linux-kernel - Re: [PATCH] x86: show cpuinfo only for online CPUs

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Message-ID: <472A2523.2030201@zytor.com>
Date:	Thu, 01 Nov 2007 12:12:35 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Glauber de Oliveira Costa <gcosta@...hat.com>
CC:	Andreas Herrmann3 <andreas.herrmann3@....com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	akpm@...ux-foundation.org, travis@....com
Subject: Re: [PATCH] x86: show cpuinfo only for online CPUs

Glauber de Oliveira Costa wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> Andreas Herrmann3 escreveu:
>> On Thu, Nov 01, 2007 at 06:35:43PM +0100, Andreas Herrmann3 wrote:
>>> On Thu, Nov 01, 2007 at 03:12:25PM -0200, Glauber de Oliveira Costa wrote:
>>>> So it could even work, but as accident. Unless I'm wrong about it, I'd
>>>> prefer to see an explicit attribution of cpu_index = 0 somewhere for the
>>>> boot cpu.
>>> Hmm, will look at this as well.
>> BTW, isn't it zero initialized anyway?
>> So, no need to explicitely set cpuinfo->cpu_index=0 for the boot cpu.
> 
> Well, it should be, but as far as I know it is not exactly a guarantee
> given by all compilers. So it should be safer to do it explicitly, with
> no prejudice. Unless it's really guaranteed. If it is, yeah, no need.

Any uninitialized field in a static section (.data or .bss) is 
guaranteed to be initialized to zero.  This is guaranteed by the C 
standard.  In the former case, it is the responsibility of the compiler 
and in the latter by the runtime.

The Linux percpu handling creates a .data.percpu section which is then 
replicated into each of the CPU data blocks; thus, percpu data counts as 
static data for this purpose, and initialization is guaranteed.

	-hpa
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