OpenStep 4.2J (Developer)

home *** CD-ROM | disk | FTP | other *** search

/ OpenStep 4.2J (Developer) / os42jdev.iso / NextDeveloper / Source / GNU / gcc / gcc.info-22 < prev next >

Wrap

GNU Info File | 1995-06-16 | 49.1 KB | 1,117 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 59 Temple Place - Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995 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: Library Calls, Next: Addressing Modes, Prev: Trampolines, Up: Target Macros Implicit Calls to Library Routines ================================== Here is an explanation of implicit calls to library routines. `MULSI3_LIBCALL' A C string constant giving the name of the function to call for multiplication of one signed full-word by another. If you do not define this macro, the default name is used, which is `__mulsi3', a function defined in `libgcc.a'. `DIVSI3_LIBCALL' A C string constant giving the name of the function to call for division of one signed full-word by another. If you do not define this macro, the default name is used, which is `__divsi3', a function defined in `libgcc.a'. `UDIVSI3_LIBCALL' A C string constant giving the name of the function to call for division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is `__udivsi3', a function defined in `libgcc.a'. `MODSI3_LIBCALL' A C string constant giving the name of the function to call for the remainder in division of one signed full-word by another. If you do not define this macro, the default name is used, which is `__modsi3', a function defined in `libgcc.a'. `UMODSI3_LIBCALL' A C string constant giving the name of the function to call for the remainder in division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is `__umodsi3', a function defined in `libgcc.a'. `MULDI3_LIBCALL' A C string constant giving the name of the function to call for multiplication of one signed double-word by another. If you do not define this macro, the default name is used, which is `__muldi3', a function defined in `libgcc.a'. `DIVDI3_LIBCALL' A C string constant giving the name of the function to call for division of one signed double-word by another. If you do not define this macro, the default name is used, which is `__divdi3', a function defined in `libgcc.a'. `UDIVDI3_LIBCALL' A C string constant giving the name of the function to call for division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is `__udivdi3', a function defined in `libgcc.a'. `MODDI3_LIBCALL' A C string constant giving the name of the function to call for the remainder in division of one signed double-word by another. If you do not define this macro, the default name is used, which is `__moddi3', a function defined in `libgcc.a'. `UMODDI3_LIBCALL' A C string constant giving the name of the function to call for the remainder in division of one unsigned full-word by another. If you do not define this macro, the default name is used, which is `__umoddi3', a function defined in `libgcc.a'. `INIT_TARGET_OPTABS' Define this macro as a C statement that declares additional library routines renames existing ones. `init_optabs' calls this macro after initializing all the normal library routines. `TARGET_EDOM' The value of `EDOM' on the target machine, as a C integer constant expression. If you don't define this macro, GNU CC does not attempt to deposit the value of `EDOM' into `errno' directly. Look in `/usr/include/errno.h' to find the value of `EDOM' on your system. If you do not define `TARGET_EDOM', then compiled code reports domain errors by calling the library function and letting it report the error. If mathematical functions on your system use `matherr' when there is an error, then you should leave `TARGET_EDOM' undefined so that `matherr' is used normally. `GEN_ERRNO_RTX' Define this macro as a C expression to create an rtl expression that refers to the global "variable" `errno'. (On certain systems, `errno' may not actually be a variable.) If you don't define this macro, a reasonable default is used. `TARGET_MEM_FUNCTIONS' Define this macro if GNU CC should generate calls to the System V (and ANSI C) library functions `memcpy' and `memset' rather than the BSD functions `bcopy' and `bzero'. `LIBGCC_NEEDS_DOUBLE' Define this macro if only `float' arguments cannot be passed to library routines (so they must be converted to `double'). This macro affects both how library calls are generated and how the library routines in `libgcc1.c' accept their arguments. It is useful on machines where floating and fixed point arguments are passed differently, such as the i860. `FLOAT_ARG_TYPE' Define this macro to override the type used by the library routines to pick up arguments of type `float'. (By default, they use a union of `float' and `int'.) The obvious choice would be `float'--but that won't work with traditional C compilers that expect all arguments declared as `float' to arrive as `double'. To avoid this conversion, the library routines ask for the value as some other type and then treat it as a `float'. On some systems, no