cmd/nm: windows pe handling fixes

- output absolute addresses, not relative;
- accept negative section numbers.

Update #6936
Fixes #7738

LGTM=rsc
R=golang-codereviews, bradfitz, ruiu, rsc
CC=golang-codereviews
https://golang.org/cl/85240046

src/cmd/nm/doc.go

@@ -19,6 +19,7 @@
 //	d	static data segment symbol
 //	B	bss segment symbol
 //	b	static bss segment symbol
+//	C	constant address
 //	U	referenced but undefined symbol
 //
 // Following established convention, the address is omitted for undefined

src/cmd/nm/nm_test.go

@@ -0,0 +1,40 @@
+// Copyright 2014 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
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+func TestNM(t *testing.T) {
+	out, err := exec.Command("go", "build", "-o", "testnm.exe", "cmd/nm").CombinedOutput()
+	if err != nil {
+		t.Fatalf("go build -o testnm.exe cmd/nm: %v\n%s", err, string(out))
+	}
+	defer os.Remove("testnm.exe")
+
+	testfiles := []string{
+		"elf/testdata/gcc-386-freebsd-exec",
+		"elf/testdata/gcc-amd64-linux-exec",
+		"macho/testdata/gcc-386-darwin-exec",
+		"macho/testdata/gcc-amd64-darwin-exec",
+		"pe/testdata/gcc-amd64-mingw-exec",
+		"pe/testdata/gcc-386-mingw-exec",
+		"plan9obj/testdata/amd64-plan9-exec",
+		"plan9obj/testdata/386-plan9-exec",
+	}
+	for _, f := range testfiles {
+		exepath := filepath.Join(runtime.GOROOT(), "src", "pkg", "debug", f)
+		cmd := exec.Command("./testnm.exe", exepath)
+		out, err := cmd.CombinedOutput()
+		if err != nil {
+			t.Fatalf("go tool nm %v: %v\n%s", exepath, err, string(out))
+		}
+	}
+}

src/cmd/nm/pe.go

@@ -18,12 +18,41 @@ func peSymbols(f *os.File) []Sym {
 		return nil
 	}
 
+	var imageBase uint64
+	switch oh := p.OptionalHeader.(type) {
+	case *pe.OptionalHeader32:
+		imageBase = uint64(oh.ImageBase)
+	case *pe.OptionalHeader64:
+		imageBase = oh.ImageBase
+	default:
+		errorf("parsing %s: file format not recognized", f.Name())
+		return nil
+	}
+
 	var syms []Sym
 	for _, s := range p.Symbols {
+		const (
+			N_UNDEF = 0  // An undefined (extern) symbol
+			N_ABS   = -1 // An absolute symbol (e_value is a constant, not an address)
+			N_DEBUG = -2 // A debugging symbol
+		)
 		sym := Sym{Name: s.Name, Addr: uint64(s.Value), Code: '?'}
-		if s.SectionNumber == 0 {
+		switch s.SectionNumber {
+		case N_UNDEF:
 			sym.Code = 'U'
-		} else if int(s.SectionNumber) <= len(p.Sections) {
+		case N_ABS:
+			sym.Code = 'C'
+		case N_DEBUG:
+			sym.Code = '?'
+		default:
+			if s.SectionNumber < 0 {
+				errorf("parsing %s: invalid section number %d", f.Name(), s.SectionNumber)
+				return nil
+			}
+			if len(p.Sections) < int(s.SectionNumber) {
+				errorf("parsing %s: section number %d is large then max %d", f.Name(), s.SectionNumber, len(p.Sections))
+				return nil
+			}
 			sect := p.Sections[s.SectionNumber-1]
 			const (
 				text  = 0x20
@@ -46,6 +75,7 @@ func peSymbols(f *os.File) []Sym {
 			case ch&bss != 0:
 				sym.Code = 'B'
 			}
+			sym.Addr += imageBase + uint64(sect.VirtualAddress)
 		}
 		syms = append(syms, sym)
 	}