src/cmd/covdata/metamerge.go - go - Git at Google

 // Copyright 2022 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 package main

 // This file contains functions and apis that support merging of
 // meta-data information.  It helps implement the "merge", "subtract",
 // and "intersect" subcommands.

 import (
 	"crypto/md5"
 	"fmt"
 	"internal/coverage"
 	"internal/coverage/calloc"
 	"internal/coverage/cmerge"
 	"internal/coverage/decodecounter"
 	"internal/coverage/decodemeta"
 	"internal/coverage/encodecounter"
 	"internal/coverage/encodemeta"
 	"internal/coverage/slicewriter"
 	"io"
 	"os"
 	"path/filepath"
 	"sort"
 	"time"
 	"unsafe"
 )

 // metaMerge provides state and methods to help manage the process
 // of selecting or merging meta data files. There are three cases
 // of interest here: the "-pcombine" flag provided by merge, the
 // "-pkg" option provided by all merge/subtract/intersect, and
 // a regular vanilla merge with no package selection
 //
 // In the -pcombine case, we're essentially glomming together all the
 // meta-data for all packages and all functions, meaning that
 // everything we see in a given package needs to be added into the
 // meta-data file builder; we emit a single meta-data file at the end
 // of the run.
 //
 // In the -pkg case, we will typically emit a single meta-data file
 // per input pod, where that new meta-data file contains entries for
 // just the selected packages.
 //
 // In the third case (vanilla merge with no combining or package
 // selection) we can carry over meta-data files without touching them
 // at all (only counter data files will be merged).
 type metaMerge struct {
 	calloc.BatchCounterAlloc
 	cmerge.Merger
 	// maps package import path to package state
 	pkm map[string]*pkstate
 	// list of packages
 	pkgs []*pkstate
 	// current package state
 	p *pkstate
 	// current pod state
 	pod *podstate
 	// counter data file osargs/goos/goarch state
 	astate *argstate
 }

 // pkstate
 type pkstate struct {
 	// index of package within meta-data file.
 	pkgIdx uint32
 	// this maps function index within the package to counter data payload
 	ctab map[uint32]decodecounter.FuncPayload
 	// pointer to meta-data blob for package
 	mdblob []byte
 	// filled in only for -pcombine merges
 	*pcombinestate
 }

 type podstate struct {
 	pmm      map[pkfunc]decodecounter.FuncPayload
 	mdf      string
 	mfr      *decodemeta.CoverageMetaFileReader
 	fileHash [16]byte
 }

 type pkfunc struct {
 	pk, fcn uint32
 }

 // pcombinestate
 type pcombinestate struct {
 	// Meta-data builder for the package.
 	cmdb *encodemeta.CoverageMetaDataBuilder
 	// Maps function meta-data hash to new function index in the
 	// new version of the package we're building.
 	ftab map[[16]byte]uint32
 }

 func newMetaMerge() *metaMerge {
 	return &metaMerge{
 		pkm:    make(map[string]*pkstate),
 		astate: &argstate{},
 	}
 }

 func (mm *metaMerge) visitMetaDataFile(mdf string, mfr *decodemeta.CoverageMetaFileReader) {
 	dbgtrace(2, "visitMetaDataFile(mdf=%s)", mdf)

 	// Record meta-data file name.
 	mm.pod.mdf = mdf
 	// Keep a pointer to the file-level reader.
 	mm.pod.mfr = mfr
 	// Record file hash.
 	mm.pod.fileHash = mfr.FileHash()
 	// Counter mode and granularity -- detect and record clashes here.
 	newgran := mfr.CounterGranularity()
 	newmode := mfr.CounterMode()
 	if err := mm.SetModeAndGranularity(mdf, newmode, newgran); err != nil {
 		fatal("%v", err)
 	}
 }

 func (mm *metaMerge) beginCounterDataFile(cdr *decodecounter.CounterDataReader) {
 	state := argvalues{
 		osargs: cdr.OsArgs(),
 		goos:   cdr.Goos(),
 		goarch: cdr.Goarch(),
 	}
 	mm.astate.Merge(state)
 }

 func copyMetaDataFile(inpath, outpath string) {
 	inf, err := os.Open(inpath)
 	if err != nil {
 		fatal("opening input meta-data file %s: %v", inpath, err)
 	}
 	defer inf.Close()

 	fi, err := inf.Stat()
 	if err != nil {
 		fatal("accessing input meta-data file %s: %v", inpath, err)
 	}

 	outf, err := os.OpenFile(outpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, fi.Mode())
 	if err != nil {
 		fatal("opening output meta-data file %s: %v", outpath, err)
 	}

