[tsan] Introduce a "ignore_interceptors_accesses" option

On OS X, TSan already passes all unit and lit tests, but for real-world applications (even very simple ones), we currently produce a lot of false positive reports about data races. This makes TSan useless at this point, because the noise dominates real bugs. This introduces a runtime flag, "ignore_interceptors_accesses", off by default, which makes TSan ignore all memory accesses that happen from interceptors. This will significantly lower the coverage and miss a lot of bugs, but it eliminates most of the current false positives on OS X.

Differential Revision: http://reviews.llvm.org/D15189



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@257760 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 56 insertions, 0 deletions

diff --git a/test/tsan/Darwin/ignored-interceptors.mm b/test/tsan/Darwin/ignored-interceptors.mm
new file mode 100644
index 000000000..8a4ecf1ee
--- /dev/null
+++ b/test/tsan/Darwin/ignored-interceptors.mm
@@ -0,0 +1,56 @@
+// Check that ignore_interceptors_accesses=1 supresses reporting races from
+// system libraries on OS X. There are currently false positives coming from
+// libxpc, libdispatch, CoreFoundation and others, because these libraries use
+// TSan-invisible atomics as synchronization.
+
+// RUN: %clang_tsan %s -o %t -framework Foundation
+
+// Check that without the flag, there are false positives.
+// RUN: %deflake %run %t 2>&1 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-RACE
+
+// With ignore_interceptors_accesses=1, no races are reported.
+// RUN: %env_tsan_opts=ignore_interceptors_accesses=1 %run %t 2>&1 | FileCheck %s --check-prefix=CHECK
+
+// With ignore_interceptors_accesses=1, races in user's code are still reported.
+// RUN: %env_tsan_opts=ignore_interceptors_accesses=1 %deflake %run %t race 2>&1 | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-RACE
+
+#import <Foundation/Foundation.h>
+
+#import "../test.h"
+
+long global;
+
+void *Thread1(void *x) {
+  barrier_wait(&barrier);
+  global = 42;
+  return NULL;
+}
+
+void *Thread2(void *x) {
+  global = 43;
+  barrier_wait(&barrier);
+  return NULL;
+}
+
+int main(int argc, char *argv[]) {
+  NSLog(@"Hello world.");
+  
+  // NSUserDefaults uses XPC which triggers the false positive.
+  NSDictionary *d = [[NSUserDefaults standardUserDefaults] dictionaryRepresentation];
+  NSLog(@"d = %@", d);
+
+  if (argc > 1 && strcmp(argv[1], "race") == 0) {
+    barrier_init(&barrier, 2);
+    pthread_t t[2];
+    pthread_create(&t[0], NULL, Thread1, NULL);
+    pthread_create(&t[1], NULL, Thread2, NULL);
+    pthread_join(t[0], NULL);
+    pthread_join(t[1], NULL);
+  }
+
+  NSLog(@"Done.");
+}
+
+// CHECK: Hello world.
+// CHECK-RACE: SUMMARY: ThreadSanitizer: data race
+// CHECK: Done.