[2018-01] Update README.md #24
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akoeplinger
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Jun 25, 2019
We recently switched the AOT compiler for iOS armv7 from 32bit host to 64bit host. At the same time we _also_ switched from LLVM 3.6 to the newer LLVM 6.0 fork we support. In a Xamarin.iOS Release build for iOS armv7 exception handling would crash. Specifically the problem was that the exception object wasn't properly injected into the handler block. The way it works is, that the exception handler machinery passes the pointer to the exception object via `r0`. With the newer LLVM the generated code of the exception handling block looks like this: ``` LBB1_15: @ %EH_CLAUSE0_BB3 Ltmp8: ldr r0, [sp, #24] str r0, [sp, #4] ldr r0, [sp, #28] ldr r0, [sp, #12] ldr r0, [r0] cmp r0, #0 beq LBB1_17 ``` thus overwriting `r0`, so that the pointer to the exception object is lost. With the older LLVM 3.6 the generated code looks like this: ``` LBB1_8: @ %EH_CLAUSE0_BB3 Ltmp8: str r0, [sp, #4] ldr r0, [r6] cmp r0, #0 beq LBB1_10 ``` correctly storing the exception object into a stack slot for later usage. After some time I figured out that there are _different_ exception handling models. Depending on the model, the exception pointer is passed in `r0` or not: https://github.com/mono/llvm/blob/2bd2f1db1803f7b36687e5abf912c69baa848305/lib/Target/ARM/ARMISelLowering.cpp#L14416-L14428 `SjLj` stands for "SetJump / LongJump" and means that exception handling is implemented with this. On iOS this is the default model that is used. We want `dwarf` instead, so we tell this `llc` now and the generated code handles it correctly. So why was it working before? In our older LLVM 3.6 fork we hardcoded it: https://github.com/mono/llvm/blob/f80899cb3eb75f7f5640b4519e83bd96991bffb8/lib/Target/ARM/ARMISelLowering.cpp#L756-L762 The `-exception-model=` option is also not available in LLVM 3.6. Contributes to mono#15058 and mono#9621
akoeplinger
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Jul 2, 2019
We recently switched the AOT compiler for iOS armv7 from 32bit host to 64bit host. At the same time we _also_ switched from LLVM 3.6 to the newer LLVM 6.0 fork we support. In a Xamarin.iOS Release build for iOS armv7 exception handling would crash. Specifically the problem was that the exception object wasn't properly injected into the handler block. The way it works is, that the exception handler machinery passes the pointer to the exception object via `r0`. With the newer LLVM the generated code of the exception handling block looks like this: ``` LBB1_15: @ %EH_CLAUSE0_BB3 Ltmp8: ldr r0, [sp, #24] str r0, [sp, #4] ldr r0, [sp, #28] ldr r0, [sp, #12] ldr r0, [r0] cmp r0, #0 beq LBB1_17 ``` thus overwriting `r0`, so that the pointer to the exception object is lost. With the older LLVM 3.6 the generated code looks like this: ``` LBB1_8: @ %EH_CLAUSE0_BB3 Ltmp8: str r0, [sp, #4] ldr r0, [r6] cmp r0, #0 beq LBB1_10 ``` correctly storing the exception object into a stack slot for later usage. After some time I figured out that there are _different_ exception handling models. Depending on the model, the exception pointer is passed in `r0` or not: https://github.com/mono/llvm/blob/2bd2f1db1803f7b36687e5abf912c69baa848305/lib/Target/ARM/ARMISelLowering.cpp#L14416-L14428 `SjLj` stands for "SetJump / LongJump" and means that exception handling is implemented with this. On iOS this is the default model that is used. We want `dwarf` instead, so we tell this `llc` now and the generated code handles it correctly. So why was it working before? In our older LLVM 3.6 fork we hardcoded it: https://github.com/mono/llvm/blob/f80899cb3eb75f7f5640b4519e83bd96991bffb8/lib/Target/ARM/ARMISelLowering.cpp#L756-L762 The `-exception-model=` option is also not available in LLVM 3.6. Contributes to mono#15058 and mono#9621
akoeplinger
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Sep 25, 2019
