[tip: sched/core] selftests/rseq: check if libc rseq support is registered

[tip-bot2 for Michael Jeanson]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     d1a997ba4c1bf65497d956aea90de42a6398f73a
Gitweb:        https://git.kernel.org/tip/d1a997ba4c1bf65497d956aea90de42a6398f73a
Author:        Michael Jeanson <mjeanson@xxxxxxxxxxxx>
AuthorDate:    Tue, 14 Jun 2022 11:48:30 -04:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Tue, 28 Jun 2022 09:08:28 +02:00

selftests/rseq: check if libc rseq support is registered

When checking for libc rseq support in the library constructor, don't
only depend on the symbols presence, check that the registration was
completed.

This targets a scenario where the libc has rseq support but it is not
wired for the current architecture in 'bits/rseq.h', we want to fallback
to our internal registration mechanism.

Signed-off-by: Michael Jeanson <mjeanson@xxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20220614154830.1367382-4-mjeanson@xxxxxxxxxxxx
---
 tools/testing/selftests/rseq/rseq.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 986b945..4177f95 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -111,7 +111,8 @@ void rseq_init(void)
 	libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset");
 	libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size");
 	libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags");
-	if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p) {
+	if (libc_rseq_size_p && libc_rseq_offset_p && libc_rseq_flags_p &&
+			*libc_rseq_size_p != 0) {
 		/* rseq registration owned by glibc */
 		rseq_offset = *libc_rseq_offset_p;
 		rseq_size = *libc_rseq_size_p;