This is Info file gcc.info, produced by Makeinfo-1.47 from the input file gcc.texi. This file documents the use and the internals of the GNU compiler. Copyright (C) 1988, 1989, 1992 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" and "Boycott" 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" and "Boycott", 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: Costs, Next: Sections, Prev: Condition Code, Up: Target Macros Describing Relative Costs of Operations ======================================= These macros let you describe the relative speed of various operations on the target machine. `CONST_COSTS (X, CODE, OUTER_CODE)' A part of a C `switch' statement that describes the relative costs of constant RTL expressions. It must contain `case' labels for expression codes `const_int', `const', `symbol_ref', `label_ref' and `const_double'. Each case must ultimately reach a `return' statement to return the relative cost of the use of that kind of constant value in an expression. The cost may depend on the precise value of the constant, which is available for examination in X, and the rtx code of the expression in which it is contained, found in OUTER_CODE. CODE is the expression code--redundant, since it can be obtained with `GET_CODE (X)'. `RTX_COSTS (X, CODE, OUTER_CODE)' Like `CONST_COSTS' but applies to nonconstant RTL expressions. This can be used, for example, to indicate how costly a multiply instruction is. In writing this macro, you can use the construct `COSTS_N_INSNS (N)' to specify a cost equal to N fast instructions. OUTER_CODE is the code of the expression in which X is contained. This macro is optional; do not define it if the default cost assumptions are adequate for the target machine. `ADDRESS_COST (ADDRESS)' An expression giving the cost of an addressing mode that contains ADDRESS. If not defined, the cost is computed from the ADDRESS expression and the `CONST_COSTS' values. For most CISC machines, the default cost is a good approximation of the true cost of the addressing mode. However, on RISC machines, all instructions normally have the same length and execution time. Hence all addresses will have equal costs. In cases where more than one form of an address is known, the form with the lowest cost will be used. If multiple forms have the same, lowest, cost, the one that is the most complex will be used. For example, suppose an address that is equal to the sum of a register and a constant is used twice in the same basic block. When this macro is not defined, the address will be computed in a register and memory references will be indirect through that register. On machines where the cost of the addressing mode containing the sum is no higher than that of a simple indirect reference, this will produce an additional instruction and possibly require an additional register. Proper specification of this macro eliminates this overhead for such machines. Similar use of this macro is made in strength reduction of loops. ADDRESS need not be valid as an address. In such a case, the cost is not relevant and can be any value; invalid addresses need not be assigned a different cost. On machines where an address involving more than one register is as cheap as an address computation involving only one register, defining `ADDRESS_COST' to reflect this can cause two registers to be live over a region of code where only one would have been if `ADDRESS_COST' were not defined in that manner. This effect should be considered in the definition of this macro. Equivalent costs should probably only be given to addresses with different numbers of registers on machines with lots of registers. This macro will normally either not be defined or be defined as a constant. `REGISTER_MOVE_COST (FROM, TO)' A C expression for the cost of moving data from a register in class FROM to one in class TO. The classes are expressed using the enumeration values such as `GENERAL_REGS'. A value of 2 is the default; other values are interpreted relative to that. It is not required that the cost always equal 2 when FROM is the same as TO; on some machines it is expensive to move between registers if they are not general registers. If reload sees an insn consisting of a single `set' between two hard registers, and if `REGISTER_MOVE_COST' applied to their classes returns a value of 2, reload does not check to ensure that the constraints of the insn are met. Setting a cost of other than 2 will allow reload to verify that the constraints are met. You should do this if the `movM' pattern's constraints