Add a "dalvik.vm.gc.overwritefree" property. When set to "true", the

VM will be given the "-Xgc:overwritefree" flag, and the GC will
clobber the memory of freed objects.

core/jni/AndroidRuntime.cpp

@@ -656,6 +656,15 @@ int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv)
         }
     }
 
+    /* enable poisoning of memory of freed objects */
+    property_get("dalvik.vm.gc.overwritefree", propBuf, "false");
+    if (strcmp(propBuf, "true") == 0) {
+        opt.optionString = "-Xgc:overwritefree";
+        mOptions.add(opt);
+    } else if (strcmp(propBuf, "false") != 0) {
+        LOGW("dalvik.vm.gc.overwritefree should be 'true' or 'false'");
+    }
+
     /* enable debugging; set suspend=y to pause during VM init */
 #ifdef HAVE_ANDROID_OS
     /* use android ADB transport */