libcorkscrew/backtrace.c - android_system_core - Gitiles

 /*
  * Copyright (C) 2011 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #define LOG_TAG "Corkscrew"
 //#define LOG_NDEBUG 0

 #include "backtrace-arch.h"
 #include "backtrace-helper.h"
 #include "ptrace-arch.h"
 #include <corkscrew/map_info.h>
 #include <corkscrew/symbol_table.h>
 #include <corkscrew/ptrace.h>
 #include <corkscrew/demangle.h>

 #include <unistd.h>
 #include <signal.h>
 #include <stdlib.h>
 #include <string.h>
 #include <pthread.h>
 #include <unwind.h>
 #include <cutils/log.h>
 #include <cutils/atomic.h>

 #define __USE_GNU // For dladdr(3) in glibc.
 #include <dlfcn.h>

 #if defined(__BIONIC__)

 // Bionic implements and exports gettid but only implements tgkill.
 extern int tgkill(int tgid, int tid, int sig);

 #elif defined(__APPLE__)

 #include <sys/syscall.h>

 // Mac OS >= 10.6 has a system call equivalent to Linux's gettid().
 static pid_t gettid() {
   return syscall(SYS_thread_selfid);
 }

 #else

 // glibc doesn't implement or export either gettid or tgkill.

 #include <unistd.h>
 #include <sys/syscall.h>

 static pid_t gettid() {
   return syscall(__NR_gettid);
 }

 static int tgkill(int tgid, int tid, int sig) {
   return syscall(__NR_tgkill, tgid, tid, sig);
 }

 #endif

 typedef struct {
     backtrace_frame_t* backtrace;
     size_t ignore_depth;
     size_t max_depth;
     size_t ignored_frames;
     size_t returned_frames;
     memory_t memory;
 } backtrace_state_t;

 static _Unwind_Reason_Code unwind_backtrace_callback(struct _Unwind_Context* context, void* arg) {
     backtrace_state_t* state = (backtrace_state_t*)arg;
     uintptr_t pc = _Unwind_GetIP(context);
     if (pc) {
         // TODO: Get information about the stack layout from the _Unwind_Context.
         //       This will require a new architecture-specific function to query
         //       the appropriate registers.  Current callers of unwind_backtrace
         //       don't need this information, so we won't bother collecting it just yet.
         add_backtrace_entry(rewind_pc_arch(&state->memory, pc), state->backtrace,
                 state->ignore_depth, state->max_depth,
                 &state->ignored_frames, &state->returned_frames);
     }
     return state->returned_frames < state->max_depth ? _URC_NO_REASON : _URC_END_OF_STACK;
 }

 ssize_t unwind_backtrace(backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) {
     ALOGV("Unwinding current thread %d.", gettid());

     map_info_t* milist = acquire_my_map_info_list();

     backtrace_state_t state;
     state.backtrace = backtrace;
     state.ignore_depth = ignore_depth;
     state.max_depth = max_depth;
     state.ignored_frames = 0;
     state.returned_frames = 0;
     init_memory(&state.memory, milist);

     _Unwind_Reason_Code rc = _Unwind_Backtrace(unwind_backtrace_callback, &state);

     release_my_map_info_list(milist);

     if (state.returned_frames) {
         return state.returned_frames;
     }
     return rc == _URC_END_OF_STACK ? 0 : -1;
 }

 #ifdef CORKSCREW_HAVE_ARCH
 static const int32_t STATE_DUMPING = -1;
 static const int32_t STATE_DONE = -2;
 static const int32_t STATE_CANCEL = -3;

 static pthread_mutex_t g_unwind_signal_mutex = PTHREAD_MUTEX_INITIALIZER;
 static volatile struct {
     int32_t tid_state;
     const map_info_t* map_info_list;
     backtrace_frame_t* backtrace;
     size_t ignore_depth;
     size_t max_depth;
     size_t returned_frames;
 } g_unwind_signal_state;

