libpayload: memmove: Don't make expectations of architecture memcpy

default_memmove() calls memcpy() when (src > dst). This is safe for the
default_memcpy() implementation, but just calling memcpy() may invoke an
architecture-specific implementation. Architectures are free to
implement memcpy() however they want and may assume that buffers don't
overlap in either direction. So while this happens to work for all
current architecture implementations of memcpy(), it's safer not to rely
on that and only rely on the known implementation of default_memcpy()
for the forwards-overlapping case.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: I7ece4ce9e6622a36612bfade3deb62f351877789
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44691
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/libc/memory.c

@@ -90,7 +90,7 @@ static void *default_memmove(void *dst, const void *src, size_t n)
 	ssize_t i;
 
 	if (src > dst)
-		return memcpy(dst, src, n);
+		return default_memcpy(dst, src, n);
 
 	if (!IS_ALIGNED((uintptr_t)dst, sizeof(unsigned long)) ||
 	    !IS_ALIGNED((uintptr_t)src, sizeof(unsigned long))) {