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Message-ID: <498344E9.5030707@zytor.com> Date: Fri, 30 Jan 2009 10:20:25 -0800 From: "H. Peter Anvin" <hpa@...or.com> To: blp@...stanford.edu CC: linux-kernel@...r.kernel.org Subject: Re: [PATCH] x86: do not expose CONFIG_BSWAP to userspace Ben Pfaff wrote: > Harvey Harrison <harvey.harrison@...il.com> writes: > >> Is there a byteswap builtin in gcc? At least AVR32 >> seems to use it, but perhaps it's not generally exposed...perhaps we >> could ask the gcc-folk? > > Yes, GCC has byteswap builtins on x86 documented as follows: > > -- Built-in Function: int32_t __builtin_bswap32 (int32_t x) > Returns X with the order of the bytes reversed; for example, > `0xaabbccdd' becomes `0xddccbbaa'. Byte here always means exactly > 8 bits. > > -- Built-in Function: int64_t __builtin_bswap64 (int64_t x) > Similar to `__builtin_bswap32', except the argument and return > types are 64-bit. > > These were only added as of GCC 4.3 though. It would make sense to use them if gcc >= 4.3 (both for userspace and kernel space.) IMO, for older compilers we can just punt on the enhancement for userspace and fall back to the i386 code. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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