This is doc/gcc.info, produced by makeinfo version 4.0 from
doc/gcc.texi.

INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
END-INFO-DIR-ENTRY
   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, 1996, 1997, 1998,
1999, 2000, 2001 Free Software Foundation, Inc.


   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding Free
Software", the Front-Cover texts being (a) (see below), and with the
Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

   (a) The FSF's Front-Cover Text is:

   A GNU Manual

   (b) The FSF's Back-Cover Text is:

   You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.


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.

`OUTPUT_ADDR_CONST_EXTRA (STREAM, X, FAIL)'
     A C statement to recognize RTX patterns that `output_addr_const'
     can't deal with, and output assembly code to STREAM corresponding
     to the pattern X.  This may be used to allow machine-dependent
     `UNSPEC's to appear within constants.

     If `OUTPUT_ADDR_CONST_EXTRA' fails to recognize a pattern, it must
     `goto fail', so that a standard error message is printed.  If it
     prints an error message itself, by calling, for example,
     `output_operand_lossage', it may just complete normally.

`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, including spacing, giving the pseudo-op to
     use for a sequence of single-byte constants.  If this macro is not
     defined, the default is `"\t.byte\t"'.

`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'.

`CONSTANT_POOL_BEFORE_FUNCTION'
     You may define this macro as a C expression.  You should define the
     expression to have a nonzero value if GCC should output the
     constant pool for a function before the code for the function, or
     a zero value if GCC should output the constant pool after the
     function.  If you do not define this macro, the usual case, GCC
     will output the constant pool before the function.

`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.

`CONSTANT_AFTER_FUNCTION_P (EXP)'
     Define this macro as a C expression which is nonzero if the
     constant EXP, of type `tree', should be output after the code for a
     function.  The compiler will normally output all constants before
     the function; you need not define this macro if this is OK.

`ASM_OUTPUT_POOL_EPILOGUE (FILE FUNNAME FUNDECL SIZE)'
     A C statement to output assembler commands to at the end 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, you can obtain it via FUNDECL.  SIZE is the size, in
     bytes, of the constant pool that GCC wrote immediately before this
     call.

     If no constant-pool epilogue is required, the usual case, you need
     not define this macro.

`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 constants, 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.


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
     common 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.  The alignment is
     specified as the number of bits.

`ASM_OUTPUT_ALIGNED_DECL_COMMON (STREAM, DECL, NAME, SIZE, ALIGNMENT)'
     Like `ASM_OUTPUT_ALIGNED_COMMON' except that DECL of the variable
     to be output, if there is one, or `NULL_TREE' if there is no
     corresponding variable.  If you define this macro, GCC will use it
     in place of both `ASM_OUTPUT_COMMON' and
     `ASM_OUTPUT_ALIGNED_COMMON'.  Define this macro when you need to
     see the variable's decl in order to chose what to output.

`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_BSS (STREAM, DECL, NAME, SIZE, ROUNDED)'
     A C statement (sans semicolon) to output to the stdio stream
     STREAM the assembler definition of uninitialized global DECL named
     NAME whose size is SIZE bytes.  The variable ROUNDED is the size
     rounded up to whatever alignment the caller wants.

     Try to use function `asm_output_bss' defined in `varasm.c' when
     defining this macro.  If unable, 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.  This macro exists to properly
     support languages like C++ which do not have `common' data.
     However, this macro currently is not defined for all targets.  If
     this macro and `ASM_OUTPUT_ALIGNED_BSS' are not defined then
     `ASM_OUTPUT_COMMON' or `ASM_OUTPUT_ALIGNED_COMMON' or
     `ASM_OUTPUT_ALIGNED_DECL_COMMON' is used.

`ASM_OUTPUT_ALIGNED_BSS (STREAM, DECL, NAME, SIZE, ALIGNMENT)'
     Like `ASM_OUTPUT_BSS' except takes the required alignment as a
     separate, explicit argument.  If you define this macro, it is used
     in place of `ASM_OUTPUT_BSS', and gives you more flexibility in
     handling the required alignment of the variable.  The alignment is
     specified as the number of bits.

     Try to use function `asm_output_aligned_bss' defined in file
     `varasm.c' when defining this macro.