 	_, err = io.Copy(outf, inf)
 	outf.Close()
 	if err != nil {
 		fatal("writing output meta-data file %s: %v", outpath, err)
 	}
 }

 func (mm *metaMerge) beginPod() {
 	mm.pod = &podstate{
 		pmm: make(map[pkfunc]decodecounter.FuncPayload),
 	}
 }

 // metaEndPod handles actions needed when we're done visiting all of
 // the things in a pod -- counter files and meta-data file. There are
 // three cases of interest here:
 //
 // Case 1: in an unconditional merge (we're not selecting a specific set of
 // packages using "-pkg", and the "-pcombine" option is not in use),
 // we can simply copy over the meta-data file from input to output.
 //
 // Case 2: if this is a select merge (-pkg is in effect), then at
 // this point we write out a new smaller meta-data file that includes
 // only the packages of interest. At this point we also emit a merged
 // counter data file as well.
 //
 // Case 3: if "-pcombine" is in effect, we don't write anything at
 // this point (all writes will happen at the end of the run).
 func (mm *metaMerge) endPod(pcombine bool) {
 	if pcombine {
 		// Just clear out the pod data, we'll do all the
 		// heavy lifting at the end.
 		mm.pod = nil
 		return
 	}

 	finalHash := mm.pod.fileHash
 	if matchpkg != nil {
 		// Emit modified meta-data file for this pod.
 		finalHash = mm.emitMeta(*outdirflag, pcombine)
 	} else {
 		// Copy meta-data file for this pod to the output directory.
 		inpath := mm.pod.mdf
 		mdfbase := filepath.Base(mm.pod.mdf)
 		outpath := filepath.Join(*outdirflag, mdfbase)
 		copyMetaDataFile(inpath, outpath)
 	}

 	// Emit accumulated counter data for this pod.
 	mm.emitCounters(*outdirflag, finalHash)

 	// Reset package state.
 	mm.pkm = make(map[string]*pkstate)
 	mm.pkgs = nil
 	mm.pod = nil

 	// Reset counter mode and granularity
 	mm.ResetModeAndGranularity()
 }

 // emitMeta encodes and writes out a new coverage meta-data file as
 // part of a merge operation, specifically a merge with the
 // "-pcombine" flag.
 func (mm *metaMerge) emitMeta(outdir string, pcombine bool) [16]byte {
 	fh := md5.New()
 	blobs := [][]byte{}
 	tlen := uint64(unsafe.Sizeof(coverage.MetaFileHeader{}))
 	for _, p := range mm.pkgs {
 		var blob []byte
 		if pcombine {
 			mdw := &slicewriter.WriteSeeker{}
 			p.cmdb.Emit(mdw)
 			blob = mdw.BytesWritten()
 		} else {
 			blob = p.mdblob
 		}
 		ph := md5.Sum(blob)
 		blobs = append(blobs, blob)
 		if _, err := fh.Write(ph[:]); err != nil {
 			panic(fmt.Sprintf("internal error: md5 sum failed: %v", err))
 		}
 		tlen += uint64(len(blob))
 	}
 	var finalHash [16]byte
 	fhh := fh.Sum(nil)
 	copy(finalHash[:], fhh)

 	// Open meta-file for writing.
 	fn := fmt.Sprintf("%s.%x", coverage.MetaFilePref, finalHash)
 	fpath := filepath.Join(outdir, fn)
 	mf, err := os.OpenFile(fpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
 	if err != nil {
 		fatal("unable to open output meta-data file %s: %v", fpath, err)
 	}

