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>