Hi, Richard, Thanks a lot for you review.
Although these comments are not made on the latest patch (7th version) :-), all the comments are valid since the parts you commented are not changed in the 7th version. > On Aug 9, 2021, at 9:09 AM, Richard Biener <rguent...@suse.de> wrote: > > On Tue, 27 Jul 2021, Qing Zhao wrote: > >> Hi, >> >> This is the 6th version of the patch for the new security feature for GCC. >> >> I have tested it with bootstrap on both x86 and aarch64, regression testing >> on both x86 and aarch64. >> Also compile CPU2017 (running is ongoing), without any issue. (With the fix >> to bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101586). >> >> Please take a look and let me know any issue. > > +/* 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) > +{ > + if (!VAR_P (*node)) > + { > + warning (OPT_Wattributes, "%qE attribute ignored", name); > + *no_add_attrs = true; > + } > > you are documenting this attribute for automatic variables but > here you allow placement on globals as well (not sure if at this > point TREE_STATIC / DECL_EXTERNAL are set correctly). Right, I should warn when the attribute is placed for globals or static variables. I will try TREE_STATIC/DECL_EXTERNAL to see whether it’s work or not. > > + /* for languages that do not support BUILT_IN_CLEAR_PADDING, create the > + function node for padding initialization. */ > + if (!fn) > + { > + tree ftype = build_function_type_list (void_type_node, > + ptr_type_node, > > the "appropriate" place to do this would be > tree.c:build_common_builtin_nodes Sure, will move the creation of function node of BUILT_IN_CLEAR_PADDING for Fortran etc. to tree.c:build_common_builtin_nodes. > > You seem to marshall the is_vla argument as for_auto_init when > expanding/folding the builtin and there it's used to suppress > diagnostics (and make covered pieces not initialized?). Yes, I added an extra argument “for_auto_init” for “BUILT_IN_CLEAR_PADDING”, this argument is added to suppress errors emitted during folding BUILT_IN_CLEAR_PADDING for flexible array member . Such errors should Not be emitted when “BUILT_IN_CLEAR_PADDING” is called with compiler automatic initialization. Please see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101586, comment #6 from Jakub Jelinek. > I suggest > to re-name is_vla/for_auto_init to something more descriptive. Okay, I will. > > + gimple_fold_builtin_clear_padding. If FOR_AUTO_INIT, > + not emit some of the error messages since doing that > + might confuse the end user. */ > > doesn't explain to me whether errors still might be raised or > what the actual behavior is. Okay, will make this more clear in the comments. > > +static gimple * > +build_deferred_init (tree decl, > + enum auto_init_type init_type, > + bool is_vla) > +{ > + gcc_assert ((is_vla && TREE_CODE (decl) == WITH_SIZE_EXPR) > + || (!is_vla && TREE_CODE (decl) != WITH_SIZE_EXPR)); > > so the is_vla parameter looks redundant (and the assert dangerous?). > Either the caller knows it deals with a VLA, then that should be > passed through - constant sizes can also later appear during > optimization after all - or is_vla should be determined here > based on whether the size at gimplification time is constant. The routine “build_deferred_init” is ONLY called during gimplification phase by the routine “gimple_add_init_for_auto_var", at this place, Is_vla should be determined by the caller to check the size of the DECL. If it’s a vla, the “maybe_with_size_expr” will be applied for DECL to make it to a WITH_SIZE_EXPR. So, the assertion is purely to make sure this at gimplification phase. Yes, the size of the VLA decl might become a constant later due to constant propagation, etc. but during the gimplification phase, the assertion should be true. > > + /* If the user requests to initialize automatic variables, we > + should initialize paddings inside the variable. Add a call to > + __BUILTIN_CLEAR_PADDING (&object, 0, for_auto_init = true) to > + initialize paddings of object always to zero regardless of > + INIT_TYPE. */ > + if (opt_for_fn (current_function_decl, flag_auto_var_init) > + > AUTO_INIT_UNINITIALIZED > + && VAR_P (object) > + && !DECL_EXTERNAL (object) > + && !TREE_STATIC (object)) > + gimple_add_padding_init_for_auto_var (object, false, pre_p); > + return ret; > > I think you want to use either auto_var_p (object) or > auto_var_in_fn_p (object, current_function_decl). Don't you also > want to check for the 'uninitialized' attribute here? I suggest > to abstract the check on whether 'object' should be subject > to autoinit to a helper function. Thanks for the suggestion, I will do this. > > There's another path above this calling gimplify_init_constructor > for the case of > > const struct S x = { ... }; > struct S y = x; > > where it will try to init 'y' from the CTOR directly, it seems you > do not cover this case. Yes, you are right, this case was not covered right now, and