do not allow such copying. `MEMORY_MOVE_COST (M)' A C expression for the cost of moving data of mode M between a register and memory. A value of 2 is the default; this cost is relative to those in `REGISTER_MOVE_COST'. If moving between registers and memory is more expensive than between two registers, you should define this macro to express the relative cost. `BRANCH_COST' A C expression for the cost of a branch instruction. A value of 1 is the default; other values are interpreted relative to that. Here are additional macros which do not specify precise relative costs, but only that certain actions are more expensive than GNU CC would ordinarily expect. `SLOW_BYTE_ACCESS' Define this macro as a C expression which is nonzero if accessing less than a word of memory (i.e. a `char' or a `short') is no faster than accessing a word of memory, i.e., if such access require more than one instruction or if there is no difference in cost between byte and (aligned) word loads. When this macro is not defined, the compiler will access a field by finding the smallest containing object; when it is defined, a fullword load will be used if alignment permits. Unless bytes accesses are faster than word accesses, using word accesses is preferable since it may eliminate subsequent memory access if subsequent accesses occur to other fields in the same word of the structure, but to different bytes. `SLOW_ZERO_EXTEND' Define this macro if zero-extension (of a `char' or `short' to an `int') can be done faster if the destination is a register that is known to be zero. If you define this macro, you must have instruction patterns that recognize RTL structures like this: (set (strict_low_part (subreg:QI (reg:SI ...) 0)) ...) and likewise for `HImode'. `SLOW_UNALIGNED_ACCESS' Define this macro to be the value 1 if unaligned accesses have a cost many times greater than aligned accesses, for example if they are emulated in a trap handler. When this macro is non-zero, the compiler will act as if `STRICT_ALIGNMENT' were non-zero when generating code for block moves. This can cause significantly more instructions to be produced. Therefore, do not set this macro non-zero if unaligned accesses only add a cycle or two to the time for a memory access. If the value of this macro is always zero, it need not be defined. `DONT_REDUCE_ADDR' Define this macro to inhibit strength reduction of memory addresses. (On some machines, such strength reduction seems to do harm rather than good.) `MOVE_RATIO' The number of scalar move insns which should be generated instead of a string move insn or a library call. Increasing the value will always make code faster, but eventually incurs high cost in increased code size. If you don't define this, a reasonable default is used. `NO_FUNCTION_CSE' Define this macro if it is as good or better to call a constant function address than to call an address kept in a register. `NO_RECURSIVE_FUNCTION_CSE' Define this macro if it is as good or better for a function to call itself with an explicit address than to call an address kept in a register.  File: gcc.info, Node: Sections, Next: PIC, Prev: Costs, Up: Target Macros Dividing the Output into Sections (Texts, Data, ...) ==================================================== An object file is divided into sections containing different types of data. In the most common case, there are three sections: the "text section", which holds instructions and read-only data; the "data section", which holds initialized writable data; and the "bss section", which holds uninitialized data. Some systems have other kinds of sections. The compiler must tell the assembler when to switch sections. These macros control what commands to output to tell the assembler this. You can also define additional sections. `TEXT_SECTION_ASM_OP' A C string constant for the assembler operation that should precede instructions and read-only data. Normally `".text"' is right. `DATA_SECTION_ASM_OP' A C string constant for the assembler operation to identify the following data as writable initialized data. Normally `".data"' is right. `SHARED_SECTION_ASM_OP' If defined, a C string constant for the assembler operation to identify the following data as shared data. If not defined, `DATA_SECTION_ASM_OP' will be used. `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. `EXTRA_SECTIONS' A list of names for sections other than the standard two, which are `in_text' and `in_data'. You need not define this macro on a system with no other sections (that GCC needs to