Add profiler counters for time spent in stack unwinding

[bric3]

What does this PR do?:

Use TSC time counters for unwinding.

How to test the change?:

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.
• JIRA: PROF-11368

Unsure? Have a question? Request a review!

[github-actions]

🔧 Report generated by pr-comment-scanbuild

Scan-Build Report

User:	runner@fv-az1922-865
Working Directory:	/home/runner/work/java-profiler/java-profiler/ddprof-lib/src/test/make
Command Line:	make -j4 clean all
Clang Version:	Ubuntu clang version 18.1.3 (1ubuntu1)
Date:	Wed Mar 26 21:42:59 2025

Bug Summary

Bug Type	Quantity	Display?
All Bugs	7
Logic error
Dereference of null pointer	3
Suspicious operation
Bitwise shift	1
Unused code
Dead initialization	2
Dead nested assignment	1

Reports

Bug Group	Bug Type ▾	File	Function/Method	Line	Path Length
Suspicious operation	Bitwise shift	vmStructs.cpp	find	902	16
Unused code	Dead initialization	javaApi.cpp	Java_com_datadoghq_profiler_JavaProfiler_getStatus0	116	1
Unused code	Dead initialization	stackWalker.cpp	walkDwarf	160	1
Unused code	Dead nested assignment	vmStructs.cpp	checkNativeBinding	1007	1
Logic error	Dereference of null pointer	safeAccess.h	load	33	18
Logic error	Dereference of null pointer	symbols_linux.h	ElfParser	144	28
Logic error	Dereference of null pointer	flightRecorder.cpp	flush	1504	8

[github-actions]

🔧 Report generated by pr-comment-cppcheck

CppCheck Report

Warnings (7)

• The class 'RecordingBuffer' defines member function with name 'flushIfNeeded' also defined in its parent class 'Buffer'.
• Obsolete function 'alloca' called.
• Member variable 'ScopeDesc::_stream' is not initialized in the constructor.
• Member variable 'ScopeDesc::_method_offset' is not initialized in the constructor.
• Member variable 'ScopeDesc::_bci' is not initialized in the constructor.
• Member variable 'ElfParser::_vaddr_diff' is not initialized in the constructor.
• Either the condition 'vm_thread' is redundant or there is possible null pointer dereference: vm_thread.

Style Violations (398)

