Fix a bug in the ubldr introduced in the rev.283035. The new code

fails to properly consider memory regions when the loader is
located below of those regions or engulfs their lower limit. This
results in "not enough RAM to load kernel" panic, which is totally
bogus. On top of that, there are some variables that can be left
unitialized in those cases, which might cause it fail with memory
access violation instead of panic while trying to load kernel to
a wrong or non-existing address of memory.

sys/boot/uboot/lib/copy.c

@@ -102,14 +102,18 @@ uboot_loadaddr(u_int type, void *data, uint64_t addr)
 		biggest_size = 0;
 		subldr = rounddown2((uintptr_t)_start, KERN_ALIGN);
 		eubldr = roundup2(uboot_heap_end, KERN_ALIGN);
+		printf("subldr=%lu, eubldr=%lu\n", (unsigned long)subldr, (unsigned long)eubldr);
 		for (i = 0; i < si->mr_no; i++) {
+			printf("si->mr[%d]: .flags=%d, .start=%lu, .size=%lu\n",
+			    i, si->mr[i].flags, si->mr[i].start, si->mr[i].size);
 			if (si->mr[i].flags != MR_ATTR_DRAM)
 				continue;
 			sblock = roundup2(si->mr[i].start, KERN_ALIGN);
 			eblock = rounddown2(si->mr[i].start + si->mr[i].size,
 			    KERN_ALIGN);
 			if (biggest_size == 0)
 				sblock += KERN_MINADDR;
+			printf("    sblock=%d, eblock=%d\n", sblock, eblock);
 			if (subldr >= sblock && subldr < eblock) {
 				if (subldr - sblock > eblock - eubldr) {
 					this_block = sblock;
@@ -118,7 +122,16 @@ uboot_loadaddr(u_int type, void *data, uint64_t addr)
 					this_block = eubldr;
 					this_size = eblock - eubldr;
 				}
+			} else if (subldr < sblock && eubldr < eblock) {
+				/* Loader is below or engulfs the sblock */
+				this_block = (eubldr < sblock) ? sblock : eubldr;
+				this_size = eblock - this_block;
+			} else {
+				this_block = 0;
+				this_size = 0;
 			}
+			printf("    this_block=%lu, this_size=%lu\n",
+			    (unsigned long)this_block, (unsigned long)this_size);
 			if (biggest_size < this_size) {
 				biggest_block = this_block;
 				biggest_size  = this_size;