-fstack-protector-strong: Instrumentation for return slots

This patch fixes a loophole in the -fstack-protector-strong protection.
If a function call uses a return slot, the caller needs stack protector
instrumentation because the return slot is addressable. 

gcc/

2014-05-09  Florian Weimer  <fweimer@redhat.com>

	* cfgexpand.c (stack_protect_decl_p): New function, extracted from
	expand_used_vars.
	(stack_protect_return_slot_p): New function.
	(expand_used_vars): Call stack_protect_decl_p and
	stack_protect_return_slot_p for -fstack-protector-strong.

gcc/testsuite/

2014-05-09  Florian Weimer  <fweimer@redhat.com>

	* gcc.dg/fstack-protector-strong.c: Add coverage for return slots.
	* g++.dg/fstack-protector-strong.C: Likewise.
	* gcc.target/i386/ssp-strong-reg.c: New file.

From-SVN: r210275

1 files changed, 48 insertions, 16 deletions

diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index b57fac17eae..934f40d0627 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -1611,6 +1611,52 @@ record_or_union_type_has_array_p (const_tree tree_type)
   return 0;
 }
 
+/* Check if the current function has local referenced variables that
+   have their addresses taken, contain an array, or are arrays.  */
+
+static bool
+stack_protect_decl_p ()
+{
+  unsigned i;
+  tree var;
+
+  FOR_EACH_LOCAL_DECL (cfun, i, var)
+    if (!is_global_var (var))
+      {
+	tree var_type = TREE_TYPE (var);
+	if (TREE_CODE (var) == VAR_DECL
+	    && (TREE_CODE (var_type) == ARRAY_TYPE
+		|| TREE_ADDRESSABLE (var)
+		|| (RECORD_OR_UNION_TYPE_P (var_type)
+		    && record_or_union_type_has_array_p (var_type))))
+	  return true;
+      }
+  return false;
+}
+
+/* Check if the current function has calls that use a return slot.  */
+
+static bool
+stack_protect_return_slot_p ()
+{
+  basic_block bb;
+  
+  FOR_ALL_BB_FN (bb, cfun)
+    for (gimple_stmt_iterator gsi = gsi_start_bb (bb);
+	 !gsi_end_p (gsi); gsi_next (&gsi))
+      {
+	gimple stmt = gsi_stmt (gsi);
+	/* This assumes that calls to internal-only functions never
+	   use a return slot.  */
+	if (is_gimple_call (stmt)
+	    && !gimple_call_internal_p (stmt)
+	    && aggregate_value_p (TREE_TYPE (gimple_call_fntype (stmt)),
+				  gimple_call_fndecl (stmt)))
+	  return true;
+      }
+  return false;
+}
+
 /* Expand all variables used in the function.  */
 
 static rtx
@@ -1683,22 +1729,8 @@ expand_used_vars (void)
   pointer_map_destroy (ssa_name_decls);
 
   if (flag_stack_protect == SPCT_FLAG_STRONG)
-    FOR_EACH_LOCAL_DECL (cfun, i, var)
-      if (!is_global_var (var))
-	{
-	  tree var_type = TREE_TYPE (var);
-	  /* Examine local referenced variables that have their addresses taken,
-	     contain an array, or are arrays.  */
-	  if (TREE_CODE (var) == VAR_DECL
-	      && (TREE_CODE (var_type) == ARRAY_TYPE
-		  || TREE_ADDRESSABLE (var)
-		  || (RECORD_OR_UNION_TYPE_P (var_type)
-		      && record_or_union_type_has_array_p (var_type))))
-	    {
-	      gen_stack_protect_signal = true;
-	      break;
-	    }
-	}
+      gen_stack_protect_signal
+	= stack_protect_decl_p () || stack_protect_return_slot_p ();
 
   /* At this point all variables on the local_decls with TREE_USED
      set are not associated with any block scope.  Lay them out.  */