Add a fail-safe when we encounter double-exit from crash handler

[jbachorik]

What does this PR do?:
Adds a fail-safe when we encounter double-exit from crash handler.

Motivation:
This seems to happen sometimes in relation to longjmp. Since the crash signal handler is using depth tracking to avoid stack overflow, having this depth corrupted by double-exit may cause not intercepting and sigsegs at all.
This was witnessed in CI when cca. 1 in 4 runs quite reliable crashed in SafeAccess::load call.

With this particular patch applied no crash is observed in a series of 7 subsequent runs so this all looks like a valid hypothesis.

Additional Notes:
If a crash in SafeAccess::load is observed even with this patch applied then the safest course of action is to revert this PR and then #134

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-10605

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 (161)

• Class 'AsyncSampleMutex' has a constructor with 1 argument that is not explicit.
• Local variable 'jni' shadows outer function
• Local variable 'size' shadows outer function
• Local variable 'prev' shadows outer function
• 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 'i' shadows outer variable
• Consider using std::transform algorithm instead of a raw loop.
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• Condition 'enabled()' is always false
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• The scope of the variable 'method_sig_id' can be reduced.
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• Variable 'method_name_id' is assigned a value that is never used.
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• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
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• 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
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• The function 'check' overrides a function in a base class but is not marked with a 'override' specifier.
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• The function 'interval' overrides a function in a base class but is not marked with a 'override' specifier.
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• 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 'flag_addr' shadows outer variable
• 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.
• The scope of the variable 'delayedCounter' can be reduced.
• 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.
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• The function 'getJavaTraceInternal' is never used.
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• 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 '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.
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[github-actions]

🔧 Report generated by pr-comment-scanbuild

Scan-Build Report

User:	runner@fv-az1251-122
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 Oct 14 16:33:54 2024

Bug Summary

Bug Type	Quantity	Display?
All Bugs	5
Logic error
Assigned value is garbage or undefined	1
Dereference of null pointer	3
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	879	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

[r1viollet]

I'm OK to try this. LGTM
However I am not sure why this would be occurring.
I did add a note in previous PR on possible extra thread fencing.