code: func getMissingFunctionSource(filename string, asm map[int][]assemblyInstruction, start, end int) (graph.Nodes, string) {
  	var fnodes graph.Nodes
  	for i := start; i <= end; i++ {
  		insts := asm[i]
  		if len(insts) == 0 {
  			continue
  		}
  		var group assemblyInstruction
  		for _, insn := range insts {
  			group.flat += insn.flat
  			group.cum += insn.cum
  			group.flatDiv += insn.flatDiv
  			group.cumDiv += insn.cumDiv
  		}
  		flat := group.flatValue()
  		cum := group.cumValue()
  		fnodes = append(fnodes, &graph.Node{
  			Info: graph.NodeInfo{
  				Name:   "???",
  				Lineno: i,
  			},
  			Flat: flat,
  			Cum:  cum,
  		})
  	}
  	return fnodes, filename
  }
docs: // getMissingFunctionSource creates a dummy function body to point to
  // the source file and annotates it with the samples in asm.