) * [threads] clear small_id_key TLS when unregistering a thread Fixes ``` * thread #12, name = 'tid_a507', stop reason = EXC_BREAKPOINT (code=1, subcode=0x1be66144) * frame #0: 0x1be66144 libsystem_c.dylib`__abort + 184 frame #1: 0x1be6608c libsystem_c.dylib`abort + 152 frame #2: 0x003e1fa0 monotouchtest`log_callback(log_domain=0x00000000, log_level="error", message="* Assertion at ../../../../../mono/utils/hazard-pointer.c:158, condition `mono_bitset_test_fast (small_id_table, id)' not met\n", fatal=4, user_data=0x00000000) at runtime.m:1251:3 frame #3: 0x003abf44 monotouchtest`monoeg_g_logv_nofree(log_domain=0x00000000, log_level=G_LOG_LEVEL_ERROR, format=<unavailable>, args=<unavailable>) at goutput.c:149:2 [opt] frame #4: 0x003abfb4 monotouchtest`monoeg_assertion_message(format=<unavailable>) at goutput.c:184:22 [opt] frame #5: 0x003904dc monotouchtest`mono_thread_small_id_free(id=<unavailable>) at hazard-pointer.c:0:2 [opt] frame #6: 0x003a0a74 monotouchtest`unregister_thread(arg=0x15c88400) at mono-threads.c:588:2 [opt] frame #7: 0x00336110 monotouchtest`mono_thread_detach_if_exiting at threads.c:1571:4 [opt] frame #8: 0x003e7a14 monotouchtest`::xamarin_release_trampoline(self=0x166452f0, sel="release") at trampolines.m:644:3 frame #9: 0x001cdc40 monotouchtest`::-[__Xamarin_NSTimerActionDispatcher release](self=0x166452f0, _cmd="release") at registrar.m:83445:3 frame #10: 0x1ce2ae68 Foundation`_timerRelease + 80 frame #11: 0x1c31b56c CoreFoundation`CFRunLoopTimerInvalidate + 612 frame #12: 0x1c31a554 CoreFoundation`__CFRunLoopTimerDeallocate + 32 frame #13: 0x1c31dde4 CoreFoundation`_CFRelease + 220 frame #14: 0x1c2be6e8 CoreFoundation`__CFArrayReleaseValues + 500 frame #15: 0x1c2be4c4 CoreFoundation`CFArrayRemoveAllValues + 104 frame #16: 0x1c31ff64 CoreFoundation`__CFSetApplyFunction_block_invoke + 24 frame #17: 0x1c3b2e18 CoreFoundation`CFBasicHashApply + 116 frame #18: 0x1c31ff10 CoreFoundation`CFSetApplyFunction + 160 frame #19: 0x1c3152cc CoreFoundation`__CFRunLoopDeallocate + 204 frame #20: 0x1c31dde4 CoreFoundation`_CFRelease + 220 frame #21: 0x1c304a80 CoreFoundation`__CFTSDFinalize + 144 frame #22: 0x1bfa324c libsystem_pthread.dylib`_pthread_tsd_cleanup + 644 frame #23: 0x1bf9cc08 libsystem_pthread.dylib`_pthread_exit + 80 frame #24: 0x1bf9af24 libsystem_pthread.dylib`pthread_exit + 36 frame #25: 0x0039df84 monotouchtest`mono_threads_platform_exit(exit_code=<unavailable>) at mono-threads-posix.c:145:2 [opt] frame #26: 0x0033bb84 monotouchtest`start_wrapper(data=0x1609e1c0) at threads.c:1296:2 [opt] frame #27: 0x1bf9b914 libsystem_pthread.dylib`_pthread_body + 128 frame #28: 0x1bf9b874 libsystem_pthread.dylib`_pthread_start + 44 frame #29: 0x1bfa3b94 libsystem_pthread.dylib`thread_start + 4 ``` * Update mono/utils/mono-threads.c Co-Authored-By: Aleksey Kliger (λgeek) <[email protected]>
akoeplinger
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Sep 25, 2019
mono#17015) [2019-08] [threads] clear small_id_key TLS when unregistering a thread Fixes ``` * thread #12, name = 'tid_a507', stop reason = EXC_BREAKPOINT (code=1, subcode=0x1be66144) * frame #0: 0x1be66144 libsystem_c.dylib`__abort + 184 frame #1: 0x1be6608c libsystem_c.dylib`abort + 152 frame #2: 0x003e1fa0 monotouchtest`log_callback(log_domain=0x00000000, log_level="error", message="* Assertion at ../../../../../mono/utils/hazard-pointer.c:158, condition `mono_bitset_test_fast (small_id_table, id)' not met\n", fatal=4, user_data=0x00000000) at runtime.m:1251:3 frame #3: 0x003abf44 monotouchtest`monoeg_g_logv_nofree(log_domain=0x00000000, log_level=G_LOG_LEVEL_ERROR, format=<unavailable>, args=<unavailable>) at goutput.c:149:2 [opt] frame #4: 0x003abfb4 monotouchtest`monoeg_assertion_message(format=<unavailable>) at goutput.c:184:22 [opt] frame #5: 0x003904dc monotouchtest`mono_thread_small_id_free(id=<unavailable>) at hazard-pointer.c:0:2 [opt] frame #6: 0x003a0a74 monotouchtest`unregister_thread(arg=0x15c88400) at mono-threads.c:588:2 [opt] frame #7: 0x00336110 monotouchtest`mono_thread_detach_if_exiting at threads.c:1571:4 [opt] frame #8: 0x003e7a14 monotouchtest`::xamarin_release_trampoline(self=0x166452f0, sel="release") at trampolines.m:644:3 frame #9: 0x001cdc40 monotouchtest`::-[__Xamarin_NSTimerActionDispatcher release](self=0x166452f0, _cmd="release") at registrar.m:83445:3 frame #10: 0x1ce2ae68 Foundation`_timerRelease + 80 frame #11: 0x1c31b56c CoreFoundation`CFRunLoopTimerInvalidate + 612 frame #12: 0x1c31a554 CoreFoundation`__CFRunLoopTimerDeallocate + 32 frame #13: 0x1c31dde4 CoreFoundation`_CFRelease + 220 frame #14: 0x1c2be6e8 CoreFoundation`__CFArrayReleaseValues + 500 frame #15: 0x1c2be4c4 CoreFoundation`CFArrayRemoveAllValues + 104 frame #16: 0x1c31ff64 