On Mon, 9 Aug 2021, Qing Zhao wrote:
> 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.
So the issue is that the LHS of the .DEFERRED_INIT call is not properly
gimplified. We should not have such decl there but I see we do not
have IL verification that covers this.
The gimplifier usually does this in gimplify_var_or_parm_decl,
but you can of course substitute DECL_VALUE_EXPR yourself if the
decl was already gimplified (was it?)
>
> > 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?
I think so, yes - the change should no longer be needed.
Ricahrd.
> >
> > + 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
> >>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
