[PATCH] boot: Assure FDT is always at 8-byte aligned address

[Marek Vasut]

On 11/18/25 4:47 AM, Simon Glass wrote:

Hello Simon,

>>>> 2294         } else if (load_op != FIT_LOAD_IGNORED && image_type ==
>>>> IH_TYPE_FLATDT &&
>>>> 2295                    ((uintptr_t)buf & 7)) {
>>>> 2296                 loadbuf = memalign(8, len);
>>>> 2297                 load = map_to_sysmem(loadbuf);
>>>> 2298                 memcpy(loadbuf, buf, len);
>>>>
>>>> ...
>>>>
>>>> 2309         /* verify that image data is a proper FDT blob */
>>>> 2310         if (load_op != FIT_LOAD_IGNORED && image_type ==
>>>> IH_TYPE_FLATDT &&
>>>> 2311             fdt_check_header(loadbuf)) { <----------------- this
>>>> 2312                 puts("Subimage data is not a FDT\n");
>>>> 2313                 return -ENOEXEC;
>>>> 2314         }
>>>>
>>>>> Perhaps we should deprecate FITs with internal data, too?
>>>> We cannot break compatibility and stop supporting old fitImage, so this
>>>> is irrelevant here.
>>>
>>> OK, so please create a function which can detect an FDT header without
>>> it being aligned, like the other code you wrote. Then it will be safe
>>> to call that here, even if unaligned.
>> But we actually do want to detect unaligned broken FDT header and either
>> fix it up or stop processing, we don't want to perpetuate handling of
>> broken FDTs and pretend that is OK, it shouldn't be I think. Hence this
>> fixup.
> 
> The decision as to whether something is an FDT is made a lot earlier
> than the actual processing of it. For the former there is no need to
> allocate and copy. For the latter we need to.

The test whether the FDT is valid cannot be done earlier, this place is 
literally the first place when the FDT is decompressed/loaded to the 
target location.

> Anyway, you are doing the patches, so do what you think is best. But
> please create a function for this, rather than lots of little
> hand-crafted checks around the place.
I am confused, function for what exactly ?