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Message-Id: <20230826150704.7588-1-falcon@tinylab.org>
Date: Sat, 26 Aug 2023 23:07:04 +0800
From: Zhangjin Wu <falcon@...ylab.org>
To: ammarfaizi2@...weeb.org
Cc: falcon@...ylab.org, gwml@...r.gnuweeb.org, inori@...x.org,
linux-kernel@...r.kernel.org, linux@...ssschuh.net,
moe@...weeb.org, w@....eu
Subject: Re: [PATCH v1 1/1] tools/nolibc: i386: Fix a stack misalign bug on _start
Hi, Ammar, Hi, Nicholas
Thanks very much for your report and fixup, sorry for the missing alignment for
the new single one push instruction.
> The ABI mandates that the %esp register must be a multiple of 16 when
> executing a call instruction.
>
> Commit 2ab446336b17 simplified the _start function, but it didn't take
> care of the %esp alignment, causing SIGSEGV on SSE and AVX programs that
> use aligned move instruction (e.g., movdqa, movaps, and vmovdqa).
>
> Ensure the %esp is a multiple of 16 when executing the call instruction.
>
> Cc: Zhangjin Wu <falcon@...ylab.org>
> Fixes: 2ab446336b17aad362c6decee29b4efd83a01979 ("tools/nolibc: i386: shrink _start with _start_c")
> Reported-by: Nicholas Rosenberg <inori@...x.org>
> Signed-off-by: Ammar Faizi <ammarfaizi2@...weeb.org>
> ---
> tools/include/nolibc/arch-i386.h | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h
> index 64415b9fac77f996..4edf238eeac67aa2 100644
> --- a/tools/include/nolibc/arch-i386.h
> +++ b/tools/include/nolibc/arch-i386.h
> @@ -167,7 +167,8 @@ void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_
> __asm__ volatile (
> "xor %ebp, %ebp\n" /* zero the stack frame */
> "mov %esp, %eax\n" /* save stack pointer to %eax, as arg1 of _start_c */
> - "and $-16, %esp\n" /* last pushed argument must be 16-byte aligned */
> + "and $-16, %esp\n" /* align stack to 16 bytes */
> + "sub $12, %esp\n" /* last pushed argument must be 16-byte aligned */
Ammar, the new call of _start_c() only requires a single push, it pushes
the argument and minus %esp by 4, so, the alignment of %esp requires to
minus 12 to reserve 16-byte alignment, is this description right?
If so, What about further?
"and $-16, %esp\n" /* align stack to 16 bytes */
"sub ($16 - $4), %esp" /* the 'push %eax' breaks stack alignment, fix up it */
Thanks,
Zhangjin Wu
> "push %eax\n" /* push arg1 on stack to support plain stack modes too */
> "call _start_c\n" /* transfer to c runtime */
> "hlt\n" /* ensure it does not return */
> --
> Ammar Faizi
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