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GNU Info File | 1994-11-23 | 43.4 KB | 1,009 lines

This is Info file gcc.info, produced by Makeinfo-1.55 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1988, 1989, 1992, 1993, 1994 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. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled "GNU General Public License," "Funding for Free Software," and "Protect Your Freedom--Fight `Look And Feel'" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public License," "Funding for Free Software," and "Protect Your Freedom--Fight `Look And Feel'", and this permission notice, may be included in translations approved by the Free Software Foundation instead of in the original English. File: gcc.info, Node: Initialization, Next: Macros for Initialization, Prev: Label Output, Up: Assembler Format How Initialization Functions Are Handled ---------------------------------------- The compiled code for certain languages includes "constructors" (also called "initialization routines")--functions to initialize data in the program when the program is started. These functions need to be called before the program is "started"--that is to say, before `main' is called. Compiling some languages generates "destructors" (also called "termination routines") that should be called when the program terminates. To make the initialization and termination functions work, the compiler must output something in the assembler code to cause those functions to be called at the appropriate time. When you port the compiler to a new system, you need to specify how to do this. There are two major ways that GCC currently supports the execution of initialization and termination functions. Each way has two variants. Much of the structure is common to all four variations. The linker must build two lists of these functions--a list of initialization functions, called `__CTOR_LIST__', and a list of termination functions, called `__DTOR_LIST__'. Each list always begins with an ignored function pointer (which may hold 0, -1, or a count of the function pointers after it, depending on the environment). This is followed by a series of zero or more function pointers to constructors (or destructors), followed by a function pointer containing zero. Depending on the operating system and its executable file format, either `crtstuff.c' or `libgcc2.c' traverses these lists at startup time and exit time. Constructors are called in forward order of the list; destructors in reverse order. The best way to handle static constructors works only for object file formats which provide arbitrarily-named sections. A section is set aside for a list of constructors, and another for a list of destructors. Traditionally these are called `.ctors' and `.dtors'. Each object file that defines an initialization function also puts a word in the constructor section to point to that function. The linker accumulates all these words into one contiguous `.ctors' section. Termination functions are handled similarly. To use this method, you need appropriate definitions of the macros `ASM_OUTPUT_CONSTRUCTOR' and `ASM_OUTPUT_DESTRUCTOR'. Usually you can get them by including `svr4.h'. When arbitrary sections are available, there are two variants, depending upon how the code in `crtstuff.c' is called. On systems that support an "init" section which is executed at program startup, parts of `crtstuff.c' are compiled into that section. The program is linked by the `gcc' driver like this: ld -o OUTPUT_FILE crtbegin.o ... crtend.o -lgcc The head of a function (`__do_global_ctors') appears in the init section of `crtbegin.o'; the remainder of the function appears in the init section of `crtend.o'. The linker will pull these two parts of the section together, making a whole function. If any of the user's object files linked into the middle of it contribute code, then that code will be executed as part of the body of `__do_global_ctors'. To use this variant, you must define the `INIT_SECTION_ASM_OP' macro properly. If no init section is available, do not define `INIT_SECTION_ASM_OP'. Then `__do_global_ctors' is built into the text section like all other functions, and resides in `libgcc.a'. When GCC compiles any function called `main', it inserts a procedure call to `__main' as the first executable code after the function prologue. The `__main' function, also defined in `libgcc2.c', simply calls `__do_global_ctors'. In file formats that don't support arbitrary sections, there are again two variants. In the simplest variant, the GNU linker (GNU `ld') and an `a.out' format must be used. In this case, `ASM_OUTPUT_CONSTRUCTOR' is defined to produce a `.stabs' entry of type `N_SETT', referencing the name `__CTOR_LIST__', and with the address of the void function containing the initialization code as its value. The GNU linker recognizes this as a request to add the value to a "set"; the values are accumulated, and are eventually placed in the executable as a vector in the format