llvm-project

1
//===- llvm/BinaryFormat/COFF.cpp - The COFF format -----------------------===//
2
//
3
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4
// See https://llvm.org/LICENSE.txt for license information.
5
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6
//
7
//===----------------------------------------------------------------------===//
8

9
#include "llvm/BinaryFormat/COFF.h"
10
#include "llvm/ADT/SmallVector.h"
11
#include "llvm/ADT/Twine.h"
12

13
// Maximum offsets for different string table entry encodings.
14
enum : unsigned { Max7DecimalOffset = 9999999U };
15
enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
16

17
// Encode a string table entry offset in base 64, padded to 6 chars, and
18
// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
19
// Buffer must be at least 8 bytes large. No terminating null appended.
20
static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
21
  assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
22
         "Illegal section name encoding for value");
23

24
  static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
25
                                 "abcdefghijklmnopqrstuvwxyz"
26
                                 "0123456789+/";
27

28
  Buffer[0] = '/';
29
  Buffer[1] = '/';
30

31
  char *Ptr = Buffer + 7;
32
  for (unsigned i = 0; i < 6; ++i) {
33
    unsigned Rem = Value % 64;
34
    Value /= 64;
35
    *(Ptr--) = Alphabet[Rem];
36
  }
37
}
38

39
bool llvm::COFF::encodeSectionName(char *Out, uint64_t Offset) {
40
  if (Offset <= Max7DecimalOffset) {
41
    // Offsets of 7 digits or less are encoded in ASCII.
42
    SmallVector<char, COFF::NameSize> Buffer;
43
    Twine('/').concat(Twine(Offset)).toVector(Buffer);
44
    assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
45
    std::memcpy(Out, Buffer.data(), Buffer.size());
46
    return true;
47
  }
48

49
  if (Offset <= MaxBase64Offset) {
50
    // Starting with 10,000,000, offsets are encoded as base64.
51
    encodeBase64StringEntry(Out, Offset);
52
    return true;
53
  }
54

55
  // The offset is too large to be encoded.
56
  return false;
57
}
58