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tools/nolibc: i386: Fix a stack misalign bug on _start
The ABI mandates that the %esp register must be a multiple of 16 when executing a 'call' instruction. Commit2ab446336b
("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). The 'and $-16, %esp' aligns the %esp at a multiple of 16. Then 'push %eax' will subtract the %esp by 4; thus, it breaks the 16-byte alignment. Make sure the %esp is correctly aligned after the push by subtracting 12 before the push. Extra: Add 'add $12, %esp' before the 'and $-16, %esp' to avoid over-estimating for particular cases as suggested by Willy. A test program to validate the %esp alignment on _start can be found at: https://lore.kernel.org/lkml/ZOoindMFj1UKqo+s@biznet-home.integral.gnuweeb.org [ Thomas: trim Fixes tag commit id ] Cc: Zhangjin Wu <falcon@tinylab.org> Fixes:2ab446336b
("tools/nolibc: i386: shrink _start with _start_c") Reported-by: Nicholas Rosenberg <inori@vnlx.org> Acked-by: Thomas Weißschuh <linux@weissschuh.net> Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org> Reviewed-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org> Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
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@ -167,7 +167,9 @@ void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_
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__asm__ volatile (
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__asm__ volatile (
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"xor %ebp, %ebp\n" /* zero the stack frame */
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"xor %ebp, %ebp\n" /* zero the stack frame */
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"mov %esp, %eax\n" /* save stack pointer to %eax, as arg1 of _start_c */
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"mov %esp, %eax\n" /* save stack pointer to %eax, as arg1 of _start_c */
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"and $-16, %esp\n" /* last pushed argument must be 16-byte aligned */
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"add $12, %esp\n" /* avoid over-estimating after the 'and' & 'sub' below */
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"and $-16, %esp\n" /* the %esp must be 16-byte aligned on 'call' */
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"sub $12, %esp\n" /* sub 12 to keep it aligned after the push %eax */
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"push %eax\n" /* push arg1 on stack to support plain stack modes too */
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"push %eax\n" /* push arg1 on stack to support plain stack modes too */
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"call _start_c\n" /* transfer to c runtime */
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"call _start_c\n" /* transfer to c runtime */
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"hlt\n" /* ensure it does not return */
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"hlt\n" /* ensure it does not return */
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