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.
14enum : unsigned { Max7DecimalOffset = 9999999U };
15enum : 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.
20static 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
39bool 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(Suffix: Twine(Offset)).toVector(Out&: Buffer);
44 assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
45 std::memcpy(dest: Out, src: Buffer.data(), n: Buffer.size());
46 return true;
47 }
48
49 if (Offset <= MaxBase64Offset) {
50 // Starting with 10,000,000, offsets are encoded as base64.
51 encodeBase64StringEntry(Buffer: Out, Value: Offset);
52 return true;
53 }
54
55 // The offset is too large to be encoded.
56 return false;
57}
58