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 <[e-mail]>
CC: Benjamin Herrenschmidt <[e-mail]>
CC: Paul Mackerras <[e-mail]>
CC: Michael Ellerman <[e-mail]>
CC: Boqun Feng <[e-mail]>
CC: Peter Zijlstra <[e-mail]>
CC: "Paul E. McKenney" <[e-mail]>
CC: Alan Modra <[e-mail]>
CC: [e-mail]
Signed-off-by: Shuah Khan <[e-mail]>

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

···
  * (C) Copyright 2016-2018 - Boqun Feng <[e-mail]>
  */
 
-#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")