linux-kernel - Re: [PATCH] x86: do not expose CONFIG

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Message-ID: <4980D913.3000505@zytor.com>
Date:	Wed, 28 Jan 2009 14:15:47 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Harvey Harrison <harvey.harrison@...il.com>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Jaswinder Singh Rajput <jaswinderrajput@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] x86: do not expose CONFIG_BSWAP to userspace

Harvey Harrison wrote:
> I'm afraid my knowledge of gcc compiler flags for various models is
> lacking, I used i486 as suggested, just wanted to make sure I understood
> you corectly.

You did, but I misremembered... instead of having the __i386__, 
__i486__, __i586__, __i686__ being an additive chain as would make 
sense, gcc just has __i386__ plus whichever corresponds to the -march= 
option.  I keep forgetting this because it's just so incredibly dumb.

Bloody hell.  This really f*cks thing up.

What's worse, they seem to simply be adding new options, so at this 
point you'd actually need something like:

# if defined(__i486__) || defined(__i586__) || defined(__i686__) || \
	defined(__core2__) || defined(__k8__) || defined(__amdfam10__)

Worse, there isn't any kind of macro that can be used to compare for a 
negative (i.e. not i386).

This obviously is screaming to be abstracted away into a header of its 
own, but it really can't be done cleanly as far as I can tell because of 
this particular piece of major gcc braindamage.

So, one ends up doing something like:

#ifdef __i486__
# define __CPU_HAVE_BSWAP
#endif
#ifdef __i586__
# define __CPU_HAVE_BSWAP
#endif

... and so on, and have to keep this up to date with the latest 
inventions of the gcc people.  *Sob.*

	-hpa

	-hpa

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