pkg/cover, syz-manager: introduce the /cover?debug=1 parameter

Debugging coverage point validation warnings may require looking at
specific addresses, which are not printed anywhere. Add a URL parameter
that can be passed to prepareFileMap() to print a more meaningful error
message.

Also factor out the error message code from prepareFileMap() to reduce
its cyclomatic complexity.

3 files changed, 44 insertions, 24 deletions

diff --git a/pkg/cover/html.go b/pkg/cover/html.go
index bbfc11536..8cb9e7511 100644
--- a/pkg/cover/html.go
+++ b/pkg/cover/html.go
@@ -24,9 +24,15 @@ import (
 	"github.com/google/syzkaller/pkg/mgrconfig"
 )
 
-func (rg *ReportGenerator) DoHTML(w io.Writer, progs []Prog, coverFilter map[uint32]uint32) error {
-	progs = fixUpPCs(rg.target.Arch, progs, coverFilter)
-	files, err := rg.prepareFileMap(progs)
+type CoverHandlerParams struct {
+	Progs       []Prog
+	CoverFilter map[uint32]uint32
+	Debug       bool
+}
+
+func (rg *ReportGenerator) DoHTML(w io.Writer, params CoverHandlerParams) error {
+	var progs = fixUpPCs(rg.target.Arch, params.Progs, params.CoverFilter)
+	files, err := rg.prepareFileMap(progs, params.Debug)
 	if err != nil {
 		return err
 	}
@@ -127,9 +133,9 @@ type lineCoverExport struct {
 	Both      []int `json:",omitempty"`
 }
 
-func (rg *ReportGenerator) DoLineJSON(w io.Writer, progs []Prog, coverFilter map[uint32]uint32) error {
-	progs = fixUpPCs(rg.target.Arch, progs, coverFilter)
-	files, err := rg.prepareFileMap(progs)
+func (rg *ReportGenerator) DoLineJSON(w io.Writer, params CoverHandlerParams) error {
+	var progs = fixUpPCs(rg.target.Arch, params.Progs, params.CoverFilter)
+	files, err := rg.prepareFileMap(progs, params.Debug)
 	if err != nil {
 		return err
 	}
@@ -291,7 +297,7 @@ var csvFilesHeader = []string{
 }
 
 func (rg *ReportGenerator) convertToStats(progs []Prog) ([]fileStats, error) {
-	files, err := rg.prepareFileMap(progs)
+	files, err := rg.prepareFileMap(progs, false)
 	if err != nil {
 		return nil, err
 	}
@@ -341,8 +347,8 @@ func (rg *ReportGenerator) convertToStats(progs []Prog) ([]fileStats, error) {
 	return data, nil
 }
 
-func (rg *ReportGenerator) DoCSVFiles(w io.Writer, progs []Prog, coverFilter map[uint32]uint32) error {
-	progs = fixUpPCs(rg.target.Arch, progs, coverFilter)
+func (rg *ReportGenerator) DoCSVFiles(w io.Writer, params CoverHandlerParams) error {
+	var progs = fixUpPCs(rg.target.Arch, params.Progs, params.CoverFilter)
 	data, err := rg.convertToStats(progs)
 	if err != nil {
 		return err
@@ -441,8 +447,8 @@ func groupCoverByFilePrefixes(datas []fileStats, subsystems []mgrconfig.Subsyste
 	return d
 }
 
-func (rg *ReportGenerator) DoHTMLTable(w io.Writer, progs []Prog, coverFilter map[uint32]uint32) error {
-	progs = fixUpPCs(rg.target.Arch, progs, coverFilter)
+func (rg *ReportGenerator) DoHTMLTable(w io.Writer, params CoverHandlerParams) error {
+	var progs = fixUpPCs(rg.target.Arch, params.Progs, params.CoverFilter)
 	data, err := rg.convertToStats(progs)
 	if err != nil {
 		return err
@@ -517,8 +523,8 @@ func groupCoverByModule(datas []fileStats) map[string]map[string]string {
 	return d
 }
 