 static void unwind_backtrace_thread_signal_handler(int n __attribute__((unused)), siginfo_t* siginfo, void* sigcontext) {
     if (!android_atomic_acquire_cas(gettid(), STATE_DUMPING, &g_unwind_signal_state.tid_state)) {
         g_unwind_signal_state.returned_frames = unwind_backtrace_signal_arch(
                 siginfo, sigcontext,
                 g_unwind_signal_state.map_info_list,
                 g_unwind_signal_state.backtrace,
                 g_unwind_signal_state.ignore_depth,
                 g_unwind_signal_state.max_depth);
         android_atomic_release_store(STATE_DONE, &g_unwind_signal_state.tid_state);
     } else {
         ALOGV("Received spurious SIGURG on thread %d that was intended for thread %d.",
                 gettid(), android_atomic_acquire_load(&g_unwind_signal_state.tid_state));
     }
 }
 #endif

 ssize_t unwind_backtrace_thread(pid_t tid, backtrace_frame_t* backtrace,
         size_t ignore_depth, size_t max_depth) {
     if (tid == gettid()) {
         return unwind_backtrace(backtrace, ignore_depth + 1, max_depth);
     }

     ALOGV("Unwinding thread %d from thread %d.", tid, gettid());

     // TODO: there's no tgkill(2) on Mac OS, so we'd either need the
     // mach_port_t or the pthread_t rather than the tid.
 #if defined(CORKSCREW_HAVE_ARCH) && !defined(__APPLE__)
     struct sigaction act;
     struct sigaction oact;
     memset(&act, 0, sizeof(act));
     act.sa_sigaction = unwind_backtrace_thread_signal_handler;
     act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
     sigemptyset(&act.sa_mask);

     pthread_mutex_lock(&g_unwind_signal_mutex);
     map_info_t* milist = acquire_my_map_info_list();

     ssize_t frames = -1;
     if (!sigaction(SIGURG, &act, &oact)) {
         g_unwind_signal_state.map_info_list = milist;
         g_unwind_signal_state.backtrace = backtrace;
         g_unwind_signal_state.ignore_depth = ignore_depth;
         g_unwind_signal_state.max_depth = max_depth;
         g_unwind_signal_state.returned_frames = 0;
         android_atomic_release_store(tid, &g_unwind_signal_state.tid_state);

         // Signal the specific thread that we want to dump.
         int32_t tid_state = tid;
         if (tgkill(getpid(), tid, SIGURG)) {
             ALOGV("Failed to send SIGURG to thread %d.", tid);
         } else {
             // Wait for the other thread to start dumping the stack, or time out.
             int wait_millis = 250;
             for (;;) {
                 tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state);
                 if (tid_state != tid) {
                     break;
                 }
                 if (wait_millis--) {
                     ALOGV("Waiting for thread %d to start dumping the stack...", tid);
                     usleep(1000);
                 } else {
                     ALOGV("Timed out waiting for thread %d to start dumping the stack.", tid);
                     break;
                 }
             }
         }

         // Try to cancel the dump if it has not started yet.
         if (tid_state == tid) {
             if (!android_atomic_acquire_cas(tid, STATE_CANCEL, &g_unwind_signal_state.tid_state)) {
                 ALOGV("Canceled thread %d stack dump.", tid);
                 tid_state = STATE_CANCEL;
             } else {
                 tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state);
             }
         }

         // Wait indefinitely for the dump to finish or be canceled.
         // We cannot apply a timeout here because the other thread is accessing state that
         // is owned by this thread, such as milist.  It should not take very
         // long to take the dump once started.
         while (tid_state == STATE_DUMPING) {
             ALOGV("Waiting for thread %d to finish dumping the stack...", tid);
             usleep(1000);
             tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state);
         }

         if (tid_state == STATE_DONE) {
             frames = g_unwind_signal_state.returned_frames;
         }

         sigaction(SIGURG, &oact, NULL);
     }

     release_my_map_info_list(milist);
     pthread_mutex_unlock(&g_unwind_signal_mutex);
     return frames;
 #else
     return -1;
 #endif
 }

 ssize_t unwind_backtrace_ptrace(pid_t tid, const ptrace_context_t* context,
         backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) {
 #ifdef CORKSCREW_HAVE_ARCH
     return unwind_backtrace_ptrace_arch(tid, context, backtrace, ignore_depth, max_depth);
 #else
     return -1;
 #endif
 }

