are
2412 the same. These macros should be defined (or left undefined) in
2413 @file{nm-@var{system}.h}.
2418 If defined, then @value{GDBN} will include support for the @code{attach} and
2419 @code{detach} commands.
2421 @item CHILD_PREPARE_TO_STORE
2422 If the machine stores all registers at once in the child process, then
2423 define this to ensure that all values are correct. This usually entails
2424 a read from the child.
2426 [Note that this is incorrectly defined in @file{xm-@var{system}.h} files
2429 @item FETCH_INFERIOR_REGISTERS
2430 Define this if the native-dependent code will provide its own routines
2431 @code{fetch_inferior_registers} and @code{store_inferior_registers} in
2432 @file{@var{HOST}-nat.c}. If this symbol is @emph{not} defined, and
2433 @file{infptrace.c} is included in this configuration, the default
2434 routines in @file{infptrace.c} are used for these functions.
2436 @item FILES_INFO_HOOK
2437 (Only defined for Convex.)
2440 This macro is normally defined to be the number of the first floating
2441 point register, if the machine has such registers. As such, it would
2442 appear only in target-specific code. However, /proc support uses this
2443 to decide whether floats are in use on this target.
2445 @item GET_LONGJMP_TARGET
2446 For most machines, this is a target-dependent parameter. On the
2447 DECstation and the Iris, this is a native-dependent parameter, since
2448 <setjmp.h> is needed to define it.
2450 This macro determines the target PC address that longjmp() will jump to,
2451 assuming that we have just stopped at a longjmp breakpoint. It takes a
2452 CORE_ADDR * as argument, and stores the target PC value through this
2453 pointer. It examines the current state of the machine as needed.
2456 Define this to the address of the @code{u} structure (the ``user
2457 struct'', also known as the ``u-page'') in kernel virtual memory. @value{GDBN}
2458 needs to know this so that it can subtract this address from absolute
2459 addresses in the upage, that are obtained via ptrace or from core files.
2460 On systems that don't need this value, set it to zero.
2462 @item KERNEL_U_ADDR_BSD
2463 Define this to cause @value{GDBN} to determine the address of @code{u} at
2464 runtime, by using Berkeley-style @code{nlist} on the kernel's image in
2467 @item KERNEL_U_ADDR_HPUX
2468 Define this to cause @value{GDBN} to determine the address of @code{u} at
2469 runtime, by using HP-style @code{nlist} on the kernel's image in the
2472 @item ONE_PROCESS_WRITETEXT
2473 Define this to be able to, when a breakpoint insertion fails, warn the
2474 user that another process may be running with the same executable.
2476 @item PREPARE_TO_PROCEED @var{select_it}
2477 This (ugly) macro allows a native configuration to customize the way the
2478 @code{proceed} function in @file{infrun.c} deals with switching between
2481 In a multi-threaded task we may select another thread and then continue
2482 or step. But if the old thread was stopped at a breakpoint, it will
2483 immediately cause another breakpoint stop without any execution (i.e. it
2484 will report a breakpoint hit incorrectly). So @value{GDBN} must step over it
2487 If defined, @code{PREPARE_TO_PROCEED} should check the current thread
2488 against the thread that reported the most recent event. If a step-over
2489 is required, it returns TRUE. If @var{select_it} is non-zero, it should
2490 reselect the old thread.
2493 Defines the format for the name of a @file{/proc} device. Should be
2494 defined in @file{nm.h} @emph{only} in order to override the default
2495 definition in @file{procfs.c}.
2500 @item PTRACE_ARG3_TYPE
2501 The type of the third argument to the @code{ptrace} system call, if it
2502 exists and is different from @code{int}.
2504 @item REGISTER_U_ADDR
2505 Defines the offset of the registers in the ``u area''.
2507 @item SHELL_COMMAND_CONCAT
2508 If defined, is a string to prefix on the shell command used to start the
2512 If defined, this is the name of the shell to use to run the inferior.
2513 Defaults to @code{"/bin/sh"}.
2515 @item SOLIB_ADD (filename, from_tty, targ)
2516 Define this to expand into an expression that will cause the symbols in
2517 @var{filename} to be added to @value{GDBN}'s symbol table.
2519 @item SOLIB_CREATE_INFERIOR_HOOK
2520 Define this to expand into any shared-library-relocation code that you
2521 want to be run just after the child process has been forked.
2523 @item START_INFERIOR_TRAPS_EXPECTED
2524 When starting an inferior, @value{GDBN} normally expects to trap twice; once when
2525 the shell execs, and once when the program itself execs. If the actual
2526 number of traps is something other than 2, then define this macro to
2527 expand into the number expected.
