--- a/make/autoconf/flags-cflags.m4	Mon May 20 14:42:32 2019 +0530
+++ b/make/autoconf/flags-cflags.m4	Tue May 14 10:21:55 2019 +0200
@@ -300,6 +300,20 @@
     C_O_FLAG_DEBUG="-O0"
     C_O_FLAG_DEBUG_JVM="-O0"
     C_O_FLAG_NONE="-O0"
+    # -D_FORTIFY_SOURCE=2 hardening option needs optimization (at least -O1) enabled
+    # set for lower O-levels -U_FORTIFY_SOURCE to overwrite previous settings
+    if test "x$OPENJDK_TARGET_OS" = xlinux -a "x$DEBUG_LEVEL" = "xfastdebug"; then
+      ENABLE_FORTIFY_CFLAGS="-D_FORTIFY_SOURCE=2"
+      DISABLE_FORTIFY_CFLAGS="-U_FORTIFY_SOURCE"
+      C_O_FLAG_HIGHEST_JVM="${C_O_FLAG_HIGHEST_JVM} ${ENABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_HIGHEST="${C_O_FLAG_HIGHEST} ${ENABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_HI="${C_O_FLAG_HI} ${ENABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_NORM="${C_O_FLAG_NORM} ${ENABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_SIZE="${C_O_FLAG_SIZE} ${DISABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_DEBUG="${C_O_FLAG_DEBUG} ${DISABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_DEBUG_JVM="${C_O_FLAG_DEBUG_JVM} ${DISABLE_FORTIFY_CFLAGS}"
+      C_O_FLAG_NONE="${C_O_FLAG_NONE} ${DISABLE_FORTIFY_CFLAGS}"
+    fi
   elif test "x$TOOLCHAIN_TYPE" = xclang; then
     if test "x$OPENJDK_TARGET_OS" = xmacosx; then
       # On MacOSX we optimize for size, something

--- a/test/fmw/gtest/src/gtest.cc	Mon May 20 14:42:32 2019 +0530
+++ b/test/fmw/gtest/src/gtest.cc	Tue May 14 10:21:55 2019 +0200
@@ -34,6 +34,7 @@
 #include "gtest/internal/custom/gtest.h"
 #include "gtest/gtest-spi.h"
 
+#include <assert.h>
 #include <ctype.h>
 #include <math.h>
 #include <stdarg.h>
@@ -4388,7 +4389,8 @@
       // errors are ignored as there's nothing better we can do and we
       // don't want to fail the test because of this.
       FILE* pfile = posix::FOpen(premature_exit_filepath, "w");
-      fwrite("0", 1, 1, pfile);
+      size_t cnt= fwrite("0", 1, 1, pfile);
+      assert(cnt == (size_t)1);
       fclose(pfile);
     }
   }