 	// Encode and write.
 	mfw := encodemeta.NewCoverageMetaFileWriter(fpath, mf)
 	err = mfw.Write(finalHash, blobs, mm.Mode(), mm.Granularity())
 	if err != nil {
 		fatal("error writing %s: %v\n", fpath, err)
 	}
 	return finalHash
 }

 func (mm *metaMerge) emitCounters(outdir string, metaHash [16]byte) {
 	// Open output file. The file naming scheme is intended to mimic
 	// that used when running a coverage-instrumented binary, for
 	// consistency (however the process ID is not meaningful here, so
 	// use a value of zero).
 	var dummyPID int
 	fn := fmt.Sprintf(coverage.CounterFileTempl, coverage.CounterFilePref, metaHash, dummyPID, time.Now().UnixNano())
 	fpath := filepath.Join(outdir, fn)
 	cf, err := os.OpenFile(fpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
 	if err != nil {
 		fatal("opening counter data file %s: %v", fpath, err)
 	}
 	defer func() {
 		if err := cf.Close(); err != nil {
 			fatal("error closing output meta-data file %s: %v", fpath, err)
 		}
 	}()

 	args := mm.astate.ArgsSummary()
 	cfw := encodecounter.NewCoverageDataWriter(cf, coverage.CtrULeb128)
 	if err := cfw.Write(metaHash, args, mm); err != nil {
 		fatal("counter file write failed: %v", err)
 	}
 	mm.astate = &argstate{}
 }

 // VisitFuncs is used while writing the counter data files; it
 // implements the 'VisitFuncs' method required by the interface
 // internal/coverage/encodecounter/CounterVisitor.
 func (mm *metaMerge) VisitFuncs(f encodecounter.CounterVisitorFn) error {
 	if *verbflag >= 4 {
 		fmt.Printf("counterVisitor invoked\n")
 	}
 	// For each package, for each function, construct counter
 	// array and then call "f" on it.
 	for pidx, p := range mm.pkgs {
 		fids := make([]int, 0, len(p.ctab))
 		for fid := range p.ctab {
 			fids = append(fids, int(fid))
 		}
 		sort.Ints(fids)
 		if *verbflag >= 4 {
 			fmt.Printf("fids for pk=%d: %+v\n", pidx, fids)
 		}
 		for _, fid := range fids {
 			fp := p.ctab[uint32(fid)]
 			if *verbflag >= 4 {
 				fmt.Printf("counter write for pk=%d fid=%d len(ctrs)=%d\n", pidx, fid, len(fp.Counters))
 			}
 			if err := f(uint32(pidx), uint32(fid), fp.Counters); err != nil {
 				return err
 			}
 		}
 	}
 	return nil
 }

 func (mm *metaMerge) visitPackage(pd *decodemeta.CoverageMetaDataDecoder, pkgIdx uint32, pcombine bool) {
 	p, ok := mm.pkm[pd.PackagePath()]
 	if !ok {
 		p = &pkstate{
 			pkgIdx: uint32(len(mm.pkgs)),
 		}
 		mm.pkgs = append(mm.pkgs, p)
 		mm.pkm[pd.PackagePath()] = p
 		if pcombine {
 			p.pcombinestate = new(pcombinestate)
 			cmdb, err := encodemeta.NewCoverageMetaDataBuilder(pd.PackagePath(), pd.PackageName(), pd.ModulePath())
 			if err != nil {
 				fatal("fatal error creating meta-data builder: %v", err)
 			}
 			dbgtrace(2, "install new pkm entry for package %s pk=%d", pd.PackagePath(), pkgIdx)
 			p.cmdb = cmdb
 			p.ftab = make(map[[16]byte]uint32)
 		} else {
 			var err error
 			p.mdblob, err = mm.pod.mfr.GetPackagePayload(pkgIdx, nil)
 			if err != nil {
 				fatal("error extracting package %d payload from %s: %v",
 					pkgIdx, mm.pod.mdf, err)
 			}
 		}
 		p.ctab = make(map[uint32]decodecounter.FuncPayload)
 	}
 	mm.p = p
 }

 func (mm *metaMerge) visitFuncCounterData(data decodecounter.FuncPayload) {
 	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) {
 		t := val.Counters
 		val.Counters = mm.AllocateCounters(len(data.Counters))
 		copy(val.Counters, t)
 	}
 	err, overflow := mm.MergeCounters(val.Counters, data.Counters)
 	if err != nil {
 		fatal("%v", err)
 	}
 	if overflow {
 		warn("uint32 overflow during counter merge")
 	}
 	mm.pod.pmm[key] = val
 }