• The class 'NativeFunc' does not declare a constructor although it has private member variables which likely require initialization.
• Class 'Arguments' has a constructor with 1 argument that is not explicit.
• Local variable 'count' shadows outer function
• Local variable 'jni' shadows outer function
• Variable 'cb1' can be declared as pointer to const
• Variable 'cb2' can be declared as pointer to const
• struct member 'Multiplier::symbol' is never used.
• struct member 'Multiplier::multiplier' is never used.
• class member 'Error::OK' is never used.
• Class 'AsyncSampleMutex' has a constructor with 1 argument that is not explicit.
• Class 'SpinLock' has a constructor with 1 argument that is not explicit.
• Local variable 'size' shadows outer function
• Local variable 'prev' shadows outer function
• Variable 'keys' can be declared as pointer to const
• Parameter 'frames' can be declared as pointer to const
• Parameter 'frames' can be declared as pointer to const
• Variable 'keys' can be declared as pointer to const
• struct member 'CallTrace::truncated' is never used.
• struct member 'CallTrace::num_frames' is never used.
• class member 'CallTraceStorage::_current_table' is never used.
• class member 'CallTraceStorage::_overflow' is never used.
• class member 'CallTraceStorage::_lock' is never used.
• Local variable 'i' shadows outer variable
• Parameter 'prefixes' can be declared as reference to const
• Variable 'fd1' can be declared as pointer to const
• Variable 'fd2' can be declared as pointer to const
• Parameter 'name' can be declared as pointer to const
• Consider using std::transform algorithm instead of a raw loop.
• struct member 'Tag::value' is never used.
• class member 'Context::spanId' is never used.
• class member 'Context::rootSpanId' is never used.
• class member 'Context::checksum' is never used.
• struct member 'ContextPage::capacity' is never used.
• struct member 'ContextPage::storage' is never used.
• class member 'Contexts::_max_pages' is never used.
• class member 'Contexts::_pages' is never used.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'Shims::_tid_setter_ref' is never used.
• Class 'Dictionary' has a constructor with 1 argument that is not explicit.
• struct member 'DictRow::keys' is never used.
• struct member 'DictRow::next' is never used.
• Operator '|' with one operand equal to zero is redundant.
• Local variable 'table' shadows outer function
• Local variable 'pc_off' shadows outer variable
• Variable 'table' can be declared as pointer to const
• Operator '|' with one operand equal to zero is redundant.
• struct member 'FrameDesc::cfa' is never used.
• struct member 'FrameDesc::fp_off' is never used.
• struct member 'FrameDesc::pc_off' is never used.
• struct member 'FrameDesc::empty_frame' is never used.
• struct member 'FrameDesc::default_frame' is never used.
• class member 'DwarfParser::_name' is never used.
• class member 'DwarfParser::_image_base' is never used.
• class member 'DwarfParser::_capacity' is never used.
• class member 'DwarfParser::_prev' is never used.
• class member 'DwarfParser::_code_align' is never used.
• class member 'DwarfParser::_data_align' is never used.
• Class 'WallClockEpochEvent' has a constructor with 1 argument that is not explicit.
• class member 'LockEvent::_start_time' is never used.
• class member 'LockEvent::_end_time' is never used.
• class member 'LockEvent::_address' is never used.
• class member 'LockEvent::_timeout' is never used.
• class member 'ObjectLivenessEvent::_alloc' is never used.
• class member 'ObjectLivenessEvent::_skipped' is never used.
• class member 'ObjectLivenessEvent::_start_time' is never used.
• class member 'ObjectLivenessEvent::_age' is never used.
• class member 'ObjectLivenessEvent::_ctx' is never used.
• struct member 'QueueTimeEvent::_start' is never used.
• struct member 'QueueTimeEvent::_end' is never used.
• struct member 'QueueTimeEvent::_task' is never used.
• struct member 'QueueTimeEvent::_scheduler' is never used.
• struct member 'QueueTimeEvent::_origin' is never used.
• struct member 'QueueTimeEvent::_queueType' is never used.
• struct member 'QueueTimeEvent::_queueLength' is never used.
• The class 'VirtualSpaceSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'GCHeapSummary' does not declare a constructor although it has private member variables which likely require initialization.
• The class 'CollectedHeap' does not declare a constructor although it has private member variables which likely require initialization.
• Class 'Element' has a constructor with 1 argument that is not explicit.
• Class 'NoField' has a constructor with 1 argument that is not explicit.
• Class 'MutexLocker' has a constructor with 1 argument that is not explicit.
• Class 'MethodList' has a constructor with 1 argument that is not explicit.
• Class 'ScopeDesc' has a constructor with 1 argument that is not explicit.
• The function 'is_nofield' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• Condition 'enabled()' is always false
• Condition 'usage._maxSize==-1' is always false
• Condition 'counters' is always false
• Condition 'i<names.size()' is always false
• Condition '!TSC::initialized()' is always false
• The scope of the variable 'class_name_id' can be reduced.
• The scope of the variable 'method_name_id' can be reduced.
• The scope of the variable 'method_sig_id' can be reduced.
• Local variable 'start' shadows outer function
