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Text file src/runtime/cgo/gcc_signal_darwin_armx.c

Documentation: runtime/cgo

     1	// Copyright 2015 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// Emulation of the Unix signal SIGSEGV.
     6	//
     7	// On iOS, Go tests and apps under development are run by lldb.
     8	// The debugger uses a task-level exception handler to intercept signals.
     9	// Despite having a 'handle' mechanism like gdb, lldb will not allow a
    10	// SIGSEGV to pass to the running program. For Go, this means we cannot
    11	// generate a panic, which cannot be recovered, and so tests fail.
    12	//
    13	// We work around this by registering a thread-level mach exception handler
    14	// and intercepting EXC_BAD_ACCESS. The kernel offers thread handlers a
    15	// chance to resolve exceptions before the task handler, so we can generate
    16	// the panic and avoid lldb's SIGSEGV handler.
    17	//
    18	// The dist tool enables this by build flag when testing.
    19	
    20	// +build lldb
    21	// +build darwin
    22	// +build arm arm64
    23	
    24	#include <limits.h>
    25	#include <pthread.h>
    26	#include <stdio.h>
    27	#include <signal.h>
    28	#include <stdlib.h>
    29	#include <unistd.h>
    30	
    31	#include <mach/arm/thread_status.h>
    32	#include <mach/exception_types.h>
    33	#include <mach/mach.h>
    34	#include <mach/mach_init.h>
    35	#include <mach/mach_port.h>
    36	#include <mach/thread_act.h>
    37	#include <mach/thread_status.h>
    38	
    39	#include "libcgo.h"
    40	#include "libcgo_unix.h"
    41	
    42	uintptr_t x_cgo_panicmem;
    43	
    44	static pthread_mutex_t mach_exception_handler_port_set_mu;
    45	static mach_port_t mach_exception_handler_port_set = MACH_PORT_NULL;
    46	
    47	kern_return_t
    48	catch_exception_raise(
    49		mach_port_t exception_port,
    50		mach_port_t thread,
    51		mach_port_t task,
    52		exception_type_t exception,
    53		exception_data_t code_vector,
    54		mach_msg_type_number_t code_count)
    55	{
    56		kern_return_t ret;
    57		arm_unified_thread_state_t thread_state;
    58		mach_msg_type_number_t state_count = ARM_UNIFIED_THREAD_STATE_COUNT;
    59	
    60		// Returning KERN_SUCCESS intercepts the exception.
    61		//
    62		// Returning KERN_FAILURE lets the exception fall through to the
    63		// next handler, which is the standard signal emulation code
    64		// registered on the task port.
    65	
    66		if (exception != EXC_BAD_ACCESS) {
    67			return KERN_FAILURE;
    68		}
    69	
    70		ret = thread_get_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, &state_count);
    71		if (ret) {
    72			fprintf(stderr, "runtime/cgo: thread_get_state failed: %d\n", ret);
    73			abort();
    74		}
    75	
    76		// Bounce call to sigpanic through asm that makes it look like
    77		// we call sigpanic directly from the faulting code.
    78	#ifdef __arm64__
    79		thread_state.ts_64.__x[1] = thread_state.ts_64.__lr;
    80		thread_state.ts_64.__x[2] = thread_state.ts_64.__pc;
    81		thread_state.ts_64.__pc = x_cgo_panicmem;
    82	#else
    83		thread_state.ts_32.__r[1] = thread_state.ts_32.__lr;
    84		thread_state.ts_32.__r[2] = thread_state.ts_32.__pc;
    85		thread_state.ts_32.__pc = x_cgo_panicmem;
    86	#endif
    87	
    88		if (0) {
    89			// Useful debugging logic when panicmem is broken.
    90			//
    91			// Sends the first SIGSEGV and lets lldb catch the
    92			// second one, avoiding a loop that locks up iOS
    93			// devices requiring a hard reboot.
    94			fprintf(stderr, "runtime/cgo: caught exc_bad_access\n");
    95			fprintf(stderr, "__lr = %llx\n", thread_state.ts_64.__lr);
    96			fprintf(stderr, "__pc = %llx\n", thread_state.ts_64.__pc);