 func (mm *metaMerge) visitFunc(pkgIdx uint32, fnIdx uint32, fd *coverage.FuncDesc, verb string, pcombine bool) {
 	if *verbflag >= 3 {
 		fmt.Printf("visit pk=%d fid=%d func %s\n", pkgIdx, fnIdx, fd.Funcname)
 	}

 	var counters []uint32
 	key := pkfunc{pk: pkgIdx, fcn: fnIdx}
 	v, haveCounters := mm.pod.pmm[key]
 	if haveCounters {
 		counters = v.Counters
 	}

 	if pcombine {
 		// If the merge is running in "combine programs" mode, then hash
 		// the function and look it up in the package ftab to see if we've
 		// encountered it before. If we haven't, then register it with the
 		// meta-data builder.
 		fnhash := encodemeta.HashFuncDesc(fd)
 		gfidx, ok := mm.p.ftab[fnhash]
 		if !ok {
 			// We haven't seen this function before, need to add it to
 			// the meta data.
 			gfidx = uint32(mm.p.cmdb.AddFunc(*fd))
 			mm.p.ftab[fnhash] = gfidx
 			if *verbflag >= 3 {
 				fmt.Printf("new meta entry for fn %s fid=%d\n", fd.Funcname, gfidx)
 			}
 		}
 		fnIdx = gfidx
 	}
 	if !haveCounters {
 		return
 	}

 	// Install counters in package ctab.
 	gfp, ok := mm.p.ctab[fnIdx]
 	if ok {
 		if verb == "subtract" || verb == "intersect" {
 			panic("should never see this for intersect/subtract")
 		}
 		if *verbflag >= 3 {
 			fmt.Printf("counter merge for %s fidx=%d\n", fd.Funcname, fnIdx)
 		}
 		// Merge.
 		err, overflow := mm.MergeCounters(gfp.Counters, counters)
 		if err != nil {
 			fatal("%v", err)
 		}
 		if overflow {
 			warn("uint32 overflow during counter merge")
 		}
 		mm.p.ctab[fnIdx] = gfp
 	} else {
 		if *verbflag >= 3 {
 			fmt.Printf("null merge for %s fidx %d\n", fd.Funcname, fnIdx)
 		}
 		gfp := v
 		gfp.PkgIdx = mm.p.pkgIdx
 		gfp.FuncIdx = fnIdx
 		mm.p.ctab[fnIdx] = gfp
 	}
 }
	// Copyright 2022 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	package main

	// This file contains functions and apis that support merging of
	// meta-data information. It helps implement the "merge", "subtract",
	// and "intersect" subcommands.

	import (
	"crypto/md5"
	"fmt"
	"internal/coverage"
	"internal/coverage/calloc"
	"internal/coverage/cmerge"
	"internal/coverage/decodecounter"
	"internal/coverage/decodemeta"
	"internal/coverage/encodecounter"
	"internal/coverage/encodemeta"
	"internal/coverage/slicewriter"
	"io"
	"os"
	"path/filepath"
	"sort"
	"time"
	"unsafe"
	)

	// metaMerge provides state and methods to help manage the process
	// of selecting or merging meta data files. There are three cases
	// of interest here: the "-pcombine" flag provided by merge, the
	// "-pkg" option provided by all merge/subtract/intersect, and
	// a regular vanilla merge with no package selection
	//
	// In the -pcombine case, we're essentially glomming together all the
	// meta-data for all packages and all functions, meaning that
	// everything we see in a given package needs to be added into the
	// meta-data file builder; we emit a single meta-data file at the end
	// of the run.
	//
	// In the -pkg case, we will typically emit a single meta-data file
	// per input pod, where that new meta-data file contains entries for
	// just the selected packages.
	//
	// In the third case (vanilla merge with no combining or package
	// selection) we can carry over meta-data files without touching them
	// at all (only counter data files will be merged).
	type metaMerge struct {
	calloc.BatchCounterAlloc
	cmerge.Merger
	// maps package import path to package state
	pkm map[string]*pkstate
	// list of packages
	pkgs []*pkstate
	// current package state
	p *pkstate
	// current pod state
	pod *podstate
	// counter data file osargs/goos/goarch state
	astate *argstate
	}

