[tsan] Fix pthread_once interceptor for OS X

TSan has a re-implementation of `pthread_once` in its interceptor, which assumes that the `pthread_once_t *once_control` pointer is actually pointing to a "storage" which is zero-initialized and used for the atomic operations. However, that's not true on OS X, where pthread_once_t is a structure, that contains a header (with a magic value) and the actual storage follows after that. This patch skips the header to make the interceptor work on OS X.

Differential Revision: http://reviews.llvm.org/D14379

llvm-svn: 252160

1 files changed, 5 insertions, 1 deletions

diff --git a/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc b/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc
index 3df07e79dd7..f270f6764af 100644
--- a/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc
+++ b/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc
@@ -1293,7 +1293,11 @@ TSAN_INTERCEPTOR(int, pthread_once, void *o, void (*f)()) {
   SCOPED_INTERCEPTOR_RAW(pthread_once, o, f);
   if (o == 0 || f == 0)
     return EINVAL;
-  atomic_uint32_t *a = static_cast<atomic_uint32_t*>(o);
+  atomic_uint32_t *a;
+  if (!SANITIZER_MAC)
+    a = static_cast<atomic_uint32_t*>(o);
+  else  // On OS X, pthread_once_t has a header with a long-sized signature.
+    a = static_cast<atomic_uint32_t*>((void *)((char *)o + sizeof(long)));
   u32 v = atomic_load(a, memory_order_acquire);
   if (v == 0 && atomic_compare_exchange_strong(a, &v, 1,
                                                memory_order_relaxed)) {