 static void init_backtrace_symbol(backtrace_symbol_t* symbol, uintptr_t pc) {
     symbol->relative_pc = pc;
     symbol->relative_symbol_addr = 0;
     symbol->map_name = NULL;
     symbol->symbol_name = NULL;
     symbol->demangled_name = NULL;
 }

 void get_backtrace_symbols(const backtrace_frame_t* backtrace, size_t frames,
         backtrace_symbol_t* backtrace_symbols) {
     map_info_t* milist = acquire_my_map_info_list();
     for (size_t i = 0; i < frames; i++) {
         const backtrace_frame_t* frame = &backtrace[i];
         backtrace_symbol_t* symbol = &backtrace_symbols[i];
         init_backtrace_symbol(symbol, frame->absolute_pc);

         const map_info_t* mi = find_map_info(milist, frame->absolute_pc);
         if (mi) {
             symbol->relative_pc = frame->absolute_pc - mi->start;
             if (mi->name[0]) {
                 symbol->map_name = strdup(mi->name);
             }
             Dl_info info;
             if (dladdr((const void*)frame->absolute_pc, &info) && info.dli_sname) {
                 symbol->relative_symbol_addr = (uintptr_t)info.dli_saddr
                         - (uintptr_t)info.dli_fbase;
                 symbol->symbol_name = strdup(info.dli_sname);
                 symbol->demangled_name = demangle_symbol_name(symbol->symbol_name);
             }
         }
     }
     release_my_map_info_list(milist);
 }

 void get_backtrace_symbols_ptrace(const ptrace_context_t* context,
         const backtrace_frame_t* backtrace, size_t frames,
         backtrace_symbol_t* backtrace_symbols) {
     for (size_t i = 0; i < frames; i++) {
         const backtrace_frame_t* frame = &backtrace[i];
         backtrace_symbol_t* symbol = &backtrace_symbols[i];
         init_backtrace_symbol(symbol, frame->absolute_pc);

         const map_info_t* mi;
         const symbol_t* s;
         find_symbol_ptrace(context, frame->absolute_pc, &mi, &s);
         if (mi) {
             symbol->relative_pc = frame->absolute_pc - mi->start;
             if (mi->name[0]) {
                 symbol->map_name = strdup(mi->name);
             }
         }
         if (s) {
             symbol->relative_symbol_addr = s->start;
             symbol->symbol_name = strdup(s->name);
             symbol->demangled_name = demangle_symbol_name(symbol->symbol_name);
         }
     }
 }

 void free_backtrace_symbols(backtrace_symbol_t* backtrace_symbols, size_t frames) {
     for (size_t i = 0; i < frames; i++) {
         backtrace_symbol_t* symbol = &backtrace_symbols[i];
         free(symbol->map_name);
         free(symbol->symbol_name);
         free(symbol->demangled_name);
         init_backtrace_symbol(symbol, 0);
     }
 }

 void format_backtrace_line(unsigned frameNumber, const backtrace_frame_t* frame __attribute__((unused)),
         const backtrace_symbol_t* symbol, char* buffer, size_t bufferSize) {
     const char* mapName = symbol->map_name ? symbol->map_name : "<unknown>";
     const char* symbolName = symbol->demangled_name ? symbol->demangled_name : symbol->symbol_name;
     int fieldWidth = (bufferSize - 80) / 2;
     if (symbolName) {
         uint32_t pc_offset = symbol->relative_pc - symbol->relative_symbol_addr;
         if (pc_offset) {
             snprintf(buffer, bufferSize, "#%02u  pc %08x  %.*s (%.*s+%u)",
                     frameNumber, (unsigned int) symbol->relative_pc,
                     fieldWidth, mapName, fieldWidth, symbolName, pc_offset);
         } else {
             snprintf(buffer, bufferSize, "#%02u  pc %08x  %.*s (%.*s)",
                     frameNumber, (unsigned int) symbol->relative_pc,
                     fieldWidth, mapName, fieldWidth, symbolName);
         }
     } else {
         snprintf(buffer, bufferSize, "#%02u  pc %08x  %.*s",
                 frameNumber, (unsigned int) symbol->relative_pc,
                 fieldWidth, mapName);
     }
 }
	/*
	* Copyright (C) 2011 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#define LOG_TAG "Corkscrew"
	//#define LOG_NDEBUG 0

