fdt: Align the start of the livetree

Ensure that the block of memory used by live tree is aligned according to
the default for structures. This ensures that the root node appears at
the start of the block, so it can be used with free(), rather than being
4 bytes later in some cases.

This corrects a rather obscure bug in unflatten_device_tree().

Fixes: 8b50d526ea5 ("dm: Add a function to create a 'live' device tree")

Signed-off-by: Simon Glass <sjg@chromium.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/test/dm/ofnode.c b/test/dm/ofnode.c
index 473a8cef57..64baaf68db 100644
--- a/test/dm/ofnode.c
+++ b/test/dm/ofnode.c
@@ -1240,3 +1240,29 @@ static int dm_test_ofnode_copy_props_ot(struct unit_test_state *uts)
 	return 0;
 }
 DM_TEST(dm_test_ofnode_copy_props_ot, UT_TESTF_SCAN_FDT | UT_TESTF_OTHER_FDT);
+
+/* check that the livetree is aligned to a structure boundary */
+static int dm_test_livetree_align(struct unit_test_state *uts)
+{
+	const int align = __alignof__(struct unit_test_state);
+	struct device_node *node;
+	u32 *sentinel;
+	ulong start;
+
+	start = (ulong)gd_of_root();
+	ut_asserteq(start, ALIGN(start, align));
+
+	node = gd_of_root();
+	sentinel = (void *)node - sizeof(u32);
+
+	/*
+	 * The sentinel should be overwritten with the root node. If it isn't,
+	 * then the root node is not at the very start of the livetree memory
+	 * area, and free(root) will fail to free the memory used by the
+	 * livetree.
+	 */
+	ut_assert(*sentinel != BAD_OF_ROOT);
+
+	return 0;
+}
+DM_TEST(dm_test_livetree_align, UT_TESTF_LIVE_TREE);