[PATCH] Mark unwind info for signal trampolines in vDSOs

Mark unwind info for signal trampolines using the new S augmentation flag
introduced in: http://gcc.gnu.org/PR26208.

GCC 4.2 (or patched earlier GCC) will be able to special case unwinding
through frames right above signal trampolines.  As the augmentations start
with z flag and S is at the very end of the augmentation string, older GCCs
will just skip the S flag as unknown (that's why an augmentation flag was
chosen over say a new CFA opcode).

Signed-off-by: Jakub Jelinek <jakub@redhat.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/powerpc/kernel/vdso32/sigtramp.S

@@ -261,7 +261,7 @@ V_FUNCTION_END(__kernel_sigtramp_rt32)
 .Lcie_start:
 	.long 0			/* CIE ID */
 	.byte 1			/* Version number */
-	.string "zR"		/* NUL-terminated augmentation string */
+	.string "zRS"		/* NUL-terminated augmentation string */
 	.uleb128 4		/* Code alignment factor */
 	.sleb128 -4		/* Data alignment factor */
 	.byte 67		/* Return address register column, ap */