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INFO-DIR-SECTION Programming
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* gccint: (gccint).            Internals of the GNU Compiler Collection.
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   This file documents the internals of the GNU compilers.

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File: gccint.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:

 - Macro: 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.

 - Macro: HAS_INIT_SECTION
     If defined, `main' will not call `__main' as described above.
     This macro should be defined for systems that control start-up code
     on a symbol-by-symbol basis, such as OSF/1, and should not be
     defined explicitly for systems that support `INIT_SECTION_ASM_OP'.

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

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

 - Macro: COLLECT_SHARED_INIT_FUNC (STREAM, FUNC)
     If defined, a C statement that will write a function that can be
     automatically called when a shared library is loaded.  The function
     should call FUNC, which takes no arguments.  If not defined, and
     the object format requires an explicit initialization function,
     then a function called `_GLOBAL__DI' will be generated.

     This function and the following one are used by collect2 when
     linking a shared library that needs constructors or destructors,
     or has DWARF2 exception tables embedded in the code.

 - Macro: COLLECT_SHARED_FINI_FUNC (STREAM, FUNC)
     If defined, a C statement that will write a function that can be
     automatically called when a shared library is unloaded.  The
     function should call FUNC, which takes no arguments.  If not
     defined, and the object format requires an explicit finalization
     function, then a function called `_GLOBAL__DD' will be generated.

 - Macro: 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.

 - Macro: 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.

 - Target Hook: bool TARGET_HAVE_CTORS_DTORS
     This value is true if the target supports some "native" method of
     collecting constructors and destructors to be run at startup and
     exit.  It is false if we must use `collect2'.

 - Target Hook: void TARGET_ASM_CONSTRUCTOR (rtx SYMBOL, int PRIORITY)
     If defined, a function that outputs assembler code to arrange to
     call the function referenced by SYMBOL at initialization time.

     Assume that SYMBOL is a `SYMBOL_REF' for a function taking no
     arguments and with no return value.  If the target supports
     initialization priorities, PRIORITY is a value between 0 and
     `MAX_INIT_PRIORITY'; otherwise it must be `DEFAULT_INIT_PRIORITY'.

     If this macro is not defined by the target, a suitable default will
     be chosen if (1) the target supports arbitrary section names, (2)
     the target defines `CTORS_SECTION_ASM_OP', or (3) `USE_COLLECT2'
     is not defined.

 - Target Hook: void TARGET_ASM_DESTRUCTOR (rtx SYMBOL, int PRIORITY)
     This is like `TARGET_ASM_CONSTRUCTOR' but used for termination
     functions rather than initialization functions.

   If `TARGET_HAVE_CTORS_DTORS' is true, 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 certain kinds of systems, you can define this macro to make
`collect2' work faster (and, in some cases, make it work at all):

 - Macro: 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.

     This macro is effective only in a native compiler; `collect2' as
     part of a cross compiler always uses `nm' for the target machine.

 - Macro: 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:

 - Macro: 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.

 - Macro: 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: gccint.info,  Node: Instruction Output,  Next: Dispatch Tables,  Prev: Macros for Initialization,  Up: Assembler Format

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

   This describes assembler instruction output.

 - Macro: 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.

 - Macro: 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.

 - Macro: 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_data.operand'.

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

 - Macro: 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.

 - Macro: 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.

 - Macro: 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.

 - Macro: 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.

 - Macro: 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
     hook `TARGET_ENCODE_SECTION_INFO' to store the information into the
     `symbol_ref', and then check for it here.  *Note Assembler
     Format::.

 - Macro: 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.

 - Macro: REGISTER_PREFIX
 - Macro: LOCAL_LABEL_PREFIX
 - Macro: USER_LABEL_PREFIX
 - Macro: 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.

 - Macro: 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 uppercase 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.

 - Macro: 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', `option2', etc., if the value of
     `ASSEMBLER_DIALECT' is zero, one, two, etc.  Any special characters
     within these strings retain their usual meaning.  If there are
     fewer alternatives within the braces than the value of
     `ASSEMBLER_DIALECT', the construct outputs nothing.

     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.

 - Macro: 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.

 - Macro: 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: gccint.info,  Node: Dispatch Tables,  Next: Exception Region Output,  Prev: Instruction Output,  Up: Assembler Format

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

   This concerns dispatch tables.

 - Macro: 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
     `(*targetm.asm_out.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.

 - Macro: 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
     `(*targetm.asm_out.internal_label)'.  For example,

          fprintf (STREAM, "\t.word L%d\n", VALUE)

 - Macro: 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
     `(*targetm.asm_out.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
     `(*targetm.asm_out.internal_label)'.