• Parameter 'frame' can be declared as reference to const
• Variable 'strings' can be declared as reference to const
• Parameter 'args' can be declared as reference to const
• Parameter 'constants' can be declared as reference to const
• Parameter 'ptr' can be declared as pointer to const. However it seems that 'load32' is a callback function, if 'ptr' is declared with const you might also need to cast function pointer(s).
• Variable 'methods' can be declared as pointer to const
• Parameter 'func' can be declared as pointer to const
• Variable 'counters' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Parameter 'event' can be declared as pointer to const
• Variable 'class_name_id' is assigned a value that is never used.
• Variable 'method_name_id' is assigned a value that is never used.
• Variable 'method_sig_id' is assigned a value that is never used.
• Parameter 'ptr' can be declared as pointer to const
• struct member 'CpuTime::real' is never used.
• struct member 'CpuTime::user' is never used.
• struct member 'CpuTime::system' is never used.
• struct member 'CpuTimes::proc' is never used.
• struct member 'CpuTimes::total' is never used.
• class member 'Recording::_agent_properties' is never used.
• class member 'Recording::_jvm_args' is never used.
• class member 'Recording::_jvm_flags' is never used.
• class member 'Recording::_java_command' is never used.
• class member 'Recording::_fd' is never used.
• class member 'Recording::_start_time' is never used.
• class member 'Recording::_recording_start_time' is never used.
• class member 'Recording::_start_ticks' is never used.
• class member 'Recording::_recording_start_ticks' is never used.
• class member 'Recording::_stop_time' is never used.
• class member 'Recording::_stop_ticks' is never used.
• class member 'Recording::_base_id' is never used.
• class member 'Recording::_bytes_written' is never used.
• class member 'Recording::_tid' is never used.
• class member 'Recording::_available_processors' is never used.
• class member 'Recording::_recorded_lib_count' is never used.
• class member 'Recording::_cpu_monitor_enabled' is never used.
• class member 'Recording::_last_times' is never used.
• class member 'FlightRecorder::_filename' is never used.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'ITimer::_cstack' is never used.
• struct member 'jvmtiFrameInfoExtended::native_frame_address' is never used.
• struct member 'jvmtiStackInfoExtended::frame_buffer' is never used.
• class member 'J9Ext::InstrumentableObjectAlloc_id' is never used.
• The class 'J9WallClock' does not declare a constructor although it has private member variables which likely require initialization.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• class member 'J9WallClock::_max_stack_depth' is never used.
• class member 'J9WallClock::_running' is never used.
• Class 'ReservoirSampler' has a constructor with 1 argument that is not explicit.
• The function 'name' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'stop' overrides a function in a base class but is not marked with a 'override' specifier.
• Variable 'value' can be declared as pointer to const
• Variable 'ret' is assigned a value that is never used.
• class member 'JfrMetadata::_initialized' is never used.
• class member 'JVM::_is_readable_pointer_resolved' is never used.
• class member 'JVM::_is_readable_pointer' is never used.
• class member 'VirtualSpaceSummary::_committed_end' is never used.
• class member 'GCHeapSummary::vptr' is never used.
• class member 'CollectedHeap::vptr' is never used.
• class member 'CollectedHeap::_gc_heap_log' is never used.
• class member 'CollectedHeap::_capacity_at_last_gc' is never used.
• class member 'CollectedHeap::_used_at_last_gc' is never used.
• struct member 'Chunk::prev' is never used.
• struct member 'Chunk::offs' is never used.
• struct member 'Chunk::_padding' is never used.
• class member 'LinearAllocator::_chunk_size' is never used.
• class member 'LinearAllocator::_tail' is never used.
• class member 'LinearAllocator::_reserve' is never used.
• Local variable 'start' shadows outer function
• Local variable 'start' shadows outer function
• Parameter 'args' can be declared as reference to const
• Parameter 'event' can be declared as reference to const
• Unused variable: kept_classes
• struct member 'TrackingEntry::alloc' is never used.
• struct member 'TrackingEntry::skipped' is never used.
• struct member 'TrackingEntry::call_trace_id' is never used.
• struct member 'TrackingEntry::ctx' is never used.
• class member 'LivenessTracker::MAX_TRACKING_TABLE_SIZE' is never used.
• class member 'LivenessTracker::MIN_SAMPLING_INTERVAL' is never used.
• class member 'LivenessTracker::_table_lock' is never used.
• Condition 'level>=_level' is always true
• Parameter 'args' can be declared as reference to const
• class member 'Log::_file' is never used.
• class member 'Log::LEVEL_NAME' is never used.
• class member 'ObjectSampler::CONFIG_UPDATE_CHECK_PERIOD_SECS' is never used.
• class member 'JitWriteProtection::_prev' is never used.
• class member 'JitWriteProtection::_restore' is never used.
• class member 'OS::page_size' is never used.
• class member 'OS::page_mask' is never used.
• The function 'rewind' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'next' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'size' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'start' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'registerThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'unregisterThread' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
