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John Gilmore Cygnus Solutions Second Edition

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1. 8 3 4 Stack Analysis blockframe c machine independent code to analyze stack frames stack c machine independent stack frame analysis user level commands to manage and inspect the stack 8 3 5 Breakpoints preakpoint c Machine independent breakpoint code Handles and dispatches all forms of breakpoints including hardware breakpoints software breakpoints hardware and software watchpoints and shared library breakpoints Contains top level commands to set inspect and manipulate breakpoints and watchpoints Pro vides routine to read memory from inferior replacing any memory that may have been overwritten by a breakpoint with its saved value mem break c Implements software breakpoints To set a breakpoint at a given location GDB saves the instruction at that location and inserts a software trap instruction in its place 8 3 6 Symbol File Management The following files allow GDB to parse and manage symbol information in a variety of formats For an overview of GDB object file and symbol handling see undefined Symbol Tables page undefined Chapter 8 GDB Overview 22 objfiles c create destroy manage objfile structures symfile c top level commands to handle objfiles also handles overlays unused symmisc c various objfile and p symtab utilities mainly debugging symtab c basic symbol table utilities mainly lookup minsyms c manage minimal symbol tables buil
2. HOST BYTE ORDER The ordering of bytes in the host This must be defined to be either BIG ENDIAN or LITTLE ENDIAN INT MAX INT MIN LONG MAX UINT MAX Chapter 7 Host Definition 15 ULONG_MAX Values for host side constants ISATTY Substitute for isatty if not available LONGEST This is the longest integer type available on the host If not defined it will default to long long or long depending on CC_HAS_LONG_LONG CC_HAS_LONG_LONG Define this if the host C compiler supports long long This is set by the configure script PRINTF_HAS_LONG_LONG Define this if the host can handle printing of long long integers via the printf format directive ll This is set by the configure script HAVE_LONG_DOUBLE Define this if the host C compiler supports long double This is set by the configure script PRINTF_HAS_LONG_DOUBLE Define this if the host can handle printing of long double float point numbers via the printf format directive Lg This is set by the configure script SCANF_HAS_LONG_DOUBLE Define this if the host can handle the parsing of long double float point numbers via the scanf format directive directive Lg This is set by the configure script LSEEK_NOT_LINEAR Define this if 1seek n does not necessarily move to byte number n in the file This is only used when reading source files It is normally faster to define CRLF SOURCE FILES when possible L SET This macro is used as the a
3. sw sivs roses tues mee 5 1 Symbol Reading 2 seine id 5 2 Partial Symbol Tables 0 0 e cece eee eee A C P 5 4 Object File Formats 0 eee eee II DAA ALOU erat a da ga Qe ta Ate Some ee beatae 542 CORB IA serrure e Ee 543 EGOEE uec he telat t UE EC SAA CO E it ted RE ER 54 5 BE cue cR RI HY E Pe e Deb HAGE oia ctetuer e EE Set ted DAM SON cet dE er ee RD 5 4 8 Other File Formats 0 0 0 cece eee eee 5 5 Debugging File Formats 0 0 000 eee eee eee DOL STADE uto e dese rer Mie ae PEREAT e 5 5 2 SCORE i dehet Ret DB aorta eas 5 5 3 Mips debug Third Eye oooooooooo o 5 5 4 DWARE Lilas illite erp Rd 10 5 bib DWARE 2 voit eek ek ded ee reges 10 500 SOMA ie URSI 10 5 6 Adding a New Symbol Reader to GDB 10 6 Language Support eere 10 6 1 Adding a Source Language to GDB 10 7 Host Definition erro E URS 12 7 1 Adding a New Host sesse eee eee 12 7 2 Host Conditionals 0 0 0 eee eee eee eee eens 13 8 GDB Overview soot IE Ree IRR 17 8 1 Libraries used by GDB 0 eee eee 17 8 2 GDB Directory Structure 2 0 eee eee 18 8 3 Overview of Source Files 00 02 cece eee eee eee 19 8 9 1 Top Level uas oet Ea ae de d Re DR a 19 8 3 2 GDB Targets Program Control 19 8 3 3 Types Values and Expressions 20 8 3 4 Stack An
4. gdb gdb which works on Suns and such you can copy gdb to gdb2 and then type gdb gdb2 When you run GDB in the GDB source directory it will read a gdbinit file that sets up some simple things to make debugging gdb easier The info command when executed without a subcommand in a GDB being debugged by gdb will pop you back up to the top level gdb See gdbinit for details If you use emacs you will probably want to do a make TAGS after you configure your distribution this will put the machine dependent routines for your local machine where they will be accessed first by M Also make sure that you ve either compiled GDB with your local cc or have run fixincludes if you are compiling with gcc 16 3 Submitting Patches Thanks for thinking of offering your changes back to the community of GDB users In general we like to get well designed enhancements Thanks also for checking in advance about the best way to transfer the changes The GDB maintainers will only install cleanly designed patches This manual sum marizes what we believe to be clean design for GDB If the maintainers don t have time to put the patch in when it arrives or if there is any question about a patch it goes into a large queue with everyone else s patches and bug reports The legal issue is that to incorporate substantial changes requires a copyright assign ment from you and or your employer granting ownership of the ch
5. infptrace c are used for these functions FILES_INFO_HOOK Only defined for Convex FPO_REGNUM This macro is normally defined to be the number of the first floating point register if the machine has such registers As such it would appear only in target specific code However proc support uses this to decide whether floats are in use on this target GET_LONGJMP_TARGET For most machines this is a target dependent parameter On the DECstation and the Iris this is a native dependent parameter since lt setjmp h gt is needed to define it This macro determines the target PC address that longjmp will jump to assuming that we have just stopped at a longjmp breakpoint It takes a CORE_ADDR as argument and stores the target PC value through this pointer It examines the current state of the machine as needed KERNEL_U_ADDR Define this to the address of the u structure the user struct also known as the u page in kernel virtual memory GDB needs to know this so that it can subtract this address from absolute addresses in the upage that are obtained via ptrace or from core files On systems that don t need this value set it to zero KERNEL U ADDR BSD Define this to cause GDB to determine the address of u at runtime by using Berkeley style nlist on the kernel s image in the root directory KERNEL U ADDR HPUX Define this to cause GDB to determine the address of u at runtime by using HP style nlist on th
6. to get GCC to check on a num ber of these rules GDB sources ought not to engender any complaints unless they are caused by bogus host systems The exact set of enabled warnings is currently Wa11 Wpointer arith Wstrict prototypes Wmissing prototypes Wmissing declarations Jj 13 3 1 Formatting The standard GNU recommendations for formatting must be followed strictly Note that while in a definition the function s name must be in column zero in a function declaration the name must be on the same line as the return type In addition there must be a space between a function or macro name and the opening parenthesis of its argument list except for macro definitions as required by C There must not be a space after an open paren bracket or before a close paren bracket While additional whitespace is generally helpful for reading do not use more than one blank line to separate blocks and avoid adding whitespace after the end of a program line as of 1 99 some 600 lines had whitespace after the semicolon Excess whitespace causes difficulties for diff and patch 13 3 2 Comments The standard GNU requirements on comments must be followed strictly Chapter 13 Coding 45 Block comments must appear in the following form with no or only lines and no leading Wait for control to return from inferior to debugger If inferior gets a signal we may decide to start it up again instead of returning That is
7. top c Top level routine used by GDB Evaluates commands and provides a number of top level functions and mechanisms to set general purpose variables command c parse and evaluate gdb commands and command documentation printcmd c user commands for printing expressions and displaying memory 8 3 2 GDB Targets Program Control target c Defines the target abstraction used to encapsulate all communications between GDB and a target See the comments in target h for more information exec c Interface between executable files and the target abstraction Allows GDB to inspect analyze executable images without necessarily having a debuggable process available corefile c Interface between core images and the target abstraction Allows GDB to inspect analyze memory and register dumps from corefile images Not used in GDB 4 14 thread c Interface between GDB and multiply threaded subprocesses Not currently used by either GDB 4 14 or GDB 4 17 fork child c Code to create an inferior process on UNIX systems Chapter 8 GDB Overview infcmd c User level commands for inspecting controlling the state of process execution Commands such as step next finish and continue go here inflow c Handles terminal modes and signal handling for UNIX child processes infrun c Target independent code to control the execution of an inferior pr
8. 10 6 Builtin Simulator 11 Native Debugging Several files control GDB s configuration for native support gdb config arch xyz mh Specifies Makefile fragments needed when hosting or native on machine xyz In particular this lists the required native dependent object files by defining NATDEPFILES Also specifies the header file which describes native support on xyz by defining NAT_FILE nm xyz h You can also define NAT_CFLAGS NAT_ADD_FILES NAT_CLIBS NAT_CDEPS etc see Makefile in Chapter 11 Native Debugging 38 gdb config arch nm xyz h nm h is a link to this file created by configure Contains C macro definitions describing the native system environment such as child process control and core file support gdb xyz nat c Contains any miscellaneous C code required for this native support of this machine On some machines it doesn t exist at all There are some generic versions of routines that can be used by various systems These can be customized in various ways by macros defined in your nm xyz h file If these routines work for the xyz host you can just include the generic file s name with o not e c in NATDEPFILES Otherwise if your machine needs custom support routines you will need to write routines that perform the same functions as the generic file Put them into xyz nat c and put xyz nat o into NATDEPFILES inftarg
9. Add support code for these operations in eval c evaluate_subexp Add cases for new opcodes in two functions from parse c prefixify subexp and length of subexpO These compute the number of exp elements that a given operation takes up Update some existing code Add an enumerated identifier for your language to the enumerated type enum language in defs h Update the routines in language c so your language is included These rou tines include type predicates and such which in some cases are language dependent If your language does not appear in the switch statement an error is reported Also included in language c is the code that updates the variable current _ language and the routines that translate the language lang enumerated iden tifier into a printable string Update the function initialize language to include your language This function picks the default language upon startup so is dependent upon which languages that GDB is built for Chapter 7 Host Definition 12 Update allocate_symtab in symfile c and or symbol reading code so that the language of each symtab source file is set properly This is used to deter mine the language to use at each stack frame level Currently the language is set based upon the extension of the source file If the language can be better inferred from the symbol information please set the language of the symtab in the symbol reading code Add helper c
10. Chapter 3 Algorithms 2 2 1 The Symbol Side The symbolic side of GDB can be thought of as everything you can do in GDB without having a live program running For instance you can look at the types of variables and evaluate many kinds of expressions 2 2 The Target Side The target side of GDB is the bits and bytes manipulator Although it may make reference to symbolic info here and there most of the target side will run with only a stripped executable available or even no executable at all in remote debugging cases Operations such as disassembly stack frame crawls and register display are able to work with no symbolic info at all In some cases such as disassembly GDB will use symbolic info to present addresses relative to symbols rather than as raw numbers but it will work either way 2 3 Configurations Host refers to attributes of the system where GDB runs Target refers to the system where the program being debugged executes In most cases they are the same machine in which case a third type of Native attributes come into play Defines and include files needed to build on the host are host support Examples are tty support system defined types host byte order host float format Defines and information needed to handle the target format are target dependent Ex amples are the stack frame format instruction set breakpoint instruction registers and how to set up and tear down the stack to call a func
11. hp for HP UX gdb compiler Tests specific to a particular compiler As of this writing June 1999 there aren t currently any groups of tests in this category that couldn t just as sensibly be made platform specific but one could imagine a gdb gcc for tests of GDB s handling of GCC extensions gdb subsystem Tests that exercise a specific GDB subsystem in more depth For instance gdb disasm exercises various disassemblers while gdb stabs tests pathways through the stabs symbol reader 15 3 Writing Tests In many areas the GDB tests are already quite comprehensive you should be able to copy existing tests to handle new cases You should try to use gdb_test whenever possible since it includes cases to handle all the unexpected errors that might happen However it doesn t cost anything to add new test procedures for instance gdb base exprs exp defines a test_expr that calls gdb_test multiple times Only use send_gdb and gdb_expect when absolutely necessary such as when GDB has several valid responses to a command The source language programs do not need to be in a consistent style Since GDB is used to debug programs written in many different styles it s worth having a mix of styles in the testsuite for instance some GDB bugs involving the display of source lines would never manifest themselves if the programs used GNU coding style uniformly Chapter 16 Hints 51 16 Hints Check the
