This is Info file gdbint.info, produced by Makeinfo version 1.68 from the input file ./gdbint.texinfo. START-INFO-DIR-ENTRY * Gdb-Internals: (gdbint). The GNU debugger's internals. END-INFO-DIR-ENTRY This file documents the internals of the GNU debugger GDB. Copyright 1990-1999 Free Software Foundation, Inc. Contributed by Cygnus Solutions. Written by John Gilmore. Second Edition by Stan Shebs. 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. Permission is granted to copy or distribute modified versions of this manual under the terms of the GPL (for which purpose this text may be regarded as a program in the language TeX).  File: gdbint.info, Node: Top, Next: Requirements, Up: (dir) Scope of this Document ********************** This document documents the internals of the GNU debugger, GDB. It includes description of GDB's key algorithms and operations, as well as the mechanisms that adapt GDB to specific hosts and targets. * Menu: * Requirements:: * Overall Structure:: * Algorithms:: * User Interface:: * Symbol Handling:: * Language Support:: * Host Definition:: * Target Architecture Definition:: * Target Vector Definition:: * Native Debugging:: * Support Libraries:: * Coding:: * Porting GDB:: * Hints::  File: gdbint.info, Node: Requirements, Next: Overall Structure, Prev: Top, Up: Top 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 relatively 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.  File: gdbint.info, Node: Overall Structure, Next: Algorithms, Prev: Requirements, Up: Top 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 exceptions. 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 registers). Instead, this division is useful for understanding how the minor subsystems should fit together. 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. 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. 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. Examples are the stack frame format, instruction set, breakpoint instruction, registers, and how to set up and tear down the stack to call a function. Information that is only needed when the host and target are the same, is native dependent. 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.  File: gdbint.info, Node: Algorithms, Next: User Interface, Prev: Overall Structure, Up: Top Algorithms ********** GDB uses a number of debugging-specific algorithms. They are often not very complicated, 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. 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-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 function'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. 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 although these are not literally "hardware breakpoints", from GDB's point of view they work the same; GDB need not do nothing more than set the breakpoint and wait for something to happen. Since they depend on hardware resources, hardware breakpoints may be limited in number; when the user asks for more, GDB will start trying to set software breakpoints. Software breakpoints require GDB to do somewhat more work. The basic theory is that GDB will replace a program instruction a trap, illegal divide, or some other instruction that will cause an exception, and then when it's encountered, GDB will take the exception and stop the program. When the user says to continue, GDB will restore the original instruction, single-step, re-insert the trap, and continue on. Since it literally overwrites the program being tested, the program area must be writeable, 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 instructions may 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'. Single Stepping =============== Signal Handling =============== Thread Handling =============== Inferior Function Calls ======================= Longjmp Support =============== GDB has support for figuring out that the target is doing a `longjmp' and for stopping at the target of the jump, if we are stepping. This is done with a few specialized internal breakpoints, which are visible in the `maint info breakpoint' command. To make this work, you need to define a macro called `GET_LONGJMP_TARGET', which will examine the `jmp_buf' structure and extract the longjmp target address. Since `jmp_buf' is target specific, you will need to define it in the appropriate `tm-XYZ.h' file. Look in `tm-sun4os4.h' and `sparc-tdep.c' for examples of how to do this.  File: gdbint.info, Node: User Interface, Next: Symbol Handling, Prev: Algorithms, Up: Top User Interface ************** GDB has several user interfaces. Although the command-line interface is the most common and most familiar, there are others. Command Interpreter =================== The command interpreter in GDB is fairly simple. It is designed to allow for the set of commands to be augmented dynamically, and also has a recursive 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. Console Printing ================ TUI === libgdb ====== `libgdb' was an abortive project of years ago. The theory was to provide an API to GDB's functionality.  File: gdbint.info, Node: Symbol Handling, Next: Language Support, Prev: User Interface, Up: Top Symbol Handling *************** Symbols are a key part of GDB's operation. Symbols include variables, functions, and types. Symbol Reading ============== GDB reads symbols from "symbol files". The usual symbol file is the file containing the program which GDB is debugging. GDB can be directed to use a different file for symbols (with the `symbol-file' command), and it can also read more symbols via the "add-file" and "load" commands, or while reading symbols from shared libraries. Symbol files are initially opened by code in `symfile.c' using the BFD library. BFD identifies the type of the file by examining its header. `symfile_init' then uses this identification 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 might be a secondary symbol file whose symbols are being added to the existing symbol table. The argument to `XYZ_symfile_init' is a newly allocated `struct sym_fns' whose `bfd' field contains the BFD for the new symbol file being read. Its `private' field has been zeroed, and can be modified as desired. Typically, a struct of private information will be `malloc''d, and a pointer to it will be placed in the `private' field. There is no result from `XYZ_symfile_init', but it can call `error' if it detects an unavoidable problem. `XYZ_new_init()' Called from `symbol_file_add' when discarding existing symbols. This function need only handle the symbol-reading module's internal state; the symbol table data structures visible to the rest of GDB will be discarded by `symbol_file_add'. It has no arguments and no result. It may be called after `XYZ_symfile_init', if a new symbol table is being read, or may be called alone if all symbols are simply being discarded. `XYZ_symfile_read(struct sym_fns *sf, CORE_ADDR addr, int mainline)' Called from `symbol_file_add' to actually read the symbols from a symbol-file into a set of psymtabs or symtabs. `sf' points to the struct sym_fns originally passed to `XYZ_sym_init' for possible initialization. `addr' is the offset between the file's specified start address and its true address in memory. `mainline' is 1 if this is the main symbol table being read, and 0 if a secondary symbol file (e.g. shared library or dynamically loaded file) is being read. In addition, if a symbol-reading module creates psymtabs when XYZ_symfile_read is called, these psymtabs will contain a pointer to a function `XYZ_psymtab_to_symtab', which can be called from any point in the GDB symbol-handling code. `XYZ_psymtab_to_symtab (struct partial_symtab *pst)' Called from `psymtab_to_symtab' (or the PSYMTAB_TO_SYMTAB macro) if the psymtab has not already been read in and had its `pst->symtab' pointer set. The argument is the psymtab to be fleshed-out into a symtab. Upon return, pst->readin should have been set to 1, and pst->symtab should contain a pointer to the new corresponding symtab, or zero if there were no symbols in that part of the symbol file. Partial Symbol Tables ===================== GDB has three types of symbol tables. * full symbol tables (symtabs). These contain the main information about symbols and addresses. * partial symbol tables (psymtabs). These contain enough information to know when to read the corresponding part of the full symbol table. * minimal symbol tables (msymtabs). These contain information gleaned from non-debugging symbols. This section describes partial symbol tables. A psymtab is constructed by doing a very quick pass over an executable file's debugging information. Small amounts of information are extracted - enough to identify which parts of the symbol table will need to be re-read and fully digested later, when the user needs the information. The speed of this pass causes GDB to start up very quickly. Later, as the detailed rereading occurs, it occurs in small pieces, at various times, and the delay therefrom is mostly invisible to the user. The symbols that show up in a file's psymtab should be, roughly, those visible to the debugger's user when the program is not running code from that file. These include external symbols and types, static symbols and types, and enum values declared at file scope. 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: * 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. * by its name (e.g. the user asks to print a variable, or set a breakpoint on a function). Global names and file-scope names will be found in the psymtab, which will cause the symtab to be pulled in. Local names will have to be qualified by a global name, or a file-scope name, in which case we will have already read in the symtab as we evaluated the qualifier. Or, a local symbol can be referenced when we are "in" a local scope, in which case the first case applies. `lookup_symbol' does most of the work here. The only reason that psymtabs exist is to cause a symtab to be read in at the right moment. Any symbol that can be elided from a psymtab, while still causing that to happen, should not appear in it. Since psymtabs don't have the idea of scope, you can't put local symbols in them anyway. Psymtabs don't have the idea of the type of a symbol, either, so types need not appear, unless they will be referenced by name. It is a bug for GDB to behave one way when only a psymtab has been read, and another way if the corresponding symtab has been read in. Such bugs are typically caused by a psymtab that does not contain all the visible symbols, or which has the wrong instruction address ranges. The psymtab for a particular section 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. Types ===== Fundamental Types (e.g., FT_VOID, FT_BOOLEAN). These are the fundamental types that GDB uses internally. Fundamental types from the various debugging formats (stabs, ELF, etc) are mapped into one of these. They are basically a union of all fundamental types that gdb knows about for all the languages that GDB knows about. Type Codes (e.g., TYPE_CODE_PTR, TYPE_CODE_ARRAY). Each time GDB builds an internal type, it marks it with one of these types. The type may be a fundamental type, such as TYPE_CODE_INT, or a derived type, such as TYPE_CODE_PTR which is a pointer to another type. Typically, several FT_* types map to one TYPE_CODE_* type, and are distinguished by other members of the type struct, such as whether the type is signed or unsigned, and how many bits it uses. Builtin Types (e.g., builtin_type_void, builtin_type_char). 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. Object File Formats =================== a.out ----- The `a.out' format is the original file format for Unix. It consists of three sections: text, data, and bss, which are for program code, initialized data, and uninitialized data, respectively. The `a.out' format is so simple that it doesn't have any reserved place for debugging information. (Hey, the original Unix hackers used `adb', which is a machine-language debugger.) 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'. 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 forward, 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'. ECOFF ----- ECOFF is an extended COFF originally introduced for Mips and Alpha workstations. The basic ECOFF reader is in `mipsread.c'. 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 *Note Top: (stabs)Top. The shared library scheme has a clean interface for figuring out what shared libraries are in use, but the catch is that everything which refers to addresses (symbol tables and breakpoints at least) needs to be relocated for both shared libraries and the main executable. At least using the standard mechanism this can only be done once the program has been run (or the core file has been read). 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. 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'. 