Messages in this thread | | | Date | Sat, 26 Jul 2008 12:48:31 -0400 | From | "H. Peter Anvin" <> | Subject | Re: Fw: asm-x86/byteorder.h, CONFIG_X86_BSWAP leaks to userland |
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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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