Mac x86_64: Mach exception support

src/trusted/service_runtime/osx/mach_thread_map.c

+/*
+ * Copyright (c) 2013 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 "native_client/src/trusted/service_runtime/osx/mach_thread_map.h"
+
+#include <pthread.h>
+
+#include "native_client/src/shared/platform/nacl_check.h"
+#include "native_client/src/trusted/service_runtime/arch/sel_ldr_arch.h"
+#include "native_client/src/trusted/service_runtime/nacl_globals.h"
+
+#if NACL_ARCH(NACL_BUILD_ARCH) == NACL_x86 && NACL_BUILD_SUBARCH == 64
+
+static mach_port_t mach_threads[NACL_THREAD_MAX];
+
+uint32_t NaClGetThreadIndexForMachThread(mach_port_t mach_thread) {
+  uint32_t nacl_thread_index;
+
+  DCHECK(mach_thread != MACH_PORT_NULL);
+
+  CHECK(NACL_TLS_INDEX_INVALID < NACL_THREAD_MAX);  /* Skip the invalid slot. */
+  for (nacl_thread_index = NACL_TLS_INDEX_INVALID + 1;
+       nacl_thread_index < NACL_THREAD_MAX;
+       ++nacl_thread_index) {
+    if (mach_threads[nacl_thread_index] == mach_thread) {
+      break;

[Mark Seaborn, 2013/02/20 18:33:17]

An early return would be clearer now that you don't need to unlock a mutex.

+    }
+  }
+
+  return nacl_thread_index == NACL_THREAD_MAX ? NACL_TLS_INDEX_INVALID :
+                                                nacl_thread_index;
+}
+
+void NaClSetCurrentMachThreadForThreadIndex(uint32_t nacl_thread_index) {
+  /*
+   * This implementation relies on the Mach port for the thread stored by the
+   * pthread library, and assumes that the pthread library does not close and
+   * re-acquire the Mach port for the thread. If that happens, Mach could
+   * theoretically assign the port a different number in the process' port
+   * table. This approach avoids having to deal with ownership of the port and
+   * the system call overhad to obtain and deallocate it as would be the case
+   * with mach_thread_self().
+   *
+   * When used by the Mach exception handler, this also assumes that the
+   * thread port number when received for an exception will match the port
+   * stored in the mach_threads table. This is guaranteed by how the kernel
+   * coalesces ports in a single port namespace. (A task, or process, is a
+   * single port namespace.)
+   *
+   * An alternative implementation that works on Mac OS X 10.6 or higher is to
+   * use pthread_threadid_np() to obtain a thread ID to use as the key for
+   * this thread map. Such thread IDs are unique system-wide. An exception
+   * handler can find the thread ID for a Mach thread by calling thread_info()
+   * with flavor THREAD_IDENTIFIER_INFO. This approach is not used here
+   * because of the added system call overhead at exception time.
+   */
+  mach_port_t mach_thread = pthread_mach_thread_np(pthread_self());
+  CHECK(mach_thread != MACH_PORT_NULL);
+
+  DCHECK(nacl_thread_index > NACL_TLS_INDEX_INVALID &&
+         nacl_thread_index < NACL_THREAD_MAX);
+  DCHECK(mach_threads[nacl_thread_index] == MACH_PORT_NULL);
+  DCHECK(NaClGetThreadIndexForMachThread(mach_thread) ==
+         NACL_TLS_INDEX_INVALID);
+
+  mach_threads[nacl_thread_index] = mach_thread;
+}
+
+void NaClClearMachThreadForThreadIndex(uint32_t nacl_thread_index) {
+  DCHECK(nacl_thread_index > NACL_TLS_INDEX_INVALID &&
+         nacl_thread_index < NACL_THREAD_MAX);
+  DCHECK(mach_threads[nacl_thread_index] ==
+         pthread_mach_thread_np(pthread_self()));
+
+  mach_threads[nacl_thread_index] = MACH_PORT_NULL;
+}
+
+#endif