 - Macro: ASM_OUTPUT_CASE_END (STREAM, NUM, TABLE)
     Define this if something special must be output at the end of a
     jump-table.  The definition should be a C statement to be executed
     after the assembler code for the table is written.  It should write
     the appropriate code to stdio stream STREAM.  The argument TABLE
     is the jump-table insn, and NUM is the label-number of the
     preceding label.

     If this macro is not defined, nothing special is output at the end
     of the jump-table.


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

Assembler Commands for Exception Regions
----------------------------------------

   This describes commands marking the start and the end of an exception
region.

 - Macro: EH_FRAME_SECTION_NAME
     If defined, a C string constant for the name of the section
     containing exception handling frame unwind information.  If not
     defined, GCC will provide a default definition if the target
     supports named sections.  `crtstuff.c' uses this macro to switch
     to the appropriate section.

     You should define this symbol if your target supports DWARF 2 frame
     unwind information and the default definition does not work.

 - Macro: EH_FRAME_IN_DATA_SECTION
     If defined, DWARF 2 frame unwind information will be placed in the
     data section even though the target supports named sections.  This
     might be necessary, for instance, if the system linker does garbage
     collection and sections cannot be marked as not to be collected.

     Do not define this macro unless `TARGET_ASM_NAMED_SECTION' is also
     defined.

 - Macro: MASK_RETURN_ADDR
     An rtx used to mask the return address found via
     `RETURN_ADDR_RTX', so that it does not contain any extraneous set
     bits in it.

 - Macro: DWARF2_UNWIND_INFO
     Define this macro to 0 if your target supports DWARF 2 frame unwind
     information, but it does not yet work with exception handling.
     Otherwise, if your target supports this information (if it defines
     `INCOMING_RETURN_ADDR_RTX' and either `UNALIGNED_INT_ASM_OP' or
     `OBJECT_FORMAT_ELF'), GCC will provide a default definition of 1.

     If this macro is defined to 1, the DWARF 2 unwinder will be the
     default exception handling mechanism; otherwise,
     `setjmp'/`longjmp' will be used by default.

     If this macro is defined to anything, the DWARF 2 unwinder will be
     used instead of inline unwinders and `__unwind_function' in the
     non-`setjmp' case.

 - Macro: DWARF_CIE_DATA_ALIGNMENT
     This macro need only be defined if the target might save registers
     in the function prologue at an offset to the stack pointer that is
     not aligned to `UNITS_PER_WORD'.  The definition should be the
     negative minimum alignment if `STACK_GROWS_DOWNWARD' is defined,
     and the positive minimum alignment otherwise.  *Note SDB and
     DWARF::.  Only applicable if the target supports DWARF 2 frame
     unwind information.

 - Target Hook: void TARGET_ASM_EXCEPTION_SECTION ()
     If defined, a function that switches to the section in which the
     main exception table is to be placed (*note Sections::).  The
     default is a function that switches to a section named
     `.gcc_except_table' on machines that support named sections via
     `TARGET_ASM_NAMED_SECTION', otherwise if `-fpic' or `-fPIC' is in
     effect, the `data_section', otherwise the `readonly_data_section'.

 - Target Hook: void TARGET_ASM_EH_FRAME_SECTION ()
     If defined, a function that switches to the section in which the
     DWARF 2 frame unwind information to be placed (*note Sections::).
     The default is a function that outputs a standard GAS section
     directive, if `EH_FRAME_SECTION_NAME' is defined, or else a data
     section directive followed by a synthetic label.

 - Variable: Target Hook bool TARGET_TERMINATE_DW2_EH_FRAME_INFO
     Contains the value true if the target should add a zero word onto
     the end of a Dwarf-2 frame info section when used for exception
     handling.  Default value is false if `EH_FRAME_SECTION_NAME' is
     defined, and true otherwise.

 - Target Hook: rtx TARGET_DWARF_REGISTER_SPAN (rtx REG)
     Given a register, this hook should return a parallel of registers
     to represent where to find the register pieces.  Define this hook
     if the register and its mode are represented in Dwarf in
     non-contiguous locations, or if the register should be represented
     in more than one register in Dwarf.  Otherwise, this hook should
     return `NULL_RTX'.  If not defined, the default is to return
     `NULL_RTX'.


File: gccint.info,  Node: Alignment Output,  Prev: Exception Region Output,  Up: Assembler Format

Assembler Commands for Alignment
--------------------------------

   This describes commands for alignment.

