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Reprl for Fuzzilli fuzzing#4917

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jasnell merged 1 commit intomainfrom
reprl-2
Nov 4, 2025
Merged

Reprl for Fuzzilli fuzzing#4917
jasnell merged 1 commit intomainfrom
reprl-2

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@mschwarzl mschwarzl commented Aug 27, 2025

  • Implemented a REPRL interface that can be used for fuzzing workerd with Fuzzilli
  • Stdin.reprl opens up the shared memory and required pipes, waits for the file size and parses the file from Fuzzilli
  • Added a new fuzzilli command to main
  • Added a test for the REPRL interface

@mschwarzl mschwarzl requested review from a team as code owners August 27, 2025 14:55
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github-actions Bot commented Aug 27, 2025 •
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All contributors have signed the CLA ✍️ ✅
Posted by the CLA Assistant Lite bot.

@mschwarzl mschwarzl requested review from danlapid and jasnell August 27, 2025 14:55
@mschwarzl mschwarzl mentioned this pull request Aug 27, 2025
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github-actions Bot commented Aug 27, 2025 •
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The generated output of @cloudflare/workers-types matches the snapshot in types/generated-snapshot 🎉

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mschwarzl commented Aug 27, 2025

I have read the CLA Document and I hereby sign the CLA

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mschwarzl commented Aug 27, 2025

recheck

github-actions Bot added a commit that referenced this pull request Aug 27, 2025
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@mschwarzl has signed the CLA in #4917
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@mschwarzl mschwarzl force-pushed the reprl-2 branch 2 times, most recently from b4d4fff to 53e719f Compare August 27, 2025 15:31
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mschwarzl commented Aug 27, 2025

recheck

@mschwarzl mschwarzl force-pushed the reprl-2 branch 16 times, most recently from 6e435f0 to 55b86b3 Compare August 29, 2025 06:53
mikea
mikea reviewed Sep 25, 2025
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Comment thread src/workerd/api/global-scope.h Outdated
Comment thread src/workerd/api/global-scope.c++
Comment thread src/workerd/api/unsafe.h Outdated
Comment thread src/workerd/tests/test-reprl.c++ Outdated
Comment thread src/workerd/tests/test-reprl.c++ Outdated
Comment thread samples/reprl/README.md Outdated
@mschwarzl mschwarzl force-pushed the reprl-2 branch 5 times, most recently from b7bc1cf to 01c1059 Compare October 2, 2025 15:27
@mschwarzl mschwarzl requested a review from mikea October 21, 2025 12:15
jasnell
jasnell reviewed Oct 27, 2025
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Comment thread src/workerd/api/global-scope.c++
jasnell
jasnell reviewed Oct 27, 2025
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Comment thread src/workerd/api/global-scope.c++ Outdated
jasnell
jasnell reviewed Oct 27, 2025
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Comment thread src/workerd/util/immediate-crash.h
jasnell
jasnell reviewed Oct 27, 2025
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Comment thread src/workerd/server/server.c++
@mschwarzl mschwarzl force-pushed the reprl-2 branch 6 times, most recently from d436ec9 to c773dd9 Compare October 28, 2025 09:27
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codspeed-hq Bot commented Oct 28, 2025 •
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CodSpeed Performance Report

Merging #4917 will degrade performances by 9.25%

Comparing reprl-2 (2c32de2) with main (2376e81)

Summary

❌ 1 regression
✅ 33 untouched
⏩ 9 skipped1

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

Benchmark BASE HEAD Change
❌ Encode_ASCII_256[0/0/256] 4.4 ms 4.8 ms -9.25%

Footnotes

  1. 9 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

@mschwarzl mschwarzl force-pushed the reprl-2 branch 3 times, most recently from 543fb2a to 39fc71c Compare November 3, 2025 15:41
jasnell
jasnell approved these changes Nov 3, 2025
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Once CI is green, LGTM

@mschwarzl mschwarzl force-pushed the reprl-2 branch 2 times, most recently from 20ac51e to 2192f02 Compare November 4, 2025 08:45
@mschwarzl mschwarzl dismissed mikea’s stale review November 4, 2025 09:27

Changes were applied

@mschwarzl
Add Fuzzilli REPRL integration for fuzzing support
2c32de2 
This commit adds comprehensive support for fuzzing workerd using Fuzzilli's
REPRL (Read-Eval-Print-Reset-Loop) protocol.

Key changes:
- Implement REPRL protocol handler in workerd server with --stdin-reprl flag
- Add fuzzilli() JavaScript API for crash testing and coverage tracking
- Integrate libreprl C library for REPRL client communication
- Add KJ-based test framework integration (test-reprl.c++)
- Create example Fuzzilli configurations and mock services
- Add immediate-crash.h utility for controlled crash testing
- Fix V8 ASAN macro redefinition warnings by adding V8_USE_ADDRESS_SANITIZER
- Update .bazelrc to use clang-19 directly instead of ccache wrapper

The implementation allows Fuzzilli to:
- Execute JavaScript code in isolated REPRL sessions
- Collect sanitizer coverage feedback
- Detect crashes and memory errors
- Reset worker state between executions

Example usage:
  bazel test --config=fuzzilli //src/workerd/tests:test-reprl
  ./workerd test fuzzilli/config.capnp --experimental --stdin-reprl
@mschwarzl mschwarzl requested a review from a team November 4, 2025 16:43
@vicb vicb mentioned this pull request Nov 6, 2025
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@jasnell jasnell jasnell approved these changes

@danlapid danlapid Awaiting requested review from danlapid

@mikea mikea Awaiting requested review from mikea

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@mschwarzl @mikea @jasnell @danlapid