Reserve 1GB at the base of the address space of linux nacl_helper for Native Client module.

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 b943e2b24c6cf80ab6db7e7b332002a814fba09f..b53cf8dcf7288b2d15502fdb071c9cc195552160 100644
--- a/chrome/nacl/nacl_helper_linux.cc
+++ b/chrome/nacl/nacl_helper_linux.cc
@@ -116,14 +116,33 @@ void HandleForkRequest(const std::vector<int>& child_fds) {
 
 }  // namespace
 
-int main(int argc, char *argv[]) {
+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;
+}
+
+// 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) {
   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;
+  }
   // Send the zygote a message to let it know we are ready to help
   if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor,
                                  kNaClHelperStartupAck,
@@ -163,4 +182,5 @@ int main(int argc, char *argv[]) {
       LOG(ERROR) << "*** send() to zygote failed";
     }
   }
+  CHECK(false);  // This routine must not return
 }