1 \input texinfo @c -*- texinfo -*-
2 @setfilename gdbint.info
4 @dircategory Software development
6 * Gdb-Internals: (gdbint). The GNU debugger's internals.
10 Copyright @copyright{} 1990, 1991, 1992, 1993, 1994, 1996, 1998, 1999,
11 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2008, 2009
12 Free Software Foundation, Inc.
13 Contributed by Cygnus Solutions. Written by John Gilmore.
14 Second Edition by Stan Shebs.
16 Permission is granted to copy, distribute and/or modify this document
17 under the terms of the GNU Free Documentation License, Version 1.1 or
18 any later version published by the Free Software Foundation; with no
19 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
20 Texts. A copy of the license is included in the section entitled ``GNU
21 Free Documentation License''.
25 This file documents the internals of the GNU debugger @value{GDBN}.
30 @setchapternewpage off
31 @settitle @value{GDBN} Internals
37 @title @value{GDBN} Internals
38 @subtitle{A guide to the internals of the GNU debugger}
40 @author Cygnus Solutions
41 @author Second Edition:
43 @author Cygnus Solutions
46 \def\$#1${{#1}} % Kluge: collect RCS revision info without $...$
47 \xdef\manvers{\$Revision$} % For use in headers, footers too
49 \hfill Cygnus Solutions\par
51 \hfill \TeX{}info \texinfoversion\par
55 @vskip 0pt plus 1filll
62 @c Perhaps this should be the title of the document (but only for info,
63 @c not for TeX). Existing GNU manuals seem inconsistent on this point.
64 @top Scope of this Document
66 This document documents the internals of the GNU debugger, @value{GDBN}. It
67 includes description of @value{GDBN}'s key algorithms and operations, as well
68 as the mechanisms that adapt @value{GDBN} to specific hosts and targets.
81 * Target Architecture Definition::
82 * Target Descriptions::
83 * Target Vector Definition::
88 * Versions and Branches::
89 * Start of New Year Procedure::
94 * GDB Observers:: @value{GDBN} Currently available observers
95 * GNU Free Documentation License:: The license for this documentation
108 @section Requirements
109 @cindex requirements for @value{GDBN}
111 Before diving into the internals, you should understand the formal
112 requirements and other expectations for @value{GDBN}. Although some
113 of these may seem obvious, there have been proposals for @value{GDBN}
114 that have run counter to these requirements.
116 First of all, @value{GDBN} is a debugger. It's not designed to be a
117 front panel for embedded systems. It's not a text editor. It's not a
118 shell. It's not a programming environment.
120 @value{GDBN} is an interactive tool. Although a batch mode is
121 available, @value{GDBN}'s primary role is to interact with a human
124 @value{GDBN} should be responsive to the user. A programmer hot on
125 the trail of a nasty bug, and operating under a looming deadline, is
126 going to be very impatient of everything, including the response time
127 to debugger commands.
129 @value{GDBN} should be relatively permissive, such as for expressions.
130 While the compiler should be picky (or have the option to be made
131 picky), since source code lives for a long time usually, the
132 programmer doing debugging shouldn't be spending time figuring out to
133 mollify the debugger.
135 @value{GDBN} will be called upon to deal with really large programs.
136 Executable sizes of 50 to 100 megabytes occur regularly, and we've
137 heard reports of programs approaching 1 gigabyte in size.
139 @value{GDBN} should be able to run everywhere. No other debugger is
140 available for even half as many configurations as @value{GDBN}
144 @section Contributors
146 The first edition of this document was written by John Gilmore of
147 Cygnus Solutions. The current second edition was written by Stan Shebs
148 of Cygnus Solutions, who continues to update the manual.
150 Over the years, many others have made additions and changes to this
151 document. This section attempts to record the significant contributors
152 to that effort. One of the virtues of free software is that everyone
153 is free to contribute to it; with regret, we cannot actually
154 acknowledge everyone here.
157 @emph{Plea:} This section has only been added relatively recently (four
158 years after publication of the second edition). Additions to this
159 section are particularly welcome. If you or your friends (or enemies,
160 to be evenhanded) have been unfairly omitted from this list, we would
161 like to add your names!
164 A document such as this relies on being kept up to date by numerous
165 small updates by contributing engineers as they make changes to the
166 code base. The file @file{ChangeLog} in the @value{GDBN} distribution
167 approximates a blow-by-blow account. The most prolific contributors to
168 this important, but low profile task are Andrew Cagney (responsible
169 for over half the entries), Daniel Jacobowitz, Mark Kettenis, Jim
170 Blandy and Eli Zaretskii.
172 Eli Zaretskii and Daniel Jacobowitz wrote the sections documenting
175 Jeremy Bennett updated the sections on initializing a new architecture
176 and register representation, and added the section on Frame Interpretation.
179 @node Overall Structure
181 @chapter Overall Structure
183 @value{GDBN} consists of three major subsystems: user interface,
184 symbol handling (the @dfn{symbol side}), and target system handling (the
187 The user interface consists of several actual interfaces, plus
190 The symbol side consists of object file readers, debugging info
191 interpreters, symbol table management, source language expression
192 parsing, type and value printing.
194 The target side consists of execution control, stack frame analysis, and
195 physical target manipulation.
197 The target side/symbol side division is not formal, and there are a
198 number of exceptions. For instance, core file support involves symbolic
199 elements (the basic core file reader is in BFD) and target elements (it
200 supplies the contents of memory and the values of registers). Instead,
201 this division is useful for understanding how the minor subsystems
204 @section The Symbol Side
206 The symbolic side of @value{GDBN} can be thought of as ``everything
207 you can do in @value{GDBN} without having a live program running''.
208 For instance, you can look at the types of variables, and evaluate
209 many kinds of expressions.
211 @section The Target Side
213 The target side of @value{GDBN} is the ``bits and bytes manipulator''.
214 Although it may make reference to symbolic info here and there, most
215 of the target side will run with only a stripped executable
216 available---or even no executable at all, in remote debugging cases.
218 Operations such as disassembly, stack frame crawls, and register
219 display, are able to work with no symbolic info at all. In some cases,
220 such as disassembly, @value{GDBN} will use symbolic info to present addresses
221 relative to symbols rather than as raw numbers, but it will work either
224 @section Configurations
228 @dfn{Host} refers to attributes of the system where @value{GDBN} runs.
229 @dfn{Target} refers to the system where the program being debugged
230 executes. In most cases they are the same machine, in which case a
231 third type of @dfn{Native} attributes come into play.
233 Defines and include files needed to build on the host are host
234 support. Examples are tty support, system defined types, host byte
235 order, host float format. These are all calculated by @code{autoconf}
236 when the debugger is built.
238 Defines and information needed to handle the target format are target
239 dependent. Examples are the stack frame format, instruction set,
240 breakpoint instruction, registers, and how to set up and tear down the stack
243 Information that is only needed when the host and target are the same,
244 is native dependent. One example is Unix child process support; if the
245 host and target are not the same, calling @code{fork} to start the target
246 process is a bad idea. The various macros needed for finding the
247 registers in the @code{upage}, running @code{ptrace}, and such are all
248 in the native-dependent files.
250 Another example of native-dependent code is support for features that
251 are really part of the target environment, but which require
252 @code{#include} files that are only available on the host system. Core
253 file handling and @code{setjmp} handling are two common cases.
255 When you want to make @value{GDBN} work as the traditional native debugger
256 on a system, you will need to supply both target and native information.
258 @section Source Tree Structure
259 @cindex @value{GDBN} source tree structure
261 The @value{GDBN} source directory has a mostly flat structure---there
262 are only a few subdirectories. A file's name usually gives a hint as
263 to what it does; for example, @file{stabsread.c} reads stabs,
264 @file{dwarf2read.c} reads @sc{DWARF 2}, etc.
266 Files that are related to some common task have names that share
267 common substrings. For example, @file{*-thread.c} files deal with
268 debugging threads on various platforms; @file{*read.c} files deal with
269 reading various kinds of symbol and object files; @file{inf*.c} files
270 deal with direct control of the @dfn{inferior program} (@value{GDBN}
271 parlance for the program being debugged).
273 There are several dozens of files in the @file{*-tdep.c} family.
274 @samp{tdep} stands for @dfn{target-dependent code}---each of these
275 files implements debug support for a specific target architecture
276 (sparc, mips, etc). Usually, only one of these will be used in a
277 specific @value{GDBN} configuration (sometimes two, closely related).
279 Similarly, there are many @file{*-nat.c} files, each one for native
280 debugging on a specific system (e.g., @file{sparc-linux-nat.c} is for
281 native debugging of Sparc machines running the Linux kernel).
283 The few subdirectories of the source tree are:
287 Code that implements @dfn{CLI}, the @value{GDBN} Command-Line
288 Interpreter. @xref{User Interface, Command Interpreter}.
291 Code for the @value{GDBN} remote server.
294 Code for Insight, the @value{GDBN} TK-based GUI front-end.
297 The @dfn{GDB/MI}, the @value{GDBN} Machine Interface interpreter.
300 Target signal translation code.
303 Code for @dfn{TUI}, the @value{GDBN} Text-mode full-screen User
304 Interface. @xref{User Interface, TUI}.
312 @value{GDBN} uses a number of debugging-specific algorithms. They are
313 often not very complicated, but get lost in the thicket of special
314 cases and real-world issues. This chapter describes the basic
315 algorithms and mentions some of the specific target definitions that
318 @section Prologue Analysis
320 @cindex prologue analysis
321 @cindex call frame information
322 @cindex CFI (call frame information)
323 To produce a backtrace and allow the user to manipulate older frames'
324 variables and arguments, @value{GDBN} needs to find the base addresses
325 of older frames, and discover where those frames' registers have been
326 saved. Since a frame's ``callee-saves'' registers get saved by
327 younger frames if and when they're reused, a frame's registers may be
328 scattered unpredictably across younger frames. This means that
329 changing the value of a register-allocated variable in an older frame
330 may actually entail writing to a save slot in some younger frame.
332 Modern versions of GCC emit Dwarf call frame information (``CFI''),
333 which describes how to find frame base addresses and saved registers.
334 But CFI is not always available, so as a fallback @value{GDBN} uses a
335 technique called @dfn{prologue analysis} to find frame sizes and saved
336 registers. A prologue analyzer disassembles the function's machine
337 code starting from its entry point, and looks for instructions that
338 allocate frame space, save the stack pointer in a frame pointer
339 register, save registers, and so on. Obviously, this can't be done
340 accurately in general, but it's tractable to do well enough to be very
341 helpful. Prologue analysis predates the GNU toolchain's support for
342 CFI; at one time, prologue analysis was the only mechanism
343 @value{GDBN} used for stack unwinding at all, when the function
344 calling conventions didn't specify a fixed frame layout.
346 In the olden days, function prologues were generated by hand-written,
347 target-specific code in GCC, and treated as opaque and untouchable by
348 optimizers. Looking at this code, it was usually straightforward to
349 write a prologue analyzer for @value{GDBN} that would accurately
350 understand all the prologues GCC would generate. However, over time
351 GCC became more aggressive about instruction scheduling, and began to
352 understand more about the semantics of the prologue instructions
353 themselves; in response, @value{GDBN}'s analyzers became more complex
354 and fragile. Keeping the prologue analyzers working as GCC (and the
355 instruction sets themselves) evolved became a substantial task.
357 @cindex @file{prologue-value.c}
358 @cindex abstract interpretation of function prologues
359 @cindex pseudo-evaluation of function prologues
360 To try to address this problem, the code in @file{prologue-value.h}
361 and @file{prologue-value.c} provides a general framework for writing
362 prologue analyzers that are simpler and more robust than ad-hoc
363 analyzers. When we analyze a prologue using the prologue-value
364 framework, we're really doing ``abstract interpretation'' or
365 ``pseudo-evaluation'': running the function's code in simulation, but
366 using conservative approximations of the values registers and memory
367 would hold when the code actually runs. For example, if our function
368 starts with the instruction:
371 addi r1, 42 # add 42 to r1
374 we don't know exactly what value will be in @code{r1} after executing
375 this instruction, but we do know it'll be 42 greater than its original
378 If we then see an instruction like:
381 addi r1, 22 # add 22 to r1
384 we still don't know what @code{r1's} value is, but again, we can say
385 it is now 64 greater than its original value.
387 If the next instruction were:
390 mov r2, r1 # set r2 to r1's value
393 then we can say that @code{r2's} value is now the original value of
396 It's common for prologues to save registers on the stack, so we'll
397 need to track the values of stack frame slots, as well as the
398 registers. So after an instruction like this:
404 then we'd know that the stack slot four bytes above the frame pointer
405 holds the original value of @code{r1} plus 64.
409 Of course, this can only go so far before it gets unreasonable. If we
410 wanted to be able to say anything about the value of @code{r1} after
414 xor r1, r3 # exclusive-or r1 and r3, place result in r1
417 then things would get pretty complex. But remember, we're just doing
418 a conservative approximation; if exclusive-or instructions aren't
419 relevant to prologues, we can just say @code{r1}'s value is now
420 ``unknown''. We can ignore things that are too complex, if that loss of
421 information is acceptable for our application.
423 So when we say ``conservative approximation'' here, what we mean is an
424 approximation that is either accurate, or marked ``unknown'', but
427 Using this framework, a prologue analyzer is simply an interpreter for
428 machine code, but one that uses conservative approximations for the
429 contents of registers and memory instead of actual values. Starting
430 from the function's entry point, you simulate instructions up to the
431 current PC, or an instruction that you don't know how to simulate.
432 Now you can examine the state of the registers and stack slots you've
438 To see how large your stack frame is, just check the value of the
439 stack pointer register; if it's the original value of the SP
440 minus a constant, then that constant is the stack frame's size.
441 If the SP's value has been marked as ``unknown'', then that means
442 the prologue has done something too complex for us to track, and
443 we don't know the frame size.
446 To see where we've saved the previous frame's registers, we just
447 search the values we've tracked --- stack slots, usually, but
448 registers, too, if you want --- for something equal to the register's
449 original value. If the calling conventions suggest a standard place
450 to save a given register, then we can check there first, but really,
451 anything that will get us back the original value will probably work.
454 This does take some work. But prologue analyzers aren't
455 quick-and-simple pattern patching to recognize a few fixed prologue
456 forms any more; they're big, hairy functions. Along with inferior
457 function calls, prologue analysis accounts for a substantial portion
458 of the time needed to stabilize a @value{GDBN} port. So it's
459 worthwhile to look for an approach that will be easier to understand
460 and maintain. In the approach described above:
465 It's easier to see that the analyzer is correct: you just see
466 whether the analyzer properly (albeit conservatively) simulates
467 the effect of each instruction.
470 It's easier to extend the analyzer: you can add support for new
471 instructions, and know that you haven't broken anything that
472 wasn't already broken before.
475 It's orthogonal: to gather new information, you don't need to
476 complicate the code for each instruction. As long as your domain
477 of conservative values is already detailed enough to tell you
478 what you need, then all the existing instruction simulations are
479 already gathering the right data for you.
483 The file @file{prologue-value.h} contains detailed comments explaining
484 the framework and how to use it.
487 @section Breakpoint Handling
490 In general, a breakpoint is a user-designated location in the program
491 where the user wants to regain control if program execution ever reaches
494 There are two main ways to implement breakpoints; either as ``hardware''
495 breakpoints or as ``software'' breakpoints.
497 @cindex hardware breakpoints
498 @cindex program counter
499 Hardware breakpoints are sometimes available as a builtin debugging
500 features with some chips. Typically these work by having dedicated
501 register into which the breakpoint address may be stored. If the PC
502 (shorthand for @dfn{program counter})
503 ever matches a value in a breakpoint registers, the CPU raises an
504 exception and reports it to @value{GDBN}.
506 Another possibility is when an emulator is in use; many emulators
507 include circuitry that watches the address lines coming out from the
508 processor, and force it to stop if the address matches a breakpoint's
511 A third possibility is that the target already has the ability to do
512 breakpoints somehow; for instance, a ROM monitor may do its own
513 software breakpoints. So although these are not literally ``hardware
514 breakpoints'', from @value{GDBN}'s point of view they work the same;
515 @value{GDBN} need not do anything more than set the breakpoint and wait
516 for something to happen.
518 Since they depend on hardware resources, hardware breakpoints may be
519 limited in number; when the user asks for more, @value{GDBN} will
520 start trying to set software breakpoints. (On some architectures,
521 notably the 32-bit x86 platforms, @value{GDBN} cannot always know
522 whether there's enough hardware resources to insert all the hardware
523 breakpoints and watchpoints. On those platforms, @value{GDBN} prints
524 an error message only when the program being debugged is continued.)
526 @cindex software breakpoints
527 Software breakpoints require @value{GDBN} to do somewhat more work.
528 The basic theory is that @value{GDBN} will replace a program
529 instruction with a trap, illegal divide, or some other instruction
530 that will cause an exception, and then when it's encountered,
531 @value{GDBN} will take the exception and stop the program. When the
532 user says to continue, @value{GDBN} will restore the original
533 instruction, single-step, re-insert the trap, and continue on.
535 Since it literally overwrites the program being tested, the program area
536 must be writable, so this technique won't work on programs in ROM. It
537 can also distort the behavior of programs that examine themselves,
538 although such a situation would be highly unusual.
540 Also, the software breakpoint instruction should be the smallest size of
541 instruction, so it doesn't overwrite an instruction that might be a jump
542 target, and cause disaster when the program jumps into the middle of the
543 breakpoint instruction. (Strictly speaking, the breakpoint must be no
544 larger than the smallest interval between instructions that may be jump
545 targets; perhaps there is an architecture where only even-numbered
546 instructions may jumped to.) Note that it's possible for an instruction
547 set not to have any instructions usable for a software breakpoint,
548 although in practice only the ARC has failed to define such an
551 Basic breakpoint object handling is in @file{breakpoint.c}. However,
552 much of the interesting breakpoint action is in @file{infrun.c}.
555 @cindex insert or remove software breakpoint
556 @findex target_remove_breakpoint
557 @findex target_insert_breakpoint
558 @item target_remove_breakpoint (@var{bp_tgt})
559 @itemx target_insert_breakpoint (@var{bp_tgt})
560 Insert or remove a software breakpoint at address
561 @code{@var{bp_tgt}->placed_address}. Returns zero for success,
562 non-zero for failure. On input, @var{bp_tgt} contains the address of the
563 breakpoint, and is otherwise initialized to zero. The fields of the
564 @code{struct bp_target_info} pointed to by @var{bp_tgt} are updated
565 to contain other information about the breakpoint on output. The field
566 @code{placed_address} may be updated if the breakpoint was placed at a
567 related address; the field @code{shadow_contents} contains the real
568 contents of the bytes where the breakpoint has been inserted,
569 if reading memory would return the breakpoint instead of the
570 underlying memory; the field @code{shadow_len} is the length of
571 memory cached in @code{shadow_contents}, if any; and the field
572 @code{placed_size} is optionally set and used by the target, if
573 it could differ from @code{shadow_len}.
575 For example, the remote target @samp{Z0} packet does not require
576 shadowing memory, so @code{shadow_len} is left at zero. However,
577 the length reported by @code{gdbarch_breakpoint_from_pc} is cached in
578 @code{placed_size}, so that a matching @samp{z0} packet can be
579 used to remove the breakpoint.
581 @cindex insert or remove hardware breakpoint
582 @findex target_remove_hw_breakpoint
583 @findex target_insert_hw_breakpoint
584 @item target_remove_hw_breakpoint (@var{bp_tgt})
585 @itemx target_insert_hw_breakpoint (@var{bp_tgt})
586 Insert or remove a hardware-assisted breakpoint at address
587 @code{@var{bp_tgt}->placed_address}. Returns zero for success,
588 non-zero for failure. See @code{target_insert_breakpoint} for
589 a description of the @code{struct bp_target_info} pointed to by
590 @var{bp_tgt}; the @code{shadow_contents} and
591 @code{shadow_len} members are not used for hardware breakpoints,
592 but @code{placed_size} may be.
595 @section Single Stepping
597 @section Signal Handling
599 @section Thread Handling
601 @section Inferior Function Calls
603 @section Longjmp Support
605 @cindex @code{longjmp} debugging
606 @value{GDBN} has support for figuring out that the target is doing a
607 @code{longjmp} and for stopping at the target of the jump, if we are
608 stepping. This is done with a few specialized internal breakpoints,
609 which are visible in the output of the @samp{maint info breakpoint}
612 @findex gdbarch_get_longjmp_target
613 To make this work, you need to define a function called
614 @code{gdbarch_get_longjmp_target}, which will examine the
615 @code{jmp_buf} structure and extract the @code{longjmp} target address.
616 Since @code{jmp_buf} is target specific and typically defined in a
617 target header not available to @value{GDBN}, you will need to
618 determine the offset of the PC manually and return that; many targets
619 define a @code{jb_pc_offset} field in the tdep structure to save the
620 value once calculated.
625 Watchpoints are a special kind of breakpoints (@pxref{Algorithms,
626 breakpoints}) which break when data is accessed rather than when some
627 instruction is executed. When you have data which changes without
628 your knowing what code does that, watchpoints are the silver bullet to
629 hunt down and kill such bugs.
631 @cindex hardware watchpoints
632 @cindex software watchpoints
633 Watchpoints can be either hardware-assisted or not; the latter type is
634 known as ``software watchpoints.'' @value{GDBN} always uses
635 hardware-assisted watchpoints if they are available, and falls back on
636 software watchpoints otherwise. Typical situations where @value{GDBN}
637 will use software watchpoints are:
641 The watched memory region is too large for the underlying hardware
642 watchpoint support. For example, each x86 debug register can watch up
643 to 4 bytes of memory, so trying to watch data structures whose size is
644 more than 16 bytes will cause @value{GDBN} to use software
648 The value of the expression to be watched depends on data held in
649 registers (as opposed to memory).
652 Too many different watchpoints requested. (On some architectures,
653 this situation is impossible to detect until the debugged program is
654 resumed.) Note that x86 debug registers are used both for hardware
655 breakpoints and for watchpoints, so setting too many hardware
656 breakpoints might cause watchpoint insertion to fail.
659 No hardware-assisted watchpoints provided by the target
663 Software watchpoints are very slow, since @value{GDBN} needs to
664 single-step the program being debugged and test the value of the
665 watched expression(s) after each instruction. The rest of this
666 section is mostly irrelevant for software watchpoints.
668 When the inferior stops, @value{GDBN} tries to establish, among other
669 possible reasons, whether it stopped due to a watchpoint being hit.
670 It first uses @code{STOPPED_BY_WATCHPOINT} to see if any watchpoint
671 was hit. If not, all watchpoint checking is skipped.
673 Then @value{GDBN} calls @code{target_stopped_data_address} exactly
674 once. This method returns the address of the watchpoint which
675 triggered, if the target can determine it. If the triggered address
676 is available, @value{GDBN} compares the address returned by this
677 method with each watched memory address in each active watchpoint.
678 For data-read and data-access watchpoints, @value{GDBN} announces
679 every watchpoint that watches the triggered address as being hit.
680 For this reason, data-read and data-access watchpoints
681 @emph{require} that the triggered address be available; if not, read
682 and access watchpoints will never be considered hit. For data-write
683 watchpoints, if the triggered address is available, @value{GDBN}
684 considers only those watchpoints which match that address;
685 otherwise, @value{GDBN} considers all data-write watchpoints. For
686 each data-write watchpoint that @value{GDBN} considers, it evaluates
687 the expression whose value is being watched, and tests whether the
688 watched value has changed. Watchpoints whose watched values have
689 changed are announced as hit.
691 @c FIXME move these to the main lists of target/native defns
693 @value{GDBN} uses several macros and primitives to support hardware
697 @findex TARGET_HAS_HARDWARE_WATCHPOINTS
698 @item TARGET_HAS_HARDWARE_WATCHPOINTS
699 If defined, the target supports hardware watchpoints.
700 (Currently only used for several native configs.)
702 @findex TARGET_CAN_USE_HARDWARE_WATCHPOINT
703 @item TARGET_CAN_USE_HARDWARE_WATCHPOINT (@var{type}, @var{count}, @var{other})
704 Return the number of hardware watchpoints of type @var{type} that are
705 possible to be set. The value is positive if @var{count} watchpoints
706 of this type can be set, zero if setting watchpoints of this type is
707 not supported, and negative if @var{count} is more than the maximum
708 number of watchpoints of type @var{type} that can be set. @var{other}
709 is non-zero if other types of watchpoints are currently enabled (there
710 are architectures which cannot set watchpoints of different types at
713 @findex TARGET_REGION_OK_FOR_HW_WATCHPOINT
714 @item TARGET_REGION_OK_FOR_HW_WATCHPOINT (@var{addr}, @var{len})
715 Return non-zero if hardware watchpoints can be used to watch a region
716 whose address is @var{addr} and whose length in bytes is @var{len}.
718 @cindex insert or remove hardware watchpoint
719 @findex target_insert_watchpoint
720 @findex target_remove_watchpoint
721 @item target_insert_watchpoint (@var{addr}, @var{len}, @var{type})
722 @itemx target_remove_watchpoint (@var{addr}, @var{len}, @var{type})
723 Insert or remove a hardware watchpoint starting at @var{addr}, for
724 @var{len} bytes. @var{type} is the watchpoint type, one of the
725 possible values of the enumerated data type @code{target_hw_bp_type},
726 defined by @file{breakpoint.h} as follows:
729 enum target_hw_bp_type
731 hw_write = 0, /* Common (write) HW watchpoint */
732 hw_read = 1, /* Read HW watchpoint */
733 hw_access = 2, /* Access (read or write) HW watchpoint */
734 hw_execute = 3 /* Execute HW breakpoint */
739 These two macros should return 0 for success, non-zero for failure.
741 @findex target_stopped_data_address
742 @item target_stopped_data_address (@var{addr_p})
743 If the inferior has some watchpoint that triggered, place the address
744 associated with the watchpoint at the location pointed to by
745 @var{addr_p} and return non-zero. Otherwise, return zero. This
746 is required for data-read and data-access watchpoints. It is
747 not required for data-write watchpoints, but @value{GDBN} uses
748 it to improve handling of those also.
750 @value{GDBN} will only call this method once per watchpoint stop,
751 immediately after calling @code{STOPPED_BY_WATCHPOINT}. If the
752 target's watchpoint indication is sticky, i.e., stays set after
753 resuming, this method should clear it. For instance, the x86 debug
754 control register has sticky triggered flags.
756 @findex target_watchpoint_addr_within_range
757 @item target_watchpoint_addr_within_range (@var{target}, @var{addr}, @var{start}, @var{length})
758 Check whether @var{addr} (as returned by @code{target_stopped_data_address})
759 lies within the hardware-defined watchpoint region described by
760 @var{start} and @var{length}. This only needs to be provided if the
761 granularity of a watchpoint is greater than one byte, i.e., if the
762 watchpoint can also trigger on nearby addresses outside of the watched
765 @findex HAVE_STEPPABLE_WATCHPOINT
766 @item HAVE_STEPPABLE_WATCHPOINT
767 If defined to a non-zero value, it is not necessary to disable a
768 watchpoint to step over it. Like @code{gdbarch_have_nonsteppable_watchpoint},
769 this is usually set when watchpoints trigger at the instruction
770 which will perform an interesting read or write. It should be
771 set if there is a temporary disable bit which allows the processor
772 to step over the interesting instruction without raising the
773 watchpoint exception again.
775 @findex gdbarch_have_nonsteppable_watchpoint
776 @item int gdbarch_have_nonsteppable_watchpoint (@var{gdbarch})
777 If it returns a non-zero value, @value{GDBN} should disable a
778 watchpoint to step the inferior over it. This is usually set when
779 watchpoints trigger at the instruction which will perform an
780 interesting read or write.
782 @findex HAVE_CONTINUABLE_WATCHPOINT
783 @item HAVE_CONTINUABLE_WATCHPOINT
784 If defined to a non-zero value, it is possible to continue the
785 inferior after a watchpoint has been hit. This is usually set
786 when watchpoints trigger at the instruction following an interesting
789 @findex CANNOT_STEP_HW_WATCHPOINTS
790 @item CANNOT_STEP_HW_WATCHPOINTS
791 If this is defined to a non-zero value, @value{GDBN} will remove all
792 watchpoints before stepping the inferior.
794 @findex STOPPED_BY_WATCHPOINT
795 @item STOPPED_BY_WATCHPOINT (@var{wait_status})
796 Return non-zero if stopped by a watchpoint. @var{wait_status} is of
797 the type @code{struct target_waitstatus}, defined by @file{target.h}.
798 Normally, this macro is defined to invoke the function pointed to by
799 the @code{to_stopped_by_watchpoint} member of the structure (of the
800 type @code{target_ops}, defined on @file{target.h}) that describes the
801 target-specific operations; @code{to_stopped_by_watchpoint} ignores
802 the @var{wait_status} argument.
804 @value{GDBN} does not require the non-zero value returned by
805 @code{STOPPED_BY_WATCHPOINT} to be 100% correct, so if a target cannot
806 determine for sure whether the inferior stopped due to a watchpoint,
807 it could return non-zero ``just in case''.
810 @subsection Watchpoints and Threads
811 @cindex watchpoints, with threads
813 @value{GDBN} only supports process-wide watchpoints, which trigger
814 in all threads. @value{GDBN} uses the thread ID to make watchpoints
815 act as if they were thread-specific, but it cannot set hardware
816 watchpoints that only trigger in a specific thread. Therefore, even
817 if the target supports threads, per-thread debug registers, and
818 watchpoints which only affect a single thread, it should set the
819 per-thread debug registers for all threads to the same value. On
820 @sc{gnu}/Linux native targets, this is accomplished by using
821 @code{ALL_LWPS} in @code{target_insert_watchpoint} and
822 @code{target_remove_watchpoint} and by using
823 @code{linux_set_new_thread} to register a handler for newly created
826 @value{GDBN}'s @sc{gnu}/Linux support only reports a single event
827 at a time, although multiple events can trigger simultaneously for
828 multi-threaded programs. When multiple events occur, @file{linux-nat.c}
829 queues subsequent events and returns them the next time the program
830 is resumed. This means that @code{STOPPED_BY_WATCHPOINT} and
831 @code{target_stopped_data_address} only need to consult the current
832 thread's state---the thread indicated by @code{inferior_ptid}. If
833 two threads have hit watchpoints simultaneously, those routines
834 will be called a second time for the second thread.
836 @subsection x86 Watchpoints
837 @cindex x86 debug registers
838 @cindex watchpoints, on x86
840 The 32-bit Intel x86 (a.k.a.@: ia32) processors feature special debug
841 registers designed to facilitate debugging. @value{GDBN} provides a
842 generic library of functions that x86-based ports can use to implement
843 support for watchpoints and hardware-assisted breakpoints. This
844 subsection documents the x86 watchpoint facilities in @value{GDBN}.
846 (At present, the library functions read and write debug registers directly, and are
847 thus only available for native configurations.)
849 To use the generic x86 watchpoint support, a port should do the
853 @findex I386_USE_GENERIC_WATCHPOINTS
855 Define the macro @code{I386_USE_GENERIC_WATCHPOINTS} somewhere in the
856 target-dependent headers.
859 Include the @file{config/i386/nm-i386.h} header file @emph{after}
860 defining @code{I386_USE_GENERIC_WATCHPOINTS}.
863 Add @file{i386-nat.o} to the value of the Make variable
864 @code{NATDEPFILES} (@pxref{Native Debugging, NATDEPFILES}).
867 Provide implementations for the @code{I386_DR_LOW_*} macros described
868 below. Typically, each macro should call a target-specific function
869 which does the real work.
872 The x86 watchpoint support works by maintaining mirror images of the
873 debug registers. Values are copied between the mirror images and the
874 real debug registers via a set of macros which each target needs to
878 @findex I386_DR_LOW_SET_CONTROL
879 @item I386_DR_LOW_SET_CONTROL (@var{val})
880 Set the Debug Control (DR7) register to the value @var{val}.
882 @findex I386_DR_LOW_SET_ADDR
883 @item I386_DR_LOW_SET_ADDR (@var{idx}, @var{addr})
884 Put the address @var{addr} into the debug register number @var{idx}.
886 @findex I386_DR_LOW_RESET_ADDR
887 @item I386_DR_LOW_RESET_ADDR (@var{idx})
888 Reset (i.e.@: zero out) the address stored in the debug register
891 @findex I386_DR_LOW_GET_STATUS
892 @item I386_DR_LOW_GET_STATUS
893 Return the value of the Debug Status (DR6) register. This value is
894 used immediately after it is returned by
895 @code{I386_DR_LOW_GET_STATUS}, so as to support per-thread status
899 For each one of the 4 debug registers (whose indices are from 0 to 3)
900 that store addresses, a reference count is maintained by @value{GDBN},
901 to allow sharing of debug registers by several watchpoints. This
902 allows users to define several watchpoints that watch the same
903 expression, but with different conditions and/or commands, without
904 wasting debug registers which are in short supply. @value{GDBN}
905 maintains the reference counts internally, targets don't have to do
906 anything to use this feature.
908 The x86 debug registers can each watch a region that is 1, 2, or 4
909 bytes long. The ia32 architecture requires that each watched region
910 be appropriately aligned: 2-byte region on 2-byte boundary, 4-byte
911 region on 4-byte boundary. However, the x86 watchpoint support in
912 @value{GDBN} can watch unaligned regions and regions larger than 4
913 bytes (up to 16 bytes) by allocating several debug registers to watch
914 a single region. This allocation of several registers per a watched
915 region is also done automatically without target code intervention.
917 The generic x86 watchpoint support provides the following API for the
918 @value{GDBN}'s application code:
921 @findex i386_region_ok_for_watchpoint
922 @item i386_region_ok_for_watchpoint (@var{addr}, @var{len})
923 The macro @code{TARGET_REGION_OK_FOR_HW_WATCHPOINT} is set to call
924 this function. It counts the number of debug registers required to
925 watch a given region, and returns a non-zero value if that number is
926 less than 4, the number of debug registers available to x86
929 @findex i386_stopped_data_address
930 @item i386_stopped_data_address (@var{addr_p})
932 @code{target_stopped_data_address} is set to call this function.
934 function examines the breakpoint condition bits in the DR6 Debug
935 Status register, as returned by the @code{I386_DR_LOW_GET_STATUS}
936 macro, and returns the address associated with the first bit that is
939 @findex i386_stopped_by_watchpoint
940 @item i386_stopped_by_watchpoint (void)
941 The macro @code{STOPPED_BY_WATCHPOINT}
942 is set to call this function. The
943 argument passed to @code{STOPPED_BY_WATCHPOINT} is ignored. This
944 function examines the breakpoint condition bits in the DR6 Debug
945 Status register, as returned by the @code{I386_DR_LOW_GET_STATUS}
946 macro, and returns true if any bit is set. Otherwise, false is
949 @findex i386_insert_watchpoint
950 @findex i386_remove_watchpoint
951 @item i386_insert_watchpoint (@var{addr}, @var{len}, @var{type})
952 @itemx i386_remove_watchpoint (@var{addr}, @var{len}, @var{type})
953 Insert or remove a watchpoint. The macros
954 @code{target_insert_watchpoint} and @code{target_remove_watchpoint}
955 are set to call these functions. @code{i386_insert_watchpoint} first
956 looks for a debug register which is already set to watch the same
957 region for the same access types; if found, it just increments the
958 reference count of that debug register, thus implementing debug
959 register sharing between watchpoints. If no such register is found,
960 the function looks for a vacant debug register, sets its mirrored
961 value to @var{addr}, sets the mirrored value of DR7 Debug Control
962 register as appropriate for the @var{len} and @var{type} parameters,
963 and then passes the new values of the debug register and DR7 to the
964 inferior by calling @code{I386_DR_LOW_SET_ADDR} and
965 @code{I386_DR_LOW_SET_CONTROL}. If more than one debug register is
966 required to cover the given region, the above process is repeated for
969 @code{i386_remove_watchpoint} does the opposite: it resets the address
970 in the mirrored value of the debug register and its read/write and
971 length bits in the mirrored value of DR7, then passes these new
972 values to the inferior via @code{I386_DR_LOW_RESET_ADDR} and
973 @code{I386_DR_LOW_SET_CONTROL}. If a register is shared by several
974 watchpoints, each time a @code{i386_remove_watchpoint} is called, it
975 decrements the reference count, and only calls
976 @code{I386_DR_LOW_RESET_ADDR} and @code{I386_DR_LOW_SET_CONTROL} when
977 the count goes to zero.