use). `EXTRA_SECTION_FUNCTIONS' One or more functions to be defined in `varasm.c'. These functions should do jobs analogous to those of `text_section' and `data_section', for your additional sections. Do not define this macro if you do not define `EXTRA_SECTIONS'. `READONLY_DATA_SECTION' On most machines, read-only variables, constants, and jump tables are placed in the text section. If this is not the case on your machine, this macro should be defined to be the name of a function (either `data_section' or a function defined in `EXTRA_SECTIONS') that switches to the section to be used for read-only items. If these items should be placed in the text section, this macro should not be defined. `SELECT_SECTION (EXP, RELOC)' A C statement or statements to switch to the appropriate section for output of EXP. You can assume that EXP is either a `VAR_DECL' node or a constant of some sort. RELOC indicates whether the initial value of EXP requires link-time relocations. Select the section by calling `text_section' or one of the alternatives for other sections. Do not define this macro if you put all read-only variables and constants in the read-only data section (usually the text section). `SELECT_RTX_SECTION (MODE, RTX)' A C statement or statements to switch to the appropriate section for output of RTX in mode MODE. You can assume that RTX is some kind of constant in RTL. The argument MODE is redundant except in the case of a `const_int' rtx. Select the section by calling `text_section' or one of the alternatives for other sections. Do not define this macro if you put all constants in the read-only data section. `JUMP_TABLES_IN_TEXT_SECTION' Define this macro if jump tables (for `tablejump' insns) should be output in the text section, along with the assembler instructions. Otherwise, the readonly data section is used. This macro is irrelevant if there is no separate readonly data section. `ENCODE_SECTION_INFO (DECL)' Define this macro if references to a symbol must be treated differently depending on something about the variable or function named by the symbol (such as what section it is in). The macro definition, if any, is executed immediately after the rtl for DECL has been created and stored in `DECL_RTL (DECL)'. The value of the rtl will be a `mem' whose address is a `symbol_ref'. The usual thing for this macro to do is to record a flag in the `symbol_ref' (such as `SYMBOL_REF_FLAG') or to store a modified name string in the `symbol_ref' (if one bit is not enough information).  File: gcc.info, Node: PIC, Next: Assembler Format, Prev: Sections, Up: Target Macros Position Independent Code ========================= This section describes macros that help implement generation of position independent code. Simply defining these macros is not enough to generate valid PIC; you must also add support to the macros `GO_IF_LEGITIMATE_ADDRESS' and `LEGITIMIZE_ADDRESS', and `PRINT_OPERAND_ADDRESS' as well. You must modify the definition of `movsi' to do something appropriate when the source operand contains a symbolic address. You may also need to alter the handling of switch statements so that they use relative addresses. `PIC_OFFSET_TABLE_REGNUM' The register number of the register used to address a table of static data addresses in memory. In some cases this register is defined by a processor's "application binary interface" (ABI). When this macro is defined, RTL is generated for this register once, as with the stack pointer and frame pointer registers. If this macro is not defined, it is up to the machine-dependent files to allocate such a register (if necessary). `FINALIZE_PIC' By generating position-independent code, when two different programs (A and B) share a common library (libC.a), the text of the library can be shared whether or not the library is linked at the same address for both programs. In some of these environments, position-independent code requires not only the use of different addressing modes, but also special code to enable the use of these addressing modes. The `FINALIZE_PIC' macro serves as a hook to emit these special codes once the function is being compiled into assembly code, but not before. (It is not done before, because in the case of compiling an inline function, it would lead to multiple PIC prologues being included in functions which used inline functions and were compiled to assembly language.)  