Fix crash with poorly defined #size-cells

If you have a parent block with #size-cells improperly set to 0, and
then subsequently try to include a regs property in the child, dtc will
crash with SIGFPE while validating it. This patch fixes that crash,
instead printing the same invalid length warning that was causing it.

Test included.

Signed-off-by: Jack Miller <jack@codezen.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

checks.c

@@ -560,7 +560,7 @@ static void check_reg_format(struct check *c, struct node *dt,
 	size_cells = node_size_cells(node->parent);
 	entrylen = (addr_cells + size_cells) * sizeof(cell_t);
 
-	if ((prop->val.len % entrylen) != 0)
+	if (!entrylen || (prop->val.len % entrylen) != 0)
 		FAIL(c, "\"reg\" property in %s has invalid length (%d bytes) "
 		     "(#address-cells == %d, #size-cells == %d)",
 		     node->fullpath, prop->val.len, addr_cells, size_cells);

tests/bad-size-cells.dts

@@ -0,0 +1,12 @@
+/dts-v1/;
+
+/ {
+	mangled {
+		#address-cells = <0x0>;
+		#size-cells = <0x0>;
+
+		valid {
+            reg = <0x0 0x4000000>;
+        };
+    };
+};

tests/run_tests.sh

@@ -279,6 +279,8 @@ libfdt_tests () {
     run_dtc_test -I dts -O dtb -o embedded_nul.test.dtb embedded_nul.dts
     run_dtc_test -I dts -O dtb -o embedded_nul_equiv.test.dtb embedded_nul_equiv.dts
     run_test dtbs_equal_ordered embedded_nul.test.dtb embedded_nul_equiv.test.dtb
+
+    run_dtc_test -I dts -O dtb bad-size-cells.dts
 }
 
 dtc_tests () {