* Andi Kleen ([email protected]) wrote:
> Jeremy Fitzhardinge <[email protected]> writes:
> >
> > It's a pity that gas seems to generate plain 0x90 nops rather than
> > long-nop forms here. I thought it could do that.
>
> .p2align does it.
>
Sadly, p2align does not apply well to my context. I have to align on 4
bytes boundaries - 1 for the 4 bytes mov, so, if I would use p2align, I
would end up aligning on 4 bytes with p2align and then add 3 bytes
(worse case: adding 3 + 3 = 6 bytes of nops).
However, with the .org arithmetic, I can simply add then quantity of
nops needed to make my alignment on 4 bytes - 1, so the worse case
becomes adding 3 bytes.
The example is:
originally: address & 3 = 1
* p2align
p2align adds 3 bytes to align on 4 bytes boundaries
we add 3 bytes to align on the next 4 bytes - 1, so the immediate value
within the instruction is aligned on 4 bytes boundaries
* org
we add 2 bytes to be aligned on the next 4 bytes - 1.
And yes, it's a pity there is no way to produce the long-nops there. :(
Mathieu
> -Andi
--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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