pkg/proc: macho: Enable debugging stripped binaries (#3511)

Load a symbol table from pclntab as when debugging stripped ELF
binaries.

Documentation/backend_test_health.md

@@ -11,13 +11,16 @@ Tests skipped by each supported backend:
 	* 2 broken - cgo stacktraces
 * darwin/lldb skipped = 1
 	* 1 upstream issue
-* freebsd skipped = 6
+* freebsd skipped = 7
 	* 2 flaky
 	* 4 not implemented
-* linux/386/pie skipped = 1
+	* 1 not working on freebsd
+* linux/386/pie skipped = 2
 	* 1 broken
-* linux/ppc64le skipped = 1
+	* 1 not working on linux/386 with PIE
+* linux/ppc64le skipped = 2
 	* 1 broken - cgo stacktraces
+	* 1 not working on linux/ppc64le when -gcflags=-N -l is passed
 * linux/ppc64le/native skipped = 1
 	* 1 broken in linux ppc64le
 * linux/ppc64le/native/pie skipped = 3
@@ -28,8 +31,9 @@ Tests skipped by each supported backend:
 	* 6 broken
 	* 1 broken - global variable symbolication
 	* 4 not implemented
-* windows skipped = 4
+* windows skipped = 5
 	* 1 broken
+	* 1 not working on windows
 	* 3 see https://github.com/go-delve/delve/issues/2768
 * windows/arm64 skipped = 5
 	* 3 broken

pkg/proc/bininfo.go

@@ -1822,9 +1822,27 @@ func loadBinaryInfoMacho(bi *BinaryInfo, image *Image, path string, entryPoint u
 	if !supportedDarwinArch[exe.Cpu] {
 		return &ErrUnsupportedArch{os: "darwin", cpuArch: exe.Cpu}
 	}
-	image.dwarf, err = exe.DWARF()
-	if err != nil {
-		return err
+	var dwerr error
+	image.dwarf, dwerr = exe.DWARF()
+	if dwerr != nil {
+		if len(bi.Images) <= 1 {
+			fmt.Fprintln(os.Stderr, "Warning: no debug info found, some functionality will be missing such as stack traces and variable evaluation.")
+		}
+		symTable, err := readPcLnTableMacho(exe, path)
+		if err != nil {
+			return fmt.Errorf("could not read debug info (%v) and could not read go symbol table (%v)", dwerr, err)
+		}
+		image.symTable = symTable
+		for _, f := range image.symTable.Funcs {
+			cu := &compileUnit{}
+			cu.image = image
+			fn := Function{Name: f.Name, Entry: f.Entry + image.StaticBase, End: f.End + image.StaticBase, cu: cu}
+			bi.Functions = append(bi.Functions, fn)
+		}
+		for f := range image.symTable.Files {
+			bi.Sources = append(bi.Sources, f)
+		}
+		return nil
 	}
 	debugInfoBytes, err := godwarf.GetDebugSectionMacho(exe, "info")
 	if err != nil {

pkg/proc/pclntab.go

@@ -3,6 +3,7 @@ package proc
 import (
 	"debug/elf"
 	"debug/gosym"
+	"debug/macho"
 	"fmt"
 )
 
@@ -32,3 +33,25 @@ func readPcLnTableElf(exe *elf.File, path string) (*gosym.Table, error) {
 	}
 	return symTable, nil
 }
+
+func readPcLnTableMacho(exe *macho.File, path string) (*gosym.Table, error) {
+	// Default section label is __gopclntab
+	sectionLabel := "__gopclntab"
+
+	section := exe.Section(sectionLabel)
+	if section == nil {
+		return nil, fmt.Errorf("could not read section __gopclntab")
+	}
+	tableData, err := section.Data()
+	if err != nil {
+		return nil, fmt.Errorf("found section but could not read __gopclntab")
+	}
+
+	addr := exe.Section("__text").Addr
+	lineTable := gosym.NewLineTable(tableData, addr)
+	symTable, err := gosym.NewTable([]byte{}, lineTable)
+	if err != nil {
+		return nil, fmt.Errorf("could not create symbol table from  %s ", path)
+	}
+	return symTable, nil
+}

pkg/proc/proc_test.go

@@ -2331,7 +2331,7 @@ func TestStepCallPtr(t *testing.T) {
 			{6, 7},
 			{7, 11}}, "", t)
 	} else {
-		if runtime.GOOS == "linux" && runtime.GOARCH == "ppc64le" && buildMode == "pie"  {
+		if runtime.GOOS == "linux" && runtime.GOARCH == "ppc64le" && buildMode == "pie" {
 			testseq("teststepprog", contStep, []nextTest{
 				{9, 10},
 				{10, 5},
@@ -3179,8 +3179,9 @@ func TestShadowedFlag(t *testing.T) {
 
 func TestDebugStripped(t *testing.T) {
 	// Currently only implemented for Linux ELF executables.
-	// TODO(derekparker): Add support for Mach-O and PE.
-	skipUnlessOn(t, "linux only", "linux")
+	// TODO(derekparker): Add support for PE.
+	skipOn(t, "not working on windows", "windows")
+	skipOn(t, "not working on freebsd", "freebsd")
 	skipOn(t, "not working on linux/386 with PIE", "linux", "386", "pie")
 	skipOn(t, "not working on linux/ppc64le when -gcflags=-N -l is passed", "linux", "ppc64le")
 	withTestProcessArgs("testnextprog", t, "", []string{}, protest.LinkStrip, func(p *proc.Target, grp *proc.TargetGroup, f protest.Fixture) {