[RFC PATCH 06/15] libfdt: Don't assume that a FDT_BEGIN_NODE tag is available at offset 0

[Herve Codina <herve.codina@bootlin.com>]

In several places, libfdt assumes that a FDT_BEGIN_NODE tag is present
at the offset 0 of the structure block.

This assumption is not correct. Indeed, a FDT_NOP can be present at the
offset 0 and this is a legit case.

fdt_first_node() has been introduce recently to get the offset of the
first node (first FDT_BEGIN_NODE) in a fdt blob.

Use this function to get the first node offset instead of looking for
this node at offset 0.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 libfdt/fdt.c    | 10 ++++++++--
 libfdt/fdt_ro.c | 16 +++++++++++++---
 libfdt/fdt_rw.c |  6 ++++++
 3 files changed, 27 insertions(+), 5 deletions(-)

diff --git a/libfdt/fdt.c b/libfdt/fdt.c
index 676c7d7..ff2fa6c 100644
--- a/libfdt/fdt.c
+++ b/libfdt/fdt.c
@@ -279,11 +279,17 @@ int fdt_first_node(const void *fdt)
 
 int fdt_next_node(const void *fdt, int offset, int *depth)
 {
-	int nextoffset = 0;
+	int nextoffset = offset;
 	uint32_t tag;
 
+	if (offset <= 0) {
+		nextoffset = fdt_first_node(fdt);
+		if (nextoffset < 0)
+			return nextoffset;
+	}
+
 	if (offset >= 0)
-		if ((nextoffset = fdt_check_node_offset_(fdt, offset)) < 0)
+		if ((nextoffset = fdt_check_node_offset_(fdt, nextoffset)) < 0)
 			return nextoffset;
 
 	do {
diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index 63494fb..8e1db7d 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -229,6 +229,12 @@ int fdt_subnode_offset_namelen(const void *fdt, int offset,
 
 	FDT_RO_PROBE(fdt);
 
+	if (!offset) {
+		offset = fdt_first_node(fdt);
+		if (offset < 0)
+			return offset;
+	}
+
 	for (depth = 0;
 	     (offset >= 0) && (depth >= 0);
 	     offset = fdt_next_node(fdt, offset, &depth))
@@ -251,13 +257,17 @@ int fdt_path_offset_namelen(const void *fdt, const char *path, int namelen)
 {
 	const char *end = path + namelen;
 	const char *p = path;
-	int offset = 0;
+	int offset;
 
 	FDT_RO_PROBE(fdt);
 
 	if (!can_assume(VALID_INPUT) && namelen <= 0)
 		return -FDT_ERR_BADPATH;
 
+	offset = fdt_first_node(fdt);
+	if (offset < 0)
+		return offset;
+
 	/* see if we have an alias */
 	if (*path != '/') {
 		const char *q = memchr(path, '/', end - p);
@@ -579,7 +589,7 @@ int fdt_get_path(const void *fdt, int nodeoffset, char *buf, int buflen)
 	if (buflen < 2)
 		return -FDT_ERR_NOSPACE;
 
-	for (offset = 0, depth = 0;
+	for (offset = fdt_first_node(fdt), depth = 0;
 	     (offset >= 0) && (offset <= nodeoffset);
 	     offset = fdt_next_node(fdt, offset, &depth)) {
 		while (pdepth > depth) {
@@ -617,7 +627,7 @@ int fdt_get_path(const void *fdt, int nodeoffset, char *buf, int buflen)
 	else if (offset == -FDT_ERR_BADOFFSET)
 		return -FDT_ERR_BADSTRUCTURE;
 
-	return offset; /* error from fdt_next_node() */
+	return offset; /* error from fdt_next_node() or fdt_first_node() */
 }
 
 int fdt_supernode_atdepth_offset(const void *fdt, int nodeoffset,
diff --git a/libfdt/fdt_rw.c b/libfdt/fdt_rw.c
index 90ea14e..f5c28fc 100644
--- a/libfdt/fdt_rw.c
+++ b/libfdt/fdt_rw.c
@@ -354,6 +354,12 @@ int fdt_add_subnode_namelen(void *fdt, int parentoffset,
 
 	FDT_RW_PROBE(fdt);
 
+	if (!parentoffset) {
+		parentoffset = fdt_first_node(fdt);
+		if (parentoffset < 0)
+			return parentoffset;
+	}
+
 	offset = fdt_subnode_offset_namelen(fdt, parentoffset, name, namelen);
 	if (offset >= 0)
 		return -FDT_ERR_EXISTS;
-- 
2.52.0