2529 @item SVR4_SHARED_LIBS
2530 Define this to indicate that SVR4-style shared libraries are in use.
2533 This determines whether small routines in @file{*-tdep.c}, which
2534 translate register values between @value{GDBN}'s internal representation and the
2535 /proc representation, are compiled.
2538 This is the offset of the registers in the upage. It need only be
2539 defined if the generic ptrace register access routines in
2540 @file{infptrace.c} are being used (that is, @file{infptrace.c} is
2541 configured in, and @code{FETCH_INFERIOR_REGISTERS} is not defined). If
2542 the default value from @file{infptrace.c} is good enough, leave it
2545 The default value means that u.u_ar0 @emph{points to} the location of
2546 the registers. I'm guessing that @code{#define U_REGS_OFFSET 0} means
2547 that u.u_ar0 @emph{is} the location of the registers.
2553 Define this to debug ptrace calls.
2558 @node Support Libraries
2560 @chapter Support Libraries
2564 BFD provides support for @value{GDBN} in several ways:
2568 @item identifying executable and core files
2569 BFD will identify a variety of file types, including a.out, coff, and
2570 several variants thereof, as well as several kinds of core files.
2572 @item access to sections of files
2573 BFD parses the file headers to determine the names, virtual addresses,
2574 sizes, and file locations of all the various named sections in files
2575 (such as the text section or the data section). @value{GDBN} simply calls BFD to
2576 read or write section X at byte offset Y for length Z.
2578 @item specialized core file support
2579 BFD provides routines to determine the failing command name stored in a
2580 core file, the signal with which the program failed, and whether a core
2581 file matches (i.e. could be a core dump of) a particular executable
2584 @item locating the symbol information
2585 @value{GDBN} uses an internal interface of BFD to determine where to find the
2586 symbol information in an executable file or symbol-file. @value{GDBN} itself
2587 handles the reading of symbols, since BFD does not ``understand'' debug
2588 symbols, but @value{GDBN} uses BFD's cached information to find the symbols,
2595 The opcodes library provides @value{GDBN}'s disassembler. (It's a separate
2596 library because it's also used in binutils, for @file{objdump}).
2616 @item SIGN_EXTEND_CHAR
2618 @item SWITCH_ENUM_BUG
2634 This chapter covers topics that are lower-level than the major
2635 algorithms of @value{GDBN}.
2639 Cleanups are a structured way to deal with things that need to be done
2640 later. When your code does something (like @code{malloc} some memory,
2641 or open a file) that needs to be undone later (e.g. free the memory or
2642 close the file), it can make a cleanup. The cleanup will be done at
2643 some future point: when the command is finished, when an error occurs,
2644 or when your code decides it's time to do cleanups.
2646 You can also discard cleanups, that is, throw them away without doing
2647 what they say. This is only done if you ask that it be done.
2653 @item struct cleanup *@var{old_chain};
2654 Declare a variable which will hold a cleanup chain handle.
2656 @item @var{old_chain} = make_cleanup (@var{function}, @var{arg});
2657 Make a cleanup which will cause @var{function} to be called with
2658 @var{arg} (a @code{char *}) later. The result, @var{old_chain}, is a
2659 handle that can be passed to @code{do_cleanups} or
2660 @code{discard_cleanups} later. Unless you are going to call
2661 @code{do_cleanups} or @code{discard_cleanups} yourself, you can ignore
2662 the result from @code{make_cleanup}.
2664 @item do_cleanups (@var{old_chain});
2665 Perform all cleanups done since @code{make_cleanup} returned
2666 @var{old_chain}. E.g.:
2668 make_cleanup (a, 0);
2669 old = make_cleanup (b, 0);
2673 will call @code{b()} but will not call @code{a()}. The cleanup that
2674 calls @code{a()} will remain in the cleanup chain, and will be done
2675 later unless otherwise discarded.@refill
2677 @item discard_cleanups (@var{old_chain});
2678 Same as @code{do_cleanups} except that it just removes the cleanups from
2679 the chain and does not call the specified functions.
2683 Some functions, e.g. @code{fputs_filtered()} or @code{error()}, specify
2684 that they ``should not be called when cleanups are not in place''. This
2685 means that any actions you need to reverse in the case of an error or
2686 interruption must be on the cleanup chain before you call these
2687 functions, since they might never return to your code (they
2688 @samp{longjmp} instead).