`ASM_OUTPUT_SHARED_BSS (STREAM, DECL, NAME, SIZE, ROUNDED)'
     If defined, it is similar to `ASM_OUTPUT_BSS', except that it is
     used when NAME is shared.  If not defined, `ASM_OUTPUT_BSS' 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.  The alignment is
     specified as the number of bits.

`ASM_OUTPUT_ALIGNED_DECL_LOCAL (STREAM, DECL, NAME, SIZE, ALIGNMENT)'
     Like `ASM_OUTPUT_ALIGNED_DECL' except that DECL of the variable to
     be output, if there is one, or `NULL_TREE' if there is no
     corresponding variable.  If you define this macro, GCC will use it
     in place of both `ASM_OUTPUT_DECL' and `ASM_OUTPUT_ALIGNED_DECL'.
     Define this macro when you need to see the variable's decl in
     order to chose what to output.

`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: Initialization,  Prev: Uninitialized Data,  Up: Assembler Format

Output and Generation of Labels
-------------------------------

   This is about outputting 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_DECLARE_REGISTER_GLOBAL (STREAM, DECL, REGNO, NAME)'
     A C statement (sans semicolon) to output to the stdio stream
     STREAM any text necessary for claiming a register REGNO for a
     global variable DECL with name NAME.

     If you don't define this macro, that is equivalent to defining it
     to do nothing.

`ASM_FINISH_DECLARE_OBJECT (STREAM, DECL, TOPLEVEL, ATEND)'
     A C statement (sans semicolon) to finish up declaring a variable
     name once the compiler has processed its initializer fully and
     thus has had a chance to determine the size of an array when
     controlled by an initializer.  This is used on systems where it's
     necessary to declare something about the size of the object.

     If you don't define this macro, that is equivalent to defining it
     to do nothing.

`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_WEAKEN_LABEL'
     A C statement (sans semicolon) to output to the stdio stream
     STREAM some commands that will make the label NAME weak; that is,
     available for reference from other files but only used if no other
     definition is available.  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 weak,
     and a newline.

     If you don't define this macro, GCC will not support weak symbols
     and you should not define the `SUPPORTS_WEAK' macro.

`SUPPORTS_WEAK'
     A C expression which evaluates to true if the target supports weak
     symbols.

     If you don't define this macro, `defaults.h' provides a default
     definition.  If `ASM_WEAKEN_LABEL' is defined, the default
     definition is `1'; otherwise, it is `0'.  Define this macro if you
     want to control weak symbol support with a compiler flag such as
     `-melf'.

`MAKE_DECL_ONE_ONLY'
     A C statement (sans semicolon) to mark DECL to be emitted as a
     public symbol such that extra copies in multiple translation units
     will be discarded by the linker.  Define this macro if your object
     file format provides support for this concept, such as the `COMDAT'
     section flags in the Microsoft Windows PE/COFF format, and this
     support requires changes to DECL, such as putting it in a separate
     section.

`SUPPORTS_ONE_ONLY'
     A C expression which evaluates to true if the target supports
     one-only semantics.

     If you don't define this macro, `varasm.c' provides a default
     definition.  If `MAKE_DECL_ONE_ONLY' is defined, the default
     definition is `1'; otherwise, it is `0'.  Define this macro if you
     want to control one-only symbol support with a compiler flag, or if
     setting the `DECL_ONE_ONLY' flag is enough to mark a declaration to
     be emitted as one-only.

`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_SYMBOL_REF (STREAM, SYM)'
     A C statement (sans semicolon) to output a reference to
     `SYMBOL_REF' SYM.  If not defined, `assemble_output' will be used
     to output the name of the symbol.  This macro may be used to
     modify the way a symbol is referenced depending on information
     encoded by `ENCODE_SECTION_INFO'.

`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_OUTPUT_DEBUG_LABEL (STREAM, PREFIX, NUM)'
     A C statement to output to the stdio stream STREAM a debug info
     label whose name is made from the string PREFIX and the number
     NUM.  This is useful for VLIW targets, where debug info labels may
     need to be treated differently than branch target labels.  On some
     systems, branch target labels must be at the beginning of
     instruction bundles, but debug info labels can occur in the middle
     of instruction bundles.

