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, 16 insertions, 0 deletions

diff --git a/gcc/common.opt b/gcc/common.opt
index f103a7d..b921f5e 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -3081,6 +3081,22 @@ ftree-scev-cprop
 Common Var(flag_tree_scev_cprop) Init(1) Optimization
 Enable copy propagation of scalar-evolution information.
 
+ftrivial-auto-var-init=
+Common Joined RejectNegative Enum(auto_init_type) Var(flag_auto_var_init) Init(AUTO_INIT_UNINITIALIZED) Optimization
+-ftrivial-auto-var-init=[uninitialized|pattern|zero]	Add initializations to automatic variables.
+
+Enum
+Name(auto_init_type) Type(enum auto_init_type) UnknownError(unrecognized automatic variable initialization type %qs)
+
+EnumValue
+Enum(auto_init_type) String(uninitialized) Value(AUTO_INIT_UNINITIALIZED)
+
+EnumValue
+Enum(auto_init_type) String(pattern) Value(AUTO_INIT_PATTERN)
+
+EnumValue
+Enum(auto_init_type) String(zero) Value(AUTO_INIT_ZERO)
+
 ; -fverbose-asm causes extra commentary information to be produced in
 ; the generated assembly code (to make it more readable).  This option
 ; is generally only of use to those who actually need to read the