2690 @section Wrapping Output Lines
2692 Output that goes through @code{printf_filtered} or @code{fputs_filtered}
2693 or @code{fputs_demangled} needs only to have calls to @code{wrap_here}
2694 added in places that would be good breaking points. The utility
2695 routines will take care of actually wrapping if the line width is
2698 The argument to @code{wrap_here} is an indentation string which is
2699 printed @emph{only} if the line breaks there. This argument is saved
2700 away and used later. It must remain valid until the next call to
2701 @code{wrap_here} or until a newline has been printed through the
2702 @code{*_filtered} functions. Don't pass in a local variable and then
2705 It is usually best to call @code{wrap_here()} after printing a comma or
2706 space. If you call it before printing a space, make sure that your
2707 indentation properly accounts for the leading space that will print if
2708 the line wraps there.
2710 Any function or set of functions that produce filtered output must
2711 finish by printing a newline, to flush the wrap buffer, before switching
2712 to unfiltered (``@code{printf}'') output. Symbol reading routines that
2713 print warnings are a good example.
2715 @section @value{GDBN} Coding Standards
2717 @value{GDBN} follows the GNU coding standards, as described in
2718 @file{etc/standards.texi}. This file is also available for anonymous
2719 FTP from GNU archive sites. @value{GDBN} takes a strict interpretation of the
2720 standard; in general, when the GNU standard recommends a practice but
2721 does not require it, @value{GDBN} requires it.
2723 @value{GDBN} follows an additional set of coding standards specific to @value{GDBN},
2724 as described in the following sections.
2726 You can configure with @samp{--enable-build-warnings} to get GCC to
2727 check on a number of these rules. @value{GDBN} sources ought not to engender any
2728 complaints, unless they are caused by bogus host systems. (The exact
2729 set of enabled warnings is currently @samp{-Wall -Wpointer-arith
2730 -Wstrict-prototypes -Wmissing-prototypes -Wmissing-declarations}.
2732 @subsection Formatting
2734 The standard GNU recommendations for formatting must be followed
2737 Note that while in a definition, the function's name must be in column
2738 zero; in a function declaration, the name must be on the same line as
2741 In addition, there must be a space between a function or macro name and
2742 the opening parenthesis of its argument list (except for macro
2743 definitions, as required by C). There must not be a space after an open
2744 paren/bracket or before a close paren/bracket.
2746 While additional whitespace is generally helpful for reading, do not use
2747 more than one blank line to separate blocks, and avoid adding whitespace
2748 after the end of a program line (as of 1/99, some 600 lines had whitespace
2749 after the semicolon). Excess whitespace causes difficulties for diff and
2752 @subsection Comments
2754 The standard GNU requirements on comments must be followed strictly.
2756 Block comments must appear in the following form, with no `/*'- or
2757 '*/'-only lines, and no leading `*':
2760 /* Wait for control to return from inferior to debugger. If inferior
2761 gets a signal, we may decide to start it up again instead of
2762 returning. That is why there is a loop in this function. When
2763 this function actually returns it means the inferior should be left
2764 stopped and @value{GDBN} should read more commands. */
2767 (Note that this format is encouraged by Emacs; tabbing for a multi-line
2768 comment works correctly, and M-Q fills the block consistently.)
2770 Put a blank line between the block comments preceding function or
2771 variable definitions, and the definition itself.
2773 In general, put function-body comments on lines by themselves, rather
2774 than trying to fit them into the 20 characters left at the end of a
2775 line, since either the comment or the code will inevitably get longer
2776 than will fit, and then somebody will have to move it anyhow.
2780 Code must not depend on the sizes of C data types, the format of the
2781 host's floating point numbers, the alignment of anything, or the order
2782 of evaluation of expressions.
2784 Use functions freely. There are only a handful of compute-bound areas
2785 in @value{GDBN} that might be affected by the overhead of a function call, mainly
2786 in symbol reading. Most of @value{GDBN}'s performance is limited by the target
2787 interface (whether serial line or system call).
2789 However, use functions with moderation. A thousand one-line functions
2790 are just as hard to understand as a single thousand-line function.
2792 @subsection Function Prototypes
2794 Prototypes must be used to @emph{declare} functions, and may be used to
2795 @emph{define} them. Prototypes for @value{GDBN} functions must include both the
2796 argument type and name, with the name matching that used in the actual
2797 function definition.
2799 All external functions should have a declaration in a header file that
2800 callers include, except for @code{_initialize_*} functions, which must
2801 be external so that @file{init.c} construction works, but shouldn't be
2802 visible to random source files.
2804 All static functions must be declared in a block near the top of the
2807 @subsection Clean Design
2809 In addition to getting the syntax right, there's the little question of
2810 semantics. Some things are done in certain ways in @value{GDBN} because long
2811 experience has shown that the more obvious ways caused various kinds of
2814 You can't assume the byte order of anything that comes from a target
2815 (including @var{value}s, object files, and instructions). Such things
2816 must be byte-swapped using @code{SWAP_TARGET_AND_HOST} in @value{GDBN}, or one of
2817 the swap routines defined in @file{bfd.h}, such as @code{bfd_get_32}.
