Experimental support for fuzzing on mac.

BUG=597066

Review URL: https://codereview.chromium.org/1818273002

Cr-Commit-Position: refs/heads/master@{#383389}

BUILD.gn

@@ -644,8 +644,6 @@ group("gn_only") {
       "//media/cast:udp_proxy",
       "//native_client/src/trusted/debug_stub:gdb_rsp_unittest",
       "//storage/browser:dump_file_system",
-      "//testing/libfuzzer/fuzzers",
-      "//testing/libfuzzer/tests:libfuzzer_tests",
       "//third_party/angle:libANGLE",
       "//third_party/angle:libEGL",
       "//third_party/angle:libGLESv2",
@@ -713,6 +711,13 @@ group("gn_only") {
     }
   }
 
+  if ((is_linux && !is_chromeos && !is_chromecast) || is_mac) {
+    deps += [
+      "//testing/libfuzzer/fuzzers",
+      "//testing/libfuzzer/tests:libfuzzer_tests",
+    ]
+  }
+
   if (enable_nacl) {
     deps += [ "//native_client_sdk/src:nacl_core_sdk" ]
   }

build/config/sanitizers/BUILD.gn

@@ -28,12 +28,17 @@ group("deps") {
     }
     if (use_custom_libcxx) {
       deps += [ "//buildtools/third_party/libc++:libcxx_proxy" ]
+      if (is_mac) {
+        deps += [ ":copy_libclang_rt_dyn" ]
+      }
     }
   }
 }
 
 config("sanitizer_options_link_helper") {
-  ldflags = [ "-Wl,-u_sanitizer_options_link_helper" ]
+  if (!is_mac) {
+    ldflags = [ "-Wl,-u_sanitizer_options_link_helper" ]
+  }
 }
 
 source_set("options_sources") {
@@ -292,6 +297,10 @@ config("default_sanitizer_flags") {
       ]
     }
   }
+
+  if (is_mac && is_asan) {
+    libs = [ "clang_rt.asan_osx_dynamic" ]
+  }
 }
 
 config("default_sanitizer_coverage_flags") {
@@ -306,3 +315,17 @@ config("default_sanitizer_coverage_flags") {
     ]
   }
 }
+
+# Copy dynamic clang_rt sanitizer libraries to output directory.
+if (is_mac) {
+  copy("copy_libclang_rt_dyn") {
+    sources = [
+      "//third_party/llvm-build/Release+Asserts/compiler-rt/lib/darwin/libclang_rt.asan_osx_dynamic.dylib",
+      "//third_party/llvm-build/Release+Asserts/compiler-rt/lib/darwin/libclang_rt.tsan_osx_dynamic.dylib",
+      "//third_party/llvm-build/Release+Asserts/compiler-rt/lib/darwin/libclang_rt.ubsan_osx_dynamic.dylib",
+    ]
+    outputs = [
+      "$root_build_dir/{{source_file_part}}",
+    ]
+  }
+}

build/config/sanitizers/sanitizers.gni

@@ -69,8 +69,8 @@ declare_args() {
   # Use libc++ (buildtools/third_party/libc++ and
   # buildtools/third_party/libc++abi) instead of stdlibc++ as standard library.
   # This is intended to be used for instrumented builds.
-  use_custom_libcxx =
-      (is_asan && is_linux) || is_tsan || is_msan || is_ubsan || use_libfuzzer
+  use_custom_libcxx = (is_asan && (is_linux || is_mac)) || is_tsan || is_msan ||
+                      is_ubsan || use_libfuzzer
 
   # Enable Link Time Optimization (output programs runs faster,
   # but linking is up to 5-20x slower.

testing/libfuzzer/BUILD.gn

@@ -37,6 +37,16 @@ static_library("libfuzzer_main") {
   }
 }
 
+# A config used by all fuzzer_tests.
+config("fuzzer_test_config") {
+  if (use_libfuzzer && is_mac) {
+    ldflags = [
+      "-Wl,-U,_LLVMFuzzerCustomMutator",
+      "-Wl,-U,_LLVMFuzzerInitialize",
+    ]
+  }
+}
+
 # Noop config used to tag fuzzer tests excluded from clusterfuzz.
 # Libfuzzer build bot uses this to filter out targets while
 # building an archive for clusterfuzz.

testing/libfuzzer/fuzzer_test.gni

@@ -127,6 +127,7 @@ template("fuzzer_test") {
       if (defined(invoker.additional_configs)) {
         configs += invoker.additional_configs
       }
+      configs += [ "//testing/libfuzzer:fuzzer_test_config" ]
     }
   } else {
     # noop on unsupported platforms.