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'. Other File Formats ------------------ Other file formats that have been supported by GDB include Netware Loadable Modules (`nlmread.c'. Debugging File Formats ====================== This section describes characteristics of debugging information that are independent of the object file format. 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. COFF ---- The basic COFF definition includes debugging information. The level of support is minimal and non-extensible, and is not often used. Mips debug (Third Eye) ---------------------- ECOFF includes a definition of a special debug format. The file `mdebugread.c' implements reading for this format. 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'. DWARF 2 ------- DWARF 2 is an improved but incompatible version of DWARF 1. The DWARF 2 reader is in `dwarf2read.c'. SOM --- Like COFF, the SOM definition includes debugging information. 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 GDB.  File: gdbint.info, Node: Language Support, Next: Host Definition, Prev: Symbol Handling, Up: Top 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. 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 expressions 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 LANG_errflag #define yynerrs LANG_nerrs At the bottom of your parser, define a `struct language_defn' and initialize it with the right values for your language. Define an `initialize_LANG' routine 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 functions from `parse.c': `prefixify_subexp()' and `length_of_subexp()'. These compute the number of `exp_element's 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 routines 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 identifier into a printable string. Update the function `_initialize_language' to include your language. This function picks the default language upon startup, so is dependent upon which languages that GDB is built for. 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 determine 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 representations 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 `#ifdef's to leave out large routines that the user won't need if he or she is not using your language. Note that you do not need to do this in your YACC parser, since if GDB is not build for LANG, then `LANG-exp.tab.o' (the compiled form of your parser) is not linked into GDB at all. See the file `configure.in' for how GDB is configured for different languages. *Edit `Makefile.in'* Add dependencies in `Makefile.in'. Make sure you update the macro variables such as `HFILES' and `OBJS', otherwise your code may not get linked in, or, worse yet, it may not get `tar'red into the distribution!  File: gdbint.info, Node: Host Definition, Next: Target Architecture Definition, Prev: Language Support, Up: Top Host Definition *************** With the advent of autoconf, it's rarely necessary to have host definition machinery anymore. 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 particular, 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 most machines it doesn't exist at all. If it does exist, put `XYZ-xdep.o' into the `XDEPFILES' line in `gdb/config/ARCH/XYZ.mh'. Generic Host Support Files -------------------------- There are some "generic" versions of routines that can be used by various systems. These can be customized in various ways by macros defined in your `xm-XYZ.h' file. If these routines work for the XYZ host, you can just include the generic file's name (with `.o', not `.c') in `XDEPFILES'. Otherwise, if your machine needs custom support routines, you will need to write routines that perform the same functions as the 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. Host Conditionals ================= When GDB is configured and compiled, various macros are defined or left undefined, to control compilation based on the attributes of the host system. These macros and their meanings (or if the meaning is not documented here, then one of the source files where they are used is indicated) are: `GDBINIT_FILENAME' The default name of GDB's initialization file (normally `.gdbinit'). `MEM_FNS_DECLARED' Your host config file defines this if it includes declarations of `memcpy' and `memset'. Define this to avoid conflicts between the native include files and the declarations in `defs.h'. `NO_SYS_FILE' Define this if your system does not have a `'. `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 compiler is unusually anal. `FOPEN_RB' Define this if binary files are opened the same way as text files. `GETENV_PROVIDED' Define this if the system declares `getenv' in its headers included in `defs.h'. This isn't needed unless your compiler is unusually anal. `HAVE_MMAP' In some cases, use the system call `mmap' for reading symbol tables. For some machines this allows for sharing and quick updates. `HAVE_SIGSETMASK' Define this if the host system has job control, but does not define `sigsetmask()'. Currently, this is only true of the RS/6000. `HAVE_TERMIO' Define this if the host system has `termio.h'. `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 "ll". This is set by the configure script. `HAVE_LONG_DOUBLE' Define this if the host C compiler supports "long double". This is set by the configure script. `PRINTF_HAS_LONG_DOUBLE' Define this if the host can handle printing of long double float-point numbers via the printf format directive "Lg". This is set by the configure script. `SCANF_HAS_LONG_DOUBLE' Define this if the host can handle the parsing of long double float-point numbers via the scanf format directive directive "Lg". This is set by the configure script. `LSEEK_NOT_LINEAR' Define this if `lseek (n)' does not necessarily move to byte number `n' in the file. This is only used when reading source files. It is normally faster to define `CRLF_SOURCE_FILES' when possible. `L_SET' This macro is used as the argument to lseek (or, most commonly, bfd_seek). FIXME, should be replaced by SEEK_SET instead, which is the POSIX equivalent. `MAINTENANCE_CMDS' If the value of this is 1, then a number of optional maintenance commands are compiled in. `MALLOC_INCOMPATIBLE' Define this if the system's prototype for `malloc' differs from the ANSI definition. `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 one or more tokens, such as `__attribute__ ((noreturn))', 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_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 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 `/**/'.