2819 You can't assume that you know what interface is being used to talk to
2820 the target system. All references to the target must go through the
2821 current @code{target_ops} vector.
2823 You can't assume that the host and target machines are the same machine
2824 (except in the ``native'' support modules). In particular, you can't
2825 assume that the target machine's header files will be available on the
2826 host machine. Target code must bring along its own header files --
2827 written from scratch or explicitly donated by their owner, to avoid
2830 Insertion of new @code{#ifdef}'s will be frowned upon. It's much better
2831 to write the code portably than to conditionalize it for various
2834 New @code{#ifdef}'s which test for specific compilers or manufacturers
2835 or operating systems are unacceptable. All @code{#ifdef}'s should test
2836 for features. The information about which configurations contain which
2837 features should be segregated into the configuration files. Experience
2838 has proven far too often that a feature unique to one particular system
2839 often creeps into other systems; and that a conditional based on some
2840 predefined macro for your current system will become worthless over
2841 time, as new versions of your system come out that behave differently
2842 with regard to this feature.
2844 Adding code that handles specific architectures, operating systems,
2845 target interfaces, or hosts, is not acceptable in generic code. If a
2846 hook is needed at that point, invent a generic hook and define it for
2847 your configuration, with something like:
2850 #ifdef WRANGLE_SIGNALS
2851 WRANGLE_SIGNALS (signo);
2855 In your host, target, or native configuration file, as appropriate,
2856 define @code{WRANGLE_SIGNALS} to do the machine-dependent thing. Take a
2857 bit of care in defining the hook, so that it can be used by other ports
2858 in the future, if they need a hook in the same place.
2860 If the hook is not defined, the code should do whatever "most" machines
2861 want. Using @code{#ifdef}, as above, is the preferred way to do this,
2862 but sometimes that gets convoluted, in which case use
2865 #ifndef SPECIAL_FOO_HANDLING
2866 #define SPECIAL_FOO_HANDLING(pc, sp) (0)
2870 where the macro is used or in an appropriate header file.
2872 Whether to include a @dfn{small} hook, a hook around the exact pieces of
2873 code which are system-dependent, or whether to replace a whole function
2874 with a hook depends on the case. A good example of this dilemma can be
2875 found in @code{get_saved_register}. All machines that @value{GDBN} 2.8 ran on
2876 just needed the @code{FRAME_FIND_SAVED_REGS} hook to find the saved
2877 registers. Then the SPARC and Pyramid came along, and
2878 @code{HAVE_REGISTER_WINDOWS} and @code{REGISTER_IN_WINDOW_P} were
2879 introduced. Then the 29k and 88k required the @code{GET_SAVED_REGISTER}
2880 hook. The first three are examples of small hooks; the latter replaces
2881 a whole function. In this specific case, it is useful to have both
2882 kinds; it would be a bad idea to replace all the uses of the small hooks
2883 with @code{GET_SAVED_REGISTER}, since that would result in much
2884 duplicated code. Other times, duplicating a few lines of code here or
2885 there is much cleaner than introducing a large number of small hooks.
2887 Another way to generalize @value{GDBN} along a particular interface is with an
2888 attribute struct. For example, @value{GDBN} has been generalized to handle
2889 multiple kinds of remote interfaces -- not by #ifdef's everywhere, but
2890 by defining the "target_ops" structure and having a current target (as
2891 well as a stack of targets below it, for memory references). Whenever
2892 something needs to be done that depends on which remote interface we are
2893 using, a flag in the current target_ops structure is tested (e.g.
2894 `target_has_stack'), or a function is called through a pointer in the
2895 current target_ops structure. In this way, when a new remote interface
2896 is added, only one module needs to be touched -- the one that actually
2897 implements the new remote interface. Other examples of
2898 attribute-structs are BFD access to multiple kinds of object file
2899 formats, or @value{GDBN}'s access to multiple source languages.
2901 Please avoid duplicating code. For example, in @value{GDBN} 3.x all the code
2902 interfacing between @code{ptrace} and the rest of @value{GDBN} was duplicated in
2903 @file{*-dep.c}, and so changing something was very painful. In @value{GDBN} 4.x,
2904 these have all been consolidated into @file{infptrace.c}.