described above, with a leading (ignored) count and a trailing zero element. `ASM_OUTPUT_DESTRUCTOR' is handled similarly. Since no init section is available, the absence of `INIT_SECTION_ASM_OP' causes the compilation of `main' to call `__main' as above, starting the initialization process. The last variant uses neither arbitrary sections nor the GNU linker. This is preferable when you want to do dynamic linking and when using file formats which the GNU linker does not support, such as `ECOFF'. In this case, `ASM_OUTPUT_CONSTRUCTOR' does not produce an `N_SETT' symbol; initialization and termination functions are recognized simply by their names. This requires an extra program in the linkage step, called `collect2'. This program pretends to be the linker, for use with GNU CC; it does its job by running the ordinary linker, but also arranges to include the vectors of initialization and termination functions. These functions are called via `__main' as described above. Choosing among these configuration options has been simplified by a set of operating-system-dependent files in the `config' subdirectory. These files define all of the relevant parameters. Usually it is sufficient to include one into your specific machine-dependent configuration file. These files are: `aoutos.h' For operating systems using the `a.out' format. `next.h' For operating systems using the `MachO' format. `svr3.h' For System V Release 3 and similar systems using `COFF' format. `svr4.h' For System V Release 4 and similar systems using `ELF' format. `vms.h' For the VMS operating system. The following section describes the specific macros that control and customize the handling of initialization and termination functions. File: gcc.info, Node: Macros for Initialization, Next: Instruction Output, Prev: Initialization, Up: Assembler Format Macros Controlling Initialization Routines ------------------------------------------ Here are the macros that control how the compiler handles initialization and termination functions: `INIT_SECTION_ASM_OP' If defined, a C string constant for the assembler operation to identify the following data as initialization code. If not defined, GNU CC will assume such a section does not exist. When you are using special sections for initialization and termination functions, this macro also controls how `crtstuff.c' and `libgcc2.c' arrange to run the initialization functions. `HAS_INIT_SECTION' If defined, `main' will not call `__main' as described above. This macro should be defined for systems that control the contents of the init section on a symbol-by-symbol basis, such as OSF/1, and should not be defined explicitly for systems that support `INIT_SECTION_ASM_OP'. `INVOKE__main' If defined, `main' will call `__main' despite the presence of `INIT_SECTION_ASM_OP'. This macro should be defined for systems where the init section is not actually run automatically, but is still useful for collecting the lists of constructors and destructors. `ASM_OUTPUT_CONSTRUCTOR (STREAM, NAME)' Define this macro as a C statement to output on the stream STREAM the assembler code to arrange to call the function named NAME at initialization time. Assume that NAME is the name of a C function generated automatically by the compiler. This function takes no arguments. Use the function `assemble_name' to output the name NAME; this performs any system-specific syntactic transformations such as adding an underscore. If you don't define this macro, nothing special is output to arrange to call the function. This is correct when the function will be called in some other manner--for example, by means of the `collect2' program, which looks through the symbol table to find these functions by their names. `ASM_OUTPUT_DESTRUCTOR (STREAM, NAME)' This is like `ASM_OUTPUT_CONSTRUCTOR' but used for termination functions rather than initialization functions. If your system uses `collect2' as the means of processing constructors, then that program normally uses `nm' to scan an object file for constructor functions to be called. On certain kinds of systems, you can define these macros to make `collect2' work faster (and, in some cases, make it work at all): `OBJECT_FORMAT_COFF' Define this macro if the system uses COFF (Common Object File Format) object files, so that `collect2' can assume this format and scan object files directly for dynamic constructor/destructor functions. `OBJECT_FORMAT_ROSE' Define this macro if the system uses ROSE format object files, so that `collect2' can assume this format and scan object files directly for dynamic constructor/destructor functions. `REAL_NM_FILE_NAME' Define this macro as a C string constant containing the file name to use to execute `nm'. The default is to search the path normally for `nm'. These macros are effective only in a native compiler; `collect2' as part of a cross compiler always uses `nm' for the target machine. File: gcc.info, Node: Instruction Output, Next: Dispatch Tables, Prev: Macros for Initialization, Up: Assembler Format