GN: Add support for prebuilt instrumented libraries.

third_party/instrumented_libraries/BUILD.gn

+# Copyright 2015 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/sanitizers/sanitizers.gni")
+
+prebuilt_available =
+    is_msan && (msan_track_origins == 0 || msan_track_origins == 2)
+
+group("deps") {
+  if (use_prebuilt_instrumented_libraries) {
+    assert(prebuilt_available,
+           "Prebuilt instrumented libraries are only available when " +
+               "is_msan = true and msan_track_origins = {0, 2}")
+    deps = [
+      ":prebuilt",
+    ]
+  }
+}
+
+if (prebuilt_available) {
+  group("prebuilt") {
+    visibility = [ ":deps" ]
+    public_configs = [ ":prebuilt_link_helper" ]
+    deps = [
+      ":extract_prebuilt_instrumented_libraries",

[earthdok, 2015/05/28 18:27:46]

You have to download the archive before you can extract it. See:

https://code.google.com/p/chromium/codesearch#chromium/src/DEPS&l=758

[Sam McNally, 2015/05/29 08:33:00]

This assumes that hook would still download the archive. However, I'm not sure
what the replacement would be for GYP_DEFINES for deciding whether and what to
download. Added a TODO(GYP) for now.

[earthdok, 2015/05/29 15:28:03]

You're probably aware of this, but just in case, I want to point out that
there're a number of hooks that look at GYP defines - this is not unique to
instrumented libraries.

+    ]
+  }
+
+  if (is_msan) {
+    sanitizer_type = "msan"
+    if (msan_track_origins == 0) {
+      archive_name = "msan-no-origins"
+    } else if (msan_track_origins == 2) {
+      archive_name = "msan-chained-origins"
+    }
+  }
+
+  action("extract_prebuilt_instrumented_libraries") {
+    visibility = [ ":prebuilt" ]
+    script = "scripts/unpack_binaries.py"
+    depfile = "$target_out_dir/$archive_name.d"
+    args = [
+      archive_name,
+      rebase_path("binaries"),
+      rebase_path(root_build_dir + "/instrumented_libraries_prebuilt"),
+      rebase_path(target_out_dir, root_build_dir),
+    ]
+    outputs = [
+      "$target_out_dir/$archive_name.txt",

[earthdok, 2015/05/28 18:27:46]

The stamp file no longer references the Ubuntu release name. This means that the
user must clobber the build after performing an in-place upgrade. Unfortunately,
there won't be any user-friendly warning about this. Instead, the build will
fail at runtime in an unpredictable way, most likely with a bogus MSan report.
Can we do something about this?

[Sam McNally, 2015/05/29 08:33:00]

I don't think we can detect this unless ninja can detect an OS version change
and rerun GN.

[earthdok, 2015/05/29 15:28:03]

Ninja doesn't rerun GYP either, but GYP would at least extract the correct
archive if you rerun it explicitly. With GN you'd have to clobber or delete the
stamp file.

Anyway, this is a bit of a corner case, so I'll accept this if you can't or
don't want to run an external command from GN to get Ubuntu version. Please
leave a comment here at least (e.g. "This requires a clobber whenever Ubuntu
version changes.")

[Sam McNally, 2015/06/01 01:05:15]

Done.

+    ]
+  }
+
+  config("prebuilt_link_helper") {
+    visibility = [ ":prebuilt" ]
+    ldflags = [
+      # Add a relative RPATH entry to Chromium binaries. This puts instrumented
+      # DSOs before system-installed versions in library search path.
+      "-Wl,-R,\$ORIGIN/instrumented_libraries_prebuilt/$sanitizer_type/lib",
+      "-Wl,-z,origin",
+    ]
+  }
+}