GNU Compiler Collection (GCC) Internals: Label Output

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#### 17.20.4 Output and Generation of Labels

This is about outputting labels.

Macro: 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. A default definition of this macro is provided which is correct for most systems.

Macro: ASM_OUTPUT_FUNCTION_LABEL (stream, name, decl)

  A C statement (sans semicolon) to output to the stdio stream stream the assembler definition of a label named name of a function. 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. A default definition of this macro is provided which is correct for most systems.

  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`).

Macro: ASM_OUTPUT_INTERNAL_LABEL (stream, name)

  Identical to `ASM_OUTPUT_LABEL`, except that name is known to refer to a compiler-generated label. The default definition uses `assemble_name_raw`, which is like `assemble_name` except that it is more efficient.

Macro: SIZE_ASM_OP

  A C string containing the appropriate assembler directive to specify the size of a symbol, without any arguments. On systems that use ELF, the default (in `config/elfos.h`) is ‘`"\t.size\t"`’; on other systems, the default is not to define this macro.

  Define this macro only if it is correct to use the default definitions of `ASM_OUTPUT_SIZE_DIRECTIVE` and `ASM_OUTPUT_MEASURED_SIZE` for your system. If you need your own custom definitions of those macros, or if you do not need explicit symbol sizes at all, do not define this macro.

Macro: ASM_OUTPUT_SIZE_DIRECTIVE (stream, name, size)

  A C statement (sans semicolon) to output to the stdio stream stream a directive telling the assembler that the size of the symbol name is size. size is a `HOST_WIDE_INT`. If you define `SIZE_ASM_OP`, a default definition of this macro is provided.

Macro: ASM_OUTPUT_MEASURED_SIZE (stream, name)

  A C statement (sans semicolon) to output to the stdio stream stream a directive telling the assembler to calculate the size of the symbol name by subtracting its address from the current address.

  If you define `SIZE_ASM_OP`, a default definition of this macro is provided. The default assumes that the assembler recognizes a special ‘`.`’ symbol as referring to the current address, and can calculate the difference between this and another symbol. If your assembler does not recognize ‘`.`’ or cannot do calculations with it, you will need to redefine `ASM_OUTPUT_MEASURED_SIZE` to use some other technique.

Macro: NO_DOLLAR_IN_LABEL

  Define this macro if the assembler does not accept the character ‘`$`’ in label names. By default constructors and destructors in G++ have ‘`$`’ in the identifiers. If this macro is defined, ‘`.`’ is used instead.

Macro: NO_DOT_IN_LABEL

  Define this macro if the assembler does not accept the character ‘`.`’ in label names. By default constructors and destructors in G++ have names that use ‘`.`’. If this macro is defined, these names are rewritten to avoid ‘`.`’.

Macro: TYPE_ASM_OP

  A C string containing the appropriate assembler directive to specify the type of a symbol, without any arguments. On systems that use ELF, the default (in `config/elfos.h`) is ‘`"\t.type\t"`’; on other systems, the default is not to define this macro.

  Define this macro only if it is correct to use the default definition of `ASM_OUTPUT_TYPE_DIRECTIVE` for your system. If you need your own custom definition of this macro, or if you do not need explicit symbol types at all, do not define this macro.

Macro: TYPE_OPERAND_FMT

  A C string which specifies (using `printf` syntax) the format of the second operand to `TYPE_ASM_OP`. On systems that use ELF, the default (in `config/elfos.h`) is ‘`"@%s"`’; on other systems, the default is not to define this macro.

  Define this macro only if it is correct to use the default definition of `ASM_OUTPUT_TYPE_DIRECTIVE` for your system. If you need your own custom definition of this macro, or if you do not need explicit symbol types at all, do not define this macro.

Macro: ASM_OUTPUT_TYPE_DIRECTIVE (stream, type)

  A C statement (sans semicolon) to output to the stdio stream stream a directive telling the assembler that the type of the symbol name is type. type is a C string; currently, that string is always either ‘`"function"`’ or ‘`"object"`’, but you should not count on this.