File: gcc.info, Node: Assembler Format, Next: Debugging Info, Prev: PIC, Up: Target Macros Defining the Output Assembler Language ====================================== This section describes macros whose principal purpose is to describe how to write instructions in assembler language--rather than what the instructions do. * Menu: * File Framework:: Structural information for the assembler file. * Data Output:: Output of constants (numbers, strings, addresses). * Uninitialized Data:: Output of uninitialized variables. * Label Output:: Output and generation of labels. * Constructor Output:: Output of initialization and termination routines. * Instruction Output:: Output of actual instructions. * Dispatch Tables:: Output of jump tables. * Alignment Output:: Pseudo ops for alignment and skipping data.  File: gcc.info, Node: File Framework, Next: Data Output, Up: Assembler Format The Overall Framework of an Assembler File ------------------------------------------ `ASM_FILE_START (STREAM)' A C expression which outputs to the stdio stream STREAM some appropriate text to go at the start of an assembler file. Normally this macro is defined to output a line containing `#NO_APP', which is a comment that has no effect on most assemblers but tells the GNU assembler that it can save time by not checking for certain assembler constructs. On systems that use SDB, it is necessary to output certain commands; see `attasm.h'. `ASM_FILE_END (STREAM)' A C expression which outputs to the stdio stream STREAM some appropriate text to go at the end of an assembler file. If this macro is not defined, the default is to output nothing special at the end of the file. Most systems don't require any definition. On systems that use SDB, it is necessary to output certain commands; see `attasm.h'. `ASM_IDENTIFY_GCC (FILE)' A C statement to output assembler commands which will identify the object file as having been compiled with GNU CC (or another GNU compiler). If you don't define this macro, the string `gcc_compiled.:' is output. This string is calculated to define a symbol which, on BSD systems, will never be defined for any other reason. GDB checks for the presence of this symbol when reading the symbol table of an executable. On non-BSD systems, you must arrange communication with GDB in some other fashion. If GDB is not used on your system, you can define this macro with an empty body. `ASM_COMMENT_START' A C string constant describing how to begin a comment in the target assembler language. The compiler assumes that the comment will end at the end of the line. `ASM_APP_ON' A C string constant for text to be output before each `asm' statement or group of consecutive ones. Normally this is `"#APP"', which is a comment that has no effect on most assemblers but tells the GNU assembler that it must check the lines that follow for all valid assembler constructs. `ASM_APP_OFF' A C string constant for text to be output after each `asm' statement or group of consecutive ones. Normally this is `"#NO_APP"', which tells the GNU assembler to resume making the time-saving assumptions that are valid for ordinary compiler output. `ASM_OUTPUT_SOURCE_FILENAME (STREAM, NAME)' A C statement to output COFF information or DWARF debugging information which indicates that filename NAME is the current source file to the stdio stream STREAM. This macro need not be defined if the standard form of output for the file format in use is appropriate. `ASM_OUTPUT_SOURCE_LINE (STREAM, LINE)' A C statement to output DBX or SDB debugging information before code for line number LINE of the current source file to the stdio stream STREAM. This macro need not be defined if the standard form of debugging information for the debugger in use is appropriate. `ASM_OUTPUT_IDENT (STREAM, STRING)' A C statement to output something to the assembler file to handle a `#ident' directive containing the text STRING. If this macro is not defined, nothing is output for a `#ident' directive. `OBJC_PROLOGUE' A C statement to output any assembler statements which are required to precede any Objective C object definitions or message sending. The statement is executed only when compiling an Objective C program.  