979 @findex i386_insert_hw_breakpoint
980 @findex i386_remove_hw_breakpoint
981 @item i386_insert_hw_breakpoint (@var{bp_tgt})
982 @itemx i386_remove_hw_breakpoint (@var{bp_tgt})
983 These functions insert and remove hardware-assisted breakpoints. The
984 macros @code{target_insert_hw_breakpoint} and
985 @code{target_remove_hw_breakpoint} are set to call these functions.
986 The argument is a @code{struct bp_target_info *}, as described in
987 the documentation for @code{target_insert_breakpoint}.
988 These functions work like @code{i386_insert_watchpoint} and
989 @code{i386_remove_watchpoint}, respectively, except that they set up
990 the debug registers to watch instruction execution, and each
991 hardware-assisted breakpoint always requires exactly one debug
994 @findex i386_stopped_by_hwbp
995 @item i386_stopped_by_hwbp (void)
996 This function returns non-zero if the inferior has some watchpoint or
997 hardware breakpoint that triggered. It works like
998 @code{i386_stopped_data_address}, except that it doesn't record the
999 address whose watchpoint triggered.
1001 @findex i386_cleanup_dregs
1002 @item i386_cleanup_dregs (void)
1003 This function clears all the reference counts, addresses, and control
1004 bits in the mirror images of the debug registers. It doesn't affect
1005 the actual debug registers in the inferior process.
1012 x86 processors support setting watchpoints on I/O reads or writes.
1013 However, since no target supports this (as of March 2001), and since
1014 @code{enum target_hw_bp_type} doesn't even have an enumeration for I/O
1015 watchpoints, this feature is not yet available to @value{GDBN} running
1019 x86 processors can enable watchpoints locally, for the current task
1020 only, or globally, for all the tasks. For each debug register,
1021 there's a bit in the DR7 Debug Control register that determines
1022 whether the associated address is watched locally or globally. The
1023 current implementation of x86 watchpoint support in @value{GDBN}
1024 always sets watchpoints to be locally enabled, since global
1025 watchpoints might interfere with the underlying OS and are probably
1026 unavailable in many platforms.
1029 @section Checkpoints
1032 In the abstract, a checkpoint is a point in the execution history of
1033 the program, which the user may wish to return to at some later time.
1035 Internally, a checkpoint is a saved copy of the program state, including
1036 whatever information is required in order to restore the program to that
1037 state at a later time. This can be expected to include the state of
1038 registers and memory, and may include external state such as the state
1039 of open files and devices.
1041 There are a number of ways in which checkpoints may be implemented
1042 in gdb, e.g.@: as corefiles, as forked processes, and as some opaque
1043 method implemented on the target side.
1045 A corefile can be used to save an image of target memory and register
1046 state, which can in principle be restored later --- but corefiles do
1047 not typically include information about external entities such as
1048 open files. Currently this method is not implemented in gdb.
1050 A forked process can save the state of user memory and registers,
1051 as well as some subset of external (kernel) state. This method
1052 is used to implement checkpoints on Linux, and in principle might
1053 be used on other systems.
1055 Some targets, e.g.@: simulators, might have their own built-in
1056 method for saving checkpoints, and gdb might be able to take
1057 advantage of that capability without necessarily knowing any
1058 details of how it is done.
1061 @section Observing changes in @value{GDBN} internals
1062 @cindex observer pattern interface
1063 @cindex notifications about changes in internals
1065 In order to function properly, several modules need to be notified when
1066 some changes occur in the @value{GDBN} internals. Traditionally, these
1067 modules have relied on several paradigms, the most common ones being
1068 hooks and gdb-events. Unfortunately, none of these paradigms was
1069 versatile enough to become the standard notification mechanism in
1070 @value{GDBN}. The fact that they only supported one ``client'' was also
1071 a strong limitation.
1073 A new paradigm, based on the Observer pattern of the @cite{Design
1074 Patterns} book, has therefore been implemented. The goal was to provide
1075 a new interface overcoming the issues with the notification mechanisms
1076 previously available. This new interface needed to be strongly typed,
1077 easy to extend, and versatile enough to be used as the standard
1078 interface when adding new notifications.
1080 See @ref{GDB Observers} for a brief description of the observers
1081 currently implemented in GDB. The rationale for the current
1082 implementation is also briefly discussed.
1084 @node User Interface
1086 @chapter User Interface
1088 @value{GDBN} has several user interfaces, of which the traditional
1089 command-line interface is perhaps the most familiar.
1091 @section Command Interpreter
1093 @cindex command interpreter
1095 The command interpreter in @value{GDBN} is fairly simple. It is designed to
1096 allow for the set of commands to be augmented dynamically, and also
1097 has a recursive subcommand capability, where the first argument to
1098 a command may itself direct a lookup on a different command list.
1100 For instance, the @samp{set} command just starts a lookup on the
1101 @code{setlist} command list, while @samp{set thread} recurses
1102 to the @code{set_thread_cmd_list}.
1106 To add commands in general, use @code{add_cmd}. @code{add_com} adds to
1107 the main command list, and should be used for those commands. The usual
1108 place to add commands is in the @code{_initialize_@var{xyz}} routines at
1109 the ends of most source files.
1111 @findex add_setshow_cmd
1112 @findex add_setshow_cmd_full
1113 To add paired @samp{set} and @samp{show} commands, use
1114 @code{add_setshow_cmd} or @code{add_setshow_cmd_full}. The former is
1115 a slightly simpler interface which is useful when you don't need to
1116 further modify the new command structures, while the latter returns
1117 the new command structures for manipulation.
1119 @cindex deprecating commands
1120 @findex deprecate_cmd
1121 Before removing commands from the command set it is a good idea to
1122 deprecate them for some time. Use @code{deprecate_cmd} on commands or
1123 aliases to set the deprecated flag. @code{deprecate_cmd} takes a
1124 @code{struct cmd_list_element} as it's first argument. You can use the
1125 return value from @code{add_com} or @code{add_cmd} to deprecate the
1126 command immediately after it is created.
1128 The first time a command is used the user will be warned and offered a
1129 replacement (if one exists). Note that the replacement string passed to
1130 @code{deprecate_cmd} should be the full name of the command, i.e., the
1131 entire string the user should type at the command line.
1133 @anchor{UI-Independent Output}
1134 @section UI-Independent Output---the @code{ui_out} Functions
1135 @c This section is based on the documentation written by Fernando
1136 @c Nasser <fnasser@redhat.com>.
1138 @cindex @code{ui_out} functions
1139 The @code{ui_out} functions present an abstraction level for the
1140 @value{GDBN} output code. They hide the specifics of different user
1141 interfaces supported by @value{GDBN}, and thus free the programmer
1142 from the need to write several versions of the same code, one each for
1143 every UI, to produce output.
1145 @subsection Overview and Terminology
1147 In general, execution of each @value{GDBN} command produces some sort
1148 of output, and can even generate an input request.
1150 Output can be generated for the following purposes:
1154 to display a @emph{result} of an operation;
1157 to convey @emph{info} or produce side-effects of a requested
1161 to provide a @emph{notification} of an asynchronous event (including
1162 progress indication of a prolonged asynchronous operation);
1165 to display @emph{error messages} (including warnings);
1168 to show @emph{debug data};
1171 to @emph{query} or prompt a user for input (a special case).
1175 This section mainly concentrates on how to build result output,
1176 although some of it also applies to other kinds of output.
1178 Generation of output that displays the results of an operation
1179 involves one or more of the following:
1183 output of the actual data
1186 formatting the output as appropriate for console output, to make it
1187 easily readable by humans
1190 machine oriented formatting--a more terse formatting to allow for easy
1191 parsing by programs which read @value{GDBN}'s output
1194 annotation, whose purpose is to help legacy GUIs to identify interesting
1198 The @code{ui_out} routines take care of the first three aspects.
1199 Annotations are provided by separate annotation routines. Note that use
1200 of annotations for an interface between a GUI and @value{GDBN} is
1203 Output can be in the form of a single item, which we call a @dfn{field};
1204 a @dfn{list} consisting of identical fields; a @dfn{tuple} consisting of
1205 non-identical fields; or a @dfn{table}, which is a tuple consisting of a
1206 header and a body. In a BNF-like form:
1209 @item <table> @expansion{}
1210 @code{<header> <body>}
1211 @item <header> @expansion{}
1212 @code{@{ <column> @}}
1213 @item <column> @expansion{}
1214 @code{<width> <alignment> <title>}
1215 @item <body> @expansion{}
1220 @subsection General Conventions
1222 Most @code{ui_out} routines are of type @code{void}, the exceptions are
1223 @code{ui_out_stream_new} (which returns a pointer to the newly created
1224 object) and the @code{make_cleanup} routines.
1226 The first parameter is always the @code{ui_out} vector object, a pointer
1227 to a @code{struct ui_out}.
1229 The @var{format} parameter is like in @code{printf} family of functions.
1230 When it is present, there must also be a variable list of arguments
1231 sufficient used to satisfy the @code{%} specifiers in the supplied
1234 When a character string argument is not used in a @code{ui_out} function
1235 call, a @code{NULL} pointer has to be supplied instead.
1238 @subsection Table, Tuple and List Functions
1240 @cindex list output functions
1241 @cindex table output functions
1242 @cindex tuple output functions
1243 This section introduces @code{ui_out} routines for building lists,
1244 tuples and tables. The routines to output the actual data items
1245 (fields) are presented in the next section.
1247 To recap: A @dfn{tuple} is a sequence of @dfn{fields}, each field
1248 containing information about an object; a @dfn{list} is a sequence of
1249 fields where each field describes an identical object.
1251 Use the @dfn{table} functions when your output consists of a list of
1252 rows (tuples) and the console output should include a heading. Use this
1253 even when you are listing just one object but you still want the header.
1255 @cindex nesting level in @code{ui_out} functions
1256 Tables can not be nested. Tuples and lists can be nested up to a
1257 maximum of five levels.
1259 The overall structure of the table output code is something like this:
1274 Here is the description of table-, tuple- and list-related @code{ui_out}
1277 @deftypefun void ui_out_table_begin (struct ui_out *@var{uiout}, int @var{nbrofcols}, int @var{nr_rows}, const char *@var{tblid})
1278 The function @code{ui_out_table_begin} marks the beginning of the output
1279 of a table. It should always be called before any other @code{ui_out}
1280 function for a given table. @var{nbrofcols} is the number of columns in
1281 the table. @var{nr_rows} is the number of rows in the table.
1282 @var{tblid} is an optional string identifying the table. The string
1283 pointed to by @var{tblid} is copied by the implementation of
1284 @code{ui_out_table_begin}, so the application can free the string if it
1285 was @code{malloc}ed.
1287 The companion function @code{ui_out_table_end}, described below, marks
1288 the end of the table's output.
1291 @deftypefun void ui_out_table_header (struct ui_out *@var{uiout}, int @var{width}, enum ui_align @var{alignment}, const char *@var{colhdr})
1292 @code{ui_out_table_header} provides the header information for a single
1293 table column. You call this function several times, one each for every
1294 column of the table, after @code{ui_out_table_begin}, but before
1295 @code{ui_out_table_body}.
1297 The value of @var{width} gives the column width in characters. The
1298 value of @var{alignment} is one of @code{left}, @code{center}, and
1299 @code{right}, and it specifies how to align the header: left-justify,
1300 center, or right-justify it. @var{colhdr} points to a string that
1301 specifies the column header; the implementation copies that string, so
1302 column header strings in @code{malloc}ed storage can be freed after the
1306 @deftypefun void ui_out_table_body (struct ui_out *@var{uiout})
1307 This function delimits the table header from the table body.
1310 @deftypefun void ui_out_table_end (struct ui_out *@var{uiout})
1311 This function signals the end of a table's output. It should be called
1312 after the table body has been produced by the list and field output
1315 There should be exactly one call to @code{ui_out_table_end} for each
1316 call to @code{ui_out_table_begin}, otherwise the @code{ui_out} functions
1317 will signal an internal error.
1320 The output of the tuples that represent the table rows must follow the
1321 call to @code{ui_out_table_body} and precede the call to
1322 @code{ui_out_table_end}. You build a tuple by calling
1323 @code{ui_out_tuple_begin} and @code{ui_out_tuple_end}, with suitable
1324 calls to functions which actually output fields between them.
1326 @deftypefun void ui_out_tuple_begin (struct ui_out *@var{uiout}, const char *@var{id})
1327 This function marks the beginning of a tuple output. @var{id} points
1328 to an optional string that identifies the tuple; it is copied by the
1329 implementation, and so strings in @code{malloc}ed storage can be freed
1333 @deftypefun void ui_out_tuple_end (struct ui_out *@var{uiout})
1334 This function signals an end of a tuple output. There should be exactly
1335 one call to @code{ui_out_tuple_end} for each call to
1336 @code{ui_out_tuple_begin}, otherwise an internal @value{GDBN} error will
1340 @deftypefun {struct cleanup *} make_cleanup_ui_out_tuple_begin_end (struct ui_out *@var{uiout}, const char *@var{id})
1341 This function first opens the tuple and then establishes a cleanup
1342 (@pxref{Coding, Cleanups}) to close the tuple. It provides a convenient
1343 and correct implementation of the non-portable@footnote{The function
1344 cast is not portable ISO C.} code sequence:
1346 struct cleanup *old_cleanup;
1347 ui_out_tuple_begin (uiout, "...");
1348 old_cleanup = make_cleanup ((void(*)(void *)) ui_out_tuple_end,
1353 @deftypefun void ui_out_list_begin (struct ui_out *@var{uiout}, const char *@var{id})
1354 This function marks the beginning of a list output. @var{id} points to
1355 an optional string that identifies the list; it is copied by the
1356 implementation, and so strings in @code{malloc}ed storage can be freed
1360 @deftypefun void ui_out_list_end (struct ui_out *@var{uiout})
1361 This function signals an end of a list output. There should be exactly
1362 one call to @code{ui_out_list_end} for each call to
1363 @code{ui_out_list_begin}, otherwise an internal @value{GDBN} error will
1367 @deftypefun {struct cleanup *} make_cleanup_ui_out_list_begin_end (struct ui_out *@var{uiout}, const char *@var{id})
1368 Similar to @code{make_cleanup_ui_out_tuple_begin_end}, this function
1369 opens a list and then establishes cleanup (@pxref{Coding, Cleanups})
1370 that will close the list.
1373 @subsection Item Output Functions
1375 @cindex item output functions
1376 @cindex field output functions
1378 The functions described below produce output for the actual data
1379 items, or fields, which contain information about the object.
1381 Choose the appropriate function accordingly to your particular needs.
1383 @deftypefun void ui_out_field_fmt (struct ui_out *@var{uiout}, char *@var{fldname}, char *@var{format}, ...)
1384 This is the most general output function. It produces the
1385 representation of the data in the variable-length argument list
1386 according to formatting specifications in @var{format}, a
1387 @code{printf}-like format string. The optional argument @var{fldname}
1388 supplies the name of the field. The data items themselves are
1389 supplied as additional arguments after @var{format}.
1391 This generic function should be used only when it is not possible to
1392 use one of the specialized versions (see below).
1395 @deftypefun void ui_out_field_int (struct ui_out *@var{uiout}, const char *@var{fldname}, int @var{value})
1396 This function outputs a value of an @code{int} variable. It uses the
1397 @code{"%d"} output conversion specification. @var{fldname} specifies
1398 the name of the field.
1401 @deftypefun void ui_out_field_fmt_int (struct ui_out *@var{uiout}, int @var{width}, enum ui_align @var{alignment}, const char *@var{fldname}, int @var{value})
1402 This function outputs a value of an @code{int} variable. It differs from
1403 @code{ui_out_field_int} in that the caller specifies the desired @var{width} and @var{alignment} of the output.
1404 @var{fldname} specifies
1405 the name of the field.
1408 @deftypefun void ui_out_field_core_addr (struct ui_out *@var{uiout}, const char *@var{fldname}, CORE_ADDR @var{address})
1409 This function outputs an address.
1412 @deftypefun void ui_out_field_string (struct ui_out *@var{uiout}, const char *@var{fldname}, const char *@var{string})
1413 This function outputs a string using the @code{"%s"} conversion
1417 Sometimes, there's a need to compose your output piece by piece using
1418 functions that operate on a stream, such as @code{value_print} or
1419 @code{fprintf_symbol_filtered}. These functions accept an argument of
1420 the type @code{struct ui_file *}, a pointer to a @code{ui_file} object
1421 used to store the data stream used for the output. When you use one
1422 of these functions, you need a way to pass their results stored in a
1423 @code{ui_file} object to the @code{ui_out} functions. To this end,
1424 you first create a @code{ui_stream} object by calling
1425 @code{ui_out_stream_new}, pass the @code{stream} member of that
1426 @code{ui_stream} object to @code{value_print} and similar functions,
1427 and finally call @code{ui_out_field_stream} to output the field you
1428 constructed. When the @code{ui_stream} object is no longer needed,
1429 you should destroy it and free its memory by calling
1430 @code{ui_out_stream_delete}.
1432 @deftypefun {struct ui_stream *} ui_out_stream_new (struct ui_out *@var{uiout})
1433 This function creates a new @code{ui_stream} object which uses the
1434 same output methods as the @code{ui_out} object whose pointer is
1435 passed in @var{uiout}. It returns a pointer to the newly created
1436 @code{ui_stream} object.
1439 @deftypefun void ui_out_stream_delete (struct ui_stream *@var{streambuf})
1440 This functions destroys a @code{ui_stream} object specified by
1444 @deftypefun void ui_out_field_stream (struct ui_out *@var{uiout}, const char *@var{fieldname}, struct ui_stream *@var{streambuf})
1445 This function consumes all the data accumulated in
1446 @code{streambuf->stream} and outputs it like
1447 @code{ui_out_field_string} does. After a call to
1448 @code{ui_out_field_stream}, the accumulated data no longer exists, but
1449 the stream is still valid and may be used for producing more fields.
1452 @strong{Important:} If there is any chance that your code could bail
1453 out before completing output generation and reaching the point where
1454 @code{ui_out_stream_delete} is called, it is necessary to set up a
1455 cleanup, to avoid leaking memory and other resources. Here's a
1456 skeleton code to do that:
1459 struct ui_stream *mybuf = ui_out_stream_new (uiout);
1460 struct cleanup *old = make_cleanup (ui_out_stream_delete, mybuf);
1465 If the function already has the old cleanup chain set (for other kinds
1466 of cleanups), you just have to add your cleanup to it:
1469 mybuf = ui_out_stream_new (uiout);
1470 make_cleanup (ui_out_stream_delete, mybuf);
1473 Note that with cleanups in place, you should not call
1474 @code{ui_out_stream_delete} directly, or you would attempt to free the
1477 @subsection Utility Output Functions
1479 @deftypefun void ui_out_field_skip (struct ui_out *@var{uiout}, const char *@var{fldname})
1480 This function skips a field in a table. Use it if you have to leave
1481 an empty field without disrupting the table alignment. The argument
1482 @var{fldname} specifies a name for the (missing) filed.
1485 @deftypefun void ui_out_text (struct ui_out *@var{uiout}, const char *@var{string})
1486 This function outputs the text in @var{string} in a way that makes it
1487 easy to be read by humans. For example, the console implementation of
1488 this method filters the text through a built-in pager, to prevent it
1489 from scrolling off the visible portion of the screen.
1491 Use this function for printing relatively long chunks of text around
1492 the actual field data: the text it produces is not aligned according
1493 to the table's format. Use @code{ui_out_field_string} to output a
1494 string field, and use @code{ui_out_message}, described below, to
1495 output short messages.
1498 @deftypefun void ui_out_spaces (struct ui_out *@var{uiout}, int @var{nspaces})
1499 This function outputs @var{nspaces} spaces. It is handy to align the
1500 text produced by @code{ui_out_text} with the rest of the table or
1504 @deftypefun void ui_out_message (struct ui_out *@var{uiout}, int @var{verbosity}, const char *@var{format}, ...)
1505 This function produces a formatted message, provided that the current
1506 verbosity level is at least as large as given by @var{verbosity}. The
1507 current verbosity level is specified by the user with the @samp{set
1508 verbositylevel} command.@footnote{As of this writing (April 2001),
1509 setting verbosity level is not yet implemented, and is always returned
1510 as zero. So calling @code{ui_out_message} with a @var{verbosity}
1511 argument more than zero will cause the message to never be printed.}
1514 @deftypefun void ui_out_wrap_hint (struct ui_out *@var{uiout}, char *@var{indent})
1515 This function gives the console output filter (a paging filter) a hint
1516 of where to break lines which are too long. Ignored for all other
1517 output consumers. @var{indent}, if non-@code{NULL}, is the string to
1518 be printed to indent the wrapped text on the next line; it must remain
1519 accessible until the next call to @code{ui_out_wrap_hint}, or until an
1520 explicit newline is produced by one of the other functions. If
1521 @var{indent} is @code{NULL}, the wrapped text will not be indented.
1524 @deftypefun void ui_out_flush (struct ui_out *@var{uiout})
1525 This function flushes whatever output has been accumulated so far, if
1526 the UI buffers output.
1530 @subsection Examples of Use of @code{ui_out} functions
1532 @cindex using @code{ui_out} functions
1533 @cindex @code{ui_out} functions, usage examples
1534 This section gives some practical examples of using the @code{ui_out}
1535 functions to generalize the old console-oriented code in
1536 @value{GDBN}. The examples all come from functions defined on the
1537 @file{breakpoints.c} file.
1539 This example, from the @code{breakpoint_1} function, shows how to
1542 The original code was:
1545 if (!found_a_breakpoint++)
1547 annotate_breakpoints_headers ();
1550 printf_filtered ("Num ");
1552 printf_filtered ("Type ");
1554 printf_filtered ("Disp ");
1556 printf_filtered ("Enb ");
1560 printf_filtered ("Address ");
1563 printf_filtered ("What\n");
1565 annotate_breakpoints_table ();
1569 Here's the new version:
1572 nr_printable_breakpoints = @dots{};
1575 ui_out_table_begin (ui, 6, nr_printable_breakpoints, "BreakpointTable");
1577 ui_out_table_begin (ui, 5, nr_printable_breakpoints, "BreakpointTable");
1579 if (nr_printable_breakpoints > 0)
1580 annotate_breakpoints_headers ();
1581 if (nr_printable_breakpoints > 0)
1583 ui_out_table_header (uiout, 3, ui_left, "number", "Num"); /* 1 */
1584 if (nr_printable_breakpoints > 0)
1586 ui_out_table_header (uiout, 14, ui_left, "type", "Type"); /* 2 */
1587 if (nr_printable_breakpoints > 0)
1589 ui_out_table_header (uiout, 4, ui_left, "disp", "Disp"); /* 3 */
1590 if (nr_printable_breakpoints > 0)
1592 ui_out_table_header (uiout, 3, ui_left, "enabled", "Enb"); /* 4 */
1595 if (nr_printable_breakpoints > 0)
1597 if (gdbarch_addr_bit (current_gdbarch) <= 32)
1598 ui_out_table_header (uiout, 10, ui_left, "addr", "Address");/* 5 */
1600 ui_out_table_header (uiout, 18, ui_left, "addr", "Address");/* 5 */
1602 if (nr_printable_breakpoints > 0)
1604 ui_out_table_header (uiout, 40, ui_noalign, "what", "What"); /* 6 */
1605 ui_out_table_body (uiout);
1606 if (nr_printable_breakpoints > 0)
1607 annotate_breakpoints_table ();
1610 This example, from the @code{print_one_breakpoint} function, shows how
1611 to produce the actual data for the table whose structure was defined
1612 in the above example. The original code was:
1617 printf_filtered ("%-3d ", b->number);
1619 if ((int)b->type > (sizeof(bptypes)/sizeof(bptypes[0]))
1620 || ((int) b->type != bptypes[(int) b->type].type))
1621 internal_error ("bptypes table does not describe type #%d.",
1623 printf_filtered ("%-14s ", bptypes[(int)b->type].description);
1625 printf_filtered ("%-4s ", bpdisps[(int)b->disposition]);
1627 printf_filtered ("%-3c ", bpenables[(int)b->enable]);
1631 This is the new version:
1635 ui_out_tuple_begin (uiout, "bkpt");
1637 ui_out_field_int (uiout, "number", b->number);
1639 if (((int) b->type > (sizeof (bptypes) / sizeof (bptypes[0])))
1640 || ((int) b->type != bptypes[(int) b->type].type))
1641 internal_error ("bptypes table does not describe type #%d.",
1643 ui_out_field_string (uiout, "type", bptypes[(int)b->type].description);
1645 ui_out_field_string (uiout, "disp", bpdisps[(int)b->disposition]);
1647 ui_out_field_fmt (uiout, "enabled", "%c", bpenables[(int)b->enable]);
1651 This example, also from @code{print_one_breakpoint}, shows how to
1652 produce a complicated output field using the @code{print_expression}
1653 functions which requires a stream to be passed. It also shows how to
1654 automate stream destruction with cleanups. The original code was:
1658 print_expression (b->exp, gdb_stdout);
1664 struct ui_stream *stb = ui_out_stream_new (uiout);
1665 struct cleanup *old_chain = make_cleanup_ui_out_stream_delete (stb);
1668 print_expression (b->exp, stb->stream);
1669 ui_out_field_stream (uiout, "what", local_stream);
1672 This example, also from @code{print_one_breakpoint}, shows how to use
1673 @code{ui_out_text} and @code{ui_out_field_string}. The original code
1678 if (b->dll_pathname == NULL)
1679 printf_filtered ("<any library> ");
1681 printf_filtered ("library \"%s\" ", b->dll_pathname);
1688 if (b->dll_pathname == NULL)
1690 ui_out_field_string (uiout, "what", "<any library>");
1691 ui_out_spaces (uiout, 1);
1695 ui_out_text (uiout, "library \"");
1696 ui_out_field_string (uiout, "what", b->dll_pathname);
1697 ui_out_text (uiout, "\" ");
1701 The following example from @code{print_one_breakpoint} shows how to
1702 use @code{ui_out_field_int} and @code{ui_out_spaces}. The original
1707 if (b->forked_inferior_pid != 0)
1708 printf_filtered ("process %d ", b->forked_inferior_pid);
1715 if (b->forked_inferior_pid != 0)
1717 ui_out_text (uiout, "process ");
1718 ui_out_field_int (uiout, "what", b->forked_inferior_pid);
1719 ui_out_spaces (uiout, 1);
1723 Here's an example of using @code{ui_out_field_string}. The original
1728 if (b->exec_pathname != NULL)
1729 printf_filtered ("program \"%s\" ", b->exec_pathname);
1736 if (b->exec_pathname != NULL)
1738 ui_out_text (uiout, "program \"");
1739 ui_out_field_string (uiout, "what", b->exec_pathname);
1740 ui_out_text (uiout, "\" ");
1744 Finally, here's an example of printing an address. The original code:
1748 printf_filtered ("%s ",
1749 hex_string_custom ((unsigned long) b->address, 8));
1756 ui_out_field_core_addr (uiout, "Address", b->address);
1760 @section Console Printing
1769 @cindex @code{libgdb}
1770 @code{libgdb} 1.0 was an abortive project of years ago. The theory was
1771 to provide an API to @value{GDBN}'s functionality.
1774 @cindex @code{libgdb}
1775 @code{libgdb} 2.0 is an ongoing effort to update @value{GDBN} so that is
1776 better able to support graphical and other environments.
1778 Since @code{libgdb} development is on-going, its architecture is still
1779 evolving. The following components have so far been identified:
1783 Observer - @file{gdb-events.h}.
1785 Builder - @file{ui-out.h}
1787 Event Loop - @file{event-loop.h}
1789 Library - @file{gdb.h}
1792 The model that ties these components together is described below.
1794 @section The @code{libgdb} Model
1796 A client of @code{libgdb} interacts with the library in two ways.
1800 As an observer (using @file{gdb-events}) receiving notifications from
1801 @code{libgdb} of any internal state changes (break point changes, run
1804 As a client querying @code{libgdb} (using the @file{ui-out} builder) to
1805 obtain various status values from @value{GDBN}.
1808 Since @code{libgdb} could have multiple clients (e.g., a GUI supporting
1809 the existing @value{GDBN} CLI), those clients must co-operate when
1810 controlling @code{libgdb}. In particular, a client must ensure that
1811 @code{libgdb} is idle (i.e.@: no other client is using @code{libgdb})
1812 before responding to a @file{gdb-event} by making a query.
1814 @section CLI support
1816 At present @value{GDBN}'s CLI is very much entangled in with the core of
1817 @code{libgdb}. Consequently, a client wishing to include the CLI in
1818 their interface needs to carefully co-ordinate its own and the CLI's
1821 It is suggested that the client set @code{libgdb} up to be bi-modal
1822 (alternate between CLI and client query modes). The notes below sketch
1827 The client registers itself as an observer of @code{libgdb}.
1829 The client create and install @code{cli-out} builder using its own
1830 versions of the @code{ui-file} @code{gdb_stderr}, @code{gdb_stdtarg} and
1831 @code{gdb_stdout} streams.
1833 The client creates a separate custom @code{ui-out} builder that is only
1834 used while making direct queries to @code{libgdb}.
1837 When the client receives input intended for the CLI, it simply passes it
1838 along. Since the @code{cli-out} builder is installed by default, all
1839 the CLI output in response to that command is routed (pronounced rooted)
1840 through to the client controlled @code{gdb_stdout} et.@: al.@: streams.
1841 At the same time, the client is kept abreast of internal changes by
1842 virtue of being a @code{libgdb} observer.
1844 The only restriction on the client is that it must wait until
1845 @code{libgdb} becomes idle before initiating any queries (using the
1846 client's custom builder).
1848 @section @code{libgdb} components
1850 @subheading Observer - @file{gdb-events.h}
1851 @file{gdb-events} provides the client with a very raw mechanism that can
1852 be used to implement an observer. At present it only allows for one
1853 observer and that observer must, internally, handle the need to delay
1854 the processing of any event notifications until after @code{libgdb} has
1855 finished the current command.
1857 @subheading Builder - @file{ui-out.h}
1858 @file{ui-out} provides the infrastructure necessary for a client to
1859 create a builder. That builder is then passed down to @code{libgdb}
1860 when doing any queries.
1862 @subheading Event Loop - @file{event-loop.h}
1863 @c There could be an entire section on the event-loop
1864 @file{event-loop}, currently non-re-entrant, provides a simple event
1865 loop. A client would need to either plug its self into this loop or,
1866 implement a new event-loop that @value{GDBN} would use.
1868 The event-loop will eventually be made re-entrant. This is so that
1869 @value{GDBN} can better handle the problem of some commands blocking
1870 instead of returning.
1872 @subheading Library - @file{gdb.h}
1873 @file{libgdb} is the most obvious component of this system. It provides
1874 the query interface. Each function is parameterized by a @code{ui-out}
1875 builder. The result of the query is constructed using that builder
1876 before the query function returns.
1883 @cindex @code{value} structure
1884 @value{GDBN} uses @code{struct value}, or @dfn{values}, as an internal
1885 abstraction for the representation of a variety of inferior objects
1886 and @value{GDBN} convenience objects.
1888 Values have an associated @code{struct type}, that describes a virtual
1889 view of the raw data or object stored in or accessed through the
1892 A value is in addition discriminated by its lvalue-ness, given its
1893 @code{enum lval_type} enumeration type:
1895 @cindex @code{lval_type} enumeration, for values.
1897 @item @code{not_lval}
1898 This value is not an lval. It can't be assigned to.
1900 @item @code{lval_memory}
1901 This value represents an object in memory.
1903 @item @code{lval_register}
1904 This value represents an object that lives in a register.
1906 @item @code{lval_internalvar}
1907 Represents the value of an internal variable.
1909 @item @code{lval_internalvar_component}
1910 Represents part of a @value{GDBN} internal variable. E.g., a
1913 @cindex computed values
1914 @item @code{lval_computed}
1915 These are ``computed'' values. They allow creating specialized value
1916 objects for specific purposes, all abstracted away from the core value
1917 support code. The creator of such a value writes specialized
1918 functions to handle the reading and writing to/from the value's
1919 backend data, and optionally, a ``copy operator'' and a
1922 Pointers to these functions are stored in a @code{struct lval_funcs}
1923 instance (declared in @file{value.h}), and passed to the
1924 @code{allocate_computed_value} function, as in the example below.
1928 nil_value_read (struct value *v)
1930 /* This callback reads data from some backend, and stores it in V.
1931 In this case, we always read null data. You'll want to fill in
1932 something more interesting. */
1934 memset (value_contents_all_raw (v),
1936 TYPE_LENGTH (value_type (v)));
1940 nil_value_write (struct value *v, struct value *fromval)
1942 /* Takes the data from FROMVAL and stores it in the backend of V. */
1944 to_oblivion (value_contents_all_raw (fromval),
1946 TYPE_LENGTH (value_type (fromval)));
1949 static struct lval_funcs nil_value_funcs =
1956 make_nil_value (void)
1961 type = make_nils_type ();
1962 v = allocate_computed_value (type, &nil_value_funcs, NULL);
1968 See the implementation of the @code{$_siginfo} convenience variable in
1969 @file{infrun.c} as a real example use of lval_computed.
1974 @chapter Stack Frames
1977 @cindex call stack frame
1978 A frame is a construct that @value{GDBN} uses to keep track of calling
1979 and called functions.
1981 @cindex unwind frame
1982 @value{GDBN}'s frame model, a fresh design, was implemented with the
1983 need to support @sc{dwarf}'s Call Frame Information in mind. In fact,
1984 the term ``unwind'' is taken directly from that specification.
1985 Developers wishing to learn more about unwinders, are encouraged to
1986 read the @sc{dwarf} specification, available from
1987 @url{http://www.dwarfstd.org}.
1989 @findex frame_register_unwind
1990 @findex get_frame_register
1991 @value{GDBN}'s model is that you find a frame's registers by
1992 ``unwinding'' them from the next younger frame. That is,
1993 @samp{get_frame_register} which returns the value of a register in
1994 frame #1 (the next-to-youngest frame), is implemented by calling frame
1995 #0's @code{frame_register_unwind} (the youngest frame). But then the
1996 obvious question is: how do you access the registers of the youngest
1999 @cindex sentinel frame
2000 @findex get_frame_type
2001 @vindex SENTINEL_FRAME
2002 To answer this question, @value{GDBN} has the @dfn{sentinel} frame, the
2003 ``-1st'' frame. Unwinding registers from the sentinel frame gives you
2004 the current values of the youngest real frame's registers. If @var{f}
2005 is a sentinel frame, then @code{get_frame_type (@var{f}) @equiv{}
2008 @section Selecting an Unwinder
2010 @findex frame_unwind_prepend_unwinder
2011 @findex frame_unwind_append_unwinder
2012 The architecture registers a list of frame unwinders (@code{struct
2013 frame_unwind}), using the functions
2014 @code{frame_unwind_prepend_unwinder} and
2015 @code{frame_unwind_append_unwinder}. Each unwinder includes a
2016 sniffer. Whenever @value{GDBN} needs to unwind a frame (to fetch the
2017 previous frame's registers or the current frame's ID), it calls
2018 registered sniffers in order to find one which recognizes the frame.
2019 The first time a sniffer returns non-zero, the corresponding unwinder
2020 is assigned to the frame.
2022 @section Unwinding the Frame ID
2025 Every frame has an associated ID, of type @code{struct frame_id}.
2026 The ID includes the stack base and function start address for
2027 the frame. The ID persists through the entire life of the frame,
2028 including while other called frames are running; it is used to
2029 locate an appropriate @code{struct frame_info} from the cache.
2031 Every time the inferior stops, and at various other times, the frame
2032 cache is flushed. Because of this, parts of @value{GDBN} which need
2033 to keep track of individual frames cannot use pointers to @code{struct
2034 frame_info}. A frame ID provides a stable reference to a frame, even
2035 when the unwinder must be run again to generate a new @code{struct
2036 frame_info} for the same frame.
