Ok as a first step, I would recommend replacing an existing extension (starting with xh_ prefix) within UOBJLIST.in instead of adding a new one. This will help us get the shortest path towards getting your new extension in the mix.
So, perhaps replace xh_hyperdep with xh_uhcalltest
Well after you replace an existing app within UOBJLIST.in you will need to take the following steps:
replace XMHFGEEC_SLAB_XH_HYPERDEP with XMHFGEEC_SLAB_XH_UHCALLTEST within include/xmhf-config.h; keep the numbering as is (13 in this case)
replace XMHFGEEC_SLAB_XH_HYPERDEP with XMHFGEEC_SLAB_XH_UHCALLTEST in the static xc_hypapp_info_t _xcihub_hypapp_info_table[] definition within xmhf-uobjs/include/xc.h
add xh_uhcalltest.hwithin xmhf-uobjs/include/; use xmhf-uobjs/include/xh_hyperdep.h as a reference and adapt and change definitions to have the UHCALLTEST/uhcalltest prefix where appropriate. Ensure you use non-conflicting hypercall ids (e.g., 0xC0, 0xC1 should be changed to something else so that if we use hyperdep and uhcalltest they wont conflict)
use xmhf-uobjs/xh_hyperdep/* as a template for your uhcalltest extension. Ensure you edit the .gsm file and change uobj-name, uobj-callees and uobj-uapicallees based on whether your extension calls other uobjs or provides APIs for other uobjs.
There were missing entries in some of the *.gsm files that can call the new hypapp. Specifically, xh_uhcalltest needed to be added to xc_init.gsm and xc_ihub.gsm