	#include "backtrace-arch.h"
	#include "backtrace-helper.h"
	#include "ptrace-arch.h"
	#include <corkscrew/map_info.h>
	#include <corkscrew/symbol_table.h>
	#include <corkscrew/ptrace.h>
	#include <corkscrew/demangle.h>

	#include <unistd.h>
	#include <signal.h>
	#include <stdlib.h>
	#include <string.h>
	#include <pthread.h>
	#include <unwind.h>
	#include <cutils/log.h>
	#include <cutils/atomic.h>

	#define __USE_GNU // For dladdr(3) in glibc.
	#include <dlfcn.h>

	#if defined(__BIONIC__)

	// Bionic implements and exports gettid but only implements tgkill.
	extern int tgkill(int tgid, int tid, int sig);

	#elif defined(__APPLE__)

	#include <sys/syscall.h>

	// Mac OS >= 10.6 has a system call equivalent to Linux's gettid().
	static pid_t gettid() {
	return syscall(SYS_thread_selfid);
	}

	#else

	// glibc doesn't implement or export either gettid or tgkill.

	#include <unistd.h>
	#include <sys/syscall.h>

	static pid_t gettid() {
	return syscall(__NR_gettid);
	}

	static int tgkill(int tgid, int tid, int sig) {
	return syscall(__NR_tgkill, tgid, tid, sig);
	}

	#endif

	typedef struct {
	backtrace_frame_t* backtrace;
	size_t ignore_depth;
	size_t max_depth;
	size_t ignored_frames;
	size_t returned_frames;
	memory_t memory;
	} backtrace_state_t;

	static _Unwind_Reason_Code unwind_backtrace_callback(struct _Unwind_Context* context, void* arg) {
	backtrace_state_t* state = (backtrace_state_t*)arg;
	uintptr_t pc = _Unwind_GetIP(context);
	if (pc) {
	// TODO: Get information about the stack layout from the _Unwind_Context.
	// This will require a new architecture-specific function to query
	// the appropriate registers. Current callers of unwind_backtrace
	// don't need this information, so we won't bother collecting it just yet.
	add_backtrace_entry(rewind_pc_arch(&state->memory, pc), state->backtrace,
	state->ignore_depth, state->max_depth,
	&state->ignored_frames, &state->returned_frames);
	}
	return state->returned_frames < state->max_depth ? _URC_NO_REASON : _URC_END_OF_STACK;
	}

	ssize_t unwind_backtrace(backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) {
	ALOGV("Unwinding current thread %d.", gettid());

	map_info_t* milist = acquire_my_map_info_list();

	backtrace_state_t state;
	state.backtrace = backtrace;
	state.ignore_depth = ignore_depth;
	state.max_depth = max_depth;
	state.ignored_frames = 0;
	state.returned_frames = 0;
	init_memory(&state.memory, milist);

	_Unwind_Reason_Code rc = _Unwind_Backtrace(unwind_backtrace_callback, &state);

	release_my_map_info_list(milist);

	if (state.returned_frames) {
	return state.returned_frames;
	}
	return rc == _URC_END_OF_STACK ? 0 : -1;
	}

	#ifdef CORKSCREW_HAVE_ARCH
	static const int32_t STATE_DUMPING = -1;
	static const int32_t STATE_DONE = -2;
	static const int32_t STATE_CANCEL = -3;

	static pthread_mutex_t g_unwind_signal_mutex = PTHREAD_MUTEX_INITIALIZER;
	static volatile struct {
	int32_t tid_state;
	const map_info_t* map_info_list;
	backtrace_frame_t* backtrace;
	size_t ignore_depth;
	size_t max_depth;
	size_t returned_frames;
	} g_unwind_signal_state;