2038 The frame's unwinder's @code{this_id} method is called to find the ID.
2039 Note that this is different from register unwinding, where the next
2040 frame's @code{prev_register} is called to unwind this frame's
2043 Both stack base and function address are required to identify the
2044 frame, because a recursive function has the same function address for
2045 two consecutive frames and a leaf function may have the same stack
2046 address as its caller. On some platforms, a third address is part of
2047 the ID to further disambiguate frames---for instance, on IA-64
2048 the separate register stack address is included in the ID.
2050 An invalid frame ID (@code{null_frame_id}) returned from the
2051 @code{this_id} method means to stop unwinding after this frame.
2053 @section Unwinding Registers
2055 Each unwinder includes a @code{prev_register} method. This method
2056 takes a frame, an associated cache pointer, and a register number.
2057 It returns a @code{struct value *} describing the requested register,
2058 as saved by this frame. This is the value of the register that is
2059 current in this frame's caller.
2061 The returned value must have the same type as the register. It may
2062 have any lvalue type. In most circumstances one of these routines
2063 will generate the appropriate value:
2066 @item frame_unwind_got_optimized
2067 @findex frame_unwind_got_optimized
2068 This register was not saved.
2070 @item frame_unwind_got_register
2071 @findex frame_unwind_got_register
2072 This register was copied into another register in this frame. This
2073 is also used for unchanged registers; they are ``copied'' into the
2076 @item frame_unwind_got_memory
2077 @findex frame_unwind_got_memory
2078 This register was saved in memory.
2080 @item frame_unwind_got_constant
2081 @findex frame_unwind_got_constant
2082 This register was not saved, but the unwinder can compute the previous
2083 value some other way.
2085 @item frame_unwind_got_address
2086 @findex frame_unwind_got_address
2087 Same as @code{frame_unwind_got_constant}, except that the value is a target
2088 address. This is frequently used for the stack pointer, which is not
2089 explicitly saved but has a known offset from this frame's stack
2090 pointer. For architectures with a flat unified address space, this is
2091 generally the same as @code{frame_unwind_got_constant}.
2094 @node Symbol Handling
2096 @chapter Symbol Handling
2098 Symbols are a key part of @value{GDBN}'s operation. Symbols include
2099 variables, functions, and types.
2101 Symbol information for a large program can be truly massive, and
2102 reading of symbol information is one of the major performance
2103 bottlenecks in @value{GDBN}; it can take many minutes to process it
2104 all. Studies have shown that nearly all the time spent is
2105 computational, rather than file reading.
2107 One of the ways for @value{GDBN} to provide a good user experience is
2108 to start up quickly, taking no more than a few seconds. It is simply
2109 not possible to process all of a program's debugging info in that
2110 time, and so we attempt to handle symbols incrementally. For instance,
2111 we create @dfn{partial symbol tables} consisting of only selected
2112 symbols, and only expand them to full symbol tables when necessary.
2114 @section Symbol Reading
2116 @cindex symbol reading
2117 @cindex reading of symbols
2118 @cindex symbol files
2119 @value{GDBN} reads symbols from @dfn{symbol files}. The usual symbol
2120 file is the file containing the program which @value{GDBN} is
2121 debugging. @value{GDBN} can be directed to use a different file for
2122 symbols (with the @samp{symbol-file} command), and it can also read
2123 more symbols via the @samp{add-file} and @samp{load} commands. In
2124 addition, it may bring in more symbols while loading shared
2127 @findex find_sym_fns
2128 Symbol files are initially opened by code in @file{symfile.c} using
2129 the BFD library (@pxref{Support Libraries}). BFD identifies the type
2130 of the file by examining its header. @code{find_sym_fns} then uses
2131 this identification to locate a set of symbol-reading functions.
2133 @findex add_symtab_fns
2134 @cindex @code{sym_fns} structure
2135 @cindex adding a symbol-reading module
2136 Symbol-reading modules identify themselves to @value{GDBN} by calling
2137 @code{add_symtab_fns} during their module initialization. The argument
2138 to @code{add_symtab_fns} is a @code{struct sym_fns} which contains the
2139 name (or name prefix) of the symbol format, the length of the prefix,
2140 and pointers to four functions. These functions are called at various
2141 times to process symbol files whose identification matches the specified
2144 The functions supplied by each module are:
2147 @item @var{xyz}_symfile_init(struct sym_fns *sf)
2149 @cindex secondary symbol file
2150 Called from @code{symbol_file_add} when we are about to read a new
2151 symbol file. This function should clean up any internal state (possibly
2152 resulting from half-read previous files, for example) and prepare to
2153 read a new symbol file. Note that the symbol file which we are reading
2154 might be a new ``main'' symbol file, or might be a secondary symbol file
2155 whose symbols are being added to the existing symbol table.
2157 The argument to @code{@var{xyz}_symfile_init} is a newly allocated
2158 @code{struct sym_fns} whose @code{bfd} field contains the BFD for the
2159 new symbol file being read. Its @code{private} field has been zeroed,
2160 and can be modified as desired. Typically, a struct of private
2161 information will be @code{malloc}'d, and a pointer to it will be placed
2162 in the @code{private} field.
2164 There is no result from @code{@var{xyz}_symfile_init}, but it can call
2165 @code{error} if it detects an unavoidable problem.
2167 @item @var{xyz}_new_init()
2169 Called from @code{symbol_file_add} when discarding existing symbols.
2170 This function needs only handle the symbol-reading module's internal
2171 state; the symbol table data structures visible to the rest of
2172 @value{GDBN} will be discarded by @code{symbol_file_add}. It has no
2173 arguments and no result. It may be called after
2174 @code{@var{xyz}_symfile_init}, if a new symbol table is being read, or
2175 may be called alone if all symbols are simply being discarded.
2177 @item @var{xyz}_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)
2179 Called from @code{symbol_file_add} to actually read the symbols from a
2180 symbol-file into a set of psymtabs or symtabs.
2182 @code{sf} points to the @code{struct sym_fns} originally passed to
2183 @code{@var{xyz}_sym_init} for possible initialization. @code{addr} is
2184 the offset between the file's specified start address and its true
2185 address in memory. @code{mainline} is 1 if this is the main symbol
2186 table being read, and 0 if a secondary symbol file (e.g., shared library
2187 or dynamically loaded file) is being read.@refill
2190 In addition, if a symbol-reading module creates psymtabs when
2191 @var{xyz}_symfile_read is called, these psymtabs will contain a pointer
2192 to a function @code{@var{xyz}_psymtab_to_symtab}, which can be called
2193 from any point in the @value{GDBN} symbol-handling code.
2196 @item @var{xyz}_psymtab_to_symtab (struct partial_symtab *pst)
2198 Called from @code{psymtab_to_symtab} (or the @code{PSYMTAB_TO_SYMTAB} macro) if
2199 the psymtab has not already been read in and had its @code{pst->symtab}
2200 pointer set. The argument is the psymtab to be fleshed-out into a
2201 symtab. Upon return, @code{pst->readin} should have been set to 1, and
2202 @code{pst->symtab} should contain a pointer to the new corresponding symtab, or
2203 zero if there were no symbols in that part of the symbol file.
2206 @section Partial Symbol Tables
2208 @value{GDBN} has three types of symbol tables:
2211 @cindex full symbol table
2214 Full symbol tables (@dfn{symtabs}). These contain the main
2215 information about symbols and addresses.
2219 Partial symbol tables (@dfn{psymtabs}). These contain enough
2220 information to know when to read the corresponding part of the full
2223 @cindex minimal symbol table
2226 Minimal symbol tables (@dfn{msymtabs}). These contain information
2227 gleaned from non-debugging symbols.
2230 @cindex partial symbol table
2231 This section describes partial symbol tables.
2233 A psymtab is constructed by doing a very quick pass over an executable
2234 file's debugging information. Small amounts of information are
2235 extracted---enough to identify which parts of the symbol table will
2236 need to be re-read and fully digested later, when the user needs the
2237 information. The speed of this pass causes @value{GDBN} to start up very
2238 quickly. Later, as the detailed rereading occurs, it occurs in small
2239 pieces, at various times, and the delay therefrom is mostly invisible to
2241 @c (@xref{Symbol Reading}.)
2243 The symbols that show up in a file's psymtab should be, roughly, those
2244 visible to the debugger's user when the program is not running code from
2245 that file. These include external symbols and types, static symbols and
2246 types, and @code{enum} values declared at file scope.
2248 The psymtab also contains the range of instruction addresses that the
2249 full symbol table would represent.
2251 @cindex finding a symbol
2252 @cindex symbol lookup
2253 The idea is that there are only two ways for the user (or much of the
2254 code in the debugger) to reference a symbol:
2257 @findex find_pc_function
2258 @findex find_pc_line
2260 By its address (e.g., execution stops at some address which is inside a
2261 function in this file). The address will be noticed to be in the
2262 range of this psymtab, and the full symtab will be read in.
2263 @code{find_pc_function}, @code{find_pc_line}, and other
2264 @code{find_pc_@dots{}} functions handle this.
2266 @cindex lookup_symbol
2269 (e.g., the user asks to print a variable, or set a breakpoint on a
2270 function). Global names and file-scope names will be found in the
2271 psymtab, which will cause the symtab to be pulled in. Local names will
2272 have to be qualified by a global name, or a file-scope name, in which
2273 case we will have already read in the symtab as we evaluated the
2274 qualifier. Or, a local symbol can be referenced when we are ``in'' a
2275 local scope, in which case the first case applies. @code{lookup_symbol}
2276 does most of the work here.
2279 The only reason that psymtabs exist is to cause a symtab to be read in
2280 at the right moment. Any symbol that can be elided from a psymtab,
2281 while still causing that to happen, should not appear in it. Since
2282 psymtabs don't have the idea of scope, you can't put local symbols in
2283 them anyway. Psymtabs don't have the idea of the type of a symbol,
2284 either, so types need not appear, unless they will be referenced by
2287 It is a bug for @value{GDBN} to behave one way when only a psymtab has
2288 been read, and another way if the corresponding symtab has been read
2289 in. Such bugs are typically caused by a psymtab that does not contain
2290 all the visible symbols, or which has the wrong instruction address
2293 The psymtab for a particular section of a symbol file (objfile) could be
2294 thrown away after the symtab has been read in. The symtab should always
2295 be searched before the psymtab, so the psymtab will never be used (in a
2296 bug-free environment). Currently, psymtabs are allocated on an obstack,
2297 and all the psymbols themselves are allocated in a pair of large arrays
2298 on an obstack, so there is little to be gained by trying to free them
2299 unless you want to do a lot more work.
2303 @unnumberedsubsec Fundamental Types (e.g., @code{FT_VOID}, @code{FT_BOOLEAN}).
2305 @cindex fundamental types
2306 These are the fundamental types that @value{GDBN} uses internally. Fundamental
2307 types from the various debugging formats (stabs, ELF, etc) are mapped
2308 into one of these. They are basically a union of all fundamental types
2309 that @value{GDBN} knows about for all the languages that @value{GDBN}
2312 @unnumberedsubsec Type Codes (e.g., @code{TYPE_CODE_PTR}, @code{TYPE_CODE_ARRAY}).
2315 Each time @value{GDBN} builds an internal type, it marks it with one
2316 of these types. The type may be a fundamental type, such as
2317 @code{TYPE_CODE_INT}, or a derived type, such as @code{TYPE_CODE_PTR}
2318 which is a pointer to another type. Typically, several @code{FT_*}
2319 types map to one @code{TYPE_CODE_*} type, and are distinguished by
2320 other members of the type struct, such as whether the type is signed
2321 or unsigned, and how many bits it uses.
2323 @unnumberedsubsec Builtin Types (e.g., @code{builtin_type_void}, @code{builtin_type_char}).
2325 These are instances of type structs that roughly correspond to
2326 fundamental types and are created as global types for @value{GDBN} to
2327 use for various ugly historical reasons. We eventually want to
2328 eliminate these. Note for example that @code{builtin_type_int}
2329 initialized in @file{gdbtypes.c} is basically the same as a
2330 @code{TYPE_CODE_INT} type that is initialized in @file{c-lang.c} for
2331 an @code{FT_INTEGER} fundamental type. The difference is that the
2332 @code{builtin_type} is not associated with any particular objfile, and
2333 only one instance exists, while @file{c-lang.c} builds as many
2334 @code{TYPE_CODE_INT} types as needed, with each one associated with
2335 some particular objfile.
2337 @section Object File Formats
2338 @cindex object file formats
2342 @cindex @code{a.out} format
2343 The @code{a.out} format is the original file format for Unix. It
2344 consists of three sections: @code{text}, @code{data}, and @code{bss},
2345 which are for program code, initialized data, and uninitialized data,
2348 The @code{a.out} format is so simple that it doesn't have any reserved
2349 place for debugging information. (Hey, the original Unix hackers used
2350 @samp{adb}, which is a machine-language debugger!) The only debugging
2351 format for @code{a.out} is stabs, which is encoded as a set of normal
2352 symbols with distinctive attributes.
2354 The basic @code{a.out} reader is in @file{dbxread.c}.
2359 The COFF format was introduced with System V Release 3 (SVR3) Unix.
2360 COFF files may have multiple sections, each prefixed by a header. The
2361 number of sections is limited.
2363 The COFF specification includes support for debugging. Although this
2364 was a step forward, the debugging information was woefully limited.
2365 For instance, it was not possible to represent code that came from an
2366 included file. GNU's COFF-using configs often use stabs-type info,
2367 encapsulated in special sections.
2369 The COFF reader is in @file{coffread.c}.
2373 @cindex ECOFF format
2374 ECOFF is an extended COFF originally introduced for Mips and Alpha
2377 The basic ECOFF reader is in @file{mipsread.c}.
2381 @cindex XCOFF format
2382 The IBM RS/6000 running AIX uses an object file format called XCOFF.
2383 The COFF sections, symbols, and line numbers are used, but debugging
2384 symbols are @code{dbx}-style stabs whose strings are located in the
2385 @code{.debug} section (rather than the string table). For more
2386 information, see @ref{Top,,,stabs,The Stabs Debugging Format}.
2388 The shared library scheme has a clean interface for figuring out what
2389 shared libraries are in use, but the catch is that everything which
2390 refers to addresses (symbol tables and breakpoints at least) needs to be
2391 relocated for both shared libraries and the main executable. At least
2392 using the standard mechanism this can only be done once the program has
2393 been run (or the core file has been read).
2397 @cindex PE-COFF format
2398 Windows 95 and NT use the PE (@dfn{Portable Executable}) format for their
2399 executables. PE is basically COFF with additional headers.
2401 While BFD includes special PE support, @value{GDBN} needs only the basic
2407 The ELF format came with System V Release 4 (SVR4) Unix. ELF is
2408 similar to COFF in being organized into a number of sections, but it
2409 removes many of COFF's limitations. Debugging info may be either stabs
2410 encapsulated in ELF sections, or more commonly these days, DWARF.
2412 The basic ELF reader is in @file{elfread.c}.
2417 SOM is HP's object file and debug format (not to be confused with IBM's
2418 SOM, which is a cross-language ABI).
2420 The SOM reader is in @file{somread.c}.
2422 @section Debugging File Formats
2424 This section describes characteristics of debugging information that
2425 are independent of the object file format.
2429 @cindex stabs debugging info
2430 @code{stabs} started out as special symbols within the @code{a.out}
2431 format. Since then, it has been encapsulated into other file
2432 formats, such as COFF and ELF.
2434 While @file{dbxread.c} does some of the basic stab processing,
2435 including for encapsulated versions, @file{stabsread.c} does
2440 @cindex COFF debugging info
2441 The basic COFF definition includes debugging information. The level
2442 of support is minimal and non-extensible, and is not often used.
2444 @subsection Mips debug (Third Eye)
2446 @cindex ECOFF debugging info
2447 ECOFF includes a definition of a special debug format.
2449 The file @file{mdebugread.c} implements reading for this format.
2451 @c mention DWARF 1 as a formerly-supported format
2455 @cindex DWARF 2 debugging info
2456 DWARF 2 is an improved but incompatible version of DWARF 1.
2458 The DWARF 2 reader is in @file{dwarf2read.c}.
2460 @subsection Compressed DWARF 2
2462 @cindex Compressed DWARF 2 debugging info
2463 Compressed DWARF 2 is not technically a separate debugging format, but
2464 merely DWARF 2 debug information that has been compressed. In this
2465 format, every object-file section holding DWARF 2 debugging
2466 information is compressed and prepended with a header. (The section
2467 is also typically renamed, so a section called @code{.debug_info} in a
2468 DWARF 2 binary would be called @code{.zdebug_info} in a compressed
2469 DWARF 2 binary.) The header is 12 bytes long:
2473 4 bytes: the literal string ``ZLIB''
2475 8 bytes: the uncompressed size of the section, in big-endian byte
2479 The same reader is used for both compressed an normal DWARF 2 info.
2480 Section decompression is done in @code{zlib_decompress_section} in
2481 @file{dwarf2read.c}.
2485 @cindex DWARF 3 debugging info
2486 DWARF 3 is an improved version of DWARF 2.
2490 @cindex SOM debugging info
2491 Like COFF, the SOM definition includes debugging information.
2493 @section Adding a New Symbol Reader to @value{GDBN}
2495 @cindex adding debugging info reader
2496 If you are using an existing object file format (@code{a.out}, COFF, ELF, etc),
2497 there is probably little to be done.
2499 If you need to add a new object file format, you must first add it to
2500 BFD. This is beyond the scope of this document.
2502 You must then arrange for the BFD code to provide access to the
2503 debugging symbols. Generally @value{GDBN} will have to call swapping
2504 routines from BFD and a few other BFD internal routines to locate the
2505 debugging information. As much as possible, @value{GDBN} should not
2506 depend on the BFD internal data structures.
2508 For some targets (e.g., COFF), there is a special transfer vector used
2509 to call swapping routines, since the external data structures on various
2510 platforms have different sizes and layouts. Specialized routines that
2511 will only ever be implemented by one object file format may be called
2512 directly. This interface should be described in a file
2513 @file{bfd/lib@var{xyz}.h}, which is included by @value{GDBN}.
2515 @section Memory Management for Symbol Files
2517 Most memory associated with a loaded symbol file is stored on
2518 its @code{objfile_obstack}. This includes symbols, types,
2519 namespace data, and other information produced by the symbol readers.
2521 Because this data lives on the objfile's obstack, it is automatically
2522 released when the objfile is unloaded or reloaded. Therefore one
2523 objfile must not reference symbol or type data from another objfile;
2524 they could be unloaded at different times.
2526 User convenience variables, et cetera, have associated types. Normally
2527 these types live in the associated objfile. However, when the objfile
2528 is unloaded, those types are deep copied to global memory, so that
2529 the values of the user variables and history items are not lost.
2532 @node Language Support
2534 @chapter Language Support
2536 @cindex language support
2537 @value{GDBN}'s language support is mainly driven by the symbol reader,
2538 although it is possible for the user to set the source language
2541 @value{GDBN} chooses the source language by looking at the extension
2542 of the file recorded in the debug info; @file{.c} means C, @file{.f}
2543 means Fortran, etc. It may also use a special-purpose language
2544 identifier if the debug format supports it, like with DWARF.
2546 @section Adding a Source Language to @value{GDBN}
2548 @cindex adding source language
2549 To add other languages to @value{GDBN}'s expression parser, follow the
2553 @item Create the expression parser.
2555 @cindex expression parser
2556 This should reside in a file @file{@var{lang}-exp.y}. Routines for
2557 building parsed expressions into a @code{union exp_element} list are in
2560 @cindex language parser
2561 Since we can't depend upon everyone having Bison, and YACC produces
2562 parsers that define a bunch of global names, the following lines
2563 @strong{must} be included at the top of the YACC parser, to prevent the
2564 various parsers from defining the same global names:
2567 #define yyparse @var{lang}_parse
2568 #define yylex @var{lang}_lex
2569 #define yyerror @var{lang}_error
2570 #define yylval @var{lang}_lval
2571 #define yychar @var{lang}_char
2572 #define yydebug @var{lang}_debug
2573 #define yypact @var{lang}_pact
2574 #define yyr1 @var{lang}_r1
2575 #define yyr2 @var{lang}_r2
2576 #define yydef @var{lang}_def
2577 #define yychk @var{lang}_chk
2578 #define yypgo @var{lang}_pgo
2579 #define yyact @var{lang}_act
2580 #define yyexca @var{lang}_exca
2581 #define yyerrflag @var{lang}_errflag
2582 #define yynerrs @var{lang}_nerrs
2585 At the bottom of your parser, define a @code{struct language_defn} and
2586 initialize it with the right values for your language. Define an
2587 @code{initialize_@var{lang}} routine and have it call
2588 @samp{add_language(@var{lang}_language_defn)} to tell the rest of @value{GDBN}
2589 that your language exists. You'll need some other supporting variables
2590 and functions, which will be used via pointers from your
2591 @code{@var{lang}_language_defn}. See the declaration of @code{struct
2592 language_defn} in @file{language.h}, and the other @file{*-exp.y} files,
2593 for more information.
2595 @item Add any evaluation routines, if necessary
2597 @cindex expression evaluation routines
2598 @findex evaluate_subexp
2599 @findex prefixify_subexp
2600 @findex length_of_subexp
2601 If you need new opcodes (that represent the operations of the language),
2602 add them to the enumerated type in @file{expression.h}. Add support
2603 code for these operations in the @code{evaluate_subexp} function
2604 defined in the file @file{eval.c}. Add cases
2605 for new opcodes in two functions from @file{parse.c}:
2606 @code{prefixify_subexp} and @code{length_of_subexp}. These compute
2607 the number of @code{exp_element}s that a given operation takes up.
2609 @item Update some existing code
2611 Add an enumerated identifier for your language to the enumerated type
2612 @code{enum language} in @file{defs.h}.
2614 Update the routines in @file{language.c} so your language is included.
2615 These routines include type predicates and such, which (in some cases)
2616 are language dependent. If your language does not appear in the switch
2617 statement, an error is reported.
2619 @vindex current_language
2620 Also included in @file{language.c} is the code that updates the variable
2621 @code{current_language}, and the routines that translate the
2622 @code{language_@var{lang}} enumerated identifier into a printable
2625 @findex _initialize_language
2626 Update the function @code{_initialize_language} to include your
2627 language. This function picks the default language upon startup, so is
2628 dependent upon which languages that @value{GDBN} is built for.
2630 @findex allocate_symtab
2631 Update @code{allocate_symtab} in @file{symfile.c} and/or symbol-reading
2632 code so that the language of each symtab (source file) is set properly.
2633 This is used to determine the language to use at each stack frame level.
2634 Currently, the language is set based upon the extension of the source
2635 file. If the language can be better inferred from the symbol
2636 information, please set the language of the symtab in the symbol-reading
2639 @findex print_subexp
2640 @findex op_print_tab
2641 Add helper code to @code{print_subexp} (in @file{expprint.c}) to handle any new
2642 expression opcodes you have added to @file{expression.h}. Also, add the
2643 printed representations of your operators to @code{op_print_tab}.
2645 @item Add a place of call
2648 Add a call to @code{@var{lang}_parse()} and @code{@var{lang}_error} in
2649 @code{parse_exp_1} (defined in @file{parse.c}).
2651 @item Edit @file{Makefile.in}
2653 Add dependencies in @file{Makefile.in}. Make sure you update the macro
2654 variables such as @code{HFILES} and @code{OBJS}, otherwise your code may
2655 not get linked in, or, worse yet, it may not get @code{tar}red into the
2660 @node Host Definition
2662 @chapter Host Definition
2664 With the advent of Autoconf, it's rarely necessary to have host
2665 definition machinery anymore. The following information is provided,
2666 mainly, as an historical reference.
2668 @section Adding a New Host
2670 @cindex adding a new host
2671 @cindex host, adding
2672 @value{GDBN}'s host configuration support normally happens via Autoconf.
2673 New host-specific definitions should not be needed. Older hosts
2674 @value{GDBN} still use the host-specific definitions and files listed
2675 below, but these mostly exist for historical reasons, and will
2676 eventually disappear.
2679 @item gdb/config/@var{arch}/@var{xyz}.mh
2680 This file is a Makefile fragment that once contained both host and
2681 native configuration information (@pxref{Native Debugging}) for the
2682 machine @var{xyz}. The host configuration information is now handled
2685 Host configuration information included definitions for @code{CC},
2686 @code{SYSV_DEFINE}, @code{XM_CFLAGS}, @code{XM_ADD_FILES},
2687 @code{XM_CLIBS}, @code{XM_CDEPS}, etc.; see @file{Makefile.in}.
2689 New host-only configurations do not need this file.
2693 (Files named @file{gdb/config/@var{arch}/xm-@var{xyz}.h} were once
2694 used to define host-specific macros, but were no longer needed and
2695 have all been removed.)
2697 @subheading Generic Host Support Files
2699 @cindex generic host support
2700 There are some ``generic'' versions of routines that can be used by
2704 @cindex remote debugging support
2705 @cindex serial line support
2707 This contains serial line support for Unix systems. It is included by
2708 default on all Unix-like hosts.
2711 This contains serial pipe support for Unix systems. It is included by
2712 default on all Unix-like hosts.
2715 This contains serial line support for 32-bit programs running under
2716 Windows using MinGW.
2719 This contains serial line support for 32-bit programs running under DOS,
2720 using the DJGPP (a.k.a.@: GO32) execution environment.
2722 @cindex TCP remote support
2724 This contains generic TCP support using sockets. It is included by
2725 default on all Unix-like hosts and with MinGW.
2728 @section Host Conditionals
2730 When @value{GDBN} is configured and compiled, various macros are
2731 defined or left undefined, to control compilation based on the
2732 attributes of the host system. While formerly they could be set in
2733 host-specific header files, at present they can be changed only by
2734 setting @code{CFLAGS} when building, or by editing the source code.
2736 These macros and their meanings (or if the meaning is not documented
2737 here, then one of the source files where they are used is indicated)
2741 @item @value{GDBN}INIT_FILENAME
2742 The default name of @value{GDBN}'s initialization file (normally
2745 @item SIGWINCH_HANDLER
2746 If your host defines @code{SIGWINCH}, you can define this to be the name
2747 of a function to be called if @code{SIGWINCH} is received.
2749 @item SIGWINCH_HANDLER_BODY
2750 Define this to expand into code that will define the function named by
2751 the expansion of @code{SIGWINCH_HANDLER}.
2753 @item CRLF_SOURCE_FILES
2754 @cindex DOS text files
2755 Define this if host files use @code{\r\n} rather than @code{\n} as a
2756 line terminator. This will cause source file listings to omit @code{\r}
2757 characters when printing and it will allow @code{\r\n} line endings of files
2758 which are ``sourced'' by gdb. It must be possible to open files in binary
2759 mode using @code{O_BINARY} or, for fopen, @code{"rb"}.
2761 @item DEFAULT_PROMPT
2763 The default value of the prompt string (normally @code{"(gdb) "}).
2766 @cindex terminal device
2767 The name of the generic TTY device, defaults to @code{"/dev/tty"}.
2770 Substitute for isatty, if not available.
2773 Define this if binary files are opened the same way as text files.
2775 @item CC_HAS_LONG_LONG
2776 @cindex @code{long long} data type
2777 Define this if the host C compiler supports @code{long long}. This is set
2778 by the @code{configure} script.
2780 @item PRINTF_HAS_LONG_LONG
2781 Define this if the host can handle printing of long long integers via
2782 the printf format conversion specifier @code{ll}. This is set by the
2783 @code{configure} script.
2785 @item LSEEK_NOT_LINEAR
2786 Define this if @code{lseek (n)} does not necessarily move to byte number
2787 @code{n} in the file. This is only used when reading source files. It
2788 is normally faster to define @code{CRLF_SOURCE_FILES} when possible.
2791 If defined, this should be one or more tokens, such as @code{volatile},
2792 that can be used in both the declaration and definition of functions to
2793 indicate that they never return. The default is already set correctly
2794 if compiling with GCC. This will almost never need to be defined.
2797 If defined, this should be one or more tokens, such as
2798 @code{__attribute__ ((noreturn))}, that can be used in the declarations
2799 of functions to indicate that they never return. The default is already
2800 set correctly if compiling with GCC. This will almost never need to be
2804 Define this to help placate @code{lint} in some situations.
2807 Define this to override the defaults of @code{__volatile__} or
2812 @node Target Architecture Definition
2814 @chapter Target Architecture Definition
2816 @cindex target architecture definition
2817 @value{GDBN}'s target architecture defines what sort of
2818 machine-language programs @value{GDBN} can work with, and how it works
2821 The target architecture object is implemented as the C structure
2822 @code{struct gdbarch *}. The structure, and its methods, are generated
2823 using the Bourne shell script @file{gdbarch.sh}.
2826 * OS ABI Variant Handling::
2827 * Initialize New Architecture::
2828 * Registers and Memory::
2829 * Pointers and Addresses::
2831 * Register Representation::
2832 * Frame Interpretation::
2833 * Inferior Call Setup::
2834 * Adding support for debugging core files::
2835 * Defining Other Architecture Features::
2836 * Adding a New Target::
2839 @node OS ABI Variant Handling
2840 @section Operating System ABI Variant Handling
2841 @cindex OS ABI variants
2843 @value{GDBN} provides a mechanism for handling variations in OS
2844 ABIs. An OS ABI variant may have influence over any number of
2845 variables in the target architecture definition. There are two major
2846 components in the OS ABI mechanism: sniffers and handlers.
2848 A @dfn{sniffer} examines a file matching a BFD architecture/flavour pair
2849 (the architecture may be wildcarded) in an attempt to determine the
2850 OS ABI of that file. Sniffers with a wildcarded architecture are considered
2851 to be @dfn{generic}, while sniffers for a specific architecture are
2852 considered to be @dfn{specific}. A match from a specific sniffer
2853 overrides a match from a generic sniffer. Multiple sniffers for an
2854 architecture/flavour may exist, in order to differentiate between two
2855 different operating systems which use the same basic file format. The
2856 OS ABI framework provides a generic sniffer for ELF-format files which
2857 examines the @code{EI_OSABI} field of the ELF header, as well as note
2858 sections known to be used by several operating systems.
2860 @cindex fine-tuning @code{gdbarch} structure
2861 A @dfn{handler} is used to fine-tune the @code{gdbarch} structure for the
2862 selected OS ABI. There may be only one handler for a given OS ABI
2863 for each BFD architecture.
2865 The following OS ABI variants are defined in @file{defs.h}:
2869 @findex GDB_OSABI_UNINITIALIZED
2870 @item GDB_OSABI_UNINITIALIZED
2871 Used for struct gdbarch_info if ABI is still uninitialized.
2873 @findex GDB_OSABI_UNKNOWN
2874 @item GDB_OSABI_UNKNOWN
2875 The ABI of the inferior is unknown. The default @code{gdbarch}
2876 settings for the architecture will be used.
2878 @findex GDB_OSABI_SVR4
2879 @item GDB_OSABI_SVR4
2880 UNIX System V Release 4.
2882 @findex GDB_OSABI_HURD
2883 @item GDB_OSABI_HURD
2884 GNU using the Hurd kernel.
2886 @findex GDB_OSABI_SOLARIS
2887 @item GDB_OSABI_SOLARIS
2890 @findex GDB_OSABI_OSF1
2891 @item GDB_OSABI_OSF1
2892 OSF/1, including Digital UNIX and Compaq Tru64 UNIX.
2894 @findex GDB_OSABI_LINUX
2895 @item GDB_OSABI_LINUX
2896 GNU using the Linux kernel.
2898 @findex GDB_OSABI_FREEBSD_AOUT
2899 @item GDB_OSABI_FREEBSD_AOUT
2900 FreeBSD using the @code{a.out} executable format.
2902 @findex GDB_OSABI_FREEBSD_ELF
2903 @item GDB_OSABI_FREEBSD_ELF
2904 FreeBSD using the ELF executable format.
2906 @findex GDB_OSABI_NETBSD_AOUT
2907 @item GDB_OSABI_NETBSD_AOUT
2908 NetBSD using the @code{a.out} executable format.
2910 @findex GDB_OSABI_NETBSD_ELF
2911 @item GDB_OSABI_NETBSD_ELF
2912 NetBSD using the ELF executable format.
2914 @findex GDB_OSABI_OPENBSD_ELF
2915 @item GDB_OSABI_OPENBSD_ELF
2916 OpenBSD using the ELF executable format.
2918 @findex GDB_OSABI_WINCE
2919 @item GDB_OSABI_WINCE
2922 @findex GDB_OSABI_GO32
2923 @item GDB_OSABI_GO32
2926 @findex GDB_OSABI_IRIX
2927 @item GDB_OSABI_IRIX
2930 @findex GDB_OSABI_INTERIX
2931 @item GDB_OSABI_INTERIX
2932 Interix (Posix layer for MS-Windows systems).
2934 @findex GDB_OSABI_HPUX_ELF
2935 @item GDB_OSABI_HPUX_ELF
2936 HP/UX using the ELF executable format.
2938 @findex GDB_OSABI_HPUX_SOM
2939 @item GDB_OSABI_HPUX_SOM
2940 HP/UX using the SOM executable format.
2942 @findex GDB_OSABI_QNXNTO
2943 @item GDB_OSABI_QNXNTO
2946 @findex GDB_OSABI_CYGWIN
2947 @item GDB_OSABI_CYGWIN
2950 @findex GDB_OSABI_AIX
2956 Here are the functions that make up the OS ABI framework:
2958 @deftypefun {const char *} gdbarch_osabi_name (enum gdb_osabi @var{osabi})
2959 Return the name of the OS ABI corresponding to @var{osabi}.
2962 @deftypefun void gdbarch_register_osabi (enum bfd_architecture @var{arch}, unsigned long @var{machine}, enum gdb_osabi @var{osabi}, void (*@var{init_osabi})(struct gdbarch_info @var{info}, struct gdbarch *@var{gdbarch}))
2963 Register the OS ABI handler specified by @var{init_osabi} for the
2964 architecture, machine type and OS ABI specified by @var{arch},
2965 @var{machine} and @var{osabi}. In most cases, a value of zero for the
2966 machine type, which implies the architecture's default machine type,
2970 @deftypefun void gdbarch_register_osabi_sniffer (enum bfd_architecture @var{arch}, enum bfd_flavour @var{flavour}, enum gdb_osabi (*@var{sniffer})(bfd *@var{abfd}))
2971 Register the OS ABI file sniffer specified by @var{sniffer} for the
2972 BFD architecture/flavour pair specified by @var{arch} and @var{flavour}.
2973 If @var{arch} is @code{bfd_arch_unknown}, the sniffer is considered to
2974 be generic, and is allowed to examine @var{flavour}-flavoured files for
2978 @deftypefun {enum gdb_osabi} gdbarch_lookup_osabi (bfd *@var{abfd})
2979 Examine the file described by @var{abfd} to determine its OS ABI.
2980 The value @code{GDB_OSABI_UNKNOWN} is returned if the OS ABI cannot
2984 @deftypefun void gdbarch_init_osabi (struct gdbarch info @var{info}, struct gdbarch *@var{gdbarch}, enum gdb_osabi @var{osabi})
2985 Invoke the OS ABI handler corresponding to @var{osabi} to fine-tune the
2986 @code{gdbarch} structure specified by @var{gdbarch}. If a handler
2987 corresponding to @var{osabi} has not been registered for @var{gdbarch}'s
2988 architecture, a warning will be issued and the debugging session will continue
2989 with the defaults already established for @var{gdbarch}.
2992 @deftypefun void generic_elf_osabi_sniff_abi_tag_sections (bfd *@var{abfd}, asection *@var{sect}, void *@var{obj})
2993 Helper routine for ELF file sniffers. Examine the file described by
2994 @var{abfd} and look at ABI tag note sections to determine the OS ABI
2995 from the note. This function should be called via
2996 @code{bfd_map_over_sections}.
2999 @node Initialize New Architecture
3000 @section Initializing a New Architecture
3003 * How an Architecture is Represented::
3004 * Looking Up an Existing Architecture::
3005 * Creating a New Architecture::
3008 @node How an Architecture is Represented
3009 @subsection How an Architecture is Represented
3010 @cindex architecture representation
3011 @cindex representation of architecture
3013 Each @code{gdbarch} is associated with a single @sc{bfd} architecture,
3014 via a @code{bfd_arch_@var{arch}} in the @code{bfd_architecture}
3015 enumeration. The @code{gdbarch} is registered by a call to
3016 @code{register_gdbarch_init}, usually from the file's
3017 @code{_initialize_@var{filename}} routine, which will be automatically
3018 called during @value{GDBN} startup. The arguments are a @sc{bfd}
3019 architecture constant and an initialization function.
