linux-kernel - Re: [RFC][PATCH 01/22] x86 user stack frame reads: switch to explicit __get

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Message-ID: <CAHk-=wiTXXVn=Zxn4kYMG8sOJr0xL+6TzdVzi+XhAdx2Pu0UBg@mail.gmail.com>
Date:   Sun, 29 Mar 2020 11:55:33 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC][PATCH 01/22] x86 user stack frame reads: switch to explicit __get_user()

On Sun, Mar 29, 2020 at 11:32 AM David Laight <David.Laight@...lab.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