imgtool: dumpinfo: Fixed support for the custom alignment

[mingulov]

Fixed support for the custom alignment (in case if BOOT_MAGIC_2 is provided). Current version fails to parse it with an error:

ValueError: invalid literal for int() with base 0: b'...

Using the same solution as 'swap_size' parsing as a fix.

[utzig]

The proposal solution doesn't seem correct to me. For swap_size it was OK because it is always written in little endian, but max align is written according to the given endiannes, as can be seen here: https://github.com/mcu-tools/mcuboot/blob/main/scripts/imgtool/image.py#L179

int(trailer_magic[:2], 0) is obviously wrong because it is converting a string representing a number which is not what we have here.

One simple way to do it, is to convert in both little and big endian, maybe just get a min of those, and check the value against the list of valid max align values, eg:

ma = trailer_magic[:2]
max_align = min(int.from_bytes(ma, "little"), int.from_bytes(ma, "big"))
assert max_align in [8, 16, 32], "Invalid alignment"

Well, something like that...

[mingulov]

Thank you.

I have checked deeper, unfortunately dumpinfo does not support big endian images at all (or to be more precise - images with non sys.byteorder endianness), it fails much earlier due to the 1st data parsing:
https://github.com/mcu-tools/mcuboot/blob/main/scripts/imgtool/dumpinfo.py#L71

_header = struct.unpack('IIHHIIBBHI', b[:28])

(incorrect protected_tlv_size, img_size will trigger struct.error).

So there is no need to implement separate support for 'max_align' only, but at that line it should not be "little" at least, as it should be that "default sys.byteorder".

Almost the same issue with 'verify' command: https://github.com/mcu-tools/mcuboot/blob/main/scripts/imgtool/image.py#L629

Might be I will take a look, can Big Endian images just started to be supported properly by dumpinfo / verify.

[mingulov]

After more checks - it would be better to do it properly and not re-write again when add proper support for little/big endianness.