this should be covered. Looks like that I need to move the “gimple_add_padding_init_for_auto_var” inside the routine “gimplify_init_constructor” to Cover all the cases. > I also think that the above place applies > to all aggregate assignment statements, not only to INIT_EXPRs? > So don't you want to restrict clear-padding emit here? You are right, I might need to restrict it Only to INIT_EXPR. Will update. > > +static void > +expand_DEFERRED_INIT (internal_fn, gcall *stmt) > +{ > + tree var = gimple_call_lhs (stmt); > + tree size_of_var = gimple_call_arg (stmt, 0); > + tree vlaaddr = NULL_TREE; > + tree var_type = TREE_TYPE (var); > + bool is_vla = (bool) TREE_INT_CST_LOW (gimple_call_arg (stmt, 2)); > + enum auto_init_type init_type > + = (enum auto_init_type) TREE_INT_CST_LOW (gimple_call_arg (stmt, 1)); > + > + gcc_assert (init_type > AUTO_INIT_UNINITIALIZED); > + > + /* if this variable is a VLA, get its SIZE and ADDR first. */ > + if (is_vla) > + { > + /* The temporary address variable for this vla should have been > + created during gimplification phase. Refer to gimplify_vla_decl > + for details. */ > + tree var_decl = (TREE_CODE (var) == SSA_NAME) ? > + SSA_NAME_VAR (var) : var; > + gcc_assert (DECL_HAS_VALUE_EXPR_P (var_decl)); > + gcc_assert (TREE_CODE (DECL_VALUE_EXPR (var_decl)) == > INDIRECT_REF); > + /* Get the address of this vla variable. */ > + vlaaddr = TREE_OPERAND (DECL_VALUE_EXPR (var_decl), 0); > > err - isn't the address of the decl represented by the LHS > regardless whether this is a VLA or not? The LHS of the call to .DEFERRED_INIT is the DECL itself whatever it’s a VLA or not. In order to create a memset call, we need the Address of this DECL as the first argument. If the DECL is not a VLA, we just simply apply “build_fold_addr_expr” on this DECL to get its address, However, for VLA, during gimplification phase “gimplify_vla_decl”, we have already created a temporary address variable for this DECL, and recorded this address variable with “DECL_VALUE_EXPR(DECL), We should use this already created address variable for VLAs. > Looking at DECL_VALUE_EXPR > looks quite fragile since that's not sth data dependence honors. > It looks you only partly gimplify the build init here? All > DECL_VALUE_EXPRs should have been resolved. Don’t quite understand here. you mean that all the “DECL_VALUE_EXPRs” have been resolved at the phase RTL expansion, So I cannot use this to get the address variable of the VLA? (However, my unit testing cases for VLAs are all looks fine). > > + if (is_vla || (!use_register_for_decl (var))) > ... > + else > + { > + /* If this variable is in a register, use expand_assignment might > + generate better code. */ > > you compute the patter initializer even when not needing it, > that's wasteful. Okay, I will restrict the pattern initializer computation when really needed. > It's also quite ugly, IMHO you should > use can_native_interpret_type_p (var_type) and native_interpret > a char [] array initialized to the pattern and if > !can_native_interpret_type_p () go the memset route. Thanks for the suggestion. Will try this. > > + /* We will not verify the arguments for the calls to .DEFERRED_INIT. > + Such call is not a real call, just a placeholder for a later > + initialization during expand phase. > + This is mainly to avoid assertion failure for the following > + case: > + > + uni_var = .DEFERRED_INIT (var_size, INIT_TYPE, is_vla); > + foo (&uni_var); > + > + in the above, the uninitialized auto variable "uni_var" is > + addressable, therefore should not be in registers, resulting > + the assertion failure in the following argument verification. */ > + if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)) > + return false; > + > /* ??? The C frontend passes unpromoted arguments in case it > didn't see a function declaration before the call. So for now > leave the call arguments mostly unverified. Once we gimplify > unit-at-a-time we have a chance to fix this. */ > > - for (i = 0; i < gimple_call_num_args (stmt); ++i) > > isn't that from the time there was a decl argument to .DEFERRED_INIT? You mean this issue is only there when the decl is the first argument (the old design for .DEFERRED_INIT). With the new design, this issue is not there anymore? > > + if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT)) > + { > + tree size_of_arg0 = gimple_call_arg (stmt, 0); > + tree size_of_lhs = TYPE_SIZE_UNIT (TREE_TYPE (lhs)); > + tree is_vla_node = gimple_call_arg (stmt, 2); > + bool is_vla = (bool) TREE_INT_CST_LOW (is_vla_node); > + > + if (TREE_CODE (lhs) == SSA_NAME) > + lhs = SSA_NAME_VAR (lhs); > + > > 'lhs' is not looked at after this, no need to look at SSA_NAME_VAR. Okay, will update this. > > > Thanks and sorry for the delay in reviewing this (again). Thanks again for your detailed review and suggestions. I will update the patch accordingly and send the updated patch soon. Qing > > Richard. > > >> Thanks >>