CoreFoundation`__CFSetApplyFunction_block_invoke + 24 frame #17: 0x1c3b2e18 CoreFoundation`CFBasicHashApply + 116 frame #18: 0x1c31ff10 CoreFoundation`CFSetApplyFunction + 160 frame #19: 0x1c3152cc CoreFoundation`__CFRunLoopDeallocate + 204 frame #20: 0x1c31dde4 CoreFoundation`_CFRelease + 220 frame #21: 0x1c304a80 CoreFoundation`__CFTSDFinalize + 144 frame #22: 0x1bfa324c libsystem_pthread.dylib`_pthread_tsd_cleanup + 644 frame #23: 0x1bf9cc08 libsystem_pthread.dylib`_pthread_exit + 80 frame #24: 0x1bf9af24 libsystem_pthread.dylib`pthread_exit + 36 frame #25: 0x0039df84 monotouchtest`mono_threads_platform_exit(exit_code=<unavailable>) at mono-threads-posix.c:145:2 [opt] frame #26: 0x0033bb84 monotouchtest`start_wrapper(data=0x1609e1c0) at threads.c:1296:2 [opt] frame #27: 0x1bf9b914 libsystem_pthread.dylib`_pthread_body + 128 frame #28: 0x1bf9b874 libsystem_pthread.dylib`_pthread_start + 44 frame #29: 0x1bfa3b94 libsystem_pthread.dylib`thread_start + 4 ``` Debugged by @lambdageek. Contributes to mono#10641 Edit: C/p into PR description so it's in the commit message: We think what happens is: 1. `start_wrapper` runs `unregister_thread` when the thread is exiting. At that point the `small_id` for the thread is cleared from the hazard pointer bitset by `mono_thread_small_id_free (small_id)` 2. Some other TLS destructor runs and attaches the thread again (which runs `mono_thread_info_register_small_id` which first calls `mono_thread_info_get_small_id` which tries to get the small id from the `small_id_key` TLS key and so the new `MonoThreadInfo` has the same `small_id` as the previously destroyed `MonoThreadInfo` - but the hazard pointer bitset is **not** updated). 3. This other TLS destructor runs and calls `mono_thread_detach_if_exiting` which calls `unregister_thread` again. 4. `unregister_thread` calls ` mono_thread_small_id_free (small_id)` a second time which asserts because we already cleared that id from the hazard pointer bitset. Backport of mono#16973. /cc @lewurm
akoeplinger
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Dec 10, 2019
When the debugger tries to suspend all the VM threads, it can happen with cooperative-suspend that it tries to suspend a thread that has previously been attached, but then did a "light" detach (that only unsets the domain). With the domain set to `NULL`, looking up a JitInfo for a given `ip` will result into a crash, but it isn't even necessarily needed for the purpose of suspending a thread. More details: Consider the following: ``` (lldb) c error: Process is running. Use 'process interrupt' to pause execution. Process 12832 stopped * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 2713 MonoDomain *domain = (MonoDomain *) mono_thread_info_get_suspend_state (info)->unwind_data [MONO_UNWIND_DATA_DOMAIN]; 2714 if (!domain) { 2715 /* not attached */ -> 2716 ji = NULL; 2717 } else { 2718 ji = mono_jit_info_table_find_internal ( domain, MONO_CONTEXT_GET_IP (&mono_thread_info_get_suspend_state (info)->ctx), TRUE, TRUE); 2719 } Target 0: (WatchWCSessionAppWatchOSExtension) stopped. (lldb) bt * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 * frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 frame #1: 0x004e177b WatchWCSessionAppWatchOSExtension`mono_thread_info_safe_suspend_and_run(id=0xb0767000, interrupt_kernel=0, callback=(WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical at debugger-agent.c:2708), user_data=0xb04dc718) at mono-threads.c:1358:19 frame #2: 0x00222799 WatchWCSessionAppWatchOSExtension`notify_thread(key=0x03994508, value=0x81378c00, user_data=0x00000000) at debugger-agent.c:2747:2 frame #3: 0x00355bd8 WatchWCSessionAppWatchOSExtension`mono_g_hash_table_foreach(hash=0x8007b4e0, func=(WatchWCSessionAppWatchOSExtension`notify_thread at debugger-agent.c:2733), user_data=0x00000000) at mono-hash.c:310:4 frame #4: 0x0021e955 WatchWCSessionAppWatchOSExtension`suspend_vm at debugger-agent.c:2844:3 frame #5: 0x00225ff0 WatchWCSessionAppWatchOSExtension`process_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0, il_offset=0, ctx=0x00000000, events=0x805b28e0, suspend_policy=2) at debugger-agent.c:4012:3 frame #6: 0x00227c7c WatchWCSessionAppWatchOSExtension`process_profiler_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0) at debugger-agent.c:4072:2 frame #7: 0x0021b174 WatchWCSessionAppWatchOSExtension`thread_startup(prof=0x00000000, tid=2957889536) at