linux-kernel - Re: [git pull] x86 updates for v2.6.28, phase #1

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Date:	Fri, 10 Oct 2008 14:07:12 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Vegard Nossum <vegard.nossum@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [git pull] x86 updates for v2.6.28, phase #1

On Fri, 10 Oct 2008, H. Peter Anvin wrote:
> 
> Double underscores aren't the problem per se, the problem is having changes
> _ASM_X86_ to ASM_X86__ and therefore violating the namespace.

Yeah. If I recall the namespace rules correctly, you have to have a 
underscore followed by another underscore or an upper-case letter. Those 
cannot even be used for local variables by a conforming program.

Single-underscore + lower-case letter is only reserved as an external 
identifier. I _think_. So a conforming program could still do

	int main(int argc, char **argv)
	{
		int _asm_x86_types_h = 1;
		return _asm_x86_types_h;
	}

and I _think_ it should be ok.

So a system macro definition that could mess with something (admittedly 
crazy as that) has to be either double underscores or underscore + 
uppercase, so as long as the prefix is "_ASM" (or _LINUX), we're ok.

Double underscores in the _middle_ of the identifiers are a non-issue, and 
are just ugly.

> That being said, I don't personally like the double underscores.

I agree, inside the identifier in particular they do seem pointless. At 
the beginning, they are useful for things like __i386__ or __x86, where 
you need the double underscore because 'i' is lower-case.

Or maybe I mis-remember the name space rules.

			Linus
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