Lennyk <lennyk430@xxxxxxxxx> writes:
> According to the guide - the corresponding GCC translation - should
> look like this:
>
> void bswap(int* n)
> {
> asm("movl %0, %%eax" : : "g" (*n));
> asm("bswap %eax");
> asm("movl %%eax, %0" : "=g" (*n));
> }
>
> But, for some reason, the result is not a "bswapped" n.
> Why?
* What does the generated code look like?
* You shouldn't break up the asm statements like that--write one asm
with three assembler statements.
* Let the compiler do the data movement for you; it's good at it.
* If you're going to clobber %eax in an asm, you need to say so
explicitly; that's probably why this code sequence is breaking.
asm("bswap %%eax" : : : "eax");
Anyhow, I would write it like this:
void bswap(int* n)
{
asm("bswap %0" : "=r" (*n) : "0" (*n));
}
Ian
