Re: [PATCH] Add limited read-only support for older (V2 and V3) device tree to libfdt.

Nathan Whitehorn <nwhitehorn@xxxxxxxxxxx> · Fri, 29 Dec 2017 10:12:04 -0800

Has anyone had a chance to look at this? We need it, or something like 
it, to support some older firmwares with the FreeBSD kernel and I would 
like to make sure that our copy of libfdt does not diverge from upstream.

Thanks,
Nathan

On 12/07/17 22:31, Nathan Whitehorn wrote:
This can be useful in particular in the kernel when booting on systems
with FDT-emitting firmware that is out of date. Releases of kexec-tools
on ppc64 prior to the end of 2014 are notable examples of such.

Signed-off-by: Nathan Whitehorn <nwhitehorn@xxxxxxxxxxx>
---
  fdtget.c        |  4 +--
  libfdt/fdt.c    |  8 ++++--
  libfdt/fdt_ro.c | 77 ++++++++++++++++++++++++++++++++++++++++++++++++++-------
  libfdt/libfdt.h |  5 +++-
  4 files changed, 79 insertions(+), 15 deletions(-)

diff --git a/fdtget.c b/fdtget.c
index 6cc5242..34d8194 100644
--- a/fdtget.c
+++ b/fdtget.c
@@ -140,7 +140,6 @@ static int show_data(struct display_info *disp, const char *data, int len)
   */
  static int list_properties(const void *blob, int node)
  {
-	const struct fdt_property *data;
  	const char *name;
  	int prop;
  
@@ -149,8 +148,7 @@ static int list_properties(const void *blob, int node)
  		/* Stop silently when there are no more properties */
  		if (prop < 0)
  			return prop == -FDT_ERR_NOTFOUND ? 0 : prop;
-		data = fdt_get_property_by_offset(blob, prop, NULL);
-		name = fdt_string(blob, fdt32_to_cpu(data->nameoff));
+		fdt_getprop_by_offset(blob, prop, &name, NULL);
  		if (name)
  			puts(name);
  		prop = fdt_next_property_offset(blob, prop);
diff --git a/libfdt/fdt.c b/libfdt/fdt.c
index fd13236..e783e6a 100644
--- a/libfdt/fdt.c
+++ b/libfdt/fdt.c
@@ -84,8 +84,9 @@ const void *fdt_offset_ptr(const void *fdt, int offset, unsigned int len)
  		return NULL;
  
  	if (fdt_version(fdt) >= 0x11)
-		if (((offset + len) < offset)
-		    || ((offset + len) > fdt_size_dt_struct(fdt)))
+		if (((offset + len) < offset) ||
+		    (fdt_version(fdt) >= 0x10 &&
+		     (offset + len) > fdt_size_dt_struct(fdt)))
  			return NULL;
  
  	return fdt_offset_ptr_(fdt, offset);
@@ -123,6 +124,9 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset)
  		/* skip-name offset, length and value */
  		offset += sizeof(struct fdt_property) - FDT_TAGSIZE
  			+ fdt32_to_cpu(*lenp);
+		if (fdt_version(fdt) < 0x10 && fdt32_to_cpu(*lenp) > 8 &&
+		    ((offset - fdt32_to_cpu(*lenp)) % 8) != 0)
+			offset += 4;
  		break;
  
  	case FDT_END:
diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
index ce17814..025dd0f 100644
--- a/libfdt/fdt_ro.c
+++ b/libfdt/fdt_ro.c
@@ -233,16 +233,26 @@ int fdt_path_offset(const void *fdt, const char *path)
  const char *fdt_get_name(const void *fdt, int nodeoffset, int *len)
  {
  	const struct fdt_node_header *nh = fdt_offset_ptr_(fdt, nodeoffset);
+	const char *nameptr;
  	int err;
  
  	if (((err = fdt_check_header(fdt)) != 0)
  	    || ((err = fdt_check_node_offset_(fdt, nodeoffset)) < 0))
  			goto fail;
  
+	nameptr = nh->name;
+
+	if (fdt_version(fdt) < 0x10) {
+		const char *leaf;
+		leaf = strrchr(nameptr, '/');
+		if (leaf != NULL)
+			nameptr = leaf+1;
+	}
+
  	if (len)
-		*len = strlen(nh->name);
+		*len = strlen(nameptr);
  
-	return nh->name;
+	return nameptr;
  
   fail:
  	if (len)
@@ -268,9 +278,9 @@ int fdt_next_property_offset(const void *fdt, int offset)
  	return nextprop_(fdt, offset);
  }
  
