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From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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Subject: [RFC PATCH for 5.2 06/10] rseq/selftests: s390: use trap4 for RSEQ_SIG
Date:   Wed, 24 Apr 2019 11:24:58 -0400
Message-Id: <20190424152502.14246-7-mathieu.desnoyers@efficios.com>
In-Reply-To: <20190424152502.14246-1-mathieu.desnoyers@efficios.com>
References: <20190424152502.14246-1-mathieu.desnoyers@efficios.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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

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

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 tools/testing/selftests/rseq/rseq-s390.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rseq/rseq-s390.h b/tools/testing/selftests/rseq/rseq-s390.h
index 7c4f3a70b6c7..1d05c5187ae6 100644
--- 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()
-- 
2.11.0