4 files changed, 21 insertions, 13 deletions
diff --git a/compiler-rt/lib/hwasan/hwasan_thread.cpp b/compiler-rt/lib/hwasan/hwasan_thread.cpp
index 46dcddd4288..cabf614c005 100644
--- a/compiler-rt/lib/hwasan/hwasan_thread.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_thread.cpp
@@ -27,6 +27,11 @@ static u32 RandomSeed() {
 
 void Thread::InitRandomState() {
   random_state_ = flags()->random_tags ? RandomSeed() : unique_id_;
+
+  // Push a random number of zeros onto the ring buffer so that the first stack
+  // tag base will be random.
+  for (tag_t i = 0, e = GenerateRandomTag(); i != e; ++i)
+    stack_allocations_->push(0);
 }
 
 void Thread::Init(uptr stack_buffer_start, uptr stack_buffer_size) {
diff --git a/compiler-rt/test/hwasan/TestCases/random-align-right.c b/compiler-rt/test/hwasan/TestCases/random-align-right.c
index 8c524ef4784..e6e634179b8 100644
--- a/compiler-rt/test/hwasan/TestCases/random-align-right.c
+++ b/compiler-rt/test/hwasan/TestCases/random-align-right.c
@@ -1,9 +1,11 @@
 // Tests malloc_align_right=1 and 8 (randomly aligning right).
 // RUN: %clang_hwasan  %s -o %t
 //
-// RUN: %run %t
-// RUN: %env_hwasan_opts=malloc_align_right=1 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK1
-// RUN: %env_hwasan_opts=malloc_align_right=8 not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK8
+// RUN: %run %t 20
+// RUN: %run %t 30
+// RUN: %env_hwasan_opts=malloc_align_right=1 not %run %t 20 2>&1 | FileCheck %s --check-prefix=CHECK20
+// RUN: %env_hwasan_opts=malloc_align_right=1 not %run %t 30 2>&1 | FileCheck %s --check-prefix=CHECK30
+// RUN: %env_hwasan_opts=malloc_align_right=8 not %run %t 30 2>&1 | FileCheck %s --check-prefix=CHECK30
 
 // REQUIRES: stable-runtime
 
@@ -15,6 +17,7 @@ static volatile void *sink;
 
 int main(int argc, char **argv) {
   __hwasan_enable_allocator_tagging();
+  int index = atoi(argv[1]);
 
   // Perform 1000 buffer overflows within the 16-byte granule,
   // so that random right-alignment has a very high chance of
@@ -22,14 +25,11 @@ int main(int argc, char **argv) {
   for (int i = 0; i < 1000; i++) {
     char *p = (char*)malloc(20);
     sink = p;
-    fprintf(stderr, "[%d] p: %p; accessing p[20]:\n", i, p);
-    p[20 * argc] = 0;  // requires malloc_align_right=1 to catch
-    fprintf(stderr, "[%d] p: %p; accessing p[30]:\n", i, p);
-    p[30 * argc] = 0;  // requires malloc_align_right={1,8} to catch
-// CHECK1: accessing p[20]
-// CHECK1-NEXT: HWAddressSanitizer: tag-mismatch
-// CHECK8: accessing p[30]:
-// CHECK8-NEXT: HWAddressSanitizer: tag-mismatch
+    p[index] = 0;
+// index=20 requires malloc_align_right=1 to catch
+// CHECK20: HWAddressSanitizer: tag-mismatch
+// index=30 requires malloc_align_right={1,8} to catch
+// CHECK30: HWAddressSanitizer: tag-mismatch
   }
 }
 
diff --git a/compiler-rt/test/hwasan/TestCases/stack-history-length.c b/compiler-rt/test/hwasan/TestCases/stack-history-length.c
index 0aefd40bebb..584046ee6ce 100644
--- a/compiler-rt/test/hwasan/TestCases/stack-history-length.c
+++ b/compiler-rt/test/hwasan/TestCases/stack-history-length.c
@@ -1,5 +1,5 @@
 // RUN: %clang_hwasan -O1 %s -o %t
-// RUN: %env_hwasan_opts=stack_history_size=2048 not %run %t 2046 2>&1 | FileCheck %s --check-prefix=YES
+// RUN: %env_hwasan_opts=stack_history_size=2048 not %run %t 2045 2>&1 | FileCheck %s --check-prefix=YES
 // RUN: %env_hwasan_opts=stack_history_size=2048 not %run %t 2047 2>&1 | FileCheck %s --check-prefix=NO
 
 // REQUIRES: stable-runtime
@@ -22,6 +22,9 @@ int main(int argc, char **argv) {
   FUNC0();
   for (int i = 0; i < X; ++i)
     FUNC();
+  // Make at least one call to OOB where base tag != 0 so that the bug is caught
+  // at least once.
+  OOB();
   OOB();
 }
 
diff --git a/compiler-rt/test/hwasan/lit.cfg b/compiler-rt/test/hwasan/lit.cfg
index 66008a632bc..b9f98208171 100644
--- a/compiler-rt/test/hwasan/lit.cfg
+++ b/compiler-rt/test/hwasan/lit.cfg
@@ -11,7 +11,7 @@ config.test_source_root = os.path.dirname(__file__)
 # Setup default compiler flags used with -fsanitize=memory option.
 clang_cflags = [config.target_cflags] + config.debug_info_flags
 clang_cxxflags = config.cxx_mode_flags + clang_cflags
-clang_hwasan_cflags = ["-fsanitize=hwaddress", "-mllvm", "-hwasan-generate-tags-with-calls"] + clang_cflags
+clang_hwasan_cflags = ["-fsanitize=hwaddress"] + clang_cflags
 clang_hwasan_cxxflags = config.cxx_mode_flags + clang_hwasan_cflags
 
 def build_invocation(compile_flags):