linux-kernel - Re: Confusion in usr/include/asm-generic/fcntl.h

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Date:	Fri, 23 Jan 2009 20:48:20 +0530
From:	Jaswinder Singh Rajput <jaswinder@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	David Miller <davem@...emloft.net>, mingo@...e.hu, x86@...nel.org,
	linux-kernel@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: Confusion in usr/include/asm-generic/fcntl.h

On Tue, 2009-01-20 at 16:48 -0800, H. Peter Anvin wrote:
> David Miller wrote:
> > From: Jaswinder Singh Rajput <jaswinder@...nel.org>
> > Date: Wed, 21 Jan 2009 05:34:17 +0530
> > 
> >> usr/include/asm-generic/fcntl.h is giving 2 'make headers_check' warnings:
> >>  usr/include/asm-generic/fcntl.h:127: leaks CONFIG_64BIT to userspace where it is not valid
> >>  usr/include/asm-generic/fcntl.h:149: leaks CONFIG_64BIT to userspace where it is not valid
> >>
> >> usr/include/asm-generic/fcntl.h:
> > ...
> >> #ifndef CONFIG_64BIT will always be true for userspace. So what is the use of #ifndef CONFIG_64BIT ?
> > 
> > Good catch.
> > 
> > This file needs to test for 64-bit'ness using some non-CONFIG_*
> > test.  And the standard built-in CPP macros which can be used
> > to check for that are different on every platform.
> > 
> 
> There are a few ways to check for 64-bitness that are 
> platform-independent, unfortunately each of them have drawbacks.
> 

So who wins the race for CONFIG_64BIT and will be right candidate for
usr/include/asm-generic/fcntl.h:

1. #if BITS_PER_LONG == 64

OR

2. #if __BITS_PER_LONG == 64

OR

3. #ifdef __LP64__

OR

4. #if __SIZEOF_POINTER__ == 8

OR

5. #if LONG_MAX > 2147483647L

OR

6. #ifdef __64BIT


Thanks
--
JSR

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