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

shell/out_of_process_native_runner.cc

Index: shell/out_of_process_native_runner.cc
diff --git a/shell/out_of_process_native_runner.cc b/shell/out_of_process_native_runner.cc
index 39cf1f7003abfef747ed59f21afdebf9d08b04ab..4100b48293ef99134a82305e6ac751e7443000d2 100644
--- a/shell/out_of_process_native_runner.cc
+++ b/shell/out_of_process_native_runner.cc
@@ -4,10 +4,14 @@
 
 #include "shell/out_of_process_native_runner.h"
 
+#include <elf.h>
+#include <string>
+
 #include "base/bind.h"
 #include "base/callback_helpers.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
+#include "base/strings/string_util.h"
 #include "shell/child_controller.mojom.h"
 #include "shell/child_process_host.h"
 #include "shell/in_process_native_runner.h"
@@ -27,6 +31,27 @@ OutOfProcessNativeRunner::~OutOfProcessNativeRunner() {
   }
 }
 
+// Determines if content handler must be run as 32 bit application
+// based on elf header. Returns false on error.
+bool Require32Bit(const base::FilePath& app_path) {

[Mark Seaborn, 2015/09/15 22:25:43]

This could go in an anon namespace.

[Sean Klein, 2015/09/15 22:56:05]

Done.

+#if defined(ARCH_CPU_32_BITS)

[Mark Seaborn, 2015/09/15 22:25:43]

You could use "if (sizeof(void *) == 4)".  This way, both branches get
compile-tested.

if() is often preferable to #if:
http://lackingrhoticity.blogspot.com/2015/01/conditionalising-c-ifdef-vs-if.html

If you do use ARCH_*, though, you should make sure to #include
"build/build_config.h".

Same in other file too.

[Sean Klein, 2015/09/15 22:56:05]

Using "sizeof(void *) == 4", along with a comment.

+  return true;
+#else
+  bool require_32_bit = false;
+  char data[EI_NIDENT];
+  // Read e_ident from the elf file
+  if (EI_NIDENT != ReadFile(app_path, data, sizeof(data)))

[Mark Seaborn, 2015/09/15 22:25:43]

Nit: Also "EI_NIDENT" -> "sizeof(data)" (as before)

[Sean Klein, 2015/09/15 22:56:05]

Done.

+    return false;
+  // Check the magic elf number
+  if (memcmp(data, ELFMAG, SELFMAG))
+    return false;
+  // Identify the architecture required
+  if (data[EI_CLASS] == ELFCLASS32)

[Mark Seaborn, 2015/09/15 22:25:43]

Can simplify to:
return data[EI_CLASS] == ELFCLASS32;

[Sean Klein, 2015/09/15 22:56:05]

Done.

+    require_32_bit = true;
+  return require_32_bit;
+#endif
+}
+
 void OutOfProcessNativeRunner::Start(
     const base::FilePath& app_path,
     mojo::InterfaceRequest<mojo::Application> application_request,
@@ -37,7 +62,7 @@ void OutOfProcessNativeRunner::Start(
   app_completed_callback_ = app_completed_callback;
 
   child_process_host_.reset(new ChildProcessHost(context_));
-  child_process_host_->Start();
+  child_process_host_->Start(Require32Bit(app_path));
 
   // TODO(vtl): |app_path.AsUTF8Unsafe()| is unsafe.
   child_process_host_->StartApp(