rseq/selftests: powerpc code signature: generate valid instructions

Use "twui" as the guard instruction for the restartable sequence abort
handler.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <paulus@samba.org>
CC: Michael Ellerman <mpe@ellerman.id.au>
CC: Boqun Feng <boqun.feng@gmail.com>
CC: Peter Zijlstra <peterz@infradead.org>
CC: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
CC: Alan Modra <amodra@gmail.com>
CC: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/rseq/rseq-ppc.h

@@ -6,7 +6,15 @@
  * (C) Copyright 2016-2018 - Boqun Feng <boqun.feng@gmail.com>
  */
 
-#define RSEQ_SIG	0x53053053
+/*
+ * RSEQ_SIG is used with the following trap instruction:
+ *
+ * powerpc-be:    0f e5 00 0b           twui   r5,11
+ * powerpc64-le:  0b 00 e5 0f           twui   r5,11
+ * powerpc64-be:  0f e5 00 0b           twui   r5,11
+ */
+
+#define RSEQ_SIG	0x0fe5000b
 
 #define rseq_smp_mb()		__asm__ __volatile__ ("sync"	::: "memory", "cc")
 #define rseq_smp_lwsync()	__asm__ __volatile__ ("lwsync"	::: "memory", "cc")