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1. 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 Chapter 10 Native Debugging 34 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 Le 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 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 10 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 virtual
2. 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 Chapter 15 Hints 46 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 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 14 3 Writing Tests In many areas the GDB tests are already qui
3. 00 Soo CD WARE Di a Gein bd tes Ree ae atid 10 000 BOM i e tient ath ia seus 10 5 6 Adding a New Symbol Reader to GDB 10 6 Language Support ooooooo o 11 6 1 Adding a Source Language to GDB 11 T Host Definitions 13 7 1 Adding a New Host 0 cece eee eee eee ees 13 7 2 Host Conditionals 2 a a Bie ar 14 8 Target Architecture Definition 17 8 1 Registers and Memory 0 0 ce eee eee e ee eens 17 8 2 Using Different Register and Memory Data Representations ade a a A N AE 18 8 3 Frame Interpretation 0 eee eee eee 19 8 4 Inferior Call Setup 0 cece eee eee eee 19 8 5 Compiler CharacteristiCS o oooooooooooooommoo 19 8 6 Target Conditionals o 0oooooocooorrrrroom 19 8 7 Adding a New Target 0 00 cc cece cee cee neces 31 9 Target Vector Definition 32 Onl File Tarreo ahaa hte day be Ag pie td 32 9 2 Standard Protocol and Remote Stubs 32 9 3 ROM Monitor Interface anaana eee 33 9 4 Custom Protocols 0 00 ccc cence cnet nee E 33 9 5 Transport Layer iit fees et ee aad a a ed ee et 33 9 6 Builtin Simulator 00 00 33 10 Native Debugging 33 10 1 Native core file Support 0 0 0 e cece eee eens 34 LOLA ptrdce yn cu asthe bo Are er A O er le halts s 35 10 35 PROG exc Oi Se DIES 35 LOA BINS iia
4. 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 SYMBOLS_CAN_START_WITH_DOLLAR Some systems have routines whose names start with Giving this macro a non zero value tells GDB s expression parser to check for such routines when parsing tokens that begin with On HP UX certain system routines millicode have names beginning with or For example dyncal1 is a millicode routine that handles inter space procedure calls on PA RISC TEEE_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 gt extra_info Space for frame gt 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 point
5. 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 fu
6. 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 Chapter 8 Target Architecture Definition 30 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 This 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 fl
7. 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 18500 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 REGISTER_CONVERTIBLE reg Return non zero if reg uses different raw and virtual formats See Chapter 8 Using Different Register and Memory Data Representations page 17 REGISTER_RAW_SIZE reg Return the raw size of reg See Chapter 8 Using Different Register and Memory Data Representations page 17 REGISTER_VIRTUAL_SIZE reg Return the virtual size of reg See Chapter 8 Using Different Register and Memory Data Representations page 17 REGISTER_VIRTUAL_TYPE reg Return the virtual type of reg See Chapter 8 Using Different Register and Memory Data Representations page 17 REGISTER_CONVERT_TO_VIRTUAL reg type from to Convert the value of register reg from its raw form to its virtual form See Chap ter 8 Using Different Register and Memory Data Representations page 17 REGISTER_CONVERT_TO_RAW type reg from to Convert the value of register reg from its virtual form to its raw form See Chap ter 8 Using Different Register and Memory Data Representations page 17 Chapter 8 Target Architecture Defi
8. 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 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 infptrace c are used for these functions Chapter 10 Native Debugging 36 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 thr
9. 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 patchesOsourceware cygnus com 15 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 interpreting 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 PYRAMID_CORE pyr xdep c PYRAMID_PTRACE pyr xdep c REG_STACK_SEGMENT eXeC C Table of
10. Target Macro This is the type of the virtual representation of register number reg Note that there is no need for a macro giving a type for the register s raw form once the register s value has been obtained GDB always uses the virtual form void REGISTER_CONVERT_TO_VIRTUAL int reg Target Macro struct type type char from char to Convert the value of register number reg to type which should always be REGISTER_ VIRTUAL_TYPE reg The buffer at from holds the register s value in raw format the macro should convert the value to virtual format and place it at to Chapter 8 Target Architecture Definition 19 Note that REGISTER CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAWE take their reg and type arguments in different orders void REGISTER_CONVERT_TO_RAW struct type Target Macro type int reg char from char to Convert the value of register number reg to type which should always be REGISTER_ VIRTUAL_TYPE reg The buffer at from holds the register s value in raw format the macro should convert the value to virtual format and place it at to Note that REGISTER_CONVERT_TO_VIRTUAL and REGISTER_CONVERT_TO_RAWH take their reg and type arguments in different orders 8 3 Frame Interpretation 8 4 Inferior Call Setup 8 5 Compiler Characteristics 8 6 Target Conditionals This section describes the macros that you can use to define the target machine ADDITIONAL_OPTIONS ADDITIONAL_OPTION_CASES ADDITIONAL_OPTION_HANDLE
11. 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 Add support code for these operations in eval c evaluate_subexp Add cases for new opcodes in two Chapter 7 Host Definition 12 functions from parse c prefixify_subexp and length_of_subexp 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 funct
12. too You just look at the N_FUN stabs that appear before and after the N_SO stab and guess the starting and ending addresses of the compilation unit from them 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 Chapter 8 Target Architecture Definition 28 PARM_BOUNDARY If non zero round arguments to a boundary of this many bits before pushing them on the stack 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
13. Contents Scope of this Document o o o o o 1 Requirements Lia RR e 2 Overall Structure id RES 2 1 The symbol Side va cic cng paddy da ii ble dae 2 2 The Target Side 0 celle eect eens 2 3 Confipurations o 004 4 cides eae a 3 AlgoritbhMS i033 sees A Hees Oli FAME A tg 3 2 Breakpoint Handling 0 0 eee 3 8 Single Stepping 4 0 ets dvb dee eden dais 3 4 Signal Handling osare uua e e a eee eee eens 3 5 Thread Handling cece eee rene 3 6 Inferior Function Calls 0 0 ooo 31 ons jmp Support sic gcse ia gees A User Interfaces stare 4 1 Command Interpreter oooococococcccococcc 4 27 Console PTINtINE s posto asut ie tt Lage te daa a did TUE sta A da Ti a AA ER A A O a 5 Symbol Handling s m BLE Symbol Reading aia a id 5 2 Partial Symbol Tables 0 cece eee eee Did Types miseen tt dha Dede thee eh Gees raoa ia n AAA es 5 4 Object File Formats 0 cece eee eee ee eens DA AOS Aleta ocho dee a tite tee JAA CORE A Saggy et et P peta bho S 5 433 HCOBF crates eee a ae ead asta Beet BAA eX CORE td tai Ghee tate BALD A EN 54 6 BB eo ccaiok oon eentes eta dees Peas tdeselen cae RNs AR SOM se a tat dd A A ia DA 5 4 8 Other File Formats 0oooocoooccoccooc o oo 5 5 Debugging File Formats 0 0 00 cece eee eens Biv basic elethons 5 5 2 COFF ear a ceca ea eee 5 5 3 Mips debug Third Eye
14. by removing it stepping one instruction and re inserting the breakpoint However permanent breakpoints are hardwired into the inferior and can t be removed so this strategy doesn t work Calling SKIP_PERMANENT_BREAKPOINT adjusts the processor s state so that ex ecution will resume just after the breakpoint This macro does the right thing even when the breakpoint is in the delay slot of a branch or jump 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 instead 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
15. 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 So alt
16. 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 SIGWINCH_HANDLER If your host defines SIGWINCH you can define this to be the name of a function to be called if SIGWINCH is received SIGWINCH_HANDLER_BODY Define this to expand into code that will define the function named by the expansion of SIGWINCH_HANDLER ALIGN_STACK_ON_STARTUP Define this if your system is of a sort that will crash in tgetent if the stack happens not to be longword aligned when main is called This is a rare situation but is known to occur on several different types of systems CRLF_SOURCE_FILES Define this if host files use r n rather than n as a line terminator This will cause source file listings to omit r characters when printing and it will allow r n line endings of files which are sourced by gdb It must be possible to open files in binary mode using O_BINARY or for fopen rb DEFAULT_PROMPT The default value of the prompt string normally gdb DEV_TTY The name of the generic TTY device defaults to dev tty FCLOSE_PROVIDED Define this if the system declares fclose in the headers included in defs h This isn t needed unless your c
17. function such as _start generic_ file_frame_chain_valid and generic_func_frame_chain_valid are equiv alent implementations for targets using generic dummy frames 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 Chapter 8 Target Architecture Definition 24 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 return the pc saved there That is the return address 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 FUNCTION_START_OFFSET An integer giving the offset in bytes from a function s address as used in the values of symbols function pointers etc and the function s first genuine instruction This is zero on almost all machines the function s address is usually the address of its first instruction However on the VAX for example each function starts with two bytes containing a bitmask indicating whic