Output of Assembler Instructions -------------------------------- This describes assembler instruction output. `REGISTER_NAMES' A C initializer containing the assembler's names for the machine registers, each one as a C string constant. This is what translates register numbers in the compiler into assembler language. `ADDITIONAL_REGISTER_NAMES' If defined, a C initializer for an array of structures containing a name and a register number. This macro defines additional names for hard registers, thus allowing the `asm' option in declarations to refer to registers using alternate names. `ASM_OUTPUT_OPCODE (STREAM, PTR)' Define this macro if you are using an unusual assembler that requires different names for the machine instructions. The definition is a C statement or statements which output an assembler instruction opcode to the stdio stream STREAM. The macro-operand PTR is a variable of type `char *' which points to the opcode name in its "internal" form--the form that is written in the machine description. The definition should output the opcode name to STREAM, performing any translation you desire, and increment the variable PTR to point at the end of the opcode so that it will not be output twice. In fact, your macro definition may process less than the entire opcode name, or more than the opcode name; but if you want to process text that includes `%'-sequences to substitute operands, you must take care of the substitution yourself. Just be sure to increment PTR over whatever text should not be output normally. If you need to look at the operand values, they can be found as the elements of `recog_operand'. If the macro definition does nothing, the instruction is output in the usual way. `FINAL_PRESCAN_INSN (INSN, OPVEC, NOPERANDS)' If defined, a C statement to be executed just prior to the output of assembler code for INSN, to modify the extracted operands so they will be output differently. Here the argument OPVEC is the vector containing the operands extracted from INSN, and NOPERANDS is the number of elements of the vector which contain meaningful data for this insn. The contents of this vector are what will be used to convert the insn template into assembler code, so you can change the assembler output by changing the contents of the vector. This macro is useful when various assembler syntaxes share a single file of instruction patterns; by defining this macro differently, you can cause a large class of instructions to be output differently (such as with rearranged operands). Naturally, variations in assembler syntax affecting individual insn patterns ought to be handled by writing conditional output routines in those patterns. If this macro is not defined, it is equivalent to a null statement. `PRINT_OPERAND (STREAM, X, CODE)' A C compound statement to output to stdio stream STREAM the assembler syntax for an instruction operand X. X is an RTL expression. CODE is a value that can be used to specify one of several ways of printing the operand. It is used when identical operands must be printed differently depending on the context. CODE comes from the `%' specification that was used to request printing of the operand. If the specification was just `%DIGIT' then CODE is 0; if the specification was `%LTR DIGIT' then CODE is the ASCII code for LTR. If X is a register, this macro should print the register's name. The names can be found in an array `reg_names' whose type is `char *[]'. `reg_names' is initialized from `REGISTER_NAMES'. When the machine description has a specification `%PUNCT' (a `%' followed by a punctuation character), this macro is called with a null pointer for X and the punctuation character for CODE. `PRINT_OPERAND_PUNCT_VALID_P (CODE)' A C expression which evaluates to true if CODE is a valid punctuation character for use in the `PRINT_OPERAND' macro. If `PRINT_OPERAND_PUNCT_VALID_P' is not defined, it means that no punctuation characters (except for the standard one, `%') are used in this way. `PRINT_OPERAND_ADDRESS (STREAM, X)' A C compound statement to output to stdio stream STREAM the assembler syntax for an instruction operand that is a memory reference whose address is X. X is an RTL expression. On some machines, the syntax for a symbolic address depends on the section that the address refers to. On these machines, define the macro `ENCODE_SECTION_INFO' to store the information into the `symbol_ref', and then check for it here. *Note Assembler Format::. `DBR_OUTPUT_SEQEND(FILE)' A C statement, to be executed after all slot-filler instructions have been output. If necessary, call `dbr_sequence_length' to determine the number of slots filled in a sequence (zero if not currently outputting a sequence), to decide how many no-ops to output, or whatever. Don't define this macro if it has nothing to do, but it is helpful in reading assembly output if the extent of the delay sequence is made explicit (e.g. with white space). Note that output routines for instructions with delay slots must be prepared to deal with not