fix pclntab example

examples/pclnttab/darwin.go

@@ -1,23 +1,37 @@
-//+build darwin
+//go:build darwin
+// +build darwin
 
 package main
 
 import (
+	"debug/gosym"
 	"debug/macho"
-	"errors"
-	"fmt"
 	"os"
 )
 
-func gopclntab() ([]byte, error) {
-	file, err := macho.Open(os.Args[0])
+// from https://github.com/lizrice/debugger-from-scratch/blob/master/symbols.go
+func goSymTable() (*gosym.Table, error) {
+	exe, err := macho.Open(os.Args[0])
 	if err != nil {
-		return nil, fmt.Errorf("elf.Open: %w", err)
+		return nil, nil
 	}
-	for _, s := range file.Sections {
-		if s.Name == "__gopclntab" {
-			return s.Data()
-		}
+	defer exe.Close()
+
+	addr := exe.Section("__text").Addr
+
+	lineTableData, err := exe.Section("__gopclntab").Data()
+	if err != nil {
+		return nil, nil
 	}
-	return nil, errors.New("could not find .gopclntab")
+	lineTable := gosym.NewLineTable(lineTableData, addr)
+	if err != nil {
+		return nil, nil
+	}
+
+	symTableData, err := exe.Section("__gosymtab").Data()
+	if err != nil {
+		return nil, nil
+	}
+
+	return gosym.NewTable(symTableData, lineTable)
 }

examples/pclnttab/linux.go

@@ -1,4 +1,5 @@
-//+build linux
+//go:build linux
+// +build linux
 
 package main
 
@@ -9,15 +10,29 @@ import (
 	"os"
 )
 
-func gopclntab() ([]byte, error) {
-	file, err := elf.Open(os.Args[0])
+// from https://github.com/lizrice/debugger-from-scratch/blob/master/symbols.go
+func goSymTable() (*gosym.Table, error) {
+	exe, err := elf.Open(os.Args[0])
 	if err != nil {
-		return nil, fmt.Errorf("elf.Open: %w", err)
+		return nil, nil
 	}
-	for _, s := range file.Sections {
-		if s.Name == ".gopclntab" {
-			return s.Data()
-		}
+	defer exe.Close()
+
+	addr := exe.Section(".text").Addr
+
+	lineTableData, err := exe.Section(".gopclntab").Data()
+	if err != nil {
+		return nil, nil
 	}
-	return nil, errors.New("could not find .gopclntab")
+	lineTable := gosym.NewLineTable(lineTableData, addr)
+	if err != nil {
+		return nil, nil
+	}
+
+	symTableData, err := exe.Section(".gosymtab").Data()
+	if err != nil {
+		return nil, nil
+	}
+
+	return gosym.NewTable(symTableData, lineTable)
 }

examples/pclnttab/main.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"debug/gosym"
 	"fmt"
 	"os"
 	"runtime"
@@ -15,22 +14,15 @@ func main() {
 }
 
 func run() error {
-	data, err := gopclntab()
+	symTable, err := goSymTable()
 	if err != nil {
-		return fmt.Errorf("gopclntab: %w", err)
+		return err
 	}
-	return debugSymtab(data)
-}
-
-type StackTrace struct {
-	Frames []StackFrame
-}
-
-type StackFrame struct {
-	PC       int
-	Function string
-	File     string
-	Line     int
+	for _, pc := range callers() {
+		file, line, fn := symTable.PCToLine(uint64(pc))
+		fmt.Printf("%x: %s() %s:%d\n", pc, fn.Name, file, line)
+	}
+	return nil
 }
 
 func callers() []uintptr {
@@ -39,16 +31,3 @@ func callers() []uintptr {
 	pcs = pcs[0:n]
 	return pcs
 }
-
-func debugSymtab(gopclntab []byte) error {
-	table, err := gosym.NewTable(nil, gosym.NewLineTable(gopclntab, 0))
-	if err != nil {
-		return fmt.Errorf("gosym.NewTable: %w", err)
-	}
-
-	for _, pc := range callers() {
-		file, line, fn := table.PCToLine(uint64(pc))
-		fmt.Printf("%x: %s() %s:%d\n", pc, fn.Name, file, line)
-	}
-	return nil
-}