18. newly allocated struct sym_fns whose bfd field contains the BFD for the new symbol file being read Its private field has been zeroed and can be modified as desired Typically a struct of private information will be malloc d and a pointer to it will be placed in the private field There is no result from xyz_symfile_init but it can call error if it detects an unavoidable problem xyz_new_init Called from symbo1_file_add when discarding existing symbols This function need only handle the symbol reading module s internal state the symbol table data structures visible to the rest of GDB will be discarded by symbol_file_ add It has no arguments and no result It may be called after xyz_symfile_ init if a new symbol table is being read or may be called alone if all symbols are simply being discarded xyz_symfile_read struct sym_fns sf CORE_ADDR addr int mainline Called from symbol_file_add to actually read the symbols from a symbol file into a set of psymtabs or symtabs sf points to the struct sym_fns originally passed to xyz_sym_init for possible initialization addr is the offset between the file s specified start address and its true address in memory mainline is 1 if this is the main symbol table being read and 0 if a secondary symbol file e g shared library or dynamically loaded file is being read In addition if a symbol reading module creates psymtabs when xyz_symfile_read is called these psymtabs will contain a
19. 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 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 mmcheck 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 C
20. 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 have some idea of how GDB s internal symbol tables are stored see symtab h gdbtypes h you will find it much easier to understand 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 look
21. 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 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 Chapter 5 Symbol Handling 7 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 va
22. 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 15 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 changes 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 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 t
23. time GDB builds an internal type it marks it with one of these types The type may be a fundamental type such as TYPE_CODE_INT or a derived type such as TYPE_CODE_PTR which is a pointer to another type Typically several FT_ types map to one TYPE_CODE type and are distinguished by other members of the type struct such as whether the type is signed or unsigned and how many bits it uses Builtin Types e g builtin_type_void builtin type_char These are instances of type structs that roughly correspond to fundamental types and are created as global types for GDB to use for various ugly historical reasons We eventually want to eliminate these Note for example that builtin_type_int initialized in gdbtypes c is basically the same as a TYPE_CODE_INT type that is initialized in c lang c for an FT_INTEGER fundamental type The difference is that the builtin_type is not associated with any particular objfile and only one instance exists while c lang c builds as many TYPE_CODE_INT types as needed with each one associated with some particular objfile 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
24. 35 10 5 shared libraries oo0 ooocoorroorrrrrrrrroomoo 35 10 6 Native Conditionals o o oooooooroorrorrmoooo 35 11 Support Libraries 38 EL BED A A add dae dt 38 11 2 opeodes ii a laa 38 LES Ted A a di 38 HA MAO e E le 38 11 5 Tibiberty ie cian a a att 38 DE E E E E e a A ia 38 A NT 39 12 COME ra stiesee pecan EEEE 39 PA Cleanups el ad sa See E ela ee ard anki 39 12 2 Wrapping Output Lines 0 0 0 c eee eee eee 40 123 GDB Coding Standards ooocoococccooocccnccocco 40 12 301 Formatting 12 4000 dadas 40 12 3 27 Comments iseia aan ado eh ble 40 123 3 E Usa aii a eee eee 41 12 3 4 Function Prototypes oooooccoocoooomoo 41 12 3 5 Clean Design 0 0 ec nebo eee eee Al 13 Porting GDB jcc ss ee eS cee dk GE Rees 43 13 1 Configuring GDB for Release 00oooocooococoooo 43 TA DeStSUl te curia as EOS 44 14 1 Using the Testsuite 00 0 eee 44 14 2 Testsuite Organization 000 0 cece eee ee eens 45 143 Writing Tests it poet date Sat agit gee thee tells 46 15 Hints AA asec sooth E tard eae Aad Tapa tm te ak we 46 15 1 Getting Started 0 0 cece eee ee eee 46 15 2 Debugging GDB with itself ooooooococooocoooo 48 15 3 Submitting Patches 0 0 c cee eee eee 48 15 4 Obsolete Conditionals oooooooooocooooo 49 iii
25. B 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 Chapter 8 Target Architecture Definition 18 8 2 Using Different Register and Memory Data Representations Some architectures use one representation for a value when it lives in a register but use a different representation when it lives in memory In GDB s terminology the raw representation is the one used in the target registers and the virtual representation is the one used in memory and within GDB struct value objects For almost all data types on almost all architectures the virtual and raw representations are identical and no special handling is needed However they do occasionally differ For example e The x86 architecture supports an 80 bit long double type However when we store those values in memory they occupy twelve bytes the floating point number occupies the first ten and the final two bytes are unused This keeps the values aligned on four byte boundaries allow