being output as part of a sequence (i.e. when the scheduling pass is not run, or when no slot fillers could be found.) The variable `final_sequence' is null when not processing a sequence, otherwise it contains the `sequence' rtx being output. `REGISTER_PREFIX' `LOCAL_LABEL_PREFIX' `USER_LABEL_PREFIX' `IMMEDIATE_PREFIX' If defined, C string expressions to be used for the `%R', `%L', `%U', and `%I' options of `asm_fprintf' (see `final.c'). These are useful when a single `md' file must support multiple assembler formats. In that case, the various `tm.h' files can define these macros differently. `ASSEMBLER_DIALECT' If your target supports multiple dialects of assembler language (such as different opcodes), define this macro as a C expression that gives the numeric index of the assembler langauge dialect to use, with zero as the first variant. If this macro is defined, you may use `{option0|option1|option2...}' constructs in the output templates of patterns (*note Output Template::.) or in the first argument of `asm_fprintf'. This construct outputs `option0', `option1' or `option2', etc., if the value of `ASSEMBLER_DIALECT' is zero, one or two, etc. Any special characters within these strings retain their usual meaning. If you do not define this macro, the characters `{', `|' and `}' do not have any special meaning when used in templates or operands to `asm_fprintf'. Define the macros `REGISTER_PREFIX', `LOCAL_LABEL_PREFIX', `USER_LABEL_PREFIX' and `IMMEDIATE_PREFIX' if you can express the variations in assemble language syntax with that mechanism. Define `ASSEMBLER_DIALECT' and use the `{option0|option1}' syntax if the syntax variant are larger and involve such things as different opcodes or operand order. `ASM_OUTPUT_REG_PUSH (STREAM, REGNO)' A C expression to output to STREAM some assembler code which will push hard register number REGNO onto the stack. The code need not be optimal, since this macro is used only when profiling. `ASM_OUTPUT_REG_POP (STREAM, REGNO)' A C expression to output to STREAM some assembler code which will pop hard register number REGNO off of the stack. The code need not be optimal, since this macro is used only when profiling. File: gcc.info, Node: Dispatch Tables, Next: Alignment Output, Prev: Instruction Output, Up: Assembler Format Output of Dispatch Tables ------------------------- This concerns dispatch tables. `ASM_OUTPUT_ADDR_DIFF_ELT (STREAM, VALUE, REL)' This macro should be provided on machines where the addresses in a dispatch table are relative to the table's own address. The definition should be a C statement to output to the stdio stream STREAM an assembler pseudo-instruction to generate a difference between two labels. VALUE and REL are the numbers of two internal labels. The definitions of these labels are output using `ASM_OUTPUT_INTERNAL_LABEL', and they must be printed in the same way here. For example, fprintf (STREAM, "\t.word L%d-L%d\n", VALUE, REL) `ASM_OUTPUT_ADDR_VEC_ELT (STREAM, VALUE)' This macro should be provided on machines where the addresses in a dispatch table are absolute. The definition should be a C statement to output to the stdio stream STREAM an assembler pseudo-instruction to generate a reference to a label. VALUE is the number of an internal label whose definition is output using `ASM_OUTPUT_INTERNAL_LABEL'. For example, fprintf (STREAM, "\t.word L%d\n", VALUE) `ASM_OUTPUT_CASE_LABEL (STREAM, PREFIX, NUM, TABLE)' Define this if the label before a jump-table needs to be output specially. The first three arguments are the same as for `ASM_OUTPUT_INTERNAL_LABEL'; the fourth argument is the jump-table which follows (a `jump_insn' containing an `addr_vec' or `addr_diff_vec'). This feature is used on system V to output a `swbeg' statement for the table. If this macro is not defined, these labels are output with `ASM_OUTPUT_INTERNAL_LABEL'. `ASM_OUTPUT_CASE_END (STREAM, NUM, TABLE)' Define this if something special must be output at the end of a jump-table. The definition should be a C statement to be executed after the assembler code for the table is written. It should write the appropriate code to stdio stream STREAM. The argument TABLE is the jump-table insn, and NUM is the label-number of the preceding label. If this macro is not defined, nothing special is output at the end of the jump-table. File: gcc.info, Node: Alignment Output, Prev: Dispatch Tables, Up: Assembler Format Assembler Commands for Alignment -------------------------------- This describes commands for alignment. `ASM_OUTPUT_ALIGN_CODE (FILE)' A C expression to output text to align the location counter in the way that is desirable at a point in the code that is reached only by jumping. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. `ASM_OUTPUT_LOOP_ALIGN (FILE)' A C expression to output text to align the location counter in the way that is desirable at the beginning of a loop. