[Cronet] Enforce ARMv7 Cronet doesn't inadvertently use ARM Neon instructions

components/cronet/android/BUILD.gn

Index: components/cronet/android/BUILD.gn
diff --git a/components/cronet/android/BUILD.gn b/components/cronet/android/BUILD.gn
index dece98533f630a4238816b03b8b0ff065fbf9bc3..270e2f99193da4f9fc080c342b915b983e6db695 100644
--- a/components/cronet/android/BUILD.gn
+++ b/components/cronet/android/BUILD.gn
@@ -846,6 +846,25 @@ action("generate_javadoc") {
   ]
 }
 
+action("enforce_no_neon") {
+  script = "//components/cronet/tools/check_no_neon.py"
+  args = [
+    rebase_path("${android_tool_prefix}objdump", root_build_dir),
+
+    # libcronet.so may contain ARM Neon instructions from BoringSSL, but these
+    # are only used after checking whether the CPU supports NEON at runtime,
+    # so instead check base/ as it represents a large swath of code that only
+    # contains Neon instructions when Neon is enabled by default.
+    rebase_path("$root_out_dir/obj/base/base/*.o", root_build_dir),
+  ]
+  outputs = [
+    "$root_out_dir/cronet_$target_name.d",
+  ]
+  deps = [
+    "//base:base",
+  ]
+}
+
 copy("cronet_package_copy") {
   sources = [
     "$root_out_dir/lib.java/components/cronet/android/cronet_api.jar",
@@ -898,4 +917,7 @@ group("cronet_package") {
     ":jar_cronet_sample_source",
     ":repackage_extracted_jars",
   ]
+  if (current_cpu == "arm" && arm_version == 7) {
+    deps += [ ":enforce_no_neon" ]

[jbudorick, 2016/07/19 18:49:16]

This is an interesting way to handle this. You could also assert that
arm_use_neon is false in this scenario, though you may also want to check the
build artifact.

[pauljensen, 2016/07/20 15:04:37]

Done.

+  }
 }