Enabling 64-bit mojo shell to launch 32-bit child to handle nonsfi content.

shell/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/ui.gni")
 import("//mojo/public/mojo.gni")
 import("//mojo/public/mojo_application.gni")
 import("//mojo/public/tools/bindings/mojom.gni")
 import("//mojo/tools/embed/rules.gni")
 import("//testing/test.gni")
@@ skipping 65 matching lines @@
              ]
 
       data_deps = shell_common_data_deps
     }
   } else {
     executable("mojo_shell") {
       sources = [
         "desktop/main.cc",
       ]
 
-      deps = shell_common_deps
+      deps = shell_common_deps + [ ":mojo_shell_child_32_bit" ]
 
       data_deps = shell_common_data_deps
     }
   }
 
   executable("mojo_shell_child") {
     sources = [
       "child_main.cc",
     ]
 
     deps = [
       ":child_controller_bindings",
       ":common_lib",
       "//base",
       "//base/allocator",
       "//build/config/sanitizers:deps",
       "//mojo/edk/system",
       "//mojo/environment:chromium",
       "//mojo/message_pump",
     ]
   }
+
+  if (current_cpu == "x86") {
+    # The 32-bit version of the mojo_shell_child should be accessible in the
+    # root build directory, just like the regular mojo_shell_child, so that
+    # the 32-bit version can be accessed by simply adding a suffix to the path.
+    copy("mojo_shell_child_32_bit_copy") {
+      sources = [
+        "${root_out_dir}/mojo_shell_child",
+      ]
+      outputs = [
+        "${root_build_dir}/mojo_shell_child_32",
+      ]
+      deps = [
+        ":mojo_shell_child",
+      ]
+    }
+  }
+
+  group("mojo_shell_child_32_bit") {
+    # This group is required to run any 32-bit child process.
+    deps = []
+    if ((target_cpu == "x64" || target_cpu == "x86") && is_linux) {
+      # The toolchain is hardcoded as 32-bit clang here -- although it must
+      # be 32 bit (for nonsfi), it assumes clang. Ideally, the toolchain would
+      # be defined as the 32 bit variant of whatever is being used (be it clang,
+      # gcc, or something else).
+      deps = [
+        ":mojo_shell_child_32_bit_copy(//build/toolchain/linux:clang_x86)",
+      ]
+    }
+  }
 }  # !mojo_use_prebuilt_mojo_shell
 
 # Files used both by mojo_shell and mojo_shell_child (and tests).
 source_set("common_lib") {
   sources = [
     "child_switches.cc",
     "child_switches.h",
     "init.cc",
     "init.h",
   ]
@@ skipping 493 matching lines @@
       "${root_out_dir}/libmojo_shell.so",
     ]
   } else {
     sources += [ "${root_out_dir}/mojo_shell" ]
   }
 
   outputs = [
     "${root_out_dir}/symbols/{{source_file_part}}",
   ]
 }