[llvm-dev] llvm.read_register for %RIP on x86_64

[Kostya Serebryany via llvm-dev]

On Tue, Jan 31, 2017 at 3:11 PM, Renato Golin <renato.golin at linaro.org>
wrote:

> On 31 Jan 2017 8:58 p.m., "Kostya Serebryany" <kcc at google.com> wrote:
>
> hmm. I am not sure I understood you. The last two paragraphs seem to
> contradict each other.
> So, you recommend to extend read_register to read the PC, or
> "read_register is locked at the stack pointer as a design decision"?
>
>
> Both. :-)
>
> There was a design decision to only support SP because we had no clear
> case for anything other than the stack pointer.
>
> If you have one for the PC, it would be a much better technical decision
> to reuse the machinery that already exists, is documented and tested, than
> come up with an independent implementation.
>
> The discussion whether to support it in clang or not is orthogonal. But
> once decided that we should support reading the PC, then read_register is
> the obvious place.
>
> If the clang developers refuse the idea, then inline assembly is the only
> option that would work across compilers.
>
> Makes sense?
>

Yep, will give it a try.


>
> Cheers,
> Renato
>
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