debug/elf: add (*File).DynamicSymbols, ErrNoSymbols, and tests for…

debug/elf: add (*File).DynamicSymbols, ErrNoSymbols, and tests for (*File).Symbols and (*File).DynamicSymbols, and formalize symbol order.

Added a complement to (*File).Symbols for the dynamic symbol table.
Would be useful, for instance, if seraching for certain shared objects
compatible with certain libraries (for instance, LADSPA requires an
exported symbol "ladspa_descriptor").

Added a variable ErrNoSymbols that canonicalizes a return from
(*File).Symbols and (*File).DyanmicSymbols if the file has no symbols.

Added tests for both (*File).Symbols and (*File).DynamicSymbols;
there was never a test for (*File).Symbols at all. A small C program using
libelf, included in the test data, was used to produce the golden
symbols to compare against.

As part of the requirements for testing, (*File).Symbols and (*File).DynamicSymbols now document the order in which the symbol tables are returned (in the order the symbols appear in the file).

All tests currently pass.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/107530043

src/pkg/debug/elf/file.go

@@ -405,10 +405,14 @@ func (f *File) getSymbols(typ SectionType) ([]Symbol, []byte, error) {
 	return nil, nil, errors.New("not implemented")
 }
 
+// ErrNoSymbols is returned by File.Symbols and File.DynamicSymbols
+// if there is no such section in the File.
+var ErrNoSymbols = errors.New("no symbol section")
+
 func (f *File) getSymbols32(typ SectionType) ([]Symbol, []byte, error) {
 	symtabSection := f.SectionByType(typ)
 	if symtabSection == nil {
-		return nil, nil, errors.New("no symbol section")
+		return nil, nil, ErrNoSymbols
 	}
 
 	data, err := symtabSection.Data()
@@ -451,7 +455,7 @@ func (f *File) getSymbols32(typ SectionType) ([]Symbol, []byte, error) {
 func (f *File) getSymbols64(typ SectionType) ([]Symbol, []byte, error) {
 	symtabSection := f.SectionByType(typ)
 	if symtabSection == nil {
-		return nil, nil, errors.New("no symbol section")
+		return nil, nil, ErrNoSymbols
 	}
 
 	data, err := symtabSection.Data()
@@ -698,7 +702,8 @@ func (f *File) DWARF() (*dwarf.Data, error) {
 	return d, nil
 }
 
-// Symbols returns the symbol table for f.
+// Symbols returns the symbol table for f. The symbols will be listed in the order
+// they appear in f.
 //
 // For compatibility with Go 1.0, Symbols omits the null symbol at index 0.
 // After retrieving the symbols as symtab, an externally supplied index x
@@ -708,6 +713,17 @@ func (f *File) Symbols() ([]Symbol, error) {
 	return sym, err
 }
 
+// DynamicSymbols returns the dynamic symbol table for f. The symbols
+// will be listed in the order they appear in f.
+//
+// For compatibility with Symbols, DynamicSymbols omits the null symbol at index 0.
+// After retrieving the symbols as symtab, an externally supplied index x
+// corresponds to symtab[x-1], not symtab[x].
+func (f *File) DynamicSymbols() ([]Symbol, error) {
+	sym, _, err := f.getSymbols(SHT_DYNSYM)
+	return sym, err
+}
+
 type ImportedSymbol struct {
 	Name    string
 	Version string

