linux-kernel - Re: [PATCH] x86/vdso: fix lsl operand order

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Message-ID: <CALCETrXeeW0RhJws0oLQAHomZ539B00PL=_NtPGOsfd=aw+TTw@mail.gmail.com>
Date:   Sat, 1 Sep 2018 13:43:52 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Samuel Neves <sneves@....uc.pt>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] x86/vdso: fix lsl operand order

On Sat, Sep 1, 2018 at 1:14 PM, Samuel Neves <sneves@....uc.pt> wrote:
> In the __getcpu function, lsl was using the wrong target
> and destination registers. Luckily, the compiler tends to
> choose %eax for both variables, so it has been working
> so far.
>
> Cc: x86@...nel.org
> Cc: stable@...r.kernel.org
> Signed-off-by: Samuel Neves <sneves@....uc.pt>

Acked-by: Andy Lutomirski <luto@...nel.org>
Fixes: a582c540ac1b ("x86/vdso: Use RDPID in preference to LSL when available")

Whoops!  I even wrote a selftest just for the offending commit, but,
of course, the selftest passes :(  I tested this by giving gcc some
gentle encouragement to allocate different registers, and the existing
code is indeed wrong and the fix indeed fixes it.

--Andy