     If this macro is not defined, then `ASM_OUTPUT_INTERNAL_LABEL'
     will be used.

`ASM_OUTPUT_ALTERNATE_LABEL_NAME (STREAM, STRING)'
     A C statement to output to the stdio stream STREAM the string
     STRING.

     The default definition of this macro is as follows:

          fprintf (STREAM, "%s:\n", LABEL_ALTERNATE_NAME (INSN))

`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 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.

     The string will be used as an 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.

`ASM_OUTPUT_DEF (STREAM, NAME, VALUE)'
     A C statement to output to the stdio stream STREAM assembler code
     which defines (equates) the symbol NAME to have the value VALUE.

     If `SET_ASM_OP' is defined, a default definition is provided which
     is correct for most systems.

`ASM_OUTPUT_DEF_FROM_DECLS (STREAM, DECL_OF_NAME, DECL_OF_VALUE)'
     A C statement to output to the stdio stream STREAM assembler code
     which defines (equates) the symbol whose tree node is DECL_OF_NAME
     to have the value of the tree node DECL_OF_VALUE.  This macro will
     be used in preference to `ASM_OUTPUT_DEF' if it is defined and if
     the tree nodes are available.

`ASM_OUTPUT_DEFINE_LABEL_DIFFERENCE_SYMBOL (STREAM, SYMBOL, HIGH, LOW)'
     A C statement to output to the stdio stream STREAM assembler code
     which defines (equates) the symbol SYMBOL to have a value equal to
     the difference of the two symbols HIGH and LOW, i.e. HIGH minus
     LOW.  GCC guarantees that the symbols HIGH and LOW are already
     known by the assembler so that the difference resolves into a
     constant.

     If `SET_ASM_OP' is defined, a default definition is provided which
     is correct for most systems.

`ASM_OUTPUT_WEAK_ALIAS (STREAM, NAME, VALUE)'
     A C statement to output to the stdio stream STREAM assembler code
     which defines (equates) the weak symbol NAME to have the value
     VALUE.  If VALUE is `NULL', it defines NAME as an undefined weak
     symbol.

     Define this macro if the target only supports weak aliases; define
     `ASM_OUTPUT_DEF' instead if possible.

`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: Initialization,  Next: Macros for Initialization,  Prev: Label Output,  Up: Assembler Format

How Initialization Functions Are Handled
----------------------------------------

   The compiled code for certain languages includes "constructors"
(also called "initialization routines")--functions to initialize data
in the program when the program is started.  These functions need to be
called before the program is "started"--that is to say, before `main'
is called.

   Compiling some languages generates "destructors" (also called
"termination routines") that should be called when the program
terminates.

   To make the initialization and termination functions work, the
compiler must output something in the assembler code to cause those
functions to be called at the appropriate time.  When you port the
compiler to a new system, you need to specify how to do this.

   There are two major ways that GCC currently supports the execution of
initialization and termination functions.  Each way has two variants.
Much of the structure is common to all four variations.

   The linker must build two lists of these functions--a list of
initialization functions, called `__CTOR_LIST__', and a list of
termination functions, called `__DTOR_LIST__'.

   Each list always begins with an ignored function pointer (which may
hold 0, -1, or a count of the function pointers after it, depending on
the environment).  This is followed by a series of zero or more function
pointers to constructors (or destructors), followed by a function
pointer containing zero.

   Depending on the operating system and its executable file format,
either `crtstuff.c' or `libgcc2.c' traverses these lists at startup
time and exit time.  Constructors are called in reverse order of the
list; destructors in forward order.

   The best way to handle static constructors works only for object file
formats which provide arbitrarily-named sections.  A section is set
aside for a list of constructors, and another for a list of destructors.
Traditionally these are called `.ctors' and `.dtors'.  Each object file
that defines an initialization function also puts a word in the
constructor section to point to that function.  The linker accumulates
all these words into one contiguous `.ctors' section.  Termination
functions are handled similarly.

   To use this method, you need appropriate definitions of the macros
`ASM_OUTPUT_CONSTRUCTOR' and `ASM_OUTPUT_DESTRUCTOR'.  Usually you can
get them by including `svr4.h'.

