[C, C++] Implement -Wstatic-local

[Florian Weimer <fweimer at redhat dot com>]

We sometimes deal with code bases which use static local variables to 
cut down frame size, for compatibility with legacy targets.  Obviously, 
this is bad for thread safety.  This new warning can be used to track 
down such cases once you suspect they exist.

Bootstrapped and regression-tested on x86_64-redhat-linux-gnu.  Okay for 
trunk?

--
Florian Weimer / Red Hat Product Security Team

gcc/ChangeLog:

2013-07-23  Florian Weimer  <fweimer@redhat.com>

	* doc/invoke.texi (Warning Options): Document -Wstatic-local.

c-family/ChangeLog:

2013-07-23  Florian Weimer  <fweimer@redhat.com>

	* c.opt (Wstatic-local): Add option -Wstatic-local.

c/ChangeLog:

2013-07-23  Florian Weimer  <fweimer@redhat.com>

	* c-decl.c (pushdecl): Implement -Wstatic-local.

cp/ChangeLog:

2013-07-23  Florian Weimer  <fweimer@redhat.com>

	* decl.c (cp_finish_decl): Implement -Wstatic-local.

testsuite/ChangeLog:

2013-07-23  Florian Weimer  <fweimer@redhat.com>

	* c-c++-common/Wstatic-local.c: New.
	* g++.dg/warn/Wstatic-local-1.C: New.
	* g++.dg/warn/Wstatic-local-2.C: New.

diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
index 9690a08..7b9f3a2 100644
--- a/gcc/c-family/c.opt
+++ b/gcc/c-family/c.opt
@@ -745,6 +745,10 @@ Wmaybe-uninitialized
 C ObjC C++ ObjC++ LangEnabledBy(C ObjC C++ ObjC++,Wall)
 ;
 
+Wstatic-local
+C ObjC C++ ObjC++ Warning Var(warn_static_local)
+Warn about static local variables
+
 Wunknown-pragmas
 C ObjC C++ ObjC++ Warning Var(warn_unknown_pragmas) LangEnabledBy(C ObjC C++ ObjC++,Wall, 1, 0)
 Warn about unrecognized pragmas
diff --git a/gcc/c/c-decl.c b/gcc/c/c-decl.c
index f7ae648..9c718b5 100644
--- a/gcc/c/c-decl.c
+++ b/gcc/c/c-decl.c
@@ -2608,6 +2608,14 @@ pushdecl (tree x)
 	  || DECL_INITIAL (x) || !DECL_EXTERNAL (x)))
     DECL_CONTEXT (x) = current_function_decl;
 
+  /* Optionally warn about non-const static variables declared inside
+     functions. */
+  if (current_function_decl && warn_static_local
+      && TREE_CODE (x) == VAR_DECL && TREE_STATIC (x)
+      && !TREE_READONLY (x))
+    warning_at (DECL_SOURCE_LOCATION (x), OPT_Wstatic_local,
+		"local variable declared static, but not const");
+
   /* Anonymous decls are just inserted in the scope.  */
   if (!name)
     {
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 6fe4fed..1cd3726 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6387,6 +6387,14 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
 	   non local class. Record the types it uses
 	   so that we can decide later to emit debug info for them.  */
 	record_types_used_by_current_var_decl (decl);
+
+      /* Optionally warn about static local variables which are
+	 not const. */
+      if (warn_static_local && TREE_STATIC (decl)
+	  && DECL_FUNCTION_SCOPE_P (decl)
+	  && !TREE_READONLY (decl) && TREE_CODE (type) != REFERENCE_TYPE)
+	warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wstatic_local,
+		    "local variable declared static, but not const");
     }
   else if (TREE_CODE (decl) == FIELD_DECL
 	   && TYPE_FOR_JAVA (type) && MAYBE_CLASS_TYPE_P (type))
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 3df4662..df94214 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -4393,6 +4393,13 @@ programs.
 Warn for variables that might be changed by @samp{longjmp} or
 @samp{vfork}.  This warning is also enabled by @option{-Wextra}.
 
+@item -Wstatic-local
+@opindex Wstatic-local
+@opindex Wno-static-local
+Warn for variables declared inside functions which are static, but not
+declared const.  These local variables represent potential thread
+safety hazards.
+
 @item -Wconditionally-supported @r{(C++ and Objective-C++ only)}
 @opindex Wconditionally-supported
 @opindex Wno-conditionally-supported
diff --git a/gcc/testsuite/c-c++-common/Wstatic-local.c b/gcc/testsuite/c-c++-common/Wstatic-local.c
new file mode 100644
index 0000000..a900569
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wstatic-local.c
@@ -0,0 +1,26 @@
+/* Test for -Wstatic-local */
+
+/* { dg-do compile } */
+/* { dg-options "-Wstatic-local" } */
+
+int a;
+static int b;
+const int c = 1;
+static const int d = 2;
+
+void
+g (void)
+{
+  static int v; /* { dg-warning "local variable declared static" } */
+  static const int v1 = 3;
+  static int *v2 = &v; /* { dg-warning "local variable declared static" } */
+  static const int *v3 = &v1; /* { dg-warning "local variable declared static" } */
+  static int *const v4 = &v;
+  static const char *w1 = "string"; /* { dg-warning "local variable declared static" } */
+  static const char *const w2 = "string";
+  static const char *x[] = {"string", 0};  /* { dg-warning "local variable declared static" } */
+  static const char *const x1[] = {"string", 0};
+
+  int z1;
+  const int z2 = 1;
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wstatic-local-1.C b/gcc/testsuite/g++.dg/warn/Wstatic-local-1.C
new file mode 100644
index 0000000..bf6b965
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wstatic-local-1.C
@@ -0,0 +1,27 @@
+// Test -Wstatic-local.  Also see c-c++-common/Wstatic-local.c.
+
+// { dg-do compile }
+// { dg-options "-Wstatic-local" }
+
+template <class T> void
+g1()
+{
+  static T a = T(); // { dg-warning "local variable declared static" }
+  static const T b = a;
+}
+
+template <class T> void
+g2()
+{
+  static T a = T();
+  static const T b = a;
+}
+
+void
+h()
+{
+  g1<int>();
+  g2<const int>();
+  static int a = 5; // { dg-warning "local variable declared static" }
+  static int &b = a;
+}
diff --git a/gcc/testsuite/g++.dg/warn/Wstatic-local-2.C b/gcc/testsuite/g++.dg/warn/Wstatic-local-2.C
new file mode 100644
index 0000000..6f8b2c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wstatic-local-2.C
@@ -0,0 +1,28 @@
+// Test -Wstatic-local.  Also see c-c++-common/Wstatic-local.c.
+
+// { dg-do compile }
+// { dg-options "-std=c++11 -Wstatic-local" }
+
+static constexpr int a = 1;
+
+template <class T> void
+g1()
+{
+  static constexpr T a = T();
+  static constexpr T b = a;
+}
+
+template <class T> void
+g2()
+{
+  static constexpr T a = T();
+  static constexpr T b = a;
+}
+
+void
+h()
+{
+  g1<int>();
+  static constexpr int a = 5;
+  static int b = a; // { dg-warning "local variable declared static" }
+}