I want to call objc_msg_sendv explicitely.
I need to know what's arglist_t and how too manipulate/build
I don't think you want to construct arglists. They are too hard and difficult to get portable (see the mframe.m code for instance). You really want to construct the method call via NSInvocation. You could probably look at some other bindings that are already written (like gnustep-guile) for examples. If you absolutely can't use Objective-C code to construct the method, I suppose you could construct the function call frame by hand (using either code from GSFFIInvocation.m or GSFFCallInvocation.m).