use call_sv or call_pv to call yourself again. You can also do the hackish
in reply to Recursing in XS?
Which bypasses the Interp almost completely and is more efficient. The problem with the above is, if the child XSUB being called raw dies/croaks, the error message will put the blame as the parent XSUB since the global state info wasn't updated in the interp. Also note the parent XSUB is passing its CV to the child XSUB, so ALIAS/XSANY will break if the parent isn't the child and the child relies on XSANY/ALIAS to operate. How to calculate the number of items XS_Foo__Bar_Func returned IDK. It probably involves the delta between C auto SV * mark and SP and +0, +1 or -1 SV*. Another thing, Perl uses malloc memory to implement pure perl opcode recursion, XSUBs use C stack memory. You might get an access vio/segv on deep recursion instead of a descriptive fatal error in pure perl.
retval = POPs; /* did we get 1 elem? this code just assumes*/
/* ?????? */