[PATCH] PPC64: fix stack alignment for signal handlers

The PPC64 ABI specifies that the stack should be kept aligned to 16
bytes.  However, signal handlers on PPC64 are getting run with the stack
misaligned (sp % 16 == 8).  This patch fixes that by ensuring that the
signal frame allocated is a multiple of 16 bytes.

In addition to the PPC64 signal frame itself being of misaligned size,
the explicit alignment of the starting stack pointer is also to 8
instead of 16.  I've corrected this as well, so signal frames are
aligned even if the interrupted registers contained a misaligned stack
pointer. 
Signed-off-by: Roland McGrath <roland@redhat.com>

[ Paul Mackerras <paulus@samba.org> acked the original patch (which
  also did it for the 32-bit cases), and pointed out that the 32-bit
  cases all already did the alignment elsewhere and didn't need this.
  Patch edited down accordingly. ]
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/ppc64/kernel/signal.c

@@ -67,7 +67,7 @@ struct rt_sigframe {
 	struct siginfo info;
 	/* 64 bit ABI allows for 288 bytes below sp before decrementing it. */
 	char abigap[288];
-};
+} __attribute__ ((aligned (16)));
 
 
 /*
@@ -254,7 +254,7 @@ static inline void __user * get_sigframe(struct k_sigaction *ka, struct pt_regs
 			newsp = (current->sas_ss_sp + current->sas_ss_size);
 	}
 
-        return (void __user *)((newsp - frame_size) & -8ul);
+        return (void __user *)((newsp - frame_size) & -16ul);
 }
 
 /*