26. DB Chapter 6 Language Support 11 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 building parsed expres sions into a union exp_element list are in parse c Since we can t depend upon everyone having Bison and YACC produces parsers that define a bunch of global names the following lines must be included at the top of the YACC parser to prevent the various parsers from defining the same global names define yyparse lang_parse define yylex lang_lex define yyerror lang_error define yylval lang_lval define yychar lang_char define yydebug lang_debug define yypact lang_pact define yyr1 lang_r1 define yyr2 lang_r2 define yydef lang_def define yychk lang_chk define yypgo lang_pgo define yyact lang_act define yyexca lang_exca define yyerrflag Jlang_errflag define yynerrs lang_nerrs At the bottom of your parser define a struct language_defn and initialize
27. E_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 BELIEVE_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 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 th
28. GDB Chapter 9 Target Vector Definition 32 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 target 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 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 9 Target Vector Definition The target vector defines the interface between GDB s abstract handling of target sys tems and the n
29. GDB Internals A guide to the internals of the GNU debugger John Gilmore Cygnus Solutions Second Edition Stan Shebs Cygnus Solutions Cygnus Solutions Revision 1 142 T Xinfo 1 1 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 rela
30. ORDS 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 CANNOT_FETCH_REGISTER 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 DO_DEFERRED_STORES Chapter 8 Target Architecture Definition 22 CLEAR_DEFERRED_STORES Define this to execute any deferred stores of registers into the inferior and to cancel any deferr
31. R 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 a raw machine instruction 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 This is only used for addresses of instructions and even then not in all contexts For example the two low order bits of the PC on the Hewlett Packard PA 2 0 architecture contain the privilege level of the corresponding instruction Since instructions must always be aligned on four byte boundaries the pro cessor masks out these bits to generate the actual address of the instruction ADDR_BITS_REMOVE should filter out these bits with an expression such as Caddr 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 Chapter 8 Target Architecture Definition 20 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 BELIEV
32. 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_addr 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 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 i 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 ofstack 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 Chapter 8 Target Architecture Definition 29 SHIFT_INST_REGS Only used for m88k targets SKIP_PERMANENT_BREAKPOINT Advance the inferior s PC past a permanent breakpoint GDB normally steps over a breakpoint
33. 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 Chapter 11 Support Libraries 38 11 Support Libraries 11 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 support BFD provides routines to determine the failing command name stored in a core
34. d 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 infptrace c at all Don t put debugging printfs in the code 13 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 an
35. d 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 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 Several common definitions are available file_frame_chain_valid is nonzero if the chain pointer is nonzero and given frame s PC is not inside the startup file such as crt0 o func_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
36. d 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 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 13 1 Configuring GDB for Release From the top level directory containing gdb bfd libiberty and so on make f Makefile in gdb tar gz Chapter 14 Testsuite 44 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 ma
37. e 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 12 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 to get GCC to check on a num ber of these rules GDB sources ought not to engender an
38. e most recent event If a step over is required it returns TRUE If select_it is non zero it should reselect the old thread 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 Chapter 11 Support Libraries 37 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 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 Define this to indicate that SVR4 style shared libraries are in use USE_PROC_FS
39. e program counter to determine the contents and size of a breakpoint instruction It returns a pointer to a string of bytes that encode 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 Chapter 8 Target Architecture Definition 21 MEMORY_INSERT_BREAKPOINT addr contents_cache MEMORY_REMOVE_BREAKPOINT addr contents_cache Insert or remove memory based breakpoints Reasonable defaults default_ memory_insert_breakpoint and default_memory_remove_breakpoint re spectively have been provided so that it is not necessary to define these for most architectures Architectures which may want to define MEM ORY_INSERT_BREAKPOINT and MEMORY_REMOVE_BREAKPOINT will likely have instructions that are oddly sized or are not stored in a conven tional manner It may also be desirable from an efficiency standpoint to define custom break point insertion and removal routines if BREAKPOINT_FROM_PC needs to read the target s memory for some reason CALL_DUMMY_P A C expresson that is non zero when the target suports inferior function calls CALL_DUMMY_W
