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.