[PATCH 1/1] rseq/selftests: add __rseq_abi misalignment check

[Vasily Gorbik]

The kernel rseq syscall expects that struct rseq is 32 bytes aligned and
returns EINVAL otherwise. Even though __rseq_abi is declared as static
and proper aligned attribute is present __rseq_abi is a part of thread
local storage. It turns out that on some platforms TLS itself is not
properly aligned (at least for threads created), which is a glibc nptl
bug and should be eventually fixed and backported. But in a meanwhile
add __rseq_abi misalignment check, which would detect this situation
and skip rseq test with some user friendly message.

glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23403

Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
---
 tools/testing/selftests/rseq/rseq.c           | 19 +++++++++++++++++++
 .../testing/selftests/rseq/run_param_test.sh  |  4 ++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 4847e97ed049..50b13318395a 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -64,6 +64,23 @@ static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
 	return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
 }
 
+/*
+ * rseq syscall might fail on some platforms due to wrong alignment of TLS
+ * variables:
+ * https://sourceware.org/bugzilla/show_bug.cgi?id=23403
+ *
+ * check if glibc bug is present and skip the test in this case
+ */
+static void assert_rseq_abi_aligned()
+{
+	if ((unsigned long)&__rseq_abi & (__alignof__(__rseq_abi) - 1)) {
+		fputs("__rseq_abi is not properly aligned, which is a known \n"
+		      "glibc nptl bug (https://sourceware.org/bugzilla/show_bug.cgi?id=23403).\n"
+		      "You need a fixed version of glibc to run this test.\n", stderr);
+		exit(4); /* skip this test */
+	}
+}
+
 int rseq_register_current_thread(void)
 {
 	int rc, ret = 0;
@@ -72,6 +89,7 @@ int rseq_register_current_thread(void)
 	signal_off_save(&oldset);
 	if (refcount++)
 		goto end;
+	assert_rseq_abi_aligned();
 	rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
 	if (!rc) {
 		assert(rseq_current_cpu_raw() >= 0);
@@ -94,6 +112,7 @@ int rseq_unregister_current_thread(void)
 	signal_off_save(&oldset);
 	if (--refcount)
 		goto end;
+	assert_rseq_abi_aligned();
 	rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
 		      RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
 	if (!rc)
diff --git a/tools/testing/selftests/rseq/run_param_test.sh b/tools/testing/selftests/rseq/run_param_test.sh
index 3acd6d75ff9f..56caf5e3de3e 100755
--- a/tools/testing/selftests/rseq/run_param_test.sh
+++ b/tools/testing/selftests/rseq/run_param_test.sh
@@ -34,9 +34,9 @@ function do_tests()
 	local i=0
 	while [ "$i" -lt "${#TEST_LIST[@]}" ]; do
 		echo "Running test ${TEST_NAME[$i]}"
-		./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+		./param_test ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
 		echo "Running compare-twice test ${TEST_NAME[$i]}"
-		./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit 1
+		./param_test_compare_twice ${TEST_LIST[$i]} -r ${REPS} ${@} ${EXTRA_ARGS} || exit $?
 		let "i++"
 	done
 }
-- 
2.18.0.13.gd42ae10