scx schedulers installed from cargo are segfaulting

[arighi]

ubuntu@ubuntu:~$ sudo ~/.cargo/bin/scx_bpfland
08:40:08 [INFO] scx_bpfland 1.0.8 x86_64-unknown-linux-gnu SMT off
...
Segmentation fault
ubuntu@ubuntu:~$ sudo ~/.cargo/bin/scx_lavd
08:40:13 [INFO] Autopilot mode is enabled by default.
...
Segmentation fault

It seems to happen both on Ubuntu and CachyOS.

[likewhatevs]

gentoo also (so probably everywhere)

[JohnRTitor]

I believe we had the same problem on NixOS (#927), it was solved by adding proper include paths of compiled libbpf through environment variables BPF_EXTRA_CFLAGS_PRE_INCL and RUSTFLAGS.

https://github.com/NixOS/nixpkgs/blob/909365d2203fe5570203a5032af3a564b6ab4705/pkgs/os-specific/linux/scx/scx_rustscheds.nix#L37-L48

If that's hard to read, we are just adding include paths of the compiled libbpf.

When using meson to compile scx, this is done automatically.

scx/meson.build

Lines 321 to 327 in b4db5ee

	foreach header: libbpf_h
	cargo_env.append('BPF_EXTRA_CFLAGS_PRE_INCL', '-I' + header, separator: ' ')
	endforeach
	cargo_env.append('RUSTFLAGS',
	'-C relocation-model=pic -C link-args=-lelf -C link-args=-lz -C link-args=-lzstd -L '
	+ fs.parent(libbpf_a), separator: ' ')

[etsal]

gentoo also (so probably everywhere)

Yeah can reproduce on arch too.

[likewhatevs]

BTW i think the "fix" is folks need to install scx schedulers using cargo install --locked. Not the first time I've seen this on a project (iirc zellij does that also), so maybe this is why.

• that or (maybe and) we pin more versions of packages to avoid this issue.

[likewhatevs]

something is pulling in libbpf-sys v1.5.0+v1.5.0 when cargo install runs so I think pinning to versions specified here might fix this: #1015

[etsal]

I think that's fair as a temporary measure, however we should also check why 1.5.0 is failing because we need it to support multiple compilation units in Rust.

[etsal]

Turns out that the versions specified in #1015 are perfectly fine for multiple compilation units, so there is no downside to going with them.