On Hardened we add some options like -fstack-clash-protection.

--- a/gcc/common.opt	2018-03-28 16:51:09.000000000 +0200
+++ a/gcc/common.opt	2018-04-30 15:35:55.274096877 +0200
@@ -2367,7 +2367,7 @@ Common Alias(fstack-check=, specific, no
 Insert stack checking code into the program.  Same as -fstack-check=specific.
 
 fstack-clash-protection
-Common Report Var(flag_stack_clash_protection) Optimization
+Common Report Var(flag_stack_clash_protection) Optimization Init(-1)
 Insert code to probe each page of stack space as it is allocated to protect
 from stack-clash style attacks.
 
--- a/gcc/defaults.h	2018-01-03 11:03:58.000000000 +0100
+++ b/gcc/defaults.h	2018-05-01 12:41:29.522851451 +0200
@@ -1435,6 +1435,15 @@ see the files COPYING3 and COPYING.RUNTI
 #define STACK_CHECK_MAX_VAR_SIZE (STACK_CHECK_MAX_FRAME_SIZE / 100)
 #endif
 
+/* Default value for flag_clash_protector when flag_clash_protector is
+   initialized to -1.  */
+#ifdef EXTRA_OPTIONS
+#define DEFAULT_FLAG_SCP 1
+#endif
+#ifndef DEFAULT_FLAG_SCP
+#define DEFAULT_FLAG_SCP 0
+#endif
+
 /* By default, the C++ compiler will use function addresses in the
    vtable entries.  Setting this nonzero tells the compiler to use
    function descriptors instead.  The value of this macro says how
--- a/gcc/toplev.c	2018-02-13 17:18:37.000000000 +0100
+++ b/gcc/toplev.c	2018-04-30 16:46:37.244027303 +0200
@@ -1682,6 +1682,10 @@ process_options (void)
 
   /* -fstack-clash-protection is not currently supported on targets
      where the stack grows up.  */
+  if (flag_stack_clash_protection == -1)
+    {
+      flag_stack_clash_protection = DEFAULT_FLAG_SCP;
+    }
   if (flag_stack_clash_protection && !STACK_GROWS_DOWNWARD)
     {
       warning_at (UNKNOWN_LOCATION, 0,

--- a/libgcc/Makefile.in	2011-11-22 04:01:02.000000000 +0100
+++ b/libgcc/Makefile.in	2011-12-25 15:18:22.449610631 +0100
@@ -225,7 +225,7 @@ endif
 LIBGCC2_DEBUG_CFLAGS = -g
 LIBGCC2_CFLAGS = -O2 $(LIBGCC2_INCLUDES) $(GCC_CFLAGS) $(HOST_LIBGCC2_CFLAGS) \
 		 $(LIBGCC2_DEBUG_CFLAGS) -DIN_LIBGCC2 \
-		 -fbuilding-libgcc -fno-stack-protector \
+		 -fbuilding-libgcc -fno-stack-protector -fno-stack-clash-protection \
 		 $(INHIBIT_LIBC_CFLAGS)
 
 # Additional options to use when compiling libgcc2.a.
@@ -279,7 +290,7 @@ INTERNAL_CFLAGS = $(CFLAGS) $(LIBGCC2_CF
   $(NO_PIE_CFLAGS) -finhibit-size-directive -fno-inline -fno-exceptions \
   -fno-zero-initialized-in-bss -fno-toplevel-reorder -fno-tree-vectorize \
   -fbuilding-libgcc -fno-stack-protector $(FORCE_EXPLICIT_EH_REGISTRY) \
-  $(INHIBIT_LIBC_CFLAGS) $(USE_TM_CLONE_REGISTRY)
+  -fno-stack-clash-protection $(INHIBIT_LIBC_CFLAGS) $(USE_TM_CLONE_REGISTRY)
 
 # Extra flags to use when compiling crt{begin,end}.o.
 CRTSTUFF_T_CFLAGS =