[NativeAOT] Fire First Chance Exceptions if Debugger is Attached

[tommcdon]

Both NativeAOT and .NET Core share the same exception model, where managed exceptions and processed and handled inside of the runtime and we avoid OS notifications for them unless they are unhandled. For NativeAOT, we recommend setting a breakpoint on RhThrowEx to debug exceptions when they are thrown. To make it easier to stop on these exceptions, it would be useful to report the exceptions to the OS in NativeAOT so that native debuggers will automatically be notified, similar to .NET Core's mechanism:

runtime/src/coreclr/vm/exceptionhandling.cpp

Lines 1558 to 1573 in c53ccee

	void FirstChanceExceptionNotification()
	{
	#ifndef TARGET_UNIX
	if (minipal_is_native_debugger_present())
	{
	PAL_TRY(VOID *, unused, NULL)
	{
	RaiseException(EXCEPTION_COMPLUS, 0, 0, NULL);
	}
	PAL_EXCEPT(EXCEPTION_EXECUTE_HANDLER)
	{
	}
	PAL_ENDTRY;
	}
	#endif // TARGET_UNIX
	}

.

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[tommcdon]

cc @janvorli

[agocke]

Also @jkotas @MichalStrehovsky. I suppose this would give us a dependency on C++ EH on windows? That doesn’t seem as big a deal as it would be on Linux.

[jkotas]

I suppose this would give us a dependency on C++ EH on windows?

Nit: This introduces a dependency on Windows SEH that's fine. It does not introduce dependency on C++ EH. We actually explicitly disable C++ EH support for NAOT runtime: https://github.com/dotnet/runtime/blob/main/src/coreclr/nativeaot/CMakeLists.txt#L7

[jkotas]

Linux

I do not think that this makes sense on Linux. There is no OS concept of exceptions on Linux. If a Linux debugger has a support for stopping on an exception, it is just a shortcut for setting a regular breakpoint on a symbol.