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. `ASM_OUTPUT_SKIP (STREAM, NBYTES)' A C statement to output to the stdio stream STREAM an assembler instruction to advance the location counter by NBYTES bytes. Those bytes should be zero when loaded. NBYTES will be a C expression of type `int'. `ASM_NO_SKIP_IN_TEXT' Define this macro if `ASM_OUTPUT_SKIP' should not be used in the text section because it fails put zeros in the bytes that are skipped. This is true on many Unix systems, where the pseudo-op to skip bytes produces no-op instructions rather than zeros when used in the text section. `ASM_OUTPUT_ALIGN (STREAM, POWER)' A C statement to output to the stdio stream STREAM an assembler command to advance the location counter to a multiple of 2 to the POWER bytes. POWER will be a C expression of type `int'. File: gcc.info, Node: Debugging Info, Next: Cross-compilation, Prev: Assembler Format, Up: Target Macros Controlling Debugging Information Format ======================================== This describes how to specify debugging information. * Menu: * All Debuggers:: Macros that affect all debugging formats uniformly. * DBX Options:: Macros enabling specific options in DBX format. * DBX Hooks:: Hook macros for varying DBX format. * File Names and DBX:: Macros controlling output of file names in DBX format. * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. File: gcc.info, Node: All Debuggers, Next: DBX Options, Up: Debugging Info Macros Affecting All Debugging Formats -------------------------------------- These macros affect all debugging formats. `DBX_REGISTER_NUMBER (REGNO)' A C expression that returns the DBX register number for the compiler register number REGNO. In simple cases, the value of this expression may be REGNO itself. But sometimes there are some registers that the compiler knows about and DBX does not, or vice versa. In such cases, some register may need to have one number in the compiler and another for DBX. If two registers have consecutive numbers inside GNU CC, and they can be used as a pair to hold a multiword value, then they *must* have consecutive numbers after renumbering with `DBX_REGISTER_NUMBER'. Otherwise, debuggers will be unable to access such a pair, because they expect register pairs to be consecutive in their own numbering scheme. If you find yourself defining `DBX_REGISTER_NUMBER' in way that does not preserve register pairs, then what you must do instead is redefine the actual register numbering scheme. `DEBUGGER_AUTO_OFFSET (X)' A C expression that returns the integer offset value for an automatic variable having address X (an RTL expression). The default computation assumes that X is based on the frame-pointer and gives the offset from the frame-pointer. This is required for targets that produce debugging output for DBX or COFF-style debugging output for SDB and allow the frame-pointer to be eliminated when the `-g' options is used. `DEBUGGER_ARG_OFFSET (OFFSET, X)' A C expression that returns the integer offset value for an argument having address X (an RTL expression). The nominal offset is OFFSET. `PREFERRED_DEBUGGING_TYPE' A C expression that returns the type of debugging output GNU CC produces when the user specifies `-g' or `-ggdb'. Define this if you have arranged for GNU CC to support more than one format of debugging output. Currently, the allowable values are `DBX_DEBUG', `SDB_DEBUG', `DWARF_DEBUG', and `XCOFF_DEBUG'. The value of this macro only affects the default debugging output; the user can always get a specific type of output by using `-gstabs', `-gcoff', `-gdwarf', or `-gxcoff'. File: gcc.info, Node: DBX Options, Next: DBX Hooks, Prev: All Debuggers, Up: Debugging Info Specific Options for DBX Output ------------------------------- These are specific options for DBX output. `DBX_DEBUGGING_INFO' Define this macro if GNU CC should produce debugging output for DBX in response to the `-g' option. `XCOFF_DEBUGGING_INFO' Define this macro if GNU CC should produce XCOFF format debugging output in response to the `-g' option. This is a variant of DBX format. `DEFAULT_GDB_EXTENSIONS' Define this macro to control whether GNU CC should by default generate GDB's extended version of DBX debugging information (assuming DBX-format debugging information is enabled at all). If you don't define the macro, the default is 1: always generate the extended information if there is any occasion to. `DEBUG_SYMS_TEXT' Define this macro if all `.stabs' commands should be output while in the text section. `ASM_STABS_OP' A C string constant naming the assembler pseudo op to use instead of `.stabs' to define an ordinary debugging symbol. If you don't define this macro, `.stabs' is used. This macro applies only to DBX debugging information format. `ASM_STABD_OP' A C string constant naming the assembler pseudo op to use instead of `.stabd' to define a debugging symbol whose value is the current location. If you don't define this macro, `.stabd' is used. This macro applies only to DBX debugging information format. `ASM_STABN_OP' A C string constant naming the assembler pseudo op to use instead of `.stabn' to define a debugging