[libfuzzer] supporting libfuzzer on mac with asan

build/config/sanitizers/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 # Contains the dependencies needed for sanitizers to link into executables and
 # shared_libraries. Unconditionally depend upon this target as it is empty if
@@ skipping 10 matching lines @@
     ]
     deps = [
       ":options_sources",
     ]
 
     if (use_prebuilt_instrumented_libraries) {
       deps += [ "//third_party/instrumented_libraries:deps" ]
     }
     if (use_custom_libcxx) {
       deps += [ "//buildtools/third_party/libc++:libcxx_proxy" ]
+      if (is_mac) {

[Alexander Potapenko, 2016/03/30 11:05:00]

Why is this flag checked only under use_custom_libcxx?

+        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") {
   visibility = [
     ":deps",
     "//:gn_visibility",
   ]
   sources = [
     "//build/sanitizers/sanitizer_options.cc",
   ]
@@ skipping 230 matching lines @@
     if (use_custom_libcxx) {
       prefix = "//buildtools/third_party"
       include = "trunk/include"
       cflags_cc += [
         "-nostdinc++",
         "-isystem" + rebase_path("$prefix/libc++/$include", root_build_dir),
         "-isystem" + rebase_path("$prefix/libc++abi/$include", root_build_dir),
       ]
     }
   }
+
+  if (is_mac && is_asan) {
+    libs = [ "clang_rt.asan_osx_dynamic" ]
+  }
 }
 
 config("default_sanitizer_coverage_flags") {
   cflags = []
 
   if (use_sanitizer_coverage) {
     # FIXME: make this configurable.
     cflags += [ "-fsanitize-coverage=edge,indirect-calls,8bit-counters" ]
   }
 }
+
+# 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",

[Alexander Potapenko, 2016/03/30 11:05:00]

This path is incorrect.

[kjellander_chromium, 2016/03/30 14:25:08]

Right, on my Mac the path is:
third_party/llvm-build/Release+Asserts/lib/clang/3.9.0/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}}",
+    ]
+  }
+}