Commit 2e83886c authored Oct 24, 2021 by Willy Tarreau Committed by Greg Kroah-Hartman Jan 27, 2022

tools/nolibc: i386: fix initial stack alignment

commit ebbe0d8a449d183fa43b42d84fcb248e25303985 upstream.

After re-checking in the spec and comparing stack offsets with glibc,
The last pushed argument must be 16-byte aligned (i.e. aligned before the
call) so that in the callee esp+4 is multiple of 16, so the principle is
the 32-bit equivalent to what Ammar fixed for x86_64. It's possible that
32-bit code using SSE2 or MMX could have been affected. In addition the
frame pointer ought to be zero at the deepest level.

Link: https://gitlab.com/x86-psABIs/i386-ABI/-/wikis/Intel386-psABI


Cc: Ammar Faizi <ammar.faizi@students.amikom.ac.id>
Cc: stable@vger.kernel.org
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent aca2988e

tools/include/nolibc/nolibc.h

+9 −1

Original line number	Diff line number	Diff line
		@@ -606,13 +606,21 @@ struct sys_stat_struct {
		})

		/* startup code */
		/*
		* i386 System V ABI mandates:
		* 1) last pushed argument must be 16-byte aligned.
		* 2) The deepest stack frame should be set to zero
		*
		*/
		asm(".section .text\n"
		".global _start\n"
		"_start:\n"
		"pop %eax\n" // argc (first arg, %eax)
		"mov %esp, %ebx\n" // argv[] (second arg, %ebx)
		"lea 4(%ebx,%eax,4),%ecx\n" // then a NULL then envp (third arg, %ecx)
		"and $-16, %esp\n" // x86 ABI : esp must be 16-byte aligned when
		"xor %ebp, %ebp\n" // zero the stack frame
		"and $-16, %esp\n" // x86 ABI : esp must be 16-byte aligned before
		"sub $4, %esp\n" // the call instruction (args are aligned)
		"push %ecx\n" // push all registers on the stack so that we
		"push %ebx\n" // support both regparm and plain stack modes
		"push %eax\n"