bug#33639: ISO installer image is broken on i686

["Ludovic Courtès" <ludo@gnu.org>]

Dear Xorriso hackers,

While building an ISO for i686, running Xorriso 1.5.0 built for i686
(actually ‘grub-mkrescue’, but that’s just a wrapper around Xorriso) in
qemu-system-i386, we end up with an ISO image containing files that lead
to I/O errors (“attempt to access beyond end of device”):

--8<---------------cut here---------------start------------->8---
ludo@ribbon ~/src/guix$ sudo losetup /dev/loop0 /gnu/store/1yanxg3cz5wi6vhpvhipxvmjwm201fbm-image.iso
ludo@ribbon ~/src/guix$ sudo mount -t iso9660 /dev/loop /mnt/disk/
mount: /mnt/disk: WARNING: device write-protected, mounted read-only.
ludo@ribbon ~/src/guix$ cat < /mnt/disk/var/guix/db/db.sqlite > /dev/null
cat: -: Eraro de en-eligo
ludo@ribbon ~/src/guix$ dmesg |tail
[   41.186408] shepherd[1]: Service guix-daemon has been started.
[   45.725418] IPv6: ADDRCONF(NETDEV_UP): enp0s31f6: link is not ready
[   45.933911] IPv6: ADDRCONF(NETDEV_UP): enp0s31f6: link is not ready
[   49.496112] e1000e: enp0s31f6 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: None
[   49.496165] IPv6: ADDRCONF(NETDEV_CHANGE): enp0s31f6: link becomes ready
[  203.358136] ISO 9660 Extensions: RRIP_1991A
[  215.199352] attempt to access beyond end of device
[  215.199357] loop0: rw=524288, want=1903876, limit=1899264
[  215.199362] attempt to access beyond end of device
[  215.199363] loop0: rw=0, want=1903532, limit=1899264
--8<---------------cut here---------------end--------------->8---

The output of Xorriso and the kernel when it builds the image looks
good.

(More info at <https://issues.guix.info/issue/33639>.)

Using the exact same build process for x86_64 leads to valid ISO images.

Does that ring a bell or would you have advice to further debug it?

Thanks,
Ludo’.