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Message-Id: <20230826163647.8178-1-falcon@tinylab.org>
Date: Sun, 27 Aug 2023 00:36:47 +0800
From: Zhangjin Wu <falcon@...ylab.org>
To: ammarfaizi2@...weeb.org
Cc: falcon@...ylab.org, gwml@...r.gnuweeb.org, inori@...x.org,
linux-kernel@...r.kernel.org, linux@...ssschuh.net,
moe@...weeb.org, w@....eu
Subject: Re: [PATCH v1 0/1] Fix a stack misalign bug on _start
Hi, Ammar
> On Sat, Aug 26, 2023 at 11:20:24PM +0800, Zhangjin Wu wrote:
> > > $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?
>
> Here is a simple program to test the stack alignment.
>
> #include "tools/include/nolibc/nolibc.h"
>
> __asm__ (
> "main:\n"
> /*
> * When the call main is executed, the
> * %esp is 16 bytes aligned.
> *
> * Then, on function entry (%esp mod 16) == 12
> * because the call instruction pushes 4 bytes
> * onto the stack.
> *
> * subl $12, %esp will make (%esp mod 16) == 0
> * again.
> */
> "subl $12, %esp\n"
>
> /*
> * These move instructions will crash if %esp is
> * not a multiple of 16.
> */
> "movdqa (%esp), %xmm0\n"
> "movdqa %xmm0, (%esp)\n"
> "movaps (%esp), %xmm0\n"
> "movaps %xmm0, (%esp)\n"
>
> "addl $12, %esp\n"
> "xorl %eax, %eax\n"
> "ret\n"
> );
>
Thanks very much for sharing this code.
> > Perhaps it is time for us to add a new 'stack alignment' test case for
> > all of the architectures.
>
> I don't know the alignment rules for other architectures (I only work on
> x86 and x86-64). While waiting for the maintainers' comment, I'll leave
> the test case decision to you. Feel free to take the above code.
>
Yes, the stack alignment rule is architecture dependent, so, we need
more discussion and more work, not sure if there is a 'C' test function
for all, let's delay this after v6.6.
> Extra:
> It's also fine if you take my patch with the 'sub $(16 - 4), %esp'
> change and batch it together in your next series.
>
Ammar, your fixup patch is urgent since our _start_c() is for v6.6-rc1 (already
in linux-next), let's wait for comments from Thomas or Willy, they will
determine that merge it directly or require a v2. I'm ok with v1 code, but the
old comment looks not that clear.
Thanks,
Zhangjin
> --
> Ammar Faizi
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