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// Copyright (c) 2018, Google Inc.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
// read_symbols.go scans one or more .a files and, for each object contained in
// the .a files, reads the list of symbols in that object file.
package main
import (
"bytes"
"debug/elf"
"debug/macho"
"flag"
"fmt"
"os"
"runtime"
"sort"
"strings"
"boringssl.googlesource.com/boringssl/util/ar"
)
const (
ObjFileFormatELF = "elf"
ObjFileFormatMachO = "macho"
)
var outFlag = flag.String("out", "-", "File to write output symbols")
var objFileFormat = flag.String("obj-file-format", defaultObjFileFormat(runtime.GOOS), "Object file format to expect (options are elf, macho)")
func defaultObjFileFormat(goos string) string {
switch goos {
case "linux":
return ObjFileFormatELF
case "darwin":
return ObjFileFormatMachO
default:
// By returning a value here rather than panicking, the user can still
// cross-compile from an unsupported platform to a supported platform by
// overriding this default with a flag. If the user doesn't provide the
// flag, we will panic during flag parsing.
return "unsupported"
}
}
func main() {
flag.Parse()
if flag.NArg() < 1 {
fmt.Fprintf(os.Stderr, "Usage: %s [-out OUT] [-obj-file-format FORMAT] ARCHIVE_FILE [ARCHIVE_FILE [...]]\n", os.Args[0])
os.Exit(1)
}
archiveFiles := flag.Args()
out := os.Stdout
if *outFlag != "-" {
var err error
out, err = os.Create(*outFlag)
nilOrPanic(err, "failed to open output file")
defer out.Close()
}
var symbols []string
// Only add first instance of any symbol; keep track of them in this map.
added := make(map[string]bool)
for _, archive := range archiveFiles {
f, err := os.Open(archive)
nilOrPanic(err, "failed to open archive file %s", archive)
objectFiles, err := ar.ParseAR(f)
nilOrPanic(err, "failed to read archive file %s", archive)
for name, contents := range objectFiles {
if !strings.HasSuffix(name, ".o") {
continue
}
for _, s := range listSymbols(name, contents) {
if !added[s] {
added[s] = true
symbols = append(symbols, s)
}
}
}
}
sort.Strings(symbols)
for _, s := range symbols {
// Filter out C++ mangled names.
prefix := "_Z"
if runtime.GOOS == "darwin" {
prefix = "__Z"
}
if !strings.HasPrefix(s, prefix) {
fmt.Fprintln(out, s)
}
}
}
// listSymbols lists the exported symbols from an object file.
func listSymbols(name string, contents []byte) []string {
switch *objFileFormat {
case ObjFileFormatELF:
return listSymbolsELF(name, contents)
case ObjFileFormatMachO:
return listSymbolsMachO(name, contents)
default:
panic(fmt.Errorf("unsupported object file format %v", *objFileFormat))
}
}
func listSymbolsELF(name string, contents []byte) []string {
f, err := elf.NewFile(bytes.NewReader(contents))
nilOrPanic(err, "failed to parse ELF file %s", name)
syms, err := f.Symbols()
nilOrPanic(err, "failed to read symbol names from ELF file %s", name)
var names []string
for _, sym := range syms {
// Only include exported, defined symbols
if elf.ST_BIND(sym.Info) != elf.STB_LOCAL && sym.Section != elf.SHN_UNDEF {
names = append(names, sym.Name)
}
}
return names
}
func listSymbolsMachO(name string, contents []byte) []string {
f, err := macho.NewFile(bytes.NewReader(contents))
nilOrPanic(err, "failed to parse Mach-O file %s", name)
if f.Symtab == nil {
return nil
}
var names []string
for _, sym := range f.Symtab.Syms {
// Source: https://opensource.apple.com/source/xnu/xnu-3789.51.2/EXTERNAL_HEADERS/mach-o/nlist.h.auto.html
const (
N_PEXT uint8 = 0x10 // Private external symbol bit
N_EXT uint8 = 0x01 // External symbol bit, set for external symbols
N_TYPE uint8 = 0x0e // mask for the type bits
N_UNDF uint8 = 0x0 // undefined, n_sect == NO_SECT
N_ABS uint8 = 0x2 // absolute, n_sect == NO_SECT
N_SECT uint8 = 0xe // defined in section number n_sect
N_PBUD uint8 = 0xc // prebound undefined (defined in a dylib)
N_INDR uint8 = 0xa // indirect
)
// Only include exported, defined symbols.
if sym.Type&N_EXT != 0 && sym.Type&N_TYPE != N_UNDF {
if len(sym.Name) == 0 || sym.Name[0] != '_' {
panic(fmt.Errorf("unexpected symbol without underscore prefix: %v", sym.Name))
}
names = append(names, sym.Name[1:])
}
}
return names
}
func nilOrPanic(err error, f string, args ...interface{}) {
if err != nil {
panic(fmt.Errorf(f+": %v", append(args, err)...))
}
}
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