12. 39 TAA c wInd2n un eere a b DA Ue Od RR RR ED sus 39 11 5 shared libraties nitore toe 39 11 6 Native Conditionals eee 39 12 Support Libraries o a 41 DA BED ei iA IRE Sk ete ie RUBER IS 42 12 2 OP COU GS oec eee red Raye ese Pease eae VER 42 12 95 xeadline over gene kuveidztercQ ee ea ee ia a noe pe 42 VD As MM AOC i oui e PR ca t tar at ea e el Ra a e RA 42 12 5 biberty setenta be eor t e oce ln 42 12 0 gn cfegex con A P e ae ee eae EAS RU CAS 42 1276 ancl de ui iae ECCLE ERES 43 135 Coding 2o di ma om eee ned QUEUE ois 43 13s Gleanu ps d dm bett et eye ERR AER TR ER 43 13 2 Wrapping Output Lines 0 0 00 enses 44 13 8 GDB Coding Standards cee eee eee eee eee 44 13 3 1 Formatting 0 eee eee eee 44 13 3 2 Comments ase Sad Gane o ON Oo Mase eke 44 13 33 USaBe icine epe Des 45 13 3 4 Function Prototypes seeeeese esses 45 13 3 5 Clean Design i ios n 46 14 Porting GDB ccoo aee ep ta 47 14 1 Configuring GDB for Release oocoooooommommo o 48 Te DestsulbO s iat SG eG wae bs hi e e ss 48 15 1 Using th Testsuite 3 30050 nt Cro RU 49 15 2 Testsuite Organization eeeeeee n 49 15 8 Writing Tests eee een mk e na dede oe 50 16 bs ii a aba a Rm a dde ane 51 16 1 Getting Started 51 16 2 Debugging GDB with itself 0 cee eee 52 16 3 Submitting Patches sese 52 16 4 O
13. 4 17 and the GDB 4 14 4 17 hybrid that shipped with DR1 from the same source tree GDB 4 17 was built in gdb and used files from gdb next and gdb in that order and GDB 4 14 was built in gdb 4 14 and used the files from gdb next 4 14 gdb next gdb 4 14 and gdb also in that order As of January 8 I have stopped building GDB 4 14 along with GDB 4 17 from the same sources I suspect GDB 4 14 will no longer build from these sources without modification although I suspect the necessary changes would be relatively minor GDB also uses the following subdirectories Chapter 8 GDB Overview 19 include Header files shared by GDB and all of the libraries it uses These files typically will typically apply to either General operating system functions such as symbol reading IEEE floats etc for which GDB and it s libraries want to have a common interface Interfaces between GDB and one of its libraries such as remote sim h and libiberty h gdb config Contains GDB specific configuration files For more information see undefined Config page undefined 8 3 Overview of Source Files 8 3 1 Top Level main c Contains the GDB top level interpreter Parses command line arguments per forms GDB initialization and passes control to command line interpreter maint c Collection of utility functions for viewing debugging the internal state of GDB
14. Define this to indicate that SVR4 style shared libraries are in use USE_PROC_FS This determines whether small routines in tdep c which translate register values between GDB s internal representation and the proc representation are compiled U_REGS_OFFSET This is the offset of the registers in the upage It need only be defined if the generic ptrace register access routines in infptrace c are being used that is infptrace c is configured in and FETCH_INFERIOR_REGISTERS is not defined If the default value from infptrace c is good enough leave it undefined The default value means that u u_ar0 points to the location of the registers I m guessing that define U_REGS_OFFSET O means that u u_ar0 is the location of the registers CLEAR_SOLIB objfiles c DEBUG_PTRACE Define this to debug ptrace calls 12 Support Libraries Chapter 12 Support Libraries 42 12 1 BFD BFD provides support for GDB in several ways identifying executable and core files BFD will identify a variety of file types including a out coff and several vari ants thereof as well as several kinds of core files access to sections of files BFD parses the file headers to determine the names virtual addresses sizes and file locations of all the various named sections in files such as the text section or the data section GDB simply calls BFD to read or write section X at byte offset Y for length Z specialized core file
15. associated with it Otherwise return 0 FRAME ARGS ADDRESS CORRECT stack c FRAME CHAIN frame Given frame return a pointer to the calling frame FRAME_CHAIN_COMBINE chain frame Define this to take the frame chain pointer and the frame s nominal address and produce the nominal address of the caller s frame Presently only defined for HP PA FRAME CHAIN VALID chain thisframe Define this to be an expression that returns zero if the given frame is an outer most frame with no caller and nonzero otherwise Three common definitions are available default frame chain valid the default is nonzero if the chain pointer is nonzero and given frame s PC is not inside the startup file such as crt0 o alternate frame chain valid is nonzero if the chain pointer is nonzero and the given frame s PC is not in main or a known entry point function such as start O FRAME INIT SAVED REGS frame See frame h Determines the address of all registers in the current stack frame storing each in frame gt saved_regs Space for frame gt saved_regs shall be allocated by FRAME INIT SAVED REGS using either frame saved regs zalloc or frame obstack alloc FRAME FIND SAVED REGS and EXTRA FRAME INFO are deprecated FRAME NUM ARGS fi For the frame described by fi return the number of arguments that are being passed If the number of arguments is not known return 1 FRAME SAVED PC frame Given frame r
16. cleanups that is throw them away without doing what they say This is only done if you ask that it be done Syntax struct cleanup old_chain Declare a variable which will hold a cleanup chain handle old chain make cleanup function arg Make a cleanup which will cause function to be called with arg a char later The result old chain is a handle that can be passed to do_cleanups or discard cleanups later Unless you are going to call do cleanups or discard cleanups yourself you can ignore the result from make cleanup do cleanups old chain Perform all cleanups done since make cleanup returned old_chain E g make cleanup a 0 old make cleanup b 0 do cleanups old will call bO but will not call ad The cleanup that calls ad will remain in the cleanup chain and will be done later unless otherwise discarded discard cleanups old chain Same as do cleanups except that it just removes the cleanups from the chain and does not call the specified functions Some functions e g fputs filtered or error specify that they should not be called when cleanups are not in place This means that any actions you need to reverse in the case of an error or interruption must be on the cleanup chain before you call these functions since they might never return to your code they longjmp instead Chapter 13 Coding 13 2 Wrapping Output Lines Output that goes through printf_filtered or fputs_fil
17. for some reason while unresolved and untested cases often indicate some minor catastrophe such as the compiler being unable to deal with a test program When making any significant change to GDB you should run the testsuite before and after the change to confirm that there are no regressions Note that truly complete testing would require that you run the testsuite with all supported configurations and a variety of compilers however this is more than really necessary In many cases testing with a single configuration is sufficient Other useful options are to test one big endian Sparc and one little endian x86 host a cross config with a builtin simulator powerpc eabi mips elf or a 64 bit host Alpha If you add new functionality to GDB please consider adding tests for it as well this way future GDB hackers can detect and fix their changes that break the functionality you added Similarly if you fix a bug that was not previously reported as a test failure please add a test case for it Some cases are extremely difficult to test such as code that handles host OS failures or bugs in particular versions of compilers and it s OK not to try to write tests for all of those 15 2 Testsuite Organization The testsuite is entirely contained in gdb testsuite While the testsuite includes some makefiles and configury these are very minimal and used for little besides cleaning up since the tests themselves handle the compilation of
18. library BFD is split into two parts the front end and the back ends one for each object file format e The front end of BFD provides the interface to the user It manages mem ory and various canonical data structures The front end also decides which back end to use and when to call back end routines e The back ends provide BFD its view of the real world Each back end provides a set of calls which the BFD front end can use to maintain its canonical form The back ends also may keep around information for their own use for greater efficiency For more information on BFD see bfd doc bfd texi For more information on the use of BFD in GDB see undefined BFD support for GDB page un defined opcodes A collection of routines to parse print machine language instructions and ar guments for a number of processors mmalloc The gnu malloc library sim Simulators for a number of common microprocessors Allows GDB to debug machine code for architectures for which no CPU is readily available or which are not yet capable of interacting with GDB directly Generally used to simulate and or debug embedded systems Chapter 8 GDB Overview 18 texinfo Texinfo is a documentation system that uses a single source file to produce both online information and printed output Most GDB related documentation is produced using this system For more information see texinfo doc texinfo texi Jj libiber
19. of a symbol file objfile could be thrown away after the symtab has been read in The symtab should always be searched before the psymtab so the psymtab will never be used in a bug free environment Currently psymtabs are allocated on an obstack and all the psymbols themselves are allocated in a pair of large arrays on an obstack so there is little to be gained by trying to free them unless you want to do a lot more work 5 3 Types Fundamental Types e g FT VOID FT BOOLEAN These are the fundamental types that GDB uses internally Fundamental types from the various debugging formats stabs ELF etc are mapped into one of these They are basically a union of all fundamental types that gdb knows about for all the languages that GDB knows about Type Codes e g TYPE CODE PTR TYPE CODE ARRAY Each time GDB builds an internal type it marks it with one of these types The type may be a fundamental type such as TYPE CODE INT or a derived type such as TYPE CODE PTR which is a pointer to another type Typically several FT_ types map to one TYPE CODE type and are distinguished by other members of the type struct such as whether the type is signed or unsigned and how many bits it uses Builtin Types e g builtin type_void builtin type char Chapter 5 Symbol Handling 8 These are instances of type structs that roughly correspond to fundamental types and are created as global types for GDB to use for various ugl
20. support BFD provides routines to determine the failing command name stored in a core file the signal with which the program failed and whether a core file matches i e could be a core dump of a particular executable file locating the symbol information GDB uses an internal interface of BFD to determine where to find the symbol information in an executable file or symbol file GDB itself handles the reading of symbols since BFD does not understand debug symbols but GDB uses BFD s cached information to find the symbols string table etc 12 2 opcodes The opcodes library provides GDB s disassembler It s a separate library because it s also used in binutils for objdump 12 3 readline 12 4 mmalloc 12 5 libiberty 12 6 gnu regex Regex conditionals C ALLOCA NFAILURES RE NREGS SIGN EXTEND CHAR SWITCH ENUM BUG SYNTAX TABLE Chapter 13 Coding 43 Sword sparc 12 7 include 13 Coding This chapter covers topics that are lower level than the major algorithms of GDB 13 1 Cleanups Cleanups are a structured way to deal with things that need to be done later When your code does something like malloc some memory or open a file that needs to be undone later e g free the memory or close the file it can make a cleanup The cleanup will be done at some future point when the command is finished when an error occurs or when your code decides it s time to do cleanups You can also discard
21. the code which uses and creates those symbol tables You may wish to process the information you are getting somehow to enhance your understanding of it Summarize it translate it to another language add some perhaps trivial or non useful feature to GDB use the code to predict what a test case would do and write the test case and verify your prediction etc If you are reading code and your eyes are starting to glaze over this is a sign you need to use a more active approach Once you have a part of GDB to start with you can find more specifically the part you are looking for by stepping through each function with the next command Do not use step or you will quickly get distracted when the function you are stepping through calls another function try only to get a big picture understanding perhaps using the comment at the beginning of the function being called of what it does This way you can identify which of the functions being called by the function you are stepping through is the one which you are interested in You may need to examine the data structures generated at each stage with reference to the comments in the header files explaining what the data structures are supposed to look like Of course this same technique can be used if you are just reading the code rather than actually stepping through it The same general principle applies when the code you are looking at calls something else just try to understand generally what
22. the code being called does rather than worrying about all its details Chapter 16 Hints 52 A good place to start when tracking down some particular area is with a command which invokes that feature Suppose you want to know how single stepping works As a GDB user you know that the step command invokes single stepping The command is invoked via command tables see command h by convention the function which actually performs the command is formed by taking the name of the command and adding _command or in the case of an info subcommand _info For example the step command invokes the step_command function and the info display command invokes display_info When this convention is not followed you might have to use grep or M x tags search in emacs or run GDB on itself and set a breakpoint in execute command If all of the above fail it may be appropriate to ask for information on bug gdb But never post a generic question like I was wondering if anyone could give me some tips about understanding GDB if we had some magic secret we would put it in this manual Suggestions for improving the manual are always welcome of course 16 2 Debugging GDB with itself If GDB is limping on your machine this is the preferred way to get it fully functional Be warned that in some ancient Unix systems like Ultrix 4 2 a program can t be running in one process while it is being debugged in another Rather than typing the command
