linux-kernel - x86: fls64() exported to user space but not fls()?

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Message-ID: <4EEA77E1.6050009@zytor.com>
Date:	Thu, 15 Dec 2011 14:42:41 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	David Howells <dhowells@...hat.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Alexander van Heukelum <heukelum@...lshack.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: x86: fls64() exported to user space but not fls()?

I'm trying to grok why fls64() seems to be exported to user space in
<asm/bitops.h> on x86 by unconditional inclusion of
<asm-generic/bitops/fls64.h>:

...
#endif /* __KERNEL__ */

#include <asm-generic/bitops/fls64.h>

#ifdef __KERNEL__
...


 whereas fls() isn't (although __fls() is!)

This is even more bizarre since <asm-generic/bitops/fls64.h> contains:

...
#if BITS_PER_LONG == 32
static __always_inline int fls64(__u64 x)
{
        __u32 h = x >> 32;
        if (h)
                return fls(h) + 32;
        return fls(x);
}
#elif BITS_PER_LONG == 64
static __always_inline int fls64(__u64 x)
{
        if (x == 0)
                return 0;
        return __fls(x) + 1;
}
#else
#error BITS_PER_LONG not 32 or 64
#endif
...

Both BITS_PER_LONG and fls() are non-user-visible symbols, so this code
should fail on user space.  Finally, <asm-generic/bitops/*> are
non-exported headers; they are not installed by make headers_install.

Is the #endif..#ifdef in <asm/bitops.h> a bug, plain and simple?

	-hpa
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