JVM Flags access API

[jbachorik]

What does this PR do?:
It extracts the profiling-independent part of the 'libjavaProfiler' library Java API such that it might be used even if the profiler itself is not used.
It adds a new API for direct access to JVM flags.

Motivation:
The main reason is not be dependent on JMX to eg. read the value of -XX:ErrorFile etc.

Additional Notes:

How to test the change?:
Existing unit/integration tests are passing and added unit tests for the JVM flag access are passing as well.

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-10836

Unsure? Have a question? Request a review!

[github-actions]

🔧 Report generated by pr-comment-cppcheck

CppCheck Report

Warnings (6)

• 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 (177)

• Class 'AsyncSampleMutex' has a constructor with 1 argument that is not explicit.
• The class 'NativeFunc' does not declare a constructor although it has private member variables which likely require initialization.
• Local variable 'count' shadows outer function
• Local variable 'jni' shadows outer function
• Local variable 'size' shadows outer function
• Local variable 'prev' shadows outer function
• Local variable 'i' shadows outer variable
• Consider using std::transform algorithm instead of a raw loop.
• struct member 'Tag::value' is never used.
• struct member 'ContextPage::capacity' is never used.
• struct member 'ContextPage::storage' 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 '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.
• Local variable 'pc_off' shadows outer variable
• Class 'WallClockEpochEvent' has a constructor with 1 argument that is not explicit.
• 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.
• 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
• 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.
• 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.
• struct member 'CpuTime::real' is never used.
• struct member 'CpuTime::user' is never used.
• struct member 'CpuTime::system' 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.
• struct member 'jvmtiStackInfoExtended::frame_buffer' 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 '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.
• Unused variable: kept_classes
• Condition 'level>=_level' is always true
• Condition 'frames_size>0' is always true
• 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.
• 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.
• Unused private function: 'StackFrame::withinCurrentStack'
• 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.
• 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 'version' shadows outer variable
• Local variable 'flag_addr' shadows outer variable
• Variable 'version.major' is assigned a value that is never used.
• Variable 'version.update' is assigned a value that is never used.
• Variable 'version.update' is assigned a value that is never used.
• struct member 'ASGCT_CallTrace::env' is never used.
• struct member 'ASGCT_CallTrace::frames' 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.
• The scope of the variable 'delayedCounter' can be reduced.
• 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.
• struct member 'ThreadEntry::native' is never used.
• The function 'Agent_OnLoad' is never used.
• The function 'GetJ9vmThread' is never used.
• The function 'JNI_OnLoad' is never used.
• The function 'JNI_OnUnload' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_findBooleanJVMFlag0' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_findFloatJVMFlag0' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_findIntJVMFlag0' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_findStringJVMFlag0' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_healthCheck0' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_setBooleanJVMFlag0' is never used.
• The function 'Java_com_datadoghq_profiler_JVMAccess_setStringJVMFlag0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_currentTicks0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_describeDebugCounters0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_dump0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_execute0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_filterThread0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_getContextPage0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_getContextPageOffset0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_getDebugCounters0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_getMaxContextPages0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_getSamples' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_getTid0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_init0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_mallocArenaMax0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_recordQueueEnd0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_recordSettingEvent0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_recordTrace0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_registerConstant0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_stop0' is never used.
• The function 'Java_com_datadoghq_profiler_JavaProfiler_tscFrequency0' is never used.
• The function '_min' is never used.
• The function 'appendRecording' is never used.
• The function 'arg0' is never used.
• The function 'arg2' is never used.
• The function 'assign' is never used.
• The function 'body' is never used.
• The function 'clearParsingCaches' is never used.
• The function 'compiledMethod' is never used.
• The function 'copyTo' is never used.
• The function 'covers' is never used.
• The function 'cpuMonitorCycle' is never used.
• The function 'cputime' is never used.
• The function 'deallocateLineNumberTable' is never used.
• The function 'fileSize' is never used.
• The function 'flushJfr' is never used.
• The function 'fromHandle' is never used.
• The function 'fromMethodID' is never used.
• The function 'getCounter' is never used.
• The function 'getJavaTraceInternal' is never used.
• The function 'getJavaTraceJvmti' is never used.
• The function 'getThreadId' is never used.
• The function 'hasClassNames' is never used.
• The function 'hasCompilerStructs' is never used.
• The function 'inJava' is never used.
• The function 'install' is never used.
• The function 'isDeepCrashHandler' is never used.
• The function 'isEntryFrame' is never used.
• The function 'is_readable_pointer' is never used.
• The function 'jarg0' is never used.
• The function 'lastJavaFP' is never used.
• The function 'loaded' is never used.
• The function 'notify' is never used.
• The function 'ntoh64' is never used.
• The function 'patchImport' is never used.
• The function 'restart' is never used.
• The function 'schedPolicy' is never used.
• The function 'supported' is never used.
• The function 'uninstall' is never used.
• The function 'units' is never used.
• The function 'updateCounter' is never used.
• The function 'waitUntil' is never used.
• The function 'writeListSetting' is never used.

[github-actions]

🔧 Report generated by pr-comment-scanbuild

Scan-Build Report

User:	runner@fv-az1535-492
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 14.0.0-1ubuntu1.1
Date:	Mon Nov 11 13:45:04 2024

Bug Summary

Bug Type	Quantity	Display?
All Bugs	6
Logic error
Assigned value is garbage or undefined	1
Dereference of null pointer	3
Result of operation is garbage or undefined	1
Unused code
Dead nested assignment	1

Reports

Bug Group	Bug Type ▾	File	Function/Method	Line	Path Length
Logic error	Assigned value is garbage or undefined	dwarf.cpp	parseInstructions	244	20
Unused code	Dead nested assignment	vmStructs.cpp	checkNativeBinding	939	1
Logic error	Dereference of null pointer	safeAccess.h	load	33	18
Logic error	Dereference of null pointer	symbols_linux.h	ElfParser	129	32
Logic error	Dereference of null pointer	flightRecorder.cpp	flush	1504	8
Logic error	Result of operation is garbage or undefined	vmStructs.cpp	find	834	16

[MattAlp]

Need to verify a few things with this PR and its interaction with dd-trace-java, will follow-up & approve if no troubles emerge.

[MattAlp]

I would specify as-of details here

[jbachorik]

Sorry, I don't understand - what should I specify here?

[jbachorik]

@MattAlp I have decoupled the library initialization from the profiler initialization. Now, when you don't use profiler only the most important parts will be initialized - basically just the JNI bindings, vmstructs and safeacees. Anything related to JVMTI, capabilities, hooks etc. is registered only when one asks for JavaProfiler.instance()