linux-kernel - Re: [patch] use __asm__ and __volatile__ in asm-x86

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Message-ID: <46794BE2.5020108@zytor.com>
Date:	Wed, 20 Jun 2007 08:46:42 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <ak@...e.de>
CC:	Christoph Hellwig <hch@...radead.org>,
	Mike Frysinger <vapier@...too.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] use __asm__ and __volatile__ in asm-x86_64/msr.h

Andi Kleen wrote:
>> asm-i386/msr.h should not be exported to userspace at all, it contains
>> nothing but kernel-internal helpers.
> 
> Actually rdtsc and rdtscll and potentially rdpmc which is in there can be very 
> useful in user space if you know what you're doing. Unfortunately a lot of its users don't,
> but not having the include probably won't stop them either.

More likely, people will just re-implement them incorrectly.

However, the rdtsc() definition in the kernel is weird (and removable, I
think there are no more users -- I have it removed in my MSR driver
rewrite tree which I need to get off my arse and push.)  Most users
would expect the rdtscll() functionality with the rdtsc() name.

	-hpa
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