s390/rseq: use trap4 for RSEQ_SIG

Use trap4 as the guard instruction for the restartable sequence abort
handler.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
index 1069e85..0afdf79 100644 (file)
--- a/tools/testing/selftests/rseq/rseq-s390.h
+++ b/tools/testing/selftests/rseq/rseq-s390.h
@@ -1,6 +1,13 @@
 /* SPDX-License-Identifier: LGPL-2.1 OR MIT */
 
-#define RSEQ_SIG       0x53053053
+/*
+ * RSEQ_SIG uses the trap4 instruction. As Linux does not make use of the
+ * access-register mode nor the linkage stack this instruction will always
+ * cause a special-operation exception (the trap-enabled bit in the DUCT
+ * is and will stay 0). The instruction pattern is
+ *     b2 ff 0f ff     trap4   4095(%r0)
+ */
+#define RSEQ_SIG       0xB2FF0FFF
 
 #define rseq_smp_mb()  __asm__ __volatile__ ("bcr 15,0" ::: "memory")
 #define rseq_smp_rmb() rseq_smp_mb()