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

On Tue Feb 10, 2026 at 6:33 PM CET, Herve Codina wrote:
> 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
                            ^
			    introduced

> 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 <[email protected]>
> ---
>  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 =3D 0;
> +	int nextoffset =3D offset;
>  	uint32_t tag;
>
> +	if (offset <=3D 0) {

What is the difference between 0 and a engative value?

This is where the parameter value is not obvious to the newcomer and I'd
love seeing it concisely documented.

Otherwise this patch looks good to me.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com