23. the programs that GDB will run The file testsuite lib gdb exp contains common utility procs useful for all GDB tests while the directory testsuite config contains configuration specific files typically used for special purpose definitions of procs like gdb_load and gdb_start Chapter 16 Hints The tests themselves are to be found in testsuite gdb and subdirectories of those The names of the test files must always end with exp DejaGNU collects the test files by wildcarding in the test directories so both subdirectories and individual files get chosen and run in alphabetical order The following table lists the main types of subdirectories and what they are for Since DejaGNU finds test files no matter where they are located and since each test file sets up its own compilation and execution environment this organization is simply for convenience and intelligibility gdb base This is the base testsuite The tests in it should apply to all configurations of GDB but generic native only tests may live here The test programs should be in the subset of C that is valid K amp R ANSI ISO and C ifdefs are allowed if necessary for instance for prototypes gdb lang Language specific tests for all languages besides C Examples are gdb c and gdb java gdb platform Non portable tests The tests are specific to a specific configuration host or target such as HP UX or eCos Example is gdb
24. why there is a loop in this function When this function actually returns it means the inferior should be left stopped and GDB should read more commands Note that this format is encouraged by Emacs tabbing for a multi line comment works correctly and M Q fills the block consistently Put a blank line between the block comments preceding function or variable definitions and the definition itself In general put function body comments on lines by themselves rather than trying to fit them into the 20 characters left at the end of a line since either the comment or the code will inevitably get longer than will fit and then somebody will have to move it anyhow 13 3 3 C Usage Code must not depend on the sizes of C data types the format of the host s floating point numbers the alignment of anything or the order of evaluation of expressions Use functions freely There are only a handful of compute bound areas in GDB that might be affected by the overhead of a function call mainly in symbol reading Most of GDB s performance is limited by the target interface whether serial line or system call However use functions with moderation A thousand one line functions are just as hard to understand as a single thousand line function 13 3 4 Function Prototypes Prototypes must be used to declare functions but never to define them Prototypes for GDB functions must include both the argument type and name with the name matching th
25. you know what interface is being used to talk to the target system All references to the target must go through the current target_ops vector You can t assume that the host and target machines are the same machine except in the native support modules In particular you can t assume that the target machine s header files will be available on the host machine Target code must bring along its own header files written from scratch or explicitly donated by their owner to avoid copyright problems Insertion of new ifdef s will be frowned upon It s much better to write the code portably than to conditionalize it for various systems New ifdef s which test for specific compilers or manufacturers or operating systems are unacceptable All ifdef s should test for features The information about which configu rations contain which features should be segregated into the configuration files Experience has proven far too often that a feature unique to one particular system often creeps into other systems and that a conditional based on some predefined macro for your current sys tem will become worthless over time as new versions of your system come out that behave differently with regard to this feature Adding code that handles specific architectures operating systems target interfaces or hosts is not acceptable in generic code If a hook is needed at that point invent a generic hook and define it for your configurati
26. E PCC PROMOTION TYPE Define this if GDB should believe the type of a short argument when compiled by pcc but look within a full int space to get its value Only defined for Sun 3 at present BITS BIG ENDIAN Define this if the numbering of bits in the targets does not match the endi anness of the target byte order A value of 1 means that the bits are numbered in a big endian order 0 means little endian BREAKPOINT This is the character array initializer for the bit pattern to put into memory where a breakpoint is set Although it s common to use a trap instruction for a breakpoint it s not required for instance the bit pattern could be an invalid instruction The breakpoint must be no longer than the shortest instruction of the architecture BREAKPOINT has been deprecated in favour of BREAKPOINT FROM PC BIG BREAKPOINT Chapter 9 Target Architecture Definition LITTLE_BREAKPOINT Similar to BREAKPOINT but used for bi endian targets BIG_BREAKPOINT and LITTLE BREAKPOINT have been deprecated in favour of BREAKPOINT_FROM_PC REMOTE_BREAKPOINT LITTLE_REMOTE_BREAKPOINT BIG_REMOTE_BREAKPOINT Similar to BREAKPOINT but used for remote targets BIG_REMOTE_BREAKPOINT and LITTLE REMOTE BREAKPOINT havell been deprecated in favour of BREAKPOINT FROM PC BREAKPOINT FROM PC pcptr lenptr Use the program counter to determine the contents and size of a breakpoint instruction It returns a pointer to a string of bytes that en
27. GDB Internals A guide to the internals of the GNU debugger John Gilmore Cygnus Solutions Second Edition Stan Shebs Cygnus Solutions Cygnus Solutions Revision 1 127 TFXinfo 2 257 Copyright 1990 1999 Free Software Foundation Inc Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies Chapter 2 Overall Structure 1 Scope of this Document This document documents the internals of the GNU debugger GDB It includes descrip tion of GDB s key algorithms and operations as well as the mechanisms that adapt GDB to specific hosts and targets 1 Requirements Before diving into the internals you should understand the formal requirements and other expectations for GDB Although some of these may seem obvious there have been proposals for GDB that have run counter to these requirements First of all GDB is a debugger It s not designed to be a front panel for embedded systems It s not a text editor It s not a shell It s not a programming environment GDB is an interactive tool Although a batch mode is available GDB s primary role is to interact with a human programmer GDB should be responsive to the user A programmer hot on the trail of a nasty bug and operating under a looming deadline is going to be very impatient of everything including the response time to debugger commands GDB should be relat
28. IN_SIGTRAMP pc name Define this to return true if the given pc and or name indicates that the current function is a sigtramp SIGTRAMP_START pc SIGTRAMP_END pc Define these to be the start and end address of the sigtramp for the given pc On machines where the address is just a compile time constant the macro expansion will typically just ignore the supplied pc IN_SOLIB_CALL_TRAMPOLINE pc name Define this to evaluate to nonzero if the program is stopped in the trampoline that connects to a shared library IN_SOLIB_RETURN_TRAMPOLINE pc name Define this to evaluate to nonzero if the program is stopped in the trampoline that returns from a shared library IS_TRAPPED_INTERNALVAR name This is an ugly hook to allow the specification of special actions that should occur as a side effect of setting the value of a variable internal to GDB Cur rently only used by the h8500 Note that this could be either a host or target conditional NEED_TEXT_START_END Define this if GDB should determine the start and end addresses of the text section Seems dubious NO_HIF_SUPPORT Specific to the a29k SOFTWARE_SINGLE_STEP_P Define this as 1 if the target does not have a hardware single step mechanism The macro SOFTWARE_SINGLE_STEP must also be defined Chapter 9 Target Architecture Definition 32 SOFTWARE_SINGLE_STEP signal insert_breapoints_p A function that inserts or removes dependant on insert_breapoints_p break points at
29. ITE SP TARGET READ FP TARGET WRITE FP These change the behavior of read pc write pc read sp write sp read fp and write fp For most targets these may be left undefined GDB will call the read and write register functions with the relevant REGNUM argument These macros are useful when a target keeps one of these registers in a hard to get at place for example part in a segment register and part in an ordinary register TARGET VIRTUAL FRAME POINTER pc regp offsetp Returns a register offset pair representing the virtual frame pointer in use at the code address pc If virtual frame pointers are not used a default definition simply returns FP REGNUM with an offset of zero USE STRUCT CONVENTION gcc p type If defined this must be an expression that is nonzero if a value of the given type being returned from a function must have space allocated for it on the stack gcc p is true if the function being considered is known to have been compiled by GCC this is helpful for systems where GCC is known to use different calling convention than other compilers VARIABLES INSIDE BLOCK desc gcc p For dbx style debugging information if the compiler puts variable declarations inside LBRAC RBRAC blocks this should be defined to be nonzero desc is the value of n desc from the N_RBRAC symbol and gcc p is true if GDB has no ticed the presence of either the GCC COMPILED SYMBOL or the GCC2_COMPILED_ SYMBOL By default t
30. R regno A C expression that should be nonzero if regno cannot be fetched from an inferior process This is only relevant if FETCH INFERIOR REGISTERS is not defined CANNOT STORE REGISTER regno A C expression that should be nonzero if regno should not be written to the target This is often the case for program counters status words and other special registers If this is not defined GDB will assume that all registers may be written D0 DEFERRED STORES CLEAR DEFERRED STORES Define this to execute any deferred stores of registers into the inferior and to cancel any deferred stores Currently only implemented correctly for native Sparc configurations CPLUS MARKER Define this to expand into the character that G uses to distinguish compiler generated identifiers from programmer specified identifiers By default this expands into Most System V targets should define this to DBX PARM SYMBOL CLASS Hook for the SYMBOL CLASS of a parameter when decoding DBX symbol infor mation In the 1960 parameters can be stored as locals or as args depending on the type of the debug record DECR PC AFTER BREAK Define this to be the amount by which to decrement the PC after the program encounters a breakpoint This is often the number of bytes in BREAKPOINT though not always For most targets this value will be 0 DECR PC AFTER HW BREAK Similarly for hardware breakpoints DISABLE UNSETTABLE BREAK addr If def
31. README file it often has useful information that does not appear anywhere else in the directory 16 1 Getting Started GDB is a large and complicated program and if you first starting to work on it it can be hard to know where to start Fortunately if you know how to go about it there are ways to figure out what is going on This manual the GDB Internals manual has information which applies generally to many parts of GDB Information about particular functions or data structures are located in comments with those functions or data structures If you run across a function or a global variable which does not have a comment correctly explaining what is does this can be thought of as a bug in GDB feel free to submit a bug report with a suggested comment if you can figure out what the comment should say If you find a comment which is actually wrong be especially sure to report that Comments explaining the function of macros defined in host target or native dependent files can be in several places Sometimes they are repeated every place the macro is defined Sometimes they are where the macro is used Sometimes there is a header file which supplies a default definition of the macro and the comment is there This manual also documents all the available macros Start with the header files Once you some idea of how GDB s internal symbol tables are stored see symtab h gdbtypes h you will find it much easier to understand
32. ad SKIP_TRAMPOLINE_CODE pc If the target machine has trampoline code that sits between callers and the functions being called then define this macro to return a new PC that is at the start of the real function SP_REGNUM If the stack pointer is kept in a register then define this macro to be the number greater than or equal to zero of that register This should only need to be defined if TARGET_WRITE_SP and TARGET_WRITE_SP are not defined STAB_REG_TO_REGNUM Define this to convert stab register numbers as gotten from r declarations into GDB regnums If not defined no conversion will be done STACK_ALIGN addr Define this to adjust the address to the alignment required for the processor s stack Chapter 9 Target Architecture Definition STEP_SKIPS_DELAY addr Define this to return true if the address is of an instruction with a delay slot If a breakpoint has been placed in the instruction s delay slot GDB will single step over that instruction before resuming normally Currently only defined for the Mips STORE_RETURN_VALUE type valbuf A C expression that stores a function return value of type type where valbuf is the address of the value to be stored SUN_FIXED_LBRAC_BUG Used only for Sun 3 and Sun 4 targets SYMBOL RELOADING DEFAULT The default value of the symbol reloading variable Never defined in current sources TARGET BYTE ORDER DEFAULT The ordering of bytes in the target Th
33. alysis 0 00 cece eee ee eee 21 8 3 5 Breakpoinis i ct eee cay ee ee be ies 21 8 3 6 Symbol File Management 0 21 8 3 7 Language Specific Sources ooooococoooco oo 23 8 3 8 Kernel Debugging 00 00000000005 23 8 3 9 Sources Specific to Mac OS X ss 23 8 3 10 PowerPC specific Sources 0oo oooooo o 24 8 3 11 Miscellaneous 00 cee eee ee eee 24 8 3 12 Assorted Utilities 00ooooooooocooo 24 9 Target Architecture Definition 25 9 1 Registers and Memory lseeeeeee eene 25 9 2 Frame Interpretation leeeeeeee enn 25 9 3 Inferior Call Setup oooooooocccccoccccoccc eee 25 9 4 Compiler Characteristics 00 0 cece cece een eens 25 9 5 Target Conditionals 0 26 9 6 Adding a New Target 0 cece cece eee ee eee 35 10 Target Vector Definition 36 10 1 File Target eR er Roe FRA artes 36 10 2 Standard Protocol and Remote Stubs 36 10 3 ROM Monitor Interface 0 0 eee eee eee eee 37 10 4 Custom Protocols 0 cece cece eee tenes 37 10 5 Transport Layer 0 0 0 eee 37 10 6 Builtin Simulator 0 00 eee 37 ii 11 Native Debugging o ooo o o ooooo o 37 11 1 Native core file Support 00 eese 38 LLL DITA v chek bole tA ceed he eed Sy 39 HGS DLO eos de vt Sr oro eee pee kee seats
