linux-kernel - Re: [PATCH v2 1/1] tools/nolibc: i386: Fix a stack misalign bug on

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Date:   Tue, 29 Aug 2023 14:24:27 +0200
From:   Willy Tarreau <w@....eu>
To:     Ammar Faizi <ammarfaizi2@...weeb.org>
Cc:     Thomas Weißschuh <linux@...ssschuh.net>,
        Zhangjin Wu <falcon@...ylab.org>,
        Nicholas Rosenberg <inori@...x.org>,
        Michael William Jonathan <moe@...weeb.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] tools/nolibc: i386: Fix a stack misalign bug on
 _start

On Tue, Aug 29, 2023 at 07:17:10PM +0700, Ammar Faizi wrote:
> On Tue, Aug 29, 2023 at 08:21:47AM +0200, Willy Tarreau wrote:
> > Indeed, good catch! However if we want to do it cleany (i.e not punch a
> > 16 to 28 byes hole in the stack), we should do this instead:
> > 
> > 		add  $12, %esp   /* the stack must be aligned to 16 ... */
> > 		and  $-16, %esp  /* ... bytes after eax is pushed and ... */
> > 		sub  $12, %esp   /* ... before the call. */
> > 
> > This will only add 0 to 12 bytes depending on the existing alignment.
> > 
> > What do you think ?
> 
> Good point. I'll send a v3 revision tomorrow.

OK thanks!

> I just saw that Linus has pulled the PR from Shuah that contains this
> bug. IOW, I missed this fix for the 6.6 merge window. Let's see if it
> can go to 6.6-rc2. Or maybe sooner than that.

No worries, we all know that -rc1 gets more exposure than individual
branches and raises bugs like this one.

Cheers,
Willy