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
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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 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
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