40. e 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 9 3 ROM Monitor Interface 9 4 Custom Protocols 9 5 Transport Layer 9 6 Builtin Simulator 10 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 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
41. e subcommand capability where the first argument to a command may itself direct a lookup on a different command list For instance the set command just starts a lookup on the setlist command list while set thread recurses to the set_thread_cmd_list To add commands in general use add_cmd add_com adds to the main command list and should be used for those commands The usual place to add commands is in the _initialize_xyz routines at the ends of most source files Chapter 5 Symbol Handling 5 Before removing commands from the command set it is a good idea to deprecate them for some time Use deprecate_cmd on commands or aliases to set the deprecated flag deprecate_cmd takes a struct cmd_list_element as it s first argument You can use the return value from add_com or add_cmd to deprecate the command immediately after it is created The first time a comamnd is used the user will be warned and offered a replacement if one exists Note that the replacement string passed to deprecate_cmd should be the full name of the command i e the entire string the user should type at the command line 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 i
42. ed stores Currently only implemented correctly for native Sparc configurations COERCE_FLOAT_TO_DOUBLE formal actual If we are calling a function by hand and the function was declared according to the debug info without a prototype should we automatically promote floats to doubles This macro must evaluate to non zero if we should or zero if we should leave the value alone The argument actual is the type of the value we want to pass to the function The argument formal is the type of this argument as it appears in the function s definition Note that formal may be zero if we have no debugging information for the function or if we re passing more arguments than are officially declared for example varargs This macro is never invoked if the function definitely has a prototype The default behavior is to promote only when we have no type information for the formal parameter This is different from the obvious behavior which would be to promote whenever we have no prototype just as the compiler does It s annoying but some older targets rely on this If you want GDB to follow the typical compiler behavior to always promote when there is no prototype in scope your gdbarch init function can call set_gdbarch_coerce_float_to_ double and select the standard_coerce_float_to_double function CPLUS_MARKER Define this to expand into the character that G uses to distinguish compiler generated identifiers from programmer specified ide
43. ed 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 1hs lt rhs if the target s stack grows downward in memory or 1hs gt rsh if the stack grows upward 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 Chapter 8 Target Architecture Definition 26 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 IN_SOLIB_DYNSYM_RESOLVE_CODE pc Define this to evaluate to nonzero if the program is stopped in the dynamic linker SKIP_SOLIB_RESOLVER pc Define this to evaluate to the nonzero address at which execution should continue to get past the dynamic linker s symbol resolution function A zero value indicates that it is not important or necessary to set a breakpoint to get through the dynamic linker and that single stepping will suffice IS_TRAPPED_INTERNALVAR name
44. en 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 Chapter 14 Testsuite 45 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 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 a
45. en used 5 5 3 Mips debug Third Eye ECOFF includes a definition of a special debug format The file mdebugread c implements reading for this format 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 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 G
46. 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 11 2 opcodes The opcodes library provides GDB s disassembler It s a separate library because it s also used in binutils for objdump 11 3 readline 11 4 mmalloc 11 5 libiberty 11 6 gnu regex Regex conditionals C_ALLOCA NFAILURES RE_NREGS Chapter 12 Coding 39 SIGN_EXTEND_CHAR SWITCH_ENUM_BUG SYNTAX_TABLE Sword sparc 11 7 include 12 Coding This chapter covers topics that are lower level than the major algorithms of GDB 12 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 cleanups that is throw them away without doing what they say This is only done if you a
47. fine 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 Chapter 7 Host Definition 16 L_SET This macro is used as the argument 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 ATTR_NORETURN If defined this should be
48. g the standard mechanism this can only be done once the program has been run or the core file has been read 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 format 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 Chapter 6 Language Support 10 5 5 2 COFF The basic COFF definition includes debugging information The level of support is minimal and non extensible and is not oft