debugger-agent.c:4149:2 frame #8: 0x0037912d WatchWCSessionAppWatchOSExtension`mono_profiler_raise_thread_started(tid=2957889536) at profiler-events.h:103:1 frame #9: 0x003d53da WatchWCSessionAppWatchOSExtension`fire_attach_profiler_events(tid=0xb04dd000) at threads.c:1120:2 frame #10: 0x003d4d83 WatchWCSessionAppWatchOSExtension`mono_thread_attach(domain=0x801750a0) at threads.c:1547:2 frame #11: 0x003df1a1 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop_internal(domain=0x801750a0, cookie=0xb04dcc0c, stackdata=0xb04dcba8) at threads.c:6008:3 frame #12: 0x003df287 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop(domain=0x00000000, dummy=0xb04dcc0c) at threads.c:6045:9 frame #13: 0x005034b8 WatchWCSessionAppWatchOSExtension`::xamarin_switch_gchandle(self=0x80762c20, to_weak=false) at runtime.m:1805:2 frame #14: 0x005065c1 WatchWCSessionAppWatchOSExtension`::xamarin_retain_trampoline(self=0x80762c20, sel="retain") at trampolines.m:693:2 frame #15: 0x657ea520 libobjc.A.dylib`objc_retain + 64 frame #16: 0x4b4d9caa WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke + 279 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb26e Foundation`____addOperations_block_invoke_4 + 20 frame #24: 0x65de007b libdispatch.dylib`_dispatch_call_block_and_release + 15 frame #25: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #26: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #27: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #28: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #29: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #30: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #31: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` Going further, `info` is about this thread: ``` (lldb) p/x *(int *)(((char *) info->node.key) + 0xa0) (int) $2 = 0x01243f93 (lldb) thread list Process 12832 stopped thread #1: tid = 0x1243ee1, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_303', queue = 'com.apple.main-thread' thread #2: tid = 0x1243ee6, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10 thread #3: tid = 0x1243ee7, 0x65f81aea libsystem_kernel.dylib`__psynch_cvwait + 10, name = 'SGen worker' thread #4: tid = 0x1243ee9, 0x65f7e3d2 libsystem_kernel.dylib`semaphore_wait_trap + 10, name = 'Finalizer' thread #5: tid = 0x1243eea, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10, name = 'Debugger agent' thread #6: tid = 0x1243f1d, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'com.apple.uikit.eventfetch-thread' thread #8: tid = 0x1243f93, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * thread #9: tid = 0x12443a9, 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 thread #10: tid = 0x1244581, 0x65f7fd32 libsystem_kernel.dylib`__workq_kernreturn + 10 (lldb) thread select 8 * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 libsystem_kernel.dylib`mach_msg_trap: -> 0x65f7e396 <+10>: retl 0x65f7e397 <+11>: nop libsystem_kernel.dylib`mach_msg_overwrite_trap: 0x65f7e398 <+0>: movl $0xffffffe0, %eax ; imm = 0xFFFFFFE0 0x65f7e39d <+5>: calll 0x65f85f44 ; _sysenter_trap (lldb) bt * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 frame #1: 0x65f7e8ff libsystem_kernel.dylib`mach_msg + 47 frame #2: 0x66079679 libxpc.dylib`_xpc_send_serializer + 104 frame #3: 0x660794da libxpc.dylib`_xpc_pipe_simpleroutine + 80 frame #4: 0x66079852 libxpc.dylib`xpc_pipe_simpleroutine + 43 frame #5: 0x66043a8f libsystem_trace.dylib`___os_activity_stream_reflect_block_invoke_2 + 30 frame #6: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #7: 0x65de3d71 libdispatch.dylib`_dispatch_block_invoke_direct + 257 frame #8: 0x65de3c62 libdispatch.dylib`dispatch_block_perform + 112 frame #9: 0x6604349a libsystem_trace.dylib`_os_activity_stream_reflect + 725 frame #10: 0x6604ef19 libsystem_trace.dylib`_os_log_impl_stream + 468 frame #11: 0x6604e44d libsystem_trace.dylib`_os_log_impl_flatten_and_send + 6410 frame #12: 0x6604cb3b libsystem_trace.dylib`_os_log + 137 frame #13: 0x6604f4aa libsystem_trace.dylib`_os_log_impl + 31 frame #14: 0x4b4eb4e9 WatchConnectivity`WCSerializePayloadDictionary + 393 frame #15: 0x4b4d7c4d WatchConnectivity`-[WCSession onqueue_sendResponseDictionary:identifier:] + 195 frame #16: 0x4b4da435 WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke.411 + 35 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb067 