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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 12 Oct 2020 13:57:00 -0700
Message-ID: <CAHk-=whnq+JmKsRwCbUnpZm4ZJLgaiX-KSFMkp7OeeE-RXwRGg@mail.gmail.com>
Subject: Re: [GIT PULL] x86/asm updates for v5.10
To:     Uros Bizjak <ubizjak@gmail.com>
Cc:     Borislav Petkov <bp@suse.de>, x86-ml <x86@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>
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On Mon, Oct 12, 2020 at 1:22 PM Uros Bizjak <ubizjak@gmail.com> wrote:
>
> No, this fact is not documented, although there are close to zero
> chances it will ever change. High registers are independent from their
> 8bit lowparts, but they still clobber corresponding 16bit, 32bit and
> 64bit representations. I guess this limitation is so severe that the
> compiler writers will be more than happy to document that %ah and %al
> can't be independent.

Ok, if we can get that agreed upon (and the clang people too), then I
have no concerns about the patch.

Just so that we don't have any nasty surprises in the future where
some clever compiler change ends up breaking this (very rare)
exception case.

                Linus