From: Martin Schwidefsky <schwidefsky@de.ibm.com>

This patch adds support for 6 system call arguments on s390.  The first
exploiter of this will be the sys_futex system call for the
FUTEX_CMP_REQUEUE operation.  The idea is simple: use register %r7 for the
6th argument.  This can be extended to 7/8/9/...  arguments if there ever
will be the need for it.  To call the system call function in the kernel
the additional arguments needs to get stored on the stack.  8 bytes are
added to the head of struct pt_regs.  %r7 is stored to the additional field
for all system calls.  The store is hidden in a
address-generation-interlock slot, it doesn't slow down the system call
path.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>