bug#33639: ISO installer image is broken on i686

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

I wrote:
> > If all files and directories have the same names and the same content,
> > then xorriso runs with the same arguments and the same SOURCE_DATE_EPOCH
> > value are supposed to create byte-identical result ISOs.

Ludovic Courtès wrote:
> I’ve tried setting it but that doesn’t make any difference.

We should investigate this ...
... yes, there is some problem. But not always.

Timestamps of the root directory differ after mapping to an address
that is not the ISO root directory (here: /x):

  xorriso -outdev test.iso -map x /x
  xorriso -outdev test2.iso -map x /x

but not after mapping to the root directory:

  xorriso -outdev test.iso -map x /
  xorriso -outdev test2.iso -map x /

This would explain why my tests for Debian ISOs do not show this problem.

Do i get it right that gnu/build/vm.scm maps no files to "/" but all to
deeper paths:
                "etc=/tmp/root/etc"
                "var=/tmp/root/var"
                "run=/tmp/root/run"
I am unsure about
                "-path-list" "-"


I will now dig into the source to find the reason and maybe a preliminary
remedy.


> How did you visualize differences, Florian?

(I'm aware that i am not Florian.)

I made myself a little program "hxd" for combined hex-cleartext-decimal dump,
positional diff, and (not to be focused too much) CD-Text decoding.

===========================================================================

$ export SOURCE_DATE_EPOCH=$(date +%s)
$ xorriso -outdev test.iso -map x /x
...
xorriso : NOTE : Environment variable SOURCE_DATE_EPOCH encountered with value 1555311212
...
$ xorriso -outdev test2.iso -map x /x
...
xorriso : NOTE : Environment variable SOURCE_DATE_EPOCH encountered with value 1555311212
...
$ hxd -diff test.iso test2.iso

   32944 :    15   7  38  43   0   2   0   0   1   0   0   1   1   0  32  32
                       &   +
000080b0 :    0f  07  26  2b  00  02  00  00  01  00  00  01  01  00  20  20
                         ###
000080b0 :    0f  07  26  36  00  02  00  00  01  00  00  01  01  00  20  20
                       &   6
   32944 :    15   7  38  54   0   2   0   0   1   0   0   1   1   0  32  32

... more differences ...

===========================================================================

It looks like the root directory got the current timestamp. The other
differences are with the ".." directory entries of the directories in
the first level under "/".


The source of "hxd" is pure C, no special dependencies, 8141 bytes.
Shall i upload it somewhere ?


Have a nice day :)

Thomas