Messages in this thread | | | Date | Wed, 20 Nov 2013 12:13:15 -0800 | Subject | Re: [tip:x86/asm] x86-64, copy_user: Remove zero byte check before copy user buffer. | From | Linus Torvalds <> |
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On Wed, Nov 20, 2013 at 11:28 AM, H. Peter Anvin <hpa@linux.intel.com> 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.
Linus
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