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

chrome/nacl/nacl_helper_linux.cc

 // Copyright (c) 2011 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.
 
 // A mini-zygote specifically for Native Client.
 
 #include "chrome/common/nacl_helper_linux.h"
 
 #include <errno.h>
 #include <stdlib.h>
@@ skipping 98 matching lines @@
   // Now tell childpid to the Chrome zygote.
   if (HANDLE_EINTR(send(kNaClZygoteDescriptor,
                         &childpid, sizeof(childpid), MSG_EOR))
       != sizeof(childpid)) {
     LOG(ERROR) << "*** send() to zygote failed";
   }
 }
 
 }  // 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,
                                  sizeof(kNaClHelperStartupAck), empty)) {
     LOG(ERROR) << "*** send() to zygote failed";
   }
 
   while (true) {
     int badpid = -1;
     std::vector<int> fds;
@@ skipping 19 matching lines @@
         LOG(ERROR) << "nacl_helper unrecognized request: %s";
         _exit(-1);
       }
     }
     // if fork fails, send PID=-1 to zygote
     if (!UnixDomainSocket::SendMsg(kNaClZygoteDescriptor, &badpid,
                                    sizeof(badpid), empty)) {
       LOG(ERROR) << "*** send() to zygote failed";
     }
   }
+  CHECK(false);  // This routine must not return
 }