• The function 'enableEvents' overrides a function in a base class but is identical to the overridden function
• The function 'registerThread' overrides a function in a base class but is identical to the overridden function
• The function 'unregisterThread' overrides a function in a base class but is identical to the overridden function
• Condition 'i<PROBE_SP_LIMIT' is always false
• Condition 'event_name==NULL' is always true
• Parameter 'args' can be declared as reference to const
• Parameter 'java_ctx' can be declared as pointer to const
• Variable 'error' is assigned a value that is never used.
• Variable 'error' is assigned a value that is never used.
• Variable 'error' is assigned a value that is never used.
• Variable 'error' is assigned a value that is never used.
• Condition 'length>0' is always false
• class member 'Profiler::_signals_initialized' is never used.
• class member 'Profiler::_class_map_lock' is never used.
• class member 'Profiler::_locks' is never used.
• Condition 'strcmp(name,"forward_copy_longs")==0' is always false
• Condition 'strcmp(name,"backward_copy_longs")==0' is always false
• Variable 'ip' can be declared as pointer to const
• Parameter 'ip' can be declared as pointer to const
• Variable 'ip' can be declared as pointer to const
• Parameter 'pc' can be declared as pointer to const
• Unused private function: 'StackFrame::withinCurrentStack'
• Variable 'ip' can be declared as pointer to const
• Parameter 'entry' can be declared as pointer to const
• Variable 'ip' can be declared as pointer to const
• Parameter 'pc' can be declared as pointer to const
• Variable 'ip' can be declared as pointer to const
• Variable 'ip' can be declared as pointer to const
• Variable 'entry' can be declared as pointer to const
• Parameter 'pc' can be declared as pointer to const
• Parameter 'sp' can be declared as reference to const
• Variable 'inst' can be declared as pointer to const
• Variable 'inst' can be declared as pointer to const
• Parameter 'pc' can be declared as pointer to const
• Variable 'ip' can be declared as pointer to const
• Parameter 'pc' can be declared as pointer to const
• Local variable 'pc' shadows outer function
• Return value 'ptr>(const void*)-DEAD_ZONE' is always true
• Condition '!inDeadZone(method)' is always false
• Condition '!inDeadZone(method_id)' is always false
• Condition 'inDeadZone(pc)' is always true
• Condition 'inDeadZone(pc)' is always true
• Condition 'is_plausible_interpreter_frame' is always false
• Condition 'inDeadZone(pc)' is always true
• The comparison 'EMPTY_FRAME_SIZE > 0' is always false.
• The comparison 'EMPTY_FRAME_SIZE > 0' is always false.
• The scope of the variable 'prev_sp' can be reduced.
• Local variable 'frame' shadows outer variable
• Variable 'page_start' is assigned a value that is never used.
• The comparison 'EMPTY_FRAME_SIZE > 0' is always false.
• The comparison 'EMPTY_FRAME_SIZE > 0' is always false.
• Class 'SymbolDesc' has a constructor with 1 argument that is not explicit.
• Class 'MemoryMapDesc' has a constructor with 1 argument that is not explicit.
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Local variable 'section' shadows outer function
• Variable 'ident' can be declared as pointer to const
• Parameter 'section' can be declared as pointer to const
• Variable 'checked' can be declared as pointer to const
• Variable 'pheader' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'chain' can be declared as pointer to const
• Variable 'plt' can be declared as pointer to const
• Variable 'note' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Variable 'sym' can be declared as pointer to const
• Local variable 'tid' shadows outer function
• Local variable 'tid' shadows outer function
• class member 'ProfiledThread::_buffer_size' is never used.
• class member 'ProfiledThread::_buffer' is never used.
• Local variable 'word' shadows outer function
• class member 'ThreadFilter::_max_bitmaps' is never used.
• class member 'ThreadInfo::_thread_names' is never used.
• class member 'ThreadInfo::_thread_ids' is never used.
• class member 'Trap::_page_start' is never used.
• Local variable 'frequency' shadows outer function
• Variable 'idx' can be declared as pointer to const
• Parameter 'prop_value' can be declared as pointer to const
• Variable 'flag_addr' can be declared as pointer to const
• Parameter 'options' can be declared as pointer to const
• struct member 'ASGCT_CallTrace::env' is never used.
• struct member 'ASGCT_CallTrace::frames' is never used.
• struct member 'VMManagement::unused' is never used.
• struct member 'JVMTIFunctions::unused1' is never used.
• struct member 'JVMTIFunctions::unused2' is never used.
• struct member 'JavaFullVersion::major' is never used.
• struct member 'JavaFullVersion::update' is never used.
• class member 'VM::_can_intercept_binding' is never used.
• class member 'VM::_libjvm' is never used.
• class member 'VM::_libjava' is never used.
• class member 'VM::_asyncGetCallTrace' is never used.
• The scope of the variable 'delayedCounter' can be reduced.
• Local variable 'type' shadows outer function
• Parameter 'ptr' can be declared as pointer to const. However it seems that 'load32' is a callback function, if 'ptr' is declared with const you might also need to cast function pointer(s).
• Variable 'code_heap_array' can be declared as pointer to const
