xref: /freebsd/contrib/llvm-project/llvm/lib/BinaryFormat/COFF.cpp (revision d781ede639f2289ccf0889dd138169e1194b656b)
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.
encodeBase64StringEntry(char * Buffer,uint64_t Value)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  
encodeSectionName(char * Out,uint64_t Offset)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