emacs reproducible builds part1 of 2 : eln

[Bernhard M. Wiedemann]

Dear emacs devs,

I'm working on reproducible builds for openSUSE
and in that process found that our emacs-29.1
package varies across builds from 2 different issues

The diff is visible at
https://rb.zq1.de/compare.factory-20231231/diffs/emacs-compare.out

Here is a simple reproducer that works in our build env:

cd ~/rpmbuild/BUILD/emacs-29.1/native-lisp &&
 for i in $(seq 10) ; do
  ../src/emacs -batch \
  --eval "(batch-native-compile t)" ../lisp/term/x-win.el &&
  md5sum 29.1-70b784e9/x-win-3c49581f-6ddb7e08.eln
 done | sort | uniq -c


That prints variations of
      6 0c749bdbef8d9fa7b1afc2f042caf45b 
29.1-70b784e9/x-win-3c49581f-6ddb7e08.eln
      2 3022ea8c675b69ac79005281fd824179 
29.1-70b784e9/x-win-3c49581f-6ddb7e08.eln
      2 57bc581456c38395e9ac6409bbcb0d6e 
29.1-70b784e9/x-win-3c49581f-6ddb7e08.eln


while the same with setarch -R ../src/emacs
produces deterministic
     10 0c749bdbef8d9fa7b1afc2f042caf45b 
29.1-70b784e9/x-win-3c49581f-6ddb7e08.eln

So somewhere in the batch-native-compile code is a place that adds 
ASLR-related non-determinism into the .eln file. From the diff, it 
probably is some ordering issue.

I'd appreciate pointers to where that non-determinism gets added and how 
to patch it out.

And once that is solved, there is still part2: pdmp

Ciao
Bernhard M.

OpenPGP_signature.asc
Description: OpenPGP digital signature