34. anges to the Free Soft ware Foundation You can get the standard documents for doing this by sending mail to gnu gnu org and asking for it We recommend that people write in All programs owned Chapter 16 Hints 53 by the Free Software Foundation as NAME OF PROGRAM so that changes in many programs not just GDB but GAS Emacs GCC etc can be contributed with only one piece of legalese pushed through the bureacracy and filed with the FSF We can t start merging changes until this paperwork is received by the FSF their rules which we follow since we maintain it for them Technically the easiest way to receive changes is to receive each feature as a small context diff or unidiff suitable for patch Each message sent to me should include the changes to C code and header files for a single feature plus ChangeLog entries for each directory where files were modified and diffs for any changes needed to the manuals gdb doc gdb texinfo or gdb doc gdbint texinfo If there are a lot of changes for a single feature they can be split down into multiple messages In this way if we read and like the feature we can add it to the sources with a single patch command do some testing and check it in If you leave out the ChangeLog we have to write one If you leave out the doc we have to puzzle out what needs documenting Etc The reason to send each change in a separate message is that we will not install some of the changes They ll be
35. at c file and be sure xyz nat o is in the NATDEPFILES list If you have your own fetch core registers you may not need a separate register addr Many Chapter 11 Native Debugging 39 custom fetch_core_registers implementations simply locate the registers themselves When making GDB run native on a new operating system to make it possible to debug core files you will need to either write specific code for parsing your OS s core files or customize bfd trad core c First use whatever include files your machine uses to define the struct of registers that is accessible possibly in the u area in a core file rather than machine reg h and an include file that defines whatever header exists on a core file e g the u area or a struct core Then modify trad_unix_core_file_p to use these values to set up the section information for the data segment stack segment any other segments in the core file perhaps shared library contents or control information registers segment and if there are two discontiguous sets of registers e g integer and float the reg2 segment This section information basically delimits areas in the core file in a standard way which the section reading routines in BFD know how to seek around in Then back in GDB you need a matching routine called fetch_core_registers If you can use the generic one it s in core aout c if not it s in your xyz nat c file It
36. at used in the actual function definition For the sake of compatibility with pre ANSI compilers define prototypes with the PARAMS macro extern int memory_remove_breakpoint PARAMS CORE_ADDR addr char contents_cache Note the double parentheses around the parameter types This allows an arbitrary number of parameters to be described without freaking out the C preprocessor When the function has no parameters it should be described like extern void noprocess PARAMS void The PARAMS macro expands to its argument in ANSI C or to a simple O in traditional C Chapter 13 Coding 46 All external functions should have a PARAMS declaration in a header file that callers include except for _initialize_ functions which must be external so that init c construction works but shouldn t be visible to random source files All static functions must be declared in a block near the top of the source file 13 3 5 Clean Design In addition to getting the syntax right there s the little question of semantics Some things are done in certain ways in GDB because long experience has shown that the more obvious ways caused various kinds of trouble You can t assume the byte order of anything that comes from a target including values object files and instructions Such things must be byte swapped using SWAP_TARGET_AND_ HOST in GDB or one of the swap routines defined in bfd h such as bfd_get_32 You can t assume that
37. ation The argument to add symtab fns is a struct sym fns which contains the name or name prefix of the symbol format the length of the prefix and pointers to four functions These functions are called at various times to process symbol files whose identification matches the specified prefix The functions supplied by each module are xyz Symfile init struct sym fns sf Called from symbol file add when we are about to read a new symbol file This function should clean up any internal state possibly resulting from half read previous files for example and prepare to read a new symbol file Note that the symbol file which we are reading might be a new main symbol file or might be a secondary symbol file whose symbols are being added to the existing symbol table The argument to xyz symfile init is a newly allocated struct sym fns whose bfd field contains the BFD for the new symbol file being read Its private field has been zeroed and can be modified as desired Typically a struct of private information will be malloc d and a pointer to it will be placed in the private field There is no result from xyz_symfile_init but it can call error if it detects an unavoidable problem Chapter 5 Symbol Handling 6 xyz_new_init Called from symbol_file_add when discarding existing symbols This function need only handle the symbol reading module s internal state the symbol table data structures visible to the rest of GDB will
38. be discarded by symbol_file_ add It has no arguments and no result It may be called after xyz_symfile_ init if a new symbol table is being read or may be called alone if all symbols are simply being discarded xyz_symfile_read struct sym_fns sf CORE_ADDR addr int mainline Called from symbol_file_add to actually read the symbols from a symbol file into a set of psymtabs or symtabs sf points to the struct sym fns originally passed to xyz_sym_init for possible initialization addr is the offset between the file s specified start address and its true address in memory mainline is 1 if this is the main symbol table being read and 0 if a secondary symbol file e g shared library or dynamically loaded file is being read In addition if a symbol reading module creates psymtabs when xyz_symfile_read is called these psymtabs will contain a pointer to a function xyz psymtab to symtab which can be called from any point in the GDB symbol handling code xyz psymtab to symtab struct partial symtab pst Called from psymtab to symtab or the PSYMTAB_TO_SYMTAB macro if the psymtab has not already been read in and had its pst gt symtab pointer set The argument is the psymtab to be fleshed out into a symtab Upon return pst gt readin should have been set to 1 and pst gt symtab should contain a pointer to the new corresponding symtab or zero if there were no symbols in that part of the symbol file 5 2 Partial Symbol Tables GDB
39. bsolete Conditionals see 53 111
40. c This contains the target_ops vector that supports Unix child processes on sys tems which use ptrace and wait to control the child procfs c This contains the target_ops vector that supports Unix child processes on sys tems which use proc to control the child fork child c This does the low level grunge that uses Unix system calls to do a fork and exec to start up a child process infptrace c This is the low level interface to inferior processes for systems using the Unix ptrace call in a vanilla way 11 1 Native core file Support core aout c fetch_core_registers Support for reading registers out of a core file This routine calls register_ addr see below Now that BFD is used to read core files virtually all machines should use core aout c and should just provide fetch_core_ registers in xyz nat c or REGISTER_U_ADDR in nm xyz h core aout c register_addr If your nm xyz h file defines the macro REGISTER_U_ADDR addr blockend regno it should be defined to set addr to the offset within the user struct of GDB register number regno blockend is the offset within the upage of u u_ arO If REGISTER U ADDR is defined core aout c will define the register addr function and use the macro in it If you do not define REGISTER U ADDR but you are using the standard fetch core registers you will need to define your own version of register addr put it into your xyz n
41. code a breakpoint instruction stores the length of the string to lenptr and adjusts pc if neces sary to point to the actual memory location where the breakpoint should be inserted Although it is common to use a trap instruction for a breakpoint it s not required for instance the bit pattern could be an invalid instruction The breakpoint must be no longer than the shortest instruction of the architecture Replaces all the other BREAKPOINT macros CALL DUMMY P A C expresson that is non zero when the target suports inferior function calls CALL DUMMY WORDS Pointer to an array of LONGEST words of data containing host byte ordered REGISTER_BYTES sized values that partially specify the sequence of instruc tions needed for an inferior function call Should be deprecated in favour of a macro that uses target byte ordered data SIZEOF CALL DUMMY WORDS The size of CALL DUMMY_WORDS When CALL DUMMY P this must re turn a positive value See also CALL DUMMY LENGTH CALL DUMMY A static initializer for CALL DUMMY WORDS Deprecated CALL DUMMY LOCATION inferior h CALL DUMMY STACK ADJUST Stack adjustment needed when performing an inferior function call Should be deprecated in favor of something like STACK ALIGN CALL DUMMY STACK ADJUST P Predicate for use of CALL DUMMY STACK ADJUST Should be deprecated in favor of something like STACK ALIGN Chapter 9 Target Architecture Definition 28 CANNOT FETCH REGISTE
42. ddr Define this to push arguments onto the stack for inferior function call Return the updated stack pointer value PUSH DUMMY FRAME Used in call function by hand to create an artificial stack frame Chapter 9 Target Architecture Definition 33 REGISTER_BYTES The total amount of space needed to store GDB s copy of the machine s register state REGISTER NAME i Return the name of register i as a string May return NULL or NUL to indicate that register 1 is not valid REGISTER NAMES Deprecated in favor of REGISTER NAME REG STRUCT HAS ADDR gcc p type Define this to return 1 if the given type will be passed by pointer rather than directly SAVE_DUMMY_FRAME_TOS sp Used in call_function_by_hand to notify the target dependent code of the top of stack value that will be passed to the the inferior code This is the value of the SP after both the dummy frame and space for parameters results have been allocated on the stack SDB_REG_TO_REGNUM Define this to convert sdb register numbers into GDB regnums If not defined no conversion will be done SHIFT_INST_REGS Only used for m88k targets SKIP_PROLOGUE pc A C expression that returns the address of the real code beyond the function entry prologue found at pc SKIP_PROLOGUE_FRAMELESS_P A C expression that should behave similarly but that can stop as soon as the function is known to have a frame If not defined SKIP_PROLOGUE will be used inste
43. dependent code So FP REGNUM can have any value that is convenient for the code that creates new frames create new frame calls INIT EXTRA FRAME INFO if it is defined that is where you should use the FP REGNUM value if your frames are nonstandard Given a GDB frame define FRAME CHAIN to determine the address of the calling func tion s frame This will be used to create a new GDB frame struct and then INIT EXTRA FRAME INFO and INIT FRAME PC will be called for the new frame 3 2 Breakpoint Handling In general a breakpoint is a user designated location in the program where the user wants to regain control if program execution ever reaches that location There are two main ways to implement breakpoints either as hardware breakpoints or as software breakpoints Hardware breakpoints are sometimes available as a builtin debugging features with some chips Typically these work by having dedicated register into which the breakpoint address may be stored If the PC ever matches a value in a breakpoint registers the CPU raises an exception and reports it to GDB Another possibility is when an emulator is in use many emulators include circuitry that watches the address lines coming out from the processor and force it to stop if the address matches a breakpoint s address A third possibility is that the target already has the ability to do breakpoints somehow for instance a ROM monitor may do its own software breakpoints S
44. dsym c build complete symbol data structures The following source files provide symbol reading interfaces for various file formats Al though all these files are compiled into GDB for Mac OS X only the first three stabsread dbxread and machoread are actively used by the rest of GDB stabsread c common stabs parsing routines dbxread c read DBX stabs symbol files machoread c read Mach O stabs symbol files nlmread c read Netware NLM symbol files unused os9kread c read OS9 OS9K symbol files unused dwarf 2read c read DWARF 2 symbol files unused dwarfread c read DWARF symbol files unused elfread c read ELF symbol files unused coffread c read COFF symbol files unused mdebugread c read ECOFF symbol files unused mipsread c read MIPS symbol files unused Chapter 8 GDB Overview 23 8 3 7 Language Specific Sources The following files are used to provide language specific expression evaluation and print ing support The file lang exp handles expression parsing lang typeprint prints human readable versions of GDB type structures and lang valprint prints human readable ver sions of GDB value structures and lang lang provides general language specific support functions For more information on language specific support in GDB see undefined Languages page undefined C c exp c lang c
45. e address which is inside a function in this file The address will be noticed to be in the range of this psymtab and the full symtab will be read in find_pc_function find_pc_line and other find_pc_ functions handle this e by its name e g the user asks to print a variable or set a breakpoint on a function Global names and file scope names will be found in the psymtab which will cause the symtab to be pulled in Local names will have to be qualified by a global name or a file scope name in which case we will have already read in the symtab as we evaluated the qualifier Or a local symbol can be referenced when we are in a local scope in which case the first case applies lookup symbol does most of the work here The only reason that psymtabs exist is to cause a symtab to be read in at the right moment Any symbol that can be elided from a psymtab while still causing that to happen should not appear in it Since psymtabs don t have the idea of scope you can t put local symbols in them anyway Psymtabs don t have the idea of the type of a symbol either so types need not appear unless they will be referenced by name It is a bug for GDB to behave one way when only a psymtab has been read and another way if the corresponding symtab has been read in Such bugs are typically caused by a psymtab that does not contain all the visible symbols or which has the wrong instruction address ranges The psymtab for a particular section