3021 @findex _initialize_@var{arch}_tdep
3022 @cindex @file{@var{arch}-tdep.c}
3023 A @value{GDBN} description for a new architecture, @var{arch} is created by
3024 defining a global function @code{_initialize_@var{arch}_tdep}, by
3025 convention in the source file @file{@var{arch}-tdep.c}. For example,
3026 in the case of the OpenRISC 1000, this function is called
3027 @code{_initialize_or1k_tdep} and is found in the file
3030 @cindex @file{configure.tgt}
3031 @cindex @code{gdbarch}
3032 @findex gdbarch_register
3033 The resulting object files containing the implementation of the
3034 @code{_initialize_@var{arch}_tdep} function are specified in the @value{GDBN}
3035 @file{configure.tgt} file, which includes a large case statement
3036 pattern matching against the @code{--target} option of the
3037 @code{configure} script. The new @code{struct gdbarch} is created
3038 within the @code{_initialize_@var{arch}_tdep} function by calling
3039 @code{gdbarch_register}:
3042 void gdbarch_register (enum bfd_architecture @var{architecture},
3043 gdbarch_init_ftype *@var{init_func},
3044 gdbarch_dump_tdep_ftype *@var{tdep_dump_func});
3047 The @var{architecture} will identify the unique @sc{bfd} to be
3048 associated with this @code{gdbarch}. The @var{init_func} funciton is
3049 called to create and return the new @code{struct gdbarch}. The
3050 @var{tdep_dump_func} function will dump the target specific details
3051 associated with this architecture.
3053 For example the function @code{_initialize_or1k_tdep} creates its
3054 architecture for 32-bit OpenRISC 1000 architectures by calling:
3057 gdbarch_register (bfd_arch_or32, or1k_gdbarch_init, or1k_dump_tdep);
3060 @node Looking Up an Existing Architecture
3061 @subsection Looking Up an Existing Architecture
3062 @cindex @code{gdbarch} lookup
3064 The initialization function has this prototype:
3067 static struct gdbarch *
3068 @var{arch}_gdbarch_init (struct gdbarch_info @var{info},
3069 struct gdbarch_list *@var{arches})
3072 The @var{info} argument contains parameters used to select the correct
3073 architecture, and @var{arches} is a list of architectures which
3074 have already been created with the same @code{bfd_arch_@var{arch}}
3077 The initialization function should first make sure that @var{info}
3078 is acceptable, and return @code{NULL} if it is not. Then, it should
3079 search through @var{arches} for an exact match to @var{info}, and
3080 return one if found. Lastly, if no exact match was found, it should
3081 create a new architecture based on @var{info} and return it.
3083 @findex gdbarch_list_lookup_by_info
3084 @cindex @code{gdbarch_info}
3085 The lookup is done using @code{gdbarch_list_lookup_by_info}. It is
3086 passed the list of existing architectures, @var{arches}, and the
3087 @code{struct gdbarch_info}, @var{info}, and returns the first matching
3088 architecture it finds, or @code{NULL} if none are found. If an
3089 architecture is found it can be returned as the result from the
3090 initialization function, otherwise a new @code{struct gdbach} will need
3093 The struct gdbarch_info has the following components:
3098 const struct bfd_arch_info *bfd_arch_info;
3101 struct gdbarch_tdep_info *tdep_info;
3102 enum gdb_osabi osabi;
3103 const struct target_desc *target_desc;
3107 @vindex bfd_arch_info
3108 The @code{bfd_arch_info} member holds the key details about the
3109 architecture. The @code{byte_order} member is a value in an
3110 enumeration indicating the endianism. The @code{abfd} member is a
3111 pointer to the full @sc{bfd}, the @code{tdep_info} member is
3112 additional custom target specific information, @code{osabi} identifies
3113 which (if any) of a number of operating specific ABIs are used by this
3114 architecture and the @code{target_desc} member is a set of name-value
3115 pairs with information about register usage in this target.
3117 When the @code{struct gdbarch} initialization function is called, not
3118 all the fields are provided---only those which can be deduced from the
3119 @sc{bfd}. The @code{struct gdbarch_info}, @var{info} is used as a
3120 look-up key with the list of existing architectures, @var{arches} to
3121 see if a suitable architecture already exists. The @var{tdep_info},
3122 @var{osabi} and @var{target_desc} fields may be added before this
3123 lookup to refine the search.
3125 Only information in @var{info} should be used to choose the new
3126 architecture. Historically, @var{info} could be sparse, and
3127 defaults would be collected from the first element on @var{arches}.
3128 However, @value{GDBN} now fills in @var{info} more thoroughly,
3129 so new @code{gdbarch} initialization functions should not take
3130 defaults from @var{arches}.
3132 @node Creating a New Architecture
3133 @subsection Creating a New Architecture
3134 @cindex @code{struct gdbarch} creation
3136 @findex gdbarch_alloc
3137 @cindex @code{gdbarch_tdep} when allocating new @code{gdbarch}
3138 If no architecture is found, then a new architecture must be created,
3139 by calling @code{gdbarch_alloc} using the supplied @code{@w{struct
3140 gdbarch_info}} and any additional custom target specific
3141 information in a @code{struct gdbarch_tdep}. The prototype for
3142 @code{gdbarch_alloc} is:
3145 struct gdbarch *gdbarch_alloc (const struct gdbarch_info *@var{info},
3146 struct gdbarch_tdep *@var{tdep});
3149 @cindex @code{set_gdbarch} functions
3150 @cindex @code{gdbarch} accessor functions
3151 The newly created struct gdbarch must then be populated. Although
3152 there are default values, in most cases they are not what is
3155 For each element, @var{X}, there is are a pair of corresponding accessor
3156 functions, one to set the value of that element,
3157 @code{set_gdbarch_@var{X}}, the second to either get the value of an
3158 element (if it is a variable) or to apply the element (if it is a
3159 function), @code{gdbarch_@var{X}}. Note that both accessor functions
3160 take a pointer to the @code{@w{struct gdbarch}} as first
3161 argument. Populating the new @code{gdbarch} should use the
3162 @code{set_gdbarch} functions.
3164 The following sections identify the main elements that should be set
3165 in this way. This is not the complete list, but represents the
3166 functions and elements that must commonly be specified for a new
3167 architecture. Many of the functions and variables are described in the
3168 header file @file{gdbarch.h}.
3170 This is the main work in defining a new architecture. Implementing the
3171 set of functions to populate the @code{struct gdbarch}.
3173 @cindex @code{gdbarch_tdep} definition
3174 @code{struct gdbarch_tdep} is not defined within @value{GDBN}---it is up
3175 to the user to define this struct if it is needed to hold custom target
3176 information that is not covered by the standard @code{@w{struct
3177 gdbarch}}. For example with the OpenRISC 1000 architecture it is used to
3178 hold the number of matchpoints available in the target (along with other
3181 If there is no additional target specific information, it can be set to
3184 @node Registers and Memory
3185 @section Registers and Memory
3187 @value{GDBN}'s model of the target machine is rather simple.
3188 @value{GDBN} assumes the machine includes a bank of registers and a
3189 block of memory. Each register may have a different size.
3191 @value{GDBN} does not have a magical way to match up with the
3192 compiler's idea of which registers are which; however, it is critical
3193 that they do match up accurately. The only way to make this work is
3194 to get accurate information about the order that the compiler uses,
3195 and to reflect that in the @code{gdbarch_register_name} and related functions.
3197 @value{GDBN} can handle big-endian, little-endian, and bi-endian architectures.
3199 @node Pointers and Addresses
3200 @section Pointers Are Not Always Addresses
3201 @cindex pointer representation
3202 @cindex address representation
3203 @cindex word-addressed machines
3204 @cindex separate data and code address spaces
3205 @cindex spaces, separate data and code address
3206 @cindex address spaces, separate data and code
3207 @cindex code pointers, word-addressed
3208 @cindex converting between pointers and addresses
3209 @cindex D10V addresses
3211 On almost all 32-bit architectures, the representation of a pointer is
3212 indistinguishable from the representation of some fixed-length number
3213 whose value is the byte address of the object pointed to. On such
3214 machines, the words ``pointer'' and ``address'' can be used interchangeably.
3215 However, architectures with smaller word sizes are often cramped for
3216 address space, so they may choose a pointer representation that breaks this
3217 identity, and allows a larger code address space.
3219 @c D10V is gone from sources - more current example?
3221 For example, the Renesas D10V is a 16-bit VLIW processor whose
3222 instructions are 32 bits long@footnote{Some D10V instructions are
3223 actually pairs of 16-bit sub-instructions. However, since you can't
3224 jump into the middle of such a pair, code addresses can only refer to
3225 full 32 bit instructions, which is what matters in this explanation.}.
3226 If the D10V used ordinary byte addresses to refer to code locations,
3227 then the processor would only be able to address 64kb of instructions.
3228 However, since instructions must be aligned on four-byte boundaries, the
3229 low two bits of any valid instruction's byte address are always
3230 zero---byte addresses waste two bits. So instead of byte addresses,
3231 the D10V uses word addresses---byte addresses shifted right two bits---to
3232 refer to code. Thus, the D10V can use 16-bit words to address 256kb of
3235 However, this means that code pointers and data pointers have different
3236 forms on the D10V. The 16-bit word @code{0xC020} refers to byte address
3237 @code{0xC020} when used as a data address, but refers to byte address
3238 @code{0x30080} when used as a code address.
3240 (The D10V also uses separate code and data address spaces, which also
3241 affects the correspondence between pointers and addresses, but we're
3242 going to ignore that here; this example is already too long.)
3244 To cope with architectures like this---the D10V is not the only
3245 one!---@value{GDBN} tries to distinguish between @dfn{addresses}, which are
3246 byte numbers, and @dfn{pointers}, which are the target's representation
3247 of an address of a particular type of data. In the example above,
3248 @code{0xC020} is the pointer, which refers to one of the addresses
3249 @code{0xC020} or @code{0x30080}, depending on the type imposed upon it.
3250 @value{GDBN} provides functions for turning a pointer into an address
3251 and vice versa, in the appropriate way for the current architecture.
3253 Unfortunately, since addresses and pointers are identical on almost all
3254 processors, this distinction tends to bit-rot pretty quickly. Thus,
3255 each time you port @value{GDBN} to an architecture which does
3256 distinguish between pointers and addresses, you'll probably need to
3257 clean up some architecture-independent code.
3259 Here are functions which convert between pointers and addresses:
3261 @deftypefun CORE_ADDR extract_typed_address (void *@var{buf}, struct type *@var{type})
3262 Treat the bytes at @var{buf} as a pointer or reference of type
3263 @var{type}, and return the address it represents, in a manner
3264 appropriate for the current architecture. This yields an address
3265 @value{GDBN} can use to read target memory, disassemble, etc. Note that
3266 @var{buf} refers to a buffer in @value{GDBN}'s memory, not the
3269 For example, if the current architecture is the Intel x86, this function
3270 extracts a little-endian integer of the appropriate length from
3271 @var{buf} and returns it. However, if the current architecture is the
3272 D10V, this function will return a 16-bit integer extracted from
3273 @var{buf}, multiplied by four if @var{type} is a pointer to a function.
3275 If @var{type} is not a pointer or reference type, then this function
3276 will signal an internal error.
3279 @deftypefun CORE_ADDR store_typed_address (void *@var{buf}, struct type *@var{type}, CORE_ADDR @var{addr})
3280 Store the address @var{addr} in @var{buf}, in the proper format for a
3281 pointer of type @var{type} in the current architecture. Note that
3282 @var{buf} refers to a buffer in @value{GDBN}'s memory, not the
3285 For example, if the current architecture is the Intel x86, this function
3286 stores @var{addr} unmodified as a little-endian integer of the
3287 appropriate length in @var{buf}. However, if the current architecture
3288 is the D10V, this function divides @var{addr} by four if @var{type} is
3289 a pointer to a function, and then stores it in @var{buf}.
3291 If @var{type} is not a pointer or reference type, then this function
3292 will signal an internal error.
3295 @deftypefun CORE_ADDR value_as_address (struct value *@var{val})
3296 Assuming that @var{val} is a pointer, return the address it represents,
3297 as appropriate for the current architecture.
3299 This function actually works on integral values, as well as pointers.
3300 For pointers, it performs architecture-specific conversions as
3301 described above for @code{extract_typed_address}.
3304 @deftypefun CORE_ADDR value_from_pointer (struct type *@var{type}, CORE_ADDR @var{addr})
3305 Create and return a value representing a pointer of type @var{type} to
3306 the address @var{addr}, as appropriate for the current architecture.
3307 This function performs architecture-specific conversions as described
3308 above for @code{store_typed_address}.
3311 Here are two functions which architectures can define to indicate the
3312 relationship between pointers and addresses. These have default
3313 definitions, appropriate for architectures on which all pointers are
3314 simple unsigned byte addresses.
3316 @deftypefun CORE_ADDR gdbarch_pointer_to_address (struct gdbarch *@var{current_gdbarch}, struct type *@var{type}, char *@var{buf})
3317 Assume that @var{buf} holds a pointer of type @var{type}, in the
3318 appropriate format for the current architecture. Return the byte
3319 address the pointer refers to.
3321 This function may safely assume that @var{type} is either a pointer or a
3322 C@t{++} reference type.
3325 @deftypefun void gdbarch_address_to_pointer (struct gdbarch *@var{current_gdbarch}, struct type *@var{type}, char *@var{buf}, CORE_ADDR @var{addr})
3326 Store in @var{buf} a pointer of type @var{type} representing the address
3327 @var{addr}, in the appropriate format for the current architecture.
3329 This function may safely assume that @var{type} is either a pointer or a
3330 C@t{++} reference type.
3333 @node Address Classes
3334 @section Address Classes
3335 @cindex address classes
3336 @cindex DW_AT_byte_size
3337 @cindex DW_AT_address_class
3339 Sometimes information about different kinds of addresses is available
3340 via the debug information. For example, some programming environments
3341 define addresses of several different sizes. If the debug information
3342 distinguishes these kinds of address classes through either the size
3343 info (e.g, @code{DW_AT_byte_size} in @w{DWARF 2}) or through an explicit
3344 address class attribute (e.g, @code{DW_AT_address_class} in @w{DWARF 2}), the
3345 following macros should be defined in order to disambiguate these
3346 types within @value{GDBN} as well as provide the added information to
3347 a @value{GDBN} user when printing type expressions.
3349 @deftypefun int gdbarch_address_class_type_flags (struct gdbarch *@var{current_gdbarch}, int @var{byte_size}, int @var{dwarf2_addr_class})
3350 Returns the type flags needed to construct a pointer type whose size
3351 is @var{byte_size} and whose address class is @var{dwarf2_addr_class}.
3352 This function is normally called from within a symbol reader. See
3353 @file{dwarf2read.c}.
3356 @deftypefun {char *} gdbarch_address_class_type_flags_to_name (struct gdbarch *@var{current_gdbarch}, int @var{type_flags})
3357 Given the type flags representing an address class qualifier, return
3360 @deftypefun int gdbarch_address_class_name_to_type_flags (struct gdbarch *@var{current_gdbarch}, int @var{name}, int *@var{type_flags_ptr})
3361 Given an address qualifier name, set the @code{int} referenced by @var{type_flags_ptr} to the type flags
3362 for that address class qualifier.
3365 Since the need for address classes is rather rare, none of
3366 the address class functions are defined by default. Predicate
3367 functions are provided to detect when they are defined.
3369 Consider a hypothetical architecture in which addresses are normally
3370 32-bits wide, but 16-bit addresses are also supported. Furthermore,
3371 suppose that the @w{DWARF 2} information for this architecture simply
3372 uses a @code{DW_AT_byte_size} value of 2 to indicate the use of one
3373 of these "short" pointers. The following functions could be defined
3374 to implement the address class functions:
3377 somearch_address_class_type_flags (int byte_size,
3378 int dwarf2_addr_class)
3381 return TYPE_FLAG_ADDRESS_CLASS_1;
3387 somearch_address_class_type_flags_to_name (int type_flags)
3389 if (type_flags & TYPE_FLAG_ADDRESS_CLASS_1)
3396 somearch_address_class_name_to_type_flags (char *name,
3397 int *type_flags_ptr)
3399 if (strcmp (name, "short") == 0)
3401 *type_flags_ptr = TYPE_FLAG_ADDRESS_CLASS_1;
3409 The qualifier @code{@@short} is used in @value{GDBN}'s type expressions
3410 to indicate the presence of one of these ``short'' pointers. For
3411 example if the debug information indicates that @code{short_ptr_var} is
3412 one of these short pointers, @value{GDBN} might show the following
3416 (gdb) ptype short_ptr_var
3417 type = int * @@short
3421 @node Register Representation
3422 @section Register Representation
3425 * Raw and Cooked Registers::
3426 * Register Architecture Functions & Variables::
3427 * Register Information Functions::
3428 * Register and Memory Data::
3429 * Register Caching::
3432 @node Raw and Cooked Registers
3433 @subsection Raw and Cooked Registers
3434 @cindex raw register representation
3435 @cindex cooked register representation
3436 @cindex representations, raw and cooked registers
3438 @value{GDBN} considers registers to be a set with members numbered
3439 linearly from 0 upwards. The first part of that set corresponds to real
3440 physical registers, the second part to any @dfn{pseudo-registers}.
3441 Pseudo-registers have no independent physical existence, but are useful
3442 representations of information within the architecture. For example the
3443 OpenRISC 1000 architecture has up to 32 general purpose registers, which
3444 are typically represented as 32-bit (or 64-bit) integers. However the
3445 GPRs are also used as operands to the floating point operations, and it
3446 could be convenient to define a set of pseudo-registers, to show the
3447 GPRs represented as floating point values.
3449 For any architecture, the implementer will decide on a mapping from
3450 hardware to @value{GDBN} register numbers. The registers corresponding to real
3451 hardware are referred to as @dfn{raw} registers, the remaining registers are
3452 @dfn{pseudo-registers}. The total register set (raw and pseudo) is called
3453 the @dfn{cooked} register set.
3456 @node Register Architecture Functions & Variables
3457 @subsection Functions and Variables Specifying the Register Architecture
3458 @cindex @code{gdbarch} register architecture functions
3460 These @code{struct gdbarch} functions and variables specify the number
3461 and type of registers in the architecture.
3463 @deftypefn {Architecture Function} CORE_ADDR read_pc (struct regcache *@var{regcache})
3465 @deftypefn {Architecture Function} void write_pc (struct regcache *@var{regcache}, CORE_ADDR @var{val})
3467 Read or write the program counter. The default value of both
3468 functions is @code{NULL} (no function available). If the program
3469 counter is just an ordinary register, it can be specified in
3470 @code{struct gdbarch} instead (see @code{pc_regnum} below) and it will
3471 be read or written using the standard routines to access registers. This
3472 function need only be specified if the program counter is not an
3475 Any register information can be obtained using the supplied register
3476 cache, @var{regcache}. @xref{Register Caching, , Register Caching}.
3480 @deftypefn {Architecture Function} void pseudo_register_read (struct gdbarch *@var{gdbarch}, struct regcache *@var{regcache}, int @var{regnum}, const gdb_byte *@var{buf})
3482 @deftypefn {Architecture Function} void pseudo_register_write (struct gdbarch *@var{gdbarch}, struct regcache *@var{regcache}, int @var{regnum}, const gdb_byte *@var{buf})
3484 These functions should be defined if there are any pseudo-registers.
3485 The default value is @code{NULL}. @var{regnum} is the number of the
3486 register to read or write (which will be a @dfn{cooked} register
3487 number) and @var{buf} is the buffer where the value read will be
3488 placed, or from which the value to be written will be taken. The
3489 value in the buffer may be converted to or from a signed or unsigned
3490 integral value using one of the utility functions (@pxref{Register and
3491 Memory Data, , Using Different Register and Memory Data
3494 The access should be for the specified architecture,
3495 @var{gdbarch}. Any register information can be obtained using the
3496 supplied register cache, @var{regcache}. @xref{Register Caching, ,
3501 @deftypevr {Architecture Variable} int sp_regnum
3503 @cindex stack pointer
3506 This specifies the register holding the stack pointer, which may be a
3507 raw or pseudo-register. It defaults to -1 (not defined), but it is an
3508 error for it not to be defined.
3510 The value of the stack pointer register can be accessed withing
3511 @value{GDBN} as the variable @kbd{$sp}.
3515 @deftypevr {Architecture Variable} int pc_regnum
3517 @cindex program counter
3520 This specifies the register holding the program counter, which may be a
3521 raw or pseudo-register. It defaults to -1 (not defined). If
3522 @code{pc_regnum} is not defined, then the functions @code{read_pc} and
3523 @code{write_pc} (see above) must be defined.
3525 The value of the program counter (whether defined as a register, or
3526 through @code{read_pc} and @code{write_pc}) can be accessed withing
3527 @value{GDBN} as the variable @kbd{$pc}.
3531 @deftypevr {Architecture Variable} int ps_regnum
3533 @cindex processor status register
3534 @cindex status register
3537 This specifies the register holding the processor status (often called
3538 the status register), which may be a raw or pseudo-register. It
3539 defaults to -1 (not defined).
3541 If defined, the value of this register can be accessed withing
3542 @value{GDBN} as the variable @kbd{$ps}.
3546 @deftypevr {Architecture Variable} int fp0_regnum
3548 @cindex first floating point register
3550 This specifies the first floating point register. It defaults to
3551 0. @code{fp0_regnum} is not needed unless the target offers support
3556 @node Register Information Functions
3557 @subsection Functions Giving Register Information
3558 @cindex @code{gdbarch} register information functions
3560 These functions return information about registers.
3562 @deftypefn {Architecture Function} {const char *} register_name (struct gdbarch *@var{gdbarch}, int @var{regnum})
3564 This function should convert a register number (raw or pseudo) to a
3565 register name (as a C @code{const char *}). This is used both to
3566 determine the name of a register for output and to work out the meaning
3567 of any register names used as input. The function may also return
3568 @code{NULL}, to indicate that @var{regnum} is not a valid register.
3570 For example with the OpenRISC 1000, @value{GDBN} registers 0-31 are the
3571 General Purpose Registers, register 32 is the program counter and
3572 register 33 is the supervision register (i.e.@: the processor status
3573 register), which map to the strings @code{"gpr00"} through
3574 @code{"gpr31"}, @code{"pc"} and @code{"sr"} respectively. This means
3575 that the @value{GDBN} command @kbd{print $gpr5} should print the value of
3576 the OR1K general purpose register 5@footnote{
3577 @cindex frame pointer
3579 Historically, @value{GDBN} always had a concept of a frame pointer
3580 register, which could be accessed via the @value{GDBN} variable,
3581 @kbd{$fp}. That concept is now deprecated, recognizing that not all
3582 architectures have a frame pointer. However if an architecture does
3583 have a frame pointer register, and defines a register or
3584 pseudo-register with the name @code{"fp"}, then that register will be
3585 used as the value of the @kbd{$fp} variable.}.
3587 The default value for this function is @code{NULL}, meaning
3588 undefined. It should always be defined.
3590 The access should be for the specified architecture, @var{gdbarch}.
3594 @deftypefn {Architecture Function} {struct type *} register_type (struct gdbarch *@var{gdbarch}, int @var{regnum})
3596 Given a register number, this function identifies the type of data it
3597 may be holding, specified as a @code{struct type}. @value{GDBN} allows
3598 creation of arbitrary types, but a number of built in types are
3599 provided (@code{builtin_type_void}, @code{builtin_type_int32} etc),
3600 together with functions to derive types from these.
3602 Typically the program counter will have a type of ``pointer to
3603 function'' (it points to code), the frame pointer and stack pointer
3604 will have types of ``pointer to void'' (they point to data on the stack)
3605 and all other integer registers will have a type of 32-bit integer or
3608 This information guides the formatting when displaying register
3609 information. The default value is @code{NULL} meaning no information is
3610 available to guide formatting when displaying registers.
3614 @deftypefn {Architecture Function} void print_registers_info (struct gdbarch *@var{gdbarch}, struct ui_file *@var{file}, struct frame_info *@var{frame}, int @var{regnum}, int @var{all})
3616 Define this function to print out one or all of the registers for the
3617 @value{GDBN} @kbd{info registers} command. The default value is the
3618 function @code{default_print_registers_info}, which uses the register
3619 type information (see @code{register_type} above) to determine how each
3620 register should be printed. Define a custom version of this function
3621 for fuller control over how the registers are displayed.
3623 The access should be for the specified architecture, @var{gdbarch},
3624 with output to the the file specified by the User Interface
3625 Independent Output file handle, @var{file} (@pxref{UI-Independent
3626 Output, , UI-Independent Output---the @code{ui_out}
3629 The registers should show their values in the frame specified by
3630 @var{frame}. If @var{regnum} is -1 and @var{all} is zero, then all
3631 the ``significant'' registers should be shown (the implementer should
3632 decide which registers are ``significant''). Otherwise only the value of
3633 the register specified by @var{regnum} should be output. If
3634 @var{regnum} is -1 and @var{all} is non-zero (true), then the value of
3635 all registers should be shown.
3637 By default @code{default_print_registers_info} prints one register per
3638 line, and if @var{all} is zero omits floating-point registers.
3642 @deftypefn {Architecture Function} void print_float_info (struct gdbarch *@var{gdbarch}, struct ui_file *@var{file}, struct frame_info *@var{frame}, const char *@var{args})
3644 Define this function to provide output about the floating point unit and
3645 registers for the @value{GDBN} @kbd{info float} command respectively.
3646 The default value is @code{NULL} (not defined), meaning no information
3649 The @var{gdbarch} and @var{file} and @var{frame} arguments have the same
3650 meaning as in the @code{print_registers_info} function above. The string
3651 @var{args} contains any supplementary arguments to the @kbd{info float}
3654 Define this function if the target supports floating point operations.
3658 @deftypefn {Architecture Function} void print_vector_info (struct gdbarch *@var{gdbarch}, struct ui_file *@var{file}, struct frame_info *@var{frame}, const char *@var{args})
3660 Define this function to provide output about the vector unit and
3661 registers for the @value{GDBN} @kbd{info vector} command respectively.
3662 The default value is @code{NULL} (not defined), meaning no information
3665 The @var{gdbarch}, @var{file} and @var{frame} arguments have the
3666 same meaning as in the @code{print_registers_info} function above. The
3667 string @var{args} contains any supplementary arguments to the @kbd{info
3670 Define this function if the target supports vector operations.
3674 @deftypefn {Architecture Function} int register_reggroup_p (struct gdbarch *@var{gdbarch}, int @var{regnum}, struct reggroup *@var{group})
3676 @value{GDBN} groups registers into different categories (general,
3677 vector, floating point etc). This function, given a register,
3678 @var{regnum}, and group, @var{group}, returns 1 (true) if the register
3679 is in the group and 0 (false) otherwise.
3681 The information should be for the specified architecture,
3684 The default value is the function @code{default_register_reggroup_p}
3685 which will do a reasonable job based on the type of the register (see
3686 the function @code{register_type} above), with groups for general
3687 purpose registers, floating point registers, vector registers and raw
3688 (i.e not pseudo) registers.
3692 @node Register and Memory Data
3693 @subsection Using Different Register and Memory Data Representations
3694 @cindex register representation
3695 @cindex memory representation
3696 @cindex representations, register and memory
3697 @cindex register data formats, converting
3698 @cindex @code{struct value}, converting register contents to
3700 Some architectures have different representations of data objects,
3701 depending whether the object is held in a register or memory. For
3707 The Alpha architecture can represent 32 bit integer values in
3708 floating-point registers.
3711 The x86 architecture supports 80-bit floating-point registers. The
3712 @code{long double} data type occupies 96 bits in memory but only 80
3713 bits when stored in a register.
3717 In general, the register representation of a data type is determined by
3718 the architecture, or @value{GDBN}'s interface to the architecture, while
3719 the memory representation is determined by the Application Binary
3722 For almost all data types on almost all architectures, the two
3723 representations are identical, and no special handling is needed.
3724 However, they do occasionally differ. An architecture may define the
3725 following @code{struct gdbarch} functions to request conversions
3726 between the register and memory representations of a data type:
3728 @deftypefn {Architecture Function} int gdbarch_convert_register_p (struct gdbarch *@var{gdbarch}, int @var{reg})
3730 Return non-zero (true) if the representation of a data value stored in
3731 this register may be different to the representation of that same data
3732 value when stored in memory. The default value is @code{NULL}
3735 If this function is defined and returns non-zero, the @code{struct
3736 gdbarch} functions @code{gdbarch_register_to_value} and
3737 @code{gdbarch_value_to_register} (see below) should be used to perform
3738 any necessary conversion.
3740 If defined, this function should return zero for the register's native
3741 type, when no conversion is necessary.
3744 @deftypefn {Architecture Function} void gdbarch_register_to_value (struct gdbarch *@var{gdbarch}, int @var{reg}, struct type *@var{type}, char *@var{from}, char *@var{to})
3746 Convert the value of register number @var{reg} to a data object of
3747 type @var{type}. The buffer at @var{from} holds the register's value
3748 in raw format; the converted value should be placed in the buffer at
3752 @emph{Note:} @code{gdbarch_register_to_value} and
3753 @code{gdbarch_value_to_register} take their @var{reg} and @var{type}
3754 arguments in different orders.
3757 @code{gdbarch_register_to_value} should only be used with registers
3758 for which the @code{gdbarch_convert_register_p} function returns a
3763 @deftypefn {Architecture Function} void gdbarch_value_to_register (struct gdbarch *@var{gdbarch}, struct type *@var{type}, int @var{reg}, char *@var{from}, char *@var{to})
3765 Convert a data value of type @var{type} to register number @var{reg}'
3769 @emph{Note:} @code{gdbarch_register_to_value} and
3770 @code{gdbarch_value_to_register} take their @var{reg} and @var{type}
3771 arguments in different orders.
3774 @code{gdbarch_value_to_register} should only be used with registers
3775 for which the @code{gdbarch_convert_register_p} function returns a
3780 @node Register Caching
3781 @subsection Register Caching
3782 @cindex register caching
3784 Caching of registers is used, so that the target does not need to be
3785 accessed and reanalyzed multiple times for each register in
3786 circumstances where the register value cannot have changed.
3788 @cindex @code{struct regcache}
3789 @value{GDBN} provides @code{struct regcache}, associated with a
3790 particular @code{struct gdbarch} to hold the cached values of the raw
3791 registers. A set of functions is provided to access both the raw
3792 registers (with @code{raw} in their name) and the full set of cooked
3793 registers (with @code{cooked} in their name). Functions are provided
3794 to ensure the register cache is kept synchronized with the values of
3795 the actual registers in the target.
3797 Accessing registers through the @code{struct regcache} routines will
3798 ensure that the appropriate @code{struct gdbarch} functions are called
3799 when necessary to access the underlying target architecture. In general
3800 users should use the @dfn{cooked} functions, since these will map to the
3801 @dfn{raw} functions automatically as appropriate.
3803 @findex regcache_cooked_read
3804 @findex regcache_cooked_write
3805 @cindex @code{gdb_byte}
3806 @findex regcache_cooked_read_signed
3807 @findex regcache_cooked_read_unsigned
3808 @findex regcache_cooked_write_signed
3809 @findex regcache_cooked_write_unsigned
3810 The two key functions are @code{regcache_cooked_read} and
3811 @code{regcache_cooked_write} which read or write a register from or to
3812 a byte buffer (type @code{gdb_byte *}). For convenience the wrapper
3813 functions @code{regcache_cooked_read_signed},
3814 @code{regcache_cooked_read_unsigned},
3815 @code{regcache_cooked_write_signed} and
3816 @code{regcache_cooked_write_unsigned} are provided, which read or
3817 write the value using the buffer and convert to or from an integral
3818 value as appropriate.
3820 @node Frame Interpretation
3821 @section Frame Interpretation
3824 * All About Stack Frames::
3825 * Frame Handling Terminology::
3827 * Functions and Variable to Analyze Frames::
3828 * Functions to Access Frame Data::
3829 * Analyzing Stacks---Frame Sniffers::
3832 @node All About Stack Frames
3833 @subsection All About Stack Frames
3835 @value{GDBN} needs to understand the stack on which local (automatic)
3836 variables are stored. The area of the stack containing all the local
3837 variables for a function invocation is known as the @dfn{stack frame}
3838 for that function (or colloquially just as the @dfn{frame}). In turn the
3839 function that called the function will have its stack frame, and so on
3840 back through the chain of functions that have been called.
3842 Almost all architectures have one register dedicated to point to the
3843 end of the stack (the @dfn{stack pointer}). Many have a second register
3844 which points to the start of the currently active stack frame (the
3845 @dfn{frame pointer}). The specific arrangements for an architecture are
3846 a key part of the ABI.
3848 A diagram helps to explain this. Here is a simple program to compute
3861 return n * fact (n - 1);
3869 for (i = 0; i < 10; i++)
3872 printf ("%d! = %d\n", i, f);
3877 Consider the state of the stack when the code reaches line 6 after the
3878 main program has called @code{fact@w{ }(3)}. The chain of function
3879 calls will be @code{main ()}, @code{fact@w{ }(3)}, @code{fact@w{
3880 }(2)}, @code{@w{fact (1)}} and @code{fact@w{ }(0)}.
3882 In this illustration the stack is falling (as used for example by the
3883 OpenRISC 1000 ABI). The stack pointer (SP) is at the end of the stack
3884 (lowest address) and the frame pointer (FP) is at the highest address
3885 in the current stack frame. The following diagram shows how the stack
3888 @center @image{stack_frame,14cm}
3890 In each stack frame, offset 0 from the stack pointer is the frame
3891 pointer of the previous frame and offset 4 (this is illustrating a
3892 32-bit architecture) from the stack pointer is the return address.
3893 Local variables are indexed from the frame pointer, with negative
3894 indexes. In the function @code{fact}, offset -4 from the frame
3895 pointer is the argument @var{n}. In the @code{main} function, offset
3896 -4 from the frame pointer is the local variable @var{i} and offset -8
3897 from the frame pointer is the local variable @var{f}@footnote{This is
3898 a simplified example for illustrative purposes only. Good optimizing
3899 compilers would not put anything on the stack for such simple
3900 functions. Indeed they might eliminate the recursion and use of the
3903 It is very easy to get confused when examining stacks. @value{GDBN}
3904 has terminology it uses rigorously throughout. The stack frame of the
3905 function currently executing, or where execution stopped is numbered
3906 zero. In this example frame #0 is the stack frame of the call to
3907 @code{fact@w{ }(0)}. The stack frame of its calling function
3908 (@code{fact@w{ }(1)} in this case) is numbered #1 and so on back
3909 through the chain of calls.
3911 The main @value{GDBN} data structure describing frames is
3912 @code{@w{struct frame_info}}. It is not used directly, but only via
3913 its accessor functions. @code{frame_info} includes information about
3914 the registers in the frame and a pointer to the code of the function
3915 with which the frame is associated. The entire stack is represented as
3916 a linked list of @code{frame_info} structs.
3918 @node Frame Handling Terminology
3919 @subsection Frame Handling Terminology
3921 It is easy to get confused when referencing stack frames. @value{GDBN}
3922 uses some precise terminology.
3928 @cindex stack frame, definition of THIS frame
3929 @cindex frame, definition of THIS frame
3930 @dfn{THIS} frame is the frame currently under consideration.
3934 @cindex stack frame, definition of NEXT frame
3935 @cindex frame, definition of NEXT frame
3936 The @dfn{NEXT} frame, also sometimes called the inner or newer frame is the
3937 frame of the function called by the function of THIS frame.
3940 @cindex PREVIOUS frame
3941 @cindex stack frame, definition of PREVIOUS frame
3942 @cindex frame, definition of PREVIOUS frame
3943 The @dfn{PREVIOUS} frame, also sometimes called the outer or older frame is
3944 the frame of the function which called the function of THIS frame.
3948 So in the example in the previous section (@pxref{All About Stack
3949 Frames, , All About Stack Frames}), if THIS frame is #3 (the call to
3950 @code{fact@w{ }(3)}), the NEXT frame is frame #2 (the call to
3951 @code{fact@w{ }(2)}) and the PREVIOUS frame is frame #4 (the call to
3952 @code{main@w{ }()}).
