David> ==================== David> [PATCH] sparc64: Fix several bugs in memmove(). David> Firstly, handle zero length calls properly. Believe it or not there David> are a few of these happening during early boot. David> Next, we can't just drop to a memcpy() call in the forward copy case David> where dst <= src. The reason is that the cache initializing stores David> used in the Niagara memcpy() implementations can end up clearing out David> cache lines before we've sourced their original contents completely. David> For example, considering NG4memcpy, the main unrolled loop begins like David> this: David> load src + 0x00 David> load src + 0x08 David> load src + 0x10 David> load src + 0x18 David> load src + 0x20 David> store dst + 0x00 David> Assume dst is 64 byte aligned and let's say that dst is src - 8 for David> this memcpy() call. That store at the end there is the one to the David> first line in the cache line, thus clearing the whole line, which thus David> clobbers "src + 0x28" before it even gets loaded. David> To avoid this, just fall through to a simple copy only mildly David> optimized for the case where src and dst are 8 byte aligned and the David> length is a multiple of 8 as well. We could get fancy and call David> GENmemcpy() but this is good enough for how this thing is actually David> used. Would it make sense to have some memmove()/memcopy() tests on bootup to catch problems like this? I know this is a strange case, and probably not too common, but how hard would it be to wire up tests that go through 1 to 128 byte memmove() on bootup to make sure things work properly? This seems like one of those critical, but subtle things to be checked. And doing it only on bootup wouldn't slow anything down and would (ideally) automatically get us coverage when people add new archs or update the code. John -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>