46. e kernel s image in the root directory ONE PROCESS WRITETEXT Define this to be able to when a breakpoint insertion fails warn the user that another process may be running with the same executable PROC NAME FMT Defines the format for the name of a proc device Should be defined in nm h only in order to override the default definition in procfs c PTRACE FP BUG mach386 xdep c PTRACE ARG3 TYPE The type of the third argument to the ptrace system call if it exists and is different from int Chapter 12 Support Libraries 41 REGISTER U ADDR Defines the offset of the registers in the u area SHELL COMMAND CONCAT If defined is a string to prefix on the shell command used to start the inferior SHELL FILE If defined this is the name of the shell to use to run the inferior Defaults to bin sh SOLIB_ADD filename from_tty targ Define this to expand into an expression that will cause the symbols in filename to be added to GDB s symbol table SOLIB_CREATE_INFERIOR_HOOK Define this to expand into any shared library relocation code that you want to be run just after the child process has been forked START_INFERIOR_TRAPS_EXPECTED When starting an inferior GDB normally expects to trap twice once when the shell execs and once when the program itself execs If the actual number of traps is something other than 2 then define this macro to expand into the number expected SVR4_SHARED_LIBS
47. each possible destinations of the next instruction See sparc tdep c and rs6000 tdep c for examples PCC_SOL_BROKEN Used only in the Convex target PC_IN_CALL_DUMMY inferior h PC_LOAD_SEGMENT If defined print information about the load segment for the program counter Defined only for the RS 6000 PC_REGNUM If the program counter is kept in a register then define this macro to be the number greater than or equal to zero of that register This should only need to be defined if TARGET READ PC and TARGET WRITE PC are not defined NPC REGNUM The number of the next program counter register if defined NNPC REGNUM The number of the next next program counter register if defined Currently this is only defined for the Motorola 88K PRINT REGISTER HOOK regno If defined this must be a function that prints the contents of the given register to standard output PRINT TYPELESS INTEGER This is an obscure substitute for print longest that seems to have been de fined for the Convex target PROCESS LINENUMBER HOOK A hook defined for XCOFF reading PROLOGUE FIRSTLINE OVERLAP Only used in unsupported Convex configuration PS REGNUM If defined this is the number of the processor status register This definition is only used in generic code when parsing ps POP FRAME Used in call function by hand to remove an artificial stack frame PUSH ARGUMENTS nargs args sp struct return struct a
48. et machine s processor chip registers stack etc If used it is included by tm ttt h It can be shared among many targets that use the same processor gdb arch tdep c Similarly there are often common subroutines that are shared by all target machines that use this particular architecture If you are adding a new operating system for an existing CPU chip add a config tm os h f file that describes the operating system facilities that are unusual extra symbol table info the breakpoint instruction needed etc Then write a arch tm os h that just includes tm arch h and config tm os h 10 Target Vector Definition The target vector defines the interface between GDB s abstract handling of target sys tems and the nitty gritty code that actually exercises control over a process or a serial port GDB includes some 30 40 different target vectors however each configuration of GDB includes only a few of them 10 1 File Targets Both executables and core files have target vectors 10 2 Standard Protocol and Remote Stubs GDB s file remote c talks a serial protocol to code that runs in the target system GDB provides several sample stubs that can be integrated into target programs or operating systems for this purpose they are named stub c Chapter 11 Native Debugging The GDB user s manual describes how to put such a stub into your target code What follows is a discussion of i
49. eturn the pc saved there That is the return address Chapter 9 Target Architecture Definition FUNCTION_EPILOGUE_SIZE For some COFF targets the x_sym x_misc x_fsize field of the function end symbol is 0 For such targets you must define FUNCTION_EPILOGUE_SIZE to expand into the standard size of a function s epilogue GCC_COMPILED_FLAG_SYMBOL GCC2_COMPILED_FLAG_SYMBOL If defined these are the names of the symbols that GDB will look for to detect that GCC compiled the file The default symbols are gcc_compiled and gcc2_compiled respectively Currently only defined for the Delta 68 GDB_MULTI_ARCH If defined and non zero enables suport for multiple architectures within GDB The support can be enabled at two levels At level one only definitions for previously undefined macros are provided at level two a multi arch definition of all architecture dependant macros will be defined GDB_TARGET_IS_HPPA This determines whether horrible kludge code in dbxread c and partial stab h is used to mangle multiple symbol table files from HPPA s This should all be ripped out and a scheme like elfread c used GDB_TARGET_IS_MACH386 GDB_TARGET_IS_SUN3 GDB_TARGET_IS_SUN386 Kludges that should go away GET_LONGJMP_TARGET For most machines this is a target dependent parameter On the DECstation and the Iris this is a native dependent parameter since lt setjmp h gt is needed to define it This macro determines the target PC addres
50. for some reason One example is the DECstation where its RPC library can t cope with our redefinition of malloc to call mmalloc When defining USE MMALLOC you will also have to set MMALLOC in the Makefile to point to the mmalloc library This define is set when you configure with with mmalloc NO MMCHECK Define this if you are using mmalloc but don t want the overhead of checking the heap with mmcheck Note that on some systems the C runtime makes calls to malloc prior to calling main and if free is ever called with these pointers after calling mncheck to enable checking a memory corruption abort is certain to occur These systems can still use mmalloc but must define NO MMCHECK MMCHECK FORCE Define this to 1 if the C runtime allocates memory prior to mmcheck being called but that memory is never freed so we don t have to worry about it triggering a memory corruption abort The default is 0 which means that mmcheck will only install the heap checking functions if there has not yet been any memory allocation calls and if it fails to install the functions gdb will issue a warning This is currently defined if you configure using with mmalloc NO SIGINTERRUPT Define this to indicate that siginterrupt is not available R OK Define if this is not in a system h file SEEK CUR SEEK SET Define these to appropriate value for the system lseek if not already defined STOP SIGNAL This is the signal for stopping GDB Defa
51. g Mac OS X process on the same machine nextstep tdep c extra functions needed for all nextstep targets empty nextstep xdep c extra functions needed for nextstep hosts empty 8 3 10 PowerP C specific Sources ppc frameinfo c determine print PPC stack frame info find prologue etc ppc frameops c basic PPC stack frame operations push dummy push args pop find saved regs ppc next tcore c fetch store PPC registers to from running Mach thread ppc next tdep c fetch store PPC registers from Mach data structure ppc tdep c PPC analysis functions used by rest of GDB 8 3 11 Miscellaneous demangle Allow user to explicitly select function name demangling style e g k r lucid GNU language Multiple language support for GDB Contains dispatch tables to the language specific routines routines to detect the language of a source file object module and explicit commands to print set the current language environment source View and navigate through source files Also responsible for directory search path mechanisms 8 3 12 Assorted Utilities bcache efficiency additions for obstack gnu regex regular expression library Chapter 9 Target Architecture Definition 25 dcache caches inferior memory accesses for remote targets complaints error printing for symbol file reading allows error messages to be printed only once per operation rat
52. h duplicated code Other times duplicating a few lines of code here or there is much cleaner than introducing a large number of small hooks Another way to generalize GDB along a particular interface is with an attribute struct For example GDB has been generalized to handle multiple kinds of remote interfaces not by ifdef s everywhere but by defining the target_ops structure and having a current target as well as a stack of targets below it for memory references Whenever something needs to be done that depends on which remote interface we are using a flag in the current target ops structure is tested e g target has stack or a function is called through a pointer in the current target ops structure In this way when a new remote interface is added only one module needs to be touched the one that actually implements the new remote interface Other examples of attribute structs are BFD access to multiple kinds of object file formats or GDB s access to multiple source languages Please avoid duplicating code For example in GDB 3 x all the code interfacing be tween ptrace and the rest of GDB was duplicated in dep c and so changing something was very painful In GDB 4 x these have all been consolidated into infptrace c infptrace c can deal with variations between systems the same way any system independent file would hooks if defined etc and machines which are radically different don t need to use i
53. has three types of symbol tables e full symbol tables symtabs These contain the main information about symbols and addresses e partial symbol tables psymtabs These contain enough information to know when to read the corresponding part of the full symbol table e minimal symbol tables msymtabs These contain information gleaned from non debugging symbols This section describes partial symbol tables A psymtab is constructed by doing a very quick pass over an executable file s debugging information Small amounts of information are extracted enough to identify which parts of the symbol table will need to be re read and fully digested later when the user needs the information The speed of this pass causes GDB to start up very quickly Later as the detailed rereading occurs it occurs in small pieces at various times and the delay therefrom is mostly invisible to the user The symbols that show up in a file s psymtab should be roughly those visible to the debugger s user when the program is not running code from that file These include external symbols and types static symbols and types and enum values declared at file scope Chapter 5 Symbol Handling 7 The psymtab also contains the range of instruction addresses that the full symbol table would represent The idea is that there are only two ways for the user or much of the code in the debugger to reference a symbol e by its address e g execution stops at som
54. her than repeated incessantly copying prints license warranty information version automatically generated contains version string annotate convenience functions to print annotations for libgdb environ utilities to read modify the process environment utils Utilities used by GDB Provides routines to provide formatted output memory management and data conversion routines 9 Target Architecture Definition GDB s target architecture defines what sort of machine language programs GDB can work with and how it works with them At present the target architecture definition consists of a number of C macros 9 1 Registers and Memory GDB s model of the target machine is rather simple GDB assumes the machine includes a bank of registers and a block of memory Each register may have a different size GDB does not have a magical way to match up with the compiler s idea of which registers are which however it is critical that they do match up accurately The only way to make this work is to get accurate information about the order that the compiler uses and to reflect that in the REGISTER_NAME and related macros GDB can handle big endian little endian and bi endian architectures 9 2 Frame Interpretation 9 3 Inferior Call Setup 9 4 Compiler Characteristics Chapter 9 Target Architecture Definition 26 9 5 Target Conditionals This section describes the macros that you can use to define the ta
55. his is 0 OS9K VARIABLES INSIDE BLOCK desc gcc p Similarly for OS 9000 Defaults to 1 Motorola M68K target conditionals BPT VECTOR Define this to be the 4 bit location of the breakpoint trap vector If not defined it will default to Oxf REMOTE BPT VECTOR Defaults to 1 9 6 Adding a New Target The following files define a target to GDB Chapter 10 Target Vector Definition 36 gdb config arch ttt mt Contains a Makefile fragment specific to this target Specifies what object files are needed for target ttt by defining TDEPFILES Also specifies the header file which describes ttt by defining TM_FILE tm ttt h You can also define TM_CFLAGS TM_CLIBS TM_CDEPS but these are now deprecated and may go away in future versions of GDB gdb config arch tm ttt h tm h is a link to this file created by configure Contains macro definitions about the target machine s registers stack frame format and instructions gdb ttt tdep c Contains any miscellaneous code required for this target machine On some machines it doesn t exist at all Sometimes the macros in tm ttt h become very complicated so they are implemented as functions here instead and the macro is simply defined to call the function This is vastly preferable since it is easier to understand and debug gdb config arch tm arch h This often exists to describe the basic layout of the targ
