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Subject[PATCH v1 1/1] tools/nolibc: i386: Fix a stack misalign bug on _start
Date
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@tinylab.org>
Fixes: 2ab446336b17aad362c6decee29b4efd83a01979 ("tools/nolibc: i386: shrink _start with _start_c")
Reported-by: Nicholas Rosenberg <inori@vnlx.org>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.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 */
"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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