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From: "akihiko.odaki at daynix dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/114217] -fsanitize=alignment false positive with intended unaligned struct member access
Date: Sun, 03 Mar 2024 07:19:29 +0000 [thread overview]
Message-ID: <bug-114217-4-Qw939UeVnJ@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-114217-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114217
--- Comment #3 from Akihiko Odaki <akihiko.odaki at daynix dot com> ---
(In reply to Andrew Pinski from comment #1)
> >but also emits code to assert alignment.
>
>
> Yes because the code is broken still.
>
> The alignment is not about when the access happens but rather when the
> pointer is casted to.
>
> So in this case when passing in the argument to f, the argument entry should
> be aligned to what the `struct dir_entry` is aligned to; otherwise it is
> undefined code.
I had a similar thought when I faced the same issue before and didn't report it
then, but this time I realized GCC still emits code to perform slow unaligned
access for such a construct. Whichever is right, to assume an aligned or
unaligned access, it is not consistent.
Theoretically, it also makes sense to emit unaligned memory access for such a
construct instead of ignoring it when -fsanitize=address, but I'm worried that
such a change will break too many things.
next prev parent reply other threads:[~2024-03-03 7:19 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-03 7:03 [Bug sanitizer/114217] New: " akihiko.odaki at daynix dot com
2024-03-03 7:10 ` [Bug sanitizer/114217] " pinskia at gcc dot gnu.org
2024-03-03 7:15 ` pinskia at gcc dot gnu.org
2024-03-03 7:19 ` akihiko.odaki at daynix dot com [this message]
2024-03-03 7:22 ` pinskia at gcc dot gnu.org
2024-03-03 7:29 ` akihiko.odaki at daynix dot com
2024-03-03 7:46 ` akihiko.odaki at daynix dot com
2024-03-03 19:01 ` jakub at gcc dot gnu.org
2024-03-04 5:26 ` akihiko.odaki at daynix dot com
2024-03-04 7:46 ` jakub at gcc dot gnu.org
2024-03-04 7:54 ` jakub at gcc dot gnu.org
2024-03-04 8:11 ` akihiko.odaki at daynix dot com
2024-03-04 8:35 ` jakub at gcc dot gnu.org
2024-03-04 8:45 ` akihiko.odaki at daynix dot com
2024-03-04 21:48 ` i at maskray dot me
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