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/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 != 32

[Mark Seaborn, 2013/02/14 23:55:02]

Again, probably better to say:
#if NACL_ARCH(NACL_BUILD_ARCH) == NACL_x86 && NACL_BUILD_SUBARCH = 64

+
+static mach_port_t mach_threads[NACL_THREAD_MAX];
+
+size_t NaClGetThreadIndexForMachThread(mach_port_t mach_thread) {
+  size_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;
+    }
+  }
+
+  return nacl_thread_index == NACL_THREAD_MAX ? NACL_TLS_INDEX_INVALID :
+                                                nacl_thread_index;
+}
+
+void NaClSetCurrentMachThreadForThreadIndex(size_t nacl_thread_index) {
+  mach_port_t mach_thread = pthread_mach_thread_np(pthread_self());

[Mark Seaborn, 2013/02/14 23:55:02]

It might be worth commenting that:

We assume that the pthread library does not close and re-acquire the Mach port
for the thread.  If that happens, Mach could assign the port a different number
in the process's port table.

I assume OS X does not provide any globally-valid thread IDs that we can use for
this, unlike on Windows and Linux?

We're also assuming that when the kernel sends the thread port to our Mach
exception handler, Mach reuses the same index for the port in the process's port
table.  (Presumably Mach doesn't have any other mechanism for comparing two
ports for equality?)

That's my understanding of this, anyway. :-)

[Mark Mentovai, 2013/02/15 17:36:42]

Mark Seaborn wrote:
Your understanding is correct.

As of Mac OS X 10.6, there actually is a system-wide thread ID that’s exposed to
user space. I believe that this would also work for our needs, but I wasn’t sure
if Native Client still needed to support Mac OS X 10.5. Chrome dropped 10.5
support last summer. Did Native Client too?

I have a response ready for the rest of your comment, but it might be moot
depending on the answer to this question.

[Mark Seaborn, 2013/02/15 22:48:08]

What's this interface called?

Whether it's worth using it depends on how likely it is that Apple will change
it.

As I understand it, even the Mach interfaces are not officially supported,
although they aren't likely to change too much since the Mach layer is fairly
stable (or stale :-) ).  An alternative thread ID might be more likely to be
removed in future.
Yes, we don't need to support 10.5.

+  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(size_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