 - Macro: JUMP_ALIGN (LABEL)
     The alignment (log base 2) to put in front of LABEL, which is a
     common destination of jumps and has no fallthru incoming edge.

     This macro need not be defined if you don't want any special
     alignment to be done at such a time.  Most machine descriptions do
     not currently define the macro.

     Unless it's necessary to inspect the LABEL parameter, it is better
     to set the variable ALIGN_JUMPS in the target's
     `OVERRIDE_OPTIONS'.  Otherwise, you should try to honor the user's
     selection in ALIGN_JUMPS in a `JUMP_ALIGN' implementation.

 - Macro: LABEL_ALIGN_AFTER_BARRIER (LABEL)
     The alignment (log base 2) to put in front of LABEL, which follows
     a `BARRIER'.

     This macro need not be defined if you don't want any special
     alignment to be done at such a time.  Most machine descriptions do
     not currently define the macro.

 - Macro: LABEL_ALIGN_AFTER_BARRIER_MAX_SKIP
     The maximum number of bytes to skip when applying
     `LABEL_ALIGN_AFTER_BARRIER'.  This works only if
     `ASM_OUTPUT_MAX_SKIP_ALIGN' is defined.

 - Macro: LOOP_ALIGN (LABEL)
     The alignment (log base 2) to put in front of LABEL, which follows
     a `NOTE_INSN_LOOP_BEG' note.

     This macro need not be defined if you don't want any special
     alignment to be done at such a time.  Most machine descriptions do
     not currently define the macro.

     Unless it's necessary to inspect the LABEL parameter, it is better
     to set the variable `align_loops' in the target's
     `OVERRIDE_OPTIONS'.  Otherwise, you should try to honor the user's
     selection in `align_loops' in a `LOOP_ALIGN' implementation.

 - Macro: LOOP_ALIGN_MAX_SKIP
     The maximum number of bytes to skip when applying `LOOP_ALIGN'.
     This works only if `ASM_OUTPUT_MAX_SKIP_ALIGN' is defined.

 - Macro: LABEL_ALIGN (LABEL)
     The alignment (log base 2) to put in front of LABEL.  If
     `LABEL_ALIGN_AFTER_BARRIER' / `LOOP_ALIGN' specify a different
     alignment, the maximum of the specified values is used.

     Unless it's necessary to inspect the LABEL parameter, it is better
     to set the variable `align_labels' in the target's
     `OVERRIDE_OPTIONS'.  Otherwise, you should try to honor the user's
     selection in `align_labels' in a `LABEL_ALIGN' implementation.

 - Macro: LABEL_ALIGN_MAX_SKIP
     The maximum number of bytes to skip when applying `LABEL_ALIGN'.
     This works only if `ASM_OUTPUT_MAX_SKIP_ALIGN' is defined.

 - Macro: ASM_OUTPUT_SKIP (STREAM, NBYTES)
     A C statement to output to the stdio stream STREAM an assembler
     instruction to advance the location counter by NBYTES bytes.
     Those bytes should be zero when loaded.  NBYTES will be a C
     expression of type `int'.

 - Macro: ASM_NO_SKIP_IN_TEXT
     Define this macro if `ASM_OUTPUT_SKIP' should not be used in the
     text section because it fails to put zeros in the bytes that are
     skipped.  This is true on many Unix systems, where the pseudo-op
     to skip bytes produces no-op instructions rather than zeros when
     used in the text section.

 - Macro: ASM_OUTPUT_ALIGN (STREAM, POWER)
     A C statement to output to the stdio stream STREAM an assembler
     command to advance the location counter to a multiple of 2 to the
     POWER bytes.  POWER will be a C expression of type `int'.

 - Macro: ASM_OUTPUT_ALIGN_WITH_NOP (STREAM, POWER)
     Like `ASM_OUTPUT_ALIGN', except that the "nop" instruction is used
     for padding, if necessary.

 - Macro: ASM_OUTPUT_MAX_SKIP_ALIGN (STREAM, POWER, MAX_SKIP)
     A C statement to output to the stdio stream STREAM an assembler
     command to advance the location counter to a multiple of 2 to the
     POWER bytes, but only if MAX_SKIP or fewer bytes are needed to
     satisfy the alignment request.  POWER and MAX_SKIP will be a C
     expression of type `int'.


File: gccint.info,  Node: Debugging Info,  Next: Floating Point,  Prev: Assembler Format,  Up: Target Macros

Controlling Debugging Information Format
========================================

   This describes how to specify debugging information.