	static void unwind_backtrace_thread_signal_handler(int n __attribute__((unused)), siginfo_t* siginfo, void* sigcontext) {
	if (!android_atomic_acquire_cas(gettid(), STATE_DUMPING, &g_unwind_signal_state.tid_state)) {
	g_unwind_signal_state.returned_frames = unwind_backtrace_signal_arch(
	siginfo, sigcontext,
	g_unwind_signal_state.map_info_list,
	g_unwind_signal_state.backtrace,
	g_unwind_signal_state.ignore_depth,
	g_unwind_signal_state.max_depth);
	android_atomic_release_store(STATE_DONE, &g_unwind_signal_state.tid_state);
	} else {
	ALOGV("Received spurious SIGURG on thread %d that was intended for thread %d.",
	gettid(), android_atomic_acquire_load(&g_unwind_signal_state.tid_state));
	}
	}
	#endif

	ssize_t unwind_backtrace_thread(pid_t tid, backtrace_frame_t* backtrace,
	size_t ignore_depth, size_t max_depth) {
	if (tid == gettid()) {
	return unwind_backtrace(backtrace, ignore_depth + 1, max_depth);
	}

	ALOGV("Unwinding thread %d from thread %d.", tid, gettid());

	// TODO: there's no tgkill(2) on Mac OS, so we'd either need the
	// mach_port_t or the pthread_t rather than the tid.
	#if defined(CORKSCREW_HAVE_ARCH) && !defined(__APPLE__)
	struct sigaction act;
	struct sigaction oact;
	memset(&act, 0, sizeof(act));
	act.sa_sigaction = unwind_backtrace_thread_signal_handler;
	act.sa_flags = SA_RESTART \| SA_SIGINFO \| SA_ONSTACK;
	sigemptyset(&act.sa_mask);

	pthread_mutex_lock(&g_unwind_signal_mutex);
	map_info_t* milist = acquire_my_map_info_list();

	ssize_t frames = -1;
	if (!sigaction(SIGURG, &act, &oact)) {
	g_unwind_signal_state.map_info_list = milist;
	g_unwind_signal_state.backtrace = backtrace;
	g_unwind_signal_state.ignore_depth = ignore_depth;
	g_unwind_signal_state.max_depth = max_depth;
	g_unwind_signal_state.returned_frames = 0;
	android_atomic_release_store(tid, &g_unwind_signal_state.tid_state);

	// Signal the specific thread that we want to dump.
	int32_t tid_state = tid;
	if (tgkill(getpid(), tid, SIGURG)) {
	ALOGV("Failed to send SIGURG to thread %d.", tid);
	} else {
	// Wait for the other thread to start dumping the stack, or time out.
	int wait_millis = 250;
	for (;;) {
	tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state);
	if (tid_state != tid) {
	break;
	}
	if (wait_millis--) {
	ALOGV("Waiting for thread %d to start dumping the stack...", tid);
	usleep(1000);
	} else {
	ALOGV("Timed out waiting for thread %d to start dumping the stack.", tid);
	break;
	}
	}
	}

	// Try to cancel the dump if it has not started yet.
	if (tid_state == tid) {
	if (!android_atomic_acquire_cas(tid, STATE_CANCEL, &g_unwind_signal_state.tid_state)) {
	ALOGV("Canceled thread %d stack dump.", tid);
	tid_state = STATE_CANCEL;
	} else {
	tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state);
	}
	}

	// Wait indefinitely for the dump to finish or be canceled.
	// We cannot apply a timeout here because the other thread is accessing state that
	// is owned by this thread, such as milist. It should not take very
	// long to take the dump once started.
	while (tid_state == STATE_DUMPING) {
	ALOGV("Waiting for thread %d to finish dumping the stack...", tid);
	usleep(1000);
	tid_state = android_atomic_acquire_load(&g_unwind_signal_state.tid_state);
	}

	if (tid_state == STATE_DONE) {
	frames = g_unwind_signal_state.returned_frames;
	}

	sigaction(SIGURG, &oact, NULL);
	}

	release_my_map_info_list(milist);
	pthread_mutex_unlock(&g_unwind_signal_mutex);
	return frames;
	#else
	return -1;
	#endif
	}

	ssize_t unwind_backtrace_ptrace(pid_t tid, const ptrace_context_t* context,
	backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) {
	#ifdef CORKSCREW_HAVE_ARCH
	return unwind_backtrace_ptrace_arch(tid, context, backtrace, ignore_depth, max_depth);
	#else
	return -1;
	#endif
	}

