grcov collects and aggregates code coverage information for multiple source files. grcov processes .profraw and .gcda files which can be generated from llvm/clang or gcc. grcov also processes lcov files (for JS coverage) and JaCoCo files (for Java coverage). Linux, macOS and Windows are supported.
This is a project initiated by Mozilla to gather code coverage results on Firefox.
Table of Contents
- man grcov
- How to get grcov
- Example: How to generate source-based coverage for a Rust project
- Example: How to generate .gcda files for C/C++
- Example: How to generate .gcda files for a Rust project
- Generate a coverage report from coverage artifacts
- Alternative reports
- Hosting HTML reports and using coverage badges
- Enabling symlinks on Windows
- Build & Test
- Minimum requirements
Usage: grcov [OPTIONS] <PATHS>... Arguments: <PATHS>... Sets the input paths to use Options: -b, --binary-path <PATH> Sets the path to the compiled binary to be used --llvm-path <PATH> Sets the path to the LLVM bin directory -t, --output-types <OUTPUT TYPE> Comma separated list of custom output types: - *html* for a HTML coverage report; - *coveralls* for the Coveralls specific format; - *lcov* for the lcov INFO format; - *covdir* for the covdir recursive JSON format; - *coveralls+* for the Coveralls specific format with function information; - *ade* for the ActiveData-ETL specific format; - *files* to only return a list of files. - *markdown* for human easy read. - *cobertura* for output in cobertura format. [default: lcov] -o, --output-path <PATH> Specifies the output path. This is a file for a single output type and must be a folder for multiple output types --output-config-file <PATH> Specifies the output config file -s, --source-dir <DIRECTORY> Specifies the root directory of the source files -p, --prefix-dir <PATH> Specifies a prefix to remove from the paths (e.g. if grcov is run on a different machine than the one that generated the code coverage information) --ignore-not-existing Ignore source files that can't be found on the disk --ignore <PATH> Ignore files/directories specified as globs --keep-only <PATH> Keep only files/directories specified as globs --path-mapping <PATH> --branch Enables parsing branch coverage information --filter <FILTER> Filters out covered/uncovered files. Use 'covered' to only return covered files, 'uncovered' to only return uncovered files [possible values: covered, uncovered] --llvm Speeds-up parsing, when the code coverage information is exclusively coming from a llvm build --token <TOKEN> Sets the repository token from Coveralls, required for the 'coveralls' and 'coveralls+' formats --commit-sha <COMMIT HASH> Sets the hash of the commit used to generate the code coverage data --service-name <SERVICE NAME> Sets the service name --service-number <SERVICE NUMBER> Sets the service number --service-job-id <SERVICE JOB ID> Sets the service job id [aliases: service-job-number] --service-pull-request <SERVICE PULL REQUEST> Sets the service pull request number --parallel Sets the build type to be parallel for 'coveralls' and 'coveralls+' formats --threads <NUMBER> --precision <NUMBER> Sets coverage decimal point precision on output reports [default: 2] --guess-directory-when-missing --vcs-branch <VCS BRANCH> Set the branch for coveralls report. Defaults to 'master' [default: master] --log <LOG> Set the file where to log (or stderr or stdout). Defaults to 'stderr' [default: stderr] --log-level <LEVEL> Set the log level [default: ERROR] [possible values: OFF, ERROR, WARN, INFO, DEBUG, TRACE] --excl-line <regex> Lines in covered files containing this marker will be excluded --excl-start <regex> Marks the beginning of an excluded section. The current line is part of this section --excl-stop <regex> Marks the end of an excluded section. The current line is part of this section --excl-br-line <regex> Lines in covered files containing this marker will be excluded from branch coverage --excl-br-start <regex> Marks the beginning of a section excluded from branch coverage. The current line is part of this section --excl-br-stop <regex> Marks the end of a section excluded from branch coverage. The current line is part of this section --no-demangle No symbol demangling -h, --help Print help (see a summary with '-h') -V, --version Print version
How to get grcov
Grcov can be downloaded from releases or, if you have Rust installed,
you can run
cargo install grcov.
Example: How to generate source-based coverage for a Rust project
Install the llvm-tools or llvm-tools-preview component:
rustup component add llvm-tools-preview
Ensure that the following environment variable is set up:
Build your code:
Ensure each test runs gets its own profile information by defining the LLVM_PROFILE_FILE environment variable (%p will be replaced by the process ID, and %m by the binary signature):
Run your tests:
In the CWD, you will see a
.profraw file has been generated. This contains the profiling information that grcov will parse, alongside with your binaries.
