Hi Willy,
This is a v2 revision.
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).
$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 ()
Ensure the %esp is a multiple of 16 when executing the call instruction.
Changes since v1:
- Change 'sub $12, %esp' to 'sub $(16 - 4), %esp' (per Zhangjin).
- Fix the reference format (per Thomas).
- Explain more about the logic behind the fix (per Thomas).
- Append an Acked-by tag from Thomas.
Signed-off-by: Ammar Faizi <[email protected]>
---
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