56. ined this should evaluate to 1 if addr is in a shared library in which breakpoints cannot be set and so should be disabled DO REGISTERS INFO If defined use this to print the value of a register or all registers END OF TEXT DEFAULT This is an expression that should designate the end of the text section FIXME 7 EXTRACT RETURN VALUE type regbuf valbuf Define this to extract a function s return value of type type from the raw register state regbuf and copy that in virtual format into valbuf EXTRACT STRUCT VALUE ADDRESS regbuf When EXTRACT STRUCT VALUE ADDRESS P this is used to to extract from an array regbuf containing the raw register state the address in which a Chapter 9 Target Architecture Definition 29 function should return its structure value as a CORE_ADDR or an expression that can be used as one EXTRACT STRUCT VALUE ADDRESS P Predicate for EXTRACT STRUCT VALUE ADDRESS FLOAT INFO If defined then the info float command will print information about the pro cessor s floating point unit FP REGNUM If the virtual frame pointer is kept in a register then define this macro to be the number greater than or equal to zero of that register This should only need to be defined if TARGET READ FP and TARGET WRITE FP are not defined FRAMELESS FUNCTION INVOCATION fi Define this to an expression that returns 1 if the function invocation represented by fi does not have a stack frame
57. is must be either BIG ENDIAN or LITTLE _ ENDIAN This macro replaces TARGET BYTE ORDER which is deprecated TARGET BYTE ORDER SELECTABLE P Non zero if the target has both BIG ENDIAN and LITTLE ENDIAN variants This macro replaces TARGET BYTE ORDER SELECTABLE which is deprecated TARGET CHAR BIT Number of bits in a char defaults to 8 TARGET COMPLEX BIT Number of bits in a complex number defaults to 2 TARGET FLOAT BIT At present this macro is not used TARGET DOUBLE BIT Number of bits in a double float defaults to 8 TARGET CHAR BIT TARGET DOUBLE COMPLEX BIT Number of bits in a double complex defaults to 2 TARGET DOUBLE BIT At present this macro is not used TARGET FLOAT BIT Number of bits in a float defaults to 4 TARGET CHAR BIT TARGET INT BIT Number of bits in an integer defaults to 4 TARGET CHAR BIT TARGET LONG BIT Number of bits in a long integer defaults to 4 TARGET CHAR BIT TARGET LONG DOUBLE BIT Number of bits in a long double float defaults to 2 TARGET DOUBLE BIT TARGET LONG LONG BIT Number of bits in a long long integer defaults to 2 TARGET LONG BIT TARGET PTR BIT Number of bits in a pointer defaults to TARGET INT BIT Chapter 9 Target Architecture Definition 35 TARGET SHORT BIT Number of bits in a short integer defaults to 2 TARGET CHAR BIT TARGET READ PC TARGET WRITE PC val pid TARGET READ SP TARGET WR
58. ively permissive such as for expressions While the compiler should be picky or have the option to be made picky since source code lives for a long time usually the programmer doing debugging shouldn t be spending time figuring out to mollify the debugger GDB will be called upon to deal with really large programs Executable sizes of 50 to 100 megabytes occur regularly and we ve heard reports of programs approaching 1 gigabyte in size GDB should be able to run everywhere No other debugger is available for even half as many configurations as GDB supports 2 Overall Structure GDB consists of three major subsystems user interface symbol handling the symbol side and target system handling the target side Ther user interface consists of several actual interfaces plus supporting code The symbol side consists of object file readers debugging info interpreters symbol table management source language expression parsing type and value printing The target side consists of execution control stack frame analysis and physical target manipulation The target side symbol side division is not formal and there are a number of excep tions For instance core file support involves symbolic elements the basic core file reader is in BFD and target elements it supplies the contents of memory and the values of reg isters Instead this division is useful for understanding how the minor subsystems should fit together
59. luded file The COFF reader is in coffread c 5 4 3 ECOFF ECOFF is an extended COFF originally introduced for Mips and Alpha workstations The basic ECOFF reader is in mipsread c 5 4 4 XCOFF The IBM RS 6000 running AIX uses an object file format called XCOFF The COFF sections symbols and line numbers are used but debugging symbols are dbx style stabs whose strings are located in the debug section rather than the string table For more information see See section Top in The Stabs Debugging Format The shared library scheme has a clean interface for figuring out what shared libraries are in use but the catch is that everything which refers to addresses symbol tables and breakpoints at least needs to be relocated for both shared libraries and the main executable At least using the standard mechanism this can only be done once the program has been run or the core file has been read Chapter 5 Symbol Handling 9 5 4 5 PE Windows 95 and NT use the PE Portable Executable format for their executables PE is basically COFF with additional headers While BFD includes special PE support GDB needs only the basic COFF reader 5 4 6 ELF The ELF format came with System V Release 4 SVR4 Unix ELF is similar to COFF in being organized into a number of sections but it removes many of COFF s limitations The basic ELF reader is in elfread c 5 4 7 SOM SOM is HP s object file and debug for
60. mand capability where the first argument to a command may itself direct a lookup on a different command list For instance the set command just starts a lookup on the setlist command list while set thread recurses to the set thread cmd list To add commands in general use add cmd add com adds to the main command list and should be used for those commands The usual place to add commands is in the initialize xyz routines at the ends of most source files Chapter 5 Symbol Handling 5 4 2 Console Printing 4 3 TUI 4 4 libgdb libgdb was an abortive project of years ago The theory was to provide an API to GDB s functionality 5 Symbol Handling Symbols are a key part of GDB s operation Symbols include variables functions and types 5 1 Symbol Reading GDB reads symbols from symbol files The usual symbol file is the file containing the program which GDB is debugging GDB can be directed to use a different file for symbols with the symbol file command and it can also read more symbols via the add file and load commands or while reading symbols from shared libraries Symbol files are initially opened by code in symfile c using the BFD library BFD identifies the type of the file by examining its header symfile init then uses this identi fication to locate a set of symbol reading functions Symbol reading modules identify themselves to GDB by calling add symtab fns during their module initializ
61. mat not to be confused with IBM s SOM which is a cross language ABI The SOM reader is in hpread c 5 4 8 Other File Formats Other file formats that have been supported by GDB include Netware Loadable Modules nlmread c 5 5 Debugging File Formats This section describes characteristics of debugging information that are independent of the object file format 5 5 1 stabs stabs started out as special symbols within the a out format Since then it has been encapsulated into other file formats such as COFF and ELF While dbxread c does some of the basic stab processing including for encapsulated versions stabsread c does the real work 5 5 2 COFF The basic COFF definition includes debugging information The level of support is minimal and non extensible and is not often used 5 5 3 Mips debug Third Eye ECOFF includes a definition of a special debug format The file tmdebugread c implements reading for this format Chapter 6 Language Support 10 5 5 4 DWARF 1 DWARF 1 is a debugging format that was originally designed to be used with ELF in SVR4 systems The DWARF 1 reader is in dwarfread c 5 5 5 DWARF 2 DWARF 2 is an improved but incompatible version of DWARF 1 The DWARF 2 reader is in dwarf2read c 5 5 6 SOM Like COFF the SOM definition includes debugging information 5 6 Adding a New Symbol Reader to GDB If you are using an existing object file format a
62. n of SIGWINCH_HANDLER ALIGN_STACK_ON_STARTUP Define this if your system is of a sort that will crash in tgetent if the stack happens not to be longword aligned when main is called This is a rare situation but is known to occur on several different types of systems CRLF_SOURCE_FILES Define this if host files use r n rather than n as a line terminator This will cause source file listings to omit r characters when printing and it will allow r n line endings of files which are sourced by gdb It must be possible to open files in binary mode using O_BINARY or for fopen rb DEFAULT_PROMPT The default value of the prompt string normally gdb DEV_TTY The name of the generic TTY device defaults to dev tty FCLOSE PROVIDED Define this if the system declares fclose in the headers included in defs h This isn t needed unless your compiler is unusually anal FOPEN RB Define this if binary files are opened the same way as text files GETENV PROVIDED Define this if the system declares getenv in its headers included in defs h This isn t needed unless your compiler is unusually anal HAVE MMAP In some cases use the system call mmap for reading symbol tables For some machines this allows for sharing and quick updates HAVE SIGSETMASK Define this if the host system has job control but does not define sigsetmask Currently this is only true of the RS 6000 HAVE TERMIO Define this if the host system has termio h
63. nfptrace c at all Don t put debugging printfs in the code 14 Porting GDB Most of the work in making GDB compile on a new machine is in specifying the config uration of the machine This is done in a dizzying variety of header files and configuration scripts which we hope to make more sensible soon Let s say your new host is called an xyz e g sun4 and its full three part configuration name is arch xvend xos e g sparc sun sunos4 In particular In the top level directory edit config sub and add arch xvend and xos to the lists of supported architectures vendors and operating systems near the bottom of the file Also add xyz as an alias that maps to arch xvend xos You can test your changes by running config sub xyz and config sub arch xvend xos which should both respond with arch xvend xos and no error messages You need to port BFD if that hasn t been done already Porting BFD is beyond the scope of this manual Chapter 15 Testsuite 48 To configure GDB itself edit gdb configure host to recognize your system and set gdb_host to xyz and unless your desired target is already available also edit gdb configure tgt setting gdb_target to something appropriate for instance xyz Finally you ll need to specify and define GDB s host native and target dependent h and c files used for your configuration 14 1 Configuring GDB for Release From the top level directo
64. noticed for some time The GDB testsuite uses the DejaGNU testing framework DejaGNU is built using tcl and expect The tests themselves are calls to various tcl procs the framework runs all the procs and summarizes the passes and fails Chapter 15 Testsuite 49 15 1 Using the Testsuite To run the testsuite simply go to the GDB object directory or to the testsuite s objdir and type make check This just sets up some environment variables and invokes DejaGNU s runtest script While the testsuite is running you ll get mentions of which test file is in use and a mention of any unexpected passes or fails When the testsuite is finished you ll get a summary that looks like this gdb Summary of expected passes 6016 of unexpected failures 58 of unexpected successes 5 of expected failures 183 of unresolved testcases 3 of untested testcases 5 The ideal test run consists of expected passes only however reality conspires to keep us from this ideal Unexpected failures indicate real problems whether in GDB or in the testsuite Expected failures are still failures but ones which have been decided are too hard to deal with at the time for instance a test case might work everywhere except on AIX and there is no prospect of the AIX case being fixed in the near future Expected failures should not be added lightly since you may be masking serious bugs in GDB Unexpected successes are expected fails that are passing
65. ns Expressions are parsed evaluated and printed using the language dispatching mechanisms described in language c and Section 8 3 7 Language Specific Sources page 23 GDB source files to manipulate type structures typeprint c Prints type information structures in readable form Interfaces to the language specific type printing routines described in Section 8 3 7 Language Specific Sources page 23 gdbtypes c Fundamental type definitions used by GDB GDB source files to manipulate expression structures parse c Parse expressions typed at the command line into expression Interfaces to the language specific expression parsing routines described in Section 8 3 7 Language Specific Sources page 23 Chapter 8 GDB Overview 21 eval c Evaluates expression structures in the current execution context expprint c Prints expression structures in readable infix form Interfaces to the language specific type printing routines described in Section 8 3 7 Language Specific Sources page 23 GDB source files to manipulate value structures valarith c perform arithmetic operations on values valops c perform non arithmetic operations on values valprint c print functions for values values c low level packing unpacking of value objects to from raw format findvar c resolve variables to their value structures as appropriate to the current stack environment
66. ntegrating the SPARC stub into a complicated operating system rather than a simple program by Stu Grossman the author of this stub The trap handling code in the stub assumes the following upon entry to trap_low 1 9611 and 9612 contain pc and npc respectively at the time of the trap 2 traps are disabled 3 you are in the correct trap window As long as your trap handler can guarantee those conditions then there is no rea son why you shouldn t be able to share traps with the stub The stub has no require ment that it be jumped to directly from the hardware trap vector That is why it calls exceptionHandler O which is provided by the external environment For instance this could setup the hardware traps to actually execute code which calls the stub first and then transfers to its own trap handler For the most point there probably won t be much of an issue with sharing traps as the traps we use are usually not used by the kernel and often indicate unrecoverable error conditions Anyway this is all controlled by a table and is trivial to modify The most important trap for us is for ta 1 Without that we can t single step or do breakpoints Everything else is unnecessary for the proper operation of the debugger stub From reading the stub it s probably not obvious how breakpoints work They are simply done by deposit examine operations from GDB 10 3 ROM Monitor Interface 10 4 Custom Protocols 10 5 Transport Layer
