This concerns dispatch tables.
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.
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
fprintf (stream, "\t.word L%d\n", value)
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_table_data containing an
This feature is used on system V to output a
for the table.
If this macro is not defined, these labels are output with
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.
This target hook is used to emit assembly strings required by the target after the .cfi_startproc directive. The first argument is the file stream to write the strings to and the second argument is the function’s declaration. The expected use is to add more .cfi_* directives.
The default is to not output any assembly strings.
This target hook emits a label at the beginning of each FDE. It should be defined on targets where FDEs need special labels, and it should write the appropriate label, for the FDE associated with the function declaration decl, to the stdio stream stream. The third argument, for_eh, is a boolean: true if this is for an exception table. The fourth argument, empty, is a boolean: true if this is a placeholder label for an omitted FDE.
The default is that FDEs are not given nonlocal labels.
This target hook emits a label at the beginning of the exception table. It should be defined on targets where it is desirable for the table to be broken up according to function.
The default is that no label is emitted.
If the target implements
TARGET_ASM_UNWIND_EMIT, this hook may be
used to emit a directive to install a personality hook into the unwind
info. This hook should not be used if dwarf2 unwind info is used.
This target hook emits assembly directives required to unwind the
given instruction. This is only used when
If necessary, modify personality and LSDA references to handle indirection.
The original symbol is in
origsymbol and if
pubvis is true
the symbol is visible outside the TU.
True if the
TARGET_ASM_UNWIND_EMIT hook should be called before
the assembly for insn has been emitted, false if the hook should
be called afterward.
For DWARF-based unwind frames, two CFI instructions provide for save and restore of register state. GCC maintains the current frame address (CFA) separately from the register bank but the unwinder in libgcc preserves this state along with the registers (and this is expected by the code that writes the unwind frames). This hook allows the target to specify that the CFA data is not saved/restored along with the registers by the target unwinder so that suitable additional instructions should be emitted to restore it.