9.24.4 Directives to override the size of symbols
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 dla $4,sym is usually:
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
whereas the 32-bit expansion is simply:
lui $4,%hi(sym) daddiu $4,$4,%lo(sym)
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
.set sym32 directive to tell the assembler
that, from this point on, all expressions of the form
symbol or symbol + offset
have 32-bit values. For example:
.set sym32 dla $4,sym lw $4,sym+16 sw $4,sym+0x8000($4)
will cause the assembler to treat sym,
sym+0x8000 as 32-bit values. The handling of non-symbolic
addresses is not affected.
.set nosym32 ends a
.set sym32 block and
reverts to the normal behavior. It is also possible to change the
symbol size using the command-line options -msym32 and
These options and directives are always accepted, but at present, they have no effect for anything other than n64.