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Message-ID: <alpine.LSU.2.20.2110141234390.3481@wotan.suse.de>
Date: Thu, 14 Oct 2021 12:44:27 +0000 (UTC)
From: Michael Matz <matz@...e.de>
To: Borislav Petkov <bp@...en8.de>
cc: Willy Tarreau <w@....eu>,
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>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] tools/nolibc: x86: Remove `r8`, `r9` and `r10` from the
clobber list
Hello,
On Wed, 13 Oct 2021, Borislav Petkov 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.
>
> Great, why are we dealing with some funky document when the law is in
> glibc sources?!
In theory, theory and practice are the same, in practice, they are not.
Usually it's good to resolve a conflict towards what the document says, or
intended to say. But glibc of course provides a huge amount of pressure
to resolve toward it ;-)
(laws are also changed toward practice when the latter overtakes :) )
Ciao,
Michael.
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