49. h registers to save upon entry to the function The VAX call instructions check this value and save the appropriate registers automatically Thus since the offset from the function s address to its first instruction is two bytes FUNCTION_START_OFFSET would be 2 on the VAX 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 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 Chapter 8 Target Architecture Definition 25
50. hapter 8 Target Architecture Definition 17 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 Defaults 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 lint Define this to help placate lint in some situations volatile Define this to override the defaults of __volatile__ or 8 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 8 1 Registers and Memory GD
51. he 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 Chapter 15 Hints 49 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 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
52. hough 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 with a trap illegal divide or some other instruction that will cause an exception and then when it s encountered GDB will take the exception and stop the program When the user says to continue GDB will restore the original instruction single step re insert the trap and continue on Since it literally overwrites the program being tested the program area must be 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 ins
53. ing 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 the code being called does rather than worrying about all its details 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 inv
54. ing more efficient access Thus the x86 80 bit floating point type is the raw representation and the twelve byte loosely packed arrangement is the virtual representation e Some 64 bit MIPS targets present 32 bit registers to GDB as 64 bit registers with garbage in their upper bits GDB ignores the top 32 bits Thus the 64 bit form with garbage in the upper 32 bits is the raw representation and the trimmed 32 bit representation is the virtual representation In general the raw representation is determined by the architecture or GDB s interface to the architecture while the virtual representation can be chosen for GDB s convenience GDB s register file registers holds the register contents in raw format and the GDB remote protocol transmits register values in raw format Your architecture may define the following macros to request raw virtual conversions int REGISTER_CONVERTIBLE int reg Target Macro Return non zero if register number reg s value needs different raw and virtual formats int REGISTER_RAW_SIZE int reg Target Macro The size of register number reg s raw value This is the number of bytes the register will occupy in registers or in a GDB remote protocol packet int REGISTER_VIRTUAL_SIZE int reg Target Macro The size of register number reg s value in its virtual format This is the size a struct value s buffer will have holding that register s value struct type REGISTER_VIRTUAL_TYPE int reg
55. ion _initialize_language to include your language This function picks the default language upon startup so is dependent upon which languages that GDB is built for Update allocate_symtab in symfile c and or symbol reading code so that the language of each symtab source file is set properly This is used to 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 code 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 configu
56. 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 included 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 Chapter 5 Symbol Handling 9 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 usin
57. itty 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 9 1 File Targets Both executables and core files have target vectors 9 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 The GDB user s manual describes how to put such a stub into your target code What follows is a discussion of integrating 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 ll and 12 contain pc and npc respectively at the time of the trap 2 traps are disabled Chapter 10 Native Debugging 33 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 which is provided by the external environment For instance this could setup the hardware traps to actually execute code which calls th
58. ly 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_ ar0 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 nat 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 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 Chapter 10 Native Debugging 35 file e g the u area or a st
