Messages in this thread | | | Date | Sat, 26 Aug 2023 22:55:07 +0700 | From | Ammar Faizi <> | Subject | Re: [PATCH v1 1/1] tools/nolibc: i386: Fix a stack misalign bug on _start |
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On Sat, Aug 26, 2023 at 11:07:04PM +0800, Zhangjin Wu wrote: > > @@ -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 */ > > Ammar, the new call of _start_c() only requires a single push, it pushes > the argument and minus %esp by 4, so, the alignment of %esp requires to > minus 12 to reserve 16-byte alignment, is this description right?
Yes, that's correct.
> If so, What about further? > > "and $-16, %esp\n" /* align stack to 16 bytes */ > "sub ($16 - $4), %esp" /* the 'push %eax' breaks stack alignment, fix up it */
The sub part should have been:
"sub $(16 - 4), %esp\n"
It's fine to me writing it that way too.
-- Ammar Faizi
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