[Gardening] De-RST libFuzzerIntegration

Author: CodaFi

docs/contents.rst

@@ -16,7 +16,6 @@ Contents
    SIL
    TypeChecker
    OptimizationTips
-   libFuzzerIntegration
    ABI: TypeMetadata <ABI/TypeMetadata>
    ABI: TypeLayout <ABI/TypeLayout>
    ABI: Mangling <ABI/Mangling>

docs/libFuzzerIntegration.md

@@ -0,0 +1,37 @@
+libFuzzer Integration
+---------------------
+
+Swift compiler comes with a built-in `libFuzzer` integration.
+In order to use it on a file `myfile.swift`, we define an entry point fuzzing function
+with a `@_cdecl("LLVMFuzzerTestOneInput")` annotation:
+
+
+```swift
+@_cdecl("LLVMFuzzerTestOneInput") public func fuzzMe(Data: UnsafePointer<CChar>, Size: CInt) -> CInt{
+    // Test our code using provided Data.
+  }
+}
+```
+
+To compile it, we use `-sanitize=fuzzer` flag to link `libFuzzer`
+and enable coverage annotation, and `-parse-as-library` flag not to insert
+the `main` symbol, such that the fuzzer entry point can be used:
+
+```bash
+% swiftc -sanitize=fuzzer -parse-as-library myfile.swift
+```
+
+`libFuzzer` can be also combined with other sanitizers:
+
+```bash
+% swiftc -sanitize=fuzzer,address -parse-as-library myfile.swift
+```
+
+Finally, we launch the fuzzing process:
+
+```bash
+% ./a.out
+```
+
+Refer to the official `libFuzzer` documentation at http://llvm.org/docs/LibFuzzer.html
+for the description of flags the resulting binary has.