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Diffstat (limited to 'gas/doc/c-mips.texi')
| -rw-r--r-- | gas/doc/c-mips.texi | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/gas/doc/c-mips.texi b/gas/doc/c-mips.texi index 6446c92..b62b7eb 100644 --- a/gas/doc/c-mips.texi +++ b/gas/doc/c-mips.texi @@ -26,6 +26,7 @@ Assembly Language Programming'' in the same work. * MIPS Object:: ECOFF object code * MIPS Stabs:: Directives for debugging information * MIPS ISA:: Directives to override the ISA level +* MIPS symbol sizes:: Directives to override the size of symbols * MIPS autoextend:: Directives for extending MIPS 16 bit instructions * MIPS insn:: Directive to mark data as an instruction * MIPS option stack:: Directives to save and restore options @@ -197,6 +198,13 @@ identical to @samp{-march=@var{cpu}}. Record which ABI the source code uses. The recognized arguments are: @samp{32}, @samp{n32}, @samp{o64}, @samp{64} and @samp{eabi}. +@item -msym32 +@itemx -mno-sym32 +@cindex -msym32 +@cindex -mno-sym32 +Equivalent to adding @code{.set sym32} or @code{.set nosym32} to +the beginning of the assembler input. @xref{MIPS symbol sizes}. + @cindex @code{-nocpp} ignored (MIPS) @item -nocpp This option is ignored. It is accepted for command-line compatibility with @@ -297,6 +305,61 @@ not by traditional @sc{mips} debuggers (this enhancement is required to fully support C++ debugging). These directives are primarily used by compilers, not assembly language programmers! +@node MIPS symbol sizes +@section Directives to override the size of symbols + +@cindex @code{.set sym32} +@cindex @code{.set nosym32} +The n64 ABI allows symbols to have any 64-bit value. Although this +provides a great deal of flexibility, it means that some macros have +much longer expansions than their 32-bit counterparts. For example, +the non-PIC expansion of @samp{dla $4,sym} is usually: + +@smallexample +lui $4,%highest(sym) +lui $1,%hi(sym) +daddiu $4,$4,%higher(sym) +daddiu $1,$1,%lo(sym) +dsll32 $4,$4,0 +daddu $4,$4,$1 +@end smallexample + +whereas the 32-bit expansion is simply: + +@smallexample +lui $4,%hi(sym) +daddiu $4,$4,%lo(sym) +@end smallexample + +n64 code is sometimes constructed in such a way that all symbolic +constants are known to have 32-bit values, and in such cases, it's +preferable to use the 32-bit expansion instead of the 64-bit +expansion. + +You can use the @code{.set sym32} directive to tell the assembler +that, from this point on, all expressions of the form +@samp{@var{symbol}} or @samp{@var{symbol} + @var{offset}} +have 32-bit values. For example: + +@smallexample +.set sym32 +dla $4,sym +lw $4,sym+16 +sw $4,sym+0x8000($4) +@end smallexample + +will cause the assembler to treat @samp{sym}, @code{sym+16} and +@code{sym+0x8000} as 32-bit values. The handling of non-symbolic +addresses is not affected. + +The directive @code{.set nosym32} ends a @code{.set sym32} block and +reverts to the normal behavior. It is also possible to change the +symbol size using the command-line options @option{-msym32} and +@option{-mno-sym32}. + +These options and directives are always accepted, but at present, +they have no effect for anything other than n64. + @node MIPS ISA @section Directives to override the ISA level |