* Menu:

* All Debuggers::      Macros that affect all debugging formats uniformly.
* DBX Options::        Macros enabling specific options in DBX format.
* DBX Hooks::          Hook macros for varying DBX format.
* File Names and DBX:: Macros controlling output of file names in DBX format.
* SDB and DWARF::      Macros for SDB (COFF) and DWARF formats.
* VMS Debug::          Macros for VMS debug format.


File: gccint.info,  Node: All Debuggers,  Next: DBX Options,  Up: Debugging Info

Macros Affecting All Debugging Formats
--------------------------------------

   These macros affect all debugging formats.

 - Macro: DBX_REGISTER_NUMBER (REGNO)
     A C expression that returns the DBX register number for the
     compiler register number REGNO.  In the default macro provided,
     the value of this expression will be REGNO itself.  But sometimes
     there are some registers that the compiler knows about and DBX
     does not, or vice versa.  In such cases, some register may need to
     have one number in the compiler and another for DBX.

     If two registers have consecutive numbers inside GCC, and they can
     be used as a pair to hold a multiword value, then they _must_ have
     consecutive numbers after renumbering with `DBX_REGISTER_NUMBER'.
     Otherwise, debuggers will be unable to access such a pair, because
     they expect register pairs to be consecutive in their own
     numbering scheme.

     If you find yourself defining `DBX_REGISTER_NUMBER' in way that
     does not preserve register pairs, then what you must do instead is
     redefine the actual register numbering scheme.

 - Macro: DEBUGGER_AUTO_OFFSET (X)
     A C expression that returns the integer offset value for an
     automatic variable having address X (an RTL expression).  The
     default computation assumes that X is based on the frame-pointer
     and gives the offset from the frame-pointer.  This is required for
     targets that produce debugging output for DBX or COFF-style
     debugging output for SDB and allow the frame-pointer to be
     eliminated when the `-g' options is used.

 - Macro: DEBUGGER_ARG_OFFSET (OFFSET, X)
     A C expression that returns the integer offset value for an
     argument having address X (an RTL expression).  The nominal offset
     is OFFSET.

 - Macro: PREFERRED_DEBUGGING_TYPE
     A C expression that returns the type of debugging output GCC should
     produce when the user specifies just `-g'.  Define this if you
     have arranged for GCC to support more than one format of debugging
     output.  Currently, the allowable values are `DBX_DEBUG',
     `SDB_DEBUG', `DWARF_DEBUG', `DWARF2_DEBUG', `XCOFF_DEBUG',
     `VMS_DEBUG', and `VMS_AND_DWARF2_DEBUG'.

     When the user specifies `-ggdb', GCC normally also uses the value
     of this macro to select the debugging output format, but with two
     exceptions.  If `DWARF2_DEBUGGING_INFO' is defined and
     `LINKER_DOES_NOT_WORK_WITH_DWARF2' is not defined, GCC uses the
     value `DWARF2_DEBUG'.  Otherwise, if `DBX_DEBUGGING_INFO' is
     defined, GCC uses `DBX_DEBUG'.

     The value of this macro only affects the default debugging output;
     the user can always get a specific type of output by using
     `-gstabs', `-gcoff', `-gdwarf-1', `-gdwarf-2', `-gxcoff', or
     `-gvms'.


File: gccint.info,  Node: DBX Options,  Next: DBX Hooks,  Prev: All Debuggers,  Up: Debugging Info

Specific Options for DBX Output
-------------------------------

   These are specific options for DBX output.

 - Macro: DBX_DEBUGGING_INFO
     Define this macro if GCC should produce debugging output for DBX
     in response to the `-g' option.

 - Macro: XCOFF_DEBUGGING_INFO
     Define this macro if GCC should produce XCOFF format debugging
     output in response to the `-g' option.  This is a variant of DBX
     format.

 - Macro: DEFAULT_GDB_EXTENSIONS
     Define this macro to control whether GCC should by default generate
     GDB's extended version of DBX debugging information (assuming
     DBX-format debugging information is enabled at all).  If you don't
     define the macro, the default is 1: always generate the extended
     information if there is any occasion to.

 - Macro: DEBUG_SYMS_TEXT
     Define this macro if all `.stabs' commands should be output while
     in the text section.

 - Macro: ASM_STABS_OP
     A C string constant, including spacing, naming the assembler
     pseudo op to use instead of `"\t.stabs\t"' to define an ordinary
     debugging symbol.  If you don't define this macro, `"\t.stabs\t"'
     is used.  This macro applies only to DBX debugging information
     format.