3954 @cindex innermost frame
3955 @cindex stack frame, definition of innermost frame
3956 @cindex frame, definition of innermost frame
3957 The @dfn{innermost} frame is the frame of the current executing
3958 function, or where the program stopped, in this example, in the middle
3959 of the call to @code{@w{fact (0))}}. It is always numbered frame #0.
3961 @cindex base of a frame
3962 @cindex stack frame, definition of base of a frame
3963 @cindex frame, definition of base of a frame
3964 The @dfn{base} of a frame is the address immediately before the start
3965 of the NEXT frame. For a stack which grows down in memory (a
3966 @dfn{falling} stack) this will be the lowest address and for a stack
3967 which grows up in memory (a @dfn{rising} stack) this will be the
3968 highest address in the frame.
3970 @value{GDBN} functions to analyze the stack are typically given a
3971 pointer to the NEXT frame to determine information about THIS
3972 frame. Information about THIS frame includes data on where the
3973 registers of the PREVIOUS frame are stored in this stack frame. In
3974 this example the frame pointer of the PREVIOUS frame is stored at
3975 offset 0 from the stack pointer of THIS frame.
3978 @cindex stack frame, definition of unwinding
3979 @cindex frame, definition of unwinding
3980 The process whereby a function is given a pointer to the NEXT
3981 frame to work out information about THIS frame is referred to as
3982 @dfn{unwinding}. The @value{GDBN} functions involved in this typically
3983 include unwind in their name.
3986 @cindex stack frame, definition of sniffing
3987 @cindex frame, definition of sniffing
3988 The process of analyzing a target to determine the information that
3989 should go in struct frame_info is called @dfn{sniffing}. The functions
3990 that carry this out are called sniffers and typically include sniffer
3991 in their name. More than one sniffer may be required to extract all
3992 the information for a particular frame.
3994 @cindex sentinel frame
3995 @cindex stack frame, definition of sentinel frame
3996 @cindex frame, definition of sentinel frame
3997 Because so many functions work using the NEXT frame, there is an issue
3998 about addressing the innermost frame---it has no NEXT frame. To solve
3999 this @value{GDBN} creates a dummy frame #-1, known as the
4000 @dfn{sentinel} frame.
4002 @node Prologue Caches
4003 @subsection Prologue Caches
4005 @cindex function prologue
4006 @cindex prologue of a function
4007 All the frame sniffing functions typically examine the code at the
4008 start of the corresponding function, to determine the state of
4009 registers. The ABI will save old values and set new values of key
4010 registers at the start of each function in what is known as the
4011 function @dfn{prologue}.
4013 @cindex prologue cache
4014 For any particular stack frame this data does not change, so all the
4015 standard unwinding functions, in addition to receiving a pointer to
4016 the NEXT frame as their first argument, receive a pointer to a
4017 @dfn{prologue cache} as their second argument. This can be used to store
4018 values associated with a particular frame, for reuse on subsequent
4019 calls involving the same frame.
4021 It is up to the user to define the structure used (it is a
4022 @code{void@w{ }*} pointer) and arrange allocation and deallocation of
4023 storage. However for general use, @value{GDBN} provides
4024 @code{@w{struct trad_frame_cache}}, with a set of accessor
4025 routines. This structure holds the stack and code address of
4026 THIS frame, the base address of the frame, a pointer to the
4027 struct @code{frame_info} for the NEXT frame and details of
4028 where the registers of the PREVIOUS frame may be found in THIS
4031 Typically the first time any sniffer function is called with NEXT
4032 frame, the prologue sniffer for THIS frame will be @code{NULL}. The
4033 sniffer will analyze the frame, allocate a prologue cache structure
4034 and populate it. Subsequent calls using the same NEXT frame will
4035 pass in this prologue cache, so the data can be returned with no
4036 additional analysis.
4038 @node Functions and Variable to Analyze Frames
4039 @subsection Functions and Variable to Analyze Frames
4041 These struct @code{gdbarch} functions and variable should be defined
4042 to provide analysis of the stack frame and allow it to be adjusted as
4045 @deftypefn {Architecture Function} CORE_ADDR skip_prologue (struct gdbarch *@var{gdbarch}, CORE_ADDR @var{pc})
4047 The prologue of a function is the code at the beginning of the
4048 function which sets up the stack frame, saves the return address
4049 etc. The code representing the behavior of the function starts after
4052 This function skips past the prologue of a function if the program
4053 counter, @var{pc}, is within the prologue of a function. The result is
4054 the program counter immediately after the prologue. With modern
4055 optimizing compilers, this may be a far from trivial exercise. However
4056 the required information may be within the binary as DWARF2 debugging
4057 information, making the job much easier.
4059 The default value is @code{NULL} (not defined). This function should always
4060 be provided, but can take advantage of DWARF2 debugging information,
4061 if that is available.
4065 @deftypefn {Architecture Function} int inner_than (CORE_ADDR @var{lhs}, CORE_ADDR @var{rhs})
4066 @findex core_addr_lessthan
4067 @findex core_addr_greaterthan
4069 Given two frame or stack pointers, return non-zero (true) if the first
4070 represents the @dfn{inner} stack frame and 0 (false) otherwise. This
4071 is used to determine whether the target has a stack which grows up in
4072 memory (rising stack) or grows down in memory (falling stack).
4073 @xref{All About Stack Frames, , All About Stack Frames}, for an
4074 explanation of @dfn{inner} frames.
4076 The default value of this function is @code{NULL} and it should always
4077 be defined. However for almost all architectures one of the built-in
4078 functions can be used: @code{core_addr_lessthan} (for stacks growing
4079 down in memory) or @code{core_addr_greaterthan} (for stacks growing up
4084 @anchor{frame_align}
4085 @deftypefn {Architecture Function} CORE_ADDR frame_align (struct gdbarch *@var{gdbarch}, CORE_ADDR @var{address})
4089 The architecture may have constraints on how its frames are
4090 aligned. For example the OpenRISC 1000 ABI requires stack frames to be
4091 double-word aligned, but 32-bit versions of the architecture allocate
4092 single-word values to the stack. Thus extra padding may be needed at
4093 the end of a stack frame.
4095 Given a proposed address for the stack pointer, this function
4096 returns a suitably aligned address (by expanding the stack frame).
4098 The default value is @code{NULL} (undefined). This function should be defined
4099 for any architecture where it is possible the stack could become
4100 misaligned. The utility functions @code{align_down} (for falling
4101 stacks) and @code{align_up} (for rising stacks) will facilitate the
4102 implementation of this function.
4106 @deftypevr {Architecture Variable} int frame_red_zone_size
4108 Some ABIs reserve space beyond the end of the stack for use by leaf
4109 functions without prologue or epilogue or by exception handlers (for
4110 example the OpenRISC 1000).
4112 This is known as a @dfn{red zone} (AMD terminology). The @sc{amd64}
4113 (nee x86-64) ABI documentation refers to the @dfn{red zone} when
4114 describing this scratch area.
4116 The default value is 0. Set this field if the architecture has such a
4117 red zone. The value must be aligned as required by the ABI (see
4118 @code{frame_align} above for an explanation of stack frame alignment).
4122 @node Functions to Access Frame Data
4123 @subsection Functions to Access Frame Data
4125 These functions provide access to key registers and arguments in the
4128 @deftypefn {Architecture Function} CORE_ADDR unwind_pc (struct gdbarch *@var{gdbarch}, struct frame_info *@var{next_frame})
4130 This function is given a pointer to the NEXT stack frame (@pxref{All
4131 About Stack Frames, , All About Stack Frames}, for how frames are
4132 represented) and returns the value of the program counter in the
4133 PREVIOUS frame (i.e.@: the frame of the function that called THIS
4134 one). This is commonly referred to as the @dfn{return address}.
4136 The implementation, which must be frame agnostic (work with any frame),
4137 is typically no more than:
4141 pc = frame_unwind_register_unsigned (next_frame, @var{ARCH}_PC_REGNUM);
4142 return gdbarch_addr_bits_remove (gdbarch, pc);
4147 @deftypefn {Architecture Function} CORE_ADDR unwind_sp (struct gdbarch *@var{gdbarch}, struct frame_info *@var{next_frame})
4149 This function is given a pointer to the NEXT stack frame
4150 (@pxref{All About Stack Frames, , All About Stack Frames} for how
4151 frames are represented) and returns the value of the stack pointer in
4152 the PREVIOUS frame (i.e.@: the frame of the function that called
4155 The implementation, which must be frame agnostic (work with any frame),
4156 is typically no more than:
4160 sp = frame_unwind_register_unsigned (next_frame, @var{ARCH}_SP_REGNUM);
4161 return gdbarch_addr_bits_remove (gdbarch, sp);
4166 @deftypefn {Architecture Function} int frame_num_args (struct gdbarch *@var{gdbarch}, struct frame_info *@var{this_frame})
4168 This function is given a pointer to THIS stack frame (@pxref{All
4169 About Stack Frames, , All About Stack Frames} for how frames are
4170 represented), and returns the number of arguments that are being
4171 passed, or -1 if not known.
4173 The default value is @code{NULL} (undefined), in which case the number of
4174 arguments passed on any stack frame is always unknown. For many
4175 architectures this will be a suitable default.
4179 @node Analyzing Stacks---Frame Sniffers
4180 @subsection Analyzing Stacks---Frame Sniffers
4182 When a program stops, @value{GDBN} needs to construct the chain of
4183 struct @code{frame_info} representing the state of the stack using
4184 appropriate @dfn{sniffers}.
4186 Each architecture requires appropriate sniffers, but they do not form
4187 entries in @code{@w{struct gdbarch}}, since more than one sniffer may
4188 be required and a sniffer may be suitable for more than one
4189 @code{@w{struct gdbarch}}. Instead sniffers are associated with
4190 architectures using the following functions.
4195 @findex frame_unwind_append_sniffer
4196 @code{frame_unwind_append_sniffer} is used to add a new sniffer to
4197 analyze THIS frame when given a pointer to the NEXT frame.
4200 @findex frame_base_append_sniffer
4201 @code{frame_base_append_sniffer} is used to add a new sniffer
4202 which can determine information about the base of a stack frame.
4205 @findex frame_base_set_default
4206 @code{frame_base_set_default} is used to specify the default base
4211 These functions all take a reference to @code{@w{struct gdbarch}}, so
4212 they are associated with a specific architecture. They are usually
4213 called in the @code{gdbarch} initialization function, after the
4214 @code{gdbarch} struct has been set up. Unless a default has been set, the
4215 most recently appended sniffer will be tried first.
4217 The main frame unwinding sniffer (as set by
4218 @code{frame_unwind_append_sniffer)} returns a structure specifying
4219 a set of sniffing functions:
4221 @cindex @code{frame_unwind}
4225 enum frame_type type;
4226 frame_this_id_ftype *this_id;
4227 frame_prev_register_ftype *prev_register;
4228 const struct frame_data *unwind_data;
4229 frame_sniffer_ftype *sniffer;
4230 frame_prev_pc_ftype *prev_pc;
4231 frame_dealloc_cache_ftype *dealloc_cache;
4235 The @code{type} field indicates the type of frame this sniffer can
4236 handle: normal, dummy (@pxref{Functions Creating Dummy Frames, ,
4237 Functions Creating Dummy Frames}), signal handler or sentinel. Signal
4238 handlers sometimes have their own simplified stack structure for
4239 efficiency, so may need their own handlers.
4241 The @code{unwind_data} field holds additional information which may be
4242 relevant to particular types of frame. For example it may hold
4243 additional information for signal handler frames.
4245 The remaining fields define functions that yield different types of
4246 information when given a pointer to the NEXT stack frame. Not all
4247 functions need be provided. If an entry is @code{NULL}, the next sniffer will
4253 @code{this_id} determines the stack pointer and function (code
4254 entry point) for THIS stack frame.
4257 @code{prev_register} determines where the values of registers for
4258 the PREVIOUS stack frame are stored in THIS stack frame.
4261 @code{sniffer} takes a look at THIS frame's registers to
4262 determine if this is the appropriate unwinder.
4265 @code{prev_pc} determines the program counter for THIS
4266 frame. Only needed if the program counter is not an ordinary register
4267 (@pxref{Register Architecture Functions & Variables,
4268 , Functions and Variables Specifying the Register Architecture}).
4271 @code{dealloc_cache} frees any additional memory associated with
4272 the prologue cache for this frame (@pxref{Prologue Caches, , Prologue
4277 In general it is only the @code{this_id} and @code{prev_register}
4278 fields that need be defined for custom sniffers.
4280 The frame base sniffer is much simpler. It is a @code{@w{struct
4281 frame_base}}, which refers to the corresponding @code{frame_unwind}
4282 struct and whose fields refer to functions yielding various addresses
4285 @cindex @code{frame_base}
4289 const struct frame_unwind *unwind;
4290 frame_this_base_ftype *this_base;
4291 frame_this_locals_ftype *this_locals;
4292 frame_this_args_ftype *this_args;
4296 All the functions referred to take a pointer to the NEXT frame as
4297 argument. The function referred to by @code{this_base} returns the
4298 base address of THIS frame, the function referred to by
4299 @code{this_locals} returns the base address of local variables in THIS
4300 frame and the function referred to by @code{this_args} returns the
4301 base address of the function arguments in this frame.
4303 As described above, the base address of a frame is the address
4304 immediately before the start of the NEXT frame. For a falling
4305 stack, this is the lowest address in the frame and for a rising stack
4306 it is the highest address in the frame. For most architectures the
4307 same address is also the base address for local variables and
4308 arguments, in which case the same function can be used for all three
4309 entries@footnote{It is worth noting that if it cannot be determined in any
4310 other way (for example by there being a register with the name
4311 @code{"fp"}), then the result of the @code{this_base} function will be
4312 used as the value of the frame pointer variable @kbd{$fp} in
4313 @value{GDBN}. This is very often not correct (for example with the
4314 OpenRISC 1000, this value is the stack pointer, @kbd{$sp}). In this
4315 case a register (raw or pseudo) with the name @code{"fp"} should be
4316 defined. It will be used in preference as the value of @kbd{$fp}.}.
4318 @node Inferior Call Setup
4319 @section Inferior Call Setup
4320 @cindex calls to the inferior
4323 * About Dummy Frames::
4324 * Functions Creating Dummy Frames::
4327 @node About Dummy Frames
4328 @subsection About Dummy Frames
4329 @cindex dummy frames
4331 @value{GDBN} can call functions in the target code (for example by
4332 using the @kbd{call} or @kbd{print} commands). These functions may be
4333 breakpointed, and it is essential that if a function does hit a
4334 breakpoint, commands like @kbd{backtrace} work correctly.
4336 This is achieved by making the stack look as though the function had
4337 been called from the point where @value{GDBN} had previously stopped.
4338 This requires that @value{GDBN} can set up stack frames appropriate for
4339 such function calls.
4341 @node Functions Creating Dummy Frames
4342 @subsection Functions Creating Dummy Frames
4344 The following functions provide the functionality to set up such
4345 @dfn{dummy} stack frames.
4347 @deftypefn {Architecture Function} CORE_ADDR push_dummy_call (struct gdbarch *@var{gdbarch}, struct value *@var{function}, struct regcache *@var{regcache}, CORE_ADDR @var{bp_addr}, int @var{nargs}, struct value **@var{args}, CORE_ADDR @var{sp}, int @var{struct_return}, CORE_ADDR @var{struct_addr})
4349 This function sets up a dummy stack frame for the function about to be
4350 called. @code{push_dummy_call} is given the arguments to be passed
4351 and must copy them into registers or push them on to the stack as
4352 appropriate for the ABI.
4354 @var{function} is a pointer to the function
4355 that will be called and @var{regcache} the register cache from which
4356 values should be obtained. @var{bp_addr} is the address to which the
4357 function should return (which is breakpointed, so @value{GDBN} can
4358 regain control, hence the name). @var{nargs} is the number of
4359 arguments to pass and @var{args} an array containing the argument
4360 values. @var{struct_return} is non-zero (true) if the function returns
4361 a structure, and if so @var{struct_addr} is the address in which the
4362 structure should be returned.
4364 After calling this function, @value{GDBN} will pass control to the
4365 target at the address of the function, which will find the stack and
4366 registers set up just as expected.
4368 The default value of this function is @code{NULL} (undefined). If the
4369 function is not defined, then @value{GDBN} will not allow the user to
4370 call functions within the target being debugged.
4374 @deftypefn {Architecture Function} {struct frame_id} unwind_dummy_id (struct gdbarch *@var{gdbarch}, struct frame_info *@var{next_frame})
4376 This is the inverse of @code{push_dummy_call} which restores the stack
4377 pointer and program counter after a call to evaluate a function using
4378 a dummy stack frame. The result is a @code{@w{struct frame_id}}, which
4379 contains the value of the stack pointer and program counter to be
4382 The NEXT frame pointer is provided as argument,
4383 @var{next_frame}. THIS frame is the frame of the dummy function,
4384 which can be unwound, to yield the required stack pointer and program
4385 counter from the PREVIOUS frame.
4387 The default value is @code{NULL} (undefined). If @code{push_dummy_call} is
4388 defined, then this function should also be defined.
4392 @deftypefn {Architecture Function} CORE_ADDR push_dummy_code (struct gdbarch *@var{gdbarch}, CORE_ADDR @var{sp}, CORE_ADDR @var{funaddr}, struct value **@var{args}, int @var{nargs}, struct type *@var{value_type}, CORE_ADDR *@var{real_pc}, CORE_ADDR *@var{bp_addr}, struct regcache *@var{regcache})
4394 If this function is not defined (its default value is @code{NULL}), a dummy
4395 call will use the entry point of the currently loaded code on the
4396 target as its return address. A temporary breakpoint will be set
4397 there, so the location must be writable and have room for a
4400 It is possible that this default is not suitable. It might not be
4401 writable (in ROM possibly), or the ABI might require code to be
4402 executed on return from a call to unwind the stack before the
4403 breakpoint is encountered.
4405 If either of these is the case, then push_dummy_code should be defined
4406 to push an instruction sequence onto the end of the stack to which the
4407 dummy call should return.
4409 The arguments are essentially the same as those to
4410 @code{push_dummy_call}. However the function is provided with the
4411 type of the function result, @var{value_type}, @var{bp_addr} is used
4412 to return a value (the address at which the breakpoint instruction
4413 should be inserted) and @var{real pc} is used to specify the resume
4414 address when starting the call sequence. The function should return
4415 the updated innermost stack address.
4418 @emph{Note:} This does require that code in the stack can be executed.
4419 Some Harvard architectures may not allow this.
4424 @node Adding support for debugging core files
4425 @section Adding support for debugging core files
4428 The prerequisite for adding core file support in @value{GDBN} is to have
4429 core file support in BFD.
4431 Once BFD support is available, writing the apropriate
4432 @code{regset_from_core_section} architecture function should be all
4433 that is needed in order to add support for core files in @value{GDBN}.
4435 @node Defining Other Architecture Features
4436 @section Defining Other Architecture Features
4438 This section describes other functions and values in @code{gdbarch},
4439 together with some useful macros, that you can use to define the
4440 target architecture.
4444 @item CORE_ADDR gdbarch_addr_bits_remove (@var{gdbarch}, @var{addr})
4445 @findex gdbarch_addr_bits_remove
4446 If a raw machine instruction address includes any bits that are not
4447 really part of the address, then this function is used to zero those bits in
4448 @var{addr}. This is only used for addresses of instructions, and even then not
4451 For example, the two low-order bits of the PC on the Hewlett-Packard PA
4452 2.0 architecture contain the privilege level of the corresponding
4453 instruction. Since instructions must always be aligned on four-byte
4454 boundaries, the processor masks out these bits to generate the actual
4455 address of the instruction. @code{gdbarch_addr_bits_remove} would then for
4456 example look like that:
4458 arch_addr_bits_remove (CORE_ADDR addr)
4460 return (addr &= ~0x3);
4464 @item int address_class_name_to_type_flags (@var{gdbarch}, @var{name}, @var{type_flags_ptr})
4465 @findex address_class_name_to_type_flags
4466 If @var{name} is a valid address class qualifier name, set the @code{int}
4467 referenced by @var{type_flags_ptr} to the mask representing the qualifier
4468 and return 1. If @var{name} is not a valid address class qualifier name,
4471 The value for @var{type_flags_ptr} should be one of
4472 @code{TYPE_FLAG_ADDRESS_CLASS_1}, @code{TYPE_FLAG_ADDRESS_CLASS_2}, or
4473 possibly some combination of these values or'd together.
4474 @xref{Target Architecture Definition, , Address Classes}.
4476 @item int address_class_name_to_type_flags_p (@var{gdbarch})
4477 @findex address_class_name_to_type_flags_p
4478 Predicate which indicates whether @code{address_class_name_to_type_flags}
4481 @item int gdbarch_address_class_type_flags (@var{gdbarch}, @var{byte_size}, @var{dwarf2_addr_class})
4482 @findex gdbarch_address_class_type_flags
4483 Given a pointers byte size (as described by the debug information) and
4484 the possible @code{DW_AT_address_class} value, return the type flags
4485 used by @value{GDBN} to represent this address class. The value
4486 returned should be one of @code{TYPE_FLAG_ADDRESS_CLASS_1},
4487 @code{TYPE_FLAG_ADDRESS_CLASS_2}, or possibly some combination of these
4488 values or'd together.
4489 @xref{Target Architecture Definition, , Address Classes}.
4491 @item int gdbarch_address_class_type_flags_p (@var{gdbarch})
4492 @findex gdbarch_address_class_type_flags_p
4493 Predicate which indicates whether @code{gdbarch_address_class_type_flags_p} has
4496 @item const char *gdbarch_address_class_type_flags_to_name (@var{gdbarch}, @var{type_flags})
4497 @findex gdbarch_address_class_type_flags_to_name
4498 Return the name of the address class qualifier associated with the type
4499 flags given by @var{type_flags}.
4501 @item int gdbarch_address_class_type_flags_to_name_p (@var{gdbarch})
4502 @findex gdbarch_address_class_type_flags_to_name_p
4503 Predicate which indicates whether @code{gdbarch_address_class_type_flags_to_name} has been defined.
4504 @xref{Target Architecture Definition, , Address Classes}.
4506 @item void gdbarch_address_to_pointer (@var{gdbarch}, @var{type}, @var{buf}, @var{addr})
4507 @findex gdbarch_address_to_pointer
4508 Store in @var{buf} a pointer of type @var{type} representing the address
4509 @var{addr}, in the appropriate format for the current architecture.
4510 This function may safely assume that @var{type} is either a pointer or a
4511 C@t{++} reference type.
4512 @xref{Target Architecture Definition, , Pointers Are Not Always Addresses}.
4514 @item int gdbarch_believe_pcc_promotion (@var{gdbarch})
4515 @findex gdbarch_believe_pcc_promotion
4516 Used to notify if the compiler promotes a @code{short} or @code{char}
4517 parameter to an @code{int}, but still reports the parameter as its
4518 original type, rather than the promoted type.
4520 @item gdbarch_bits_big_endian (@var{gdbarch})
4521 @findex gdbarch_bits_big_endian
4522 This is used if the numbering of bits in the targets does @strong{not} match
4523 the endianism of the target byte order. A value of 1 means that the bits
4524 are numbered in a big-endian bit order, 0 means little-endian.
4526 @item set_gdbarch_bits_big_endian (@var{gdbarch}, @var{bits_big_endian})
4527 @findex set_gdbarch_bits_big_endian
4528 Calling set_gdbarch_bits_big_endian with a value of 1 indicates that the
4529 bits in the target are numbered in a big-endian bit order, 0 indicates
4534 This is the character array initializer for the bit pattern to put into
4535 memory where a breakpoint is set. Although it's common to use a trap
4536 instruction for a breakpoint, it's not required; for instance, the bit
4537 pattern could be an invalid instruction. The breakpoint must be no
4538 longer than the shortest instruction of the architecture.
4540 @code{BREAKPOINT} has been deprecated in favor of
4541 @code{gdbarch_breakpoint_from_pc}.
4543 @item BIG_BREAKPOINT
4544 @itemx LITTLE_BREAKPOINT
4545 @findex LITTLE_BREAKPOINT
4546 @findex BIG_BREAKPOINT
4547 Similar to BREAKPOINT, but used for bi-endian targets.
4549 @code{BIG_BREAKPOINT} and @code{LITTLE_BREAKPOINT} have been deprecated in
4550 favor of @code{gdbarch_breakpoint_from_pc}.
4552 @item const gdb_byte *gdbarch_breakpoint_from_pc (@var{gdbarch}, @var{pcptr}, @var{lenptr})
4553 @findex gdbarch_breakpoint_from_pc
4554 @anchor{gdbarch_breakpoint_from_pc} Use the program counter to determine the
4555 contents and size of a breakpoint instruction. It returns a pointer to
4556 a static string of bytes that encode a breakpoint instruction, stores the
4557 length of the string to @code{*@var{lenptr}}, and adjusts the program
4558 counter (if necessary) to point to the actual memory location where the
4559 breakpoint should be inserted. May return @code{NULL} to indicate that
4560 software breakpoints are not supported.
4562 Although it is common to use a trap instruction for a breakpoint, it's
4563 not required; for instance, the bit pattern could be an invalid
4564 instruction. The breakpoint must be no longer than the shortest
4565 instruction of the architecture.
4567 Provided breakpoint bytes can be also used by @code{bp_loc_is_permanent} to
4568 detect permanent breakpoints. @code{gdbarch_breakpoint_from_pc} should return
4569 an unchanged memory copy if it was called for a location with permanent
4570 breakpoint as some architectures use breakpoint instructions containing
4571 arbitrary parameter value.
4573 Replaces all the other @var{BREAKPOINT} macros.
4575 @item int gdbarch_memory_insert_breakpoint (@var{gdbarch}, @var{bp_tgt})
4576 @itemx gdbarch_memory_remove_breakpoint (@var{gdbarch}, @var{bp_tgt})
4577 @findex gdbarch_memory_remove_breakpoint
4578 @findex gdbarch_memory_insert_breakpoint
4579 Insert or remove memory based breakpoints. Reasonable defaults
4580 (@code{default_memory_insert_breakpoint} and
4581 @code{default_memory_remove_breakpoint} respectively) have been
4582 provided so that it is not necessary to set these for most
4583 architectures. Architectures which may want to set
4584 @code{gdbarch_memory_insert_breakpoint} and @code{gdbarch_memory_remove_breakpoint} will likely have instructions that are oddly sized or are not stored in a
4585 conventional manner.
4587 It may also be desirable (from an efficiency standpoint) to define
4588 custom breakpoint insertion and removal routines if
4589 @code{gdbarch_breakpoint_from_pc} needs to read the target's memory for some
4592 @item CORE_ADDR gdbarch_adjust_breakpoint_address (@var{gdbarch}, @var{bpaddr})
4593 @findex gdbarch_adjust_breakpoint_address
4594 @cindex breakpoint address adjusted
4595 Given an address at which a breakpoint is desired, return a breakpoint
4596 address adjusted to account for architectural constraints on
4597 breakpoint placement. This method is not needed by most targets.
4599 The FR-V target (see @file{frv-tdep.c}) requires this method.
4600 The FR-V is a VLIW architecture in which a number of RISC-like
4601 instructions are grouped (packed) together into an aggregate
4602 instruction or instruction bundle. When the processor executes
4603 one of these bundles, the component instructions are executed
4606 In the course of optimization, the compiler may group instructions
4607 from distinct source statements into the same bundle. The line number
4608 information associated with one of the latter statements will likely
4609 refer to some instruction other than the first one in the bundle. So,
4610 if the user attempts to place a breakpoint on one of these latter
4611 statements, @value{GDBN} must be careful to @emph{not} place the break
4612 instruction on any instruction other than the first one in the bundle.
4613 (Remember though that the instructions within a bundle execute
4614 in parallel, so the @emph{first} instruction is the instruction
4615 at the lowest address and has nothing to do with execution order.)
4617 The FR-V's @code{gdbarch_adjust_breakpoint_address} method will adjust a
4618 breakpoint's address by scanning backwards for the beginning of
4619 the bundle, returning the address of the bundle.
4621 Since the adjustment of a breakpoint may significantly alter a user's
4622 expectation, @value{GDBN} prints a warning when an adjusted breakpoint
4623 is initially set and each time that that breakpoint is hit.
4625 @item int gdbarch_call_dummy_location (@var{gdbarch})
4626 @findex gdbarch_call_dummy_location
4627 See the file @file{inferior.h}.
4629 This method has been replaced by @code{gdbarch_push_dummy_code}
4630 (@pxref{gdbarch_push_dummy_code}).
4632 @item int gdbarch_cannot_fetch_register (@var{gdbarch}, @var{regum})
4633 @findex gdbarch_cannot_fetch_register
4634 This function should return nonzero if @var{regno} cannot be fetched
4635 from an inferior process.
4637 @item int gdbarch_cannot_store_register (@var{gdbarch}, @var{regnum})
4638 @findex gdbarch_cannot_store_register
4639 This function should return nonzero if @var{regno} should not be
4640 written to the target. This is often the case for program counters,
4641 status words, and other special registers. This function returns 0 as
4642 default so that @value{GDBN} will assume that all registers may be written.
4644 @item int gdbarch_convert_register_p (@var{gdbarch}, @var{regnum}, struct type *@var{type})
4645 @findex gdbarch_convert_register_p
4646 Return non-zero if register @var{regnum} represents data values of type
4647 @var{type} in a non-standard form.
4648 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
4650 @item int gdbarch_fp0_regnum (@var{gdbarch})
4651 @findex gdbarch_fp0_regnum
4652 This function returns the number of the first floating point register,
4653 if the machine has such registers. Otherwise, it returns -1.
4655 @item CORE_ADDR gdbarch_decr_pc_after_break (@var{gdbarch})
4656 @findex gdbarch_decr_pc_after_break
4657 This function shall return the amount by which to decrement the PC after the
4658 program encounters a breakpoint. This is often the number of bytes in
4659 @code{BREAKPOINT}, though not always. For most targets this value will be 0.
4661 @item DISABLE_UNSETTABLE_BREAK (@var{addr})
4662 @findex DISABLE_UNSETTABLE_BREAK
4663 If defined, this should evaluate to 1 if @var{addr} is in a shared
4664 library in which breakpoints cannot be set and so should be disabled.
4666 @item int gdbarch_dwarf2_reg_to_regnum (@var{gdbarch}, @var{dwarf2_regnr})
4667 @findex gdbarch_dwarf2_reg_to_regnum
4668 Convert DWARF2 register number @var{dwarf2_regnr} into @value{GDBN} regnum.
4669 If not defined, no conversion will be performed.
4671 @item int gdbarch_ecoff_reg_to_regnum (@var{gdbarch}, @var{ecoff_regnr})
4672 @findex gdbarch_ecoff_reg_to_regnum
4673 Convert ECOFF register number @var{ecoff_regnr} into @value{GDBN} regnum. If
4674 not defined, no conversion will be performed.
4676 @item GCC_COMPILED_FLAG_SYMBOL
4677 @itemx GCC2_COMPILED_FLAG_SYMBOL
4678 @findex GCC2_COMPILED_FLAG_SYMBOL
4679 @findex GCC_COMPILED_FLAG_SYMBOL
4680 If defined, these are the names of the symbols that @value{GDBN} will
4681 look for to detect that GCC compiled the file. The default symbols
4682 are @code{gcc_compiled.} and @code{gcc2_compiled.},
4683 respectively. (Currently only defined for the Delta 68.)
4685 @item gdbarch_get_longjmp_target
4686 @findex gdbarch_get_longjmp_target
4687 This function determines the target PC address that @code{longjmp}
4688 will jump to, assuming that we have just stopped at a @code{longjmp}
4689 breakpoint. It takes a @code{CORE_ADDR *} as argument, and stores the
4690 target PC value through this pointer. It examines the current state
4691 of the machine as needed, typically by using a manually-determined
4692 offset into the @code{jmp_buf}. (While we might like to get the offset
4693 from the target's @file{jmpbuf.h}, that header file cannot be assumed
4694 to be available when building a cross-debugger.)
4696 @item DEPRECATED_IBM6000_TARGET
4697 @findex DEPRECATED_IBM6000_TARGET
4698 Shows that we are configured for an IBM RS/6000 system. This
4699 conditional should be eliminated (FIXME) and replaced by
4700 feature-specific macros. It was introduced in haste and we are
4701 repenting at leisure.
4703 @item I386_USE_GENERIC_WATCHPOINTS
4704 An x86-based target can define this to use the generic x86 watchpoint
4705 support; see @ref{Algorithms, I386_USE_GENERIC_WATCHPOINTS}.
4707 @item gdbarch_in_function_epilogue_p (@var{gdbarch}, @var{addr})
4708 @findex gdbarch_in_function_epilogue_p
4709 Returns non-zero if the given @var{addr} is in the epilogue of a function.
4710 The epilogue of a function is defined as the part of a function where
4711 the stack frame of the function already has been destroyed up to the
4712 final `return from function call' instruction.
4714 @item int gdbarch_in_solib_return_trampoline (@var{gdbarch}, @var{pc}, @var{name})
4715 @findex gdbarch_in_solib_return_trampoline
4716 Define this function to return nonzero if the program is stopped in the
4717 trampoline that returns from a shared library.
4719 @item target_so_ops.in_dynsym_resolve_code (@var{pc})
4720 @findex in_dynsym_resolve_code
4721 Define this to return nonzero if the program is stopped in the
4724 @item SKIP_SOLIB_RESOLVER (@var{pc})
4725 @findex SKIP_SOLIB_RESOLVER
4726 Define this to evaluate to the (nonzero) address at which execution
4727 should continue to get past the dynamic linker's symbol resolution
4728 function. A zero value indicates that it is not important or necessary
4729 to set a breakpoint to get through the dynamic linker and that single
4730 stepping will suffice.
4732 @item CORE_ADDR gdbarch_integer_to_address (@var{gdbarch}, @var{type}, @var{buf})
4733 @findex gdbarch_integer_to_address
4734 @cindex converting integers to addresses
4735 Define this when the architecture needs to handle non-pointer to address
4736 conversions specially. Converts that value to an address according to
4737 the current architectures conventions.
4739 @emph{Pragmatics: When the user copies a well defined expression from
4740 their source code and passes it, as a parameter, to @value{GDBN}'s
4741 @code{print} command, they should get the same value as would have been
4742 computed by the target program. Any deviation from this rule can cause
4743 major confusion and annoyance, and needs to be justified carefully. In
4744 other words, @value{GDBN} doesn't really have the freedom to do these
4745 conversions in clever and useful ways. It has, however, been pointed
4746 out that users aren't complaining about how @value{GDBN} casts integers
4747 to pointers; they are complaining that they can't take an address from a
4748 disassembly listing and give it to @code{x/i}. Adding an architecture
4749 method like @code{gdbarch_integer_to_address} certainly makes it possible for
4750 @value{GDBN} to ``get it right'' in all circumstances.}
4752 @xref{Target Architecture Definition, , Pointers Are Not Always
4755 @item CORE_ADDR gdbarch_pointer_to_address (@var{gdbarch}, @var{type}, @var{buf})
4756 @findex gdbarch_pointer_to_address
4757 Assume that @var{buf} holds a pointer of type @var{type}, in the
4758 appropriate format for the current architecture. Return the byte
4759 address the pointer refers to.
4760 @xref{Target Architecture Definition, , Pointers Are Not Always Addresses}.
4762 @item void gdbarch_register_to_value(@var{gdbarch}, @var{frame}, @var{regnum}, @var{type}, @var{fur})
4763 @findex gdbarch_register_to_value
4764 Convert the raw contents of register @var{regnum} into a value of type
4766 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
4768 @item REGISTER_CONVERT_TO_VIRTUAL(@var{reg}, @var{type}, @var{from}, @var{to})
4769 @findex REGISTER_CONVERT_TO_VIRTUAL
4770 Convert the value of register @var{reg} from its raw form to its virtual
4772 @xref{Target Architecture Definition, , Raw and Virtual Register Representations}.
4774 @item REGISTER_CONVERT_TO_RAW(@var{type}, @var{reg}, @var{from}, @var{to})
4775 @findex REGISTER_CONVERT_TO_RAW
4776 Convert the value of register @var{reg} from its virtual form to its raw
4778 @xref{Target Architecture Definition, , Raw and Virtual Register Representations}.
