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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Thu, 24 May 2018 13:52:16 -0700
Message-ID: <CAKwvOdmQER7XtO_uygYDBxGgUr-EruGyjUq9DMbNwQFh11=9gg@mail.gmail.com>
Subject: Re: [clang] stack protector and f1f029c7bf
To:     hpa@zytor.com
Cc:     Alistair Strachan <astrachan@google.com>,
        Manoj Gupta <manojgupta@google.com>,
        Matthias Kaehlcke <mka@google.com>,
        Greg Hackmann <ghackmann@google.com>, sedat.dilek@gmail.com,
        tstellar@redhat.com, LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@google.com>
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On Thu, May 24, 2018 at 1:26 PM Nick Desaulniers <ndesaulniers@google.com>
wrote:
> On Thu, May 24, 2018 at 11:59 AM <hpa@zytor.com> wrote:
> > Issue 3: Let's face it, reading and writing the flags should be
builtins,
> exactly because it has to do stack operations, which really means the
> compiler should be involved.

> I'm happy to propose that as a feature request to llvm+gcc.

Oh, looks like both clang and gcc have:
__builtin_ia32_readeflags_u64()

https://godbolt.org/g/SwPjhq

Maybe native_save_fl() and native_restore_fl() should be replaced in the
kernel with
__builtin_ia32_readeflags_u64() and __builtin_ia32_writeeflags_u64()?
-- 
Thanks,
~Nick Desaulniers