Add -ftrivial-auto-var-init option and uninitialized variable attribute.

Initialize automatic variables with either a pattern or with zeroes to increase
the security and predictability of a program by preventing uninitialized memory
disclosure and use.
GCC still considers an automatic variable that doesn't have an explicit
initializer as uninitialized, -Wuninitialized will still report warning messages
on such automatic variables.
With this option, GCC will also initialize any padding of automatic variables
that have structure or union types to zeroes.
You can control this behavior for a specific variable by using the variable
attribute "uninitialized" to control runtime overhead.

gcc/ChangeLog:

2021-09-09  qing zhao  <qing.zhao@oracle.com>

	* builtins.c (expand_builtin_memset): Make external visible.
	* builtins.h (expand_builtin_memset): Declare extern.
	* common.opt (ftrivial-auto-var-init=): New option.
	* doc/extend.texi: Document the uninitialized attribute.
	* doc/invoke.texi: Document -ftrivial-auto-var-init.
	* flag-types.h (enum auto_init_type): New enumerated type
	auto_init_type.
	* gimple-fold.c (clear_padding_type): Add one new parameter.
	(clear_padding_union): Likewise.
	(clear_padding_emit_loop): Likewise.
	(clear_type_padding_in_mask): Likewise.
	(gimple_fold_builtin_clear_padding): Handle this new parameter.
	* gimplify.c (gimple_add_init_for_auto_var): New function.
	(gimple_add_padding_init_for_auto_var): New function.
	(is_var_need_auto_init): New function.
	(gimplify_decl_expr): Add initialization to automatic variables per
	users' requests.
	(gimplify_call_expr): Add one new parameter for call to
	__builtin_clear_padding.
	(gimplify_init_constructor): Add padding initialization in the end.
	* internal-fn.c (INIT_PATTERN_VALUE): New macro.
	(expand_DEFERRED_INIT): New function.
	* internal-fn.def (DEFERRED_INIT): New internal function.
	* tree-cfg.c (verify_gimple_call): Verify calls to .DEFERRED_INIT.
	* tree-sra.c (generate_subtree_deferred_init): New function.
	(scan_function): Avoid setting cannot_scalarize_away_bitmap for
	calls to .DEFERRED_INIT.
	(sra_modify_deferred_init): New function.
	(sra_modify_function_body): Handle calls to DEFERRED_INIT specially.
	* tree-ssa-structalias.c (find_func_aliases_for_call): Likewise.
	* tree-ssa-uninit.c (warn_uninit): Handle calls to DEFERRED_INIT
	specially.
	(check_defs): Likewise.
	(warn_uninitialized_vars): Likewise.
	* tree-ssa.c (ssa_undefined_value_p): Likewise.
	* tree.c (build_common_builtin_nodes): Build tree node for
	BUILT_IN_CLEAR_PADDING when needed.

gcc/c-family/ChangeLog:

2021-09-09  qing zhao  <qing.zhao@oracle.com>

	* c-attribs.c (handle_uninitialized_attribute): New function.
	(c_common_attribute_table): Add "uninitialized" attribute.

gcc/testsuite/ChangeLog:

