Messages in this thread | ![/](/images/icornerl.gif) | | From | Zhangjin Wu <> | Subject | Re: [PATCH v1 0/1] Fix a stack misalign bug on _start | Date | Sat, 26 Aug 2023 23:20:24 +0800 |
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Hi, Ammar
> 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). >
Yeah, I have learned carefully about the old 'sub $4, %esp' instruction for the old 3 'push' instructions, but at last forgot to add a new instruction for the new single 'push' instruction to reserve the 16-byte alignment, very sorry for this bad regression.
> $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 () >
Since we have a new 'startup' test group, do you have a short function to trigger this error?
Perhaps it is time for us to add a new 'stack alignment' test case for all of the architectures.
Thanks, Zhangjin
> Ensure the %esp is a multiple of 16 when executing the call instruction. > > Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> > --- > 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
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