+GAS will call this for each fixup that passes the @code{TC_VALIDATE_FIX} test
+when @var{linkrelax} is not set. It should store the correct value in the
+object file. @code{struct fix *@var{fixP}} is the fixup @code{md_apply_fix}
+is operating on. @code{valueT *@var{valP}} is the value to store into the
+object files, or at least is the generic code's best guess. Specifically,
+*@var{valP} is the value of the fixup symbol, perhaps modified by
+@code{MD_APPLY_SYM_VALUE}, plus @code{@var{fixP}->fx_offset} (symbol addend),
+less @code{MD_PCREL_FROM_SECTION} for pc-relative fixups.
+@code{segT @var{seg}} is the section the fix is in.
+@code{fixup_segment} performs a generic overflow check on *@var{valP} after
+@code{md_apply_fix} returns. If the overflow check is relevant for the target
+machine, then @code{md_apply_fix} should modify *@var{valP}, typically to the
+value stored in the object file.
+
+@item TC_FORCE_RELOCATION (@var{fix})
+@cindex TC_FORCE_RELOCATION
+If this macro returns non-zero, it guarantees that a relocation will be emitted
+even when the value can be resolved locally, as @code{fixup_segment} tries to
+reduce the number of relocations emitted. For example, a fixup expression
+against an absolute symbol will normally not require a reloc. If undefined,
+a default of @w{@code{(S_FORCE_RELOC ((@var{fix})->fx_addsy))}} is used.
+
+@item TC_FORCE_RELOCATION_ABS (@var{fix})
+@cindex TC_FORCE_RELOCATION_ABS
+Like @code{TC_FORCE_RELOCATION}, but used only for fixup expressions against an
+absolute symbol. If undefined, @code{TC_FORCE_RELOCATION} will be used.
+
+@item TC_FORCE_RELOCATION_LOCAL (@var{fix})
+@cindex TC_FORCE_RELOCATION_LOCAL
+Like @code{TC_FORCE_RELOCATION}, but used only for fixup expressions against a
+symbol in the current section. If undefined, fixups that are not
+@code{fx_pcrel} or for which @code{TC_FORCE_RELOCATION}
+returns non-zero, will emit relocs.
+
+@item TC_FORCE_RELOCATION_SUB_SAME (@var{fix}, @var{seg})
+@cindex TC_FORCE_RELOCATION_SUB_SAME
+This macro controls resolution of fixup expressions involving the
+difference of two symbols in the same section. If this macro returns zero,
+the subtrahend will be resolved and @code{fx_subsy} set to @code{NULL} for
+@code{md_apply_fix}. If undefined, the default of
+@w{@code{! SEG_NORMAL (@var{seg})}} will be used.
+
+@item TC_FORCE_RELOCATION_SUB_ABS (@var{fix}, @var{seg})
+@cindex TC_FORCE_RELOCATION_SUB_ABS
+Like @code{TC_FORCE_RELOCATION_SUB_SAME}, but used when the subtrahend is an
+absolute symbol. If the macro is undefined a default of @code{0} is used.
+
+@item TC_FORCE_RELOCATION_SUB_LOCAL (@var{fix}, @var{seg})
+@cindex TC_FORCE_RELOCATION_SUB_LOCAL
+Like @code{TC_FORCE_RELOCATION_SUB_ABS}, but the subtrahend is a symbol in the
+same section as the fixup.
+
+@item TC_VALIDATE_FIX_SUB (@var{fix}, @var{seg})
+@cindex TC_VALIDATE_FIX_SUB
+This macro is evaluated for any fixup with a @code{fx_subsy} that
+@code{fixup_segment} cannot reduce to a number. If the macro returns
+@code{false} an error will be reported.
+
+@item TC_GLOBAL_REGISTER_SYMBOL_OK
+@cindex TC_GLOBAL_REGISTER_SYMBOL_OK
+Define this macro if global register symbols are supported. The default
+is to disallow global register symbols.
+
+@item MD_APPLY_SYM_VALUE (@var{fix})
+@cindex MD_APPLY_SYM_VALUE
+This macro controls whether the symbol value becomes part of the value passed
+to @code{md_apply_fix}. If the macro is undefined, or returns non-zero, the
+symbol value will be included. For ELF, a suitable definition might simply be
+@code{0}, because ELF relocations don't include the symbol value in the addend.
+
+@item S_FORCE_RELOC (@var{sym}, @var{strict})
+@cindex S_FORCE_RELOC
+This function returns true for symbols
+that should not be reduced to section symbols or eliminated from expressions,
+because they may be overridden by the linker. ie. for symbols that are
+undefined or common, and when @var{strict} is set, weak, or global (for ELF
+assemblers that support ELF shared library linking semantics).
+
+@item EXTERN_FORCE_RELOC
+@cindex EXTERN_FORCE_RELOC
+This macro controls whether @code{S_FORCE_RELOC} returns true for global
+symbols. If undefined, the default is @code{true} for ELF assemblers, and
+@code{false} for non-ELF.