Source file src/pkg/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	}
    69	

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