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From: David Laight <David.Laight@ACULAB.COM>
To: 'Nick Desaulniers' <ndesaulniers@google.com>,
	YingChi Long <me@inclyc.cn>
Cc: "bp@alien8.de" <bp@alien8.de>,
	"chang.seok.bae@intel.com" <chang.seok.bae@intel.com>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"x86@kernel.org" <x86@kernel.org>,
	"peterz@infradead.org" <peterz@infradead.org>
Subject: RE: [PATCH v2] x86/fpu: use _Alignof to avoid UB in TYPE_ALIGN
Date: Thu, 6 Oct 2022 08:12:04 +0000	[thread overview]
Message-ID: <aa329b6fa5764e03ad6891142c2311fc@AcuMS.aculab.com> (raw)
In-Reply-To: <CAKwvOd=H5kB=nsParYME2KoQxj-eDC_DAN09y1T2E7yqS43H4Q@mail.gmail.com>

From: Nick Desaulniers
> Sent: 05 October 2022 19:58
...
> https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3054.pdf
> Section 6.2.8 "Alignment of objects" refers to "fundamental alignment"
> and "extended alignment."
> 
> I wonder if it would be precise to say that "_Alignof evaluates to the
> fundamental alignment while __alignof__ evaluates to the extended
> alignment (which is implementation defined, typically by the machine
> specific ABI)." Though even that seems imprecise since it sounds like
> a fundamental alignment could be less than or equal to what alignof
> evaluates to.

Except that neither of those terms makes any sense to most
people.
Something like "__alignof__() is the preferred alignment and
_Alignof() the minimal alignment. For 'long long' on x86 these
are 8 and 4 respectively."

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

  reply	other threads:[~2022-10-06  8:12 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
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 [this message]
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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