	// pkstate
	type pkstate struct {
	// index of package within meta-data file.
	pkgIdx uint32
	// this maps function index within the package to counter data payload
	ctab map[uint32]decodecounter.FuncPayload
	// pointer to meta-data blob for package
	mdblob []byte
	// filled in only for -pcombine merges
	*pcombinestate
	}

	type podstate struct {
	pmm map[pkfunc]decodecounter.FuncPayload
	mdf string
	mfr *decodemeta.CoverageMetaFileReader
	fileHash [16]byte
	}

	type pkfunc struct {
	pk, fcn uint32
	}

	// pcombinestate
	type pcombinestate struct {
	// Meta-data builder for the package.
	cmdb *encodemeta.CoverageMetaDataBuilder
	// Maps function meta-data hash to new function index in the
	// new version of the package we're building.
	ftab map[[16]byte]uint32
	}

	func newMetaMerge() *metaMerge {
	return &metaMerge{
	pkm: make(map[string]*pkstate),
	astate: &argstate{},
	}
	}

	func (mm metaMerge) visitMetaDataFile(mdf string, mfr decodemeta.CoverageMetaFileReader) {
	dbgtrace(2, "visitMetaDataFile(mdf=%s)", mdf)

	// Record meta-data file name.
	mm.pod.mdf = mdf
	// Keep a pointer to the file-level reader.
	mm.pod.mfr = mfr
	// Record file hash.
	mm.pod.fileHash = mfr.FileHash()
	// Counter mode and granularity -- detect and record clashes here.
	newgran := mfr.CounterGranularity()
	newmode := mfr.CounterMode()
	if err := mm.SetModeAndGranularity(mdf, newmode, newgran); err != nil {
	fatal("%v", err)
	}
	}

	func (mm metaMerge) beginCounterDataFile(cdr decodecounter.CounterDataReader) {
	state := argvalues{
	osargs: cdr.OsArgs(),
	goos: cdr.Goos(),
	goarch: cdr.Goarch(),
	}
	mm.astate.Merge(state)
	}

	func copyMetaDataFile(inpath, outpath string) {
	inf, err := os.Open(inpath)
	if err != nil {
	fatal("opening input meta-data file %s: %v", inpath, err)
	}
	defer inf.Close()

	fi, err := inf.Stat()
	if err != nil {
	fatal("accessing input meta-data file %s: %v", inpath, err)
	}

	outf, err := os.OpenFile(outpath, os.O_WRONLY\|os.O_CREATE\|os.O_TRUNC, fi.Mode())
	if err != nil {
	fatal("opening output meta-data file %s: %v", outpath, err)
	}

	_, err = io.Copy(outf, inf)
	outf.Close()
	if err != nil {
	fatal("writing output meta-data file %s: %v", outpath, err)
	}
	}

	func (mm *metaMerge) beginPod() {
	mm.pod = &podstate{
	pmm: make(map[pkfunc]decodecounter.FuncPayload),
	}
	}

	// metaEndPod handles actions needed when we're done visiting all of
	// the things in a pod -- counter files and meta-data file. There are
	// three cases of interest here:
	//
	// Case 1: in an unconditional merge (we're not selecting a specific set of
	// packages using "-pkg", and the "-pcombine" option is not in use),
	// we can simply copy over the meta-data file from input to output.
	//
	// Case 2: if this is a select merge (-pkg is in effect), then at
	// this point we write out a new smaller meta-data file that includes
	// only the packages of interest. At this point we also emit a merged
	// counter data file as well.
	//
	// Case 3: if "-pcombine" is in effect, we don't write anything at
	// this point (all writes will happen at the end of the run).
	func (mm *metaMerge) endPod(pcombine bool) {
	if pcombine {
	// Just clear out the pod data, we'll do all the
	// heavy lifting at the end.
	mm.pod = nil
	return
	}

	finalHash := mm.pod.fileHash
	if matchpkg != nil {
	// Emit modified meta-data file for this pod.
	finalHash = mm.emitMeta(*outdirflag, pcombine)
	} else {
	// Copy meta-data file for this pod to the output directory.
	inpath := mm.pod.mdf
	mdfbase := filepath.Base(mm.pod.mdf)
	outpath := filepath.Join(*outdirflag, mdfbase)
	copyMetaDataFile(inpath, outpath)
	}