  If you define `TYPE_ASM_OP` and `TYPE_OPERAND_FMT`, a default definition of this macro is provided.

Macro: 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_FUNCTION_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_FUNCTION_LABEL`).

  You may wish to use `ASM_OUTPUT_TYPE_DIRECTIVE` in the definition of this macro.

Macro: 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.

  You may wish to use `ASM_OUTPUT_MEASURED_SIZE` in the definition of this macro.

Macro: ASM_DECLARE_COLD_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 cold function partition which is being defined. This macro is responsible for outputting the label definition (perhaps using `ASM_OUTPUT_FUNCTION_LABEL`). The argument decl is the `FUNCTION_DECL` tree node representing the function.

  If this macro is not defined, then the cold partition name is defined in the usual manner as a label (by means of `ASM_OUTPUT_LABEL`).

  You may wish to use `ASM_OUTPUT_TYPE_DIRECTIVE` in the definition of this macro.

Macro: ASM_DECLARE_COLD_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 cold function partition which is being defined. The argument name is the name of the cold partition of the function. The argument decl is the `FUNCTION_DECL` tree node representing the function.

  If this macro is not defined, then the partition size is not defined.

  You may wish to use `ASM_OUTPUT_MEASURED_SIZE` in the definition of this macro.

Macro: 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`).

  You may wish to use `ASM_OUTPUT_TYPE_DIRECTIVE` and/or `ASM_OUTPUT_SIZE_DIRECTIVE` in the definition of this macro.

Target Hook: void TARGET_ASM_DECLARE_CONSTANT_NAME (FILE *file, const char *name, const_tree expr, HOST_WIDE_INT size)

  A target hook to output to the stdio stream file any text necessary for declaring the name name of a constant which is being defined. This target hook is responsible for outputting the label definition (perhaps using `assemble_label`). The argument exp is the value of the constant, and size is the size of the constant in bytes. The name will be an internal label.

  The default version of this target hook, define the name in the usual manner as a label (by means of `assemble_label`).

  You may wish to use `ASM_OUTPUT_TYPE_DIRECTIVE` in this target hook.

Macro: 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.

Macro: 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.

  You may wish to use `ASM_OUTPUT_SIZE_DIRECTIVE` and/or `ASM_OUTPUT_MEASURED_SIZE` in the definition of this macro.

Target Hook: void TARGET_ASM_GLOBALIZE_LABEL (FILE *stream, const char *name)

  This target hook is a function to output to the stdio stream stream some commands that will make the label name global; that is, available for reference from other files.

  The default implementation relies on a proper definition of `GLOBAL_ASM_OP`.

Target Hook: void TARGET_ASM_GLOBALIZE_DECL_NAME (FILE *stream, tree decl)

  This target hook is a function to output to the stdio stream stream some commands that will make the name associated with decl global; that is, available for reference from other files.

  The default implementation uses the TARGET_ASM_GLOBALIZE_LABEL target hook.

Target Hook: void TARGET_ASM_ASSEMBLE_UNDEFINED_DECL (FILE *stream, const char *name, const_tree decl)

  This target hook is a function to output to the stdio stream stream some commands that will declare the name associated with decl which is not defined in the current translation unit. Most assemblers do not require anything to be output in this case.

Macro: ASM_WEAKEN_LABEL (stream, name)

  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 or `ASM_WEAKEN_DECL`, GCC will not support weak symbols and you should not define the `SUPPORTS_WEAK` macro.

Macro: ASM_WEAKEN_DECL (stream, decl, name, value)

  Combines (and replaces) the function of `ASM_WEAKEN_LABEL` and `ASM_OUTPUT_WEAK_ALIAS`, allowing access to the associated function or variable decl. If value is not `NULL`, this C statement should 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 should output commands to make name weak.

Macro: ASM_OUTPUT_WEAKREF (stream, decl, name, value)

  Outputs a directive that enables name to be used to refer to symbol value with weak-symbol semantics. `decl` is the declaration of `name`.

