libgo/go/debug/pe/string.go

   1 // Copyright 2016 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package pe
   6
   7 import (
   8         "bytes"
   9         "encoding/binary"
  10         "fmt"
  11         "io"
  12 )
  13
  14 // cstring converts ASCII byte sequence b to string.
  15 // It stops once it finds 0 or reaches end of b.
  16 func cstring(b []byte) string {
  17         i := bytes.IndexByte(b, 0)
  18         if i == -1 {
  19                 i = len(b)
  20         }
  21         return string(b[:i])
  22 }
  23
  24 // StringTable is a COFF string table.
  25 type StringTable []byte
  26
  27 func readStringTable(fh *FileHeader, r io.ReadSeeker) (StringTable, error) {
  28         // COFF string table is located right after COFF symbol table.
  29         if fh.PointerToSymbolTable <= 0 {
  30                 return nil, nil
  31         }
  32         offset := fh.PointerToSymbolTable + COFFSymbolSize*fh.NumberOfSymbols
  33         _, err := r.Seek(int64(offset), seekStart)
  34         if err != nil {
  35                 return nil, fmt.Errorf("fail to seek to string table: %v", err)
  36         }
  37         var l uint32
  38         err = binary.Read(r, binary.LittleEndian, &l)
  39         if err != nil {
  40                 return nil, fmt.Errorf("fail to read string table length: %v", err)
  41         }
  42         // string table length includes itself
  43         if l <= 4 {
  44                 return nil, nil
  45         }
  46         l -= 4
  47         buf := make([]byte, l)
  48         _, err = io.ReadFull(r, buf)
  49         if err != nil {
  50                 return nil, fmt.Errorf("fail to read string table: %v", err)
  51         }
  52         return StringTable(buf), nil
  53 }
  54
  55 // TODO(brainman): decide if start parameter should be int instead of uint32
  56
  57 // String extracts string from COFF string table st at offset start.
  58 func (st StringTable) String(start uint32) (string, error) {
  59         // start includes 4 bytes of string table length
  60         if start < 4 {
  61                 return "", fmt.Errorf("offset %d is before the start of string table", start)
  62         }
  63         start -= 4
  64         if int(start) > len(st) {
  65                 return "", fmt.Errorf("offset %d is beyond the end of string table", start)
  66         }
  67         return cstring(st[start:]), nil
  68 }