Handle integer overflow in check_property_phandle_args()

If the corresponding '#xxx-cells' value is much too large, an integer
overflow can prevent the checks in check_property_phandle_args() from
correctly determining that the checked property is too short for the
given cells value.  This leads to an infinite loops.

This patch fixes the bug, and adds a testcase for it.  Further
information in https://github.com/dgibson/dtc/issues/64

Reported-by: Anciety <anciety@pku.edu.cn>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/phandle-args-overflow.dts

@@ -0,0 +1,18 @@
+/dts-v1/;
+
+/*
+ * https://github.com/dgibson/dtc/issues/64
+ *
+ * Certain dtc versions had a bug where this input caused an infinite
+ * loop in check_property_phandle_args().
+ *
+ */
+
+/ {
+    clocks = <&ref &ref>;
+
+    ref: poc {
+        phandle = <1>;
+        #clock-cells = <0xffffffff>;
+    };
+};

tests/run_tests.sh

@@ -513,6 +513,9 @@ libfdt_tests () {
     run_dtc_test -I fs -O dtb -o fs.test_tree1.test.dtb $FSBASE/test_tree1
     run_test dtbs_equal_unordered -m fs.test_tree1.test.dtb test_tree1.dtb
 
+    ## https://github.com/dgibson/dtc/issues/64
+    check_tests "$SRCDIR/phandle-args-overflow.dts" clocks_property
+
     # check full tests
     for good in test_tree1.dtb; do
 	run_test check_full $good