[PATCH v1 0/1] Fix a stack misalign bug on _start

From: Ammar Faizi
Date: Sat Aug 26 2023 - 10:17:46 EST


Hi Willy,

Just a single quick fix.

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).

$eax : 0x56559000 → 0x00003f90
$ebx : 0x56559000 → 0x00003f90
$ecx : 0x1
$edx : 0xf7fcaaa0 → endbr32
$esp : 0xffffcdbc → 0x00000001
$ebp : 0x0
$esi : 0xffffce7c → 0xffffd096
$edi : 0x56556060 → <_start+0> xor %ebp, %ebp
$eip : 0x56556489 → <sse_pq_add+25> movaps %xmm0, 0x30(%esp)

<sse_pq_add+11> pop %eax
<sse_pq_add+12> add $0x2b85, %eax
<sse_pq_add+18> movups -0x1fd0(%eax), %xmm0
→ <sse_pq_add+25> movaps %xmm0, 0x30(%esp) <== trapping instruction
<sse_pq_add+30> movups -0x1fe0(%eax), %xmm1
<sse_pq_add+37> movaps %xmm1, 0x20(%esp)
<sse_pq_add+42> movups -0x1ff0(%eax), %xmm2
<sse_pq_add+49> movaps %xmm2, 0x10(%esp)
<sse_pq_add+54> movups -0x2000(%eax), %xmm3

[#0] Id 1, Name: "test", stopped 0x56556489 in sse_pq_add (), reason: SIGSEGV

(gdb) bt
#0 0x56556489 in sse_pq_add ()
#1 0x5655608e in main ()

Ensure the %esp is a multiple of 16 when executing the call instruction.

Signed-off-by: Ammar Faizi <ammarfaizi2@xxxxxxxxxxx>
---
Ammar Faizi (1):
tools/nolibc: i386: Fix a stack misalign bug on _start

tools/include/nolibc/arch-i386.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)


base-commit: 6269320850097903b30be8f07a5c61d9f7592393
--
Ammar Faizi