2021-09-09  qing zhao  <qing.zhao@oracle.com>

	* c-c++-common/auto-init-1.c: New test.
	* c-c++-common/auto-init-10.c: New test.
	* c-c++-common/auto-init-11.c: New test.
	* c-c++-common/auto-init-12.c: New test.
	* c-c++-common/auto-init-13.c: New test.
	* c-c++-common/auto-init-14.c: New test.
	* c-c++-common/auto-init-15.c: New test.
	* c-c++-common/auto-init-16.c: New test.
	* c-c++-common/auto-init-2.c: New test.
	* c-c++-common/auto-init-3.c: New test.
	* c-c++-common/auto-init-4.c: New test.
	* c-c++-common/auto-init-5.c: New test.
	* c-c++-common/auto-init-6.c: New test.
	* c-c++-common/auto-init-7.c: New test.
	* c-c++-common/auto-init-8.c: New test.
	* c-c++-common/auto-init-9.c: New test.
	* c-c++-common/auto-init-esra.c: New test.
	* c-c++-common/auto-init-padding-1.c: New test.
	* c-c++-common/auto-init-padding-2.c: New test.
	* c-c++-common/auto-init-padding-3.c: New test.
	* g++.dg/auto-init-uninit-pred-1_a.C: New test.
	* g++.dg/auto-init-uninit-pred-2_a.C: New test.
	* g++.dg/auto-init-uninit-pred-3_a.C: New test.
	* g++.dg/auto-init-uninit-pred-4.C: New test.
	* gcc.dg/auto-init-sra-1.c: New test.
	* gcc.dg/auto-init-sra-2.c: New test.
	* gcc.dg/auto-init-uninit-1.c: New test.
	* gcc.dg/auto-init-uninit-12.c: New test.
	* gcc.dg/auto-init-uninit-13.c: New test.
	* gcc.dg/auto-init-uninit-14.c: New test.
	* gcc.dg/auto-init-uninit-15.c: New test.
	* gcc.dg/auto-init-uninit-16.c: New test.
	* gcc.dg/auto-init-uninit-17.c: New test.
	* gcc.dg/auto-init-uninit-18.c: New test.
	* gcc.dg/auto-init-uninit-19.c: New test.
	* gcc.dg/auto-init-uninit-2.c: New test.
	* gcc.dg/auto-init-uninit-20.c: New test.
	* gcc.dg/auto-init-uninit-21.c: New test.
	* gcc.dg/auto-init-uninit-22.c: New test.
	* gcc.dg/auto-init-uninit-23.c: New test.
	* gcc.dg/auto-init-uninit-24.c: New test.
	* gcc.dg/auto-init-uninit-25.c: New test.
	* gcc.dg/auto-init-uninit-26.c: New test.
	* gcc.dg/auto-init-uninit-3.c: New test.
	* gcc.dg/auto-init-uninit-34.c: New test.
	* gcc.dg/auto-init-uninit-36.c: New test.
	* gcc.dg/auto-init-uninit-37.c: New test.
	* gcc.dg/auto-init-uninit-4.c: New test.
	* gcc.dg/auto-init-uninit-5.c: New test.
	* gcc.dg/auto-init-uninit-6.c: New test.
	* gcc.dg/auto-init-uninit-8.c: New test.
	* gcc.dg/auto-init-uninit-9.c: New test.
	* gcc.dg/auto-init-uninit-A.c: New test.
	* gcc.dg/auto-init-uninit-B.c: New test.
	* gcc.dg/auto-init-uninit-C.c: New test.
	* gcc.dg/auto-init-uninit-H.c: New test.
	* gcc.dg/auto-init-uninit-I.c: New test.
	* gcc.target/aarch64/auto-init-1.c: New test.
	* gcc.target/aarch64/auto-init-2.c: New test.
	* gcc.target/aarch64/auto-init-3.c: New test.
	* gcc.target/aarch64/auto-init-4.c: New test.
	* gcc.target/aarch64/auto-init-5.c: New test.
	* gcc.target/aarch64/auto-init-6.c: New test.
	* gcc.target/aarch64/auto-init-7.c: New test.
	* gcc.target/aarch64/auto-init-8.c: New test.
	* gcc.target/aarch64/auto-init-padding-1.c: New test.
	* gcc.target/aarch64/auto-init-padding-10.c: New test.
	* gcc.target/aarch64/auto-init-padding-11.c: New test.
	* gcc.target/aarch64/auto-init-padding-12.c: New test.
	* gcc.target/aarch64/auto-init-padding-2.c: New test.
	* gcc.target/aarch64/auto-init-padding-3.c: New test.
	* gcc.target/aarch64/auto-init-padding-4.c: New test.
	* gcc.target/aarch64/auto-init-padding-5.c: New test.
	* gcc.target/aarch64/auto-init-padding-6.c: New test.
	* gcc.target/aarch64/auto-init-padding-7.c: New test.
	* gcc.target/aarch64/auto-init-padding-8.c: New test.
	* gcc.target/aarch64/auto-init-padding-9.c: New test.
	* gcc.target/i386/auto-init-1.c: New test.
	* gcc.target/i386/auto-init-2.c: New test.
	* gcc.target/i386/auto-init-21.c: New test.
	* gcc.target/i386/auto-init-22.c: New test.
	* gcc.target/i386/auto-init-23.c: New test.
	* gcc.target/i386/auto-init-24.c: New test.
	* gcc.target/i386/auto-init-3.c: New test.
	* gcc.target/i386/auto-init-4.c: New test.
	* gcc.target/i386/auto-init-5.c: New test.
	* gcc.target/i386/auto-init-6.c: New test.
	* gcc.target/i386/auto-init-7.c: New test.
	* gcc.target/i386/auto-init-8.c: New test.
	* gcc.target/i386/auto-init-padding-1.c: New test.
	* gcc.target/i386/auto-init-padding-10.c: New test.
	* gcc.target/i386/auto-init-padding-11.c: New test.
	* gcc.target/i386/auto-init-padding-12.c: New test.
	* gcc.target/i386/auto-init-padding-2.c: New test.
	* gcc.target/i386/auto-init-padding-3.c: New test.
	* gcc.target/i386/auto-init-padding-4.c: New test.
	* gcc.target/i386/auto-init-padding-5.c: New test.
	* gcc.target/i386/auto-init-padding-6.c: New test.
	* gcc.target/i386/auto-init-padding-7.c: New test.
	* gcc.target/i386/auto-init-padding-8.c: New test.
	* gcc.target/i386/auto-init-padding-9.c: New test.