	// Emit accumulated counter data for this pod.
	mm.emitCounters(*outdirflag, finalHash)

	// Reset package state.
	mm.pkm = make(map[string]*pkstate)
	mm.pkgs = nil
	mm.pod = nil

	// Reset counter mode and granularity
	mm.ResetModeAndGranularity()
	}

	// emitMeta encodes and writes out a new coverage meta-data file as
	// part of a merge operation, specifically a merge with the
	// "-pcombine" flag.
	func (mm *metaMerge) emitMeta(outdir string, pcombine bool) [16]byte {
	fh := md5.New()
	blobs := [][]byte{}
	tlen := uint64(unsafe.Sizeof(coverage.MetaFileHeader{}))
	for _, p := range mm.pkgs {
	var blob []byte
	if pcombine {
	mdw := &slicewriter.WriteSeeker{}
	p.cmdb.Emit(mdw)
	blob = mdw.BytesWritten()
	} else {
	blob = p.mdblob
	}
	ph := md5.Sum(blob)
	blobs = append(blobs, blob)
	if _, err := fh.Write(ph[:]); err != nil {
	panic(fmt.Sprintf("internal error: md5 sum failed: %v", err))
	}
	tlen += uint64(len(blob))
	}
	var finalHash [16]byte
	fhh := fh.Sum(nil)
	copy(finalHash[:], fhh)

	// Open meta-file for writing.
	fn := fmt.Sprintf("%s.%x", coverage.MetaFilePref, finalHash)
	fpath := filepath.Join(outdir, fn)
	mf, err := os.OpenFile(fpath, os.O_WRONLY\|os.O_CREATE\|os.O_TRUNC, 0666)
	if err != nil {
	fatal("unable to open output meta-data file %s: %v", fpath, err)
	}

	// Encode and write.
	mfw := encodemeta.NewCoverageMetaFileWriter(fpath, mf)
	err = mfw.Write(finalHash, blobs, mm.Mode(), mm.Granularity())
	if err != nil {
	fatal("error writing %s: %v\n", fpath, err)
	}
	return finalHash
	}

	func (mm *metaMerge) emitCounters(outdir string, metaHash [16]byte) {
	// Open output file. The file naming scheme is intended to mimic
	// that used when running a coverage-instrumented binary, for
	// consistency (however the process ID is not meaningful here, so
	// use a value of zero).
	var dummyPID int
	fn := fmt.Sprintf(coverage.CounterFileTempl, coverage.CounterFilePref, metaHash, dummyPID, time.Now().UnixNano())
	fpath := filepath.Join(outdir, fn)
	cf, err := os.OpenFile(fpath, os.O_WRONLY\|os.O_CREATE\|os.O_TRUNC, 0666)
	if err != nil {
	fatal("opening counter data file %s: %v", fpath, err)
	}
	defer func() {
	if err := cf.Close(); err != nil {
	fatal("error closing output meta-data file %s: %v", fpath, err)
	}
	}()

	args := mm.astate.ArgsSummary()
	cfw := encodecounter.NewCoverageDataWriter(cf, coverage.CtrULeb128)
	if err := cfw.Write(metaHash, args, mm); err != nil {
	fatal("counter file write failed: %v", err)
	}
	mm.astate = &argstate{}
	}

	// VisitFuncs is used while writing the counter data files; it
	// implements the 'VisitFuncs' method required by the interface
	// internal/coverage/encodecounter/CounterVisitor.
	func (mm *metaMerge) VisitFuncs(f encodecounter.CounterVisitorFn) error {
	if *verbflag >= 4 {
	fmt.Printf("counterVisitor invoked\n")
	}
	// For each package, for each function, construct counter
	// array and then call "f" on it.
	for pidx, p := range mm.pkgs {
	fids := make([]int, 0, len(p.ctab))
	for fid := range p.ctab {
	fids = append(fids, int(fid))
	}
	sort.Ints(fids)
	if *verbflag >= 4 {
	fmt.Printf("fids for pk=%d: %+v\n", pidx, fids)
	}
	for _, fid := range fids {
	fp := p.ctab[uint32(fid)]
	if *verbflag >= 4 {
	fmt.Printf("counter write for pk=%d fid=%d len(ctrs)=%d\n", pidx, fid, len(fp.Counters))
	}
	if err := f(uint32(pidx), uint32(fid), fp.Counters); err != nil {
	return err
	}
	}
	}
	return nil
	}

