New configure option to default enable Smart Stack Protection

--- a/gcc/configure.ac	2014-12-05 00:53:24.000000000 +0100
+++ b/gcc/configure.ac	2015-06-08 23:27:11.744348211 +0200
@@ -5221,6 +5119,25 @@  if test x$gcc_cv_libc_provides_ssp = xye
 	    [Define if your target C library provides stack protector support])
 fi
 
+# Check whether --enable-default-ssp was given.
+AC_ARG_ENABLE(default-ssp,
+[AS_HELP_STRING([--enable-default-ssp],
+  [enable Smart Stack Protection as default])],[
+if test x$gcc_cv_libc_provides_ssp = xyes; then
+  case "$target" in
+    ia64*-*-*) enable_default_ssp=no ;;
+    *) enable_default_ssp=$enableval ;;
+  esac
+else
+  enable_default_ssp=no
+fi],
+enable_default_ssp=no)
+if test x$enable_default_ssp == xyes ; then
+  AC_DEFINE(ENABLE_DEFAULT_SSP, 1,
+      [Define if your target supports default stack protector and it is enabled.])
+fi
+AC_SUBST([enable_default_ssp])
+
 # Test for <sys/sdt.h> on the target.
 GCC_TARGET_TEMPLATE([HAVE_SYS_SDT_H])
 AC_MSG_CHECKING(sys/sdt.h in the target C library)
--- a/gcc/defaults.h	2014-11-01 09:13:09.000000000 +0100
+++ b/gcc/defaults.h	2015-06-08 22:43:18.764269749 +0200
@@ -1263,6 +1263,18 @@  see the files COPYING3 and COPYING.RUNTI
 #define STACK_SIZE_MODE word_mode
 #endif
 
+/* Default value for flag_stack_protect when flag_stack_protect is initialized to -1:
+   --enable-default-ssp: Default flag_stack_protect to -fstack-protector-strong.
+   --disable-default-ssp: Default flag_stack_protect to 0.
+ */
+#ifdef ENABLE_DEFAULT_SSP
+# ifndef DEFAULT_FLAG_SSP
+#  define DEFAULT_FLAG_SSP 3
+# endif
+#else
+# define DEFAULT_FLAG_SSP 0
+#endif
+
 /* Provide default values for the macros controlling stack checking.  */
 
 /* The default is neither full builtin stack checking...  */
--- a/gcc/common.opt	2014-10-28 11:33:04.000000000 +0100
+++ b/gcc/common.opt	2015-06-08 22:41:30.114266512 +0200
@@ -2054,15 +2054,15 @@  Common RejectNegative Joined Var(common_
 -fstack-limit-symbol=<name>	Trap if the stack goes past symbol <name>
 
 fstack-protector
-Common Report Var(flag_stack_protect, 1)
+Common Report Var(flag_stack_protect, 1) Init(-1)
 Use propolice as a stack protection method
 
 fstack-protector-all
-Common Report RejectNegative Var(flag_stack_protect, 2)
+Common Report RejectNegative Var(flag_stack_protect, 2) Init(-1)
 Use a stack protection method for every function
 
 fstack-protector-strong
-Common Report RejectNegative Var(flag_stack_protect, 3)
+Common Report RejectNegative Var(flag_stack_protect, 3) Init(-1)
 Use a smart stack protection method for certain functions
 
 fstack-protector-explicit
-Common Report RejectNegative Var(flag_stack_protect, 4)
+Common Report RejectNegative Var(flag_stack_protect, 4) Init(-1)
 Use stack protection method only for functions with the stack_protect attribute
 
 fstack-usage
--- a/gcc/opts.c	2015-06-10 02:37:39.000000000 +0200
+++ b/gcc/opts.c	2015-07-03 23:47:50.868752099 +0200
@@ -757,6 +757,11 @@  finish_options (struct gcc_options *opts
       opts->x_flag_opts_finished = true;
     }
 
+  /* We initialize opts->x_flag_stack_protect to -1 so that targets
+     can set a default value.  */
+  if (opts->x_flag_stack_protect == -1)
+    opts->x_flag_stack_protect = DEFAULT_FLAG_SSP;
+
   if (opts->x_optimize == 0)
     {
       /* Inlining does not work if not optimizing,
--- a/gcc/doc/install.texi	2015-06-03 18:38:10.000000000 +0200
+++ bgcc/doc/install.texi	2015-07-03 22:18:41.498592691 +0200
@@ -1642,6 +1642,9 @@  Using the GNU Compiler Collection (GCC)}
 See ``RS/6000 and PowerPC Options'' in the main manual
 @end ifhtml
 
+@item --enable-default-ssp
+Turn on @option{-fstack-protector-strong} by default.
+
 @item --enable-cld
 This option enables @option{-mcld} by default for 32-bit x86 targets.
 @ifnothtml
--- a/gcc/testsuite/lib/target-supports.exp	2015-05-21 15:30:24.000000000 +0200
+++ b/gcc/testsuite/lib/target-supports.exp	2015-07-03 21:55:53.748551933 +0200
@@ -1124,6 +1124,16 @@  proc check_effective_target_pie_enabled
     }]
 }
 
+# Return 1 if the target generates -fstack-protector by default.
+
+proc check_effective_target_fstack_protector_enabled {} {
+    return [ check_no_compiler_messages fstack_protector_enabled assembly {
+    #if !defined (__SSP__) || !defined (__SSP_ALL__) || !defined (__SSP_STRONG__) || !defined (__SSP_EXPICIT__)
+    #error unsupported
+    #endif
+    }]
+}
+
 # Return 1 if the target does not use a status wrapper.
 
 proc check_effective_target_unwrapped { } {
--- a/gcc/testsuite/gcc.target/i386/ssp-default.c	2015-02-24 22:14:09.930176831 +0100
+++ b/gcc/testsuite/gcc.target/i386/ssp-default.c	2015-07-04 13:45:43.930250213 +0200
@@ -0,0 +1,22 @@ 
+/* { dg-do run { target native } } */
+/* { dg-require-effective-target fstack_protector_enabled } */
+
+#include <stdlib.h>
+
+void
+__stack_chk_fail (void)
+{
+  exit (0); /* pass */
+}
+
+int main ()
+{
+  int i;
+  char foo[255];
+
+  /* smash stack */
+  for (i = 0; i <= 400; i++)
+    foo[i] = 42;
+
+  return 1; /* fail */
+}