67. o although these are not literally hardware breakpoints from GDB s point of view they work the same GDB need not do nothing more than set the breakpoint and wait for something to happen Since they depend on hardware resources hardware breakpoints may be limited in num ber when the user asks for more GDB will start trying to set software breakpoints Software breakpoints require GDB to do somewhat more work The basic theory is that GDB will replace a program instruction a trap illegal divide or some other instruction that will cause an exception and then when it s encountered GDB will take the exception and stop the program When the user says to continue GDB will restore the original instruction single step re insert the trap and continue on Since it literally overwrites the program being tested the program area must be write able so this technique won t work on programs in ROM It can also distort the behavior of programs that examine themselves although the situation would be highly unusual Also the software breakpoint instruction should be the smallest size of instruction so it doesn t overwrite an instruction that might be a jump target and cause disaster when the program jumps into the middle of the breakpoint instruction Strictly speaking the breakpoint must be no larger than the smallest interval between instructions that may be jump targets perhaps there is an architecture where only even numbered instructi
68. ocess Handles breakpoints signal handling shared library handling on some systems as well as far too many other things Contains wait_for_inferior probably the hairiest function in all of GDB inftarg c Interface between the GDB target abstraction and UNIX child processes Many of the functions in the file are overridden via macros in the nextstep functions 8 3 3 Types Values and Expressions A type is the fundamental data structure in GDB for representing type information Each type structure is associated with a particular object file with the exception of a few pre created type structures used for backwards compatibility with other parts of GDB GDB provides a number of fundamental data types more complex data types can be represented by nesting type structures within each other See Section 8 3 3 Types page 20 for more information A value is the GDB data structure for representing both R and L values of any type A value contains a pointer to a GDB type structure as well as a region of memory containing the value s contents for an R value or address for an L value A expression is the GDB data structure for all expressions in all programming lan guages Expressions can be parsed and evaluated interactively according to the current language syntax can be used by breakpoints and watchpoints to compute values and can cause execution to take place within a target process by evaluating function expressio
69. ode to expprint c print_subexp to handle any new expression opcodes you have added to expression h Also add the printed representa tions of your operators to op_print_tab Add a place of call Add a call to lang_parse and lang_error in parse c parse_exp_1 Use macros to trim code The user has the option of building GDB for some or all of the languages If the user decides to build GDB for the language lang then every file dependent on language h will have the macro _LANG_lang defined in it Use ifdefs to leave out large routines that the user won t need if he or she is not using your language Note that you do not need to do this in your YACC parser since if GDB is not build for lang then lang exp tab o the compiled form of your parser is not linked into GDB at all See the file configure in for how GDB is configured for different languages Edit Makefile in Add dependencies in Makefile in Make sure you update the macro variables such as HFILES and OBJS otherwise your code may not get linked in or worse yet it may not get tarred into the distribution 7 Host Definition With the advent of autoconf it s rarely necessary to have host definition machinery anymore 7 1 Adding a New Host Most of GDB s host configuration support happens via autoconf It should be rare to need new host specific definitions GDB still uses the host specific definitions and files listed below but the
70. on with something like ifdef WRANGLE_SIGNALS WRANGLE_SIGNALS signo endif In your host target or native configuration file as appropriate define WRANGLE_SIGNALS to do the machine dependent thing Take a bit of care in defining the hook so that it can be used by other ports in the future if they need a hook in the same place If the hook is not defined the code should do whatever most machines want Using ifdef as above is the preferred way to do this but sometimes that gets convoluted in which case use ifndef SPECIAL_FOO_HANDLING define SPECIAL_FOO_HANDLING pc sp 0 endif where the macro is used or in an appropriate header file Chapter 14 Porting GDB Whether to include a small hook a hook around the exact pieces of code which are system dependent or whether to replace a whole function with a hook depends on the case A good example of this dilemma can be found in get_saved_register All machines that GDB 2 8 ran on just needed the FRAME_FIND_SAVED_REGS hook to find the saved registers Then the SPARC and Pyramid came along and HAVE REGISTER WINDOWS and REGISTER_ IN WINDOW P were introduced Then the 29k and 88k required the GET SAVED REGISTER hook The first three are examples of small hooks the latter replaces a whole function In this specific case it is useful to have both kinds it would be a bad idea to replace all the uses of the small hooks with GET SAVED REGISTER since that would result in muc
71. ons may Chapter 4 User Interface 4 jumped to Note that it s possible for an instruction set not to have any instructions usable for a software breakpoint although in practice only the ARC has failed to define such an instruction The basic definition of the software breakpoint is the macro BREAKPOINT Basic breakpoint object handling is in breakpoint c However much of the interesting breakpoint action is in infrun c 3 3 Single Stepping 3 4 Signal Handling 3 5 Thread Handling 3 6 Inferior Function Calls 3 7 Longjmp Support GDB has support for figuring out that the target is doing a longjmp and for stopping at the target of the jump if we are stepping This is done with a few specialized internal breakpoints which are visible in the maint info breakpoint command To make this work you need to define a macro called GET_LONGJMP_TARGET which will examine the jmp_buf structure and extract the longjmp target address Since jmp_buf is target specific you will need to define it in the appropriate tm xyz h file Look in tm sun4os4 h and sparc tdep c for examples of how to do this 4 User Interface GDB has several user interfaces Although the command line interface is the most common and most familiar there are others 4 1 Command Interpreter The command interpreter in GDB is fairly simple It is designed to allow for the set of commands to be augmented dynamically and also has a recursive subcom
72. out COFF ELF etc there is probably little to be done If you need to add a new object file format you must first add it to BFD This is beyond the scope of this document You must then arrange for the BFD code to provide access to the debugging symbols Generally GDB will have to call swapping routines from BFD and a few other BFD internal routines to locate the debugging information As much as possible GDB should not depend on the BFD internal data structures For some targets e g COFF there is a special transfer vector used to call swapping routines since the external data structures on various platforms have different sizes and layouts Specialized routines that will only ever be implemented by one object file format may be called directly This interface should be described in a file bfd libxyz h which is included by GDB 6 Language Support GDB s language support is mainly driven by the symbol reader although it is possible for the user to set the source language manually GDB chooses the source language by looking at the extension of the file recorded in the debug info c means C f means Fortran etc It may also use a special purpose language identifier if the debug format supports it such as DWARF 6 1 Adding a Source Language to GDB To add other languages to GDB s expression parser follow the following steps Create the expression parser This should reside in a file lang exp y Routines for b
73. returned to you with questions or comments If we re doing our job correctly the message back to you will say what you have to fix in order to make the change acceptable The reason to have separate messages for separate features is so that the acceptable changes can be installed while one or more changes are being reworked If multiple features are sent in a single message we tend to not put in the effort to sort out the acceptable changes from the unacceptable so none of the features get installed until all are acceptable If this sounds painful or authoritarian well it is But we get a lot of bug reports and a lot of patches and many of them don t get installed because we don t have the time to finish the job that the bug reporter or the contributor could have done Patches that arrive complete working and well designed tend to get installed on the day they arrive The others go into a queue and get installed as time permits which since the maintainers have many demands to meet may not be for quite some time Please send patches directly to the GDB maintainers at gdb patches sourceware cygnus com f 16 4 Obsolete Conditionals Fragments of old code in GDB sometimes reference or set the following configuration macros They should not be used by new code and old uses should be removed as those parts of the debugger are otherwise touched STACK_END_ADDR This macro used to define where the end of the stack appeared for use in inte
74. rget machine ADDITIONAL_OPTIONS ADDITIONAL_OPTION_CASES ADDITIONAL_OPTION_HANDLER ADDITIONAL_OPTION_HELP These are a set of macros that allow the addition of additional command line options to GDB They are currently used only for the unsupported i960 Nindy target and should not be used in any other configuration ADDR_BITS_REMOVE addr If araw machine address includes any bits that are not really part of the address then define this macro to expand into an expression that zeros those bits in addr For example the two low order bits of a Motorola 88K address may be used by some kernels for their own purposes since addresses must always be 4 byte aligned and so are of no use for addressing Those bits should be filtered out with an expression such as addr amp 3 BEFORE MAIN LOOP HOOK Define this to expand into any code that you want to execute before the main loop starts Although this is not strictly speaking a target conditional that is how it is currently being used Note that if a configuration were to define it one way for a host and a different way for the target GDB will probably not compile let alone run correctly This is currently used only for the unsupported 1960 Nindy target and should not be used in any other configuration BELIEVE PCC PROMOTION Define if the compiler promotes a short or char parameter to an int but still reports the parameter as its original type rather than the promoted type BELIEV
75. rgument to lseek or most commonly bfd seek FIXME should be replaced by SEEK SET instead which is the POSIX equiv alent MALLOC INCOMPATIBLE Define this if the system s prototype for malloc differs from the ANSI defini tion MMAP BASE ADDRESS When using HAVE MMAP the first mapping should go at this address MMAP INCREMENT when using HAVE MMAP this is the increment between mappings NEED POSIX SETPGID Define this to use the POSIX version of setpgid to determine whether job control is available NORETURN If defined this should be one or more tokens such as volatile that can be used in both the declaration and definition of functions to indicate that they never return The default is already set correctly if compiling with GCC This will almost never need to be defined Chapter 7 Host Definition 16 ATTR_NORETURN If defined this should be one or more tokens such as __attribute__ noreturn Jj that can be used in the declarations of functions to indicate that they never return The default is already set correctly if compiling with GCC This will almost never need to be defined USE_GENERIC_DUMMY_FRAMES Define this to 1 if the target is using the generic inferior function call code See blockframe c for more information USE_MMALLOC GDB will use the mmalloc library for memory allocation for symbol reading if this symbol is defined Be careful defining it since there are systems on which mmalloc does not work
76. ric file Put them into xyz xdep c and put xyz xdep o into XDEPFILES ser unix c This contains serial line support for Unix systems This is always included via the makefile variable SER HARDWIRE override this variable in the mh file to avoid it ser go32 c This contains serial line support for 32 bit programs running under DOS using the GO32 execution environment ser tcp c This contains generic TCP support using sockets 7 2 Host Conditionals When GDB is configured and compiled various macros are defined or left undefined to control compilation based on the attributes of the host system These macros and their meanings or if the meaning is not documented here then one of the source files where they are used is indicated are GDBINIT_FILENAME The default name of GDB s initialization file normally gdbinit MEM_FNS_DECLARED Your host config file defines this if it includes declarations of memcpy and memset Define this to avoid conflicts between the native include files and the declara tions in defs h NO_STD_REGS This macro is deprecated NO_SYS_FILE Define this if your system does not have a lt sys file h gt Chapter 7 Host Definition 14 SIGWINCH_HANDLER If your host defines SIGWINCH you can define this to be the name of a function to be called if SIGWINCH is received SIGWINCH_HANDLER_BODY Define this to expand into code that will define the function named by the expansio
77. rpreting core file formats that don t record this address in the core file itself This information is now configured in BFD and GDB gets the info portably from there The values in GDB s configuration files should be moved into BFD configuration files if needed there and deleted from all of GDB s config files Any foo xdep c file that references STACK_END_ADDR is so old that it has never been converted to use BFD Now that s old PYRAMID CONTROL FRAME DEBUGGING pyr xdep c Chapter 16 Hints PYRAMID_CORE pyr xdep c PYRAMID_PTRACE pyr xdep c REG_STACK_SEGMENT exec c Table of Contents Scope of this Document o oooooooooo o 1 Requirements eee eren 2 Overall Structure ss 28s soho se ee da 2 1 The Symbol 31de 2 irr RE Rr URET bees 22 The Target iden ree ei vac ero 2 3 Configurations 0 eee cece rhe gi A ee LEE ea aie dient ES 3 2 Breakpoint Handling 0 eee eee 2 9 OlN gle Stepping wien ciues oy a sees Gee die SEE pO RD DP RS 3 4 Signal Handling isc cre eA rte bes 3 5 Thread Handling 0 00 ee eee 3 6 Inferior Function Calls 0 0 00 eee eee ee 3 0 Longjmp SUpport o a e teehee eek HER 4 User Interracial 4 1 Command Interpreter 0c eect ee eee 4 2 Console Printing 0 0 cece cece eee ATE eee ar AL NO S gentia e RS AARAU TA ties Qe aa AA hbgdbiczm mi RR eb DERE oa eb geo 5 Symbol Handling
