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