symbol with no name. If you don't define this macro, `.stabn' is used. This macro applies only to DBX debugging information format. `DBX_NO_XREFS' Define this macro if DBX on your system does not support the construct `xsTAGNAME'. On some systems, this construct is used to describe a forward reference to a structure named TAGNAME. On other systems, this construct is not supported at all. `DBX_CONTIN_LENGTH' A symbol name in DBX-format debugging information is normally continued (split into two separate `.stabs' directives) when it exceeds a certain length (by default, 80 characters). On some operating systems, DBX requires this splitting; on others, splitting must not be done. You can inhibit splitting by defining this macro with the value zero. You can override the default splitting-length by defining this macro as an expression for the length you desire. `DBX_CONTIN_CHAR' Normally continuation is indicated by adding a `\' character to the end of a `.stabs' string when a continuation follows. To use a different character instead, define this macro as a character constant for the character you want to use. Do not define this macro if backslash is correct for your system. `DBX_STATIC_STAB_DATA_SECTION' Define this macro if it is necessary to go to the data section before outputting the `.stabs' pseudo-op for a non-global static variable. `DBX_TYPE_DECL_STABS_CODE' The value to use in the "code" field of the `.stabs' directive for a typedef. The default is `N_LSYM'. `DBX_STATIC_CONST_VAR_CODE' The value to use in the "code" field of the `.stabs' directive for a static variable located in the text section. DBX format does not provide any "right" way to do this. The default is `N_FUN'. `DBX_REGPARM_STABS_CODE' The value to use in the "code" field of the `.stabs' directive for a parameter passed in registers. DBX format does not provide any "right" way to do this. The default is `N_RSYM'. `DBX_REGPARM_STABS_LETTER' The letter to use in DBX symbol data to identify a symbol as a parameter passed in registers. DBX format does not customarily provide any way to do this. The default is `'P''. `DBX_MEMPARM_STABS_LETTER' The letter to use in DBX symbol data to identify a symbol as a stack parameter. The default is `'p''. `DBX_FUNCTION_FIRST' Define this macro if the DBX information for a function and its arguments should precede the assembler code for the function. Normally, in DBX format, the debugging information entirely follows the assembler code. `DBX_LBRAC_FIRST' Define this macro if the `N_LBRAC' symbol for a block should precede the debugging information for variables and functions defined in that block. Normally, in DBX format, the `N_LBRAC' symbol comes first. `DBX_BLOCKS_FUNCTION_RELATIVE' Define this macro if the value of a symbol describing the scope of a block (`N_LBRAC' or `N_RBRAC') should be relative to the start of the enclosing function. Normally, GNU C uses an absolute address. File: gcc.info, Node: DBX Hooks, Next: File Names and DBX, Prev: DBX Options, Up: Debugging Info Open-Ended Hooks for DBX Format ------------------------------- These are hooks for DBX format. `DBX_OUTPUT_LBRAC (STREAM, NAME)' Define this macro to say how to output to STREAM the debugging information for the start of a scope level for variable names. The argument NAME is the name of an assembler symbol (for use with `assemble_name') whose value is the address where the scope begins. `DBX_OUTPUT_RBRAC (STREAM, NAME)' Like `DBX_OUTPUT_LBRAC', but for the end of a scope level. `DBX_OUTPUT_ENUM (STREAM, TYPE)' Define this macro if the target machine requires special handling to output an enumeration type. The definition should be a C statement (sans semicolon) to output the appropriate information to STREAM for the type TYPE. `DBX_OUTPUT_FUNCTION_END (STREAM, FUNCTION)' Define this macro if the target machine requires special output at the end of the debugging information for a function. The definition should be a C statement (sans semicolon) to output the appropriate information to STREAM. FUNCTION is the `FUNCTION_DECL' node for the function. `DBX_OUTPUT_STANDARD_TYPES (SYMS)' Define this macro if you need to control the order of output of the standard data types at the beginning of compilation. The argument SYMS is a `tree' which is a chain of all the predefined global symbols, including names of data types. Normally, DBX output starts with definitions of the types for integers and characters, followed by all the other predefined types of the particular language in no particular order. On some machines, it is necessary to output different particular types first. To do this, define `DBX_OUTPUT_STANDARD_TYPES' to output those symbols in the necessary order. Any predefined types that you don't explicitly output will be output afterward in no particular order. Be careful not to define this macro so that it works only for C. There are no global variables to access most of the built-in types, because another language may have another set of types. The way to