How is CLR instance id set?

[huoyaoyuan]

When implementing eventing for #91400, GetClrInstanceId is used.

The only definition I can find is:

runtime/src/coreclr/nativeaot/Runtime/gcenv.h

Lines 80 to 88 in 808c523

	EXTERN_C uint32_t _tls_index;
	inline uint16_t GetClrInstanceId()
	{
	#ifdef HOST_WINDOWS
	return (uint16_t)_tls_index;
	#else
	return 0;
	#endif
	}

On Unix it just returns 0. On Windows I can't find any write for _tls_index.

[jkotas]

_tls_index is intrinsic. It is initialized by the Windows OS loader to the index of thread-static block for the given .dll.