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49 lines
2.0 KiB
Markdown
49 lines
2.0 KiB
Markdown
# AFL++ Fuzzer for Libghostty
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- Build all fuzzer with `zig build`
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- The list of available fuzzers is in `build.zig` (search for `fuzzers`).
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- Run a specific fuzzer with `zig build run-<name>` (e.g. `zig build run-parser`)
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- Corpus directories follow the naming convention `corpus/<fuzzer>-<variant>`
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(e.g. `corpus/parser-initial`, `corpus/stream-cmin`).
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- Do NOT run `afl-tmin` unless explicitly requested — it is very slow.
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- After running `afl-cmin`, run `corpus/sanitize-filenames.sh`
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before committing to replace colons with underscores (colons are invalid
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on Windows NTFS).
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## Important: stdin-based input
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The instrumented binaries (`afl.c` harness) read fuzz input from **stdin**,
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not from a file argument. This affects how you invoke AFL++ tools:
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- **`afl-fuzz`**: Uses shared-memory fuzzing automatically; `@@` works
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because AFL writes directly to shared memory, bypassing file I/O.
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- **`afl-showmap`**: Must pipe input via stdin, **not** `@@`:
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```sh
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cat testcase | afl-showmap -o map.txt -- zig-out/bin/fuzz-stream
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```
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- **`afl-cmin`**: Do **not** use `@@`. Requires `AFL_NO_FORKSRV=1` with
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the bash version due to a bug in the Python `afl-cmin` (AFL++ 4.35c):
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```sh
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AFL_NO_FORKSRV=1 /opt/homebrew/Cellar/afl++/4.35c/libexec/afl-cmin.bash \
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-i afl-out/fuzz-stream/default/queue -o corpus/stream-cmin \
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-- zig-out/bin/fuzz-stream
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```
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If you pass `@@` or a filename argument, `afl-showmap`/`afl-cmin`
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will see only ~4 tuples (the C main paths) and produce useless results.
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## Replaying crashes
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Use `replay-crashes.nu` (Nushell) to list or replay AFL++ crash files.
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- **List all crash files:** `nu replay-crashes.nu --list`
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- **JSON output (for structured processing):** `nu replay-crashes.nu --json`
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Returns an array of objects with `fuzzer`, `file`, `binary`, and `replay_cmd`.
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- **Filter by fuzzer:** `nu replay-crashes.nu --list --fuzzer stream`
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- **Replay all crashes:** `nu replay-crashes.nu`
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Pipes each crash file into its fuzzer binary via stdin and exits non-zero
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if any crashes still reproduce.
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