Does diffoscope compares disk partitions

Thomas Schmitt scdbackup at
Wed Mar 1 21:59:32 UTC 2023


Mattia Rizzolo wrote:
> I already knew that hybrid ISO 9660 are pretty much devil's offspring,
> and I guess I could have done without your introduction to them /o\

Since i am helping to create them i feel obligated to warn the public.

> FWIW, currently diffoscope _does_ have a iso9660 comparator, but that
> just runs libarchive on it, so I _believe_ it ignores the existence of
> an eventual partition table and just goes straight to the really
> compliant "data part" of the image.

That's a bit naive. The file tree and the data files' content is only
a part of a bootable ISO 9660 image. There's executable code in the
blind spots of such a view: MBR legacy BIOS boot code, EFI programs in
the EFI partition, "hidden" El Torito boot images, ...

> I know that thing has been used to work on reproducible bootable image,

Possibly because typical pitfalls aren't tested. Like FAT timestamps in
the EFI partition.

> so I guess it just always happened that the "hybrid part" of them were
> already reproducible :3

It is possible to make reproducible ISOs by xorriso and SOURCE_DATE_EPOCH.
But the input files for the ISO production have to be identical, too.
Both, the use of SOURCE_DATE_EPOCH and care for identical input are not
tradition with bootable ISO production.

So another reason for no protests might be that bootable ISOs aren't often
challenged by reproducibility tests which use diffoscope.

Have a nice day :)


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