check initializer to be zero in .bss-like sections

Just like gas, which has recently learned to reject such initializers,
gcc shouldn't accept such either.

gcc/
2016-07-01  Jan Beulich  <jbeulich@suse.com>

	* varasm.c (get_variable_section): Validate initializer in
	named .bss-like sections.

gcc/testsuite/
2016-07-01  Jan Beulich  <jbeulich@suse.com>

	* gcc.dg/bss.c: New.

From-SVN: r237913

gcc/ChangeLog

+2016-07-01  Jan Beulich  <jbeulich@suse.com>
+
+	* varasm.c (get_variable_section): Validate initializer in
+	named .bss-like sections.
+
 2016-07-01  Kelvin Nilsen  <kelvin@gcc.gnu.org>
 
 	* config/rs6000/altivec.md (*altivec_vpermr_<mode>_internal):

gcc/testsuite/ChangeLog

+2016-07-01  Jan Beulich  <jbeulich@suse.com>
+
+	* gcc.dg/bss.c: New.
+
 2016-07-01  Peter Bergner  <bergner@vnet.ibm.com>
 
 	PR target/71698

gcc/testsuite/gcc.dg/bss.c

+/* Test non-zero initializers in .bss-like sections get properly refused.  */
+/* { dg-do compile } */
+/* { dg-require-named-sections "" } */
+
+int __attribute__((section(".bss.local"))) x = 1; /* { dg-error "" "zero init" } */
+int *__attribute__((section(".bss.local"))) px = &x; /* { dg-error "" "zero init" } */
+int __attribute__((section(".bss.local"))) y = 0;
+int *__attribute__((section(".bss.local"))) py = (void*)0;

gcc/varasm.c

@@ -1150,7 +1150,18 @@ get_variable_section (tree decl, bool prefer_noswitch_p)
 
   resolve_unique_section (decl, reloc, flag_data_sections);
   if (IN_NAMED_SECTION (decl))
-    return get_named_section (decl, NULL, reloc);
+    {
+      section *sect = get_named_section (decl, NULL, reloc);
+
+      if ((sect->common.flags & SECTION_BSS) && !bss_initializer_p (decl))
+	{
+	  error_at (DECL_SOURCE_LOCATION (decl),
+		    "only zero initializers are allowed in section %qs",
+		    sect->named.name);
+	  DECL_INITIAL (decl) = error_mark_node;
+	}
+      return sect;
+    }
 
   if (ADDR_SPACE_GENERIC_P (as)
       && !DECL_THREAD_LOCAL_P (decl)