Re: [PATCH] i386: fix stack alignment for signal handlers

["Markus F.X.J. Oberhumer" <markus@oberhumer.com>]

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I've just seen that Linus has merged my second patch, so here is one more 
missing piece to fix ia64 in ia32 emulation as well.

~Markus

p.s. this patch has not been tested due to lack of hardware


Andi Kleen wrote:
> On Sunday 09 October 2005 18:54, Markus F.X.J. Oberhumer wrote:
> 
> 
>>Here is a somewhat simplified version of my previous patch with
>>updated comments.
>>
>>Attached is also a new small user-space test program which does not
>>depend on any special gcc features and should trigger the problem on all
>>machines.
> 
> 
> I already have a version of the patch in my queue, but it's not a strict 
> bugfix so it's only for after 2.6.14.
> 
> -Andi
> 
> ftp://ftp.firstfloor.org/pub/ak/x86_64/quilt-current/patches/sigframe-alignment
> 
> 

-- 
Markus Oberhumer, <markus@oberhumer.com>, http://www.oberhumer.com/

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[PATCH] i386: fix stack alignment for signal handlers (ia64)

This fixes the setup of the alignment of the signal frame, so that all
signal handlers are run with a properly aligned stack frame.

The current code "over-aligns" the stack pointer so that the stack frame
is effectively always mis-aligned by 4 bytes.  But what we really want
is that on function entry ((sp + 4) & 15) == 0, which matches what would
happen if the stack were aligned before a "call" instruction.

[ This patch fixes ia64. i386 and x86_64 are already fixed by
  git commit d347f372273c2b3d86a66e2e1c94c790c208e166 ]

Signed-off-by: Markus F.X.J. Oberhumer <markus@oberhumer.com>



Index: linux-2.6.git/arch/ia64/ia32/ia32_signal.c
===================================================================
--- linux-2.6.git.orig/arch/ia64/ia32/ia32_signal.c
+++ linux-2.6.git/arch/ia64/ia32/ia32_signal.c
@@ -810,7 +810,11 @@
 	}
 	/* Legacy stack switching not supported */
 
-	return (void __user *)((esp - frame_size) & -8ul);
+	esp -= frame_size;
+	/* Align the stack pointer according to the i386 ABI,
+	 * i.e. so that on function entry ((sp + 4) & 15) == 0. */
+	esp = ((esp + 4) & -16ul) - 4;
+	return (void __user *) esp;
 }
 
 static int