Re: Fw: asm-x86/byteorder.h, CONFIG_X86_BSWAP leaks to userland

[H. Peter Anvin]

Harvey Harrison wrote:
> > An undefined CONFIG_foo defaults to 0 (I think), so bswap is never used.
> > Is this done on purpose, or can the CONFIG_ foo be moved inside
> > __KERNEL__ somehow?
>
> I believe it's there to prevent the bswap instruction from being used on
> early x86_32 models (i386/i486).  As this will be 0 in userspace it is
> effectively never using the bswap instruction for these routines.

i386, specifically.

However, you shouldn't leak these symbols to userspace; there is a 
warning option in gcc for undefined macros, and it's a *good thing* to 
use it.  Causing warnings in user space is not nice.

> I'm not sure if it's time yet to make the bswap ones be exported, as they
> would no longer be usable for those early machines.  X86 guys CC:d.

On i386 we still default to i386-compatible binaries; I *think* gcc has 
macros telling you if the user has used -march=i486 etc.

	-hpa
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