Re: [PATCH] x86: do not expose CONFIG_BSWAP to userspace

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 28 January 2009, H. Peter Anvin wrote:
> 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.*

Well, to put this into perspective: The bswap inline assembly was
introduced in Linux-1.3.51 "Greased Weasel", back in 1995 and at
no time it was ever visible to user space, unless the code manually
included <linux/config.h> (which we broke) or defined CONFIG_M486,
CONFIG_X86_BSWAP and/or __KERNEL__, depending on the kernel version.

I take this as a strong indication that user space applications
won't generally expect to get the bswap instruction from including
the kernel headers. For the longest time, we actually had

/* For avoiding bswap on i386 */
#ifdef __KERNEL__
#include <linux/config.h>
#endif

which I read as explicitly using the portable i386 version for
all user space.

	Arnd <><