Implement pthread_rwlock functions for NaCl newlib

src/untrusted/pthread/pthread_internal.h

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef NATIVE_CLIENT_SRC_UNTRUSTED_PTHREAD_PTHREAD_INTERNAL_H_
 #define NATIVE_CLIENT_SRC_UNTRUSTED_PTHREAD_PTHREAD_INTERNAL_H_ 1
 
 #include "native_client/src/untrusted/irt/irt.h"
+#include "native_client/src/untrusted/nacl/tls.h"
+#include "native_client/src/untrusted/nacl/tls_params.h"
 #include "native_client/src/untrusted/pthread/pthread.h"
+#include "native_client/src/untrusted/pthread/pthread_types.h"
 
-struct nc_combined_tdb;
+#define TDB_SIZE (sizeof(struct nc_combined_tdb))
 
 extern int __nc_thread_initialized;
 extern pthread_t __nc_initial_thread_id;
 
 void __nc_initialize_globals(void);
 
 void __nc_initialize_unjoinable_thread(struct nc_combined_tdb *tdb);
 
 void __nc_initialize_interfaces(void);
 
 void __nc_tsd_exit(void);
 
+static inline struct nc_thread_descriptor *__nc_get_tdb(void) {
+  /*
+   * Fetch the thread-specific data pointer.  This is usually just
+   * a wrapper around __libnacl_irt_tls.tls_get() but we don't use
+   * that here so that the IRT build can override the definition.
+   */
+  return (void *) ((char *) __nacl_read_tp_inline()
+                   + __nacl_tp_tdb_offset(TDB_SIZE));
+}
+
 #endif