Re: [PATCH 3/4] x86/asm/entry/64: use smaller insns

Borislav Petkov
2015-03-26T09:29:01Z

On Wed, Mar 25, 2015 at 05:05:50PM -0700, Linus Torvalds wrote:
> so 'as' is clearly just stupid. It already takes the size of the
> constant into account and generates different instructions. Why not
> for the common 32-bit case too?

I think the destination register mandates which insn to use:

mov $0x12345678, %rdi
mov $0x12345678, %edi

...

15: 48 c7 c7 78 56 34 12 mov $0x12345678,%rdi
1c: bf 78 56 34 12 mov $0x12345678,%edi

and 'as' is perhaps not insolent enough to go and change it when seeing
the 32-bit constant.

--
Regards/Gruss,
Boris.

ECO tip #101: Trim your mails when you reply.
--