Index: compiler-rt/lib/asan/asan_globals.cc
===================================================================
--- compiler-rt/lib/asan/asan_globals.cc
+++ compiler-rt/lib/asan/asan_globals.cc
@@ -384,6 +384,10 @@
     }
     RegisterGlobal(&globals[i]);
   }
+
+  // Poison the metadata. It should not be accessible to user code.
+  PoisonShadow(reinterpret_cast<uptr>(globals), n * sizeof(__asan_global),
+               kAsanGlobalRedzoneMagic);
 }
 
 // Unregister an array of globals.
Index: compiler-rt/test/asan/TestCases/Helpers/underflow.cc
===================================================================
--- /dev/null
+++ compiler-rt/test/asan/TestCases/Helpers/underflow.cc
@@ -0,0 +1 @@
+int YYY[3]={1,2,3};
Index: compiler-rt/test/asan/TestCases/global-underflow.cc
===================================================================
--- /dev/null
+++ compiler-rt/test/asan/TestCases/global-underflow.cc
@@ -0,0 +1,17 @@
+// RUN: %clangxx_asan -O0 %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx_asan -O1 %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx_asan -O2 %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx_asan -O3 %s %p/Helpers/underflow.cc -o %t && not %run %t 2>&1 | FileCheck %s
+
+int XXX[2] = {2, 3};
+extern int YYY[];
+#include <string.h>
+int main(int argc, char **argv) {
+  memset(XXX, 0, 2*sizeof(int));
+  // CHECK: {{READ of size 4 at 0x.* thread T0}}
+  // CHECK: {{    #0 0x.* in main .*global-underflow.cc:}}[[@LINE+3]]
+  // CHECK: {{0x.* is located 4 bytes to the left of global variable}}
+  // CHECK:   {{.*YYY.* of size 12}}
+  int res = YYY[-1];
+  return res;
+}