4780 @item const struct regset *regset_from_core_section (struct gdbarch * @var{gdbarch}, const char * @var{sect_name}, size_t @var{sect_size})
4781 @findex regset_from_core_section
4782 Return the appropriate register set for a core file section with name
4783 @var{sect_name} and size @var{sect_size}.
4785 @item SOFTWARE_SINGLE_STEP_P()
4786 @findex SOFTWARE_SINGLE_STEP_P
4787 Define this as 1 if the target does not have a hardware single-step
4788 mechanism. The macro @code{SOFTWARE_SINGLE_STEP} must also be defined.
4790 @item SOFTWARE_SINGLE_STEP(@var{signal}, @var{insert_breakpoints_p})
4791 @findex SOFTWARE_SINGLE_STEP
4792 A function that inserts or removes (depending on
4793 @var{insert_breakpoints_p}) breakpoints at each possible destinations of
4794 the next instruction. See @file{sparc-tdep.c} and @file{rs6000-tdep.c}
4797 @item set_gdbarch_sofun_address_maybe_missing (@var{gdbarch}, @var{set})
4798 @findex set_gdbarch_sofun_address_maybe_missing
4799 Somebody clever observed that, the more actual addresses you have in the
4800 debug information, the more time the linker has to spend relocating
4801 them. So whenever there's some other way the debugger could find the
4802 address it needs, you should omit it from the debug info, to make
4805 Calling @code{set_gdbarch_sofun_address_maybe_missing} with a non-zero
4806 argument @var{set} indicates that a particular set of hacks of this sort
4807 are in use, affecting @code{N_SO} and @code{N_FUN} entries in stabs-format
4808 debugging information. @code{N_SO} stabs mark the beginning and ending
4809 addresses of compilation units in the text segment. @code{N_FUN} stabs
4810 mark the starts and ends of functions.
4812 In this case, @value{GDBN} assumes two things:
4816 @code{N_FUN} stabs have an address of zero. Instead of using those
4817 addresses, you should find the address where the function starts by
4818 taking the function name from the stab, and then looking that up in the
4819 minsyms (the linker/assembler symbol table). In other words, the stab
4820 has the name, and the linker/assembler symbol table is the only place
4821 that carries the address.
4824 @code{N_SO} stabs have an address of zero, too. You just look at the
4825 @code{N_FUN} stabs that appear before and after the @code{N_SO} stab, and
4826 guess the starting and ending addresses of the compilation unit from them.
4829 @item int gdbarch_stabs_argument_has_addr (@var{gdbarch}, @var{type})
4830 @findex gdbarch_stabs_argument_has_addr
4831 @anchor{gdbarch_stabs_argument_has_addr} Define this function to return
4832 nonzero if a function argument of type @var{type} is passed by reference
4835 @item CORE_ADDR gdbarch_push_dummy_call (@var{gdbarch}, @var{function}, @var{regcache}, @var{bp_addr}, @var{nargs}, @var{args}, @var{sp}, @var{struct_return}, @var{struct_addr})
4836 @findex gdbarch_push_dummy_call
4837 @anchor{gdbarch_push_dummy_call} Define this to push the dummy frame's call to
4838 the inferior function onto the stack. In addition to pushing @var{nargs}, the
4839 code should push @var{struct_addr} (when @var{struct_return} is non-zero), and
4840 the return address (@var{bp_addr}).
4842 @var{function} is a pointer to a @code{struct value}; on architectures that use
4843 function descriptors, this contains the function descriptor value.
4845 Returns the updated top-of-stack pointer.
4847 @item CORE_ADDR gdbarch_push_dummy_code (@var{gdbarch}, @var{sp}, @var{funaddr}, @var{using_gcc}, @var{args}, @var{nargs}, @var{value_type}, @var{real_pc}, @var{bp_addr}, @var{regcache})
4848 @findex gdbarch_push_dummy_code
4849 @anchor{gdbarch_push_dummy_code} Given a stack based call dummy, push the
4850 instruction sequence (including space for a breakpoint) to which the
4851 called function should return.
4853 Set @var{bp_addr} to the address at which the breakpoint instruction
4854 should be inserted, @var{real_pc} to the resume address when starting
4855 the call sequence, and return the updated inner-most stack address.
4857 By default, the stack is grown sufficient to hold a frame-aligned
4858 (@pxref{frame_align}) breakpoint, @var{bp_addr} is set to the address
4859 reserved for that breakpoint, and @var{real_pc} set to @var{funaddr}.
4861 This method replaces @w{@code{gdbarch_call_dummy_location (@var{gdbarch})}}.
4863 @item int gdbarch_sdb_reg_to_regnum (@var{gdbarch}, @var{sdb_regnr})
4864 @findex gdbarch_sdb_reg_to_regnum
4865 Use this function to convert sdb register @var{sdb_regnr} into @value{GDBN}
4866 regnum. If not defined, no conversion will be done.
4868 @item enum return_value_convention gdbarch_return_value (struct gdbarch *@var{gdbarch}, struct type *@var{valtype}, struct regcache *@var{regcache}, void *@var{readbuf}, const void *@var{writebuf})
4869 @findex gdbarch_return_value
4870 @anchor{gdbarch_return_value} Given a function with a return-value of
4871 type @var{rettype}, return which return-value convention that function
4874 @value{GDBN} currently recognizes two function return-value conventions:
4875 @code{RETURN_VALUE_REGISTER_CONVENTION} where the return value is found
4876 in registers; and @code{RETURN_VALUE_STRUCT_CONVENTION} where the return
4877 value is found in memory and the address of that memory location is
4878 passed in as the function's first parameter.
4880 If the register convention is being used, and @var{writebuf} is
4881 non-@code{NULL}, also copy the return-value in @var{writebuf} into
4884 If the register convention is being used, and @var{readbuf} is
4885 non-@code{NULL}, also copy the return value from @var{regcache} into
4886 @var{readbuf} (@var{regcache} contains a copy of the registers from the
4887 just returned function).
4889 @emph{Maintainer note: This method replaces separate predicate, extract,
4890 store methods. By having only one method, the logic needed to determine
4891 the return-value convention need only be implemented in one place. If
4892 @value{GDBN} were written in an @sc{oo} language, this method would
4893 instead return an object that knew how to perform the register
4894 return-value extract and store.}
4896 @emph{Maintainer note: This method does not take a @var{gcc_p}
4897 parameter, and such a parameter should not be added. If an architecture
4898 that requires per-compiler or per-function information be identified,
4899 then the replacement of @var{rettype} with @code{struct value}
4900 @var{function} should be pursued.}
4902 @emph{Maintainer note: The @var{regcache} parameter limits this methods
4903 to the inner most frame. While replacing @var{regcache} with a
4904 @code{struct frame_info} @var{frame} parameter would remove that
4905 limitation there has yet to be a demonstrated need for such a change.}
4907 @item void gdbarch_skip_permanent_breakpoint (@var{gdbarch}, @var{regcache})
4908 @findex gdbarch_skip_permanent_breakpoint
4909 Advance the inferior's PC past a permanent breakpoint. @value{GDBN} normally
4910 steps over a breakpoint by removing it, stepping one instruction, and
4911 re-inserting the breakpoint. However, permanent breakpoints are
4912 hardwired into the inferior, and can't be removed, so this strategy
4913 doesn't work. Calling @code{gdbarch_skip_permanent_breakpoint} adjusts the
4914 processor's state so that execution will resume just after the breakpoint.
4915 This function does the right thing even when the breakpoint is in the delay slot
4916 of a branch or jump.
4918 @item CORE_ADDR gdbarch_skip_trampoline_code (@var{gdbarch}, @var{frame}, @var{pc})
4919 @findex gdbarch_skip_trampoline_code
4920 If the target machine has trampoline code that sits between callers and
4921 the functions being called, then define this function to return a new PC
4922 that is at the start of the real function.
4924 @item int gdbarch_deprecated_fp_regnum (@var{gdbarch})
4925 @findex gdbarch_deprecated_fp_regnum
4926 If the frame pointer is in a register, use this function to return the
4927 number of that register.
4929 @item int gdbarch_stab_reg_to_regnum (@var{gdbarch}, @var{stab_regnr})
4930 @findex gdbarch_stab_reg_to_regnum
4931 Use this function to convert stab register @var{stab_regnr} into @value{GDBN}
4932 regnum. If not defined, no conversion will be done.
4934 @item SYMBOL_RELOADING_DEFAULT
4935 @findex SYMBOL_RELOADING_DEFAULT
4936 The default value of the ``symbol-reloading'' variable. (Never defined in
4939 @item TARGET_CHAR_BIT
4940 @findex TARGET_CHAR_BIT
4941 Number of bits in a char; defaults to 8.
4943 @item int gdbarch_char_signed (@var{gdbarch})
4944 @findex gdbarch_char_signed
4945 Non-zero if @code{char} is normally signed on this architecture; zero if
4946 it should be unsigned.
4948 The ISO C standard requires the compiler to treat @code{char} as
4949 equivalent to either @code{signed char} or @code{unsigned char}; any
4950 character in the standard execution set is supposed to be positive.
4951 Most compilers treat @code{char} as signed, but @code{char} is unsigned
4952 on the IBM S/390, RS6000, and PowerPC targets.
4954 @item int gdbarch_double_bit (@var{gdbarch})
4955 @findex gdbarch_double_bit
4956 Number of bits in a double float; defaults to @w{@code{8 * TARGET_CHAR_BIT}}.
4958 @item int gdbarch_float_bit (@var{gdbarch})
4959 @findex gdbarch_float_bit
4960 Number of bits in a float; defaults to @w{@code{4 * TARGET_CHAR_BIT}}.
4962 @item int gdbarch_int_bit (@var{gdbarch})
4963 @findex gdbarch_int_bit
4964 Number of bits in an integer; defaults to @w{@code{4 * TARGET_CHAR_BIT}}.
4966 @item int gdbarch_long_bit (@var{gdbarch})
4967 @findex gdbarch_long_bit
4968 Number of bits in a long integer; defaults to @w{@code{4 * TARGET_CHAR_BIT}}.
4970 @item int gdbarch_long_double_bit (@var{gdbarch})
4971 @findex gdbarch_long_double_bit
4972 Number of bits in a long double float;
4973 defaults to @w{@code{2 * gdbarch_double_bit (@var{gdbarch})}}.
4975 @item int gdbarch_long_long_bit (@var{gdbarch})
4976 @findex gdbarch_long_long_bit
4977 Number of bits in a long long integer; defaults to
4978 @w{@code{2 * gdbarch_long_bit (@var{gdbarch})}}.
4980 @item int gdbarch_ptr_bit (@var{gdbarch})
4981 @findex gdbarch_ptr_bit
4982 Number of bits in a pointer; defaults to
4983 @w{@code{gdbarch_int_bit (@var{gdbarch})}}.
4985 @item int gdbarch_short_bit (@var{gdbarch})
4986 @findex gdbarch_short_bit
4987 Number of bits in a short integer; defaults to @w{@code{2 * TARGET_CHAR_BIT}}.
4989 @item void gdbarch_virtual_frame_pointer (@var{gdbarch}, @var{pc}, @var{frame_regnum}, @var{frame_offset})
4990 @findex gdbarch_virtual_frame_pointer
4991 Returns a @code{(@var{register}, @var{offset})} pair representing the virtual
4992 frame pointer in use at the code address @var{pc}. If virtual frame
4993 pointers are not used, a default definition simply returns
4994 @code{gdbarch_deprecated_fp_regnum} (or @code{gdbarch_sp_regnum}, if
4995 no frame pointer is defined), with an offset of zero.
4997 @c need to explain virtual frame pointers, they are recorded in agent
4998 @c expressions for tracepoints
5000 @item TARGET_HAS_HARDWARE_WATCHPOINTS
5001 If non-zero, the target has support for hardware-assisted
5002 watchpoints. @xref{Algorithms, watchpoints}, for more details and
5003 other related macros.
5005 @item int gdbarch_print_insn (@var{gdbarch}, @var{vma}, @var{info})
5006 @findex gdbarch_print_insn
5007 This is the function used by @value{GDBN} to print an assembly
5008 instruction. It prints the instruction at address @var{vma} in
5009 debugged memory and returns the length of the instruction, in bytes.
5010 This usually points to a function in the @code{opcodes} library
5011 (@pxref{Support Libraries, ,Opcodes}). @var{info} is a structure (of
5012 type @code{disassemble_info}) defined in the header file
5013 @file{include/dis-asm.h}, and used to pass information to the
5014 instruction decoding routine.
5016 @item frame_id gdbarch_dummy_id (@var{gdbarch}, @var{frame})
5017 @findex gdbarch_dummy_id
5018 @anchor{gdbarch_dummy_id} Given @var{frame} return a @w{@code{struct
5019 frame_id}} that uniquely identifies an inferior function call's dummy
5020 frame. The value returned must match the dummy frame stack value
5021 previously saved by @code{call_function_by_hand}.
5023 @item void gdbarch_value_to_register (@var{gdbarch}, @var{frame}, @var{type}, @var{buf})
5024 @findex gdbarch_value_to_register
5025 Convert a value of type @var{type} into the raw contents of a register.
5026 @xref{Target Architecture Definition, , Using Different Register and Memory Data Representations}.
5030 Motorola M68K target conditionals.
5034 Define this to be the 4-bit location of the breakpoint trap vector. If
5035 not defined, it will default to @code{0xf}.
5037 @item REMOTE_BPT_VECTOR
5038 Defaults to @code{1}.
5042 @node Adding a New Target
5043 @section Adding a New Target
5045 @cindex adding a target
5046 The following files add a target to @value{GDBN}:
5049 @cindex target dependent files
5051 @item gdb/@var{ttt}-tdep.c
5052 Contains any miscellaneous code required for this target machine. On
5053 some machines it doesn't exist at all.
5055 @item gdb/@var{arch}-tdep.c
5056 @itemx gdb/@var{arch}-tdep.h
5057 This is required to describe the basic layout of the target machine's
5058 processor chip (registers, stack, etc.). It can be shared among many
5059 targets that use the same processor architecture.
5063 (Target header files such as
5064 @file{gdb/config/@var{arch}/tm-@var{ttt}.h},
5065 @file{gdb/config/@var{arch}/tm-@var{arch}.h}, and
5066 @file{config/tm-@var{os}.h} are no longer used.)
5068 @findex _initialize_@var{arch}_tdep
5069 A @value{GDBN} description for a new architecture, arch is created by
5070 defining a global function @code{_initialize_@var{arch}_tdep}, by
5071 convention in the source file @file{@var{arch}-tdep.c}. For
5072 example, in the case of the OpenRISC 1000, this function is called
5073 @code{_initialize_or1k_tdep} and is found in the file
5076 The object file resulting from compiling this source file, which will
5077 contain the implementation of the
5078 @code{_initialize_@var{arch}_tdep} function is specified in the
5079 @value{GDBN} @file{configure.tgt} file, which includes a large case
5080 statement pattern matching against the @code{--target} option of the
5081 @kbd{configure} script.
5084 @emph{Note:} If the architecture requires multiple source files, the
5085 corresponding binaries should be included in
5086 @file{configure.tgt}. However if there are header files, the
5087 dependencies on these will not be picked up from the entries in
5088 @file{configure.tgt}. The @file{Makefile.in} file will need extending to
5089 show these dependencies.
5092 @findex gdbarch_register
5093 A new struct gdbarch, defining the new architecture, is created within
5094 the @code{_initialize_@var{arch}_tdep} function by calling
5095 @code{gdbarch_register}:
5098 void gdbarch_register (enum bfd_architecture architecture,
5099 gdbarch_init_ftype *init_func,
5100 gdbarch_dump_tdep_ftype *tdep_dump_func);
5103 This function has been described fully in an earlier
5104 section. @xref{How an Architecture is Represented, , How an
5105 Architecture is Represented}.
5107 The new @code{@w{struct gdbarch}} should contain implementations of
5108 the necessary functions (described in the previous sections) to
5109 describe the basic layout of the target machine's processor chip
5110 (registers, stack, etc.). It can be shared among many targets that use
5111 the same processor architecture.
5113 @node Target Descriptions
5114 @chapter Target Descriptions
5115 @cindex target descriptions
5117 The target architecture definition (@pxref{Target Architecture Definition})
5118 contains @value{GDBN}'s hard-coded knowledge about an architecture. For
5119 some platforms, it is handy to have more flexible knowledge about a specific
5120 instance of the architecture---for instance, a processor or development board.
5121 @dfn{Target descriptions} provide a mechanism for the user to tell @value{GDBN}
5122 more about what their target supports, or for the target to tell @value{GDBN}
5125 For details on writing, automatically supplying, and manually selecting
5126 target descriptions, see @ref{Target Descriptions, , , gdb,
5127 Debugging with @value{GDBN}}. This section will cover some related
5128 topics about the @value{GDBN} internals.
5131 * Target Descriptions Implementation::
5132 * Adding Target Described Register Support::
5135 @node Target Descriptions Implementation
5136 @section Target Descriptions Implementation
5137 @cindex target descriptions, implementation
5139 Before @value{GDBN} connects to a new target, or runs a new program on
5140 an existing target, it discards any existing target description and
5141 reverts to a default gdbarch. Then, after connecting, it looks for a
5142 new target description by calling @code{target_find_description}.
5144 A description may come from a user specified file (XML), the remote
5145 @samp{qXfer:features:read} packet (also XML), or from any custom
5146 @code{to_read_description} routine in the target vector. For instance,
5147 the remote target supports guessing whether a MIPS target is 32-bit or
5148 64-bit based on the size of the @samp{g} packet.
5150 If any target description is found, @value{GDBN} creates a new gdbarch
5151 incorporating the description by calling @code{gdbarch_update_p}. Any
5152 @samp{<architecture>} element is handled first, to determine which
5153 architecture's gdbarch initialization routine is called to create the
5154 new architecture. Then the initialization routine is called, and has
5155 a chance to adjust the constructed architecture based on the contents
5156 of the target description. For instance, it can recognize any
5157 properties set by a @code{to_read_description} routine. Also
5158 see @ref{Adding Target Described Register Support}.
5160 @node Adding Target Described Register Support
5161 @section Adding Target Described Register Support
5162 @cindex target descriptions, adding register support
5164 Target descriptions can report additional registers specific to an
5165 instance of the target. But it takes a little work in the architecture
5166 specific routines to support this.
5168 A target description must either have no registers or a complete
5169 set---this avoids complexity in trying to merge standard registers
5170 with the target defined registers. It is the architecture's
5171 responsibility to validate that a description with registers has
5172 everything it needs. To keep architecture code simple, the same
5173 mechanism is used to assign fixed internal register numbers to
5176 If @code{tdesc_has_registers} returns 1, the description contains
5177 registers. The architecture's @code{gdbarch_init} routine should:
5182 Call @code{tdesc_data_alloc} to allocate storage, early, before
5183 searching for a matching gdbarch or allocating a new one.
5186 Use @code{tdesc_find_feature} to locate standard features by name.
5189 Use @code{tdesc_numbered_register} and @code{tdesc_numbered_register_choices}
5190 to locate the expected registers in the standard features.
5193 Return @code{NULL} if a required feature is missing, or if any standard
5194 feature is missing expected registers. This will produce a warning that
5195 the description was incomplete.
5198 Free the allocated data before returning, unless @code{tdesc_use_registers}
5202 Call @code{set_gdbarch_num_regs} as usual, with a number higher than any
5203 fixed number passed to @code{tdesc_numbered_register}.
5206 Call @code{tdesc_use_registers} after creating a new gdbarch, before
5211 After @code{tdesc_use_registers} has been called, the architecture's
5212 @code{register_name}, @code{register_type}, and @code{register_reggroup_p}
5213 routines will not be called; that information will be taken from
5214 the target description. @code{num_regs} may be increased to account
5215 for any additional registers in the description.
5217 Pseudo-registers require some extra care:
5222 Using @code{tdesc_numbered_register} allows the architecture to give
5223 constant register numbers to standard architectural registers, e.g.@:
5224 as an @code{enum} in @file{@var{arch}-tdep.h}. But because
5225 pseudo-registers are always numbered above @code{num_regs},
5226 which may be increased by the description, constant numbers
5227 can not be used for pseudos. They must be numbered relative to
5228 @code{num_regs} instead.
5231 The description will not describe pseudo-registers, so the
5232 architecture must call @code{set_tdesc_pseudo_register_name},
5233 @code{set_tdesc_pseudo_register_type}, and
5234 @code{set_tdesc_pseudo_register_reggroup_p} to supply routines
5235 describing pseudo registers. These routines will be passed
5236 internal register numbers, so the same routines used for the
5237 gdbarch equivalents are usually suitable.
5242 @node Target Vector Definition
5244 @chapter Target Vector Definition
5245 @cindex target vector
5247 The target vector defines the interface between @value{GDBN}'s
5248 abstract handling of target systems, and the nitty-gritty code that
5249 actually exercises control over a process or a serial port.
5250 @value{GDBN} includes some 30-40 different target vectors; however,
5251 each configuration of @value{GDBN} includes only a few of them.
5254 * Managing Execution State::
5255 * Existing Targets::
5258 @node Managing Execution State
5259 @section Managing Execution State
5260 @cindex execution state
5262 A target vector can be completely inactive (not pushed on the target
5263 stack), active but not running (pushed, but not connected to a fully
5264 manifested inferior), or completely active (pushed, with an accessible
5265 inferior). Most targets are only completely inactive or completely
5266 active, but some support persistent connections to a target even
5267 when the target has exited or not yet started.
5269 For example, connecting to the simulator using @code{target sim} does
5270 not create a running program. Neither registers nor memory are
5271 accessible until @code{run}. Similarly, after @code{kill}, the
5272 program can not continue executing. But in both cases @value{GDBN}
5273 remains connected to the simulator, and target-specific commands
5274 are directed to the simulator.
5276 A target which only supports complete activation should push itself
5277 onto the stack in its @code{to_open} routine (by calling
5278 @code{push_target}), and unpush itself from the stack in its
5279 @code{to_mourn_inferior} routine (by calling @code{unpush_target}).
5281 A target which supports both partial and complete activation should
5282 still call @code{push_target} in @code{to_open}, but not call
5283 @code{unpush_target} in @code{to_mourn_inferior}. Instead, it should
5284 call either @code{target_mark_running} or @code{target_mark_exited}
5285 in its @code{to_open}, depending on whether the target is fully active
5286 after connection. It should also call @code{target_mark_running} any
5287 time the inferior becomes fully active (e.g.@: in
5288 @code{to_create_inferior} and @code{to_attach}), and
5289 @code{target_mark_exited} when the inferior becomes inactive (in
5290 @code{to_mourn_inferior}). The target should also make sure to call
5291 @code{target_mourn_inferior} from its @code{to_kill}, to return the
5292 target to inactive state.
5294 @node Existing Targets
5295 @section Existing Targets
5298 @subsection File Targets
5300 Both executables and core files have target vectors.
5302 @subsection Standard Protocol and Remote Stubs
5304 @value{GDBN}'s file @file{remote.c} talks a serial protocol to code that
5305 runs in the target system. @value{GDBN} provides several sample
5306 @dfn{stubs} that can be integrated into target programs or operating
5307 systems for this purpose; they are named @file{@var{cpu}-stub.c}. Many
5308 operating systems, embedded targets, emulators, and simulators already
5309 have a @value{GDBN} stub built into them, and maintenance of the remote
5310 protocol must be careful to preserve compatibility.
5312 The @value{GDBN} user's manual describes how to put such a stub into
5313 your target code. What follows is a discussion of integrating the
5314 SPARC stub into a complicated operating system (rather than a simple
5315 program), by Stu Grossman, the author of this stub.
5317 The trap handling code in the stub assumes the following upon entry to
5322 %l1 and %l2 contain pc and npc respectively at the time of the trap;
5328 you are in the correct trap window.
5331 As long as your trap handler can guarantee those conditions, then there
5332 is no reason why you shouldn't be able to ``share'' traps with the stub.
5333 The stub has no requirement that it be jumped to directly from the
5334 hardware trap vector. That is why it calls @code{exceptionHandler()},
5335 which is provided by the external environment. For instance, this could
5336 set up the hardware traps to actually execute code which calls the stub
5337 first, and then transfers to its own trap handler.
5339 For the most point, there probably won't be much of an issue with
5340 ``sharing'' traps, as the traps we use are usually not used by the kernel,
5341 and often indicate unrecoverable error conditions. Anyway, this is all
5342 controlled by a table, and is trivial to modify. The most important
5343 trap for us is for @code{ta 1}. Without that, we can't single step or
5344 do breakpoints. Everything else is unnecessary for the proper operation
5345 of the debugger/stub.
5347 From reading the stub, it's probably not obvious how breakpoints work.
5348 They are simply done by deposit/examine operations from @value{GDBN}.
5350 @subsection ROM Monitor Interface
5352 @subsection Custom Protocols
5354 @subsection Transport Layer
5356 @subsection Builtin Simulator
5359 @node Native Debugging
5361 @chapter Native Debugging
5362 @cindex native debugging
5364 Several files control @value{GDBN}'s configuration for native support:
5368 @item gdb/config/@var{arch}/@var{xyz}.mh
5369 Specifies Makefile fragments needed by a @emph{native} configuration on
5370 machine @var{xyz}. In particular, this lists the required
5371 native-dependent object files, by defining @samp{NATDEPFILES=@dots{}}.
5372 Also specifies the header file which describes native support on
5373 @var{xyz}, by defining @samp{NAT_FILE= nm-@var{xyz}.h}. You can also
5374 define @samp{NAT_CFLAGS}, @samp{NAT_ADD_FILES}, @samp{NAT_CLIBS},
5375 @samp{NAT_CDEPS}, @samp{NAT_GENERATED_FILES}, etc.; see @file{Makefile.in}.
5377 @emph{Maintainer's note: The @file{.mh} suffix is because this file
5378 originally contained @file{Makefile} fragments for hosting @value{GDBN}
5379 on machine @var{xyz}. While the file is no longer used for this
5380 purpose, the @file{.mh} suffix remains. Perhaps someone will
5381 eventually rename these fragments so that they have a @file{.mn}
5384 @item gdb/config/@var{arch}/nm-@var{xyz}.h
5385 (@file{nm.h} is a link to this file, created by @code{configure}). Contains C
5386 macro definitions describing the native system environment, such as
5387 child process control and core file support.
5389 @item gdb/@var{xyz}-nat.c
5390 Contains any miscellaneous C code required for this native support of
5391 this machine. On some machines it doesn't exist at all.
5394 There are some ``generic'' versions of routines that can be used by
5395 various systems. These can be customized in various ways by macros
5396 defined in your @file{nm-@var{xyz}.h} file. If these routines work for
5397 the @var{xyz} host, you can just include the generic file's name (with
5398 @samp{.o}, not @samp{.c}) in @code{NATDEPFILES}.
5400 Otherwise, if your machine needs custom support routines, you will need
5401 to write routines that perform the same functions as the generic file.
5402 Put them into @file{@var{xyz}-nat.c}, and put @file{@var{xyz}-nat.o}
5403 into @code{NATDEPFILES}.
5407 This contains the @emph{target_ops vector} that supports Unix child
5408 processes on systems which use ptrace and wait to control the child.
5411 This contains the @emph{target_ops vector} that supports Unix child
5412 processes on systems which use /proc to control the child.
5415 This does the low-level grunge that uses Unix system calls to do a ``fork
5416 and exec'' to start up a child process.
5419 This is the low level interface to inferior processes for systems using
5420 the Unix @code{ptrace} call in a vanilla way.
5429 @section shared libraries
5431 @section Native Conditionals
5432 @cindex native conditionals
5434 When @value{GDBN} is configured and compiled, various macros are
5435 defined or left undefined, to control compilation when the host and
5436 target systems are the same. These macros should be defined (or left
5437 undefined) in @file{nm-@var{system}.h}.
5441 @item I386_USE_GENERIC_WATCHPOINTS
5442 An x86-based machine can define this to use the generic x86 watchpoint
5443 support; see @ref{Algorithms, I386_USE_GENERIC_WATCHPOINTS}.
5445 @item SOLIB_ADD (@var{filename}, @var{from_tty}, @var{targ}, @var{readsyms})
5447 Define this to expand into an expression that will cause the symbols in
5448 @var{filename} to be added to @value{GDBN}'s symbol table. If
5449 @var{readsyms} is zero symbols are not read but any necessary low level
5450 processing for @var{filename} is still done.
5452 @item SOLIB_CREATE_INFERIOR_HOOK
5453 @findex SOLIB_CREATE_INFERIOR_HOOK
5454 Define this to expand into any shared-library-relocation code that you
5455 want to be run just after the child process has been forked.
5457 @item START_INFERIOR_TRAPS_EXPECTED
5458 @findex START_INFERIOR_TRAPS_EXPECTED
5459 When starting an inferior, @value{GDBN} normally expects to trap
5461 the shell execs, and once when the program itself execs. If the actual
5462 number of traps is something other than 2, then define this macro to
5463 expand into the number expected.
5467 @node Support Libraries
5469 @chapter Support Libraries
5474 BFD provides support for @value{GDBN} in several ways:
5477 @item identifying executable and core files
5478 BFD will identify a variety of file types, including a.out, coff, and
5479 several variants thereof, as well as several kinds of core files.
5481 @item access to sections of files
5482 BFD parses the file headers to determine the names, virtual addresses,
5483 sizes, and file locations of all the various named sections in files
5484 (such as the text section or the data section). @value{GDBN} simply
5485 calls BFD to read or write section @var{x} at byte offset @var{y} for
5488 @item specialized core file support
5489 BFD provides routines to determine the failing command name stored in a
5490 core file, the signal with which the program failed, and whether a core
5491 file matches (i.e.@: could be a core dump of) a particular executable
5494 @item locating the symbol information
5495 @value{GDBN} uses an internal interface of BFD to determine where to find the
5496 symbol information in an executable file or symbol-file. @value{GDBN} itself
5497 handles the reading of symbols, since BFD does not ``understand'' debug
5498 symbols, but @value{GDBN} uses BFD's cached information to find the symbols,
5503 @cindex opcodes library
5505 The opcodes library provides @value{GDBN}'s disassembler. (It's a separate
5506 library because it's also used in binutils, for @file{objdump}).
5509 @cindex readline library
5510 The @code{readline} library provides a set of functions for use by applications
5511 that allow users to edit command lines as they are typed in.
5514 @cindex @code{libiberty} library
5516 The @code{libiberty} library provides a set of functions and features
5517 that integrate and improve on functionality found in modern operating
5518 systems. Broadly speaking, such features can be divided into three
5519 groups: supplemental functions (functions that may be missing in some
5520 environments and operating systems), replacement functions (providing
5521 a uniform and easier to use interface for commonly used standard
5522 functions), and extensions (which provide additional functionality
5523 beyond standard functions).
5525 @value{GDBN} uses various features provided by the @code{libiberty}
5526 library, for instance the C@t{++} demangler, the @acronym{IEEE}
5527 floating format support functions, the input options parser
5528 @samp{getopt}, the @samp{obstack} extension, and other functions.
5530 @subsection @code{obstacks} in @value{GDBN}
5531 @cindex @code{obstacks}
5533 The obstack mechanism provides a convenient way to allocate and free
5534 chunks of memory. Each obstack is a pool of memory that is managed
5535 like a stack. Objects (of any nature, size and alignment) are
5536 allocated and freed in a @acronym{LIFO} fashion on an obstack (see
5537 @code{libiberty}'s documentation for a more detailed explanation of
5540 The most noticeable use of the @code{obstacks} in @value{GDBN} is in
5541 object files. There is an obstack associated with each internal
5542 representation of an object file. Lots of things get allocated on
5543 these @code{obstacks}: dictionary entries, blocks, blockvectors,
5544 symbols, minimal symbols, types, vectors of fundamental types, class
5545 fields of types, object files section lists, object files section
5546 offset lists, line tables, symbol tables, partial symbol tables,
5547 string tables, symbol table private data, macros tables, debug
5548 information sections and entries, import and export lists (som),
5549 unwind information (hppa), dwarf2 location expressions data. Plus
5550 various strings such as directory names strings, debug format strings,
5553 An essential and convenient property of all data on @code{obstacks} is
5554 that memory for it gets allocated (with @code{obstack_alloc}) at
5555 various times during a debugging session, but it is released all at
5556 once using the @code{obstack_free} function. The @code{obstack_free}
5557 function takes a pointer to where in the stack it must start the
5558 deletion from (much like the cleanup chains have a pointer to where to
5559 start the cleanups). Because of the stack like structure of the
5560 @code{obstacks}, this allows to free only a top portion of the
5561 obstack. There are a few instances in @value{GDBN} where such thing
5562 happens. Calls to @code{obstack_free} are done after some local data
5563 is allocated to the obstack. Only the local data is deleted from the
5564 obstack. Of course this assumes that nothing between the
5565 @code{obstack_alloc} and the @code{obstack_free} allocates anything
5566 else on the same obstack. For this reason it is best and safest to
5567 use temporary @code{obstacks}.
5569 Releasing the whole obstack is also not safe per se. It is safe only
5570 under the condition that we know the @code{obstacks} memory is no
5571 longer needed. In @value{GDBN} we get rid of the @code{obstacks} only
5572 when we get rid of the whole objfile(s), for instance upon reading a
5576 @cindex regular expressions library
5587 @item SIGN_EXTEND_CHAR
5589 @item SWITCH_ENUM_BUG
5598 @section Array Containers
5599 @cindex Array Containers
5602 Often it is necessary to manipulate a dynamic array of a set of
5603 objects. C forces some bookkeeping on this, which can get cumbersome
5604 and repetitive. The @file{vec.h} file contains macros for defining
5605 and using a typesafe vector type. The functions defined will be
5606 inlined when compiling, and so the abstraction cost should be zero.
5607 Domain checks are added to detect programming errors.
5609 An example use would be an array of symbols or section information.
5610 The array can be grown as symbols are read in (or preallocated), and
5611 the accessor macros provided keep care of all the necessary
5612 bookkeeping. Because the arrays are type safe, there is no danger of
5613 accidentally mixing up the contents. Think of these as C++ templates,
5614 but implemented in C.
5616 Because of the different behavior of structure objects, scalar objects
5617 and of pointers, there are three flavors of vector, one for each of
5618 these variants. Both the structure object and pointer variants pass
5619 pointers to objects around --- in the former case the pointers are
5620 stored into the vector and in the latter case the pointers are
5621 dereferenced and the objects copied into the vector. The scalar
5622 object variant is suitable for @code{int}-like objects, and the vector
5623 elements are returned by value.
5625 There are both @code{index} and @code{iterate} accessors. The iterator
5626 returns a boolean iteration condition and updates the iteration
5627 variable passed by reference. Because the iterator will be inlined,
5628 the address-of can be optimized away.
5630 The vectors are implemented using the trailing array idiom, thus they
5631 are not resizeable without changing the address of the vector object
5632 itself. This means you cannot have variables or fields of vector type
5633 --- always use a pointer to a vector. The one exception is the final
5634 field of a structure, which could be a vector type. You will have to
5635 use the @code{embedded_size} & @code{embedded_init} calls to create
5636 such objects, and they will probably not be resizeable (so don't use
5637 the @dfn{safe} allocation variants). The trailing array idiom is used
5638 (rather than a pointer to an array of data), because, if we allow
5639 @code{NULL} to also represent an empty vector, empty vectors occupy
5640 minimal space in the structure containing them.
5642 Each operation that increases the number of active elements is
5643 available in @dfn{quick} and @dfn{safe} variants. The former presumes
5644 that there is sufficient allocated space for the operation to succeed
5645 (it dies if there is not). The latter will reallocate the vector, if
5646 needed. Reallocation causes an exponential increase in vector size.
5647 If you know you will be adding N elements, it would be more efficient
5648 to use the reserve operation before adding the elements with the
5649 @dfn{quick} operation. This will ensure there are at least as many
5650 elements as you ask for, it will exponentially increase if there are
5651 too few spare slots. If you want reserve a specific number of slots,
5652 but do not want the exponential increase (for instance, you know this
5653 is the last allocation), use a negative number for reservation. You
5654 can also create a vector of a specific size from the get go.
5656 You should prefer the push and pop operations, as they append and
5657 remove from the end of the vector. If you need to remove several items
5658 in one go, use the truncate operation. The insert and remove
5659 operations allow you to change elements in the middle of the vector.
