use strict;
use warnings;
use feature qw( say );

use Inline C => <<'__EOI__';

SV* coderef2name(CV* cv) {
   const GV *   const gv        = CvGV(cv);
   const HV *   const stash     = GvSTASH(gv);
   const char * const pkg_name  = HvNAME(stash);
   const char * const func_name = GvNAME(gv);
   SV *         const fqn       = newSVpvn("", 0);

   sv_catpv(fqn, pkg_name);
   sv_catpv(fqn, "::");
   sv_catpv(fqn, func_name);

   return fqn;  // Mortalised by Inline
}

__EOI__

sub f {}

say coderef2name(\&f);