Add Rust fuzzing support.

Add a rust_fuzz module which builds a libfuzzer binary that enabes
asan+sancov. This relies on the libfuzzer-sys crate.

Bug: 147140513
Test: Local rust_fuzz example builds, fuzzes with asan+sancov.
Change-Id: I57db3b8d25869791824ccfab768d13b0bb9d42fa

rust/fuzz.go

@@ -0,0 +1,96 @@
+// Copyright 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package rust
+
+import (
+	"android/soong/android"
+	"android/soong/cc"
+	"android/soong/rust/config"
+)
+
+func init() {
+	android.RegisterModuleType("rust_fuzz", RustFuzzFactory)
+}
+
+type fuzzDecorator struct {
+	*binaryDecorator
+
+	Properties            cc.FuzzProperties
+	dictionary            android.Path
+	corpus                android.Paths
+	corpusIntermediateDir android.Path
+	config                android.Path
+	data                  android.Paths
+	dataIntermediateDir   android.Path
+}
+
+var _ compiler = (*binaryDecorator)(nil)
+
+// rust_binary produces a binary that is runnable on a device.
+func RustFuzzFactory() android.Module {
+	module, _ := NewRustFuzz(android.HostAndDeviceSupported)
+	return module.Init()
+}
+
+func NewRustFuzz(hod android.HostOrDeviceSupported) (*Module, *fuzzDecorator) {
+	module, binary := NewRustBinary(hod)
+	fuzz := &fuzzDecorator{
+		binaryDecorator: binary,
+	}
+
+	// Change the defaults for the binaryDecorator's baseCompiler
+	fuzz.binaryDecorator.baseCompiler.dir = "fuzz"
+	fuzz.binaryDecorator.baseCompiler.dir64 = "fuzz"
+	fuzz.binaryDecorator.baseCompiler.location = InstallInData
+	module.sanitize.SetSanitizer(cc.Fuzzer, true)
+	module.compiler = fuzz
+	return module, fuzz
+}
+
+func (fuzzer *fuzzDecorator) compilerFlags(ctx ModuleContext, flags Flags) Flags {
+	flags = fuzzer.binaryDecorator.compilerFlags(ctx, flags)
+
+	// `../lib` for installed fuzz targets (both host and device), and `./lib` for fuzz target packages.
+	flags.LinkFlags = append(flags.LinkFlags, `-Wl,-rpath,\$$ORIGIN/../lib`)
+	flags.LinkFlags = append(flags.LinkFlags, `-Wl,-rpath,\$$ORIGIN/lib`)
+
+	return flags
+}
+
+func (fuzzer *fuzzDecorator) compilerDeps(ctx DepsContext, deps Deps) Deps {
+	deps.StaticLibs = append(deps.StaticLibs,
+		config.LibFuzzerRuntimeLibrary(ctx.toolchain()))
+	deps.SharedLibs = append(deps.SharedLibs,
+		config.LibclangRuntimeLibrary(ctx.toolchain(), "asan"))
+	deps.SharedLibs = append(deps.SharedLibs, "libc++")
+	deps.Rlibs = append(deps.Rlibs, "liblibfuzzer_sys")
+
+	deps = fuzzer.binaryDecorator.compilerDeps(ctx, deps)
+
+	return deps
+}
+
+func (fuzzer *fuzzDecorator) compilerProps() []interface{} {
+	return append(fuzzer.binaryDecorator.compilerProps(),
+		&fuzzer.Properties)
+}
+
+func (fuzzer *fuzzDecorator) stdLinkage(ctx *depsContext) RustLinkage {
+	return RlibLinkage
+}
+
+func (fuzzer *fuzzDecorator) autoDep(ctx BaseModuleContext) autoDep {
+	return rlibAutoDep
+}