other type will work for this. For these systems, you must use `LIBGCC_NEEDS_DOUBLE' instead, to force conversion of the values `double' before they are passed. `FLOATIFY (PASSED-VALUE)' Define this macro to override the way library routines redesignate a `float' argument as a `float' instead of the type it was passed as. The default is an expression which takes the `float' field of the union. `FLOAT_VALUE_TYPE' Define this macro to override the type used by the library routines to return values that ought to have type `float'. (By default, they use `int'.) The obvious choice would be `float'--but that won't work with traditional C compilers gratuitously convert values declared as `float' into `double'. `INTIFY (FLOAT-VALUE)' Define this macro to override the way the value of a `float'-returning library routine should be packaged in order to return it. These functions are actually declared to return type `FLOAT_VALUE_TYPE' (normally `int'). These values can't be returned as type `float' because traditional C compilers would gratuitously convert the value to a `double'. A local variable named `intify' is always available when the macro `INTIFY' is used. It is a union of a `float' field named `f' and a field named `i' whose type is `FLOAT_VALUE_TYPE' or `int'. If you don't define this macro, the default definition works by copying the value through that union. `nongcc_SI_type' Define this macro as the name of the data type corresponding to `SImode' in the system's own C compiler. You need not define this macro if that type is `long int', as it usually is. `nongcc_word_type' Define this macro as the name of the data type corresponding to the word_mode in the system's own C compiler. You need not define this macro if that type is `long int', as it usually is. `perform_...' Define these macros to supply explicit C statements to carry out various arithmetic operations on types `float' and `double' in the library routines in `libgcc1.c'. See that file for a full list of these macros and their arguments. On most machines, you don't need to define any of these macros, because the C compiler that comes with the system takes care of doing them. `NEXT_OBJC_RUNTIME' Define this macro to generate code for Objective C message sending using the calling convention of the NeXT system. This calling convention involves passing the object, the selector and the method arguments all at once to the method-lookup library function. The default calling convention passes just the object and the selector to the lookup function, which returns a pointer to the method. File: gcc.info, Node: Addressing Modes, Next: Condition Code, Prev: Library Calls, Up: Target Macros Addressing Modes ================ This is about addressing modes. `HAVE_POST_INCREMENT' Define this macro if the machine supports post-increment addressing. `HAVE_PRE_INCREMENT' `HAVE_POST_DECREMENT' `HAVE_PRE_DECREMENT' Similar for other kinds of addressing. `CONSTANT_ADDRESS_P (X)' A C expression that is 1 if the RTX X is a constant which is a valid address. On most machines, this can be defined as `CONSTANT_P (X)', but a few machines are more restrictive in which constant addresses are supported. `CONSTANT_P' accepts integer-values expressions whose values are not explicitly known, such as `symbol_ref', `label_ref', and `high' expressions and `const' arithmetic expressions, in addition to `const_int' and `const_double' expressions. `MAX_REGS_PER_ADDRESS' A number, the maximum number of registers that can appear in a valid memory address. Note that it is up to you to specify a value equal to the maximum number that `GO_IF_LEGITIMATE_ADDRESS' would ever accept. `GO_IF_LEGITIMATE_ADDRESS (MODE, X, LABEL)' A C compound statement with a conditional `goto LABEL;' executed if X (an RTX) is a legitimate memory address on the target machine for a memory operand of mode MODE. It usually pays to define several simpler macros to serve as subroutines for this one. Otherwise it may be too complicated to understand. This macro must exist in two variants: a strict variant and a non-strict one. The strict variant is used in the reload pass. It must be defined so that any pseudo-register that has not been allocated a hard register is considered a memory reference. In contexts where some kind of register is required, a pseudo-register with no hard register must be rejected. The non-strict variant is used in other passes. It must be defined to accept all pseudo-registers in every context where some kind of register is required. Compiler source files that want to use the strict variant of this macro define the macro `REG_OK_STRICT'. You should use an `#ifdef REG_OK_STRICT' conditional to define the strict variant in that case and the non-strict variant otherwise. Subroutines to check for acceptable registers for various purposes (one for base registers, one for index registers, and so on) are typically among the subroutines used to define `GO_IF_LEGITIMATE_ADDRESS'. Then only these subroutine macros need have two variants; the