[compiler-rt] 481a55a - [rtsan][Apple] Add interceptor for _os_nospin_lock_lock (#131034)

[via llvm-commits]

Author: davidtrevelyan
Date: 2025-03-13T10:18:25Z
New Revision: 481a55a3d9645a6bc1540d326319b78ad8ed8db1

URL: https://github.com/llvm/llvm-project/commit/481a55a3d9645a6bc1540d326319b78ad8ed8db1
DIFF: https://github.com/llvm/llvm-project/commit/481a55a3d9645a6bc1540d326319b78ad8ed8db1.diff

LOG: [rtsan][Apple] Add interceptor for _os_nospin_lock_lock (#131034)

Follows the discussion here:
https://github.com/llvm/llvm-project/pull/129309

Recently, the test
`TestRtsan.AccessingALargeAtomicVariableDiesWhenRealtime` has been
failing on newer MacOS versions, because the internal locking mechanism
in `std::atomic<T>::load` (for types `T` that are larger than the
hardware lock-free limit), has changed to a function that wasn't being
intercepted by rtsan.

This PR introduces an interceptor for `_os_nospin_lock_lock`, which is
the new internal locking mechanism.

_Note: we'd probably do well to introduce interceptors for
`_os_nospin_lock_unlock` (and `os_unfair_lock_unlock`) too, which also
appear to have blocking implementations. This can follow in a separate
PR._

Added: 
    

Modified: 
    compiler-rt/lib/rtsan/rtsan_interceptors_posix.cpp
    compiler-rt/lib/rtsan/tests/rtsan_test_interceptors_posix.cpp

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/rtsan/rtsan_interceptors_posix.cpp b/compiler-rt/lib/rtsan/rtsan_interceptors_posix.cpp
index cd57107450a47..5bbefa3ce43f1 100644
--- a/compiler-rt/lib/rtsan/rtsan_interceptors_posix.cpp
+++ b/compiler-rt/lib/rtsan/rtsan_interceptors_posix.cpp
@@ -30,6 +30,12 @@
 extern "C" {
 typedef int32_t OSSpinLock;
 void OSSpinLockLock(volatile OSSpinLock *__lock);
+// A pointer to this type is in the interface for `_os_nospin_lock_lock`, but
+// it's an internal implementation detail of `os/lock.c` on Darwin, and
+// therefore not available in any headers. As a workaround, we forward declare
+// it here, which is enough to facilitate interception of _os_nospin_lock_lock.
+struct _os_nospin_lock_s;
+using _os_nospin_lock_t = _os_nospin_lock_s *;
 }
 #endif // TARGET_OS_MAC
 
@@ -711,6 +717,11 @@ INTERCEPTOR(void, os_unfair_lock_lock, os_unfair_lock_t lock) {
   __rtsan_notify_intercepted_call("os_unfair_lock_lock");
   return REAL(os_unfair_lock_lock)(lock);
 }
+
+INTERCEPTOR(void, _os_nospin_lock_lock, _os_nospin_lock_t lock) {
+  __rtsan_notify_intercepted_call("_os_nospin_lock_lock");
+  return REAL(_os_nospin_lock_lock)(lock);
+}
 #define RTSAN_MAYBE_INTERCEPT_OS_UNFAIR_LOCK_LOCK                              \
   INTERCEPT_FUNCTION(os_unfair_lock_lock)
 #else

diff  --git a/compiler-rt/lib/rtsan/tests/rtsan_test_interceptors_posix.cpp b/compiler-rt/lib/rtsan/tests/rtsan_test_interceptors_posix.cpp
index 47bcafff51a4d..9ef6887a9c848 100644
--- a/compiler-rt/lib/rtsan/tests/rtsan_test_interceptors_posix.cpp
+++ b/compiler-rt/lib/rtsan/tests/rtsan_test_interceptors_posix.cpp
@@ -1122,6 +1122,25 @@ TEST(TestRtsanInterceptors, OsUnfairLockLockDiesWhenRealtime) {
   ExpectRealtimeDeath(Func, "os_unfair_lock_lock");
   ExpectNonRealtimeSurvival(Func);
 }
+
+// We intercept _os_nospin_lock_lock because it's the internal
+// locking mechanism for MacOS's atomic implementation for data
+// types that are larger than the hardware's maximum lock-free size.
+// However, it's a private implementation detail and not visible in any headers,
+// so we must duplicate the required type definitions to forward declaration
+// what we need here.
+extern "C" {
+struct _os_nospin_lock_s {
+  unsigned int oul_value;
+};
+void _os_nospin_lock_lock(_os_nospin_lock_s *);
+}
+TEST(TestRtsanInterceptors, OsNoSpinLockLockDiesWhenRealtime) {
+  _os_nospin_lock_s lock{};
+  auto Func = [&]() { _os_nospin_lock_lock(&lock); };
+  ExpectRealtimeDeath(Func, "_os_nospin_lock_lock");
+  ExpectNonRealtimeSurvival(Func);
+}
 #endif
 
 #if SANITIZER_LINUX