 - Macro: ASM_STABD_OP
     A C string constant, including spacing, naming the assembler
     pseudo op to use instead of `"\t.stabd\t"' to define a debugging
     symbol whose value is the current location.  If you don't define
     this macro, `"\t.stabd\t"' is used.  This macro applies only to
     DBX debugging information format.

 - Macro: ASM_STABN_OP
     A C string constant, including spacing, naming the assembler
     pseudo op to use instead of `"\t.stabn\t"' to define a debugging
     symbol with no name.  If you don't define this macro,
     `"\t.stabn\t"' is used.  This macro applies only to DBX debugging
     information format.

 - Macro: DBX_NO_XREFS
     Define this macro if DBX on your system does not support the
     construct `xsTAGNAME'.  On some systems, this construct is used to
     describe a forward reference to a structure named TAGNAME.  On
     other systems, this construct is not supported at all.

 - Macro: DBX_CONTIN_LENGTH
     A symbol name in DBX-format debugging information is normally
     continued (split into two separate `.stabs' directives) when it
     exceeds a certain length (by default, 80 characters).  On some
     operating systems, DBX requires this splitting; on others,
     splitting must not be done.  You can inhibit splitting by defining
     this macro with the value zero.  You can override the default
     splitting-length by defining this macro as an expression for the
     length you desire.

 - Macro: DBX_CONTIN_CHAR
     Normally continuation is indicated by adding a `\' character to
     the end of a `.stabs' string when a continuation follows.  To use
     a different character instead, define this macro as a character
     constant for the character you want to use.  Do not define this
     macro if backslash is correct for your system.

 - Macro: DBX_STATIC_STAB_DATA_SECTION
     Define this macro if it is necessary to go to the data section
     before outputting the `.stabs' pseudo-op for a non-global static
     variable.

 - Macro: DBX_TYPE_DECL_STABS_CODE
     The value to use in the "code" field of the `.stabs' directive for
     a typedef.  The default is `N_LSYM'.

 - Macro: DBX_STATIC_CONST_VAR_CODE
     The value to use in the "code" field of the `.stabs' directive for
     a static variable located in the text section.  DBX format does not
     provide any "right" way to do this.  The default is `N_FUN'.

 - Macro: DBX_REGPARM_STABS_CODE
     The value to use in the "code" field of the `.stabs' directive for
     a parameter passed in registers.  DBX format does not provide any
     "right" way to do this.  The default is `N_RSYM'.

 - Macro: DBX_REGPARM_STABS_LETTER
     The letter to use in DBX symbol data to identify a symbol as a
     parameter passed in registers.  DBX format does not customarily
     provide any way to do this.  The default is `'P''.

 - Macro: DBX_MEMPARM_STABS_LETTER
     The letter to use in DBX symbol data to identify a symbol as a
     stack parameter.  The default is `'p''.

 - Macro: DBX_FUNCTION_FIRST
     Define this macro if the DBX information for a function and its
     arguments should precede the assembler code for the function.
     Normally, in DBX format, the debugging information entirely
     follows the assembler code.

 - Macro: DBX_BLOCKS_FUNCTION_RELATIVE
     Define this macro if the value of a symbol describing the scope of
     a block (`N_LBRAC' or `N_RBRAC') should be relative to the start
     of the enclosing function.  Normally, GCC uses an absolute address.

 - Macro: DBX_USE_BINCL
     Define this macro if GCC should generate `N_BINCL' and `N_EINCL'
     stabs for included header files, as on Sun systems.  This macro
     also directs GCC to output a type number as a pair of a file
     number and a type number within the file.  Normally, GCC does not
     generate `N_BINCL' or `N_EINCL' stabs, and it outputs a single
     number for a type number.


File: gccint.info,  Node: DBX Hooks,  Next: File Names and DBX,  Prev: DBX Options,  Up: Debugging Info

Open-Ended Hooks for DBX Format
-------------------------------

   These are hooks for DBX format.

 - Macro: DBX_OUTPUT_LBRAC (STREAM, NAME)
     Define this macro to say how to output to STREAM the debugging
     information for the start of a scope level for variable names.  The
     argument NAME is the name of an assembler symbol (for use with
     `assemble_name') whose value is the address where the scope begins.

 - Macro: DBX_OUTPUT_RBRAC (STREAM, NAME)
     Like `DBX_OUTPUT_LBRAC', but for the end of a scope level.