File: gcc.info, Node: Data Output, Next: Uninitialized Data, Prev: File Framework, Up: Assembler Format Output of Data -------------- `ASM_OUTPUT_LONG_DOUBLE (STREAM, VALUE)' `ASM_OUTPUT_DOUBLE (STREAM, VALUE)' `ASM_OUTPUT_FLOAT (STREAM, VALUE)' A C statement to output to the stdio stream STREAM an assembler instruction to assemble a floating-point constant of `TFmode', `DFmode' or `SFmode', respectively, whose value is VALUE. VALUE will be a C expression of type `REAL_VALUE__TYPE', usually `double'. `ASM_OUTPUT_QUADRUPLE_INT (STREAM, EXP)' `ASM_OUTPUT_DOUBLE_INT (STREAM, EXP)' `ASM_OUTPUT_INT (STREAM, EXP)' `ASM_OUTPUT_SHORT (STREAM, EXP)' `ASM_OUTPUT_CHAR (STREAM, EXP)' A C statement to output to the stdio stream STREAM an assembler instruction to assemble an integer of 16, 8, 4, 2 or 1 bytes, respectively, whose value is VALUE. The argument EXP will be an RTL expression which represents a constant value. Use `output_addr_const (STREAM, EXP)' to output this value as an assembler expression. For sizes larger than `UNITS_PER_WORD', if the action of a macro would be identical to repeatedly calling the macro corresponding to a size of `UNITS_PER_WORD', once for each word, you need not define the macro. `ASM_OUTPUT_BYTE (STREAM, VALUE)' A C statement to output to the stdio stream STREAM an assembler instruction to assemble a single byte containing the number VALUE. `ASM_BYTE_OP' A C string constant giving the pseudo-op to use for a sequence of single-byte constants. If this macro is not defined, the default is `"byte"'. `ASM_OUTPUT_ASCII (STREAM, PTR, LEN)' A C statement to output to the stdio stream STREAM an assembler instruction to assemble a string constant containing the LEN bytes at PTR. PTR will be a C expression of type `char *' and LEN a C expression of type `int'. If the assembler has a `.ascii' pseudo-op as found in the Berkeley Unix assembler, do not define the macro `ASM_OUTPUT_ASCII'. `ASM_OUTPUT_POOL_PROLOGUE (FILE FUNNAME FUNDECL SIZE)' A C statement to output assembler commands to define the start of the constant pool for a function. FUNNAME is a string giving the name of the function. Should the return type of the function be required, it can be obtained via FUNDECL. SIZE is the size, in bytes, of the constant pool that will be written immediately after this call. If no constant-pool prefix is required, the usual case, this macro need not be defined. `ASM_OUTPUT_SPECIAL_POOL_ENTRY (FILE, X, MODE, ALIGN, LABELNO, JUMPTO)' A C statement (with or without semicolon) to output a constant in the constant pool, if it needs special treatment. (This macro need not do anything for RTL expressions that can be output normally.) The argument FILE is the standard I/O stream to output the assembler code on. X is the RTL expression for the constant to output, and MODE is the machine mode (in case X is a `const_int'). ALIGN is the required alignment for the value X; you should output an assembler directive to force this much alignment. The argument LABELNO is a number to use in an internal label for the address of this pool entry. The definition of this macro is responsible for outputting the label definition at the proper place. Here is how to do this: ASM_OUTPUT_INTERNAL_LABEL (FILE, "LC", LABELNO); When you output a pool entry specially, you should end with a `goto' to the label JUMPTO. This will prevent the same pool entry from being output a second time in the usual manner. You need not define this macro if it would do nothing. `ASM_OPEN_PAREN' `ASM_CLOSE_PAREN' These macros are defined as C string constant, describing the syntax in the assembler for grouping arithmetic expressions. The following definitions are correct for most assemblers: #define ASM_OPEN_PAREN "(" #define ASM_CLOSE_PAREN ")"  File: gcc.info, Node: Uninitialized Data, Next: Label Output, Prev: Data Output, Up: Assembler Format Output of Uninitialized Variables --------------------------------- Each of the macros in this section is used to do the whole job of outputting a single uninitialized variable. `ASM_OUTPUT_COMMON (STREAM, NAME, SIZE, ROUNDED)' A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a common-label named NAME whose size is SIZE bytes. The variable ROUNDED is the size rounded up to whatever alignment the caller wants. Use the expression `assemble_name (STREAM, NAME)' to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. This macro controls how the assembler definitions of uninitialized global variables are output. `ASM_OUTPUT_ALIGNED_COMMON (STREAM, NAME, SIZE, ALIGNMENT)' Like `ASM_OUTPUT_COMMON' except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of `ASM_OUTPUT_COMMON', and gives you more flexibility in handling the required alignment of the variable. `ASM_OUTPUT_SHARED_COMMON (STREAM, NAME, SIZE, ROUNDED)' If defined, it is similar to `ASM_OUTPUT_COMMON', except that it is used when NAME is shared. If not defined, `ASM_OUTPUT_COMMON' will be used. `ASM_OUTPUT_LOCAL (STREAM, NAME, SIZE, ROUNDED)' A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a local-common-label named NAME whose size is