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Re: Should we compile x86-64 ld.so with -mno-sse -mno-sse?


On 11/02/2012 12:20 AM, H.J. Lu wrote:
On Thu, Nov 1, 2012 at 4:23 AM, Ondrej Bilka <neleai@seznam.cz> wrote:
On Wed, Oct 31, 2012 at 04:18:10PM -0700, H.J. Lu wrote:
On Wed, Oct 31, 2012 at 3:59 PM, Richard Henderson <rth@twiddle.net> wrote:
On 2012-11-01 03:10, Carlos O'Donell wrote:
What use case is there for not wanting to touch SEE in ld.so?

I can only imagine HJL is worried about AVX performance if the dynamic linker uses SSE insns.


That is not the main reason. We make sure that ld.so string/memory functions never touch SSE/AVX registers. It is not for performance, but for correctness. Otherwise callee will get random values in vector registers,

Or we can save and restore used xmm registers or I am missing something?

But it will introduce extra over head for every symbol lookup and it wouldn't be forward compatible with AVX since we would only save/restore 128bit SSE registers, not 256bit AVX registers.

HJ, will you work on a patch?


thanks,
Andreas
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