2905 @file{infptrace.c} can deal with variations between systems the same way
2906 any system-independent file would (hooks, #if defined, etc.), and
2907 machines which are radically different don't need to use infptrace.c at
2910 Don't put debugging printfs in the code.
2914 @chapter Porting @value{GDBN}
2916 Most of the work in making @value{GDBN} compile on a new machine is in specifying
2917 the configuration of the machine. This is done in a dizzying variety of
2918 header files and configuration scripts, which we hope to make more
2919 sensible soon. Let's say your new host is called an @var{xyz} (e.g.
2920 @samp{sun4}), and its full three-part configuration name is
2921 @code{@var{arch}-@var{xvend}-@var{xos}} (e.g. @samp{sparc-sun-sunos4}).
2924 In the top level directory, edit @file{config.sub} and add @var{arch},
2925 @var{xvend}, and @var{xos} to the lists of supported architectures,
2926 vendors, and operating systems near the bottom of the file. Also, add
2927 @var{xyz} as an alias that maps to
2928 @code{@var{arch}-@var{xvend}-@var{xos}}. You can test your changes by
2932 ./config.sub @var{xyz}
2937 ./config.sub @code{@var{arch}-@var{xvend}-@var{xos}}
2940 which should both respond with @code{@var{arch}-@var{xvend}-@var{xos}}
2941 and no error messages.
2943 You need to port BFD, if that hasn't been done already. Porting BFD is
2944 beyond the scope of this manual.
2946 To configure @value{GDBN} itself, edit @file{gdb/configure.host} to recognize
2947 your system and set @code{gdb_host} to @var{xyz}, and (unless your
2948 desired target is already available) also edit @file{gdb/configure.tgt},
2949 setting @code{gdb_target} to something appropriate (for instance,
2952 Finally, you'll need to specify and define @value{GDBN}'s host-, native-, and
2953 target-dependent @file{.h} and @file{.c} files used for your
2956 @section Configuring @value{GDBN} for Release
2958 From the top level directory (containing @file{gdb}, @file{bfd},
2959 @file{libiberty}, and so on):
2961 make -f Makefile.in gdb.tar.gz
2964 This will properly configure, clean, rebuild any files that are
2965 distributed pre-built (e.g. @file{c-exp.tab.c} or @file{refcard.ps}),
2966 and will then make a tarfile. (If the top level directory has already
2967 been configured, you can just do @code{make gdb.tar.gz} instead.)
2969 This procedure requires:
2971 @item symbolic links
2972 @item @code{makeinfo} (texinfo2 level)
2975 @item @code{yacc} or @code{bison}
2978 @dots{} and the usual slew of utilities (@code{sed}, @code{tar}, etc.).
2980 @subheading TEMPORARY RELEASE PROCEDURE FOR DOCUMENTATION
2982 @file{gdb.texinfo} is currently marked up using the texinfo-2 macros,
2983 which are not yet a default for anything (but we have to start using
2986 For making paper, the only thing this implies is the right generation of
2987 @file{texinfo.tex} needs to be included in the distribution.
2989 For making info files, however, rather than duplicating the texinfo2
2990 distribution, generate @file{gdb-all.texinfo} locally, and include the
2991 files @file{gdb.info*} in the distribution. Note the plural;
2992 @code{makeinfo} will split the document into one overall file and five
2993 or so included files.
2999 The testsuite is an important component of the @value{GDBN} package. While it is
3000 always worthwhile to encourage user testing, in practice this is rarely
3001 sufficient; users typically use only a small subset of the available
3002 commands, and it has proven all too common for a change to cause a
3003 significant regression that went unnoticed for some time.
3005 The @value{GDBN} testsuite uses the DejaGNU testing framework. DejaGNU is built
3006 using tcl and expect. The tests themselves are calls to various tcl
3007 procs; the framework runs all the procs and summarizes the passes and
3010 @section Using the Testsuite
3012 To run the testsuite, simply go to the @value{GDBN} object directory (or to the
3013 testsuite's objdir) and type @code{make check}. This just sets up some
3014 environment variables and invokes DejaGNU's @code{runtest} script. While
3015 the testsuite is running, you'll get mentions of which test file is in use,
3016 and a mention of any unexpected passes or fails. When the testsuite is
3017 finished, you'll get a summary that looks like this:
3021 # of expected passes 6016
3022 # of unexpected failures 58
3023 # of unexpected successes 5
3024 # of expected failures 183
3025 # of unresolved testcases 3
3026 # of untested testcases 5
3028 The ideal test run consists of expected passes only; however, reality
3029 conspires to keep us from this ideal. Unexpected failures indicate
3030 real problems, whether in @value{GDBN} or in the testsuite. Expected failures
3031 are still failures, but ones which have been decided are too hard to
3032 deal with at the time; for instance, a test case might work everywhere
3033 except on AIX, and there is no prospect of the AIX case being fixed in
3034 the near future. Expected failures should not be added lightly, since
3035 you may be masking serious bugs in @value{GDBN}. Unexpected successes are expected
3036 fails that are passing for some reason, while unresolved and untested
3037 cases often indicate some minor catastrophe, such as the compiler being
3038 unable to deal with a test program.
