Use chain-loading for Linux nacl_helper

chrome/nacl/nacl_helper_linux.cc

Index: chrome/nacl/nacl_helper_linux.cc
diff --git a/chrome/nacl/nacl_helper_linux.cc b/chrome/nacl/nacl_helper_linux.cc
index b53cf8dcf7288b2d15502fdb071c9cc195552160..7ffeadb06452b1cd6f4063daacd5bf56fe907ee8 100644
--- a/chrome/nacl/nacl_helper_linux.cc
+++ b/chrome/nacl/nacl_helper_linux.cc
@@ -23,6 +23,7 @@
 #include "content/common/main_function_params.h"
 #include "content/common/unix_domain_socket_posix.h"
 #include "ipc/ipc_switches.h"
+#include "native_client/src/trusted/service_runtime/sel_memory.h"
 
 namespace {
 
@@ -116,33 +117,20 @@ void HandleForkRequest(const std::vector<int>& child_fds) {
 
 }  // namespace
 
-static const void* g_nacl_reserved_space = NULL;
-extern "C" __attribute__((visibility("default")))
-const void* nacl_helper_get_1G_address() {
-  return g_nacl_reserved_space;
-}
+static const char kNaClHelperAtZero[] = "at-zero";

[Brad Chen, 2011/08/29 23:04:57]

Probably ought to add a comment here where copies of this string appear
(nacl_helper_bootstrap_linux.c).

 
-// nacl_helper_init does the real work of this module. It is invoked as
-// a static constructor and never returns, preventing main() from the
-// nacl_helper_bootstrap program from being called.
-//
-// NOTE This routine must not return.
-extern "C" __attribute__((visibility("default")))
-void nacl_helper_init(int argc, char *argv[],
-                      const char *nacl_reserved_space) {
+int main(int argc, char *argv[]) {
   CommandLine::Init(argc, argv);
   base::AtExitManager exit_manager;
   base::RandUint64();  // acquire /dev/urandom fd before sandbox is raised
   std::vector<int> empty; // for SendMsg() calls
 
   g_suid_sandbox_active = (NULL != getenv("SBX_D"));
-  g_nacl_reserved_space = nacl_reserved_space;
-  if (!nacl_reserved_space) {
-    VLOG(1) << "nacl_reserved_space is NULL";
-  } else {
-    VLOG(1) << "nacl_reserved_space is at "
-            << (void *)nacl_reserved_space;
+
+  if (CommandLine::ForCurrentProcess()->HasSwitch(kNaClHelperAtZero)) {
+    g_nacl_prereserved_sandbox_addr = (void *) (uintptr_t) 0x10000;
   }
+
   // Send the zygote a message to let it know we are ready to help
   if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor,
                                  kNaClHelperStartupAck,