 - Macro: DBX_OUTPUT_NFUN (STREAM, LSCOPE_LABEL, DECL)
     Define this macro if the target machine requires special handling
     to output an `N_FUN' entry for the function DECL.

 - Macro: DBX_OUTPUT_FUNCTION_END (STREAM, FUNCTION)
     Define this macro if the target machine requires special output at
     the end of the debugging information for a function.  The
     definition should be a C statement (sans semicolon) to output the
     appropriate information to STREAM.  FUNCTION is the
     `FUNCTION_DECL' node for the function.

 - Macro: DBX_OUTPUT_STANDARD_TYPES (SYMS)
     Define this macro if you need to control the order of output of the
     standard data types at the beginning of compilation.  The argument
     SYMS is a `tree' which is a chain of all the predefined global
     symbols, including names of data types.

     Normally, DBX output starts with definitions of the types for
     integers and characters, followed by all the other predefined
     types of the particular language in no particular order.

     On some machines, it is necessary to output different particular
     types first.  To do this, define `DBX_OUTPUT_STANDARD_TYPES' to
     output those symbols in the necessary order.  Any predefined types
     that you don't explicitly output will be output afterward in no
     particular order.

     Be careful not to define this macro so that it works only for C.
     There are no global variables to access most of the built-in
     types, because another language may have another set of types.
     The way to output a particular type is to look through SYMS to see
     if you can find it.  Here is an example:

          {
            tree decl;
            for (decl = syms; decl; decl = TREE_CHAIN (decl))
              if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)),
                           "long int"))
                dbxout_symbol (decl);
            ...
          }

     This does nothing if the expected type does not exist.

     See the function `init_decl_processing' in `c-decl.c' to find the
     names to use for all the built-in C types.

     Here is another way of finding a particular type:

          {
            tree decl;
            for (decl = syms; decl; decl = TREE_CHAIN (decl))
              if (TREE_CODE (decl) == TYPE_DECL
                  && (TREE_CODE (TREE_TYPE (decl))
                      == INTEGER_CST)
                  && TYPE_PRECISION (TREE_TYPE (decl)) == 16
                  && TYPE_UNSIGNED (TREE_TYPE (decl)))
                /* This must be `unsigned short'.  */
                dbxout_symbol (decl);
            ...
          }

 - Macro: NO_DBX_FUNCTION_END
     Some stabs encapsulation formats (in particular ECOFF), cannot
     handle the `.stabs "",N_FUN,,0,0,Lscope-function-1' gdb dbx
     extension construct.  On those machines, define this macro to turn
     this feature off without disturbing the rest of the gdb extensions.


File: gccint.info,  Node: File Names and DBX,  Next: SDB and DWARF,  Prev: DBX Hooks,  Up: Debugging Info

File Names in DBX Format
------------------------

   This describes file names in DBX format.

 - Macro: DBX_OUTPUT_MAIN_SOURCE_FILENAME (STREAM, NAME)
     A C statement to output DBX debugging information to the stdio
     stream STREAM which indicates that file NAME is the main source
     file--the file specified as the input file for compilation.  This
     macro is called only once, at the beginning of compilation.

     This macro need not be defined if the standard form of output for
     DBX debugging information is appropriate.

 - Macro: DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (STREAM, NAME)
     A C statement to output DBX debugging information to the stdio
     stream STREAM which indicates that the current directory during
     compilation is named NAME.

     This macro need not be defined if the standard form of output for
     DBX debugging information is appropriate.

 - Macro: DBX_OUTPUT_MAIN_SOURCE_FILE_END (STREAM, NAME)
     A C statement to output DBX debugging information at the end of
     compilation of the main source file NAME.

     If you don't define this macro, nothing special is output at the
     end of compilation, which is correct for most machines.


File: gccint.info,  Node: SDB and DWARF,  Next: VMS Debug,  Prev: File Names and DBX,  Up: Debugging Info

Macros for SDB and DWARF Output
-------------------------------

   Here are macros for SDB and DWARF output.

 - Macro: SDB_DEBUGGING_INFO
     Define this macro if GCC should produce COFF-style debugging output
     for SDB in response to the `-g' option.

 - Macro: DWARF_DEBUGGING_INFO
     Define this macro if GCC should produce dwarf format debugging
     output in response to the `-g' option.

 - Macro: DWARF2_DEBUGGING_INFO
     Define this macro if GCC should produce dwarf version 2 format
     debugging output in response to the `-g' option.