	func (mm metaMerge) visitPackage(pd decodemeta.CoverageMetaDataDecoder, pkgIdx uint32, pcombine bool) {
	p, ok := mm.pkm[pd.PackagePath()]
	if !ok {
	p = &pkstate{
	pkgIdx: uint32(len(mm.pkgs)),
	}
	mm.pkgs = append(mm.pkgs, p)
	mm.pkm[pd.PackagePath()] = p
	if pcombine {
	p.pcombinestate = new(pcombinestate)
	cmdb, err := encodemeta.NewCoverageMetaDataBuilder(pd.PackagePath(), pd.PackageName(), pd.ModulePath())
	if err != nil {
	fatal("fatal error creating meta-data builder: %v", err)
	}
	dbgtrace(2, "install new pkm entry for package %s pk=%d", pd.PackagePath(), pkgIdx)
	p.cmdb = cmdb
	p.ftab = make(map[[16]byte]uint32)
	} else {
	var err error
	p.mdblob, err = mm.pod.mfr.GetPackagePayload(pkgIdx, nil)
	if err != nil {
	fatal("error extracting package %d payload from %s: %v",
	pkgIdx, mm.pod.mdf, err)
	}
	}
	p.ctab = make(map[uint32]decodecounter.FuncPayload)
	}
	mm.p = p
	}

	func (mm *metaMerge) visitFuncCounterData(data decodecounter.FuncPayload) {
	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) {
	t := val.Counters
	val.Counters = mm.AllocateCounters(len(data.Counters))
	copy(val.Counters, t)
	}
	err, overflow := mm.MergeCounters(val.Counters, data.Counters)
	if err != nil {
	fatal("%v", err)
	}
	if overflow {
	warn("uint32 overflow during counter merge")
	}
	mm.pod.pmm[key] = val
	}

	func (mm metaMerge) visitFunc(pkgIdx uint32, fnIdx uint32, fd coverage.FuncDesc, verb string, pcombine bool) {
	if *verbflag >= 3 {
	fmt.Printf("visit pk=%d fid=%d func %s\n", pkgIdx, fnIdx, fd.Funcname)
	}

	var counters []uint32
	key := pkfunc{pk: pkgIdx, fcn: fnIdx}
	v, haveCounters := mm.pod.pmm[key]
	if haveCounters {
	counters = v.Counters
	}

	if pcombine {
	// If the merge is running in "combine programs" mode, then hash
	// the function and look it up in the package ftab to see if we've
	// encountered it before. If we haven't, then register it with the
	// meta-data builder.
	fnhash := encodemeta.HashFuncDesc(fd)
	gfidx, ok := mm.p.ftab[fnhash]
	if !ok {
	// We haven't seen this function before, need to add it to
	// the meta data.
	gfidx = uint32(mm.p.cmdb.AddFunc(*fd))
	mm.p.ftab[fnhash] = gfidx
	if *verbflag >= 3 {
	fmt.Printf("new meta entry for fn %s fid=%d\n", fd.Funcname, gfidx)
	}
	}
	fnIdx = gfidx
	}
	if !haveCounters {
	return
	}

	// Install counters in package ctab.
	gfp, ok := mm.p.ctab[fnIdx]
	if ok {
	if verb == "subtract" \|\| verb == "intersect" {
	panic("should never see this for intersect/subtract")
	}
	if *verbflag >= 3 {
	fmt.Printf("counter merge for %s fidx=%d\n", fd.Funcname, fnIdx)
	}
	// Merge.
	err, overflow := mm.MergeCounters(gfp.Counters, counters)
	if err != nil {
	fatal("%v", err)
	}
	if overflow {
	warn("uint32 overflow during counter merge")
	}
	mm.p.ctab[fnIdx] = gfp
	} else {
	if *verbflag >= 3 {
	fmt.Printf("null merge for %s fidx %d\n", fd.Funcname, fnIdx)
	}
	gfp := v
	gfp.PkgIdx = mm.p.pkgIdx
	gfp.FuncIdx = fnIdx
	mm.p.ctab[fnIdx] = gfp
	}
	}