   When arbitrary sections are available, there are two variants,
depending upon how the code in `crtstuff.c' is called.  On systems that
support an "init" section which is executed at program startup, parts
of `crtstuff.c' are compiled into that section.  The program is linked
by the `gcc' driver like this:

     ld -o OUTPUT_FILE crtbegin.o ... crtend.o -lgcc

   The head of a function (`__do_global_ctors') appears in the init
section of `crtbegin.o'; the remainder of the function appears in the
init section of `crtend.o'.  The linker will pull these two parts of
the section together, making a whole function.  If any of the user's
object files linked into the middle of it contribute code, then that
code will be executed as part of the body of `__do_global_ctors'.

   To use this variant, you must define the `INIT_SECTION_ASM_OP' macro
properly.

   If no init section is available, do not define
`INIT_SECTION_ASM_OP'.  Then `__do_global_ctors' is built into the text
section like all other functions, and resides in `libgcc.a'.  When GCC
compiles any function called `main', it inserts a procedure call to
`__main' as the first executable code after the function prologue.  The
`__main' function, also defined in `libgcc2.c', simply calls
`__do_global_ctors'.

   In file formats that don't support arbitrary sections, there are
again two variants.  In the simplest variant, the GNU linker (GNU `ld')
and an `a.out' format must be used.  In this case,
`ASM_OUTPUT_CONSTRUCTOR' is defined to produce a `.stabs' entry of type
`N_SETT', referencing the name `__CTOR_LIST__', and with the address of
the void function containing the initialization code as its value.  The
GNU linker recognizes this as a request to add the value to a "set";
the values are accumulated, and are eventually placed in the executable
as a vector in the format described above, with a leading (ignored)
count and a trailing zero element.  `ASM_OUTPUT_DESTRUCTOR' is handled
similarly.  Since no init section is available, the absence of
`INIT_SECTION_ASM_OP' causes the compilation of `main' to call `__main'
as above, starting the initialization process.

   The last variant uses neither arbitrary sections nor the GNU linker.
This is preferable when you want to do dynamic linking and when using
file formats which the GNU linker does not support, such as `ECOFF'.  In
this case, `ASM_OUTPUT_CONSTRUCTOR' does not produce an `N_SETT'
symbol; initialization and termination functions are recognized simply
by their names.  This requires an extra program in the linkage step,
called `collect2'.  This program pretends to be the linker, for use
with GCC; it does its job by running the ordinary linker, but also
arranges to include the vectors of initialization and termination
functions.  These functions are called via `__main' as described above.

   Choosing among these configuration options has been simplified by a
set of operating-system-dependent files in the `config' subdirectory.
These files define all of the relevant parameters.  Usually it is
sufficient to include one into your specific machine-dependent
configuration file.  These files are:

`aoutos.h'
     For operating systems using the `a.out' format.

`next.h'
     For operating systems using the `MachO' format.

`svr3.h'
     For System V Release 3 and similar systems using `COFF' format.

`svr4.h'
     For System V Release 4 and similar systems using `ELF' format.

`vms.h'
     For the VMS operating system.

   The following section describes the specific macros that control and
customize the handling of initialization and termination functions.


File: gcc.info,  Node: Macros for Initialization,  Next: Instruction Output,  Prev: Initialization,  Up: Assembler Format

Macros Controlling Initialization Routines
------------------------------------------

   Here are the macros that control how the compiler handles
initialization and termination functions:

`INIT_SECTION_ASM_OP'
     If defined, a C string constant, including spacing, for the
     assembler operation to identify the following data as
     initialization code.  If not defined, GCC will assume such a
     section does not exist.  When you are using special sections for
     initialization and termination functions, this macro also controls
     how `crtstuff.c' and `libgcc2.c' arrange to run the initialization
     functions.

`HAS_INIT_SECTION'
     If defined, `main' will not call `__main' as described above.
     This macro should be defined for systems that control the contents
     of the init section on a symbol-by-symbol basis, such as OSF/1,
     and should not be defined explicitly for systems that support
     `INIT_SECTION_ASM_OP'.

