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From:   Alistair Strachan <astrachan@google.com>
Date:   Thu, 24 May 2018 11:48:40 -0700
Message-ID: <CANDihLFdmbE0q8Ya5YPWkRLxXEo4DR6ZRP-s+PjZDKEgoSY6rg@mail.gmail.com>
Subject: Re: [clang] stack protector and f1f029c7bf
To:     Nick Desaulniers <ndesaulniers@google.com>
Cc:     hpa@zytor.com, Manoj Gupta <manojgupta@google.com>,
        Matthias Kaehlcke <mka@google.com>,
        Greg Hackmann <ghackmann@google.com>, sedat.dilek@gmail.com,
        tstellar@redhat.com, linux-kernel@vger.kernel.org
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On Thu, May 24, 2018 at 11:24 AM Nick Desaulniers <ndesaulniers@google.com>
wrote:

> On Thu, May 24, 2018 at 11:20 AM <hpa@zytor.com> wrote:
> > A stack canary on an *inlined* function? That's bound to break things
> elsewhere too sooner or later.

> But it's *not* inlined by GCC or Clang.

FWIW, GCC can also insert a stack guard in an out-of-lined inline function,
it just doesn't for this one. The -fstack-protector and
-fstack-protector-strong flags are heuristic and the heuristic does not
match between gcc and clang for this function. It is working on GCC purely
by chance.

> While the function is marked `static inline`, it's not in
> arch/x86/kernel/paravirt.o due to:
> arch/x86/kernel/paravirt.c:326

> 325 __visible struct pv_irq_ops pv_irq_ops = {

> 326         .save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),

> see comparison of disassembly  attached in:
> https://bugs.llvm.org/attachment.cgi?id=20338
> --
> Thanks,
> ~Nick Desaulniers