def declare_env_global(self, module, envname):
        """Declare the Environment pointer as a global of the module.

        The pointer is initialized to NULL.  It must be filled by the runtime
        with the actual address of the Env before the associated function
        can be executed.

        Parameters
        ----------
        module :
            The LLVM Module
        envname : str
            The name of the global variable.
        """
        if envname not in module.globals:
            gv = llvmir.GlobalVariable(module, cgutils.voidptr_t, name=envname)
            gv.linkage = 'common'
            gv.initializer = cgutils.get_null_value(gv.type.pointee)

        return module.globals[envname]
Declare the Environment pointer as a global of the module.

        The pointer is initialized to NULL.  It must be filled by the runtime
        with the actual address of the Env before the associated function
        can be executed.

        Parameters
        ----------
        module :
            The LLVM Module
        envname : str
            The name of the global variable.
        
numba/core/base.py