3040 When making any significant change to @value{GDBN}, you should run the testsuite
3041 before and after the change, to confirm that there are no regressions.
3042 Note that truly complete testing would require that you run the
3043 testsuite with all supported configurations and a variety of compilers;
3044 however this is more than really necessary. In many cases testing with
3045 a single configuration is sufficient. Other useful options are to test
3046 one big-endian (Sparc) and one little-endian (x86) host, a cross config
3047 with a builtin simulator (powerpc-eabi, mips-elf), or a 64-bit host
3050 If you add new functionality to @value{GDBN}, please consider adding tests for it
3051 as well; this way future @value{GDBN} hackers can detect and fix their changes
3052 that break the functionality you added. Similarly, if you fix a bug
3053 that was not previously reported as a test failure, please add a test
3054 case for it. Some cases are extremely difficult to test, such as code
3055 that handles host OS failures or bugs in particular versions of
3056 compilers, and it's OK not to try to write tests for all of those.
3058 @section Testsuite Organization
3060 The testsuite is entirely contained in @file{gdb/testsuite}. While the
3061 testsuite includes some makefiles and configury, these are very minimal,
3062 and used for little besides cleaning up, since the tests themselves
3063 handle the compilation of the programs that @value{GDBN} will run. The file
3064 @file{testsuite/lib/gdb.exp} contains common utility procs useful for
3065 all @value{GDBN} tests, while the directory @file{testsuite/config} contains
3066 configuration-specific files, typically used for special-purpose
3067 definitions of procs like @code{gdb_load} and @code{gdb_start}.
3069 The tests themselves are to be found in @file{testsuite/gdb.*} and
3070 subdirectories of those. The names of the test files must always end
3071 with @file{.exp}. DejaGNU collects the test files by wildcarding
3072 in the test directories, so both subdirectories and individual files
3073 get chosen and run in alphabetical order.
3075 The following table lists the main types of subdirectories and what they
3076 are for. Since DejaGNU finds test files no matter where they are
3077 located, and since each test file sets up its own compilation and
3078 execution environment, this organization is simply for convenience and
3085 This is the base testsuite. The tests in it should apply to all
3086 configurations of @value{GDBN} (but generic native-only tests may live here).
3087 The test programs should be in the subset of C that is valid K&R,
3088 ANSI/ISO, and C++ (ifdefs are allowed if necessary, for instance
3091 @item gdb.@var{lang}
3093 Language-specific tests for all languages besides C. Examples are
3094 @file{gdb.c++} and @file{gdb.java}.
3096 @item gdb.@var{platform}
3098 Non-portable tests. The tests are specific to a specific configuration
3099 (host or target), such as HP-UX or eCos. Example is @file{gdb.hp}, for
3102 @item gdb.@var{compiler}
3104 Tests specific to a particular compiler. As of this writing (June
3105 1999), there aren't currently any groups of tests in this category that
3106 couldn't just as sensibly be made platform-specific, but one could
3107 imagine a gdb.gcc, for tests of @value{GDBN}'s handling of GCC extensions.
3109 @item gdb.@var{subsystem}
3111 Tests that exercise a specific @value{GDBN} subsystem in more depth. For
3112 instance, @file{gdb.disasm} exercises various disassemblers, while
3113 @file{gdb.stabs} tests pathways through the stabs symbol reader.
3117 @section Writing Tests
3119 In many areas, the @value{GDBN} tests are already quite comprehensive; you
3120 should be able to copy existing tests to handle new cases.
3122 You should try to use @code{gdb_test} whenever possible, since it
3123 includes cases to handle all the unexpected errors that might happen.
3124 However, it doesn't cost anything to add new test procedures; for
3125 instance, @file{gdb.base/exprs.exp} defines a @code{test_expr} that
3126 calls @code{gdb_test} multiple times.
3128 Only use @code{send_gdb} and @code{gdb_expect} when absolutely
3129 necessary, such as when @value{GDBN} has several valid responses to a command.
3131 The source language programs do @emph{not} need to be in a consistent
3132 style. Since @value{GDBN} is used to debug programs written in many different
3133 styles, it's worth having a mix of styles in the testsuite; for
3134 instance, some @value{GDBN} bugs involving the display of source lines would
3135 never manifest themselves if the programs used GNU coding style
3142 Check the @file{README} file, it often has useful information that does not
3143 appear anywhere else in the directory.
