cloud-hypervisor/docs/coverage.md

Code coverage

LLVM provides a set of tools to collect code coverage data and present the data in human-consumable forms.

Building a suitable binary

The compiler flag to generate code coverage data has been stabilized since Rust 1.60.

An instrumented binary can be built with the following command:

cargo clean && RUSTFLAGS='-C instrument-coverage' cargo build

Using either debug or release profile is fine. You will need to adjust the path for some commands.

Running the binary

Run the binary as you normally would. When the process exits, you will see files with the prefix profraw.

Multiple runs of the same binary will produce multiple profraw files.

The more diverse the runs are, the better. Try to exercise different features as much as possible.

Combining raw data

Raw data files can be combined with llvm-profdata.

rustup component add llvm-tools-preview
# Assuming profraw files reside in the current directory and its children directories
find . -name '*.profraw' -exec llvm-profdata merge -sparse {} -o coverage.profdata \;

A file named coverage.profdata will be generated.

Generating HTML files for human consumption

This can be done either with LLVM or grcov.

Here is an example using grcov.

cargo install grcov
# Assuming the profdata file is in the top level directory of the Cloud Hypervisor repository
grcov . --binary-path ./target/x86_64-unknown-linux-gnu/release -s . -t html --branch --ignore-not-existing -o coverage-html-output/

You can then open the index.html file under coverage-html-output to see the results.