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

[via llvm-commits]

https://github.com/davidtrevelyan created https://github.com/llvm/llvm-project/pull/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.

>From 6f99abc3bf1659cc677195498162015d31f3216a Mon Sep 17 00:00:00 2001
From: David Trevelyan <david.trevelyan at gmail.com>
Date: Wed, 12 Mar 2025 21:18:38 +0000
Subject: [PATCH] [rtsan][Apple] Add interceptor for _os_nospin_lock_lock

---
 .../lib/rtsan/rtsan_interceptors_posix.cpp    | 11 +++++++++++
 .../tests/rtsan_test_interceptors_posix.cpp   | 19 +++++++++++++++++++
 2 files changed, 30 insertions(+)

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