5660 There are two remove operations, one which preserves the element
5661 ordering @code{ordered_remove}, and one which does not
5662 @code{unordered_remove}. The latter function copies the end element
5663 into the removed slot, rather than invoke a memmove operation. The
5664 @code{lower_bound} function will determine where to place an item in
5665 the array using insert that will maintain sorted order.
5667 If you need to directly manipulate a vector, then the @code{address}
5668 accessor will return the address of the start of the vector. Also the
5669 @code{space} predicate will tell you whether there is spare capacity in the
5670 vector. You will not normally need to use these two functions.
5672 Vector types are defined using a
5673 @code{DEF_VEC_@{O,P,I@}(@var{typename})} macro. Variables of vector
5674 type are declared using a @code{VEC(@var{typename})} macro. The
5675 characters @code{O}, @code{P} and @code{I} indicate whether
5676 @var{typename} is an object (@code{O}), pointer (@code{P}) or integral
5677 (@code{I}) type. Be careful to pick the correct one, as you'll get an
5678 awkward and inefficient API if you use the wrong one. There is a
5679 check, which results in a compile-time warning, for the @code{P} and
5680 @code{I} versions, but there is no check for the @code{O} versions, as
5681 that is not possible in plain C.
5683 An example of their use would be,
5686 DEF_VEC_P(tree); // non-managed tree vector.
5689 VEC(tree) *v; // A (pointer to) a vector of tree pointers.
5692 struct my_struct *s;
5694 if (VEC_length(tree, s->v)) @{ we have some contents @}
5695 VEC_safe_push(tree, s->v, decl); // append some decl onto the end
5696 for (ix = 0; VEC_iterate(tree, s->v, ix, elt); ix++)
5697 @{ do something with elt @}
5701 The @file{vec.h} file provides details on how to invoke the various
5702 accessors provided. They are enumerated here:
5706 Return the number of items in the array,
5709 Return true if the array has no elements.
5713 Return the last or arbitrary item in the array.
5716 Access an array element and indicate whether the array has been
5721 Create and destroy an array.
5723 @item VEC_embedded_size
5724 @itemx VEC_embedded_init
5725 Helpers for embedding an array as the final element of another struct.
5731 Return the amount of free space in an array.
5734 Ensure a certain amount of free space.
5736 @item VEC_quick_push
5737 @itemx VEC_safe_push
5738 Append to an array, either assuming the space is available, or making
5742 Remove the last item from an array.
5745 Remove several items from the end of an array.
5748 Add several items to the end of an array.
5751 Overwrite an item in the array.
5753 @item VEC_quick_insert
5754 @itemx VEC_safe_insert
5755 Insert an item into the middle of the array. Either the space must
5756 already exist, or the space is created.
5758 @item VEC_ordered_remove
5759 @itemx VEC_unordered_remove
5760 Remove an item from the array, preserving order or not.
5762 @item VEC_block_remove
5763 Remove a set of items from the array.
5766 Provide the address of the first element.
5768 @item VEC_lower_bound
5769 Binary search the array.
5779 This chapter covers topics that are lower-level than the major
5780 algorithms of @value{GDBN}.
5785 Cleanups are a structured way to deal with things that need to be done
5788 When your code does something (e.g., @code{xmalloc} some memory, or
5789 @code{open} a file) that needs to be undone later (e.g., @code{xfree}
5790 the memory or @code{close} the file), it can make a cleanup. The
5791 cleanup will be done at some future point: when the command is finished
5792 and control returns to the top level; when an error occurs and the stack
5793 is unwound; or when your code decides it's time to explicitly perform
5794 cleanups. Alternatively you can elect to discard the cleanups you
5800 @item struct cleanup *@var{old_chain};
5801 Declare a variable which will hold a cleanup chain handle.
5803 @findex make_cleanup
5804 @item @var{old_chain} = make_cleanup (@var{function}, @var{arg});
5805 Make a cleanup which will cause @var{function} to be called with
5806 @var{arg} (a @code{char *}) later. The result, @var{old_chain}, is a
5807 handle that can later be passed to @code{do_cleanups} or
5808 @code{discard_cleanups}. Unless you are going to call
5809 @code{do_cleanups} or @code{discard_cleanups}, you can ignore the result
5810 from @code{make_cleanup}.
5813 @item do_cleanups (@var{old_chain});
5814 Do all cleanups added to the chain since the corresponding
5815 @code{make_cleanup} call was made.
5817 @findex discard_cleanups
5818 @item discard_cleanups (@var{old_chain});
5819 Same as @code{do_cleanups} except that it just removes the cleanups from
5820 the chain and does not call the specified functions.
5823 Cleanups are implemented as a chain. The handle returned by
5824 @code{make_cleanups} includes the cleanup passed to the call and any
5825 later cleanups appended to the chain (but not yet discarded or
5829 make_cleanup (a, 0);
5831 struct cleanup *old = make_cleanup (b, 0);
5839 will call @code{c()} and @code{b()} but will not call @code{a()}. The
5840 cleanup that calls @code{a()} will remain in the cleanup chain, and will
5841 be done later unless otherwise discarded.@refill
5843 Your function should explicitly do or discard the cleanups it creates.
5844 Failing to do this leads to non-deterministic behavior since the caller
5845 will arbitrarily do or discard your functions cleanups. This need leads
5846 to two common cleanup styles.
5848 The first style is try/finally. Before it exits, your code-block calls
5849 @code{do_cleanups} with the old cleanup chain and thus ensures that your
5850 code-block's cleanups are always performed. For instance, the following
5851 code-segment avoids a memory leak problem (even when @code{error} is
5852 called and a forced stack unwind occurs) by ensuring that the
5853 @code{xfree} will always be called:
5856 struct cleanup *old = make_cleanup (null_cleanup, 0);
5857 data = xmalloc (sizeof blah);
5858 make_cleanup (xfree, data);
5863 The second style is try/except. Before it exits, your code-block calls
5864 @code{discard_cleanups} with the old cleanup chain and thus ensures that
5865 any created cleanups are not performed. For instance, the following
5866 code segment, ensures that the file will be closed but only if there is
5870 FILE *file = fopen ("afile", "r");
5871 struct cleanup *old = make_cleanup (close_file, file);
5873 discard_cleanups (old);
5877 Some functions, e.g., @code{fputs_filtered()} or @code{error()}, specify
5878 that they ``should not be called when cleanups are not in place''. This
5879 means that any actions you need to reverse in the case of an error or
5880 interruption must be on the cleanup chain before you call these
5881 functions, since they might never return to your code (they
5882 @samp{longjmp} instead).
5884 @section Per-architecture module data
5885 @cindex per-architecture module data
5886 @cindex multi-arch data
5887 @cindex data-pointer, per-architecture/per-module
5889 The multi-arch framework includes a mechanism for adding module
5890 specific per-architecture data-pointers to the @code{struct gdbarch}
5891 architecture object.
5893 A module registers one or more per-architecture data-pointers using:
5895 @deftypefn {Architecture Function} {struct gdbarch_data *} gdbarch_data_register_pre_init (gdbarch_data_pre_init_ftype *@var{pre_init})
5896 @var{pre_init} is used to, on-demand, allocate an initial value for a
5897 per-architecture data-pointer using the architecture's obstack (passed
5898 in as a parameter). Since @var{pre_init} can be called during
5899 architecture creation, it is not parameterized with the architecture.
5900 and must not call modules that use per-architecture data.
5903 @deftypefn {Architecture Function} {struct gdbarch_data *} gdbarch_data_register_post_init (gdbarch_data_post_init_ftype *@var{post_init})
5904 @var{post_init} is used to obtain an initial value for a
5905 per-architecture data-pointer @emph{after}. Since @var{post_init} is
5906 always called after architecture creation, it both receives the fully
5907 initialized architecture and is free to call modules that use
5908 per-architecture data (care needs to be taken to ensure that those
5909 other modules do not try to call back to this module as that will
5910 create in cycles in the initialization call graph).
5913 These functions return a @code{struct gdbarch_data} that is used to
5914 identify the per-architecture data-pointer added for that module.
5916 The per-architecture data-pointer is accessed using the function:
5918 @deftypefn {Architecture Function} {void *} gdbarch_data (struct gdbarch *@var{gdbarch}, struct gdbarch_data *@var{data_handle})
5919 Given the architecture @var{arch} and module data handle
5920 @var{data_handle} (returned by @code{gdbarch_data_register_pre_init}
5921 or @code{gdbarch_data_register_post_init}), this function returns the
5922 current value of the per-architecture data-pointer. If the data
5923 pointer is @code{NULL}, it is first initialized by calling the
5924 corresponding @var{pre_init} or @var{post_init} method.
5927 The examples below assume the following definitions:
5930 struct nozel @{ int total; @};
5931 static struct gdbarch_data *nozel_handle;
5934 A module can extend the architecture vector, adding additional
5935 per-architecture data, using the @var{pre_init} method. The module's
5936 per-architecture data is then initialized during architecture
5939 In the below, the module's per-architecture @emph{nozel} is added. An
5940 architecture can specify its nozel by calling @code{set_gdbarch_nozel}
5941 from @code{gdbarch_init}.
5945 nozel_pre_init (struct obstack *obstack)
5947 struct nozel *data = OBSTACK_ZALLOC (obstack, struct nozel);
5954 set_gdbarch_nozel (struct gdbarch *gdbarch, int total)
5956 struct nozel *data = gdbarch_data (gdbarch, nozel_handle);
5957 data->total = nozel;
5961 A module can on-demand create architecture dependent data structures
5962 using @code{post_init}.
5964 In the below, the nozel's total is computed on-demand by
5965 @code{nozel_post_init} using information obtained from the
5970 nozel_post_init (struct gdbarch *gdbarch)
5972 struct nozel *data = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct nozel);
5973 nozel->total = gdbarch@dots{} (gdbarch);
5980 nozel_total (struct gdbarch *gdbarch)
5982 struct nozel *data = gdbarch_data (gdbarch, nozel_handle);
5987 @section Wrapping Output Lines
5988 @cindex line wrap in output
5991 Output that goes through @code{printf_filtered} or @code{fputs_filtered}
5992 or @code{fputs_demangled} needs only to have calls to @code{wrap_here}
5993 added in places that would be good breaking points. The utility
5994 routines will take care of actually wrapping if the line width is
5997 The argument to @code{wrap_here} is an indentation string which is
5998 printed @emph{only} if the line breaks there. This argument is saved
5999 away and used later. It must remain valid until the next call to
6000 @code{wrap_here} or until a newline has been printed through the
6001 @code{*_filtered} functions. Don't pass in a local variable and then
6004 It is usually best to call @code{wrap_here} after printing a comma or
6005 space. If you call it before printing a space, make sure that your
6006 indentation properly accounts for the leading space that will print if
6007 the line wraps there.
6009 Any function or set of functions that produce filtered output must
6010 finish by printing a newline, to flush the wrap buffer, before switching
6011 to unfiltered (@code{printf}) output. Symbol reading routines that
6012 print warnings are a good example.
6014 @section @value{GDBN} Coding Standards
6015 @cindex coding standards
6017 @value{GDBN} follows the GNU coding standards, as described in
6018 @file{etc/standards.texi}. This file is also available for anonymous
6019 FTP from GNU archive sites. @value{GDBN} takes a strict interpretation
6020 of the standard; in general, when the GNU standard recommends a practice
6021 but does not require it, @value{GDBN} requires it.
6023 @value{GDBN} follows an additional set of coding standards specific to
6024 @value{GDBN}, as described in the following sections.
6029 @value{GDBN} assumes an ISO/IEC 9899:1990 (a.k.a.@: ISO C90) compliant
6032 @value{GDBN} does not assume an ISO C or POSIX compliant C library.
6035 @subsection Memory Management
6037 @value{GDBN} does not use the functions @code{malloc}, @code{realloc},
6038 @code{calloc}, @code{free} and @code{asprintf}.
6040 @value{GDBN} uses the functions @code{xmalloc}, @code{xrealloc} and
6041 @code{xcalloc} when allocating memory. Unlike @code{malloc} et.al.@:
6042 these functions do not return when the memory pool is empty. Instead,
6043 they unwind the stack using cleanups. These functions return
6044 @code{NULL} when requested to allocate a chunk of memory of size zero.
6046 @emph{Pragmatics: By using these functions, the need to check every
6047 memory allocation is removed. These functions provide portable
6050 @value{GDBN} does not use the function @code{free}.
6052 @value{GDBN} uses the function @code{xfree} to return memory to the
6053 memory pool. Consistent with ISO-C, this function ignores a request to
6054 free a @code{NULL} pointer.
6056 @emph{Pragmatics: On some systems @code{free} fails when passed a
6057 @code{NULL} pointer.}
6059 @value{GDBN} can use the non-portable function @code{alloca} for the
6060 allocation of small temporary values (such as strings).
6062 @emph{Pragmatics: This function is very non-portable. Some systems
6063 restrict the memory being allocated to no more than a few kilobytes.}
6065 @value{GDBN} uses the string function @code{xstrdup} and the print
6066 function @code{xstrprintf}.
6068 @emph{Pragmatics: @code{asprintf} and @code{strdup} can fail. Print
6069 functions such as @code{sprintf} are very prone to buffer overflow
6073 @subsection Compiler Warnings
6074 @cindex compiler warnings
6076 With few exceptions, developers should avoid the configuration option
6077 @samp{--disable-werror} when building @value{GDBN}. The exceptions
6078 are listed in the file @file{gdb/MAINTAINERS}. The default, when
6079 building with @sc{gcc}, is @samp{--enable-werror}.
6081 This option causes @value{GDBN} (when built using GCC) to be compiled
6082 with a carefully selected list of compiler warning flags. Any warnings
6083 from those flags are treated as errors.
6085 The current list of warning flags includes:
6089 Recommended @sc{gcc} warnings.
6091 @item -Wdeclaration-after-statement
6093 @sc{gcc} 3.x (and later) and @sc{c99} allow declarations mixed with
6094 code, but @sc{gcc} 2.x and @sc{c89} do not.
6096 @item -Wpointer-arith
6098 @item -Wformat-nonliteral
6099 Non-literal format strings, with a few exceptions, are bugs - they
6100 might contain unintended user-supplied format specifiers.
6101 Since @value{GDBN} uses the @code{format printf} attribute on all
6102 @code{printf} like functions this checks not just @code{printf} calls
6103 but also calls to functions such as @code{fprintf_unfiltered}.
6105 @item -Wno-pointer-sign
6106 In version 4.0, GCC began warning about pointer argument passing or
6107 assignment even when the source and destination differed only in
6108 signedness. However, most @value{GDBN} code doesn't distinguish
6109 carefully between @code{char} and @code{unsigned char}. In early 2006
6110 the @value{GDBN} developers decided correcting these warnings wasn't
6111 worth the time it would take.
6113 @item -Wno-unused-parameter
6114 Due to the way that @value{GDBN} is implemented many functions have
6115 unused parameters. Consequently this warning is avoided. The macro
6116 @code{ATTRIBUTE_UNUSED} is not used as it leads to false negatives ---
6117 it is not an error to have @code{ATTRIBUTE_UNUSED} on a parameter that
6122 @itemx -Wno-char-subscripts
6123 These are warnings which might be useful for @value{GDBN}, but are
6124 currently too noisy to enable with @samp{-Werror}.
6128 @subsection Formatting
6130 @cindex source code formatting
6131 The standard GNU recommendations for formatting must be followed
6134 A function declaration should not have its name in column zero. A
6135 function definition should have its name in column zero.
6139 static void foo (void);
6147 @emph{Pragmatics: This simplifies scripting. Function definitions can
6148 be found using @samp{^function-name}.}
6150 There must be a space between a function or macro name and the opening
6151 parenthesis of its argument list (except for macro definitions, as
6152 required by C). There must not be a space after an open paren/bracket
6153 or before a close paren/bracket.
6155 While additional whitespace is generally helpful for reading, do not use
6156 more than one blank line to separate blocks, and avoid adding whitespace
6157 after the end of a program line (as of 1/99, some 600 lines had
6158 whitespace after the semicolon). Excess whitespace causes difficulties
6159 for @code{diff} and @code{patch} utilities.
6161 Pointers are declared using the traditional K&R C style:
6175 @subsection Comments
6177 @cindex comment formatting
6178 The standard GNU requirements on comments must be followed strictly.
6180 Block comments must appear in the following form, with no @code{/*}- or
6181 @code{*/}-only lines, and no leading @code{*}:
6184 /* Wait for control to return from inferior to debugger. If inferior
6185 gets a signal, we may decide to start it up again instead of
6186 returning. That is why there is a loop in this function. When
6187 this function actually returns it means the inferior should be left
6188 stopped and @value{GDBN} should read more commands. */
6191 (Note that this format is encouraged by Emacs; tabbing for a multi-line
6192 comment works correctly, and @kbd{M-q} fills the block consistently.)
6194 Put a blank line between the block comments preceding function or
6195 variable definitions, and the definition itself.
6197 In general, put function-body comments on lines by themselves, rather
6198 than trying to fit them into the 20 characters left at the end of a
6199 line, since either the comment or the code will inevitably get longer
6200 than will fit, and then somebody will have to move it anyhow.
6204 @cindex C data types
6205 Code must not depend on the sizes of C data types, the format of the
6206 host's floating point numbers, the alignment of anything, or the order
6207 of evaluation of expressions.
6209 @cindex function usage
6210 Use functions freely. There are only a handful of compute-bound areas
6211 in @value{GDBN} that might be affected by the overhead of a function
6212 call, mainly in symbol reading. Most of @value{GDBN}'s performance is
6213 limited by the target interface (whether serial line or system call).
6215 However, use functions with moderation. A thousand one-line functions
6216 are just as hard to understand as a single thousand-line function.
6218 @emph{Macros are bad, M'kay.}
6219 (But if you have to use a macro, make sure that the macro arguments are
6220 protected with parentheses.)
6224 Declarations like @samp{struct foo *} should be used in preference to
6225 declarations like @samp{typedef struct foo @{ @dots{} @} *foo_ptr}.
6228 @subsection Function Prototypes
6229 @cindex function prototypes
6231 Prototypes must be used when both @emph{declaring} and @emph{defining}
6232 a function. Prototypes for @value{GDBN} functions must include both the
6233 argument type and name, with the name matching that used in the actual
6234 function definition.
6236 All external functions should have a declaration in a header file that
6237 callers include, except for @code{_initialize_*} functions, which must
6238 be external so that @file{init.c} construction works, but shouldn't be
6239 visible to random source files.
6241 Where a source file needs a forward declaration of a static function,
6242 that declaration must appear in a block near the top of the source file.
6245 @subsection Internal Error Recovery
6247 During its execution, @value{GDBN} can encounter two types of errors.
6248 User errors and internal errors. User errors include not only a user
6249 entering an incorrect command but also problems arising from corrupt
6250 object files and system errors when interacting with the target.
6251 Internal errors include situations where @value{GDBN} has detected, at
6252 run time, a corrupt or erroneous situation.
6254 When reporting an internal error, @value{GDBN} uses
6255 @code{internal_error} and @code{gdb_assert}.
6257 @value{GDBN} must not call @code{abort} or @code{assert}.
6259 @emph{Pragmatics: There is no @code{internal_warning} function. Either
6260 the code detected a user error, recovered from it and issued a
6261 @code{warning} or the code failed to correctly recover from the user
6262 error and issued an @code{internal_error}.}
6264 @subsection File Names
6266 Any file used when building the core of @value{GDBN} must be in lower
6267 case. Any file used when building the core of @value{GDBN} must be 8.3
6268 unique. These requirements apply to both source and generated files.
6270 @emph{Pragmatics: The core of @value{GDBN} must be buildable on many
6271 platforms including DJGPP and MacOS/HFS. Every time an unfriendly file
6272 is introduced to the build process both @file{Makefile.in} and
6273 @file{configure.in} need to be modified accordingly. Compare the
6274 convoluted conversion process needed to transform @file{COPYING} into
6275 @file{copying.c} with the conversion needed to transform
6276 @file{version.in} into @file{version.c}.}
6278 Any file non 8.3 compliant file (that is not used when building the core
6279 of @value{GDBN}) must be added to @file{gdb/config/djgpp/fnchange.lst}.
6281 @emph{Pragmatics: This is clearly a compromise.}
6283 When @value{GDBN} has a local version of a system header file (ex
6284 @file{string.h}) the file name based on the POSIX header prefixed with
6285 @file{gdb_} (@file{gdb_string.h}). These headers should be relatively
6286 independent: they should use only macros defined by @file{configure},
6287 the compiler, or the host; they should include only system headers; they
6288 should refer only to system types. They may be shared between multiple
6289 programs, e.g.@: @value{GDBN} and @sc{gdbserver}.
6291 For other files @samp{-} is used as the separator.
6294 @subsection Include Files
6296 A @file{.c} file should include @file{defs.h} first.
6298 A @file{.c} file should directly include the @code{.h} file of every
6299 declaration and/or definition it directly refers to. It cannot rely on
6302 A @file{.h} file should directly include the @code{.h} file of every
6303 declaration and/or definition it directly refers to. It cannot rely on
6304 indirect inclusion. Exception: The file @file{defs.h} does not need to
6305 be directly included.
6307 An external declaration should only appear in one include file.
6309 An external declaration should never appear in a @code{.c} file.
6310 Exception: a declaration for the @code{_initialize} function that
6311 pacifies @option{-Wmissing-declaration}.
6313 A @code{typedef} definition should only appear in one include file.
6315 An opaque @code{struct} declaration can appear in multiple @file{.h}
6316 files. Where possible, a @file{.h} file should use an opaque
6317 @code{struct} declaration instead of an include.
6319 All @file{.h} files should be wrapped in:
6322 #ifndef INCLUDE_FILE_NAME_H
6323 #define INCLUDE_FILE_NAME_H
6329 @subsection Clean Design and Portable Implementation
6332 In addition to getting the syntax right, there's the little question of
6333 semantics. Some things are done in certain ways in @value{GDBN} because long
6334 experience has shown that the more obvious ways caused various kinds of
6337 @cindex assumptions about targets
6338 You can't assume the byte order of anything that comes from a target
6339 (including @var{value}s, object files, and instructions). Such things
6340 must be byte-swapped using @code{SWAP_TARGET_AND_HOST} in
6341 @value{GDBN}, or one of the swap routines defined in @file{bfd.h},
6342 such as @code{bfd_get_32}.
6344 You can't assume that you know what interface is being used to talk to
6345 the target system. All references to the target must go through the
6346 current @code{target_ops} vector.
6348 You can't assume that the host and target machines are the same machine
6349 (except in the ``native'' support modules). In particular, you can't
6350 assume that the target machine's header files will be available on the
6351 host machine. Target code must bring along its own header files --
6352 written from scratch or explicitly donated by their owner, to avoid
6356 Insertion of new @code{#ifdef}'s will be frowned upon. It's much better
6357 to write the code portably than to conditionalize it for various
6360 @cindex system dependencies
6361 New @code{#ifdef}'s which test for specific compilers or manufacturers
6362 or operating systems are unacceptable. All @code{#ifdef}'s should test
6363 for features. The information about which configurations contain which
6364 features should be segregated into the configuration files. Experience
6365 has proven far too often that a feature unique to one particular system
6366 often creeps into other systems; and that a conditional based on some
6367 predefined macro for your current system will become worthless over
6368 time, as new versions of your system come out that behave differently
6369 with regard to this feature.
6371 Adding code that handles specific architectures, operating systems,
6372 target interfaces, or hosts, is not acceptable in generic code.
6374 @cindex portable file name handling
6375 @cindex file names, portability
6376 One particularly notorious area where system dependencies tend to
6377 creep in is handling of file names. The mainline @value{GDBN} code
6378 assumes Posix semantics of file names: absolute file names begin with
6379 a forward slash @file{/}, slashes are used to separate leading
6380 directories, case-sensitive file names. These assumptions are not
6381 necessarily true on non-Posix systems such as MS-Windows. To avoid
6382 system-dependent code where you need to take apart or construct a file
6383 name, use the following portable macros:
6386 @findex HAVE_DOS_BASED_FILE_SYSTEM
6387 @item HAVE_DOS_BASED_FILE_SYSTEM
6388 This preprocessing symbol is defined to a non-zero value on hosts
6389 whose filesystems belong to the MS-DOS/MS-Windows family. Use this
6390 symbol to write conditional code which should only be compiled for
6393 @findex IS_DIR_SEPARATOR
6394 @item IS_DIR_SEPARATOR (@var{c})
6395 Evaluates to a non-zero value if @var{c} is a directory separator
6396 character. On Unix and GNU/Linux systems, only a slash @file{/} is
6397 such a character, but on Windows, both @file{/} and @file{\} will
6400 @findex IS_ABSOLUTE_PATH
6401 @item IS_ABSOLUTE_PATH (@var{file})
6402 Evaluates to a non-zero value if @var{file} is an absolute file name.
6403 For Unix and GNU/Linux hosts, a name which begins with a slash
6404 @file{/} is absolute. On DOS and Windows, @file{d:/foo} and
6405 @file{x:\bar} are also absolute file names.
6407 @findex FILENAME_CMP
6408 @item FILENAME_CMP (@var{f1}, @var{f2})
6409 Calls a function which compares file names @var{f1} and @var{f2} as
6410 appropriate for the underlying host filesystem. For Posix systems,
6411 this simply calls @code{strcmp}; on case-insensitive filesystems it
6412 will call @code{strcasecmp} instead.
6414 @findex DIRNAME_SEPARATOR
6415 @item DIRNAME_SEPARATOR
6416 Evaluates to a character which separates directories in
6417 @code{PATH}-style lists, typically held in environment variables.
6418 This character is @samp{:} on Unix, @samp{;} on DOS and Windows.
6420 @findex SLASH_STRING
6422 This evaluates to a constant string you should use to produce an
6423 absolute filename from leading directories and the file's basename.
6424 @code{SLASH_STRING} is @code{"/"} on most systems, but might be
6425 @code{"\\"} for some Windows-based ports.
6428 In addition to using these macros, be sure to use portable library
6429 functions whenever possible. For example, to extract a directory or a
6430 basename part from a file name, use the @code{dirname} and
6431 @code{basename} library functions (available in @code{libiberty} for
6432 platforms which don't provide them), instead of searching for a slash
6433 with @code{strrchr}.
6435 Another way to generalize @value{GDBN} along a particular interface is with an
6436 attribute struct. For example, @value{GDBN} has been generalized to handle
6437 multiple kinds of remote interfaces---not by @code{#ifdef}s everywhere, but
6438 by defining the @code{target_ops} structure and having a current target (as
6439 well as a stack of targets below it, for memory references). Whenever
6440 something needs to be done that depends on which remote interface we are
6441 using, a flag in the current target_ops structure is tested (e.g.,
6442 @code{target_has_stack}), or a function is called through a pointer in the
6443 current target_ops structure. In this way, when a new remote interface
6444 is added, only one module needs to be touched---the one that actually
6445 implements the new remote interface. Other examples of
6446 attribute-structs are BFD access to multiple kinds of object file
6447 formats, or @value{GDBN}'s access to multiple source languages.
6449 Please avoid duplicating code. For example, in @value{GDBN} 3.x all
6450 the code interfacing between @code{ptrace} and the rest of
6451 @value{GDBN} was duplicated in @file{*-dep.c}, and so changing
6452 something was very painful. In @value{GDBN} 4.x, these have all been
6453 consolidated into @file{infptrace.c}. @file{infptrace.c} can deal
6454 with variations between systems the same way any system-independent
6455 file would (hooks, @code{#if defined}, etc.), and machines which are
6456 radically different don't need to use @file{infptrace.c} at all.
6458 All debugging code must be controllable using the @samp{set debug
6459 @var{module}} command. Do not use @code{printf} to print trace
6460 messages. Use @code{fprintf_unfiltered(gdb_stdlog, ...}. Do not use
6461 @code{#ifdef DEBUG}.
6466 @chapter Porting @value{GDBN}
6467 @cindex porting to new machines
6469 Most of the work in making @value{GDBN} compile on a new machine is in
6470 specifying the configuration of the machine. Porting a new
6471 architecture to @value{GDBN} can be broken into a number of steps.
6476 Ensure a @sc{bfd} exists for executables of the target architecture in
6477 the @file{bfd} directory. If one does not exist, create one by
6478 modifying an existing similar one.
6481 Implement a disassembler for the target architecture in the @file{opcodes}
6485 Define the target architecture in the @file{gdb} directory
6486 (@pxref{Adding a New Target, , Adding a New Target}). Add the pattern
6487 for the new target to @file{configure.tgt} with the names of the files
6488 that contain the code. By convention the target architecture
6489 definition for an architecture @var{arch} is placed in
6490 @file{@var{arch}-tdep.c}.
6492 Within @file{@var{arch}-tdep.c} define the function
6493 @code{_initialize_@var{arch}_tdep} which calls
6494 @code{gdbarch_register} to create the new @code{@w{struct
6495 gdbarch}} for the architecture.
6498 If a new remote target is needed, consider adding a new remote target
6499 by defining a function
6500 @code{_initialize_remote_@var{arch}}. However if at all possible
6501 use the @value{GDBN} @emph{Remote Serial Protocol} for this and implement
6502 the server side protocol independently with the target.
6505 If desired implement a simulator in the @file{sim} directory. This
6506 should create the library @file{libsim.a} implementing the interface
6507 in @file{remote-sim.h} (found in the @file{include} directory).
6510 Build and test. If desired, lobby the @sc{gdb} steering group to
6511 have the new port included in the main distribution!
6514 Add a description of the new architecture to the main @value{GDBN} user
6515 guide (@pxref{Configuration Specific Information, , Configuration
6516 Specific Information, gdb, Debugging with @value{GDBN}}).
6520 @node Versions and Branches
6521 @chapter Versions and Branches
6525 @value{GDBN}'s version is determined by the file
6526 @file{gdb/version.in} and takes one of the following forms:
6529 @item @var{major}.@var{minor}
6530 @itemx @var{major}.@var{minor}.@var{patchlevel}
6531 an official release (e.g., 6.2 or 6.2.1)
6532 @item @var{major}.@var{minor}.@var{patchlevel}.@var{YYYY}@var{MM}@var{DD}
6533 a snapshot taken at @var{YYYY}-@var{MM}-@var{DD}-gmt (e.g.,
6534 6.1.50.20020302, 6.1.90.20020304, or 6.1.0.20020308)
6535 @item @var{major}.@var{minor}.@var{patchlevel}.@var{YYYY}@var{MM}@var{DD}-cvs
6536 a @sc{cvs} check out drawn on @var{YYYY}-@var{MM}-@var{DD} (e.g.,
6537 6.1.50.20020302-cvs, 6.1.90.20020304-cvs, or 6.1.0.20020308-cvs)
6538 @item @var{major}.@var{minor}.@var{patchlevel}.@var{YYYY}@var{MM}@var{DD} (@var{vendor})
6539 a vendor specific release of @value{GDBN}, that while based on@*
6540 @var{major}.@var{minor}.@var{patchlevel}.@var{YYYY}@var{MM}@var{DD},
6541 may include additional changes
6544 @value{GDBN}'s mainline uses the @var{major} and @var{minor} version
6545 numbers from the most recent release branch, with a @var{patchlevel}
6546 of 50. At the time each new release branch is created, the mainline's
6547 @var{major} and @var{minor} version numbers are updated.
6549 @value{GDBN}'s release branch is similar. When the branch is cut, the
6550 @var{patchlevel} is changed from 50 to 90. As draft releases are
6551 drawn from the branch, the @var{patchlevel} is incremented. Once the
6552 first release (@var{major}.@var{minor}) has been made, the
6553 @var{patchlevel} is set to 0 and updates have an incremented
6556 For snapshots, and @sc{cvs} check outs, it is also possible to
6557 identify the @sc{cvs} origin:
6560 @item @var{major}.@var{minor}.50.@var{YYYY}@var{MM}@var{DD}
6561 drawn from the @sc{head} of mainline @sc{cvs} (e.g., 6.1.50.20020302)
6562 @item @var{major}.@var{minor}.90.@var{YYYY}@var{MM}@var{DD}
6563 @itemx @var{major}.@var{minor}.91.@var{YYYY}@var{MM}@var{DD} @dots{}
6564 drawn from a release branch prior to the release (e.g.,
6566 @item @var{major}.@var{minor}.0.@var{YYYY}@var{MM}@var{DD}
6567 @itemx @var{major}.@var{minor}.1.@var{YYYY}@var{MM}@var{DD} @dots{}
6568 drawn from a release branch after the release (e.g., 6.2.0.20020308)
6571 If the previous @value{GDBN} version is 6.1 and the current version is
6572 6.2, then, substituting 6 for @var{major} and 1 or 2 for @var{minor},
6573 here's an illustration of a typical sequence:
6580 +--------------------------.
6583 6.2.50.20020303-cvs 6.1.90 (draft #1)
6585 6.2.50.20020304-cvs 6.1.90.20020304-cvs
6587 6.2.50.20020305-cvs 6.1.91 (draft #2)
6589 6.2.50.20020306-cvs 6.1.91.20020306-cvs
6591 6.2.50.20020307-cvs 6.2 (release)
6593 6.2.50.20020308-cvs 6.2.0.20020308-cvs
6595 6.2.50.20020309-cvs 6.2.1 (update)
6597 6.2.50.20020310-cvs <branch closed>
6601 +--------------------------.
6604 6.3.50.20020312-cvs 6.2.90 (draft #1)
6608 @section Release Branches
6609 @cindex Release Branches
6611 @value{GDBN} draws a release series (6.2, 6.2.1, @dots{}) from a
6612 single release branch, and identifies that branch using the @sc{cvs}
6616 gdb_@var{major}_@var{minor}-@var{YYYY}@var{MM}@var{DD}-branchpoint
6617 gdb_@var{major}_@var{minor}-branch
6618 gdb_@var{major}_@var{minor}-@var{YYYY}@var{MM}@var{DD}-release
6621 @emph{Pragmatics: To help identify the date at which a branch or
6622 release is made, both the branchpoint and release tags include the
6623 date that they are cut (@var{YYYY}@var{MM}@var{DD}) in the tag. The
6624 branch tag, denoting the head of the branch, does not need this.}
6626 @section Vendor Branches
6627 @cindex vendor branches
6629 To avoid version conflicts, vendors are expected to modify the file
6630 @file{gdb/version.in} to include a vendor unique alphabetic identifier
6631 (an official @value{GDBN} release never uses alphabetic characters in
6632 its version identifier). E.g., @samp{6.2widgit2}, or @samp{6.2 (Widgit
6635 @section Experimental Branches
6636 @cindex experimental branches
6638 @subsection Guidelines
6640 @value{GDBN} permits the creation of branches, cut from the @sc{cvs}
6641 repository, for experimental development. Branches make it possible
6642 for developers to share preliminary work, and maintainers to examine
6643 significant new developments.
6645 The following are a set of guidelines for creating such branches:
6649 @item a branch has an owner
6650 The owner can set further policy for a branch, but may not change the
6651 ground rules. In particular, they can set a policy for commits (be it
6652 adding more reviewers or deciding who can commit).
6654 @item all commits are posted
6655 All changes committed to a branch shall also be posted to
6656 @email{gdb-patches@@sourceware.org, the @value{GDBN} patches
6657 mailing list}. While commentary on such changes are encouraged, people
6658 should remember that the changes only apply to a branch.
6660 @item all commits are covered by an assignment
6661 This ensures that all changes belong to the Free Software Foundation,
6662 and avoids the possibility that the branch may become contaminated.
6664 @item a branch is focused
6665 A focused branch has a single objective or goal, and does not contain
6666 unnecessary or irrelevant changes. Cleanups, where identified, being
6667 be pushed into the mainline as soon as possible.
6669 @item a branch tracks mainline
6670 This keeps the level of divergence under control. It also keeps the
6671 pressure on developers to push cleanups and other stuff into the
6674 @item a branch shall contain the entire @value{GDBN} module
6675 The @value{GDBN} module @code{gdb} should be specified when creating a
6676 branch (branches of individual files should be avoided). @xref{Tags}.
6678 @item a branch shall be branded using @file{version.in}
6679 The file @file{gdb/version.in} shall be modified so that it identifies
6680 the branch @var{owner} and branch @var{name}, e.g.,
6681 @samp{6.2.50.20030303_owner_name} or @samp{6.2 (Owner Name)}.