78. ry containing gdb bfd libiberty and so on make f Makefile in gdb tar gz This will properly configure clean rebuild any files that are distributed pre built e g c exp tab c or refcard ps and will then make a tarfile If the top level directory has already been configured you can just do make gdb tar gz instead This procedure requires e symbolic links e makeinfo texinfo2 level e TEx e dvips e yacc or bison and the usual slew of utilities sed tar etc TEMPORARY RELEASE PROCEDURE FOR DOCUMENTATION gdb texinfo is currently marked up using the texinfo 2 macros which are not yet a default for anything but we have to start using them sometime For making paper the only thing this implies is the right generation of texinfo tex needs to be included in the distribution For making info files however rather than duplicating the texinfo2 distribution generate gdb all texinfo locally and include the files gdb info in the distribution Note the plural makeinfo will split the document into one overall file and five or so included files 15 Testsuite The testsuite is an important component of the GDB package While it is always worth while to encourage user testing in practice this is rarely sufficient users typically use only a small subset of the available commands and it has proven all too common for a change to cause a significant regression that went un
79. s that longjmp will jump to assuming that we have just stopped at a longjmp breakpoint It takes a CORE_ADDR as argument and stores the target PC value through this pointer It examines the current state of the machine as needed GET_SAVED_REGISTER Define this if you need to supply your own definition for the function get_ saved_register HAVE_REGISTER_WINDOWS Define this if the target has register windows REGISTER_IN_WINDOW_P regnum Define this to be an expression that is 1 if the given register is in the window IBM6000_TARGET Shows that we are configured for an IBM RS 6000 target This conditional should be eliminated FIXME and replaced by feature specific macros It was introduced in haste and we are repenting at leisure Chapter 9 Target Architecture Definition 31 IEEE FLOAT Define this if the target system uses IEEE format floating point numbers INIT EXTRA FRAME INFO fromleaf frame If additional information about the frame is required this should be stored in frame extra info Space for frame extra info is allocated using frame _ obstack alloc INIT FRAME PC fromleaf prev This is a C statement that sets the pc of the frame pointed to by prev By default INNER THAN 1hs rhs Returns non zero if stack address Ihs is inner than nearer to the stack top stack address rhs Define this as lhs lt rhs if the target s stack grows downward in memory or 1hs gt rsh if the stack grows upward
80. se mostly exist for historical reasons and should eventually disappear Several files control GDB s configuration for host systems gdb config arch xyz mh Specifies Makefile fragments needed when hosting on machine xyz In par ticular this lists the required machine dependent object files by defining XDEPFILES Also specifies the header file which describes host xyz by defining XM_FILE xm xyz h You can also define CC SYSV_DEFINE XM_CFLAGS XM_ADD_FILES XM_CLIBS XM_CDEPS etc see Makefile in Chapter 7 Host Definition 13 gdb config arch xm xyz h xm h is a link to this file created by configure Contains C macro definitions describing the host system environment such as byte order host C compiler and library gdb xyz xdep c Contains any miscellaneous C code required for this machine as a host On most machines it doesn t exist at all If it does exist put xyz xdep o into the XDEPFILES line in gdb config arch xyz mh Generic Host Support Files There are some generic versions of routines that can be used by various systems These can be customized in various ways by macros defined in your xm xyz h file If these routines work for the xyz host you can just include the generic file s name with o not c in XDEPFILES Otherwise if your machine needs custom support routines you will need to write routines that perform the same functions as the gene
81. tered or fputs_demangled needs only to have calls to wrap_here added in places that would be good breaking points The utility routines will take care of actually wrapping if the line width is exceeded The argument to wrap_here is an indentation string which is printed only if the line breaks there This argument is saved away and used later It must remain valid until the next call to wrap_here or until a newline has been printed through the _filtered functions Don t pass in a local variable and then return It is usually best to call wrap_here after printing a comma or space If you call it before printing a space make sure that your indentation properly accounts for the leading space that will print if the line wraps there Any function or set of functions that produce filtered output must finish by printing a newline to flush the wrap buffer before switching to unfiltered printf output Symbol reading routines that print warnings are a good example 13 3 GDB Coding Standards GDB follows the GNU coding standards as described in etc standards texi This file is also available for anonymous FTP from GNU archive sites GDB takes a strict interpretation of the standard in general when the GNU standard recommends a practice but does not require it GDB requires it GDB follows an additional set of coding standards specific to GDB as described in the following sections You can configure with enable build warnings
82. tion Information that is only needed when the host and target are the same is native depen dent One example is Unix child process support if the host and target are not the same doing a fork to start the target process is a bad idea The various macros needed for finding the registers in the upage running ptrace and such are all in the native dependent files Another example of native dependent code is support for features that are really part of the target environment but which require include files that are only available on the host system Core file handling and set jmp handling are two common cases When you want to make GDB work native on a particular machine you have to include all three kinds of information 3 Algorithms GDB uses a number of debugging specific algorithms They are often not very com plicated but get lost in the thicket of special cases and real world issues This chapter describes the basic algorithms and mentions some of the specific target definitions that they use Chapter 3 Algorithms 3 3 1 Frames A frame is a construct that GDB uses to keep track of calling and called functions FRAME_FP in the machine description has no meaning to the machine independent part of GDB except that it is used when setting up a new frame from scratch as follows create_new_frame read_register FP_REGNUM read_pc Other than that all the meaning imparted to FP_REGNUM is imparted by the machine
83. ty Contains the liberty library of free software It is a collection of subroutines used by various GNU programs typically functions that are included in GNU libc but not in certain vendor versions of libc Example functions provided by liberty getopt get options from command line obstack stacks of arbitrarily sized objects Strerror error message strings corresponding to errno strtol string to long conversion strtoul string to unsigned long conversion 8 2 GDB Directory Structure The sources to GDB itself are currently stored in four subdirectories all of which are used to build the final executable gdb The main GDB sources as provided by the FSF Changes to this directory have been kept as small as possible to minimize the effort of merging them with the FSF sources though many changes still have been made gdb next Apple specific additions to the GDB source base These will eventually be merged into the gdb directory but are currently kept separate to make them easier to manage gdb 4 14 GDB sources as modified by NeXT for gdb 4 14 These are nearly obsolete but are kept around until I have merged all of the original NeXT changes into the new GDB source base gdb next 4 14 Apple specific additions to the nearly obsolete GDB 4 14 source base These are kept around solely for the purpose of building GDB 4 14 binaries when necessary Until recently it was possible to build both GDB
84. typeprint c valprint C cp valprint Objective C objc exp objc lang objc Chill ch exp ch lang ch typeprint ch valprint Fortran f exp f lang f typeprint f valprint Java jv exp jv lang jv typeprint jv valprint Modula II m2 exp m2 lang m2 typeprint m2 valprint Scheme scm exp scm lang scm valprint 8 3 8 Kernel Debugging remote kdp c interface gdb target interface to a remote Mac OS X kernel via KDP kdp udp c communications library for KDP remote utils c more serial line support unused remote c generic serial line debugging unused ser tcp c treat TCP connection as serial line unused ser unix c interface to unix serial ports unused serial c implement generic serial routines unused 8 3 9 Sources Specific to Mac OS X nextstep nat dyld c handle dyld debugging messages and take action mainly load symfiles nextstep nat inferior c interface between GDB target abstraction and Mach process control functions Chapter 8 GDB Overview nextstep nat mutils c mach functions to read write memory other manipulations nextstep nat sigthread c create manage thread to detect signals sent to the inferior process nextstep nat threads c interface gdb target interface to a runnin
85. uilding parsed expres sions into a union exp_element list are in parse c Chapter 6 Language Support 11 Since we can t depend upon everyone having Bison and YACC produces parsers that define a bunch of global names the following lines must be included at the top of the YACC parser to prevent the various parsers from defining the same global names define yyparse ang parse define yylex lang_lex define yyerror lang error define yylval lang lval define yychar lang char define yydebug ang debug define yypact lang pact define yyri lang r1 define yyr2 lang r2 define yydef lang def define yychk lang chk define yypgo lang pgo define yyact lang act define yyexca lang_exca define yyerrflag lang errflag define yynerrs Jlang_nerrs At the bottom of your parser define a struct language defn and initialize it with the right values for your language Define an initialize lang rou tine and have it call add language lang language defn to tell the rest of GDB that your language exists You ll need some other supporting variables and functions which will be used via pointers from your lang language defn See the declaration of struct language defn in language h and the other exp y files for more information Add any evaluation routines if necessary If you need new opcodes that represent the operations of the language add them to the enumerated type in expression h
86. ults to SIGTSTP Only redefined for the Convex USE_O_NOCTTY Define this if the interior s tty should be opened with the O NOCTTY flag FIXME This should be a native only flag but inflow c is always linked in USG Means that System V prior to SVR4 include files are in use FIXME This symbol is abused in infrun c regex c remote nindy c and utils c for other things at the moment Chapter 8 GDB Overview 17 lint Define this to help placate lint in some situations volatile Define this to override the defaults of volatile or x x 8 GDB Overview 8 1 Libraries used by GDB GDB relies on a number of libraries config Configuration options shared by GDB and all of the libraries it uses GDB has it s own much more extensive configuration in gdb config readline Contains the 1readline and lhistory libraries for command line process ing The 1readline library handles command line editing terminal interface keymap interfaces and file completion the 1history library handles history processing and history substitution using csh style syntax For more informa tion see readline doc hist texi and readline doc rlman texi pfd BFD is a package which allows applications to use the same routines to operate on object files whatever the object file format A new object file format can be supported simply by creating a new BFD back end and adding it to the
87. will be passed a char pointer to the entire registers segment its length and a zero or a char pointer to the entire regs2 segment its length and a 2 The routine should suck out the supplied register values and install them into GDB s registers array If your system uses proc to control processes and uses ELF format core files then you may be able to use the same routines for reading the registers out of processes and out of core files 11 2 ptrace 11 3 proc 11 4 win32 11 5 shared libraries 11 6 Native Conditionals When GDB is configured and compiled various macros are defined or left undefined to control compilation when the host and target systems are the same These macros should be defined or left undefined in nm system h ATTACH_DETACH If defined then GDB will include support for the attach and detach com mands CHILD_PREPARE_TO_STORE If the machine stores all registers at once in the child process then define this to ensure that all values are correct This usually entails a read from the child Note that this is incorrectly defined in xm system h files currently Chapter 11 Native Debugging FETCH_INFERIOR_REGISTERS Define this if the native dependent code will provide its own routines fetch_ inferior_registers and store_inferior_registers in HOST nat c If this symbol is not defined and infptrace c is included in this configuration the default routines in
88. y historical reasons We eventually want to eliminate these Note for example that builtin_type_int initialized in gdbtypes c is basically the same as a TYPE CODE INT type that is initialized in c lang c for an FT INTEGER fundamental type The difference is that the builtin type is not associated with any particular objfile and only one instance exists while c lang c builds as many TYPE CODE INT types as needed with each one associated with some particular objfile 5 4 Object File Formats 5 4 1 a out The a out format is the original file format for Unix It consists of three sections text data and bss which are for program code initialized data and uninitialized data respectively The a out format is so simple that it doesn t have any reserved place for debugging information Hey the original Unix hackers used adb which is a machine language de bugger The only debugging format for a out is stabs which is encoded as a set of normal symbols with distinctive attributes The basic a out reader is in dbxread c 5 4 2 COFF The COFF format was introduced with System V Release 3 SVR3 Unix COFF files may have multiple sections each prefixed by a header The number of sections is limited The COFF specification includes support for debugging Although this was a step for ward the debugging information was woefully limited For instance it was not possible to represent code that came from an inc

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