	static void init_backtrace_symbol(backtrace_symbol_t* symbol, uintptr_t pc) {
	symbol->relative_pc = pc;
	symbol->relative_symbol_addr = 0;
	symbol->map_name = NULL;
	symbol->symbol_name = NULL;
	symbol->demangled_name = NULL;
	}

	void get_backtrace_symbols(const backtrace_frame_t* backtrace, size_t frames,
	backtrace_symbol_t* backtrace_symbols) {
	map_info_t* milist = acquire_my_map_info_list();
	for (size_t i = 0; i < frames; i++) {
	const backtrace_frame_t* frame = &backtrace[i];
	backtrace_symbol_t* symbol = &backtrace_symbols[i];
	init_backtrace_symbol(symbol, frame->absolute_pc);

	const map_info_t* mi = find_map_info(milist, frame->absolute_pc);
	if (mi) {
	symbol->relative_pc = frame->absolute_pc - mi->start;
	if (mi->name[0]) {
	symbol->map_name = strdup(mi->name);
	}
	Dl_info info;
	if (dladdr((const void*)frame->absolute_pc, &info) && info.dli_sname) {
	symbol->relative_symbol_addr = (uintptr_t)info.dli_saddr
	- (uintptr_t)info.dli_fbase;
	symbol->symbol_name = strdup(info.dli_sname);
	symbol->demangled_name = demangle_symbol_name(symbol->symbol_name);
	}
	}
	}
	release_my_map_info_list(milist);
	}

	void get_backtrace_symbols_ptrace(const ptrace_context_t* context,
	const backtrace_frame_t* backtrace, size_t frames,
	backtrace_symbol_t* backtrace_symbols) {
	for (size_t i = 0; i < frames; i++) {
	const backtrace_frame_t* frame = &backtrace[i];
	backtrace_symbol_t* symbol = &backtrace_symbols[i];
	init_backtrace_symbol(symbol, frame->absolute_pc);

	const map_info_t* mi;
	const symbol_t* s;
	find_symbol_ptrace(context, frame->absolute_pc, &mi, &s);
	if (mi) {
	symbol->relative_pc = frame->absolute_pc - mi->start;
	if (mi->name[0]) {
	symbol->map_name = strdup(mi->name);
	}
	}
	if (s) {
	symbol->relative_symbol_addr = s->start;
	symbol->symbol_name = strdup(s->name);
	symbol->demangled_name = demangle_symbol_name(symbol->symbol_name);
	}
	}
	}

	void free_backtrace_symbols(backtrace_symbol_t* backtrace_symbols, size_t frames) {
	for (size_t i = 0; i < frames; i++) {
	backtrace_symbol_t* symbol = &backtrace_symbols[i];
	free(symbol->map_name);
	free(symbol->symbol_name);
	free(symbol->demangled_name);
	init_backtrace_symbol(symbol, 0);
	}
	}

	void format_backtrace_line(unsigned frameNumber, const backtrace_frame_t* frame __attribute__((unused)),
	const backtrace_symbol_t* symbol, char* buffer, size_t bufferSize) {
	const char* mapName = symbol->map_name ? symbol->map_name : "<unknown>";
	const char* symbolName = symbol->demangled_name ? symbol->demangled_name : symbol->symbol_name;
	int fieldWidth = (bufferSize - 80) / 2;
	if (symbolName) {
	uint32_t pc_offset = symbol->relative_pc - symbol->relative_symbol_addr;
	if (pc_offset) {
	snprintf(buffer, bufferSize, "#%02u pc %08x %.s (%.s+%u)",
	frameNumber, (unsigned int) symbol->relative_pc,
	fieldWidth, mapName, fieldWidth, symbolName, pc_offset);
	} else {
	snprintf(buffer, bufferSize, "#%02u pc %08x %.s (%.s)",
	frameNumber, (unsigned int) symbol->relative_pc,
	fieldWidth, mapName, fieldWidth, symbolName);
	}
	} else {
	snprintf(buffer, bufferSize, "#%02u pc %08x %.*s",
	frameNumber, (unsigned int) symbol->relative_pc,
	fieldWidth, mapName);
	}
	}