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Add fuzzing skill for Copilot-assisted fuzzer development#3026

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mattkur merged 2 commits intomicrosoft:mainfrom
mattkur:fuzzing-skill
Mar 18, 2026
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Add fuzzing skill for Copilot-assisted fuzzer development#3026
mattkur merged 2 commits intomicrosoft:mainfrom
mattkur:fuzzing-skill

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@mattkur mattkur commented Mar 17, 2026

Adds a new Copilot skill at .github/skills/fuzzing/SKILL.md covering the full fuzzing workflow: running, building, debugging with lldb, optimization principles, multi-target parallel campaigns, coverage collection/filtering, coverage scope rules, and coverage-guided improvement workflow.

Why is this change being made?
- No skill existed for running, optimizing, or debugging OpenVMM fuzzers
- Copilot agents need structured guidance for fuzzing workflows

What changed?
- Added .github/skills/fuzzing/SKILL.md covering:
  - Prerequisites (Linux-only, aarch64 RUSTFLAGS, cargo-fuzz)
  - Running, building, and reproducing crashes
  - Debugging with lldb (batch mode, breakpoints, wrapper types)
  - Fuzzer optimization principles (entropy efficiency, simplification)
  - Multi-target parallel campaigns (-fork=N, -ignore_crashes)
  - Code coverage collection and filtering
  - Coverage scope rules per fuzzer
  - Coverage-guided improvement workflow

How was the change tested?
- N/A (documentation only)
@mattkur mattkur requested a review from a team as a code owner March 17, 2026 18:20
Copilot AI review requested due to automatic review settings March 17, 2026 18:20
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Pull request overview

Adds a new Copilot skill guide documenting the end-to-end workflow for developing and improving OpenVMM fuzzers (run/build/repro/debug, coverage collection, and campaign strategy).

Changes:

  • Introduces a comprehensive fuzzing workflow guide under .github/skills/fuzzing/.
  • Documents lldb-based crash debugging and practical Rust type inspection patterns.
  • Adds guidance for coverage collection, filtering, and a coverage-guided improvement loop.


Everything from the main prerequisites, plus:

- **llvm-tools**: `rustup +nightly component add llvm-tools`
- Platform: 'Linux only' -> 'Linux or macOS' (libfuzzer doesn't support Windows)
- Nightly: note sanitizers are the benefit, xtask fuzz works on stable
- fuzz list: add +nightly for consistency with other commands
- Debug builds: fix 'not yet supported' -> reference --dev flag
- llvm-tools: note llvm-tools-preview as alternate component name
- Coverage grep: use generic <primary-scope-path> placeholder
- Corpus: add note that corpuses aren't committed to repo
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@mattkur mattkur merged commit b9e864d into microsoft:main Mar 18, 2026
78 of 82 checks passed
@mattkur mattkur deleted the fuzzing-skill branch March 18, 2026 17:17
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3 participants