[PATCH] KVM: selftests: Make rseq compatible with versions prior to glibc-2.30

[Liam Merwick <liam.merwick@oracle.com>]

The fix for commit e923b0537d28 ("KVM: selftests: Fix target thread to be migrated in rseq_test")
added a call to gettid() which was only added to glibc-2.30 and fails to
compile with older glibc versions.

rseq_test.c: In function 'main':
rseq_test.c:230:33: warning: implicit declaration of function 'gettid'; did you mean 'getgid'? [-Wimplicit-function-declaration]
          (void *)(unsigned long)gettid());
                                 ^~~~~~
                                 getgid

Switch the call to syscall(SYS_gettid) which was the original advice in the
gettid(2) NOTES section and which works with both new and older glibc versions.

Fixes: e923b0537d28 ("KVM: selftests: Fix target thread to be migrated in rseq_test")
Cc: stable@vger.kernel.org # v5.15
Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
---

Verified with glibc-2.28 and glibc-2.34 and ensured test case from e923b0537d28 still passes.

 tools/testing/selftests/kvm/rseq_test.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/rseq_test.c b/tools/testing/selftests/kvm/rseq_test.c
index fac248a43666..6f88da7e60be 100644
--- a/tools/testing/selftests/kvm/rseq_test.c
+++ b/tools/testing/selftests/kvm/rseq_test.c
@@ -227,7 +227,7 @@ int main(int argc, char *argv[])
 	ucall_init(vm, NULL);
 
 	pthread_create(&migration_thread, NULL, migration_worker,
-		       (void *)(unsigned long)gettid());
+		       (void *)(unsigned long)syscall(SYS_gettid));
 
 	for (i = 0; !done; i++) {
 		vcpu_run(vcpu);
-- 
2.31.1