Gothenburg 2026 - Day 2 - the remaining 1%

The remaining 1%

Which packages are not reproducible, and why?

• Profile guided optimization: systemd, gzip, gcc (see idea)
  • Saves compile time
  • Possible resolutions
    1. Disable it, 10% performance hit
    2. Make profile 100% deterministic (e.g. gzip)

• Idea: Fuzzer that make a profile for the code.

• compilers: Haskell, mono, erlang, zig, nim, ocaml, llvm, …
  • Timestamp
  • Address space memory optimizations
  • Idea: Fuzzer that “understands” the language, find inputs that are constant but non-deterministic output.
• output memory dump into result: Emacs lisp, scheme 48, Racket, Clisp, …
  • This is done to improve startup time
• Linux, grub, xen
  • Dynamic signing key of modules
• Building of images/vms

Thought: make the profile a different package, similar to the signing solution in Linux.

Idea: use a fuzzer to find an input that makes a test undeterministic. Fuzzer that make a profile for the code. Fuzzer that “understands” the language, find inputs that are constant but non-deterministic output.

Idea: Upstream instructions on how to perform a profiling run. Example: profile.sh which runs the program and outputs instrument binaries, providing profiling information and is determinstic.