output a particular type is to look through SYMS to see if you can find it. Here is an example: { tree decl; for (decl = syms; decl; decl = TREE_CHAIN (decl)) if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)), "long int")) dbxout_symbol (decl); ... } This does nothing if the expected type does not exist. See the function `init_decl_processing' in `c-decl.c' to find the names to use for all the built-in C types. Here is another way of finding a particular type: { tree decl; for (decl = syms; decl; decl = TREE_CHAIN (decl)) if (TREE_CODE (decl) == TYPE_DECL && (TREE_CODE (TREE_TYPE (decl)) == INTEGER_CST) && TYPE_PRECISION (TREE_TYPE (decl)) == 16 && TYPE_UNSIGNED (TREE_TYPE (decl))) /* This must be `unsigned short'. */ dbxout_symbol (decl); ... } File: gcc.info, Node: File Names and DBX, Next: SDB and DWARF, Prev: DBX Hooks, Up: Debugging Info File Names in DBX Format ------------------------ This describes file names in DBX format. `DBX_WORKING_DIRECTORY' Define this if DBX wants to have the current directory recorded in each object file. Note that the working directory is always recorded if GDB extensions are enabled. `DBX_OUTPUT_MAIN_SOURCE_FILENAME (STREAM, NAME)' A C statement to output DBX debugging information to the stdio stream STREAM which indicates that file NAME is the main source file--the file specified as the input file for compilation. This macro is called only once, at the beginning of compilation. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. `DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (STREAM, NAME)' A C statement to output DBX debugging information to the stdio stream STREAM which indicates that the current directory during compilation is named NAME. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. `DBX_OUTPUT_MAIN_SOURCE_FILE_END (STREAM, NAME)' A C statement to output DBX debugging information at the end of compilation of the main source file NAME. If you don't define this macro, nothing special is output at the end of compilation, which is correct for most machines. `DBX_OUTPUT_SOURCE_FILENAME (STREAM, NAME)' A C statement to output DBX debugging information to the stdio stream STREAM which indicates that file NAME is the current source file. This output is generated each time input shifts to a different source file as a result of `#include', the end of an included file, or a `#line' command. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. File: gcc.info, Node: SDB and DWARF, Prev: File Names and DBX, Up: Debugging Info Macros for SDB and DWARF Output ------------------------------- Here are macros for SDB and DWARF output. `SDB_DEBUGGING_INFO' Define this macro if GNU CC should produce COFF-style debugging output for SDB in response to the `-g' option. `DWARF_DEBUGGING_INFO' Define this macro if GNU CC should produce dwarf format debugging output in response to the `-g' option. `PUT_SDB_...' Define these macros to override the assembler syntax for the special SDB assembler directives. See `sdbout.c' for a list of these macros and their arguments. If the standard syntax is used, you need not define them yourself. `SDB_DELIM' Some assemblers do not support a semicolon as a delimiter, even between SDB assembler directives. In that case, define this macro to be the delimiter to use (usually `\n'). It is not necessary to define a new set of `PUT_SDB_OP' macros if this is the only change required. `SDB_GENERATE_FAKE' Define this macro to override the usual method of constructing a dummy name for anonymous structure and union types. See `sdbout.c' for more information. `SDB_ALLOW_UNKNOWN_REFERENCES' Define this macro to allow references to unknown structure, union, or enumeration tags to be emitted. Standard COFF does not allow handling of unknown references, MIPS ECOFF has support for it. `SDB_ALLOW_FORWARD_REFERENCES' Define this macro to allow references to structure, union, or enumeration tags that have not yet been seen to be handled. Some assemblers choke if forward tags are used, while some require it. File: gcc.info, Node: Cross-compilation, Next: Misc, Prev: Debugging Info, Up: Target Macros Cross Compilation and Floating Point ==================================== While all modern machines use 2's complement representation for integers, there are a variety of representations for floating point numbers. This means that in a cross-compiler the representation of floating point numbers in the compiled program may be different from that used in the machine doing the compilation. Because different representation systems may offer different amounts of range and precision, the cross compiler cannot safely use the host machine's floating point arithmetic. Therefore, floating point constants must be represented in the target machine's format. This means that the cross compiler cannot use `atof' to parse a floating point constant; it must have its own special routine to use instead. Also, constant folding must emulate the target machine's arithmetic (or must not be done at all). The