     To support optional call frame debugging information, you must also
     define `INCOMING_RETURN_ADDR_RTX' and either set
     `RTX_FRAME_RELATED_P' on the prologue insns if you use RTL for the
     prologue, or call `dwarf2out_def_cfa' and `dwarf2out_reg_save' as
     appropriate from `TARGET_ASM_FUNCTION_PROLOGUE' if you don't.

 - Macro: DWARF2_FRAME_INFO
     Define this macro to a nonzero value if GCC should always output
     Dwarf 2 frame information.  If `DWARF2_UNWIND_INFO' (*note
     Exception Region Output:: is nonzero, GCC will output this
     information not matter how you define `DWARF2_FRAME_INFO'.

 - Macro: LINKER_DOES_NOT_WORK_WITH_DWARF2
     Define this macro if the linker does not work with Dwarf version 2.
     Normally, if the user specifies only `-ggdb' GCC will use Dwarf
     version 2 if available; this macro disables this.  See the
     description of the `PREFERRED_DEBUGGING_TYPE' macro for more
     details.

 - Macro: DWARF2_GENERATE_TEXT_SECTION_LABEL
     By default, the Dwarf 2 debugging information generator will
     generate a label to mark the beginning of the text section.  If it
     is better simply to use the name of the text section itself,
     rather than an explicit label, to indicate the beginning of the
     text section, define this macro to zero.

 - Macro: DWARF2_ASM_LINE_DEBUG_INFO
     Define this macro to be a nonzero value if the assembler can
     generate Dwarf 2 line debug info sections.  This will result in
     much more compact line number tables, and hence is desirable if it
     works.

 - Macro: ASM_OUTPUT_DWARF_DELTA (STREAM, SIZE, LABEL1, LABEL2)
     A C statement to issue assembly directives that create a difference
     between the two given labels, using an integer of the given size.

 - Macro: ASM_OUTPUT_DWARF_OFFSET (STREAM, SIZE, LABEL)
     A C statement to issue assembly directives that create a
     section-relative reference to the given label, using an integer of
     the given size.

 - Macro: ASM_OUTPUT_DWARF_PCREL (STREAM, SIZE, LABEL)
     A C statement to issue assembly directives that create a
     self-relative reference to the given label, using an integer of
     the given size.

 - Macro: PUT_SDB_...
     Define these macros to override the assembler syntax for the
     special SDB assembler directives.  See `sdbout.c' for a list of
     these macros and their arguments.  If the standard syntax is used,
     you need not define them yourself.

 - Macro: SDB_DELIM
     Some assemblers do not support a semicolon as a delimiter, even
     between SDB assembler directives.  In that case, define this macro
     to be the delimiter to use (usually `\n').  It is not necessary to
     define a new set of `PUT_SDB_OP' macros if this is the only change
     required.

 - Macro: SDB_GENERATE_FAKE
     Define this macro to override the usual method of constructing a
     dummy name for anonymous structure and union types.  See
     `sdbout.c' for more information.

 - Macro: SDB_ALLOW_UNKNOWN_REFERENCES
     Define this macro to allow references to unknown structure, union,
     or enumeration tags to be emitted.  Standard COFF does not allow
     handling of unknown references, MIPS ECOFF has support for it.

 - Macro: SDB_ALLOW_FORWARD_REFERENCES
     Define this macro to allow references to structure, union, or
     enumeration tags that have not yet been seen to be handled.  Some
     assemblers choke if forward tags are used, while some require it.


File: gccint.info,  Node: VMS Debug,  Prev: SDB and DWARF,  Up: Debugging Info

Macros for VMS Debug Format
---------------------------

   Here are macros for VMS debug format.

 - Macro: VMS_DEBUGGING_INFO
     Define this macro if GCC should produce debugging output for VMS
     in response to the `-g' option.  The default behavior for VMS is
     to generate minimal debug info for a traceback in the absence of
     `-g' unless explicitly overridden with `-g0'.  This behavior is
     controlled by `OPTIMIZATION_OPTIONS' and `OVERRIDE_OPTIONS'.


File: gccint.info,  Node: Floating Point,  Next: Mode Switching,  Prev: Debugging Info,  Up: Target Macros

Cross Compilation and Floating Point
====================================

   While all modern machines use twos-complement representation for
integers, there are a variety of representations for floating point
numbers.  This means that in a cross-compiler the representation of
floating point numbers in the compiled program may be different from
that used in the machine doing the compilation.

