From: David Laight <David.Laight@ACULAB.COM>
To: 'YingChi Long' <me@inclyc.cn>, Peter Zijlstra <peterz@infradead.org>
Cc: "tglx@linutronix.de" <tglx@linutronix.de>,
"ndesaulniers@google.com" <ndesaulniers@google.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"x86@kernel.org" <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"Chang S. Bae" <chang.seok.bae@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] x86/fpu: use __alignof__ to avoid UB in TYPE_ALIGN
Date: Tue, 27 Sep 2022 08:20:39 +0000 [thread overview]
Message-ID: <40fca2eef36a40f4b9a4145a0f7fe57c@AcuMS.aculab.com> (raw)
In-Reply-To: <0ed40d5b-a404-f424-c9c4-2adf1bf9750b@inclyc.cn>
From: YingChi Long
> Sent: 26 September 2022 14:18
>
> Seems GCC __alignof__ is not evaluated to the minimum alignment of some
> TYPE, and depends on fields of the struct.
>
> > Notably I think 'long long' has 4 byte alignment on i386 and some other
> > 32bit archs.
>
> C11 _Alignof matches in the case (see godbolt link below). How about
> switch to _Alignof?
__alignof__() returns the preferred alignment, not the minimal one.
So one i386 it returns 8 for 'long long' rather than 4.
Using alignof(struct{long long x;}) does give the required 4.
(as does _Alignof()).
See https://godbolt.org/z/13xTYYd11
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-09-27 8:20 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-25 15:31 [PATCH] x86/fpu: use __alignof__ to avoid UB in TYPE_ALIGN YingChi Long
2022-09-26 9:01 ` Peter Zijlstra
2022-09-26 13:18 ` YingChi Long
2022-09-26 19:02 ` Nick Desaulniers
2022-09-27 8:20 ` David Laight [this message]
2022-09-27 15:33 ` [PATCH v2] x86/fpu: use _Alignof " YingChi Long
2022-09-27 15:58 ` David Laight
2022-09-27 16:44 ` YingChi Long
2022-09-27 17:07 ` YingChi Long
2022-09-28 8:09 ` David Laight
2022-09-28 11:23 ` YingChi Long
2022-10-05 7:29 ` YingChi Long
2022-10-05 18:30 ` Nick Desaulniers
2022-10-05 18:38 ` Nick Desaulniers
2022-10-05 18:57 ` Nick Desaulniers
2022-10-06 8:12 ` David Laight
2022-10-06 14:14 ` [PATCH v3] " YingChi Long
2022-10-06 17:34 ` Nick Desaulniers
2022-10-18 0:52 ` YingChi Long
2022-10-29 12:25 ` [PATCH RESEND " YingChi Long
2022-10-31 18:29 ` Nick Desaulniers
2022-11-02 16:55 ` Borislav Petkov
2022-11-02 18:07 ` YingChi Long
2022-11-02 18:14 ` [PATCH v4] " YingChi Long
2022-11-02 21:41 ` [PATCH RESEND v3] " David Laight
2022-11-18 0:55 ` [PATCH RESEND v4] " Yingchi Long
2022-11-22 16:26 ` [tip: x86/fpu] x86/fpu: Use _Alignof to avoid undefined behavior " tip-bot2 for YingChi Long
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=40fca2eef36a40f4b9a4145a0f7fe57c@AcuMS.aculab.com \
--to=david.laight@aculab.com \
--cc=bp@alien8.de \
--cc=chang.seok.bae@intel.com \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=linux-kernel@vger.kernel.org \
--cc=me@inclyc.cn \
--cc=mingo@redhat.com \
--cc=ndesaulniers@google.com \
--cc=pbonzini@redhat.com \
--cc=peterz@infradead.org \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.