Sharing this from Spack (spack.io) how they handle OpenGL or runtime type library dependencies:

If a binary is built in a CI/CD pipeline at /opt/spack/build/... and you download it to /home/user/super_long_project_name/spack/..., Spack needs to rewrite the RPATH in the ELF binary.

The Problem: You can safely shrink a string in a compiled binary, but if you try to replace a string with a longer one, you will overwrite adjacent memory and corrupt the executable.

The Solution: Spack uses a configuration called padded_length (often set to 128 characters or more). During the initial build, Spack intentionally pads the installation path with extra characters. This forces the compiler to generate massive, padded RPATH strings in the binary.

When you download the binary cache, Spack's relocation logic strips out the padding and inserts your local, shorter path. Because the original string was artificially inflated, Spack always has enough room to rewrite the path without breaking the binary.

Gonna try something like this:

AsyncPostBuildHookInfo info;
info.act = std::make_unique<Activity>(
    *logger,
    lvlTalkative,
    actPostBuildHook,
    fmt("running async-post-build-hook '%s'", worker.settings.asyncPostBuildHook),
    Logger::Fields{worker.store.printStorePath(drvPath)});
info.sink = std::make_unique<LogSink>(*info.act);
info.out = std::make_unique<Pipe>();
info.out->create();
info.out->writeSide.close();
info.handleOutput = std::thread([&](Descriptor readSide, Sink & sink) {
    drainFD(readSide, sink);
}, info.out->readSide.get(), *info.sink);

// PushActivity pact(info.act->id);

auto pid = runAsyncPostBuildHook(worker.settings, worker.store, *info.out, drvPath, outputPaths);

worker.asyncPostBuildHooks[pid] = std::move(info);

Gonna try something like this:

AsyncPostBuildHookInfo info;
info.act = std::make_unique<Activity>(
    *logger,
    lvlTalkative,
    actPostBuildHook,
    fmt("running async-post-build-hook '%s'", worker.settings.asyncPostBuildHook),
    Logger::Fields{worker.store.printStorePath(drvPath)});
info.sink = std::make_unique<LogSink>(*info.act);
info.out = std::make_unique<Pipe>();
info.out->create();
info.out->writeSide.close();
info.handleOutput = std::thread([](Descriptor readSide, Sink & sink) {
    drainFD(readSide, sink);
}, info.out->readSide.get(), *info.sink);

// PushActivity pact(info.act->id);

auto pid = runAsyncPostBuildHook(worker.settings, worker.store, *info.out, drvPath, outputPaths);

worker.asyncPostBuildHooks[pid] = std::move(info);

i have made an abomination: binfmt-misc support in nix https://github.com/dramforever/nix/tree/binfmt-misc
see also tracking stuff in https://github.com/dramforever/nix/pull/25
tl;dr nix --extra-platforms x86_64-linux --binfmt-misc 'x86_64-linux=:x86_64-linux:M:...' build ...
"just" requires 6.7+ kernel and user namespaces, and it works with diverted store and uid-range

featuring: double namespacing!

not yet even draft pr quality, docs are "i may be here to answer questions", but it's working well enough that i think it's worth having y'all take a look