6688 To simplify the identification of @value{GDBN} branches, the following
6689 branch tagging convention is strongly recommended:
6693 @item @var{owner}_@var{name}-@var{YYYYMMDD}-branchpoint
6694 @itemx @var{owner}_@var{name}-@var{YYYYMMDD}-branch
6695 The branch point and corresponding branch tag. @var{YYYYMMDD} is the
6696 date that the branch was created. A branch is created using the
6697 sequence: @anchor{experimental branch tags}
6699 cvs rtag @var{owner}_@var{name}-@var{YYYYMMDD}-branchpoint gdb
6700 cvs rtag -b -r @var{owner}_@var{name}-@var{YYYYMMDD}-branchpoint \
6701 @var{owner}_@var{name}-@var{YYYYMMDD}-branch gdb
6704 @item @var{owner}_@var{name}-@var{yyyymmdd}-mergepoint
6705 The tagged point, on the mainline, that was used when merging the branch
6706 on @var{yyyymmdd}. To merge in all changes since the branch was cut,
6707 use a command sequence like:
6709 cvs rtag @var{owner}_@var{name}-@var{yyyymmdd}-mergepoint gdb
6711 -j@var{owner}_@var{name}-@var{YYYYMMDD}-branchpoint
6712 -j@var{owner}_@var{name}-@var{yyyymmdd}-mergepoint
6715 Similar sequences can be used to just merge in changes since the last
6721 For further information on @sc{cvs}, see
6722 @uref{http://www.gnu.org/software/cvs/, Concurrent Versions System}.
6724 @node Start of New Year Procedure
6725 @chapter Start of New Year Procedure
6726 @cindex new year procedure
6728 At the start of each new year, the following actions should be performed:
6732 Rotate the ChangeLog file
6734 The current @file{ChangeLog} file should be renamed into
6735 @file{ChangeLog-YYYY} where YYYY is the year that has just passed.
6736 A new @file{ChangeLog} file should be created, and its contents should
6737 contain a reference to the previous ChangeLog. The following should
6738 also be preserved at the end of the new ChangeLog, in order to provide
6739 the appropriate settings when editing this file with Emacs:
6745 version-control: never
6751 Add an entry for the newly created ChangeLog file (@file{ChangeLog-YYYY})
6752 in @file{gdb/config/djgpp/fnchange.lst}.
6755 Update the copyright year in the startup message
6757 Update the copyright year in:
6759 @item file @file{top.c}, function @code{print_gdb_version}
6760 @item file @file{gdbserver/server.c}, function @code{gdbserver_version}
6761 @item file @file{gdbserver/gdbreplay.c}, function @code{gdbreplay_version}
6765 Add the new year in the copyright notices of all source and documentation
6766 files. This can be done semi-automatically by running the @code{copyright.sh}
6767 script. This script requires Emacs 22 or later to be installed.
6773 @chapter Releasing @value{GDBN}
6774 @cindex making a new release of gdb
6776 @section Branch Commit Policy
6778 The branch commit policy is pretty slack. @value{GDBN} releases 5.0,
6779 5.1 and 5.2 all used the below:
6783 The @file{gdb/MAINTAINERS} file still holds.
6785 Don't fix something on the branch unless/until it is also fixed in the
6786 trunk. If this isn't possible, mentioning it in the @file{gdb/PROBLEMS}
6787 file is better than committing a hack.
6789 When considering a patch for the branch, suggested criteria include:
6790 Does it fix a build? Does it fix the sequence @kbd{break main; run}
6791 when debugging a static binary?
6793 The further a change is from the core of @value{GDBN}, the less likely
6794 the change will worry anyone (e.g., target specific code).
6796 Only post a proposal to change the core of @value{GDBN} after you've
6797 sent individual bribes to all the people listed in the
6798 @file{MAINTAINERS} file @t{;-)}
6801 @emph{Pragmatics: Provided updates are restricted to non-core
6802 functionality there is little chance that a broken change will be fatal.
6803 This means that changes such as adding a new architectures or (within
6804 reason) support for a new host are considered acceptable.}
6807 @section Obsoleting code
6809 Before anything else, poke the other developers (and around the source
6810 code) to see if there is anything that can be removed from @value{GDBN}
6811 (an old target, an unused file).
6813 Obsolete code is identified by adding an @code{OBSOLETE} prefix to every
6814 line. Doing this means that it is easy to identify something that has
6815 been obsoleted when greping through the sources.
6817 The process is done in stages --- this is mainly to ensure that the
6818 wider @value{GDBN} community has a reasonable opportunity to respond.
6819 Remember, everything on the Internet takes a week.
6823 Post the proposal on @email{gdb@@sourceware.org, the GDB mailing
6824 list} Creating a bug report to track the task's state, is also highly
6829 Post the proposal on @email{gdb-announce@@sourceware.org, the GDB
6830 Announcement mailing list}.
6834 Go through and edit all relevant files and lines so that they are
6835 prefixed with the word @code{OBSOLETE}.
6837 Wait until the next GDB version, containing this obsolete code, has been
6840 Remove the obsolete code.
6844 @emph{Maintainer note: While removing old code is regrettable it is
6845 hopefully better for @value{GDBN}'s long term development. Firstly it
6846 helps the developers by removing code that is either no longer relevant
6847 or simply wrong. Secondly since it removes any history associated with
6848 the file (effectively clearing the slate) the developer has a much freer
6849 hand when it comes to fixing broken files.}
6853 @section Before the Branch
6855 The most important objective at this stage is to find and fix simple
6856 changes that become a pain to track once the branch is created. For
6857 instance, configuration problems that stop @value{GDBN} from even
6858 building. If you can't get the problem fixed, document it in the
6859 @file{gdb/PROBLEMS} file.
6861 @subheading Prompt for @file{gdb/NEWS}
6863 People always forget. Send a post reminding them but also if you know
6864 something interesting happened add it yourself. The @code{schedule}
6865 script will mention this in its e-mail.
6867 @subheading Review @file{gdb/README}
6869 Grab one of the nightly snapshots and then walk through the
6870 @file{gdb/README} looking for anything that can be improved. The
6871 @code{schedule} script will mention this in its e-mail.
6873 @subheading Refresh any imported files.
6875 A number of files are taken from external repositories. They include:
6879 @file{texinfo/texinfo.tex}
6881 @file{config.guess} et.@: al.@: (see the top-level @file{MAINTAINERS}
6884 @file{etc/standards.texi}, @file{etc/make-stds.texi}
6887 @subheading Check the ARI
6889 @uref{http://sourceware.org/gdb/ari,,A.R.I.} is an @code{awk} script
6890 (Awk Regression Index ;-) that checks for a number of errors and coding
6891 conventions. The checks include things like using @code{malloc} instead
6892 of @code{xmalloc} and file naming problems. There shouldn't be any
6895 @subsection Review the bug data base
6897 Close anything obviously fixed.
6899 @subsection Check all cross targets build
6901 The targets are listed in @file{gdb/MAINTAINERS}.
6904 @section Cut the Branch
6906 @subheading Create the branch
6911 $ V=`echo $v | sed 's/\./_/g'`
6912 $ D=`date -u +%Y-%m-%d`
6915 $ echo cvs -f -d :ext:sourceware.org:/cvs/src rtag \
6916 -D $D-gmt gdb_$V-$D-branchpoint insight
6917 cvs -f -d :ext:sourceware.org:/cvs/src rtag
6918 -D 2002-03-03-gmt gdb_5_2-2002-03-03-branchpoint insight
6921 $ echo cvs -f -d :ext:sourceware.org:/cvs/src rtag \
6922 -b -r gdb_$V-$D-branchpoint gdb_$V-branch insight
6923 cvs -f -d :ext:sourceware.org:/cvs/src rtag \
6924 -b -r gdb_5_2-2002-03-03-branchpoint gdb_5_2-branch insight
6932 By using @kbd{-D YYYY-MM-DD-gmt}, the branch is forced to an exact
6935 The trunk is first tagged so that the branch point can easily be found.
6937 Insight, which includes @value{GDBN}, is tagged at the same time.
6939 @file{version.in} gets bumped to avoid version number conflicts.
6941 The reading of @file{.cvsrc} is disabled using @file{-f}.
6944 @subheading Update @file{version.in}
6949 $ V=`echo $v | sed 's/\./_/g'`
6953 $ echo cvs -f -d :ext:sourceware.org:/cvs/src co \
6954 -r gdb_$V-branch src/gdb/version.in
6955 cvs -f -d :ext:sourceware.org:/cvs/src co
6956 -r gdb_5_2-branch src/gdb/version.in
6958 U src/gdb/version.in
6960 $ echo $u.90-0000-00-00-cvs > version.in
6962 5.1.90-0000-00-00-cvs
6963 $ cvs -f commit version.in
6968 @file{0000-00-00} is used as a date to pump prime the version.in update
6971 @file{.90} and the previous branch version are used as fairly arbitrary
6972 initial branch version number.
6976 @subheading Update the web and news pages
6980 @subheading Tweak cron to track the new branch
6982 The file @file{gdbadmin/cron/crontab} contains gdbadmin's cron table.
6983 This file needs to be updated so that:
6987 A daily timestamp is added to the file @file{version.in}.
6989 The new branch is included in the snapshot process.
6993 See the file @file{gdbadmin/cron/README} for how to install the updated
6996 The file @file{gdbadmin/ss/README} should also be reviewed to reflect
6997 any changes. That file is copied to both the branch/ and current/
6998 snapshot directories.
7001 @subheading Update the NEWS and README files
7003 The @file{NEWS} file needs to be updated so that on the branch it refers
7004 to @emph{changes in the current release} while on the trunk it also
7005 refers to @emph{changes since the current release}.
7007 The @file{README} file needs to be updated so that it refers to the
7010 @subheading Post the branch info
7012 Send an announcement to the mailing lists:
7016 @email{gdb-announce@@sourceware.org, GDB Announcement mailing list}
7018 @email{gdb@@sourceware.org, GDB Discussion mailing list} and
7019 @email{gdb-testers@@sourceware.org, GDB Testers mailing list}
7022 @emph{Pragmatics: The branch creation is sent to the announce list to
7023 ensure that people people not subscribed to the higher volume discussion
7026 The announcement should include:
7032 How to check out the branch using CVS.
7034 The date/number of weeks until the release.
7036 The branch commit policy still holds.
7039 @section Stabilize the branch
7041 Something goes here.
7043 @section Create a Release
7045 The process of creating and then making available a release is broken
7046 down into a number of stages. The first part addresses the technical
7047 process of creating a releasable tar ball. The later stages address the
7048 process of releasing that tar ball.
7050 When making a release candidate just the first section is needed.
7052 @subsection Create a release candidate
7054 The objective at this stage is to create a set of tar balls that can be
7055 made available as a formal release (or as a less formal release
7058 @subsubheading Freeze the branch
7060 Send out an e-mail notifying everyone that the branch is frozen to
7061 @email{gdb-patches@@sourceware.org}.
7063 @subsubheading Establish a few defaults.
7068 $ t=/sourceware/snapshot-tmp/gdbadmin-tmp
7070 /sourceware/snapshot-tmp/gdbadmin-tmp/gdb_5_2-branch/5.2
7074 /sourceware/snapshot-tmp/gdbadmin-tmp/gdb_5_2-branch/5.2
7076 /home/gdbadmin/bin/autoconf
7085 Check the @code{autoconf} version carefully. You want to be using the
7086 version taken from the @file{binutils} snapshot directory, which can be
7087 found at @uref{ftp://sourceware.org/pub/binutils/}. It is very
7088 unlikely that a system installed version of @code{autoconf} (e.g.,
7089 @file{/usr/bin/autoconf}) is correct.
7092 @subsubheading Check out the relevant modules:
7095 $ for m in gdb insight
7097 ( mkdir -p $m && cd $m && cvs -q -f -d /cvs/src co -P -r $b $m )
7107 The reading of @file{.cvsrc} is disabled (@file{-f}) so that there isn't
7108 any confusion between what is written here and what your local
7109 @code{cvs} really does.
7112 @subsubheading Update relevant files.
7118 Major releases get their comments added as part of the mainline. Minor
7119 releases should probably mention any significant bugs that were fixed.
7121 Don't forget to include the @file{ChangeLog} entry.
7124 $ emacs gdb/src/gdb/NEWS
7129 $ cp gdb/src/gdb/NEWS insight/src/gdb/NEWS
7130 $ cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog
7135 You'll need to update:
7147 $ emacs gdb/src/gdb/README
7152 $ cp gdb/src/gdb/README insight/src/gdb/README
7153 $ cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog
7156 @emph{Maintainer note: Hopefully the @file{README} file was reviewed
7157 before the initial branch was cut so just a simple substitute is needed
7160 @emph{Maintainer note: Other projects generate @file{README} and
7161 @file{INSTALL} from the core documentation. This might be worth
7164 @item gdb/version.in
7167 $ echo $v > gdb/src/gdb/version.in
7168 $ cat gdb/src/gdb/version.in
7170 $ emacs gdb/src/gdb/version.in
7173 ... Bump to version ...
7175 $ cp gdb/src/gdb/version.in insight/src/gdb/version.in
7176 $ cp gdb/src/gdb/ChangeLog insight/src/gdb/ChangeLog
7181 @subsubheading Do the dirty work
7183 This is identical to the process used to create the daily snapshot.
7186 $ for m in gdb insight
7188 ( cd $m/src && gmake -f src-release $m.tar )
7192 If the top level source directory does not have @file{src-release}
7193 (@value{GDBN} version 5.3.1 or earlier), try these commands instead:
7196 $ for m in gdb insight
7198 ( cd $m/src && gmake -f Makefile.in $m.tar )
7202 @subsubheading Check the source files
7204 You're looking for files that have mysteriously disappeared.
7205 @kbd{distclean} has the habit of deleting files it shouldn't. Watch out
7206 for the @file{version.in} update @kbd{cronjob}.
7209 $ ( cd gdb/src && cvs -f -q -n update )
7213 @dots{} lots of generated files @dots{}
7218 @dots{} lots of generated files @dots{}
7223 @emph{Don't worry about the @file{gdb.info-??} or
7224 @file{gdb/p-exp.tab.c}. They were generated (and yes @file{gdb.info-1}
7225 was also generated only something strange with CVS means that they
7226 didn't get suppressed). Fixing it would be nice though.}
7228 @subsubheading Create compressed versions of the release
7234 gdb/ gdb-5.2.tar insight/ insight-5.2.tar
7235 $ for m in gdb insight
7237 bzip2 -v -9 -c $m-$v.tar > $m-$v.tar.bz2
7238 gzip -v -9 -c $m-$v.tar > $m-$v.tar.gz
7248 A pipe such as @kbd{bunzip2 < xxx.bz2 | gzip -9 > xxx.gz} is not since,
7249 in that mode, @code{gzip} does not know the name of the file and, hence,
7250 can not include it in the compressed file. This is also why the release
7251 process runs @code{tar} and @code{bzip2} as separate passes.
7254 @subsection Sanity check the tar ball
7256 Pick a popular machine (Solaris/PPC?) and try the build on that.
7259 $ bunzip2 < gdb-5.2.tar.bz2 | tar xpf -
7264 $ ./gdb/gdb ./gdb/gdb
7268 Breakpoint 1 at 0x80732bc: file main.c, line 734.
7270 Starting program: /tmp/gdb-5.2/gdb/gdb
7272 Breakpoint 1, main (argc=1, argv=0xbffff8b4) at main.c:734
7273 734 catch_errors (captured_main, &args, "", RETURN_MASK_ALL);
7275 $1 = @{argc = 136426532, argv = 0x821b7f0@}
7279 @subsection Make a release candidate available
7281 If this is a release candidate then the only remaining steps are:
7285 Commit @file{version.in} and @file{ChangeLog}
7287 Tweak @file{version.in} (and @file{ChangeLog} to read
7288 @var{L}.@var{M}.@var{N}-0000-00-00-cvs so that the version update
7289 process can restart.
7291 Make the release candidate available in
7292 @uref{ftp://sourceware.org/pub/gdb/snapshots/branch}
7294 Notify the relevant mailing lists ( @email{gdb@@sourceware.org} and
7295 @email{gdb-testers@@sourceware.org} that the candidate is available.
7298 @subsection Make a formal release available
7300 (And you thought all that was required was to post an e-mail.)
7302 @subsubheading Install on sware
7304 Copy the new files to both the release and the old release directory:
7307 $ cp *.bz2 *.gz ~ftp/pub/gdb/old-releases/
7308 $ cp *.bz2 *.gz ~ftp/pub/gdb/releases
7312 Clean up the releases directory so that only the most recent releases
7313 are available (e.g.@: keep 5.2 and 5.2.1 but remove 5.1):
7316 $ cd ~ftp/pub/gdb/releases
7321 Update the file @file{README} and @file{.message} in the releases
7328 $ ln README .message
7331 @subsubheading Update the web pages.
7335 @item htdocs/download/ANNOUNCEMENT
7336 This file, which is posted as the official announcement, includes:
7339 General announcement.
7341 News. If making an @var{M}.@var{N}.1 release, retain the news from
7342 earlier @var{M}.@var{N} release.
7347 @item htdocs/index.html
7348 @itemx htdocs/news/index.html
7349 @itemx htdocs/download/index.html
7350 These files include:
7353 Announcement of the most recent release.
7355 News entry (remember to update both the top level and the news directory).
7357 These pages also need to be regenerate using @code{index.sh}.
7359 @item download/onlinedocs/
7360 You need to find the magic command that is used to generate the online
7361 docs from the @file{.tar.bz2}. The best way is to look in the output
7362 from one of the nightly @code{cron} jobs and then just edit accordingly.
7366 $ ~/ss/update-web-docs \
7367 ~ftp/pub/gdb/releases/gdb-5.2.tar.bz2 \
7369 /www/sourceware/htdocs/gdb/download/onlinedocs \
7374 Just like the online documentation. Something like:
7377 $ /bin/sh ~/ss/update-web-ari \
7378 ~ftp/pub/gdb/releases/gdb-5.2.tar.bz2 \
7380 /www/sourceware/htdocs/gdb/download/ari \
7386 @subsubheading Shadow the pages onto gnu
7388 Something goes here.
7391 @subsubheading Install the @value{GDBN} tar ball on GNU
7393 At the time of writing, the GNU machine was @kbd{gnudist.gnu.org} in
7394 @file{~ftp/gnu/gdb}.
7396 @subsubheading Make the @file{ANNOUNCEMENT}
7398 Post the @file{ANNOUNCEMENT} file you created above to:
7402 @email{gdb-announce@@sourceware.org, GDB Announcement mailing list}
7404 @email{info-gnu@@gnu.org, General GNU Announcement list} (but delay it a
7405 day or so to let things get out)
7407 @email{bug-gdb@@gnu.org, GDB Bug Report mailing list}
7412 The release is out but you're still not finished.
7414 @subsubheading Commit outstanding changes
7416 In particular you'll need to commit any changes to:
7420 @file{gdb/ChangeLog}
7422 @file{gdb/version.in}
7429 @subsubheading Tag the release
7434 $ d=`date -u +%Y-%m-%d`
7437 $ ( cd insight/src/gdb && cvs -f -q update )
7438 $ ( cd insight/src && cvs -f -q tag gdb_5_2-$d-release )
7441 Insight is used since that contains more of the release than
7444 @subsubheading Mention the release on the trunk
7446 Just put something in the @file{ChangeLog} so that the trunk also
7447 indicates when the release was made.
7449 @subsubheading Restart @file{gdb/version.in}
7451 If @file{gdb/version.in} does not contain an ISO date such as
7452 @kbd{2002-01-24} then the daily @code{cronjob} won't update it. Having
7453 committed all the release changes it can be set to
7454 @file{5.2.0_0000-00-00-cvs} which will restart things (yes the @kbd{_}
7455 is important - it affects the snapshot process).
7457 Don't forget the @file{ChangeLog}.
7459 @subsubheading Merge into trunk
7461 The files committed to the branch may also need changes merged into the
7464 @subsubheading Revise the release schedule
7466 Post a revised release schedule to @email{gdb@@sourceware.org, GDB
7467 Discussion List} with an updated announcement. The schedule can be
7468 generated by running:
7471 $ ~/ss/schedule `date +%s` schedule
7475 The first parameter is approximate date/time in seconds (from the epoch)
7476 of the most recent release.
7478 Also update the schedule @code{cronjob}.
7480 @section Post release
7482 Remove any @code{OBSOLETE} code.
7489 The testsuite is an important component of the @value{GDBN} package.
7490 While it is always worthwhile to encourage user testing, in practice
7491 this is rarely sufficient; users typically use only a small subset of
7492 the available commands, and it has proven all too common for a change
7493 to cause a significant regression that went unnoticed for some time.
7495 The @value{GDBN} testsuite uses the DejaGNU testing framework. The
7496 tests themselves are calls to various @code{Tcl} procs; the framework
7497 runs all the procs and summarizes the passes and fails.
7499 @section Using the Testsuite
7501 @cindex running the test suite
7502 To run the testsuite, simply go to the @value{GDBN} object directory (or to the
7503 testsuite's objdir) and type @code{make check}. This just sets up some
7504 environment variables and invokes DejaGNU's @code{runtest} script. While
7505 the testsuite is running, you'll get mentions of which test file is in use,
7506 and a mention of any unexpected passes or fails. When the testsuite is
7507 finished, you'll get a summary that looks like this:
7512 # of expected passes 6016
7513 # of unexpected failures 58
7514 # of unexpected successes 5
7515 # of expected failures 183
7516 # of unresolved testcases 3
7517 # of untested testcases 5
7520 To run a specific test script, type:
7522 make check RUNTESTFLAGS='@var{tests}'
7524 where @var{tests} is a list of test script file names, separated by
7527 The ideal test run consists of expected passes only; however, reality
7528 conspires to keep us from this ideal. Unexpected failures indicate
7529 real problems, whether in @value{GDBN} or in the testsuite. Expected
7530 failures are still failures, but ones which have been decided are too
7531 hard to deal with at the time; for instance, a test case might work
7532 everywhere except on AIX, and there is no prospect of the AIX case
7533 being fixed in the near future. Expected failures should not be added
7534 lightly, since you may be masking serious bugs in @value{GDBN}.
7535 Unexpected successes are expected fails that are passing for some
7536 reason, while unresolved and untested cases often indicate some minor
7537 catastrophe, such as the compiler being unable to deal with a test
7540 When making any significant change to @value{GDBN}, you should run the
7541 testsuite before and after the change, to confirm that there are no
7542 regressions. Note that truly complete testing would require that you
7543 run the testsuite with all supported configurations and a variety of
7544 compilers; however this is more than really necessary. In many cases
7545 testing with a single configuration is sufficient. Other useful
7546 options are to test one big-endian (Sparc) and one little-endian (x86)
7547 host, a cross config with a builtin simulator (powerpc-eabi,
7548 mips-elf), or a 64-bit host (Alpha).
7550 If you add new functionality to @value{GDBN}, please consider adding
7551 tests for it as well; this way future @value{GDBN} hackers can detect
7552 and fix their changes that break the functionality you added.
7553 Similarly, if you fix a bug that was not previously reported as a test
7554 failure, please add a test case for it. Some cases are extremely
7555 difficult to test, such as code that handles host OS failures or bugs
7556 in particular versions of compilers, and it's OK not to try to write
7557 tests for all of those.
7559 DejaGNU supports separate build, host, and target machines. However,
7560 some @value{GDBN} test scripts do not work if the build machine and
7561 the host machine are not the same. In such an environment, these scripts
7562 will give a result of ``UNRESOLVED'', like this:
7565 UNRESOLVED: gdb.base/example.exp: This test script does not work on a remote host.
7568 @section Testsuite Organization
7570 @cindex test suite organization
7571 The testsuite is entirely contained in @file{gdb/testsuite}. While the
7572 testsuite includes some makefiles and configury, these are very minimal,
7573 and used for little besides cleaning up, since the tests themselves
7574 handle the compilation of the programs that @value{GDBN} will run. The file
7575 @file{testsuite/lib/gdb.exp} contains common utility procs useful for
7576 all @value{GDBN} tests, while the directory @file{testsuite/config} contains
7577 configuration-specific files, typically used for special-purpose
7578 definitions of procs like @code{gdb_load} and @code{gdb_start}.
7580 The tests themselves are to be found in @file{testsuite/gdb.*} and
7581 subdirectories of those. The names of the test files must always end
7582 with @file{.exp}. DejaGNU collects the test files by wildcarding
7583 in the test directories, so both subdirectories and individual files
7584 get chosen and run in alphabetical order.
7586 The following table lists the main types of subdirectories and what they
7587 are for. Since DejaGNU finds test files no matter where they are
7588 located, and since each test file sets up its own compilation and
7589 execution environment, this organization is simply for convenience and
7594 This is the base testsuite. The tests in it should apply to all
7595 configurations of @value{GDBN} (but generic native-only tests may live here).
7596 The test programs should be in the subset of C that is valid K&R,
7597 ANSI/ISO, and C@t{++} (@code{#ifdef}s are allowed if necessary, for instance
7600 @item gdb.@var{lang}
7601 Language-specific tests for any language @var{lang} besides C. Examples are
7602 @file{gdb.cp} and @file{gdb.java}.
7604 @item gdb.@var{platform}
7605 Non-portable tests. The tests are specific to a specific configuration
7606 (host or target), such as HP-UX or eCos. Example is @file{gdb.hp}, for
7609 @item gdb.@var{compiler}
7610 Tests specific to a particular compiler. As of this writing (June
7611 1999), there aren't currently any groups of tests in this category that
7612 couldn't just as sensibly be made platform-specific, but one could
7613 imagine a @file{gdb.gcc}, for tests of @value{GDBN}'s handling of GCC
7616 @item gdb.@var{subsystem}
7617 Tests that exercise a specific @value{GDBN} subsystem in more depth. For
7618 instance, @file{gdb.disasm} exercises various disassemblers, while
7619 @file{gdb.stabs} tests pathways through the stabs symbol reader.
7622 @section Writing Tests
7623 @cindex writing tests
7625 In many areas, the @value{GDBN} tests are already quite comprehensive; you
7626 should be able to copy existing tests to handle new cases.
7628 You should try to use @code{gdb_test} whenever possible, since it
7629 includes cases to handle all the unexpected errors that might happen.
7630 However, it doesn't cost anything to add new test procedures; for
7631 instance, @file{gdb.base/exprs.exp} defines a @code{test_expr} that
7632 calls @code{gdb_test} multiple times.
7634 Only use @code{send_gdb} and @code{gdb_expect} when absolutely
7635 necessary. Even if @value{GDBN} has several valid responses to
7636 a command, you can use @code{gdb_test_multiple}. Like @code{gdb_test},
7637 @code{gdb_test_multiple} recognizes internal errors and unexpected
7640 Do not write tests which expect a literal tab character from @value{GDBN}.
7641 On some operating systems (e.g.@: OpenBSD) the TTY layer expands tabs to
7642 spaces, so by the time @value{GDBN}'s output reaches expect the tab is gone.
7644 The source language programs do @emph{not} need to be in a consistent
7645 style. Since @value{GDBN} is used to debug programs written in many different
7646 styles, it's worth having a mix of styles in the testsuite; for
7647 instance, some @value{GDBN} bugs involving the display of source lines would
7648 never manifest themselves if the programs used GNU coding style
7655 Check the @file{README} file, it often has useful information that does not
7656 appear anywhere else in the directory.
7659 * Getting Started:: Getting started working on @value{GDBN}
7660 * Debugging GDB:: Debugging @value{GDBN} with itself
7663 @node Getting Started,,, Hints
7665 @section Getting Started
7667 @value{GDBN} is a large and complicated program, and if you first starting to
7668 work on it, it can be hard to know where to start. Fortunately, if you
7669 know how to go about it, there are ways to figure out what is going on.
7671 This manual, the @value{GDBN} Internals manual, has information which applies
7672 generally to many parts of @value{GDBN}.
7674 Information about particular functions or data structures are located in
7675 comments with those functions or data structures. If you run across a
7676 function or a global variable which does not have a comment correctly
7677 explaining what is does, this can be thought of as a bug in @value{GDBN}; feel
7678 free to submit a bug report, with a suggested comment if you can figure
7679 out what the comment should say. If you find a comment which is
7680 actually wrong, be especially sure to report that.
7682 Comments explaining the function of macros defined in host, target, or
7683 native dependent files can be in several places. Sometimes they are
7684 repeated every place the macro is defined. Sometimes they are where the
7685 macro is used. Sometimes there is a header file which supplies a
7686 default definition of the macro, and the comment is there. This manual
7687 also documents all the available macros.
7688 @c (@pxref{Host Conditionals}, @pxref{Target
7689 @c Conditionals}, @pxref{Native Conditionals}, and @pxref{Obsolete
7692 Start with the header files. Once you have some idea of how
7693 @value{GDBN}'s internal symbol tables are stored (see @file{symtab.h},
7694 @file{gdbtypes.h}), you will find it much easier to understand the
7695 code which uses and creates those symbol tables.
7697 You may wish to process the information you are getting somehow, to
7698 enhance your understanding of it. Summarize it, translate it to another
7699 language, add some (perhaps trivial or non-useful) feature to @value{GDBN}, use
7700 the code to predict what a test case would do and write the test case
7701 and verify your prediction, etc. If you are reading code and your eyes
7702 are starting to glaze over, this is a sign you need to use a more active
7705 Once you have a part of @value{GDBN} to start with, you can find more
7706 specifically the part you are looking for by stepping through each
7707 function with the @code{next} command. Do not use @code{step} or you
7708 will quickly get distracted; when the function you are stepping through
7709 calls another function try only to get a big-picture understanding
7710 (perhaps using the comment at the beginning of the function being
7711 called) of what it does. This way you can identify which of the
7712 functions being called by the function you are stepping through is the
7713 one which you are interested in. You may need to examine the data
7714 structures generated at each stage, with reference to the comments in
7715 the header files explaining what the data structures are supposed to
7718 Of course, this same technique can be used if you are just reading the
7719 code, rather than actually stepping through it. The same general
7720 principle applies---when the code you are looking at calls something
7721 else, just try to understand generally what the code being called does,
7722 rather than worrying about all its details.
7724 @cindex command implementation
7725 A good place to start when tracking down some particular area is with
7726 a command which invokes that feature. Suppose you want to know how
7727 single-stepping works. As a @value{GDBN} user, you know that the
7728 @code{step} command invokes single-stepping. The command is invoked
7729 via command tables (see @file{command.h}); by convention the function
7730 which actually performs the command is formed by taking the name of
7731 the command and adding @samp{_command}, or in the case of an
7732 @code{info} subcommand, @samp{_info}. For example, the @code{step}
7733 command invokes the @code{step_command} function and the @code{info
7734 display} command invokes @code{display_info}. When this convention is
7735 not followed, you might have to use @code{grep} or @kbd{M-x
7736 tags-search} in emacs, or run @value{GDBN} on itself and set a
7737 breakpoint in @code{execute_command}.
7739 @cindex @code{bug-gdb} mailing list
7740 If all of the above fail, it may be appropriate to ask for information
7741 on @code{bug-gdb}. But @emph{never} post a generic question like ``I was
7742 wondering if anyone could give me some tips about understanding
7743 @value{GDBN}''---if we had some magic secret we would put it in this manual.
7744 Suggestions for improving the manual are always welcome, of course.
7746 @node Debugging GDB,,,Hints
7748 @section Debugging @value{GDBN} with itself
7749 @cindex debugging @value{GDBN}
7751 If @value{GDBN} is limping on your machine, this is the preferred way to get it
7752 fully functional. Be warned that in some ancient Unix systems, like
7753 Ultrix 4.2, a program can't be running in one process while it is being
7754 debugged in another. Rather than typing the command @kbd{@w{./gdb
7755 ./gdb}}, which works on Suns and such, you can copy @file{gdb} to
7756 @file{gdb2} and then type @kbd{@w{./gdb ./gdb2}}.
7758 When you run @value{GDBN} in the @value{GDBN} source directory, it will read a
7759 @file{.gdbinit} file that sets up some simple things to make debugging
7760 gdb easier. The @code{info} command, when executed without a subcommand
7761 in a @value{GDBN} being debugged by gdb, will pop you back up to the top level
7762 gdb. See @file{.gdbinit} for details.
7764 If you use emacs, you will probably want to do a @code{make TAGS} after
7765 you configure your distribution; this will put the machine dependent
7766 routines for your local machine where they will be accessed first by
7769 Also, make sure that you've either compiled @value{GDBN} with your local cc, or
7770 have run @code{fixincludes} if you are compiling with gcc.
7772 @section Submitting Patches
7774 @cindex submitting patches
7775 Thanks for thinking of offering your changes back to the community of
7776 @value{GDBN} users. In general we like to get well designed enhancements.
7777 Thanks also for checking in advance about the best way to transfer the
7780 The @value{GDBN} maintainers will only install ``cleanly designed'' patches.
7781 This manual summarizes what we believe to be clean design for @value{GDBN}.
7783 If the maintainers don't have time to put the patch in when it arrives,
7784 or if there is any question about a patch, it goes into a large queue
7785 with everyone else's patches and bug reports.
7787 @cindex legal papers for code contributions
7788 The legal issue is that to incorporate substantial changes requires a
7789 copyright assignment from you and/or your employer, granting ownership
7790 of the changes to the Free Software Foundation. You can get the
7791 standard documents for doing this by sending mail to @code{gnu@@gnu.org}
7792 and asking for it. We recommend that people write in "All programs
7793 owned by the Free Software Foundation" as "NAME OF PROGRAM", so that
7794 changes in many programs (not just @value{GDBN}, but GAS, Emacs, GCC,
7796 contributed with only one piece of legalese pushed through the
7797 bureaucracy and filed with the FSF. We can't start merging changes until
7798 this paperwork is received by the FSF (their rules, which we follow
7799 since we maintain it for them).
7801 Technically, the easiest way to receive changes is to receive each
7802 feature as a small context diff or unidiff, suitable for @code{patch}.
7803 Each message sent to me should include the changes to C code and
7804 header files for a single feature, plus @file{ChangeLog} entries for
7805 each directory where files were modified, and diffs for any changes
7806 needed to the manuals (@file{gdb/doc/gdb.texinfo} or
7807 @file{gdb/doc/gdbint.texinfo}). If there are a lot of changes for a
7808 single feature, they can be split down into multiple messages.
7810 In this way, if we read and like the feature, we can add it to the
7811 sources with a single patch command, do some testing, and check it in.
7812 If you leave out the @file{ChangeLog}, we have to write one. If you leave
7813 out the doc, we have to puzzle out what needs documenting. Etc., etc.
7815 The reason to send each change in a separate message is that we will not
7816 install some of the changes. They'll be returned to you with questions
7817 or comments. If we're doing our job correctly, the message back to you
7818 will say what you have to fix in order to make the change acceptable.
7819 The reason to have separate messages for separate features is so that
7820 the acceptable changes can be installed while one or more changes are
7821 being reworked. If multiple features are sent in a single message, we
7822 tend to not put in the effort to sort out the acceptable changes from
7823 the unacceptable, so none of the features get installed until all are
7826 If this sounds painful or authoritarian, well, it is. But we get a lot
7827 of bug reports and a lot of patches, and many of them don't get
7828 installed because we don't have the time to finish the job that the bug
7829 reporter or the contributor could have done. Patches that arrive
7830 complete, working, and well designed, tend to get installed on the day
7831 they arrive. The others go into a queue and get installed as time
7832 permits, which, since the maintainers have many demands to meet, may not
7833 be for quite some time.
7835 Please send patches directly to
7836 @email{gdb-patches@@sourceware.org, the @value{GDBN} maintainers}.
7838 @section Build Script
7840 @cindex build script
7842 The script @file{gdb_buildall.sh} builds @value{GDBN} with flag
7843 @option{--enable-targets=all} set. This builds @value{GDBN} with all supported
7844 targets activated. This helps testing @value{GDBN} when doing changes that
7845 affect more than one architecture and is much faster than using
7846 @file{gdb_mbuild.sh}.
7848 After building @value{GDBN} the script checks which architectures are
7849 supported and then switches the current architecture to each of those to get
7850 information about the architecture. The test results are stored in log files
7851 in the directory the script was called from.
7853 @include observer.texi