linux-kernel - Re: [clang] stack protector and f1f029c7bf

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Message-ID: <CAKwvOdkEHqv7Ut8H6Rb+gSvfWsMHqO=E3f7yxm=06m9yEn=h6w@mail.gmail.com>
Date:   Thu, 24 May 2018 15:31:05 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     hpa@...or.com
Cc:     Alistair Strachan <astrachan@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Matthias Kaehlcke <mka@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>, sedat.dilek@...il.com,
        tstellar@...hat.com, LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...gle.com>
Subject: Re: [clang] stack protector and f1f029c7bf

On Thu, May 24, 2018 at 3:05 PM H. Peter Anvin <hpa@...or.com> wrote:
> COMPILER AR: "=rm" should NEVER generate worse code than "=r". That is
> unequivocally a compiler bug.

Filed: https://bugs.llvm.org/show_bug.cgi?id=37583

> >> You are claiming it doesn't buy us anything, but you are only looking
at
> > the paravirt case which is kind of "special" (in the short bus kind of
way),
> >
> > That's fair.  Is another possible solution to have paravirt maybe not
use
> > native_save_fl() then, but its own
non-static-inline-without-m-constraint
> > implementation?

> KERNEL AR: change native_save_fl() to an extern inline with an assembly
> out-of-line implementation, to satisfy the paravirt requirement that no
> GPRs other than %rax are clobbered.

i'm happy to add that, do you have a recommendation if it should go in an
existing .S file or a new one (and if so where/what shall I call it?).
-- 
Thanks,
~Nick Desaulniers