[DAC][ReJIT] ReJitManager::IsReJITEnabled checked DOTNET_ProfAPI_RejitOnAttach in the wrong environment

[lambdageek]

When running in the DAC, ReJitManager::IsReJITEnabled checks the configuration environment variable in the environment of the debugger process, not in the target process:

runtime/src/coreclr/vm/rejit.inl

Lines 24 to 32 in aac3b2c

	inline BOOL ReJitManager::IsReJITEnabled()
	{
	LIMITED_METHOD_CONTRACT;
	static bool profilerStartupRejit = CORProfilerEnableRejit() != FALSE;
	static ConfigDWORD rejitOnAttachEnabled;
	return profilerStartupRejit || (rejitOnAttachEnabled.val(CLRConfig::EXTERNAL_ProfAPI_RejitOnAttach) != 0);
	}

The CLRConfig::GetConfigString (called by ConfigDWORD::val) checks the environment of the current process (the one in which the DAC is loaded), not the target runtime.
Whenever this is fixed please remember to fix the cDAC implementation as well as the DAC.

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[lambdageek]

This is called from, for example
MethodDesc::IsEligibleForReJIT:

runtime/src/coreclr/vm/method.hpp

Lines 1110 to 1128 in aac3b2c

	bool IsEligibleForReJIT()
	{
	WRAPPER_NO_CONTRACT;
	#ifdef FEATURE_REJIT
	return
	ReJitManager::IsReJITEnabled() &&
	// Previously we didn't support these methods because of functional requirements for
	// jumpstamps, keeping this in for back compat.
	IsIL() &&
	!IsWrapperStub() &&
	// Functional requirement
	CodeVersionManager::IsMethodSupported(PTR_MethodDesc(this));
	#else // FEATURE_REJIT
	return false;
	#endif
	}

Which is called from MethodDesc::IsVersionable, called from EECodeInfo::GetNativeCodeVersion, called from ExecutionManager::GetNativeCodeVersion, called from SOSDacImpl::GetMethodDescData which runs in the DAC

[lambdageek]

/cc @davidwrighton

[tommcdon]

@AaronRobinsonMSFT