SIZE bytes. The variable ROUNDED is the size rounded up to whatever alignment the caller wants. Use the expression `assemble_name (STREAM, NAME)' to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. This macro controls how the assembler definitions of uninitialized static variables are output. `ASM_OUTPUT_ALIGNED_LOCAL (STREAM, NAME, SIZE, ALIGNMENT)' Like `ASM_OUTPUT_LOCAL' except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of `ASM_OUTPUT_LOCAL', and gives you more flexibility in handling the required alignment of the variable. `ASM_OUTPUT_SHARED_LOCAL (STREAM, NAME, SIZE, ROUNDED)' If defined, it is similar to `ASM_OUTPUT_LOCAL', except that it is used when NAME is shared. If not defined, `ASM_OUTPUT_LOCAL' will be used.  File: gcc.info, Node: Label Output, Next: Constructor Output, Prev: Uninitialized Data, Up: Assembler Format Output and Generation of Labels ------------------------------- `ASM_OUTPUT_LABEL (STREAM, NAME)' A C statement (sans semicolon) to output to the stdio stream STREAM the assembler definition of a label named NAME. Use the expression `assemble_name (STREAM, NAME)' to output the name itself; before and after that, output the additional assembler syntax for defining the name, and a newline. `ASM_DECLARE_FUNCTION_NAME (STREAM, NAME, DECL)' A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name NAME of a function which is being defined. This macro is responsible for outputting the label definition (perhaps using `ASM_OUTPUT_LABEL'). The argument DECL is the `FUNCTION_DECL' tree node representing the function. If this macro is not defined, then the function name is defined in the usual manner as a label (by means of `ASM_OUTPUT_LABEL'). `ASM_DECLARE_FUNCTION_SIZE (STREAM, NAME, DECL)' A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the size of a function which is being defined. The argument NAME is the name of the function. The argument DECL is the `FUNCTION_DECL' tree node representing the function. If this macro is not defined, then the function size is not defined. `ASM_DECLARE_OBJECT_NAME (STREAM, NAME, DECL)' A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name NAME of an initialized variable which is being defined. This macro must output the label definition (perhaps using `ASM_OUTPUT_LABEL'). The argument DECL is the `VAR_DECL' tree node representing the variable. If this macro is not defined, then the variable name is defined in the usual manner as a label (by means of `ASM_OUTPUT_LABEL'). `ASM_GLOBALIZE_LABEL (STREAM, NAME)' A C statement (sans semicolon) to output to the stdio stream STREAM some commands that will make the label NAME global; that is, available for reference from other files. Use the expression `assemble_name (STREAM, NAME)' to output the name itself; before and after that, output the additional assembler syntax for making that name global, and a newline. `ASM_OUTPUT_EXTERNAL (STREAM, DECL, NAME)' A C statement (sans semicolon) to output to the stdio stream STREAM any text necessary for declaring the name of an external symbol named NAME which is referenced in this compilation but not defined. The value of DECL is the tree node for the declaration. This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything. `ASM_OUTPUT_EXTERNAL_LIBCALL (STREAM, SYMREF)' A C statement (sans semicolon) to output on STREAM an assembler pseudo-op to declare a library function name external. The name of the library function is given by SYMREF, which has type `rtx' and is a `symbol_ref'. This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything. `ASM_OUTPUT_LABELREF (STREAM, NAME)' A C statement (sans semicolon) to output to the stdio stream STREAM a reference in assembler syntax to a label named NAME. This should add `_' to the front of the name, if that is customary on your operating system, as it is in most Berkeley Unix systems. This macro is used in `assemble_name'. `ASM_OUTPUT_LABELREF_AS_INT (FILE, LABEL)' Define this macro for systems that use the program `collect2'. The definition should be a C statement to output a word containing a reference to the label LABEL. `ASM_OUTPUT_INTERNAL_LABEL (STREAM, PREFIX, NUM)' A C statement to output to the stdio stream STREAM a label whose name is made from the string PREFIX and the number NUM. It is absolutely essential that these labels be distinct from the labels used for user-level functions and variables. Otherwise, certain programs will have name conflicts with internal labels. It is desirable to exclude internal labels from the symbol table of the object file. Most