-const struct fdt_property *fdt_get_property_by_offset(const void *fdt,
-						      int offset,
-						      int *lenp)
+static const struct fdt_property *_fdt_get_property_by_offset(const void *fdt,
+						              int offset,
+						              int *lenp)
  {
  	int err;
  	const struct fdt_property *prop;
@@ -289,11 +299,35 @@ const struct fdt_property *fdt_get_property_by_offset(const void *fdt,
  	return prop;
  }
  
+const struct fdt_property *fdt_get_property_by_offset(const void *fdt,
+						      int offset,
+						      int *lenp)
+{
+	/* Prior to version 16, properties may need realignment
+	 * and this API does not work. fdt_getprop_*() will, however. */
+
+	if (fdt_version(fdt) < 0x10) {
+		if (lenp)
+			*lenp = -FDT_ERR_BADVERSION;
+		return NULL;
+	}
+
+	return _fdt_get_property_by_offset(fdt, offset, lenp);
+}
+
  const struct fdt_property *fdt_get_property_namelen(const void *fdt,
  						    int offset,
  						    const char *name,
  						    int namelen, int *lenp)
  {
+	/* Prior to version 16, properties may need realignment
+	 * and this API does not work. fdt_getprop_*() will, however. */
+	if (fdt_version(fdt) < 0x10) {
+		if (lenp)
+			*lenp = -FDT_ERR_BADVERSION;
+		return NULL;
+	}
+
  	for (offset = fdt_first_property_offset(fdt, offset);
  	     (offset >= 0);
  	     (offset = fdt_next_property_offset(fdt, offset))) {
@@ -324,12 +358,33 @@ const struct fdt_property *fdt_get_property(const void *fdt,
  const void *fdt_getprop_namelen(const void *fdt, int nodeoffset,
  				const char *name, int namelen, int *lenp)
  {
-	const struct fdt_property *prop;
+	const struct fdt_property *prop = NULL;
+	int offset = nodeoffset;
  
-	prop = fdt_get_property_namelen(fdt, nodeoffset, name, namelen, lenp);
-	if (!prop)
+	for (offset = fdt_first_property_offset(fdt, offset);
+	     (offset >= 0);
+	     (offset = fdt_next_property_offset(fdt, offset))) {
+		if (!(prop = _fdt_get_property_by_offset(fdt, offset, lenp))) {
+			if (lenp)
+				*lenp = -FDT_ERR_INTERNAL;
+			return NULL;
+		}
+
+		if (fdt_string_eq_(fdt, fdt32_to_cpu(prop->nameoff),
+				   name, namelen))
+			break;
+	}
+
+	if (lenp && offset < 0)
+		*lenp = offset;
+
+	if (!prop || offset < 0)
  		return NULL;
  
+	/* Handle realignment */
+	if (fdt_version(fdt) < 0x10 && (offset + sizeof(*prop)) % 8 &&
+	    fdt32_to_cpu(prop->len) > 8)
+		return prop->data + 4;
  	return prop->data;
  }
  
@@ -338,11 +393,15 @@ const void *fdt_getprop_by_offset(const void *fdt, int offset,
  {
  	const struct fdt_property *prop;
  
-	prop = fdt_get_property_by_offset(fdt, offset, lenp);
+	prop = _fdt_get_property_by_offset(fdt, offset, lenp);
  	if (!prop)
  		return NULL;
  	if (namep)
  		*namep = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
+
+	if (fdt_version(fdt) < 0x10 && (offset + sizeof(*prop)) % 8 &&
+	    fdt32_to_cpu(prop->len) > 8)
+		return prop->data + 4;
  	return prop->data;
  }
  
diff --git a/libfdt/libfdt.h b/libfdt/libfdt.h
index baa882c..7ac3e8a 100644
--- a/libfdt/libfdt.h
+++ b/libfdt/libfdt.h
@@ -54,7 +54,7 @@
  #include <libfdt_env.h>
  #include <fdt.h>
  
-#define FDT_FIRST_SUPPORTED_VERSION	0x10
+#define FDT_FIRST_SUPPORTED_VERSION	0x02
  #define FDT_LAST_SUPPORTED_VERSION	0x11
  
  /* Error codes: informative error codes */
@@ -526,6 +526,9 @@ int fdt_next_property_offset(const void *fdt, int offset);
   * fdt_property structure within the device tree blob at the given
   * offset.  If lenp is non-NULL, the length of the property value is
   * also returned, in the integer pointed to by lenp.
+ *
+ * Note that this code only works on device tree versions >= 16. fdt_getprop()
+ * works on all versions.
   *
   * returns:
   *	pointer to the structure representing the property

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