• Variable 'blob' can be declared as pointer to const
• Parameter 'vm_thread' can be declared as pointer to const
• Variable 'segmap' can be declared as pointer to const
• Variable 'type_name' can be declared as pointer to const
• Variable 'pcd_end' can be declared as pointer to const
• Consider using std::any_of, std::all_of, std::none_of, or std::accumulate algorithm instead of a raw loop.
• Variable 'error' is assigned a value that is never used.
• class member 'VMStructs::_has_native_thread_id' is never used.
• class member 'VMStructs::_class_loader_data_next_offset' is never used.
• class member 'VMStructs::_scopes_pcs_offset' is never used.
• class member 'VMStructs::_constmethod_constants_offset' is never used.
• class member 'VMStructs::_constmethod_idnum_offset' is never used.
• class member 'VMStructs::_pool_holder_offset' is never used.
• class member 'VMStructs::_array_data_offset' is never used.
• class member 'VMStructs::_code_heap_segmap_offset' is never used.
• class member 'VMStructs::_code_heap_segment_shift' is never used.
• class member 'VMStructs::_heap_block_used_offset' is never used.
• class member 'VMStructs::_vs_low_bound_offset' is never used.
• class member 'VMStructs::_vs_high_bound_offset' is never used.
• class member 'VMStructs::_flag_type_offset' is never used.
• class member 'VMStructs::_flags_addr' is never used.
• class member 'VMStructs::_flag_count' is never used.
• class member 'VMStructs::_flag_size' is never used.
• class member 'VMStructs::_code_heap_low_addr' is never used.
• class member 'VMStructs::_code_heap_high_addr' is never used.
• class member 'VMStructs::_klass_offset_addr' is never used.
• class member 'VMStructs::_narrow_klass_base_addr' is never used.
• class member 'VMStructs::_narrow_klass_base' is never used.
• class member 'VMStructs::_narrow_klass_shift_addr' is never used.
• class member 'VMStructs::_narrow_klass_shift' is never used.
• class member 'VMStructs::_collected_heap' is never used.
• class member 'VMStructs::_collected_heap_reserved_offset' is never used.
• class member 'VMStructs::_region_start_offset' is never used.
• class member 'VMStructs::_region_size_offset' is never used.
• class member 'VMStructs::_markword_klass_shift' is never used.
• class member 'VMStructs::_markword_monitor_value' is never used.
• class member 'VMStructs::_unsigned5_base' is never used.
• class member 'VMStructs::_call_stub_return_addr' is never used.
• class member 'VMStructs::_find_flag_func' is never used.
• class member 'VMStructs::_is_valid_method_func' is never used.
• class member 'HeapUsage::is_jmx_attempted' is never used.
• class member 'PcDesc::_pc' is never used.
• class member 'PcDesc::_scope_offset' is never used.
• class member 'PcDesc::_obj_offset' is never used.
• class member 'PcDesc::_flags' is never used.
• Local variable 'interval' shadows outer function
• Variable 'context' can be declared as reference to const
• struct member 'ThreadEntry::native' is never used.
• The function 'patchImport' is never used.
• The function 'getCounter' is never used.
• The function 'supported' is never used.
• The function 'updateCounter' is never used.
• The function 'deallocateLineNumberTable' is never used.
• The function 'copyTo' is never used.
• The function 'cpuMonitorCycle' is never used.
• The function 'appendRecording' is never used.
• The function 'writeListSetting' is never used.
• The function 'active' is never used.
• The function 'units' is never used.
• The function 'GetJ9vmThread' is never used.
• The function 'is_readable_pointer' is never used.
• The function '_min' is never used.
• The function 'trace' is never used.
• The function 'waitUntil' is never used.
• The function 'notify' is never used.
• The function 'cputime' is never used.
• The function 'ntoh64' is never used.
• The function 'schedPolicy' is never used.
• The function 'fileSize' is never used.
• The function 'flushJfr' is never used.
• The function 'restart' is never used.
• The function 'arg0' is never used.
• The function 'arg2' is never used.
• The function 'jarg0' is never used.
• The function 'ret' is never used.
• The function 'clearParsingCaches' is never used.
• The function 'isDeepCrashHandler' is never used.
• The function 'getThreadId' is never used.
• The function 'assign' is never used.
• The function 'covers' is never used.
• The function 'install' is never used.
• The function 'uninstall' is never used.
• The function 'loaded' is never used.
• The function 'hasClassNames' is never used.
• The function 'hasCompilerStructs' is never used.
• The function 'body' is never used.
• The function 'fromHandle' is never used.
• The function 'fromMethodID' is never used.
• The function 'inJava' is never used.
• The function 'compiledMethod' is never used.

[jbachorik]

HI @bric3 - you picked the right approach with the counters.
But it will be better if you have only one counter for the whole unwinding - keeping track of each unwound frame type would be too expensive.

[jbachorik]

Hm, sorry for not being clear from the beginning - I meant having just one measurement around the unwinding loop in each unwinder implementation (walkFP, walkDwarf and walkVM).
There will always be just one implementation active in the profiler so we will not be mixing up statistics from multiple implementations. And by having just one start/stop timestamp pair we will save quite a nice number of nanoseconds per unwound stack trace.