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From: Zhangjin Wu <[email protected]>
To: [email protected]
Cc: [email protected], [email protected], [email protected],
	[email protected], [email protected],
	[email protected], [email protected]
Subject: Re: [PATCH v1 1/1] tools/nolibc: i386: Fix a stack misalign bug on _start
Date: Sat, 26 Aug 2023 23:07:04 +0800	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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 <[email protected]>
> Fixes: 2ab446336b17aad362c6decee29b4efd83a01979 ("tools/nolibc: i386: shrink _start with _start_c")
> Reported-by: Nicholas Rosenberg <[email protected]>
> Signed-off-by: Ammar Faizi <[email protected]>
> ---
>  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

  reply	other threads:[~2023-08-26 15:07 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-26 14:16 [PATCH v1 0/1] Fix a stack misalign bug on _start Ammar Faizi
2023-08-26 14:16 ` [PATCH v1 1/1] tools/nolibc: i386: " Ammar Faizi
2023-08-26 15:07   ` Zhangjin Wu [this message]
2023-08-26 15:55     ` Ammar Faizi
2023-08-27  6:53   ` Thomas Weißschuh
2023-08-27  7:22     ` Ammar Faizi
2023-08-26 15:20 ` [PATCH v1 0/1] " Zhangjin Wu
2023-08-26 16:04   ` Ammar Faizi
2023-08-26 16:36     ` Zhangjin Wu

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