higher levels of macros may be the same whether strict or not. Normally, constant addresses which are the sum of a `symbol_ref' and an integer are stored inside a `const' RTX to mark them as constant. Therefore, there is no need to recognize such sums specifically as legitimate addresses. Normally you would simply recognize any `const' as legitimate. Usually `PRINT_OPERAND_ADDRESS' is not prepared to handle constant sums that are not marked with `const'. It assumes that a naked `plus' indicates indexing. If so, then you *must* reject such naked constant sums as illegitimate addresses, so that none of them will be given to `PRINT_OPERAND_ADDRESS'. On some machines, whether a symbolic address is legitimate 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. When you see a `const', you will have to look inside it to find the `symbol_ref' in order to determine the section. *Note Assembler Format::. The best way to modify the name string is by adding text to the beginning, with suitable punctuation to prevent any ambiguity. Allocate the new name in `saveable_obstack'. You will have to modify `ASM_OUTPUT_LABELREF' to remove and decode the added text and output the name accordingly, and define `STRIP_NAME_ENCODING' to access the original name string. You can check the information stored here into the `symbol_ref' in the definitions of the macros `GO_IF_LEGITIMATE_ADDRESS' and `PRINT_OPERAND_ADDRESS'. `REG_OK_FOR_BASE_P (X)' A C expression that is nonzero if X (assumed to be a `reg' RTX) is valid for use as a base register. For hard registers, it should always accept those which the hardware permits and reject the others. Whether the macro accepts or rejects pseudo registers must be controlled by `REG_OK_STRICT' as described above. This usually requires two variant definitions, of which `REG_OK_STRICT' controls the one actually used. `REG_OK_FOR_INDEX_P (X)' A C expression that is nonzero if X (assumed to be a `reg' RTX) is valid for use as an index register. The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two registers, neither one of them scaled, then either one may be labeled the "base" and the other the "index"; but whichever labeling is used must fit the machine's constraints of which registers may serve in each capacity. The compiler will try both labelings, looking for one that is valid, and will reload one or both registers only if neither labeling works. `LEGITIMIZE_ADDRESS (X, OLDX, MODE, WIN)' A C compound statement that attempts to replace X with a valid memory address for an operand of mode MODE. WIN will be a C statement label elsewhere in the code; the macro definition may use GO_IF_LEGITIMATE_ADDRESS (MODE, X, WIN); to avoid further processing if the address has become legitimate. X will always be the result of a call to `break_out_memory_refs', and OLDX will be the operand that was given to that function to produce X. The code generated by this macro should not alter the substructure of X. If it transforms X into a more legitimate form, it should assign X (which will always be a C variable) a new value. It is not necessary for this macro to come up with a legitimate address. The compiler has standard ways of doing so in all cases. In fact, it is safe for this macro to do nothing. But often a machine-dependent strategy can generate better code. `GO_IF_MODE_DEPENDENT_ADDRESS (ADDR, LABEL)' A C statement or compound statement with a conditional `goto LABEL;' executed if memory address X (an RTX) can have different meanings depending on the machine mode of the memory reference it is used for or if the address is valid for some modes but not others. Autoincrement and autodecrement addresses typically have mode-dependent effects because the amount of the increment or decrement is the size of the operand being addressed. Some machines have other mode-dependent addresses. Many RISC machines have no mode-dependent addresses. You may assume that ADDR is a valid address for the machine. `LEGITIMATE_CONSTANT_P (X)' A C expression that is nonzero if X is a legitimate constant for an immediate operand on the target machine. You can assume that X satisfies `CONSTANT_P', so you need not check this. In fact, `1' is a suitable definition for this macro on machines where anything `CONSTANT_P' is valid. File: gcc.info, Node: Condition Code, Next: Costs, Prev: Addressing Modes, Up: Target Macros Condition Code Status ===================== This describes the condition code status. The file `conditions.h' defines a variable `cc_status' to describe how the condition code was computed (in case the interpretation of the condition code depends on the instruction that it was set by). This variable contains the RTL expressions on which the condition code is currently based, and several standard flags. Sometimes additional machine-specific flags must be defined in the machine description header file. It can also add additional machine-specific information by defining `CC_STATUS_MDEP'. `CC_STATUS_MDEP' C code for a data type which is used for declaring the `mdep' component of `cc_status'. It defaults to `int'. This macro is not used on machines that do not use `cc0'. `CC_STATUS_MDEP_INIT' A C expression to initialize the `mdep' field to "empty". The default definition does nothing, since most machines don't use the field anyway. If you want to use the field, you should probably define this macro to initialize it. This macro is not used on machines that do not use `cc0'. `NOTICE_UPDATE_CC (EXP, INSN)' A C compound statement to set the components of `cc_status' appropriately for an insn INSN whose body is EXP. It is this macro's responsibility to recognize insns that set the condition code as a byproduct of other activity as well as those that explicitly set `(cc0)'. This macro is not used on machines that do not use `cc0'. If there are insns that do not set the condition code but do alter other machine registers, this macro must check to see whether they invalidate the expressions that the condition code is recorded as reflecting. For example, on the 68000, insns that store in address registers do not set the condition code, which means that usually `NOTICE_UPDATE_CC' can leave `cc_status' unaltered for such insns. But suppose that the previous insn set the condition code based on location `a4@(102)' and the current insn stores a new value in `a4'. Although the condition code is not changed by this, it will no longer be true that it reflects the contents of `a4@(102)'. Therefore, `NOTICE_UPDATE_CC' must alter `cc_status' in this case to say that nothing is known about the condition code value. The definition of `NOTICE_UPDATE_CC' must be prepared to deal with the results of peephole optimization: insns whose patterns are `parallel' RTXs containing various `reg', `mem' or constants which are just the operands. The RTL structure of these insns is not sufficient to indicate what the insns actually do. What `NOTICE_UPDATE_CC' should do when it sees one is just to run `CC_STATUS_INIT'. A possible definition of `NOTICE_UPDATE_CC' is to call a function that looks at an attribute (*note Insn Attributes::.) named, for example, `cc'. This avoids having detailed information about patterns in two places, the `md' file and in `NOTICE_UPDATE_CC'. `EXTRA_CC_MODES' A list of names to be used for additional modes for condition code values in registers (*note Jump Patterns::.). These names are added to `enum machine_mode' and all have class `MODE_CC'. By convention, they should start with `CC' and end with `mode'. You should only define this macro if your machine does not use `cc0' and only if additional modes are required. `EXTRA_CC_NAMES' A list of C strings giving the names for the modes listed in `EXTRA_CC_MODES'. For example, the Sparc defines this macro and `EXTRA_CC_MODES' as #define EXTRA_CC_MODES CC_NOOVmode, CCFPmode, CCFPEmode #define EXTRA_CC_NAMES "CC_NOOV", "CCFP", "CCFPE" This macro is not required if `EXTRA_CC_MODES' is not defined. `SELECT_CC_MODE (OP, X, Y)' Returns a mode from class `MODE_CC' to be used when comparison operation code OP is applied to rtx X and Y. For example, on the Sparc, `SELECT_CC_MODE' is defined as (see *note Jump Patterns::. for a description of the reason for this definition) #define SELECT_CC_MODE(OP,X,Y) \ (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT \ ? ((OP == EQ || OP == NE) ? CCFPmode : CCFPEmode) \ : ((GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ || GET_CODE (X) == NEG) \ ? CC_NOOVmode : CCmode)) You need not define this macro if `EXTRA_CC_MODES' is not defined. `CANONICALIZE_COMPARISON (CODE, OP0, OP1)' One some machines not all possible comparisons are defined, but you can convert an invalid comparison into a valid one. For example, the Alpha does not have a `GT' comparison, but you can use an `LT' comparison instead and swap the order of the operands. On such machines, define this macro to be a C statement to do any required conversions. CODE is the initial comparison code and OP0 and OP1 are the left and right operands of the comparison, respectively. You should modify CODE, OP0, and OP1 as required. GNU CC will not assume that the comparison resulting from this macro is valid but will see if the resulting insn matches a pattern in the `md' file. You need not define this macro if it would never change the comparison code or operands. `REVERSIBLE_CC_MODE (MODE)' A C expression whose value is one if it is always safe to reverse a comparison whose mode is MODE. If `SELECT_CC_MODE' can ever return MODE for a floating-point inequality comparison, then `REVERSIBLE_CC_MODE (MODE)' must be zero. You need not define this macro if it would always returns zero or if the floating-point format is anything other than `IEEE_FLOAT_FORMAT'. For example, here is the definition used on the Sparc, where floating-point inequality comparisons are always given `CCFPEmode': #define REVERSIBLE_CC_MODE(MODE) ((MODE) != CCFPEmode) 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 4 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. `ADJUST_COST (INSN, LINK, DEP_INSN, COST)' A C statement (sans semicolon) to update the integer variable COST based on the relationship between INSN that is dependent on DEP_INSN through the dependence LINK. The default is to make no adjustment to COST. This can be used for example to specify to the scheduler that an output- or anti-dependence does not incur the same cost as a data-dependence. 