    97			static int pass1 = 0;
    98			if (pass1) {
    99				return KERN_FAILURE;
   100			}
   101			pass1 = 1;
   102		}
   103	
   104		ret = thread_set_state(thread, ARM_UNIFIED_THREAD_STATE, (thread_state_t)&thread_state, state_count);
   105		if (ret) {
   106			fprintf(stderr, "runtime/cgo: thread_set_state failed: %d\n", ret);
   107			abort();
   108		}
   109	
   110		return KERN_SUCCESS;
   111	}
   112	
   113	void
   114	darwin_arm_init_thread_exception_port()
   115	{
   116		// Called by each new OS thread to bind its EXC_BAD_ACCESS exception
   117		// to mach_exception_handler_port_set.
   118		int ret;
   119		mach_port_t port = MACH_PORT_NULL;
   120	
   121		ret = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &port);
   122		if (ret) {
   123			fprintf(stderr, "runtime/cgo: mach_port_allocate failed: %d\n", ret);
   124			abort();
   125		}
   126		ret = mach_port_insert_right(
   127			mach_task_self(),
   128			port,
   129			port,
   130			MACH_MSG_TYPE_MAKE_SEND);
   131		if (ret) {
   132			fprintf(stderr, "runtime/cgo: mach_port_insert_right failed: %d\n", ret);
   133			abort();
   134		}
   135	
   136		ret = thread_set_exception_ports(
   137			mach_thread_self(),
   138			EXC_MASK_BAD_ACCESS,
   139			port,
   140			EXCEPTION_DEFAULT,
   141			THREAD_STATE_NONE);
   142		if (ret) {
   143			fprintf(stderr, "runtime/cgo: thread_set_exception_ports failed: %d\n", ret);
   144			abort();
   145		}
   146	
   147		ret = pthread_mutex_lock(&mach_exception_handler_port_set_mu);
   148		if (ret) {
   149			fprintf(stderr, "runtime/cgo: pthread_mutex_lock failed: %d\n", ret);
   150			abort();
   151		}
   152		ret = mach_port_move_member(
   153			mach_task_self(),
   154			port,
   155			mach_exception_handler_port_set);
   156		if (ret) {
   157			fprintf(stderr, "runtime/cgo: mach_port_move_member failed: %d\n", ret);
   158			abort();
   159		}
   160		ret = pthread_mutex_unlock(&mach_exception_handler_port_set_mu);
   161		if (ret) {
   162			fprintf(stderr, "runtime/cgo: pthread_mutex_unlock failed: %d\n", ret);
   163			abort();
   164		}
   165	}
   166	
   167	static void*
   168	mach_exception_handler(void *port)
   169	{
   170		// Calls catch_exception_raise.
   171		extern boolean_t exc_server();
   172		mach_msg_server(exc_server, 2048, (mach_port_t)port, 0);
   173		abort(); // never returns
   174	}
   175	
   176	void
   177	darwin_arm_init_mach_exception_handler()
   178	{
   179		pthread_mutex_init(&mach_exception_handler_port_set_mu, NULL);
   180	
   181		// Called once per process to initialize a mach port server, listening
   182		// for EXC_BAD_ACCESS thread exceptions.
   183		int ret;
   184		pthread_t thr = NULL;
   185		pthread_attr_t attr;
   186		sigset_t ign, oset;
   187	
   188		ret = mach_port_allocate(
   189			mach_task_self(),
   190			MACH_PORT_RIGHT_PORT_SET,
   191			&mach_exception_handler_port_set);
   192		if (ret) {
   193			fprintf(stderr, "runtime/cgo: mach_port_allocate failed for port_set: %d\n", ret);
   194			abort();
   195		}
   196	
   197		// Block all signals to the exception handler thread
   198		sigfillset(&ign);
   199		pthread_sigmask(SIG_SETMASK, &ign, &oset);
   200	
   201		// Start a thread to handle exceptions.
   202		uintptr_t port_set = (uintptr_t)mach_exception_handler_port_set;
   203		pthread_attr_init(&attr);
   204		pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
   205		ret = _cgo_try_pthread_create(&thr, &attr, mach_exception_handler, (void*)port_set);
   206	
   207		pthread_sigmask(SIG_SETMASK, &oset, nil);
   208	
   209		if (ret) {
   210			fprintf(stderr, "runtime/cgo: pthread_create failed: %d\n", ret);
   211			abort();
   212		}
   213		pthread_attr_destroy(&attr);
   214	}

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