[Chromecast] Only include all libstdc++/libgcc symbols in executable as needed

build/config/chromecast/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/chromecast_build.gni")
 
 assert(is_chromecast)
 
 config("static_config") {
   ldflags = [
@@ skipping 16 matching lines @@
   # This is explicitly disabled in Chrome for security reasons (see comments in
   # //build/config/gcc/BUILD.gn), but necessary on Chromecast so that OEM's may
   # override the default libraries shipped in the Cast receiver package.
   ldflags = [
     "-Wl,-rpath=/oem_cast_shlib",
     "-Wl,-rpath=\$ORIGIN/lib",
     "-Wl,-rpath=\$ORIGIN",
   ]
 }
 
-config("executable_config") {
-  configs = [ ":ldconfig" ]
-
+# Whole archiving libgcc.a and libstdc++ is needed if dynamic share libs are
+# used, see b/25566835.
+config("executable_whole_archive_config") {
   if (current_cpu == "arm") {
     ldflags = [
       # Export stdlibc++ and libgcc symbols to force shlibs to refer to these
       # symbols from the executable.
       "-Wl,--export-dynamic",
 
       "-lm",  # stdlibc++ requires math.h
 
-      # In case we redefined stdlibc++ symbols (e.g. tc_malloc)
+      # In case we redefined stdlibc++ symbols (e.g. tc_malloc).
       "-Wl,--allow-multiple-definition",
 
+      # Adding all symbols from libgcc and libstdc++.
       "-Wl,--whole-archive",
       "-l:libstdc++.a",
       "-l:libgcc.a",
       "-Wl,--no-whole-archive",
     ]
+  }
+}
 
-    # Despite including libstdc++/libgcc archives, we still need to specify
-    # static linking for them in order to prevent the executable from having a
-    # dynamic dependency on them.
+config("executable_config") {
+  configs = [ ":ldconfig" ]
+
+  if (current_cpu == "arm") {

[slan, 2016/08/30 22:22:53]

Why just "arm" here? What is this conditional trying to say? For example, I
think this would treat arm android builds differently than x86 android builds.

[bcf, 2016/08/30 22:36:43]

This is only a problem on our Chromecast devices because we statically link
libstdc++ . 

I believe android builds don't need this because cast_shell is built as a shared
library rather than an executable.

[slan, 2016/08/30 22:46:51]

Thanks - that's a good point. However, this wouldn't apply to our MIPS linux
builds, for instance, and I would really prefer to be consistent across
architectures when possible. That will keep things clear in case we ever
introduce an x86 Chromecast device.

Are we trying to say !is_cast_desktop_build here? And if so, is there a
disadvantage to using this configuration on desktop?

+    # Statically link libstdc++ and libgcc to avoid having a dynamic dependency
+    # on them.
     configs += [ ":static_config" ]
   }
 }
 
 config("shared_library_config") {
   configs = [ ":ldconfig" ]
   if (current_cpu == "arm") {
     configs += [ ":static_config" ]
   }
 }