Example: How to generate .gcda files for C/C++
gcc (or for older gcc versions pass
-fprofile-arcs options (see gcc docs).
Example: How to generate .gcda files for a Rust project
Nightly Rust is required to use grcov for Rust gcov-based coverage. Alternatively, you can
export RUSTC_BOOTSTRAP=1, which basically turns your stable rustc into a Nightly one.
Ensure that the following environment variables are set up:
export CARGO_INCREMENTAL=0 export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort" export RUSTDOCFLAGS="-Cpanic=abort"
These will ensure that things like dead code elimination do not skew the coverage.
Build your code:
If you look in
target/debug/depsdir you will see
.gcnofiles have appeared. These are the locations that could be covered.
Run your tests:
target/debug/deps/dir you will now also see
.gcdafiles. These contain the hit counts on which of those locations have been reached. Both sets of files are used as inputs to
Generate a coverage report from coverage artifacts
Generate a html coverage report like this:
grcov . -s . --binary-path ./target/debug/ -t html --branch --ignore-not-existing -o ./target/debug/coverage/
--binary-path argument is only necessary for source-based coverage.
You can see the report in
(or alternatively with
-t lcov grcov will output a lcov compatible coverage report that you could then feed into lcov's
-t lcov you could generate an lcov.info file and pass it to genhtml:
genhtml -o ./target/debug/coverage/ --show-details --highlight --ignore-errors source --legend ./target/debug/lcov.info
LCOV output should be used when uploading to Codecov, with the
--branch argument for branch coverage support.
Coverage can also be generated in coveralls format:
grcov . --binary-path ./target/debug/ -t coveralls -s . --token YOUR_COVERALLS_TOKEN > coveralls.json
grcov with Travis
Here is an example of .travis.yml file for source-based coverage:
language: rust before_install: - curl -L https://github.com/mozilla/grcov/releases/latest/download/grcov-x86_64-unknown-linux-gnu.tar.bz2 | tar jxf - matrix: include: - os: linux rust: stable script: - rustup component add llvm-tools-preview - export RUSTFLAGS="-Cinstrument-coverage" - cargo build --verbose - LLVM_PROFILE_FILE="your_name-%p-%m.profraw" cargo test --verbose - ./grcov . --binary-path ./target/debug/ -s . -t lcov --branch --ignore-not-existing --ignore "/*" -o lcov.info - bash <(curl -s https://codecov.io/bash) -f lcov.info
Here is an example of .travis.yml file:
language: rust before_install: - curl -L https://github.com/mozilla/grcov/releases/latest/download/grcov-x86_64-unknown-linux-gnu.tar.bz2 | tar jxf - matrix: include: - os: linux rust: stable script: - export CARGO_INCREMENTAL=0 - export RUSTFLAGS="-Zprofile -Ccodegen-units=1 -Copt-level=0 -Clink-dead-code -Coverflow-checks=off -Zpanic_abort_tests -Cpanic=abort" - export RUSTDOCFLAGS="-Cpanic=abort" - cargo build --verbose $CARGO_OPTIONS - cargo test --verbose $CARGO_OPTIONS - | zip -0 ccov.zip `find . \( -name "YOUR_PROJECT_NAME*.gc*" \) -print`; ./grcov ccov.zip -s . -t lcov --llvm --branch --ignore-not-existing --ignore "/*" -o lcov.info; bash <(curl -s https://codecov.io/bash) -f lcov.info;
grcov with Gitlab
Here is an example
.gitlab-ci.yml which will build your project, then collect coverage data in a format that Gitlab understands. It is assumed that you'll use an image which already has relevant tools installed, if that's not the case put the appropriate commands at the beginning of the
build: variables: # Set an environment variable which causes LLVM to write coverage data to the specified location. This is arbitrary, but the path passed to grcov (the first argument) must contain these files or the coverage data won't be noticed. LLVM_PROFILE_FILE: "target/coverage/%p-%m.profraw" script: # Run all your Rust-based tests - cargo test --workspace # Optionally, run some other command that exercises your code to get more coverage: - ./bin/integration-tests --foo bar # Create the output directory - mkdir target/coverage # This is a multi-line command. You can also write it all as one line if desired, just remove # the '|' and all the newlines. - | grcov # This path must match the setting in LLVM_PROFILE_FILE. If you're not getting the coverage # you expect, look for '.profraw' files in other directories. target/coverage # If your target dir is modified, this will need to match... --binary-path target/debug # Where the source directory is expected -s . # Where to write the output; this should be a directory that exists. -o target/coverage # Exclude coverage of crates and Rust stdlib code. If you get unexpected coverage results from # this (empty, for example), try different combinations of '--ignore-not-existing', # '--ignore "$HOME/.cargo/**"' and see what kind of filtering gets you the coverage you're # looking for. --keep-only 'src/*' # Doing both isn't strictly necessary, if you won't use the HTML version you can modify this # line. --output-types html,cobertura # Extract just the top-level coverage number from the XML report. - xmllint --xpath "concat('Coverage: ', 100 * string(//coverage/@line-rate), '%')" target/coverage/cobertura.xml coverage: '/Coverage: \d+(?:\.\d+)?/' artifacts: paths: - target/coverage/ reports: coverage_report: coverage_format: cobertura path: target/coverage.xml
This also ties into Gitlab's coverage percentage collection, so in merge requests you'll be able to see:
- increases or decreases of coverage
- whether particular lines of code modified by a merge request are covered or not.
