From: David Laight <David.Laight@ACULAB.COM>
To: 'Willy Tarreau' <w@1wt.eu>, "Paul E . McKenney" <paulmck@kernel.org>
Cc: 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 07:46:11 +0000 [thread overview]
Message-ID: <7e5ed287476042388779ca3c84483a92@AcuMS.aculab.com> (raw)
In-Reply-To: <20211024172816.17993-3-w@1wt.eu>
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.
ISTR the NetBSD found that it was gcc that moved the goalposts.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2021-10-25 7:46 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 [this message]
2021-10-25 8:06 ` Willy Tarreau
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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