Non-SFI mode: Use clone() instead of pthread_create()

src/nonsfi/linux/linux_pthread_private.c

 /*
  * Copyright 2014 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.
  */
 
+#include <assert.h>
 #include <errno.h>
 
+#include "native_client/src/nonsfi/linux/linux_pthread_private.h"
 #include "native_client/src/nonsfi/linux/linux_syscall_defines.h"
 #include "native_client/src/nonsfi/linux/linux_syscall_structs.h"
 #include "native_client/src/nonsfi/linux/linux_syscall_wrappers.h"
 #include "native_client/src/nonsfi/linux/linux_sys_private.h"
 #include "native_client/src/public/linux_syscalls/sched.h"
 #include "native_client/src/public/linux_syscalls/sys/syscall.h"
 #include "native_client/src/untrusted/nacl/nacl_irt.h"
 #include "native_client/src/untrusted/nacl/nacl_thread.h"
 #include "native_client/src/untrusted/pthread/pthread_internal.h"
 
@@ skipping 53 matching lines @@
                        : "r7");
 #else
 # error Unsupported architecture
 #endif
 }
 
 static int nacl_irt_thread_nice(const int nice) {
   return 0;
 }
 
+static struct nc_combined_tdb *get_irt_tdb(void *thread_ptr) {
+  struct nc_combined_tdb *tdb = (void *) ((uintptr_t) thread_ptr +
+                                          __nacl_tp_tdb_offset(sizeof(*tdb)));
+  return tdb;
+}
+
+/* Initialize a newly allocated TDB to some default values. */
+static void nc_tdb_init(nc_thread_descriptor_t *tdb,

[Mark Seaborn, 2015/07/08 04:11:21]

Rather than duplicating this from pthread/nc_thread.c, can you change
nc_thread.c's __nc_initialize_unjoinable_thread() to be defined unconditionally,
please?

[Luis Héctor Chávez, 2015/07/08 16:42:13]

Done.

+                        nc_basic_thread_data_t *basic_data) {
+  tdb->tls_base = tdb;
+  tdb->joinable = PTHREAD_CREATE_JOINABLE;
+  tdb->join_waiting = 0;
+  tdb->rdlock_count = 0;
+  tdb->stack_node = NULL;
+  tdb->tls_node = NULL;
+  tdb->start_func = NULL;
+  tdb->state = NULL;
+  tdb->irt_thread_data = NULL;
+  tdb->basic_data = basic_data;
+
+  basic_data->retval = NULL;
+  basic_data->status = THREAD_RUNNING;
+  if (pthread_cond_init(&basic_data->join_condvar, NULL) != 0)
+    __builtin_trap();
+  basic_data->tdb = tdb;
+}
+
+/*
+ * This is used by the IRT for user threads.  We initialize all fields
+ * so that we get predictable behaviour in case some IRT code does an
+ * unsupported pthread operation on a user thread.
+ */
+void __nc_initialize_unjoinable_thread(struct nc_combined_tdb *tdb) {
+  nc_tdb_init(&tdb->tdb, &tdb->basic_data);
+  tdb->tdb.joinable = 0;
+}
+
+/*
+ * This is the real first entry point for new threads.
+ */
+static void irt_start_thread() {

[Mark Seaborn, 2015/07/08 04:11:21]

Can you add a comment saying that this is based on the equivalent function in
src/untrusted/irt/irt_thread.c?  Same for the next two functions too.

[Luis Héctor Chávez, 2015/07/08 16:42:13]

Done.

+  struct nc_combined_tdb *tdb = get_irt_tdb(__nacl_read_tp());
+
+  /*
+   * Fetch the user's start routine.
+   */
+  void *(*user_start)(void *) = tdb->tdb.start_func;
+
+  /*
+   * Now do per-thread initialization for the IRT-private C library state.
+   */
+  __newlib_thread_init();
+
+  /*
+   * Finally, run the user code.
+   */
+  (*user_start)(tdb->tdb.state);
+
+  /*
+   * That should never return.  Crash hard if it does.
+   */
+  __builtin_trap();
+}
+
+int nacl_user_thread_create(void *(*start_func)(void *), void *stack,
+                            void *thread_ptr) {
+  struct nc_combined_tdb *tdb;
+
+  /*
+   * Before we start the thread, allocate the IRT-private TLS area for it.
+   */
+  size_t combined_size = __nacl_tls_combined_size(sizeof(*tdb));
+  void *combined_area = malloc(combined_size);
+  if (combined_area == NULL)
+    return EAGAIN;
+
+ /*

[Mark Seaborn, 2015/07/08 04:11:21]

Nit: fix indentation

[Luis Héctor Chávez, 2015/07/08 16:42:13]

Done.

+   * Note that __nacl_tls_initialize_memory() is not reversible,
+   * because it takes a pointer that need not be aligned and can
+   * return a pointer that is aligned.  In order to
+   * free(combined_area) later, we must save the value of
+   * combined_area.
+   */
+ void *irt_tp = __nacl_tls_initialize_memory(combined_area, sizeof(*tdb));

[Mark Seaborn, 2015/07/08 04:11:21]

Nit: fix indentation

[Luis Héctor Chávez, 2015/07/08 16:42:13]

Done.

+  tdb = get_irt_tdb(irt_tp);
+  __nc_initialize_unjoinable_thread(tdb);
+  tdb->tdb.irt_thread_data = combined_area;
+  tdb->tdb.start_func = start_func;
+  tdb->tdb.state = thread_ptr;
+
+  return nacl_irt_thread_create(irt_start_thread, stack, irt_tp);
+}
+
+void nacl_user_thread_exit(int32_t *stack_flag) {
+  struct nc_combined_tdb *tdb = get_irt_tdb(__nacl_read_tp());
+
+  __nc_tsd_exit();
+
+  /*
+   * Sanity check: Check that this function was not called on a thread
+   * created by the IRT's internal pthread_create().  For such
+   * threads, irt_thread_data == NULL.
+   */
+  assert(tdb->tdb.irt_thread_data != NULL);
+
+  free(tdb->tdb.irt_thread_data);
+
+  nacl_irt_thread_exit(stack_flag);
+}
+
 void __nc_initialize_interfaces(void) {
   const struct nacl_irt_thread init = {
     nacl_irt_thread_create,
     nacl_irt_thread_exit,
     nacl_irt_thread_nice,
   };
   __libnacl_irt_thread = init;
 }