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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun, 29 Mar 2020 11:55:33 -0700
Message-ID: <CAHk-=wiTXXVn=Zxn4kYMG8sOJr0xL+6TzdVzi+XhAdx2Pu0UBg@mail.gmail.com>
Subject: Re: [RFC][PATCH 01/22] x86 user stack frame reads: switch to explicit __get_user()
To:     David Laight <David.Laight@aculab.com>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Ingo Molnar <mingo@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>
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On Sun, Mar 29, 2020 at 11:32 AM David Laight <David.Laight@aculab.com> wrote:
>
> Can't you simplify that by using the =d constraint rather
> than relying on a asm register variable.

No, because that asm register variable can be 64-bit.

Which on x86-32 isn't "=d". It's "%edx:%ecx".

The asm register variable thing handles that automatically, but "=d" would not.

                Linus