`LD_INIT_SWITCH'
     If defined, a C string constant for a switch that tells the linker
     that the following symbol is an initialization routine.

`LD_FINI_SWITCH'
     If defined, a C string constant for a switch that tells the linker
     that the following symbol is a finalization routine.

`INVOKE__main'
     If defined, `main' will call `__main' despite the presence of
     `INIT_SECTION_ASM_OP'.  This macro should be defined for systems
     where the init section is not actually run automatically, but is
     still useful for collecting the lists of constructors and
     destructors.

`SUPPORTS_INIT_PRIORITY'
     If nonzero, the C++ `init_priority' attribute is supported and the
     compiler should emit instructions to control the order of
     initialization of objects.  If zero, the compiler will issue an
     error message upon encountering an `init_priority' attribute.

`ASM_OUTPUT_CONSTRUCTOR (STREAM, NAME)'
     Define this macro as a C statement to output on the stream STREAM
     the assembler code to arrange to call the function named NAME at
     initialization time.

     Assume that NAME is the name of a C function generated
     automatically by the compiler.  This function takes no arguments.
     Use the function `assemble_name' to output the name NAME; this
     performs any system-specific syntactic transformations such as
     adding an underscore.

     If you don't define this macro, nothing special is output to
     arrange to call the function.  This is correct when the function
     will be called in some other manner--for example, by means of the
     `collect2' program, which looks through the symbol table to find
     these functions by their names.

`ASM_OUTPUT_DESTRUCTOR (STREAM, NAME)'
     This is like `ASM_OUTPUT_CONSTRUCTOR' but used for termination
     functions rather than initialization functions.

     When `ASM_OUTPUT_CONSTRUCTOR' and `ASM_OUTPUT_DESTRUCTOR' are
     defined, the initialization routine generated for the generated
     object file will have static linkage.

   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 such systems you must
not define `ASM_OUTPUT_CONSTRUCTOR' and `ASM_OUTPUT_DESTRUCTOR' as the
object file's initialization routine must have global scope.

   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' for the target machine.

`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'.

     If your system supports shared libraries and has a program to list
     the dynamic dependencies of a given library or executable, you can
     define these macros to enable support for running initialization
     and termination functions in shared libraries:

`LDD_SUFFIX'
     Define this macro to a C string constant containing the name of the
     program which lists dynamic dependencies, like `"ldd"' under SunOS
     4.

`PARSE_LDD_OUTPUT (PTR)'
     Define this macro to be C code that extracts filenames from the
     output of the program denoted by `LDD_SUFFIX'.  PTR is a variable
     of type `char *' that points to the beginning of a line of output
     from `LDD_SUFFIX'.  If the line lists a dynamic dependency, the
     code must advance PTR to the beginning of the filename on that
     line.  Otherwise, it must set PTR to `NULL'.


File: gcc.info,  Node: Instruction Output,  Next: Dispatch Tables,  Prev: Macros for Initialization,  Up: Assembler Format

Output of Assembler Instructions
--------------------------------

   This describes assembler instruction output.

`REGISTER_NAMES'
     A C initializer containing the assembler's names for the machine
     registers, each one as a C string constant.  This is what
     translates register numbers in the compiler into assembler
     language.

`ADDITIONAL_REGISTER_NAMES'
     If defined, a C initializer for an array of structures containing
     a name and a register number.  This macro defines additional names
     for hard registers, thus allowing the `asm' option in declarations
     to refer to registers using alternate names.

`ASM_OUTPUT_OPCODE (STREAM, PTR)'
     Define this macro if you are using an unusual assembler that
     requires different names for the machine instructions.

     The definition is a C statement or statements which output an
     assembler instruction opcode to the stdio stream STREAM.  The
     macro-operand PTR is a variable of type `char *' which points to
     the opcode name in its "internal" form--the form that is written
     in the machine description.  The definition should output the
     opcode name to STREAM, performing any translation you desire, and
     increment the variable PTR to point at the end of the opcode so
     that it will not be output twice.

     In fact, your macro definition may process less than the entire
     opcode name, or more than the opcode name; but if you want to
     process text that includes `%'-sequences to substitute operands,
     you must take care of the substitution yourself.  Just be sure to
     increment PTR over whatever text should not be output normally.