Additionally, the HTML-formatted coverage report (if you leave it enabled) will be produced as an artifact.
grcov provides the following output types:
|lcov (default)||lcov's INFO format that is compatible with the linux coverage project.|
|ade||ActiveData-ETL format. Only useful for Mozilla projects.|
|coveralls||Generates coverage in Coveralls format.|
|coveralls+||Like coveralls but with function level information.|
|files||Output a file list of covered or uncovered source files.|
|covdir||Provides coverage in a recursive JSON format.|
|html||Output a HTML coverage report, including coverage badges for your README.|
|cobertura||Cobertura XML. Used for coverage analysis in some IDEs and Gitlab CI.|
Hosting HTML reports and using coverage badges
The HTML report can be hosted on static website providers like GitHub Pages, Netlify and others. It is common to provide a coverage badge in a project's readme to show the current percentage of covered code.
To still allow adding the badge when using a static site host, grcov generates coverage badges and a JSON file with coverage information that can be used with https://shields.io to dynamically generate badges.
The coverage data for https://shields.io can be found at
/coverage.json and the generated
bagdes are available as SVGs at
The design of generated badges is taken from
shields.io but may not be updated immediately if there
is any change. Using their endpoint method is recommended if other badges from their service are
Enabling symlinks on Windows
grcov uses symbolic links to avoid copying files, when processing directories
of coverage data. On Windows, by default, creating symbolic links to files
requires Administrator privileges. (The reason is to avoid security attacks in
applications that were designed before Windows added support for symbolic
When running on Windows
grcov will attempt to create a symbolic link. If that
grcov will fall back to copying the file. Copying is less efficient
but at least allows users to run
grcov will also print a warning
when it falls back to copying a file, advising the user either to enable the
privilege for their account or to run as Administrator.
You can enable the "Create Symbolic Links" privilege for your account so that
you do not need to run as Administrator to use
- Click Start, then select "Local Group Policy Editor". Or just run
gpedit.mscto open it directly.
- In the navigation tree, select "Computer Configuration", "Windows Settings", "Security Settings", "Local Policies".
- In the pane on the right, select "Create symbolic links" and double-click it.
- Click "Add User or Group", and add your account.
- Log out and then log back in.
Let's consider we have a project at with username
sample and project
awesome that is hosted with
GitHub Pages at
By using the the
shields.io endpoint we can create a Markdown badge like so:
If we want to avoid using
shields.io as well, we can use the generated badges as follows (note
the different URL for the image):
This project is using pre-commit. Please run
pre-commit install to install the git pre-commit hooks on your clone. Instructions on how to install pre-commit can be found here.
Every time you will try to commit, pre-commit will run checks on your files to make sure they follow our style standards and they aren't affected by some simple issues. If the checks fail, pre-commit won't let you commit.
Build & Test
To run unit tests:
cargo test --lib
To run integration tests, it is suggested to use the Docker image defined in tests/Dockerfile. Simply build the image to run them:
docker build -t marcocas/grcov -f tests/Dockerfile .
Otherwise, if you don't want to use Docker, the only prerequisite is to install GCC 7, setting the
GCC_CXX environment variable to
g++-7 and the
GCOV environment variable to
gcov-7. Then run the tests with:
- GCC 4.9 or higher is required (if parsing coverage artifacts generated by GCC).
- Rust 1.52
Published under the MPL 2.0 license.