Add docs on how to add a new fuzzer

diff --git a/tests/fuzz/README.md b/tests/fuzz/README.md
index 2a9bd4570b6d2c22f763c481cdb379abed6d2848..e2196e832c67f61b56b128aac7c169ed44d62733 100644 (file)
--- a/tests/fuzz/README.md
+++ b/tests/fuzz/README.md
@@ -117,3 +117,45 @@ CC=clang CXX=clang++ ./fuzz.py build all --enable-msan
 ## Fuzzing a custom sequence producer plugin
 Sequence producer plugin authors can use the zstd fuzzers to stress-test their code.
 See the documentation in `fuzz_third_party_seq_prod.h` for details.
+
+## Adding a new fuzzer
+There are several steps involved in adding a new fuzzer harness.
+
+### Build your harness
+1. Create a new your fuzzer harness `tests/fuzz/your_harness.c`.
+
+2. Add your harness to the Makefile
+
+    2.1 Follow [this example](https://github.com/facebook/zstd/blob/e124e39301381de8f323436a3e4c46539747ba24/tests/fuzz/Makefile#L216) if your fuzzer requires both compression and decompression symbols (prefix `rt_`). If your fuzzer only requires decompression symbols, follow [this example](https://github.com/facebook/zstd/blob/6a0052a409e2604bd40354b76b86272b712edd7d/tests/fuzz/Makefile#L194) (prefix `d_`).
+    
+    2.2 Add your target to [`FUZZ_TARGETS`](https://github.com/facebook/zstd/blob/6a0052a409e2604bd40354b76b86272b712edd7d/tests/fuzz/Makefile#L108).
+    
+3. Add your harness to [`fuzz.py`](https://github.com/facebook/zstd/blob/6a0052a409e2604bd40354b76b86272b712edd7d/tests/fuzz/fuzz.py#L48).
+
+### Generate seed data
+Follow the instructions above to generate seed data:
+```
+make -C ../tests decodecorpus
+./fuzz.py gen your_harness
+```
+
+### Run the harness
+Follow the instructions above to run your harness and fix any crashes:
+```
+./fuzz.py build your_harness --enable-fuzzer --enable-asan --enable-ubsan --cc clang --cxx clang++
+./fuzz.py libfuzzer your_harness
+```
+
+### Minimize and zip the corpus
+After running the fuzzer for a while, you will have a large corpus at `tests/fuzz/corpora/your_harness*`.
+This corpus must be minimized and zipped before uploading to GitHub for regression testing:
+```
+./fuzz.py minimize your_harness
+./fuzz.py zip your_harness 
+```
+
+### Upload the zip file to GitHub
+The previous step should produce a `.zip` file containing the corpus for your new harness.
+This corpus must be uploaded to GitHub here: https://github.com/facebook/zstd/releases/tag/fuzz-corpora
+
+