Index: test/tsan/Darwin/gcd-fd.mm
===================================================================
--- test/tsan/Darwin/gcd-fd.mm
+++ test/tsan/Darwin/gcd-fd.mm
@@ -17,8 +17,8 @@
       0666, queue, ^(int error) { });
   dispatch_io_set_high_water(channel, 1);
 
-  NSData *ns_data = [NSMutableData dataWithLength:1000];
-  dispatch_data_t data = dispatch_data_create(ns_data.bytes, ns_data.length, NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
+  char buf[1000];
+  dispatch_data_t data = dispatch_data_create(buf, sizeof(buf), NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
 
   my_global++;
   dispatch_io_write(channel, 0, data, queue, ^(bool done, dispatch_data_t remainingData, int error) {
Index: test/tsan/Darwin/gcd-io-barrier-race.mm
===================================================================
--- test/tsan/Darwin/gcd-io-barrier-race.mm
+++ test/tsan/Darwin/gcd-io-barrier-race.mm
@@ -21,8 +21,8 @@
   sem = dispatch_semaphore_create(0);
   NSString *ns_path = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"temp-gcd-io.%d", getpid()]];
   path = ns_path.fileSystemRepresentation;
-  NSData *ns_data = [NSMutableData dataWithLength:1000];
-  data = dispatch_data_create(ns_data.bytes, ns_data.length, NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
+  char buf[1000];
+  data = dispatch_data_create(buf, sizeof(buf), NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
   
   dispatch_io_t channel = dispatch_io_create_with_path(DISPATCH_IO_STREAM, path, O_CREAT | O_WRONLY, 0666, queue, ^(int error) { });
   if (! channel) abort();
Index: test/tsan/Darwin/gcd-io-barrier.mm
===================================================================
--- test/tsan/Darwin/gcd-io-barrier.mm
+++ test/tsan/Darwin/gcd-io-barrier.mm
@@ -17,8 +17,8 @@
   sem = dispatch_semaphore_create(0);
   NSString *ns_path = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"temp-gcd-io.%d", getpid()]];
   path = ns_path.fileSystemRepresentation;
-  NSData *ns_data = [NSMutableData dataWithLength:1000];
-  data = dispatch_data_create(ns_data.bytes, ns_data.length, NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
+  char buf[1000];
+  data = dispatch_data_create(buf, sizeof(buf), NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
   
   dispatch_io_t channel = dispatch_io_create_with_path(DISPATCH_IO_STREAM, path, O_CREAT | O_WRONLY, 0666, queue, ^(int error) { });
   if (! channel) abort();
Index: test/tsan/Darwin/gcd-io-race.mm
===================================================================
--- test/tsan/Darwin/gcd-io-race.mm
+++ test/tsan/Darwin/gcd-io-race.mm
@@ -23,8 +23,8 @@
   sem = dispatch_semaphore_create(0);
   NSString *ns_path = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"temp-gcd-io.%d", getpid()]];
   path = ns_path.fileSystemRepresentation;
-  NSData *ns_data = [NSMutableData dataWithLength:1000];
-  data = dispatch_data_create(ns_data.bytes, ns_data.length, NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
+  char buf[1000];
+  data = dispatch_data_create(buf, sizeof(buf), NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
   
   dispatch_io_t channel = dispatch_io_create_with_path(DISPATCH_IO_STREAM, path, O_CREAT | O_WRONLY, 0666, queue, ^(int error) { });
   if (! channel) abort();
Index: test/tsan/Darwin/gcd-io.mm
===================================================================
--- test/tsan/Darwin/gcd-io.mm
+++ test/tsan/Darwin/gcd-io.mm
@@ -100,8 +100,8 @@
   sem = dispatch_semaphore_create(0);
   NSString *ns_path = [NSTemporaryDirectory() stringByAppendingPathComponent:[NSString stringWithFormat:@"temp-gcd-io.%d", getpid()]];
   path = ns_path.fileSystemRepresentation;
-  NSData *ns_data = [NSMutableData dataWithLength:1000];
-  data = dispatch_data_create(ns_data.bytes, ns_data.length, NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
+  char buf[1000];
+  data = dispatch_data_create(buf, sizeof(buf), NULL, DISPATCH_DATA_DESTRUCTOR_DEFAULT);
   
   test_dispatch_io_write();
   test_dispatch_write();