linux-kernel - Re: [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber list

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Message-Id: <98e38690-6be2-4839-99a4-148b61cc9749@www.fastmail.com>
Date:   Wed, 13 Oct 2021 09:51:04 -0700
From:   "Andy Lutomirski" <luto@...nel.org>
To:     "Willy Tarreau" <w@....eu>, "Michael Matz" <matz@...e.de>
Cc:     "Borislav Petkov" <bp@...en8.de>,
        "Ammar Faizi" <ammar.faizi@...dents.amikom.ac.id>,
        "Paul Walmsley" <paul.walmsley@...ive.com>,
        "Palmer Dabbelt" <palmer@...belt.com>,
        "Albert Ou" <aou@...s.berkeley.edu>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the clobber
 list



On Wed, Oct 13, 2021, at 9:30 AM, Willy Tarreau wrote:
> Hello Michael,
>
> On Wed, Oct 13, 2021 at 04:24:28PM +0000, Michael Matz wrote:
> (...)
>> In short:  Ammars initial claim:
>> 
>> > Linux x86-64 syscall only clobbers rax, rcx and r11 (and "memory").
>> > 
>> >   - rax for the return value.
>> >   - rcx to save the return address.
>> >   - r11 to save the rflags.
>> > 
>> > Other registers are preserved.
>> 
>> is accurate and I will clarify the psABI to make that explicit.
>
> Many thanks for this very detailed explanation! Ammar, I'll take your
> patch.

Acked-by: Andy Lutomirski <luto@...nel.org>

>
> Thanks all,
> Willy