Macro: SUPPORTS_WEAK

  A preprocessor constant 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 either `ASM_WEAKEN_LABEL` or `ASM_WEAKEN_DECL` is defined, the default definition is ‘`1`’; otherwise, it is ‘`0`’.

Macro: TARGET_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. The default definition is ‘`(SUPPORTS_WEAK)`’. Define this macro if you want to control weak symbol support with a compiler flag such as `-melf`.

Macro: MAKE_DECL_ONE_ONLY (decl)

  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.

Macro: 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.

Target Hook: void TARGET_ASM_ASSEMBLE_VISIBILITY (tree decl, int visibility)

  This target hook is a function to output to asm_out_file some commands that will make the symbol(s) associated with decl have hidden, protected or internal visibility as specified by visibility.

Macro: TARGET_WEAK_NOT_IN_ARCHIVE_TOC

  A C expression that evaluates to true if the target’s linker expects that weak symbols do not appear in a static archive’s table of contents. The default is `0`.

  Leaving weak symbols out of an archive’s table of contents means that, if a symbol will only have a definition in one translation unit and will have undefined references from other translation units, that symbol should not be weak. Defining this macro to be nonzero will thus have the effect that certain symbols that would normally be weak (explicit template instantiations, and vtables for polymorphic classes with noninline key methods) will instead be nonweak.

  The C++ ABI requires this macro to be zero. Define this macro for targets where full C++ ABI compliance is impossible and where linker restrictions require weak symbols to be left out of a static archive’s table of contents.

Macro: 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.

Target Hook: void TARGET_ASM_EXTERNAL_LIBCALL (rtx symref)

  This target hook is a function to output to asm_out_file an assembler pseudo-op to declare a library function name external. The name of the library function is given by symref, which is a `symbol_ref`.

Target Hook: void TARGET_ASM_MARK_DECL_PRESERVED (const char *symbol)

  This target hook is a function to output to asm_out_file an assembler directive to annotate symbol as used. The Darwin target uses the .no_dead_code_strip directive.

Macro: 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`.

Target Hook: tree TARGET_MANGLE_ASSEMBLER_NAME (const char *name)

  Given a symbol name, perform same mangling as `varasm.c`’s `assemble_name`, but in memory rather than to a file stream, returning result as an `IDENTIFIER_NODE`. Required for correct LTO symtabs. The default implementation calls the `TARGET_STRIP_NAME_ENCODING` hook and then prepends the `USER_LABEL_PREFIX`, if any.

Macro: ASM_OUTPUT_SYMBOL_REF (stream, sym)

  A C statement (sans semicolon) to output a reference to `SYMBOL_REF` sym. If not defined, `assemble_name` 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 `TARGET_ENCODE_SECTION_INFO`.

Macro: ASM_OUTPUT_LABEL_REF (stream, buf)

  A C statement (sans semicolon) to output a reference to buf, the result of `ASM_GENERATE_INTERNAL_LABEL`. If not defined, `assemble_name` will be used to output the name of the symbol. This macro is not used by `output_asm_label`, or the `%l` specifier that calls it; the intention is that this macro should be set when it is necessary to output a label differently when its address is being taken.

Target Hook: void TARGET_ASM_INTERNAL_LABEL (FILE *stream, const char *prefix, unsigned long labelno)

  A function to output to the stdio stream stream a label whose name is made from the string prefix and the number labelno.

  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 default version of this function utilizes `ASM_GENERATE_INTERNAL_LABEL`.

Macro: 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 `(*targetm.asm_out.internal_label)` will be used.

Macro: 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 `(*targetm.asm_out.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.)

Macro: 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.

  If this macro is not defined, a default definition will be provided which is correct for most systems.

Macro: 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.

Macro: 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.

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

Macro: TARGET_DEFERRED_OUTPUT_DEFS (decl_of_name, decl_of_value)

  A C statement that evaluates to true if the 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 should be emitted near the end of the current compilation unit. The default is to not defer output of defines. This macro affects defines output by ‘`ASM_OUTPUT_DEF`’ and ‘`ASM_OUTPUT_DEF_FROM_DECLS`’.

Macro: 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.

Macro: 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.

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