coverage-analysis
Coverage analysis measures code exercised during fuzzing. Use when assessing harness effectiveness or identifying fuzzing blockers.
Security Assessment
About coverage-analysis
The coverage-analysis skill is designed to measure the extent to which code is exercised during fuzzing campaigns. It provides developers and security engineers with a clear view of which parts of their code are being executed, allowing them to identify potential fuzzing blockers such as hard-to-trigger conditional checks, also known as magic value checks. By analyzing coverage, teams can assess the effectiveness of their fuzzing harnesses and improve overall test quality, ensuring that critical code paths are not left untested.
Key capabilities of the coverage-analysis skill include support for multiple toolchains such as LLVM/Clang, GCC, and Rust's cargo-fuzz. It facilitates coverage instrumentation, corpus coverage tracking, and generating both textual and HTML coverage reports. Users can integrate this technique into their fuzzing workflow to monitor changes in coverage over time, determine if harness modifications have improved test effectiveness, and identify areas that require additional inputs or dictionaries. The skill emphasizes reproducible measurements by analyzing coverage after fuzzing campaigns rather than relying solely on real-time fuzzer statistics.
Typical use cases for this skill include initiating new fuzzing campaigns to establish a baseline, diagnosing stalled fuzzers, verifying harness improvements, and migrating between different fuzzing tools. It is targeted toward security researchers, software testers, and developers working on fuzz testing or seeking to improve code quality through systematic coverage analysis. By leveraging this skill, users gain actionable insights into fuzzing efficiency and the overall reliability of their testing setup.
FAQ
When should I apply coverage analysis in a fuzzing campaign?
Apply coverage analysis when starting a new fuzzing campaign to establish a baseline, after harness modifications, when the fuzzer appears to plateau, when migrating between fuzzers, or when identifying areas requiring additional seed inputs or dictionary entries.
Which toolchains are compatible with this skill?
This skill supports LLVM/Clang and GCC for C/C++ projects, as well as cargo-fuzz for Rust targets. Coverage instrumentation commands and reporting tools are provided for each supported toolchain.
Can I skip coverage analysis in my fuzzing workflow?
Yes, it can be skipped if the fuzzing campaign is actively finding crashes, if coverage infrastructure is not yet set up, if working with extremely large codebases where full coverage reports are impractical, or if the fuzzer's internal coverage metrics meet your needs.
What types of coverage reports can I generate?
You can generate textual coverage reports, HTML reports using llvm-cov or gcovr, and LLVM profile data that can be merged for detailed analysis.
How does coverage analysis help identify fuzzing blockers?
Coverage analysis highlights code paths that are not exercised, helping to identify hard-to-discover conditional checks or areas requiring additional inputs. This allows users to focus on improving harnesses and inputs to increase test coverage.
Install coverage-analysis
Quick Setup:
- Copy the skill folder to
.claude/skills/ - Claude will automatically detect and use the skill
Repository
trailofbits/skills