[PATCH] PPC32: Don't oops on out-of-range system call

This patch fixes a bug on PPC where the kernel will oops if a process
does a system call and the system call number is out of range.

While fixing that, I noticed that if the process is being ptraced, an
out-of-range system call will not get traced on the way in but will on
the way out.  This patch fixes that too, by making it get traced on
the way in as well as the way out.  It turned out to be less change,
and fewer instructions overall, to do that than to make the
out-of-range system call not be traced at all.

arch/ppc/kernel/entry.S

@@ -170,8 +170,6 @@ _GLOBAL(DoSyscall)
 #ifdef SHOW_SYSCALLS
 	bl	do_show_syscall
 #endif /* SHOW_SYSCALLS */
-	cmpli	0,r0,NR_syscalls
-	bge-	66f
 	rlwinm	r10,r1,0,0,18	/* current_thread_info() */
 	lwz	r11,TI_FLAGS(r10)
 	rlwinm	r11,r11,0,~_TIF_FORCE_NOERROR
@@ -179,9 +177,11 @@ _GLOBAL(DoSyscall)
 	andi.	r11,r11,_TIF_SYSCALL_TRACE
 	bne-	syscall_dotrace
 syscall_dotrace_cont:
+	cmpli	0,r0,NR_syscalls
 	lis	r10,sys_call_table@h
 	ori	r10,r10,sys_call_table@l
 	slwi	r0,r0,2
+	bge-	66f
 	lwzx	r10,r10,r0	/* Fetch system call handler [ptr] */
 	mtlr	r10
 	addi	r9,r1,STACK_FRAME_OVERHEAD
@@ -200,7 +200,7 @@ ret_from_syscall:
 	andi.	r11,r11,_TIF_FORCE_NOERROR
 	bne	30f
 	neg	r3,r3
-22:	lwz	r10,_CCR(r1)	/* Set SO bit in CR */
+	lwz	r10,_CCR(r1)	/* Set SO bit in CR */
 	oris	r10,r10,0x1000
 	stw	r10,_CCR(r1)
 
@@ -233,8 +233,8 @@ syscall_exit_cont:
 	SYNC
 	RFI
 
-66:	li	r3,ENOSYS
-	b	22b
+66:	li	r3,-ENOSYS
+	b	ret_from_syscall
 
 	.globl	ret_from_fork
 ret_from_fork: