[PATCH] x86: Align the stack to 16-bytes before making the call

[Andrew Haley]

Applied for Neil Roberts to gcc trunk.

Andrew.


>From 89d2865bcf30bc020399a74b3053d46ef7750a28 Mon Sep 17 00:00:00 2001
From: Neil Roberts <neil@linux.intel.com>
Date: Fri, 26 Feb 2010 14:42:49 +0000
Subject: [PATCH] x86: Align the stack to 16-bytes before making the call

If gcc is targetting i686 then it will use SSE registers for the
floating point operations. It will then sometimes use 16-byte
temporary variables on the stack to store the registers and it will
use aligned instructions to access them. This will segfault if the
variable is not aligned to 16-bytes. Apparently GCC assumes that the
stack is 16-byte aligned when a function is entered and it uses this
to position its temporary variables. Therefore libffi needs to align
the stack or the called function will crash in some circumstances.

2010-07-07   Neil Roberts <neil@linux.intel.com>

	* src/x86/sysv.S (ffi_call_SYSV): Align the stack pointer to
	16-bytes.

Index: libffi/src/x86/sysv.S
===================================================================
--- libffi/src/x86/sysv.S	(revision 161921)
+++ libffi/src/x86/sysv.S	(working copy)
@@ -48,6 +48,9 @@
 	movl  16(%ebp),%ecx
 	subl  %ecx,%esp
 
+        /* Align the stack pointer to 16-bytes */
+        andl  $0xfffffff0, %esp
+
 	movl  %esp,%eax
 
 	/* Place all of the ffi_prep_args in position  */