Foundation`____addOperations_block_invoke_2 + 20 frame #24: 0x65dedf49 libdispatch.dylib`_dispatch_block_async_invoke2 + 77 frame #25: 0x65de4461 libdispatch.dylib`_dispatch_block_async_invoke_and_release + 17 frame #26: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #27: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #28: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #29: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #30: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #31: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #32: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` which is a thread in a "light" detach state (aka. coop detach), where we only unset the domain: https://github.com/mono/mono/blob/4cefdcb7ce2d939ee78fb45d1b4913eb3bc064fd/mono/metadata/threads.c#L6084-L6111 Fixes mono#17926
akoeplinger
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Feb 12, 2020
[2019-08] [debugger] skip suspend for unattached threads When the debugger tries to suspend all the VM threads, it can happen with cooperative-suspend that it tries to suspend a thread that has previously been attached, but then did a "light" detach (that only unsets the domain). With the domain set to `NULL`, looking up a JitInfo for a given `ip` will result into a crash, but it isn't even necessarily needed for the purpose of suspending a thread. More details: Consider the following: ``` (lldb) c error: Process is running. Use 'process interrupt' to pause execution. Process 12832 stopped * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 2713 MonoDomain *domain = (MonoDomain *) mono_thread_info_get_suspend_state (info)->unwind_data [MONO_UNWIND_DATA_DOMAIN]; 2714 if (!domain) { 2715 /* not attached */ -> 2716 ji = NULL; 2717 } else { 2718 ji = mono_jit_info_table_find_internal ( domain, MONO_CONTEXT_GET_IP (&mono_thread_info_get_suspend_state (info)->ctx), TRUE, TRUE); 2719 } Target 0: (WatchWCSessionAppWatchOSExtension) stopped. (lldb) bt * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 * frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 frame #1: 0x004e177b WatchWCSessionAppWatchOSExtension`mono_thread_info_safe_suspend_and_run(id=0xb0767000, interrupt_kernel=0, callback=(WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical at debugger-agent.c:2708), user_data=0xb04dc718) at mono-threads.c:1358:19 frame #2: 0x00222799 WatchWCSessionAppWatchOSExtension`notify_thread(key=0x03994508, value=0x81378c00, user_data=0x00000000) at debugger-agent.c:2747:2 frame #3: 0x00355bd8 WatchWCSessionAppWatchOSExtension`mono_g_hash_table_foreach(hash=0x8007b4e0, func=(WatchWCSessionAppWatchOSExtension`notify_thread at debugger-agent.c:2733), user_data=0x00000000) at mono-hash.c:310:4 frame #4: 0x0021e955 WatchWCSessionAppWatchOSExtension`suspend_vm at debugger-agent.c:2844:3 frame #5: 0x00225ff0 WatchWCSessionAppWatchOSExtension`process_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0, il_offset=0, ctx=0x00000000, events=0x805b28e0, suspend_policy=2) at debugger-agent.c:4012:3 frame #6: 0x00227c7c WatchWCSessionAppWatchOSExtension`process_profiler_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0) at debugger-agent.c:4072:2 frame #7: 0x0021b174 WatchWCSessionAppWatchOSExtension`thread_startup(prof=0x00000000, tid=2957889536) at debugger-agent.c:4149:2 frame #8: 0x0037912d WatchWCSessionAppWatchOSExtension`mono_profiler_raise_thread_started(tid=2957889536) at profiler-events.h:103:1 frame #9: 0x003d53da WatchWCSessionAppWatchOSExtension`fire_attach_profiler_events(tid=0xb04dd000) at threads.c:1120:2 frame #10: 0x003d4d83 WatchWCSessionAppWatchOSExtension`mono_thread_attach(domain=0x801750a0) at threads.c:1547:2 frame #11: 0x003df1a1 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop_internal(domain=0x801750a0, cookie=0xb04dcc0c, stackdata=0xb04dcba8) at threads.c:6008:3 frame #12: 0x003df287 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop(domain=0x00000000, dummy=0xb04dcc0c) at threads.c:6045:9 frame #13: 0x005034b8 WatchWCSessionAppWatchOSExtension`::xamarin_switch_gchandle(self=0x80762c20, to_weak=false) at runtime.m:1805:2 frame #14: 0x005065c1 WatchWCSessionAppWatchOSExtension`::xamarin_retain_trampoline(self=0x80762c20, sel="retain") at trampolines.m:693:2 frame #15: 0x657ea520 libobjc.A.dylib`objc_retain + 64 frame #16: 0x4b4d9caa WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke + 279 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb26e Foundation`____addOperations_block_invoke_4 + 20 frame #24: 0x65de007b libdispatch.dylib`_dispatch_call_block_and_release + 15 frame #25: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #26: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #27: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #28: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #29: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #30: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #31: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` Going further, `info` is about this thread: ``` (lldb) p/x *(int *)(((char *) info->node.key) + 0xa0) (int) $2 = 0x01243f93 (lldb) thread list Process 12832 stopped thread #1: tid = 0x1243ee1, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_303', queue = 'com.apple.main-thread' thread #2: tid = 0x1243ee6, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10 thread #3: tid = 0x1243ee7, 0x65f81aea libsystem_kernel.dylib`__psynch_cvwait + 10, name = 'SGen worker' thread #4: tid = 0x1243ee9, 0x65f7e3d2 libsystem_kernel.dylib`semaphore_wait_trap + 10, name = 'Finalizer' thread #5: tid = 0x1243eea, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10, name = 'Debugger agent' thread #6: tid = 0x1243f1d, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'com.apple.uikit.eventfetch-thread' thread #8: tid = 0x1243f93, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * thread #9: tid = 0x12443a9, 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 thread #10: tid = 0x1244581, 0x65f7fd32 libsystem_kernel.dylib`__workq_kernreturn + 10 (lldb) thread select 8 * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 libsystem_kernel.dylib`mach_msg_trap: -> 0x65f7e396 <+10>: retl 0x65f7e397 <+11>: nop libsystem_kernel.dylib`mach_msg_overwrite_trap: 0x65f7e398 <+0>: movl $0xffffffe0, %eax ; imm = 0xFFFFFFE0 0x65f7e39d <+5>: calll 0x65f85f44 ; _sysenter_trap (lldb) bt * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 frame #1: 0x65f7e8ff libsystem_kernel.dylib`mach_msg + 47 frame #2: 0x66079679 libxpc.dylib`_xpc_send_serializer + 104 frame #3: 0x660794da libxpc.dylib`_xpc_pipe_simpleroutine + 80 frame #4: 0x66079852 libxpc.dylib`xpc_pipe_simpleroutine + 43 frame #5: 0x66043a8f libsystem_trace.dylib`___os_activity_stream_reflect_block_invoke_2 + 30 frame #6: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #7: 0x65de3d71 libdispatch.dylib`_dispatch_block_invoke_direct + 257 frame #8: 0x65de3c62 libdispatch.dylib`dispatch_block_perform + 112 frame #9: 0x6604349a libsystem_trace.dylib`_os_activity_stream_reflect + 725 frame #10: 0x6604ef19 libsystem_trace.dylib`_os_log_impl_stream + 468 frame #11: 0x6604e44d libsystem_trace.dylib`_os_log_impl_flatten_and_send + 6410 frame #12: 0x6604cb3b libsystem_trace.dylib`_os_log + 137 frame #13: 0x6604f4aa libsystem_trace.dylib`_os_log_impl + 31 frame #14: 0x4b4eb4e9 WatchConnectivity`WCSerializePayloadDictionary + 393 frame #15: 0x4b4d7c4d WatchConnectivity`-[WCSession onqueue_sendResponseDictionary:identifier:] + 195 frame #16: 0x4b4da435 WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke.411 + 35 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb067 Foundation`____addOperations_block_invoke_2 + 20 frame #24: 0x65dedf49 libdispatch.dylib`_dispatch_block_async_invoke2 + 77 frame #25: 0x65de4461 libdispatch.dylib`_dispatch_block_async_invoke_and_release + 17 frame #26: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #27: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #28: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #29: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #30: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #31: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #32: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` which is a thread in a "light" detach state (aka. coop detach), where we only unset the domain: https://github.com/mono/mono/blob/4cefdcb7ce2d939ee78fb45d1b4913eb3bc064fd/mono/metadata/threads.c#L6084-L6111 Fixes mono#17926 <!-- Thank you for your Pull Request! If you are new to contributing to Mono, please try to do your best at conforming to our coding guidelines http://www.mono-project.com/community/contributing/coding-guidelines/ but don't worry if you get something wrong. One of the project members will help you to get things landed. Does your pull request fix any of the existing issues? Please use the following format: Fixes #issue-number --> Backport of mono#18105. /cc @lewurm