assemblers have a naming convention for labels that should be excluded; on many systems, the letter `L' at the beginning of a label has this effect. You should find out what convention your system uses, and follow it. The usual definition of this macro is as follows: fprintf (STREAM, "L%s%d:\n", PREFIX, NUM) `ASM_GENERATE_INTERNAL_LABEL (STRING, PREFIX, NUM)' A C statement to store into the string STRING a label whose name is made from the string PREFIX and the number NUM. This string, when output subsequently by `assemble_name', should produce the same output that `ASM_OUTPUT_INTERNAL_LABEL' would produce with the same PREFIX and NUM. If the string begins with `*', then `assemble_name' will output the rest of the string unchanged. It is often convenient for `ASM_GENERATE_INTERNAL_LABEL' to use `*' in this way. If the string doesn't start with `*', then `ASM_OUTPUT_LABELREF' gets to output the string, and may change it. (Of course, `ASM_OUTPUT_LABELREF' is also part of your machine description, so you should know what it does on your machine.) `ASM_FORMAT_PRIVATE_NAME (OUTVAR, NAME, NUMBER)' A C expression to assign to OUTVAR (which is a variable of type `char *') a newly allocated string made from the string NAME and the number NUMBER, with some suitable punctuation added. Use `alloca' to get space for the string. This string will be used as the argument to `ASM_OUTPUT_LABELREF' to produce an assembler label for an internal static variable whose name is NAME. Therefore, the string must be such as to result in valid assembler code. The argument NUMBER is different each time this macro is executed; it prevents conflicts between similarly-named internal static variables in different scopes. Ideally this string should not be a valid C identifier, to prevent any conflict with the user's own symbols. Most assemblers allow periods or percent signs in assembler symbols; putting at least one of these between the name and the number will suffice. `OBJC_GEN_METHOD_LABEL (BUF, IS_INST, CLASS_NAME, CAT_NAME, SEL_NAME)' Define this macro to override the default assembler names used for Objective C methods. The default name is a unique method number followed by the name of the class (e.g. `_1_Foo'). For methods in categories, the name of the category is also included in the assembler name (e.g. `_1_Foo_Bar'). These names are safe on most systems, but make debugging difficult since the method's selector is not present in the name. Therefore, particular systems define other ways of computing names. BUF is an expression of type `char *' which gives you a buffer in which to store the name; its length is as long as CLASS_NAME, CAT_NAME and SEL_NAME put together, plus 50 characters extra. The argument IS_INST specifies whether the method is an instance method or a class method; CLASS_NAME is the name of the class; CAT_NAME is the name of the category (or NULL if the method is not in a category); and SEL_NAME is the name of the selector. On systems where the assembler can handle quoted names, you can use this macro to provide more human-readable names.  File: gcc.info, Node: Constructor Output, Next: Instruction Output, Prev: Label Output, Up: Assembler Format Output of Initialization Routines --------------------------------- 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 what assembler code is needed to do this. Here are the two macros you should define if necessary: `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 `collect' program, which looks through the symbol table to find these functions by their names. If you want to use `collect', then you need to arrange for it to be built and installed and used on your system. `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. These macros are effective only in a native compiler; `collect2' as part of a cross compiler always uses `nm'. `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'.  File: gcc.info, Node: Instruction Output, Next: Dispatch Tables, Prev: Constructor Output, Up: Assembler Format Output of Assembler Instructions -------------------------------- `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. `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 ------------------------- `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 -------------------------------- `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 ======================================== * 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 -------------------------------------- `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.