-func (rg *ReportGenerator) DoModuleCover(w io.Writer, progs []Prog, coverFilter map[uint32]uint32) error {
-	progs = fixUpPCs(rg.target.Arch, progs, coverFilter)
+func (rg *ReportGenerator) DoModuleCover(w io.Writer, params CoverHandlerParams) error {
+	var progs = fixUpPCs(rg.target.Arch, params.Progs, params.CoverFilter)
 	data, err := rg.convertToStats(progs)
 	if err != nil {
 		return err
@@ -537,9 +543,9 @@ var csvHeader = []string{
 	"Total PCs",
 }
 
-func (rg *ReportGenerator) DoCSV(w io.Writer, progs []Prog, coverFilter map[uint32]uint32) error {
-	progs = fixUpPCs(rg.target.Arch, progs, coverFilter)
-	files, err := rg.prepareFileMap(progs)
+func (rg *ReportGenerator) DoCSV(w io.Writer, params CoverHandlerParams) error {
+	var progs = fixUpPCs(rg.target.Arch, params.Progs, params.CoverFilter)
+	files, err := rg.prepareFileMap(progs, params.Debug)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/cover/report.go b/pkg/cover/report.go
index 6bf7e0a6f..9d03811ad 100644
--- a/pkg/cover/report.go
+++ b/pkg/cover/report.go
@@ -74,7 +74,20 @@ type line struct {
 	progIndex int          // example program index that covers this line
 }
 
-func (rg *ReportGenerator) prepareFileMap(progs []Prog) (map[string]*file, error) {
+func coverageCallbackMismatch(debug bool, numPCs int, unmatchedProgPCs map[uint64]bool) error {
+	debugStr := ""
+	if debug {
+		debugStr += "\n\nUnmatched PCs:\n"
+		for pc := range unmatchedProgPCs {
+			debugStr += fmt.Sprintf("%x\n", pc)
+		}
+	}
+	// nolint: lll
+	return fmt.Errorf("%d out of %d PCs returned by kcov do not have matching coverage callbacks. Check the discoverModules() code.%s",
+		len(unmatchedProgPCs), numPCs, debugStr)
+}
+
+func (rg *ReportGenerator) prepareFileMap(progs []Prog, debug bool) (map[string]*file, error) {
 	if err := rg.lazySymbolize(progs); err != nil {
 		return nil, err
 	}
@@ -131,9 +144,7 @@ func (rg *ReportGenerator) prepareFileMap(progs []Prog) (map[string]*file, error
 	// If the backend provided coverage callback locations for the binaries, use them to
 	// verify data returned by kcov.
 	if verifyCoverPoints && (len(unmatchedProgPCs) > 0) {
-		return nil, fmt.Errorf("%d out of %d PCs returned by kcov do not have matching "+
-			"coverage callbacks. Check the discoverModules() code",
-			len(unmatchedProgPCs), len(progPCs))
+		return nil, coverageCallbackMismatch(debug, len(progPCs), unmatchedProgPCs)
 	}
 	for _, unit := range rg.Units {
 		f := files[unit.Name]
diff --git a/pkg/cover/report_test.go b/pkg/cover/report_test.go
index c6c9d28f1..3d31841cc 100644
--- a/pkg/cover/report_test.go
+++ b/pkg/cover/report_test.go
@@ -365,20 +365,23 @@ func generateReport(t *testing.T, target *targets.Target, test *Test) ([]byte, [
 		progs = append(progs, Prog{Data: "main", PCs: pcs})
 	}
 	html := new(bytes.Buffer)
-	if err := rg.DoHTML(html, progs, nil); err != nil {
+	params := CoverHandlerParams{
+		Progs: progs,
+	}
+	if err := rg.DoHTML(html, params); err != nil {
 		return nil, nil, err
 	}
 	htmlTable := new(bytes.Buffer)
-	if err := rg.DoHTMLTable(htmlTable, progs, nil); err != nil {
+	if err := rg.DoHTMLTable(htmlTable, params); err != nil {
 		return nil, nil, err
 	}
 	_ = htmlTable
 	csv := new(bytes.Buffer)
-	if err := rg.DoCSV(csv, progs, nil); err != nil {
+	if err := rg.DoCSV(csv, params); err != nil {
 		return nil, nil, err
 	}
 	csvFiles := new(bytes.Buffer)
-	if err := rg.DoCSVFiles(csvFiles, progs, nil); err != nil {
+	if err := rg.DoCSVFiles(csvFiles, params); err != nil {
 		return nil, nil, err
 	}
 	_ = csvFiles