59. m a psymtab while still causing that to happen should not appear in it Since psymtabs don t have the idea of scope you can t put local symbols in them anyway Psymtabs don t have the idea of the type of a symbol either so types need not appear unless they will be referenced by name It is a bug for GDB to behave one way when only a psymtab has been read and another way if the corresponding symtab has been read in Such bugs are typically caused by a psymtab that does not contain all the visible symbols or which has the wrong instruction address ranges The psymtab for a particular section of a symbol file objfile could be thrown away after the symtab has been read in The symtab should always be searched before the psymtab so the psymtab will never be used in a bug free environment Currently psymtabs are allocated on an obstack and all the psymbols themselves are allocated in a pair of large arrays on an obstack so there is little to be gained by trying to free them unless you want to do a lot more work 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 Chapter 5 Symbol Handling 8 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
60. 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 12 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 12 3 4 Function Prototypes Prototypes must be used to declare functions and may be used to define them Proto types for GDB functions must include both the argument type and name with the name matching that used in the actual function definition All external function
61. 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 ce in XDEPFILES Otherwise if your machine needs custom support routines you will need to write routines that perform the same functions as the generic file Put them into xyz xdep c and put xyz xdep o into XDEPFILES ser unix c This contains serial line support for Unix systems This is always included via the makefile variable SER_HARDWIRE override this variable in the mh file to avoid it ser go32 c This contains serial line support for 32 bit programs running under DOS using the GO32 execution environment ser tcp c This contains generic TCP support using sockets Chapter 7 Host Definition 14 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
62. n 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 configuration 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
63. nction 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 setjmp handling are two common cases When you want to make GDB work native on a particular machine you have to include all three kinds of information 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
64. nd 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 14 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 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 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
65. nition 27 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 SOFTWARE_SINGLE_STEP signal insert_breapoints_p A function that inserts or removes dependant on insert_breapoints_p break points at each possible destinations of the next instruction See sparc tdep c and rs6000 tdep c for examples SOFUN_ADDRESS_MAYBE_MISSING Somebody clever observed that the more actual addresses you have in the debug information the more time the linker has to spend relocating them So whenever there s some other way the debugger could find the address it needs you should omit it from the debug info to make linking faster SOFUN_ADDRESS_MAYBE_MISSING indicates that a particular set of hacks of this sort are in use affecting N_SO and N_FUN entries in stabs format debugging in formation N_SO stabs mark the beginning and ending addresses of compilation units in the text segment N_FUN stabs mark the starts and ends of functions SOFUN_ADDRESS_MAYBE_MISSING means two things e N_FUN stabs have an address of zero Instead you should find the addresses where the function starts by taking the function name from the stab and then looking that up in the minsyms the linker assembler symbol table In other words the stab has the name and the linker assembler symbol table is the only place that carries the address e N_SO stabs have an address of zero
66. ntifiers 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 i960 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 defined 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 Chapter 8 Target Architecture Definition 23 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 function should return its structure value as a CORE_ADDR or an expression that can be use
67. oat 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 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_WRITE_SP TARGET_READ_FP Chapter 8 Target Architecture Definition 31 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 non
68. okes 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 Chapter 15 Hints 48 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 15 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 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
69. ompiler 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 Chapter 7 Host Definition 15 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 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 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 Il 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 De
70. ough 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 the 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 PREPARE_TO_PROCEED select_it This ugly macro allows a native configuration to customize the way the proceed function in infrun c deals with switching between threads In a multi threaded task we may select another thread and then continue or step But if the old thread was stopped at a breakpoint it will immediately cause another breakpoint stop without any execution i e it will report a breakpoint hit incorrectly So GDB must step over it first If defined PREPARE_TO_PROCEED should check the current thread against the thread that reported th
