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From: Frank Mehnert <frank.mehnert-2ptZNfhJYoRaodhZ+FW2PA@public.gmane.org>
To: devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: libfdt / fdt_check_node_offset_ with VALID_INPUT
Date: Wed, 12 Aug 2020 17:48:56 +0200	[thread overview]
Message-ID: <34725235.0rVAnNm8GT@noys4> (raw)

Hi all,

I'm not sure if I found a bug or if I mis-use libfdt.

I have a valid Linux device tree in memory and want to recursively scan
thru it. The device tree contains a root node and several subnodes.

First, I start with the root node:

  int root = fdt_next_node(fdt, -1, NULL);

Here, root is set to 0. Now I determine the offset of the first sub node:

  int subnode = fdt_first_subnode(fdt, root);

Here, subnode is either 0 if FDT_ASSUME_MASK contains ASSUME_VALID_INPUT
or 164 (in my case) if FDT_ASSUME_MASK does not contain ASSUME_VALID_INPUT.

As far as I understand, fdt_first_subnode() should not return the node
offset of the current node if there are subnodes available.

I think the problem origins at fdt_check_node_offset_() in fdt.c: If
VALID_INPUT is set, the whole code in that function is skipped. If that
flag is not set then fdt_next_tag(fdt, offset, &offset) is called and
the resulting 'offset' is returned.

In other words, fdt_check_node_offset_() has a side effect which depends
on the VALID_INPUT flag.

Thanks!

Frank

next             reply	other threads:[~2020-08-12 15:48 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-12 15:48 Frank Mehnert [this message]
2020-08-13  7:09 ` libfdt / fdt_check_node_offset_ with VALID_INPUT David Gibson
     [not found]   ` <20200813070945.GD17532-l+x2Y8Cxqc4e6aEkudXLsA@public.gmane.org>
2020-08-13  8:06     ` Frank Mehnert
2020-08-18 16:19       ` Rob Herring
     [not found]         ` <CAL_JsqLAWa-wMMiD=VffemMiqAv-3=GNehNojWrFQqED_+QDow-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-08-20 10:18           ` David Gibson

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