     If you need to look at the operand values, they can be found as the
     elements of `recog_operand'.

     If the macro definition does nothing, the instruction is output in
     the usual way.

`FINAL_PRESCAN_INSN (INSN, OPVEC, NOPERANDS)'
     If defined, a C statement to be executed just prior to the output
     of assembler code for INSN, to modify the extracted operands so
     they will be output differently.

     Here the argument OPVEC is the vector containing the operands
     extracted from INSN, and NOPERANDS is the number of elements of
     the vector which contain meaningful data for this insn.  The
     contents of this vector are what will be used to convert the insn
     template into assembler code, so you can change the assembler
     output by changing the contents of the vector.

     This macro is useful when various assembler syntaxes share a single
     file of instruction patterns; by defining this macro differently,
     you can cause a large class of instructions to be output
     differently (such as with rearranged operands).  Naturally,
     variations in assembler syntax affecting individual insn patterns
     ought to be handled by writing conditional output routines in
     those patterns.

     If this macro is not defined, it is equivalent to a null statement.

`FINAL_PRESCAN_LABEL'
     If defined, `FINAL_PRESCAN_INSN' will be called on each
     `CODE_LABEL'.  In that case, OPVEC will be a null pointer and
     NOPERANDS will be zero.

`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_FPRINTF_EXTENSIONS(FILE, ARGPTR, FORMAT)'
     If defined this macro should expand to a series of `case'
     statements which will be parsed inside the `switch' statement of
     the `asm_fprintf' function.  This allows targets to define extra
     printf formats which may useful when generating their assembler
     statements.  Note that upper case letters are reserved for future
     generic extensions to asm_fprintf, and so are not available to
     target specific code.  The output file is given by the parameter
     FILE.  The varargs input pointer is ARGPTR and the rest of the
     format string, starting the character after the one that is being
     switched upon, is pointed to by FORMAT.

`ASSEMBLER_DIALECT'
     If your target supports multiple dialects of assembler language
     (such as different opcodes), define this macro as a C expression
     that gives the numeric index of the assembler language dialect to
     use, with zero as the first variant.

     If this macro is defined, you may use constructs of the form
     `{option0|option1|option2...}' in the output templates of patterns
     (*note Output Template::) or in the first argument of
     `asm_fprintf'.  This construct outputs `option0', `option1' or
     `option2', etc., if the value of `ASSEMBLER_DIALECT' is zero, one
     or two, etc.  Any special characters within these strings retain
     their usual meaning.

     If you do not define this macro, the characters `{', `|' and `}'
     do not have any special meaning when used in templates or operands
     to `asm_fprintf'.

     Define the macros `REGISTER_PREFIX', `LOCAL_LABEL_PREFIX',
     `USER_LABEL_PREFIX' and `IMMEDIATE_PREFIX' if you can express the
     variations in assembler language syntax with that mechanism.
     Define `ASSEMBLER_DIALECT' and use the `{option0|option1}' syntax
     if the syntax variant are larger and involve such things as
     different opcodes or operand order.

`ASM_OUTPUT_REG_PUSH (STREAM, REGNO)'
     A C expression to output to STREAM some assembler code which will
     push hard register number REGNO onto the stack.  The code need not
     be optimal, since this macro is used only when profiling.

`ASM_OUTPUT_REG_POP (STREAM, REGNO)'
     A C expression to output to STREAM some assembler code which will
     pop hard register number REGNO off of the stack.  The code need
     not be optimal, since this macro is used only when profiling.


File: gcc.info,  Node: Dispatch Tables,  Next: Exception Region Output,  Prev: Instruction Output,  Up: Assembler Format

Output of Dispatch Tables
-------------------------

   This concerns dispatch tables.

`ASM_OUTPUT_ADDR_DIFF_ELT (STREAM, BODY, VALUE, REL)'
     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)

     You must provide this macro on machines where the addresses in a
     dispatch table are relative to the table's own address.  If
     defined, GCC will also use this macro on all machines when
     producing PIC.  BODY is the body of the `ADDR_DIFF_VEC'; it is
     provided so that the mode and flags can be read.

`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.

