[libfuzzer] supporting libfuzzer on mac with asan

build/config/sanitizers/BUILD.gn

Index: build/config/sanitizers/BUILD.gn
diff --git a/build/config/sanitizers/BUILD.gn b/build/config/sanitizers/BUILD.gn
index 0da971cc59443fc84d3191d445f90baff208f67c..ec55c97b7fa33ab8dd2cd86ef131b6af2fb11b4b 100644
--- a/build/config/sanitizers/BUILD.gn
+++ b/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") {
@@ -284,6 +289,10 @@ config("default_sanitizer_flags") {
       ]
     }
   }
+
+  if (is_mac && is_asan) {

[Alexander Potapenko, 2016/03/24 21:58:43]

Does is_mac mean only OSX, or both OSX and iOS/iossim?
Not sure you want to support the latter now though.

[aizatsky, 2016/03/24 22:31:33]

Ios is is_ios. No I don't want to support any of those now.

+    libs = [ "clang_rt.asan_osx_dynamic" ]
+  }
 }
 
 config("default_sanitizer_coverage_flags") {
@@ -294,3 +303,16 @@ config("default_sanitizer_coverage_flags") {
     cflags += [ "-fsanitize-coverage=edge,indirect-calls,8bit-counters" ]
   }
 }
+
+# Copy dynamic clang_rt sanitizer libraries to output directory.
+# Needed on 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",

[Alexander Potapenko, 2016/03/24 21:58:43]

You don't seem to need TSan/UBSan runtimes for ASan?

[aizatsky, 2016/03/24 22:31:33]

I do not at this time. But other sanitizers might. I figured it would be more
generic to copy all of them. BTW we do want to support libfuzzer + ubsan
eventually.

+    "//third_party/llvm-build/Release+Asserts/compiler-rt/lib/darwin/libclang_rt.ubsan_osx_dynamic.dylib",
+  ]
+  outputs = [
+    "$root_build_dir/{{source_file_part}}",
+  ]
+}