src/pkg/debug/elf/symbols_test.go

+// 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 elf
+
+import (
+	"io"
+	"path"
+	"reflect"
+	"testing"
+)
+
+// TODO: remove duplicate code
+func TestSymbols(t *testing.T) {
+	do := func(file string, ts []Symbol, getfunc func(*File) ([]Symbol, error)) {
+		var f *File
+		var err error
+		if path.Ext(file) == ".gz" {
+			var r io.ReaderAt
+			if r, err = decompress(file); err == nil {
+				f, err = NewFile(r)
+			}
+		} else {
+			f, err = Open(file)
+		}
+		if err != nil {
+			t.Errorf("TestSymbols: cannot open file %s: %v", file, err)
+			return
+		}
+		defer f.Close()
+		fs, err := getfunc(f)
+		if err != nil && err != ErrNoSymbols {
+			t.Error(err)
+			return
+		} else if err == ErrNoSymbols {
+			fs = []Symbol{}
+		}
+		if !reflect.DeepEqual(ts, fs) {
+			t.Errorf("%s: Symbols = %v, want %v", file, ts, fs)
+		}
+	}
+	for file, ts := range symbolsGolden {
+		do(file, ts, (*File).Symbols)
+	}
+	for file, ts := range dynamicSymbolsGolden {
+		do(file, ts, (*File).DynamicSymbols)
+	}
+}
+
+// golden symbol table data generated by testdata/getgoldsym.c
+
+var symbolsGolden = map[string][]Symbol{
+	"testdata/gcc-amd64-linux-exec": {
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1,
+			Value:   0x400200,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x2,
+			Value:   0x40021C,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x3,
+			Value:   0x400240,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x4,
+			Value:   0x400268,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x5,
+			Value:   0x400288,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x6,
+			Value:   0x4002E8,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x7,
+			Value:   0x400326,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x8,
+			Value:   0x400330,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x9,
+			Value:   0x400350,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xA,
+			Value:   0x400368,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xB,
+			Value:   0x400398,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x4003B0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x4003E0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xE,
+			Value:   0x400594,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xF,
+			Value:   0x4005A4,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x10,
+			Value:   0x4005B8,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x11,
+			Value:   0x4005E0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x12,
+			Value:   0x600688,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x13,
+			Value:   0x600698,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x14,
+			Value:   0x6006A8,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x15,
+			Value:   0x6006B0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x16,
+			Value:   0x600850,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x17,
+			Value:   0x600858,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x18,
+			Value:   0x600880,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x19,
+			Value:   0x600898,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1A,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1B,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1C,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1D,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1E,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1F,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x20,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x21,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "init.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "initfini.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "call_gmon_start",
+			Info:    0x2,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x40040C,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "crtstuff.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__CTOR_LIST__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x12,
+			Value:   0x600688,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__DTOR_LIST__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x13,
+			Value:   0x600698,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__JCR_LIST__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x14,
+			Value:   0x6006A8,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__do_global_dtors_aux",
+			Info:    0x2,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x400430,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "completed.6183",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x19,
+			Value:   0x600898,
+			Size:    0x1,
+		},
+		Symbol{
+			Name:    "p.6181",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x18,
+			Value:   0x600890,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "frame_dummy",
+			Info:    0x2,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x400470,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "crtstuff.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__CTOR_END__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x12,
+			Value:   0x600690,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__DTOR_END__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x13,
+			Value:   0x6006A0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__FRAME_END__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x11,
+			Value:   0x400680,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__JCR_END__",
+			Info:    0x1,
+			Other:   0x0,
+			Section: 0x14,
+			Value:   0x6006A8,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__do_global_ctors_aux",
+			Info:    0x2,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x400560,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "initfini.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "hello.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "_GLOBAL_OFFSET_TABLE_",
+			Info:    0x1,
+			Other:   0x2,
+			Section: 0x17,
+			Value:   0x600858,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__init_array_end",
+			Info:    0x0,
+			Other:   0x2,
+			Section: 0x12,
+			Value:   0x600684,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__init_array_start",
+			Info:    0x0,
+			Other:   0x2,
+			Section: 0x12,
+			Value:   0x600684,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "_DYNAMIC",
+			Info:    0x1,
+			Other:   0x2,
+			Section: 0x15,
+			Value:   0x6006B0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "data_start",
+			Info:    0x20,
+			Other:   0x0,
+			Section: 0x18,
+			Value:   0x600880,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__libc_csu_fini",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x4004C0,
+			Size:    0x2,
+		},
+		Symbol{
+			Name:    "_start",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x4003E0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__gmon_start__",
+			Info:    0x20,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "_Jv_RegisterClasses",
+			Info:    0x20,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "puts@@GLIBC_2.2.5",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x18C,
+		},
+		Symbol{
+			Name:    "_fini",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0xE,
+			Value:   0x400594,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__libc_start_main@@GLIBC_2.2.5",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x1C2,
+		},
+		Symbol{
+			Name:    "_IO_stdin_used",
+			Info:    0x11,
+			Other:   0x0,
+			Section: 0xF,
+			Value:   0x4005A4,
+			Size:    0x4,
+		},
+		Symbol{
+			Name:    "__data_start",
+			Info:    0x10,
+			Other:   0x0,
+			Section: 0x18,
+			Value:   0x600880,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__dso_handle",
+			Info:    0x11,
+			Other:   0x2,
+			Section: 0x18,
+			Value:   0x600888,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "__libc_csu_init",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x4004D0,
+			Size:    0x89,
+		},
+		Symbol{
+			Name:    "__bss_start",
+			Info:    0x10,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x600898,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "_end",
+			Info:    0x10,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x6008A0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "_edata",
+			Info:    0x10,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x600898,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "main",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x400498,
+			Size:    0x1B,
+		},
+		Symbol{
+			Name:    "_init",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0xB,
+			Value:   0x400398,
+			Size:    0x0,
+		},
+	},
+	"testdata/go-relocation-test-clang-x86.obj": {
+		Symbol{
+			Name:    "go-relocation-test-clang.c",
+			Info:    0x4,
+			Other:   0x0,
+			Section: 0xFFF1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    ".Linfo_string0",
+			Info:    0x0,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    ".Linfo_string1",
+			Info:    0x0,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x2C,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    ".Linfo_string2",
+			Info:    0x0,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x47,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    ".Linfo_string3",
+			Info:    0x0,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x4C,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    ".Linfo_string4",
+			Info:    0x0,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x4E,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x1,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x2,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x3,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x4,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x6,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x7,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x8,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xA,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xC,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xD,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xE,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0xF,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "",
+			Info:    0x3,
+			Other:   0x0,
+			Section: 0x10,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "v",
+			Info:    0x11,
+			Other:   0x0,
+			Section: 0xFFF2,
+			Value:   0x4,
+			Size:    0x4,
+		},
+	},
+	"testdata/hello-world-core.gz": {},
+}
+
+var dynamicSymbolsGolden = map[string][]Symbol{
+	"testdata/gcc-amd64-linux-exec": {
+		Symbol{
+			Name:    "__gmon_start__",
+			Info:    0x20,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x0,
+		},
+		Symbol{
+			Name:    "puts",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x18C,
+		},
+		Symbol{
+			Name:    "__libc_start_main",
+			Info:    0x12,
+			Other:   0x0,
+			Section: 0x0,
+			Value:   0x0,
+			Size:    0x1C2,
+		},
+	},
+	"testdata/go-relocation-test-clang-x86.obj": {},
+	"testdata/hello-world-core.gz":              {},
+}