1 files changed, 27 insertions, 0 deletions

diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index d14e9c4..007b928 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -83,6 +83,7 @@ static tree handle_artificial_attribute (tree *, tree, tree, int, bool *);
 static tree handle_flatten_attribute (tree *, tree, tree, int, bool *);
 static tree handle_error_attribute (tree *, tree, tree, int, bool *);
 static tree handle_used_attribute (tree *, tree, tree, int, bool *);
+static tree handle_uninitialized_attribute (tree *, tree, tree, int, bool *);
 static tree handle_externally_visible_attribute (tree *, tree, tree, int,
 						 bool *);
 static tree handle_no_reorder_attribute (tree *, tree, tree, int,
@@ -333,6 +334,8 @@ const struct attribute_spec c_common_attribute_table[] =
 			      handle_used_attribute, NULL },
   { "unused",                 0, 0, false, false, false, false,
 			      handle_unused_attribute, NULL },
+  { "uninitialized",	      0, 0, true, false, false, false,
+			      handle_uninitialized_attribute, NULL },
   { "retain",                 0, 0, true,  false, false, false,
 			      handle_retain_attribute, NULL },
   { "externally_visible",     0, 0, true,  false, false, false,
@@ -1617,6 +1620,30 @@ handle_retain_attribute (tree *pnode, tree name, tree ARG_UNUSED (args),
   return NULL_TREE;
 }
 
+/* Handle an "uninitialized" attribute; arguments as in
+   struct attribute_spec.handler.  */
+
+static tree
+handle_uninitialized_attribute (tree *node, tree name, tree ARG_UNUSED (args),
+				int ARG_UNUSED (flags), bool *no_add_attrs)
+{
+  tree decl = *node;
+  if (!VAR_P (decl))
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored because %qD "
+	       "is not a variable", name, decl);
+      *no_add_attrs = true;
+    }
+  else if (TREE_STATIC (decl) || DECL_EXTERNAL (decl))
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored because %qD "
+	       "is not a local variable", name, decl);
+      *no_add_attrs = true;
+    }
+
+  return NULL_TREE;
+}
+
 /* Handle a "externally_visible" attribute; arguments as in
    struct attribute_spec.handler.  */