[PATCH v4] tools: fit_image: Fallback to 8-byte alignment for flat_dt images

[Marek Vasut]

On 1/28/26 4:50 PM, Tom Rini wrote:
> On Wed, Jan 28, 2026 at 04:42:47PM +0100, Marek Vasut wrote:
>> On 1/28/26 4:26 PM, Padhi, Beleswar wrote:
>>>
>>> On 1/28/2026 8:26 PM, Marek Vasut wrote:
>>>> On 1/28/26 3:18 PM, Beleswar Padhi wrote:
>>>>> From: Marek Vasut <marek.vasut+renesas at mailbox.org>
>>>>
>>>> Please drop this , it isnt needed.
>>>>
>>>>> When CONFIG_SPL_MULTI_DTB_FIT is enabled, multiple device trees are
>>>>> packed inside the multidtb.fit FIT image. While the individual DTBs
>>>>> and the FIT image start address are 8-byte aligned, the DTBs embedded
>>>>> within the FIT image are not guaranteed to maintain 8-byte alignment.
>>>>>
>>>>> This misalignment causes -FDT_ERR_ALIGNMENT failure in
>>>>> setup_multi_dtb_fit() when locating the next available DTB within the
>>>>> FIT blob and setting gd->fdt_blob, because of the recent libfdt
>>>>> hardening since commit 0535e46d55d7 ("scripts/dtc: Update to upstream
>>>>> version v1.7.2-35-g52f07dcca47c")
>>>>>
>>>>> To fix this, check the image type when extracting
>>>>
>>>> "extracting" ? This code changes mkimage, so not "extracting" but
>>>> "packing" (into fitImage), right ?
>>>
>>>
>>> Well the function name is fit_extract_data(). It is documented as
>>> extracting
>>> all the data properties of a node to the end of the fit. So just keeping
>>> the
>>> same terminology. Its obviously not in the same context as extracting data
>>> out of a FIT image to consume information...
>>
>> ... check the image type when moving image data at the end of the tree ...
>> or something like that ?
>>
>>>>> FIT image data and
>>>>> set the alignment size to 8 bytes (if not already) only for flat_dt
>>>>> images. This ensures correct alignment for device tree blobs as per the
>>>>> DT spec, while also allowing different alignment sizes for other image
>>>>> types within the FIT.
>>>>
>>>> [...]
>>>>
>>>>> diff --git a/tools/fit_image.c b/tools/fit_image.c
>>>>> index e865f65a400..f842c845771 100644
>>>>> --- a/tools/fit_image.c
>>>>> +++ b/tools/fit_image.c
>>>>> @@ -682,9 +682,17 @@ static int fit_extract_data(struct
>>>>> image_tool_params *params, const char *fname)
>>>>>        for (node = fdt_first_subnode(fdt, images);
>>>>>             node >= 0;
>>>>>             node = fdt_next_subnode(fdt, node)) {
>>>>> -        const char *data;
>>>>> +        const char *data, *type;
>>>>>            int len;
>>>>>    +        /* Fallback to 8-byte alignment for DTBs if unaligned */
>>>>> +        type = fdt_getprop(fdt, node, FIT_TYPE_PROP, &len);
>>>>> +        if (type &&
>>>>> +            len == sizeof("flat_dt") &&
>>>>> +            !memcmp(type, "flat_dt", len) &&
>>>>> +            align_size & 0x7)
>>>>
>>>> What will be the resulting alignment if align_size = 0x1f ? 8 right
>>>> ? I think it should be 0x20 .
>>>
>>>
>>> I thought we agreed on resetting align_size to 8 if its not already aligned
>>> (regardless if < or > 8) in v3 version of this patch[0]. Do we really
>>> have to
>>> align the align_size var itself? It seems like a overkill to me...
>> Maybe simply call round_up(8) on the align_size , to align to the next
>> 8-byte aligned offset , but somewhat respect user wishes ?
>>
>> But looking at this code one more time , look at the calloc() in this
>> function, I think you might also have to allocate a bit more memory to
>> really hold all the newly aligned DTs, right ?
>>
>> Also, don't you need to align the buf_ptr as well ? Consider a scenario
>> where the fitImage contains two images, one ends at 4-byte aligned address,
>> followed by a DT. The users passes -B 4 to mkimage, and I think buf_ptr
>> would then be 4-byte aligned, so will the DT, no ?
> 
> I'm confused. Where did we go from "default should be 8 not 4, for
> device trees" to "take what the user passed, make sure is 8b aligned" ?
> If the user tells us to do something, we should do it, and they can
> suffer the potential consequences. If the user doesn't tell us to do
> something, we should pick a reasonable default.
You can remove the "the user passes -B 4" part from my example, keep the 
rest, the DT will likely end up 4-byte aligned, no ?