Update for new LLVM pass manager

[taiki-e]

Fixes #192

This drops support for the old nightly, but that should be fine. (See discussion in cargo-fuzz: rust-fuzz/cargo-fuzz#277)

[smoelius]

So, as expected, this change breaks afl.rs on stable.

Steps to reproduce:

git submodule update --init
cargo install --path .
cargo new dummy
cd dummy
cargo afl build
mkdir in
head -c 1 /dev/zero > in/zero
cargo afl fuzz -i in -o out target/debug/dummy

So I am wondering what the best way to handle this is. Merge this once -C passes=sancov-module hits stable?

I'm not sure we want to support the latest nightly at the expense of stable.

Thanks for doing this, BTW, @taiki-e.

[frewsxcv]

If the latest commit works, where we conditionally include the new flag with the right version, then this LGTM!

[taiki-e]

Updated PR to check for rustc and LLVM versions.

The new flag is used when Rust 1.57+ that rust-lang/rust#88243 is merged and LLVM13+.

Since rust-lang/rust#88243 is available on nightly-2021-09-26+, this drops support for the old 1.57-nightly, but I think it is fine because only nightly is affected.

(Using the way described by @smoelius, I confirmed that it works for stable(1.55.0), beta(1.56.0), and nightly(1.57.0).)

[smoelius]

Hmm. I'm having some trouble with the new flag on Linux: https://github.com/smoelius/afl.rs/runs/3779272226?check_suite_focus=true

[smoelius]

Adding -C lto=no seems to fix the problem, but I'm not sure that's the right way to fix this problem.

Adding -C link-dead-code=yes doesn't seem to be enough.

I'm curious as to why cargo-fuzz doesn't seem to be experiencing this problem.

[smoelius]

I'm curious as to why cargo-fuzz doesn't seem to be experiencing this problem.

It appears cargo-fuzz doesn't have this problem because of -C codegen-units=1:
https://github.com/rust-fuzz/cargo-fuzz/blob/8c964bf183c93cd49ad655eb2f3faecf543d0012/src/project.rs#L204-L214

In particular, if you run the following in a temporary directory with the latest version of carg-fuzz, you will get link errors:

cargo init --lib
cargo fuzz init
cd fuzz
echo -e '\n[profile.dev]\nopt-level = 1' >> Cargo.toml
cargo fuzz build --dev

What's more, if you repeat #193 (comment) with -C codegen-units=1, the target will build: https://github.com/smoelius/afl.rs/runs/3792287661?check_suite_focus=true

[smoelius]

@taiki-e, what do you think about adding -C codegen-units=1, perhaps also guarding it with the version_meta.semver.minor >= 57 check?

If you agree, could you also include a short comment about why the option is there?

Thank you again for going to this trouble.

[taiki-e]

@smoelius: Seems -C codegen-units=1 is the right solution. Thanks for finding it!

perhaps also guarding it with the version_meta.semver.minor >= 57 check?

I read a PR that forces 1 CGU and a related issue, and I feel it's fine to always force 1 CGU on release mode.

If you agree, could you also include a short comment about why the option is there?

Done in eb50593.

[smoelius]

Perfect! Thanks, @taiki-e. I'll push a new release soon.