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From: "jason at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/97595] [11 Regression] bogus -Wstringop-overflow due to DECL_SIZE_UNIT underreporting field size
Date: Mon, 16 Nov 2020 17:10:03 +0000 [thread overview]
Message-ID: <bug-97595-4-w2hpuETfa2@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-97595-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97595
--- Comment #5 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #3)
> I can confirm the warning but I'm not sure the bug is in the middle end
> code. Let me CC Jason for his comments.
>
> The warning triggers for the MEM_REF below:
>
> MEM[(char &)_10 + 224] = _24;
>
> in the following GIMPLE ("type" is char). The destination of the access is
> this_3(D)->D.45669 which is the basic_istream subobject. Its size reported
> by DECL_SIZE_UNIT() in component_ref_size() is 16. The initial offset
> (i.e., _10) is indeterminate but it's taken to be in the range bounded by
> the size of the object, or [0, 16]. Given that, the constant offset 224 is
> determined to be out of bounds.
What you're seeing is that the DECL_SIZE of the base subobject excludes any
virtual bases, because they are laid out in the most derived class, while the
TYPE_SIZE of the base type includes them. CLASSTYPE_SIZE of the base type
should match the DECL_SIZE.
It's definitely OK for a program to refer to a virtual base through any of the
derived classes.
> The change introduced in r11-3827 that triggers the warning is the assumption > that unless determined otherwise, an indeterminate offset into an object must > be bounded by the object's size.
So this assumption is invalid for base subobjects of types with virtual bases;
such an offset is only bounded by the most-derived object's size.
next prev parent reply other threads:[~2020-11-16 17:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-27 15:22 [Bug tree-optimization/97595] New: [11 Regression] warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=] redi at gcc dot gnu.org
2020-10-27 15:22 ` [Bug tree-optimization/97595] " redi at gcc dot gnu.org
2020-10-27 15:27 ` redi at gcc dot gnu.org
2020-10-27 16:28 ` [Bug tree-optimization/97595] [11 Regression] bogus -Wstringop-overflow due to DECL_SIZE_UNIT underreporting field size msebor at gcc dot gnu.org
2020-10-28 9:09 ` rguenth at gcc dot gnu.org
2020-11-14 22:19 ` msebor at gcc dot gnu.org
2020-11-16 17:10 ` jason at gcc dot gnu.org [this message]
2020-12-01 16:16 ` msebor at gcc dot gnu.org
2020-12-01 22:11 ` cvs-commit at gcc dot gnu.org
2020-12-01 22:13 ` msebor at gcc dot gnu.org
2021-02-23 23:12 ` msebor at gcc dot gnu.org
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