From: Ammar Faizi <[email protected]>
To: "Willy Tarreau" <[email protected]>, "Thomas Weißschuh" <[email protected]>
Cc: Ammar Faizi <[email protected]>,
Zhangjin Wu <[email protected]>,
Nicholas Rosenberg <[email protected]>,
Michael William Jonathan <[email protected]>,
GNU/Weeb Mailing List <[email protected]>,
Linux Kernel Mailing List <[email protected]>
Subject: [PATCH v3 1/1] tools/nolibc: i386: Fix a stack misalign bug on _start
Date: Wed, 30 Aug 2023 08:02:23 +0700 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
The ABI mandates that the %esp register must be a multiple of 16 when
executing a 'call' instruction.
Commit 2ab446336b17 ("tools/nolibc: i386: shrink _start with _start_c")
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).
The 'and $-16, %esp' aligns the %esp at a multiple of 16. Then 'push
%eax' will subtract the %esp by 4; thus, it breaks the 16-byte
alignment. Make sure the %esp is correctly aligned after the push by
subtracting 12 before the push.
Extra:
Add 'add $12, %esp' before the 'and $-16, %esp' to avoid over-estimating
for particular cases as suggested by Willy.
A test program to validate the %esp alignment on _start can be found at:
https://lore.kernel.org/lkml/[email protected]
Cc: Zhangjin Wu <[email protected]>
Fixes: 2ab446336b17aad362c6decee29b4efd83a01979 ("tools/nolibc: i386: shrink _start with _start_c")
Reported-by: Nicholas Rosenberg <[email protected]>
Acked-by: Thomas Weißschuh <[email protected]>
Signed-off-by: Ammar Faizi <[email protected]>
---
tools/include/nolibc/arch-i386.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h
index 64415b9fac77f996..28c26a00a7625f55 100644
--- a/tools/include/nolibc/arch-i386.h
+++ b/tools/include/nolibc/arch-i386.h
@@ -167,7 +167,9 @@ 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 */
+ "add $12, %esp\n" /* avoid over-estimating after the 'and' & 'sub' below */
+ "and $-16, %esp\n" /* the %esp must be 16-byte aligned on 'call' */
+ "sub $12, %esp\n" /* sub 12 to keep it aligned after the push %eax */
"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
next prev parent reply other threads:[~2023-08-30 1:02 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-30 1:02 [PATCH v3 0/1] Fix a stack misalign bug on _start Ammar Faizi
2023-08-30 1:02 ` Ammar Faizi [this message]
2023-08-30 3:45 ` Willy Tarreau
2023-08-30 4:07 ` Alviro Iskandar Setiawan
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