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When the debugger tries to suspend all the VM threads, it can happen with cooperative-suspend that it tries to suspend a thread that has previously been attached, but then did a "light" detach (that only unsets the domain). With the domain set to `NULL`, looking up a JitInfo for a given `ip` will result into a crash, but it isn't even necessarily needed for the purpose of suspending a thread. More details: Consider the following: ``` (lldb) c error: Process is running. Use 'process interrupt' to pause execution. Process 12832 stopped * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 2713 MonoDomain *domain = (MonoDomain *) mono_thread_info_get_suspend_state (info)->unwind_data [MONO_UNWIND_DATA_DOMAIN]; 2714 if (!domain) { 2715 /* not attached */ -> 2716 ji = NULL; 2717 } else { 2718 ji = mono_jit_info_table_find_internal ( domain, MONO_CONTEXT_GET_IP (&mono_thread_info_get_suspend_state (info)->ctx), TRUE, TRUE); 2719 } Target 0: (WatchWCSessionAppWatchOSExtension) stopped. (lldb) bt * thread #9, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 * frame #0: 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6 frame #1: 0x004e177b WatchWCSessionAppWatchOSExtension`mono_thread_info_safe_suspend_and_run(id=0xb0767000, interrupt_kernel=0, callback=(WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical at debugger-agent.c:2708), user_data=0xb04dc718) at mono-threads.c:1358:19 frame #2: 0x00222799 WatchWCSessionAppWatchOSExtension`notify_thread(key=0x03994508, value=0x81378c00, user_data=0x00000000) at debugger-agent.c:2747:2 frame #3: 0x00355bd8 WatchWCSessionAppWatchOSExtension`mono_g_hash_table_foreach(hash=0x8007b4e0, func=(WatchWCSessionAppWatchOSExtension`notify_thread at debugger-agent.c:2733), user_data=0x00000000) at mono-hash.c:310:4 frame #4: 0x0021e955 WatchWCSessionAppWatchOSExtension`suspend_vm at debugger-agent.c:2844:3 frame #5: 0x00225ff0 WatchWCSessionAppWatchOSExtension`process_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0, il_offset=0, ctx=0x00000000, events=0x805b28e0, suspend_policy=2) at debugger-agent.c:4012:3 frame #6: 0x00227c7c WatchWCSessionAppWatchOSExtension`process_profiler_event(event=EVENT_KIND_THREAD_START, arg=0x039945d0) at debugger-agent.c:4072:2 frame #7: 0x0021b174 WatchWCSessionAppWatchOSExtension`thread_startup(prof=0x00000000, tid=2957889536) at debugger-agent.c:4149:2 frame #8: 0x0037912d WatchWCSessionAppWatchOSExtension`mono_profiler_raise_thread_started(tid=2957889536) at profiler-events.h:103:1 frame #9: 0x003d53da WatchWCSessionAppWatchOSExtension`fire_attach_profiler_events(tid=0xb04dd000) at threads.c:1120:2 frame #10: 0x003d4d83 WatchWCSessionAppWatchOSExtension`mono_thread_attach(domain=0x801750a0) at threads.c:1547:2 frame #11: 0x003df1a1 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop_internal(domain=0x801750a0, cookie=0xb04dcc0c, stackdata=0xb04dcba8) at threads.c:6008:3 frame #12: 0x003df287 WatchWCSessionAppWatchOSExtension`mono_threads_attach_coop(domain=0x00000000, dummy=0xb04dcc0c) at threads.c:6045:9 frame #13: 0x005034b8 WatchWCSessionAppWatchOSExtension`::xamarin_switch_gchandle(self=0x80762c20, to_weak=false) at runtime.m:1805:2 frame #14: 0x005065c1 WatchWCSessionAppWatchOSExtension`::xamarin_retain_trampoline(self=0x80762c20, sel="retain") at trampolines.m:693:2 frame #15: 0x657ea520 libobjc.A.dylib`objc_retain + 64 frame #16: 0x4b4d9caa WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke + 279 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb26e Foundation`____addOperations_block_invoke_4 + 20 frame #24: 0x65de007b libdispatch.dylib`_dispatch_call_block_and_release + 15 frame #25: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #26: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #27: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #28: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #29: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #30: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #31: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` Going further, `info` is