Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64

Pavel Machek
2018-12-10T23:58:15Z

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On Thu 2018-11-29 11:11:50, Linus Torvalds wrote:
> On Thu, Nov 29, 2018 at 11:08 AM Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > What you can do then is basically add a single-byte prefix to the
> > "call" instruction that does nothing (say, cs override), and then
> > replace *that* with a 'int3' instruction.
>
> Hmm. the segment prefixes are documented as being "reserved" for
> branch instructions. I *think* that means just conditional branches
> (Intel at one point used the prefixes for static prediction
> information), not "call", but who knows..
>
> It might be better to use an empty REX prefix on x86-64 or something like that.

It might be easiest to use plain old NOP, no? :-).
Pavel
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