Re: [PATCH v3 1/2] boot: android: Always use 8-byte aligned DT with libfdt

[Mattijs Korpershoek <mkorpershoek@kernel.org>]

Hi Marek,

Thank you for the patch.

On Wed, Nov 19, 2025 at 20:32, Marek Vasut <marek.vasut+renesas@mailbox.org> wrote:

> Newer versions of libfdt strictly check whether the FDT blob
> passed to them is at 8-byte aligned offset, if it is not, then
> the library fails checks with -FDT_ERR_ALIGNMENT . Currently,
> android_image_print_dtb_contents() passed FDT directly mapped
> from abootimg to libfdt, and this FDT is not always aligned to
> 8-byte offset. Specifically, the FDTs are somewhat packed in
> the abootimg, therefore if the first FDT blob is e.g. 0xfd bytes
> long, then the next FDT blob ends up at 0xfd offset, which is
> not 8-byte aligned.
>
> Fix this by first extracting the header into 8-byte aligned buffer,
> checking only the header for validity, and then by copying the
> entire FDT into newly allocated 8-byte aligned buffer. While this
> is not efficient, it is the correct way to handle DTs, which must
> be at 8-byte aligned offsets. Mitigate the inefficiency for the
> common case by checking whether the DT might be 8-byte aligned and
> if it is, map it directly.
>
> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>

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