/zld-memory-issues

Primary LanguageStarlark

Purpose

Demonstrate that on macos + apple silicon, zig ld uses prohibitive amounts of time and memory. On larger projects, linking multiple objects in parallel with zig ld can easily OOM on a beefy M# with 64GB RAM + 64GB swap.

Minimized zig repro

For a full repro, see "Initial bazel repro" below. To minimize, I copied all the files in objs.

Zig repro: xcrun ~/Downloads/zig-macos-aarch64-0.13.0-dev.75+5c9eb4081/zig c++ -o /tmp/foo objs/*.

The activity monitor reports more than 14GB for and time says:

real    0m12.740s
user    0m11.066s
sys     0m3.427s

By comparison, clang repro: xcrun clang++ -o /tmp/foo objs/*.

real    0m0.912s
user    0m3.993s
sys     0m0.806s

Initial bazel repro

bazel build @llvm-project//llvm:opt --sandbox_debug -s

Copy the cd from last command printed by bazel, it resembles:

cd  /private/var/tmp/_bazel_${USER}/<hash>/execroot/_main

Then run:

zig c++ -target aarch64-macos-none -o /tmp/opt objs/*.a -pthread -ldl -Wl,-headerpad_max_install_names -Wl,-S -fno-lto