fuzzing: add a basic README

Signed-off-by: Arjun <[email protected]>
Reviewed-by: Andrew Clayton <[email protected]>
[ Some small edits - Andrew ]
Signed-off-by: Andrew Clayton <[email protected]>

fuzzing/README.md

@@ -0,0 +1,68 @@
+# Fuzzing unit
+
+These tests are generally advised to run only on GNU/Linux.
+
+## Build fuzzers using libFuzzer.
+
+Running `sh fuzzing/build-fuzz.sh` can build all the fuzzers with standard
+`ASan` and `UBSan`.
+
+### More comprehensive How-to Guide.
+
+#### Export flags that are to be used by Unit for fuzzing.
+
+Note that in `CFLAGS` and `CXXFLAGS`, any type of sanitizers can be added.
+
+- [AddressSanitizer](https://clang.llvm.org/docs/AddressSanitizer.html),
+    [ThreadSanitizer](https://clang.llvm.org/docs/ThreadSanitizer.html),
+    [MemorySanitizer](https://clang.llvm.org/docs/MemorySanitizer.html),
+    [UndefinedBehaviorSanitizer](https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html),
+    [LeakSanitizer](https://clang.llvm.org/docs/LeakSanitizer.html).
+
+```shell
+$ export CC=clang
+$ export CXX=clang++
+$ export CFLAGS="-g -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=fuzzer-no-link"
+$ export CXXFLAGS="-g -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION  -fsanitize=fuzzer-no-link"
+$ export LIB_FUZZING_ENGINE="-fsanitize=fuzzer"
+```
+
+#### Build Unit for Fuzzing.
+
+```shell
+$ ./configure --no-regex --no-pcre2 --fuzz=$LIB_FUZZING_ENGINE
+$ make fuzz -j$(nproc)
+```
+
+#### Running fuzzers.
+
+```shell
+$ mkdir -p build/fuzz_basic_seed
+$ mkdir -p build/fuzz_http_controller_seed
+$ mkdir -p build/fuzz_http_h1p_seed
+$ mkdir -p build/fuzz_http_h1p_peer_seed
+$ mkdir -p build/fuzz_json_seed
+
+$ ./build/fuzz_basic            build/fuzz_basic_seed            src/fuzz/fuzz_basic_seed_corpus
+$ ./build/fuzz_http_controller  build/fuzz_http_controller_seed  src/fuzz/fuzz_http_controller_seed_corpus
+$ ./build/fuzz_http_h1p         build/fuzz_http_h1p_seed         src/fuzz/fuzz_http_h1p_seed_corpus
+$ ./build/fuzz_http_h1p_peer    build/fuzz_http_h1p_peer_seed    src/fuzz/fuzz_http_h1p_peer_seed_corpus
+$ ./build/fuzz_json             build/fuzz_json_seed             src/fuzz/fuzz_json_seed_corpus
+```
+
+Here is more information about [LibFuzzer](https://llvm.org/docs/LibFuzzer.html).
+
+## Build fuzzers using other fuzzing engines.
+
+- [Honggfuzz](https://github.com/google/honggfuzz/blob/master/docs/PersistentFuzzing.md).
+- [AFLplusplus](https://github.com/AFLplusplus/AFLplusplus/blob/stable/utils/aflpp_driver/README.md).
+
+
+## Requirements.
+
+You will likely need at least the following packages installed (package names
+may vary).
+
+```
+clang, llvm & compiler-rt
+```