Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

Borislav Petkov
2015-04-27T18:47:51Z

On Mon, Apr 27, 2015 at 11:12:05AM -0700, Linus Torvalds wrote:
> So if one or two cycles in this code doesn't matter, then why are we
> adding alternate instructions just to avoid a few ALU instructions and
> a conditional branch that predicts perfectly? And if it does matter,
> then the 6-byte option looks clearly better..

You know what? I haven't even measured the tree *without* Denys'
stricter RCX canonical-ness patch. All numbers so far are from 4.0+ with
tip/master ontop which has Denys' patch.

And I *should* measure once with plain 4.1-rc1 and then with Denys'
patch ontop to see whether this all jumping-thru-alternatives-hoops is
even worth it.

If nothing else, it was a nice exercise. :-)

--
Regards/Gruss,
Boris.

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