3146 * Getting Started:: Getting started working on @value{GDBN}
3147 * Debugging @value{GDBN}:: Debugging @value{GDBN} with itself
3150 @node Getting Started,,, Hints
3152 @section Getting Started
3154 @value{GDBN} is a large and complicated program, and if you first starting to
3155 work on it, it can be hard to know where to start. Fortunately, if you
3156 know how to go about it, there are ways to figure out what is going on.
3158 This manual, the @value{GDBN} Internals manual, has information which applies
3159 generally to many parts of @value{GDBN}.
3161 Information about particular functions or data structures are located in
3162 comments with those functions or data structures. If you run across a
3163 function or a global variable which does not have a comment correctly
3164 explaining what is does, this can be thought of as a bug in @value{GDBN}; feel
3165 free to submit a bug report, with a suggested comment if you can figure
3166 out what the comment should say. If you find a comment which is
3167 actually wrong, be especially sure to report that.
3169 Comments explaining the function of macros defined in host, target, or
3170 native dependent files can be in several places. Sometimes they are
3171 repeated every place the macro is defined. Sometimes they are where the
3172 macro is used. Sometimes there is a header file which supplies a
3173 default definition of the macro, and the comment is there. This manual
3174 also documents all the available macros.
3175 @c (@pxref{Host Conditionals}, @pxref{Target
3176 @c Conditionals}, @pxref{Native Conditionals}, and @pxref{Obsolete
3179 Start with the header files. Once you have some idea of how @value{GDBN}'s internal
3180 symbol tables are stored (see @file{symtab.h}, @file{gdbtypes.h}), you
3181 will find it much easier to understand the code which uses and creates
3182 those symbol tables.
3184 You may wish to process the information you are getting somehow, to
3185 enhance your understanding of it. Summarize it, translate it to another
3186 language, add some (perhaps trivial or non-useful) feature to @value{GDBN}, use
3187 the code to predict what a test case would do and write the test case
3188 and verify your prediction, etc. If you are reading code and your eyes
3189 are starting to glaze over, this is a sign you need to use a more active
3192 Once you have a part of @value{GDBN} to start with, you can find more
3193 specifically the part you are looking for by stepping through each
3194 function with the @code{next} command. Do not use @code{step} or you
3195 will quickly get distracted; when the function you are stepping through
3196 calls another function try only to get a big-picture understanding
3197 (perhaps using the comment at the beginning of the function being
3198 called) of what it does. This way you can identify which of the
3199 functions being called by the function you are stepping through is the
3200 one which you are interested in. You may need to examine the data
3201 structures generated at each stage, with reference to the comments in
3202 the header files explaining what the data structures are supposed to
3205 Of course, this same technique can be used if you are just reading the
3206 code, rather than actually stepping through it. The same general
3207 principle applies---when the code you are looking at calls something
3208 else, just try to understand generally what the code being called does,
3209 rather than worrying about all its details.
3211 A good place to start when tracking down some particular area is with a
3212 command which invokes that feature. Suppose you want to know how
3213 single-stepping works. As a @value{GDBN} user, you know that the @code{step}
3214 command invokes single-stepping. The command is invoked via command
3215 tables (see @file{command.h}); by convention the function which actually
3216 performs the command is formed by taking the name of the command and
3217 adding @samp{_command}, or in the case of an @code{info} subcommand,
3218 @samp{_info}. For example, the @code{step} command invokes the
3219 @code{step_command} function and the @code{info display} command invokes
3220 @code{display_info}. When this convention is not followed, you might
3221 have to use @code{grep} or @kbd{M-x tags-search} in emacs, or run @value{GDBN} on
3222 itself and set a breakpoint in @code{execute_command}.
3224 If all of the above fail, it may be appropriate to ask for information
3225 on @code{bug-gdb}. But @emph{never} post a generic question like ``I was
3226 wondering if anyone could give me some tips about understanding
3227 @value{GDBN}''---if we had some magic secret we would put it in this manual.
3228 Suggestions for improving the manual are always welcome, of course.
3230 @node Debugging @value{GDBN},,,Hints
3232 @section Debugging @value{GDBN} with itself
3234 If @value{GDBN} is limping on your machine, this is the preferred way to get it
3235 fully functional. Be warned that in some ancient Unix systems, like
3236 Ultrix 4.2, a program can't be running in one process while it is being
3237 debugged in another. Rather than typing the command @code{@w{./gdb
3238 ./gdb}}, which works on Suns and such, you can copy @file{gdb} to
3239 @file{gdb2} and then type @code{@w{./gdb ./gdb2}}.
