key := pkfunc{pk: data.PkgIdx, fcn: data.FuncIdx}
	val := mm.pod.pmm[key]
	// FIXME: in theory either A) len(val.Counters) is zero, or B)
	// the two lengths are equal. Assert if not? Of course, we could
	// see odd stuff if there is source file skew.
	if *verbflag > 4 {
		fmt.Printf("visit pk=%d fid=%d len(counters)=%d\n", data.PkgIdx, data.FuncIdx, len(data.Counters))
	}
	if len(val.Counters) < len(data.Counters) {

		// Dump the function in which this opcode check was supposed to
		// pass but failed.
		funcIdx := lineFuncMap[o.fileline]
		if funcIdx != 0 && funcIdx != lastFunction {
			funcLines := lines[functionMarkers[funcIdx]:functionMarkers[funcIdx+1]]
			t.Log(strings.Join(funcLines, "\n"))
			lastFunction = funcIdx // avoid printing same function twice
		}

		if o.negative {

		writeName(ctxt.Out, "_start")       // the wasi entrypoint
		ctxt.Out.WriteByte(0x00)            // func export
		writeUleb128(ctxt.Out, uint64(idx)) // funcidx
		writeName(ctxt.Out, "memory")       // memory in wasi
		ctxt.Out.WriteByte(0x02)            // mem export
		writeUleb128(ctxt.Out, 0)           // memidx
	case "js":
		writeUleb128(ctxt.Out, 4) // number of exports

				return fmt.Errorf("reading counter data file %s: %v", cdf, err)
			}
			if !ok {
				break
			}

			// NB: sanity check on pkg and func IDs?
			key := pkfunc{pk: data.PkgIdx, fcn: data.FuncIdx}
			if prev, found := pmm[key]; found {
				// Note: no overflow reporting here.
				if err, _ := ts.cm.MergeCounters(data.Counters, prev); err != nil {
					return fmt.Errorf("processing counter data file %s: %v", cdf, err)