zyimage: make output byte order explicit - #75
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device_id and crc32 were written in native host byte order, with no byte-swap calls at all, so the on-disk output was only correct on little-endian build hosts. Make the existing little-endian behavior explicit with htole32() and document the byte layout, so a porter reading the vendor's CONFIG_TARGET_DEVICE_ID can map it to the equivalent OpenWrt ZYIMAGE_ID. Assisted-By: Claude <noreply@anthropic.com> Signed-off-by: Aleksei Sviridkin <f@lex.la>
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zyimage writes device_id and crc32 into the signature header in native host byte order — there is no htobe32/htole32 call anywhere in the tool, so the output is only correct on little-endian build hosts. This makes the existing little-endian behavior explicit with htole32() on both fields and documents the byte layout, so the relationship between OpenWrt's ZYIMAGE_ID values and the vendor's device-id constants is discoverable from the source.
I used htole32 rather than htobe32 to match the actual on-disk format: OpenWrt's ZYIMAGE_ID definitions were chosen assuming this little-endian encoding, and switching to big-endian would silently change the on-disk device id for every device that currently uses zyimage.
Testing: built with CMake on Linux and with a plain compiler on macOS. Verified the change is output-neutral on little-endian hosts by building the tool before and after the change and comparing signed output byte-for-byte across several device ids and file sizes.