   Because different representation systems may offer different amounts
of range and precision, all floating point constants must be
represented in the target machine's format.  Therefore, the cross
compiler cannot safely use the host machine's floating point
arithmetic; it must emulate the target's arithmetic.  To ensure
consistency, GCC always uses emulation to work with floating point
values, even when the host and target floating point formats are
identical.

   The following macros are provided by `real.h' for the compiler to
use.  All parts of the compiler which generate or optimize
floating-point calculations must use these macros.  They may evaluate
their operands more than once, so operands must not have side effects.

 - Macro: REAL_VALUE_TYPE
     The C data type to be used to hold a floating point value in the
     target machine's format.  Typically this is a `struct' containing
     an array of `HOST_WIDE_INT', but all code should treat it as an
     opaque quantity.

 - Macro: int REAL_VALUES_EQUAL (REAL_VALUE_TYPE X, REAL_VALUE_TYPE Y)
     Compares for equality the two values, X and Y.  If the target
     floating point format supports negative zeroes and/or NaNs,
     `REAL_VALUES_EQUAL (-0.0, 0.0)' is true, and `REAL_VALUES_EQUAL
     (NaN, NaN)' is false.

 - Macro: int REAL_VALUES_LESS (REAL_VALUE_TYPE X, REAL_VALUE_TYPE Y)
     Tests whether X is less than Y.

 - Macro: HOST_WIDE_INT REAL_VALUE_FIX (REAL_VALUE_TYPE X)
     Truncates X to a signed integer, rounding toward zero.

 - Macro: unsigned HOST_WIDE_INT REAL_VALUE_UNSIGNED_FIX
          (REAL_VALUE_TYPE X)
     Truncates X to an unsigned integer, rounding toward zero.  If X is
     negative, returns zero.

 - Macro: REAL_VALUE_TYPE REAL_VALUE_ATOF (const char *STRING, enum
          machine_mode MODE)
     Converts STRING into a floating point number in the target
     machine's representation for mode MODE.  This routine can handle
     both decimal and hexadecimal floating point constants, using the
     syntax defined by the C language for both.

 - Macro: int REAL_VALUE_NEGATIVE (REAL_VALUE_TYPE X)
     Returns 1 if X is negative (including negative zero), 0 otherwise.

 - Macro: int REAL_VALUE_ISINF (REAL_VALUE_TYPE X)
     Determines whether X represents infinity (positive or negative).

 - Macro: int REAL_VALUE_ISNAN (REAL_VALUE_TYPE X)
     Determines whether X represents a "NaN" (not-a-number).

 - Macro: void REAL_ARITHMETIC (REAL_VALUE_TYPE OUTPUT, enum tree_code
          CODE, REAL_VALUE_TYPE X, REAL_VALUE_TYPE Y)
     Calculates an arithmetic operation on the two floating point values
     X and Y, storing the result in OUTPUT (which must be a variable).

     The operation to be performed is specified by CODE.  Only the
     following codes are supported: `PLUS_EXPR', `MINUS_EXPR',
     `MULT_EXPR', `RDIV_EXPR', `MAX_EXPR', `MIN_EXPR'.

     If `REAL_ARITHMETIC' is asked to evaluate division by zero and the
     target's floating point format cannot represent infinity, it will
     call `abort'.  Callers should check for this situation first, using
     `MODE_HAS_INFINITIES'.  *Note Storage Layout::.

 - Macro: REAL_VALUE_TYPE REAL_VALUE_NEGATE (REAL_VALUE_TYPE X)
     Returns the negative of the floating point value X.

 - Macro: REAL_VALUE_TYPE REAL_VALUE_ABS (REAL_VALUE_TYPE X)
     Returns the absolute value of X.

 - Macro: REAL_VALUE_TYPE REAL_VALUE_TRUNCATE (REAL_VALUE_TYPE MODE,
          enum machine_mode X)
     Truncates the floating point value X to fit in MODE.  The return
     value is still a full-size `REAL_VALUE_TYPE', but it has an
     appropriate bit pattern to be output asa floating constant whose
     precision accords with mode MODE.

 - Macro: void REAL_VALUE_TO_INT (HOST_WIDE_INT LOW, HOST_WIDE_INT
          HIGH, REAL_VALUE_TYPE X)
     Converts a floating point value X into a double-precision integer
     which is then stored into LOW and HIGH.  If the value is not
     integral, it is truncated.

 - Macro: void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE X, HOST_WIDE_INT
          LOW, HOST_WIDE_INT HIGH, enum machine_mode MODE)
     Converts a double-precision integer found in LOW and HIGH, into a
     floating point value which is then stored into X.  The value is
     truncated to fit in mode MODE.