about this thread: ``` (lldb) p/x *(int *)(((char *) info->node.key) + 0xa0) (int) $2 = 0x01243f93 (lldb) thread list Process 12832 stopped thread #1: tid = 0x1243ee1, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_303', queue = 'com.apple.main-thread' thread #2: tid = 0x1243ee6, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10 thread #3: tid = 0x1243ee7, 0x65f81aea libsystem_kernel.dylib`__psynch_cvwait + 10, name = 'SGen worker' thread #4: tid = 0x1243ee9, 0x65f7e3d2 libsystem_kernel.dylib`semaphore_wait_trap + 10, name = 'Finalizer' thread #5: tid = 0x1243eea, 0x65f816e2 libsystem_kernel.dylib`__recvfrom + 10, name = 'Debugger agent' thread #6: tid = 0x1243f1d, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'com.apple.uikit.eventfetch-thread' thread #8: tid = 0x1243f93, 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * thread #9: tid = 0x12443a9, 0x00222870 WatchWCSessionAppWatchOSExtension`debugger_interrupt_critical(info=0x81365400, user_data=0xb04dc718) at debugger-agent.c:2716:6, name = 'tid_a31f', queue = 'NSOperationQueue 0x8069b670 (QOS: UTILITY)', stop reason = breakpoint 1.1 thread #10: tid = 0x1244581, 0x65f7fd32 libsystem_kernel.dylib`__workq_kernreturn + 10 (lldb) thread select 8 * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 libsystem_kernel.dylib`mach_msg_trap: -> 0x65f7e396 <+10>: retl 0x65f7e397 <+11>: nop libsystem_kernel.dylib`mach_msg_overwrite_trap: 0x65f7e398 <+0>: movl $0xffffffe0, %eax ; imm = 0xFFFFFFE0 0x65f7e39d <+5>: calll 0x65f85f44 ; _sysenter_trap (lldb) bt * thread #8, name = 'tid_6d0f', queue = 'NSOperationQueue 0x8069b300 (QOS: UTILITY)' * frame #0: 0x65f7e396 libsystem_kernel.dylib`mach_msg_trap + 10 frame #1: 0x65f7e8ff libsystem_kernel.dylib`mach_msg + 47 frame #2: 0x66079679 libxpc.dylib`_xpc_send_serializer + 104 frame #3: 0x660794da libxpc.dylib`_xpc_pipe_simpleroutine + 80 frame #4: 0x66079852 libxpc.dylib`xpc_pipe_simpleroutine + 43 frame #5: 0x66043a8f libsystem_trace.dylib`___os_activity_stream_reflect_block_invoke_2 + 30 frame #6: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #7: 0x65de3d71 libdispatch.dylib`_dispatch_block_invoke_direct + 257 frame #8: 0x65de3c62 libdispatch.dylib`dispatch_block_perform + 112 frame #9: 0x6604349a libsystem_trace.dylib`_os_activity_stream_reflect + 725 frame #10: 0x6604ef19 libsystem_trace.dylib`_os_log_impl_stream + 468 frame #11: 0x6604e44d libsystem_trace.dylib`_os_log_impl_flatten_and_send + 6410 frame #12: 0x6604cb3b libsystem_trace.dylib`_os_log + 137 frame #13: 0x6604f4aa libsystem_trace.dylib`_os_log_impl + 31 frame #14: 0x4b4eb4e9 WatchConnectivity`WCSerializePayloadDictionary + 393 frame #15: 0x4b4d7c4d WatchConnectivity`-[WCSession onqueue_sendResponseDictionary:identifier:] + 195 frame #16: 0x4b4da435 WatchConnectivity`__66-[WCSession onqueue_handleDictionaryMessageRequest:withPairingID:]_block_invoke.411 + 35 frame #17: 0x453c7df7 Foundation`__NSBLOCKOPERATION_IS_CALLING_OUT_TO_A_BLOCK__ + 12 frame #18: 0x453c7cf4 Foundation`-[NSBlockOperation main] + 88 frame #19: 0x453cacee Foundation`__NSOPERATION_IS_INVOKING_MAIN__ + 27 frame #20: 0x453c6ebd Foundation`-[NSOperation start] + 835 frame #21: 0x453cb606 Foundation`__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 27 frame #22: 0x453cb12e Foundation`__NSOQSchedule_f + 194 frame #23: 0x453cb067 Foundation`____addOperations_block_invoke_2 + 20 frame #24: 0x65dedf49 libdispatch.dylib`_dispatch_block_async_invoke2 + 77 frame #25: 0x65de4461 libdispatch.dylib`_dispatch_block_async_invoke_and_release + 17 frame #26: 0x65de126f libdispatch.dylib`_dispatch_client_callout + 14 frame #27: 0x65de3788 libdispatch.dylib`_dispatch_continuation_pop + 421 frame #28: 0x65de2ee3 libdispatch.dylib`_dispatch_async_redirect_invoke + 818 frame #29: 0x65df087d libdispatch.dylib`_dispatch_root_queue_drain + 354 frame #30: 0x65df0ff3 libdispatch.dylib`_dispatch_worker_thread2 + 109 frame #31: 0x66024fa0 libsystem_pthread.dylib`_pthread_wqthread + 208 frame #32: 0x66024e44 libsystem_pthread.dylib`start_wqthread + 36 ``` which is a thread in a "light" detach state (aka. coop detach), where we only unset the domain: https://github.com/mono/mono/blob/4cefdcb7ce2d939ee78fb45d1b4913eb3bc064fd/mono/metadata/threads.c#L6084-L6111 Fixes mono#17926
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Backport of #15.
/cc @akoeplinger