71. red 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 Chapter 7 Host Definition 13 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 these mostly exist for historical reasons and should eventually disappear Several files control GDB s configuration for host systems gdb config arch xyz mh Specifies Makefile fragments needed when hosting on machine xyz In 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 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
72. rious times and the delay therefrom is mostly invisible to the user The symbols that show up in a file s psymtab should be roughly those visible to the debugger s user when the program is not running code from that file These include external symbols and types static symbols and types and enum values declared at file scope The psymtab also contains the range of instruction addresses that the full symbol table would represent The idea is that there are only two ways for the user or much of the code in the debugger to reference a symbol e by its address e g execution stops at some address which is inside a function in this file The address will be noticed to be in the range of this psymtab and the full symtab will be read in find_pc_function find_pc_line and other find_pc_ functions handle this 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 fro
73. rked 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 14 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 unnoticed 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 14 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 Wh
74. ruct 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 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 10 2 ptrace 10 3 proc 10 4 win32 10 5 shared libraries 10 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
75. s should have a 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 12 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 Chapter 12 Coding 42 You can t assume that 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 tha
76. s the file containing the program which GDB is debugging GDB can be directed to use a different file for symbols with the symbol file command and it can also read more symbols via the add file and load commands or while reading symbols from shared libraries Symbol files are initially opened by code in symfile c using the BFD library BFD identifies the type of the file by examining its header find_sym_fns then uses this 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 initialization The argument to add_symtab_fns is a struct sym_fns which contains the name or name prefix of the symbol format the length of the prefix and pointers to four functions These functions are called at various times to process symbol files whose identification matches the specified prefix The functions supplied by each module are xyz_symfile_init struct sym_fns sf Called from symbol_file_add when we are about to read a new symbol file This function should clean up any internal state possibly resulting from half read previous files for example and prepare to read a new symbol file Note that the symbol file which we are reading might be a new main symbol file or Chapter 5 Symbol Handling 6 might be a secondary symbol file whose symbols are being added to the existing symbol table The argument to xyz_symfile_init is a
77. sk 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 b 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 12 Coding 40 12 2 Wrapping Output Lines Output that goes through printf_filtered or fputs_filtered or fputs_demangled needs only to have calls to wrap_here added in places that would b
78. te 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 15 Hints Check the README file it often has useful information that does not appear anywhere else in the directory 15 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 Chapter 15 Hints 47 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
79. the macro is used or in an appropriate header file 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 much 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 Chapter 13 Porting GDB 43 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 teste
80. tively 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
81. tructions 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 suntos4 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 recursiv
82. y 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 12 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 12 3 2 Comments The standard GNU requirements on comments must be followed strictly Chapter 12 Coding 41 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 why there is a loop in this function When this function actually returns it
83. zero 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 this 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 8 7 Adding a New Target The following files define a target to GDB 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 and TDEPLIBS 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 replaced by autoconf and may go away in future versions of

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