On 11/20/2013 12:13 PM, Linus Torvalds wrote: > On Wed, Nov 20, 2013 at 11:28 AM, H. Peter Anvin <hpa@xxxxxxxxxxxxxxx> wrote: >>> >>> .section .fixup,"ax" >>> 11: lea (%rdx,%rcx,8),%rcx >>> 12: movl %ecx,%edx /* ecx is zerorest also */ >> >> -> Even if %rdx+%rcx*8 > 2^32 we end up truncating at 12: -- not that it >> matters, since both arguments are prototyped as "unsigned" and therefore >> the C compiler is supposed to guarantee the upper 32 bits are ignored. > > Ahh. That was the one I thought was broken, but yes, while the upper > bits of %rcx are calculated and not zeroed, they end up not actually > getting used. So yeah, I'll believe it's correct. > That being said, "lea (%rdx,%rcx,8),%ecx" (leal, as opposed to leaq) is a perfectly legitimate instruction and actually one byte shorter. The big question is if some broken version of gas will choke on it. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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