macros in the following table should be defined only if you are cross compiling between different floating point formats. Otherwise, don't define them. Then default definitions will be set up which use `double' as the data type, `==' to test for equality, etc. You don't need to worry about how many times you use an operand of any of these macros. The compiler never uses operands which have side effects. `REAL_VALUE_TYPE' A macro for the C data type to be used to hold a floating point value in the target machine's format. Typically this would be a `struct' containing an array of `int'. `REAL_VALUES_EQUAL (X, Y)' A macro for a C expression which compares for equality the two values, X and Y, both of type `REAL_VALUE_TYPE'. `REAL_VALUES_LESS (X, Y)' A macro for a C expression which tests whether X is less than Y, both values being of type `REAL_VALUE_TYPE' and interpreted as floating point numbers in the target machine's representation. `REAL_VALUE_LDEXP (X, SCALE)' A macro for a C expression which performs the standard library function `ldexp', but using the target machine's floating point representation. Both X and the value of the expression have type `REAL_VALUE_TYPE'. The second argument, SCALE, is an integer. `REAL_VALUE_FIX (X)' A macro whose definition is a C expression to convert the target-machine floating point value X to a signed integer. X has type `REAL_VALUE_TYPE'. `REAL_VALUE_UNSIGNED_FIX (X)' A macro whose definition is a C expression to convert the target-machine floating point value X to an unsigned integer. X has type `REAL_VALUE_TYPE'. `REAL_VALUE_RNDZINT (X)' A macro whose definition is a C expression to round the target-machine floating point value X towards zero to an integer value (but still as a floating point number). X has type `REAL_VALUE_TYPE', and so does the value. `REAL_VALUE_UNSIGNED_RNDZINT (X)' A macro whose definition is a C expression to round the target-machine floating point value X towards zero to an unsigned integer value (but still represented as a floating point number). x has type `REAL_VALUE_TYPE', and so does the value. `REAL_VALUE_ATOF (STRING, MODE)' A macro for a C expression which converts STRING, an expression of type `char *', into a floating point number in the target machine's representation for mode MODE. The value has type `REAL_VALUE_TYPE'. `REAL_INFINITY' Define this macro if infinity is a possible floating point value, and therefore division by 0 is legitimate. `REAL_VALUE_ISINF (X)' A macro for a C expression which determines whether X, a floating point value, is infinity. The value has type `int'. By default, this is defined to call `isinf'. `REAL_VALUE_ISNAN (X)' A macro for a C expression which determines whether X, a floating point value, is a "nan" (not-a-number). The value has type `int'. By default, this is defined to call `isnan'. Define the following additional macros if you want to make floating point constant folding work while cross compiling. If you don't define them, cross compilation is still possible, but constant folding will not happen for floating point values. `REAL_ARITHMETIC (OUTPUT, CODE, X, Y)' A macro for a C statement which calculates an arithmetic operation of the two floating point values X and Y, both of type `REAL_VALUE_TYPE' in the target machine's representation, to produce a result of the same type and representation which is stored in OUTPUT (which will be a variable). The operation to be performed is specified by CODE, a tree code which will always be one of the following: `PLUS_EXPR', `MINUS_EXPR', `MULT_EXPR', `RDIV_EXPR', `MAX_EXPR', `MIN_EXPR'. The expansion of this macro is responsible for checking for overflow. If overflow happens, the macro expansion should execute the statement `return 0;', which indicates the inability to perform the arithmetic operation requested. `REAL_VALUE_NEGATE (X)' A macro for a C expression which returns the negative of the floating point value X. Both X and the value of the expression have type `REAL_VALUE_TYPE' and are in the target machine's floating point representation. There is no way for this macro to report overflow, since overflow can't happen in the negation operation. `REAL_VALUE_TRUNCATE (MODE, X)' A macro for a C expression which converts the floating point value X to mode MODE. Both X and the value of the expression are in the target machine's floating point representation and have type `REAL_VALUE_TYPE'. However, the value should have an appropriate bit pattern to be output properly as a floating constant whose precision accords with mode MODE. There is no way for this macro to report overflow. `REAL_VALUE_TO_INT (LOW, HIGH, X)' A macro for a C expression which converts a floating point value X into a double-precision integer which is then stored into LOW and HIGH, two variables of type INT. `REAL_VALUE_FROM_INT (X, LOW, HIGH)' A macro for a C expression which converts a double-precision integer found in LOW and HIGH, two variables of type INT, into a floating point value which is then stored into X.