Index: compiler-rt/trunk/lib/esan/esan_interceptors.cpp
===================================================================
--- compiler-rt/trunk/lib/esan/esan_interceptors.cpp
+++ compiler-rt/trunk/lib/esan/esan_interceptors.cpp
@@ -45,6 +45,7 @@
 
 // We provide our own version:
 #undef SANITIZER_INTERCEPT_SIGPROCMASK
+#undef SANITIZER_INTERCEPT_PTHREAD_SIGMASK
 
 #define COMMON_INTERCEPTOR_NOTHING_IS_INITIALIZED (!EsanIsInitialized)
 
Index: compiler-rt/trunk/lib/msan/tests/msan_test.cc
===================================================================
--- compiler-rt/trunk/lib/msan/tests/msan_test.cc
+++ compiler-rt/trunk/lib/msan/tests/msan_test.cc
@@ -2579,6 +2579,14 @@
   EXPECT_NOT_POISONED(s);
 }
 
+TEST(MemorySanitizer, pthread_sigmask) {
+  sigset_t s;
+  EXPECT_POISONED(s);
+  int res = pthread_sigmask(SIG_BLOCK, 0, &s);
+  ASSERT_EQ(0, res);
+  EXPECT_NOT_POISONED(s);
+}
+
 struct StructWithDtor {
   ~StructWithDtor();
 };
Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_common_interceptors.inc
@@ -4036,6 +4036,25 @@
 #define INIT_SIGPROCMASK
 #endif
 
+#if SANITIZER_INTERCEPT_PTHREAD_SIGMASK
+INTERCEPTOR(int, pthread_sigmask, int how, __sanitizer_sigset_t *set,
+            __sanitizer_sigset_t *oldset) {
+  void *ctx;
+  COMMON_INTERCEPTOR_ENTER(ctx, pthread_sigmask, how, set, oldset);
+  if (set) COMMON_INTERCEPTOR_READ_RANGE(ctx, set, sizeof(*set));
+  // FIXME: under ASan the call below may write to freed memory and corrupt
+  // its metadata. See
+  // https://github.com/google/sanitizers/issues/321.
+  int res = REAL(pthread_sigmask)(how, set, oldset);
+  if (!res && oldset)
+    COMMON_INTERCEPTOR_WRITE_RANGE(ctx, oldset, sizeof(*oldset));
+  return res;
+}
+#define INIT_PTHREAD_SIGMASK COMMON_INTERCEPT_FUNCTION(pthread_sigmask);
+#else
+#define INIT_PTHREAD_SIGMASK
+#endif
+
 #if SANITIZER_INTERCEPT_BACKTRACE
 INTERCEPTOR(int, backtrace, void **buffer, int size) {
   void *ctx;
@@ -9595,6 +9614,7 @@
   INIT_SIGSETOPS;
   INIT_SIGPENDING;
   INIT_SIGPROCMASK;
+  INIT_PTHREAD_SIGMASK;
   INIT_BACKTRACE;
   INIT__EXIT;
   INIT_PTHREAD_MUTEX_LOCK;
Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_interceptors.h
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_interceptors.h
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_platform_interceptors.h
@@ -311,6 +311,7 @@
   (SI_FREEBSD || SI_NETBSD || SI_MAC || SI_LINUX_NOT_ANDROID || SI_SOLARIS)
 #define SANITIZER_INTERCEPT_SIGPENDING SI_POSIX
 #define SANITIZER_INTERCEPT_SIGPROCMASK SI_POSIX
+#define SANITIZER_INTERCEPT_PTHREAD_SIGMASK SI_POSIX
 #define SANITIZER_INTERCEPT_BACKTRACE \
   (SI_FREEBSD || SI_NETBSD || SI_OPENBSD || SI_LINUX_NOT_ANDROID || SI_SOLARIS)
 #define SANITIZER_INTERCEPT_GETMNTENT SI_LINUX
Index: compiler-rt/trunk/lib/tsan/rtl/tsan_interceptors.cc
===================================================================
--- compiler-rt/trunk/lib/tsan/rtl/tsan_interceptors.cc
+++ compiler-rt/trunk/lib/tsan/rtl/tsan_interceptors.cc
@@ -2221,6 +2221,7 @@
 #define NEED_TLS_GET_ADDR
 #endif
 #undef SANITIZER_INTERCEPT_TLS_GET_ADDR
+#undef SANITIZER_INTERCEPT_PTHREAD_SIGMASK
 
 #define COMMON_INTERCEPT_FUNCTION(name) INTERCEPT_FUNCTION(name)
 #define COMMON_INTERCEPT_FUNCTION_VER(name, ver)                          \