From: Linus Torvalds <torva...@linux-foundation.org> Date: Mon, 23 Mar 2015 12:47:49 -0700
> On Mon, Mar 23, 2015 at 12:08 PM, David Miller <da...@davemloft.net> wrote: >> >> Sure you could do that in C, but I really want to avoid using memcpy() >> if dst and src overlap in any way at all. >> >> Said another way, I don't want to codify that "64" thing. The next >> chip could do 128 byte initializing stores. > > But David, THAT IS NOT WHAT YOUR BROKEN ASM DOES ANYWAY! > > Read it again. Your asm code does not check for overlap. Look at this: > > cmp %o0, %o1 > bleu,pt %xcc, 2f > > and ponder. It's wrong. Right, it's not checking for overlap. It's checking for "does a forward copy work?" That's the standard test for this, and it's what glibc uses in it's generic memmove() implementation FWIW. (granted, I know glibc is not generally a good source for "right way to do things :-) > The new asm version is better than the old one, because the new > breakage is about really bad performance rather than actively > breaking, but still.. I accept that it's suboptimal. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
