From: Willy Tarreau <w@1wt.eu>
To: David Laight <David.Laight@ACULAB.COM>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
Bedirhan KURT <windowz414@gnuweeb.org>,
Louvian Lyndal <louvianlyndal@gmail.com>,
Ammar Faizi <ammar.faizi@students.amikom.ac.id>,
Peter Cordes <peter@cordes.ca>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH 2/3] tools/nolibc: i386: fix initial stack alignment
Date: Mon, 25 Oct 2021 10:06:20 +0200 [thread overview]
Message-ID: <20211025080620.GA23398@1wt.eu> (raw)
In-Reply-To: <7e5ed287476042388779ca3c84483a92@AcuMS.aculab.com>
On Mon, Oct 25, 2021 at 07:46:11AM +0000, David Laight wrote:
> From: Willy Tarreau
> > Sent: 24 October 2021 18:28
> >
> > After re-checking in the spec and comparing stack offsets with glibc,
> > The last pushed argument must be 16-byte aligned (i.e. aligned before the
> > call) so that in the callee esp+4 is multiple of 16, so the principle is
> > the 32-bit equivalent to what Ammar fixed for x86_64. It's possible that
> > 32-bit code using SSE2 or MMX could have been affected. In addition the
> > frame pointer ought to be zero at the deepest level.
> >
> ...
> > /* startup code */
> > +/*
> > + * i386 System V ABI mandates:
> > + * 1) last pushed argument must be 16-byte aligned.
> > + * 2) The deepest stack frame should be set to zero
>
> I'm pretty sure that the historic SYSV i386 ABI only every required
> 4-byte alignment for the stack.
>
> At some point it got 'randomly' changed to 16-byte.
> I don't think this happened until after compiler support for SSE2
> intrinsics was added.
It's very possible because I've done a number of tests and noticed
that in some cases the called functions' stack doesn't seem to be
more than 4-aligned. However the deepest function in the stack starts
with an aligned stack so I prefer to follow this same rule.
Willy
next prev parent reply other threads:[~2021-10-25 8:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-24 17:28 [PATCH 0/3] nolibc fixes marked for -stable Willy Tarreau
2021-10-24 17:28 ` [PATCH 1/3] tools/nolibc: x86-64: Fix startup code bug Willy Tarreau
2021-10-24 17:28 ` [PATCH 2/3] tools/nolibc: i386: fix initial stack alignment Willy Tarreau
2021-10-25 7:46 ` David Laight
2021-10-25 8:06 ` Willy Tarreau [this message]
2021-10-25 12:48 ` David Laight
2021-10-24 17:28 ` [PATCH 3/3] tools/nolibc: fix incorrect truncation of exit code Willy Tarreau
2021-10-24 22:52 ` [PATCH 0/3] nolibc fixes marked for -stable Paul E. McKenney
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