Count overflow warning

[damienrg]

Following #555 (comment), you can find a project that triggers the problem:
https://gitlab.com/damienrg/grcov-count-overflow

/cc @calixteman

[calixteman]

Cool thx, I'll have a look on that.

[calixteman]

And I can reproduce with:

RUSTFLAGS="-Zinstrument-coverage" LLVM_PROFILE_FILE="test-%p-%m.profraw" cargo +nightly test
grcov --binary-path ./target/debug/ -s . -t html --branch --ignore-not-existing --ignore "/*" -o ./coverage/ .

[calixteman]

Interestingly, faulty counters are not same from a run to an other, so I'd say that some counters are concurrently accessed from the different threads.
So I ran tests in adding -- --test-threads 1 and no more underflow \o/.
With clang it's possible to have atomic counters when profiling:
https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fprofile-update
so we need to figure out how to pass this option to rustc.
By the way, it very likely means that no one should trust in these counters...

[dnaka91]

I wanted to run grcov on one of my older crates and got a Execution count overflow detected. error as well. That's the same thing as described in this issue right?

In the hope that this might help in further investigating the issue. The repo is https://github.com/dnaka91/chronver and I ran the following commands on it:

RUSTFLAGS="-Zinstrument-coverage" LLVM_PROFILE_FILE="coverage-%p-%m.profraw" cargo +nightly test --all-features
rustup run nightly grcov . -s . --binary-path ./target/debug/ -t html --branch --ignore-not-existing -o ./target/debug/coverage

[DanielJoyce]

-- --test-threads 1 didn't fix it for me.

[DanielJoyce]

Looks like reports ARE generated, it's just a warning it seems.

[marco-c]

Yes, it is just a warning and doesn't affect the line level coverage, just the number of times a line is hit.