Fails to build error: variable 'cons_0' set but not used

[mothran]

When building a target project cargo afl build on the following setup I get the below error:

      stderr: "GNUmakefile.llvm:68: you are using an in-development llvm version - this might break llvm_mode!\nsrc/afl-fuzz-redqueen.c:1603:20: error: variable 'cons_0' set but not used [-Werror,-Wunused-but-set-variable]\n  u8  cons_ff = 0, cons_0 = 0;\n                   ^\n1 error generated.\nmake: *** [GNUmakefile:452: afl-fuzz] Error 1\n",
  }', /home/user/.cargo/registry/src/gh.neting.cc-1ecc6299db9ec823/afl-0.12.16/build.rs:72:5

• clang version 15.0.7
• LLD 15.0.7
• Arch Linux 6.2.9-arch1-1

[smoelius]

To be clear, afl.rs installs fine (i.e., cargo install afl completes without error)?

Can you share the project that causes the problem?

[mothran]

Yup cargo install -f afl work without issue:

   Replacing /home/user/.cargo/bin/cargo-afl
    Replaced package `afl v0.12.16` with `afl v0.12.16` (executable `cargo-afl`)

This is a brand new project from cargo new afl-test the adding:

[dependencies]
afl = "*"
url = "*"

To Cargo.toml and then Using the Url fuzzer from the book here: https://rust-fuzz.github.io/book/afl/tutorial.html

main.rs:

use afl::fuzz;

fn main() {
    fuzz!(|data: &[u8]| {
        if let Ok(s) = std::str::from_utf8(data) {
            let _ = url::Url::parse(&s);
        }
    });
}

The only difference from that is I am using a specific version of the rust-toolchain by adding the following file to the crate root: rust-toolchain.toml

[toolchain]
channel = "nightly-2022-10-28"
components = [ "rustfmt", "rust-src" ]
targets = [ "wasm32-unknown-unknown" ]
profile = "minimal"

[smoelius]

Could you try cargo afl build --release and see if the problem goes away?

I think what is happening is cargo afl build causes afl.rs's build script to run. Because the default profile is dev, DEBUG gets set to true. Then this becomes a duplicate of #202 (comment). This seems to be a problem when Clang is the compiler, but not otherwise.

Ideally, we would run the build script when afl.rs is being installed, but not when it is used as a dependency. However, this issue suggests there's no easy way to do that right now: rust-lang/cargo#4001

At present, I am inclined to go with @vkleen's original proposal, which was to remove the DEBUG environment variable unconditionally.

Does anyone reading this have any better ideas?

[mothran]

@smoelius Yep that worked!

It might be nice to make a note in the book / docs but this makes sense to me. It does cause some conflicts with check-on-save tooling like cargo check|clippy but I think thats a minor issue.

[smoelius]

@mothran Earlier today, I published a new version of afl.rs that removes the DEBUG environment variable unconditionally.

Could I impose on you to install the new version and run your test again without the --release flag? I think it should work now.

[mothran]

@smoelius that worked for me, Thanks!

[smoelius]

Thank you!