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 expression whose value is a string containing the assembler operation that should precede instructions and read-only data. Normally `".text"' is right. `DATA_SECTION_ASM_OP' A C expression whose value is a string containing the assembler operation to identify the following data as writable initialized data. Normally `".data"' is right. `SHARED_SECTION_ASM_OP' if defined, a C expression whose value is a string containing 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 expression whose value is a string containing 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). `STRIP_NAME_ENCODING (VAR, SYM_NAME)' Decode SYM_NAME and store the real name part in VAR, sans the characters that encode section info. Define this macro if `ENCODE_SECTION_INFO' alters the symbol's name string. 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 `PRINT_OPERAND_ADDRESS', as well as `LEGITIMIZE_ADDRESS'. 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). `PIC_OFFSET_TABLE_REG_CALL_CLOBBERED' Define this macro if the register defined by `PIC_OFFSET_TABLE_REGNUM' is clobbered by calls. Do not define this macro if `PPIC_OFFSET_TABLE_REGNUM' is not defined. `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.) `LEGITIMATE_PIC_OPERAND_P (X)' A C expression that is nonzero if X is a legitimate immediate operand on the target machine when generating position independent code. You can assume that X satisfies `CONSTANT_P', so you need not check this. You can also assume FLAG_PIC is true, so you need not check it either. You need not define this macro if all constants (including `SYMBOL_REF') can be immediate operands when generating position independent code. 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. * Initialization:: General principles of initialization and termination routines. * Macros for Initialization:: Specific macros that control the handling 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 ------------------------------------------ This describes 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. `ASM_OUTPUT_SECTION_NAME (STREAM, DECL, NAME)' A C statement to output something to the assembler file to switch to section NAME for object DECL which is either a `FUNCTION_DECL', a `VAR_DECL' or `NULL_TREE'. Some target formats do not support arbitrary sections. Do not define this macro in such cases. At present this macro is only used to support section attributes. When this macro is undefined, section attributes are disabled. `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 -------------- This describes data output. `ASM_OUTPUT_LONG_DOUBLE (STREAM, VALUE)' `ASM_OUTPUT_DOUBLE (STREAM, VALUE)' `ASM_OUTPUT_FLOAT (STREAM, VALUE)' `ASM_OUTPUT_THREE_QUARTER_FLOAT (STREAM, VALUE)' `ASM_OUTPUT_SHORT_FLOAT (STREAM, VALUE)' `ASM_OUTPUT_BYTE_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', `SFmode', `TQFmode', `HFmode', or `QFmode', respectively, whose value is VALUE. VALUE will be a C expression of type `REAL_VALUE_TYPE'. Macros such as `REAL_VALUE_TO_TARGET_DOUBLE' are useful for writing these definitions. `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. `IS_ASM_LOGICAL_LINE_SEPARATOR (C)' Define this macro as a C expression which is nonzero if C is used as a logical line separator by the assembler. If you do not define this macro, the default is that only the character `;' is treated as a logical line separator. `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 ")" These macros are provided by `real.h' for writing the definitions of `ASM_OUTPUT_DOUBLE' and the like: `REAL_VALUE_TO_TARGET_SINGLE (X, L)' `REAL_VALUE_TO_TARGET_DOUBLE (X, L)' `REAL_VALUE_TO_TARGET_LONG_DOUBLE (X, L)' These translate X, of type `REAL_VALUE_TYPE', to the target's floating point representation, and store its bit pattern in the array of `long int' whose address is L. The number of elements in the output array is determined by the size of the desired target floating point data type: 32 bits of it go in each `long int' array element. Each array element holds 32 bits of the result, even if `long int' is wider than 32 bits on the host machine. The array element values are designed so that you can print them out using `fprintf' in the order they should appear in the target machine's memory. `REAL_VALUE_TO_DECIMAL (X, FORMAT, STRING)' This macro converts X, of type `REAL_VALUE_TYPE', to a decimal number and stores it as a string into STRING. You must pass, as STRING, the address of a long enough block of space to hold the result. The argument FORMAT is a `printf'-specification that serves as a suggestion for how to format the output string.