3241 When you run @value{GDBN} in the @value{GDBN} source directory, it will read a
3242 @file{.gdbinit} file that sets up some simple things to make debugging
3243 gdb easier. The @code{info} command, when executed without a subcommand
3244 in a @value{GDBN} being debugged by gdb, will pop you back up to the top level
3245 gdb. See @file{.gdbinit} for details.
3247 If you use emacs, you will probably want to do a @code{make TAGS} after
3248 you configure your distribution; this will put the machine dependent
3249 routines for your local machine where they will be accessed first by
3252 Also, make sure that you've either compiled @value{GDBN} with your local cc, or
3253 have run @code{fixincludes} if you are compiling with gcc.
3255 @section Submitting Patches
3257 Thanks for thinking of offering your changes back to the community of
3258 @value{GDBN} users. In general we like to get well designed enhancements.
3259 Thanks also for checking in advance about the best way to transfer the
3262 The @value{GDBN} maintainers will only install ``cleanly designed'' patches.
3263 This manual summarizes what we believe to be clean design for @value{GDBN}.
3265 If the maintainers don't have time to put the patch in when it arrives,
3266 or if there is any question about a patch, it goes into a large queue
3267 with everyone else's patches and bug reports.
3269 The legal issue is that to incorporate substantial changes requires a
3270 copyright assignment from you and/or your employer, granting ownership
3271 of the changes to the Free Software Foundation. You can get the
3272 standard documents for doing this by sending mail to @code{gnu@@gnu.org}
3273 and asking for it. We recommend that people write in "All programs
3274 owned by the Free Software Foundation" as "NAME OF PROGRAM", so that
3275 changes in many programs (not just @value{GDBN}, but GAS, Emacs, GCC, etc) can be
3276 contributed with only one piece of legalese pushed through the
3277 bureacracy and filed with the FSF. We can't start merging changes until
3278 this paperwork is received by the FSF (their rules, which we follow
3279 since we maintain it for them).
3281 Technically, the easiest way to receive changes is to receive each
3282 feature as a small context diff or unidiff, suitable for "patch". Each
3283 message sent to me should include the changes to C code and header files
3284 for a single feature, plus ChangeLog entries for each directory where
3285 files were modified, and diffs for any changes needed to the manuals
3286 (gdb/doc/gdb.texinfo or gdb/doc/gdbint.texinfo). If there are a lot of
3287 changes for a single feature, they can be split down into multiple
3290 In this way, if we read and like the feature, we can add it to the
3291 sources with a single patch command, do some testing, and check it in.
3292 If you leave out the ChangeLog, we have to write one. If you leave
3293 out the doc, we have to puzzle out what needs documenting. Etc.
3295 The reason to send each change in a separate message is that we will not
3296 install some of the changes. They'll be returned to you with questions
3297 or comments. If we're doing our job correctly, the message back to you
3298 will say what you have to fix in order to make the change acceptable.
3299 The reason to have separate messages for separate features is so that
3300 the acceptable changes can be installed while one or more changes are
3301 being reworked. If multiple features are sent in a single message, we
3302 tend to not put in the effort to sort out the acceptable changes from
3303 the unacceptable, so none of the features get installed until all are
3306 If this sounds painful or authoritarian, well, it is. But we get a lot
3307 of bug reports and a lot of patches, and many of them don't get
3308 installed because we don't have the time to finish the job that the bug
3309 reporter or the contributor could have done. Patches that arrive
3310 complete, working, and well designed, tend to get installed on the day
3311 they arrive. The others go into a queue and get installed as time
3312 permits, which, since the maintainers have many demands to meet, may not
3313 be for quite some time.
3315 Please send patches directly to the @value{GDBN} maintainers at
3316 @code{gdb-patches@@sourceware.cygnus.com}.
3318 @section Obsolete Conditionals
3320 Fragments of old code in @value{GDBN} sometimes reference or set the following
3321 configuration macros. They should not be used by new code, and old uses
3322 should be removed as those parts of the debugger are otherwise touched.
3326 @item STACK_END_ADDR
3327 This macro used to define where the end of the stack appeared, for use
3328 in interpreting core file formats that don't record this address in the
3329 core file itself. This information is now configured in BFD, and @value{GDBN}
3330 gets the info portably from there. The values in @value{GDBN}'s configuration
3331 files should be moved into BFD configuration files (if needed there),
3332 and deleted from all of @value{GDBN}'s config files.
3334 Any @file{@var{foo}-xdep.c} file that references STACK_END_ADDR
3335 is so old that it has never been converted to use BFD. Now that's old!
3337 @item PYRAMID_CONTROL_FRAME_DEBUGGING
3341 @item PYRAMID_PTRACE
3344 @item REG_STACK_SEGMENT