From 1f4c6f0691e12f1b7bed3f859352cc62e61e01ff Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Felix=20Geisend=C3=B6rfer?=
 <felix.geisendoerfer@datadoghq.com>
Date: Tue, 30 Mar 2021 14:51:41 +0200
Subject: [PATCH] wip

---
 examples/pclnttab/darwin.go | 23 ++++++++++++++++
 examples/pclnttab/go.mod    |  3 +++
 examples/pclnttab/linux.go  | 23 ++++++++++++++++
 examples/pclnttab/main.go   | 54 +++++++++++++++++++++++++++++++++++++
 4 files changed, 103 insertions(+)
 create mode 100644 examples/pclnttab/darwin.go
 create mode 100644 examples/pclnttab/go.mod
 create mode 100644 examples/pclnttab/linux.go
 create mode 100644 examples/pclnttab/main.go

diff --git a/examples/pclnttab/darwin.go b/examples/pclnttab/darwin.go
new file mode 100644
index 0000000..b8896db
--- /dev/null
+++ b/examples/pclnttab/darwin.go
@@ -0,0 +1,23 @@
+//+build darwin
+
+package main
+
+import (
+	"debug/macho"
+	"errors"
+	"fmt"
+	"os"
+)
+
+func gopclntab() ([]byte, error) {
+	file, err := macho.Open(os.Args[0])
+	if err != nil {
+		return nil, fmt.Errorf("elf.Open: %w", err)
+	}
+	for _, s := range file.Sections {
+		if s.Name == "__gopclntab" {
+			return s.Data()
+		}
+	}
+	return nil, errors.New("could not find .gopclntab")
+}
diff --git a/examples/pclnttab/go.mod b/examples/pclnttab/go.mod
new file mode 100644
index 0000000..0f9144f
--- /dev/null
+++ b/examples/pclnttab/go.mod
@@ -0,0 +1,3 @@
+module github.com/felixge/go-profiler-notes/examples/pclnttab
+
+go 1.16
diff --git a/examples/pclnttab/linux.go b/examples/pclnttab/linux.go
new file mode 100644
index 0000000..6fd16d0
--- /dev/null
+++ b/examples/pclnttab/linux.go
@@ -0,0 +1,23 @@
+//+build linux
+
+package main
+
+import (
+	"debug/elf"
+	"errors"
+	"fmt"
+	"os"
+)
+
+func gopclntab() ([]byte, error) {
+	file, err := elf.Open(os.Args[0])
+	if err != nil {
+		return nil, fmt.Errorf("elf.Open: %w", err)
+	}
+	for _, s := range file.Sections {
+		if s.Name == ".gopclntab" {
+			return s.Data()
+		}
+	}
+	return nil, errors.New("could not find .gopclntab")
+}
diff --git a/examples/pclnttab/main.go b/examples/pclnttab/main.go
new file mode 100644
index 0000000..60db0fe
--- /dev/null
+++ b/examples/pclnttab/main.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"debug/gosym"
+	"fmt"
+	"os"
+	"runtime"
+)
+
+func main() {
+	if err := run(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func run() error {
+	data, err := gopclntab()
+	if err != nil {
+		return fmt.Errorf("gopclntab: %w", err)
+	}
+	return debugSymtab(data)
+}
+
+type StackTrace struct {
+	Frames []StackFrame
+}
+
+type StackFrame struct {
+	PC       int
+	Function string
+	File     string
+	Line     int
+}
+
+func callers() []uintptr {
+	pcs := make([]uintptr, 32)
+	n := runtime.Callers(2, pcs)
+	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("%s() %s:%d\n", fn.Name, file, line)
+	}
+	return nil
+}