1 //===- StringTableBuilder.cpp - String table building utility -------------===// 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/MC/StringTableBuilder.h" 10 #include "llvm/ADT/CachedHashString.h" 11 #include "llvm/ADT/SmallString.h" 12 #include "llvm/ADT/StringRef.h" 13 #include "llvm/BinaryFormat/COFF.h" 14 #include "llvm/Support/Endian.h" 15 #include "llvm/Support/MathExtras.h" 16 #include "llvm/Support/raw_ostream.h" 17 #include <cassert> 18 #include <cstddef> 19 #include <cstdint> 20 #include <cstring> 21 #include <utility> 22 #include <vector> 23 24 using namespace llvm; 25 26 StringTableBuilder::~StringTableBuilder() = default; 27 28 void StringTableBuilder::initSize() { 29 // Account for leading bytes in table so that offsets returned from add are 30 // correct. 31 switch (K) { 32 case RAW: 33 case DWARF: 34 Size = 0; 35 break; 36 case MachO: 37 case ELF: 38 // Start the table with a NUL byte. 39 Size = 1; 40 break; 41 case XCOFF: 42 case WinCOFF: 43 // Make room to write the table size later. 44 Size = 4; 45 break; 46 } 47 } 48 49 StringTableBuilder::StringTableBuilder(Kind K, unsigned Alignment) 50 : K(K), Alignment(Alignment) { 51 initSize(); 52 } 53 54 void StringTableBuilder::write(raw_ostream &OS) const { 55 assert(isFinalized()); 56 SmallString<0> Data; 57 Data.resize(getSize()); 58 write((uint8_t *)Data.data()); 59 OS << Data; 60 } 61 62 using StringPair = std::pair<CachedHashStringRef, size_t>; 63 64 void StringTableBuilder::write(uint8_t *Buf) const { 65 assert(isFinalized()); 66 for (const StringPair &P : StringIndexMap) { 67 StringRef Data = P.first.val(); 68 if (!Data.empty()) 69 memcpy(Buf + P.second, Data.data(), Data.size()); 70 } 71 // The COFF formats store the size of the string table in the first 4 bytes. 72 // For Windows, the format is little-endian; for AIX, it is big-endian. 73 if (K == WinCOFF) 74 support::endian::write32le(Buf, Size); 75 else if (K == XCOFF) 76 support::endian::write32be(Buf, Size); 77 } 78 79 // Returns the character at Pos from end of a string. 80 static int charTailAt(StringPair *P, size_t Pos) { 81 StringRef S = P->first.val(); 82 if (Pos >= S.size()) 83 return -1; 84 return (unsigned char)S[S.size() - Pos - 1]; 85 } 86 87 // Three-way radix quicksort. This is much faster than std::sort with strcmp 88 // because it does not compare characters that we already know the same. 89 static void multikeySort(MutableArrayRef<StringPair *> Vec, int Pos) { 90 tailcall: 91 if (Vec.size() <= 1) 92 return; 93 94 // Partition items so that items in [0, I) are greater than the pivot, 95 // [I, J) are the same as the pivot, and [J, Vec.size()) are less than 96 // the pivot. 97 int Pivot = charTailAt(Vec[0], Pos); 98 size_t I = 0; 99 size_t J = Vec.size(); 100 for (size_t K = 1; K < J;) { 101 int C = charTailAt(Vec[K], Pos); 102 if (C > Pivot) 103 std::swap(Vec[I++], Vec[K++]); 104 else if (C < Pivot) 105 std::swap(Vec[--J], Vec[K]); 106 else 107 K++; 108 } 109 110 multikeySort(Vec.slice(0, I), Pos); 111 multikeySort(Vec.slice(J), Pos); 112 113 // multikeySort(Vec.slice(I, J - I), Pos + 1), but with 114 // tail call optimization. 115 if (Pivot != -1) { 116 Vec = Vec.slice(I, J - I); 117 ++Pos; 118 goto tailcall; 119 } 120 } 121 122 void StringTableBuilder::finalize() { 123 assert(K != DWARF); 124 finalizeStringTable(/*Optimize=*/true); 125 } 126 127 void StringTableBuilder::finalizeInOrder() { 128 finalizeStringTable(/*Optimize=*/false); 129 } 130 131 void StringTableBuilder::finalizeStringTable(bool Optimize) { 132 Finalized = true; 133 134 if (Optimize) { 135 std::vector<StringPair *> Strings; 136 Strings.reserve(StringIndexMap.size()); 137 for (StringPair &P : StringIndexMap) 138 Strings.push_back(&P); 139 140 multikeySort(Strings, 0); 141 initSize(); 142 143 StringRef Previous; 144 for (StringPair *P : Strings) { 145 StringRef S = P->first.val(); 146 if (Previous.endswith(S)) { 147 size_t Pos = Size - S.size() - (K != RAW); 148 if (!(Pos & (Alignment - 1))) { 149 P->second = Pos; 150 continue; 151 } 152 } 153 154 Size = alignTo(Size, Alignment); 155 P->second = Size; 156 157 Size += S.size(); 158 if (K != RAW) 159 ++Size; 160 Previous = S; 161 } 162 } 163 164 if (K == MachO) 165 Size = alignTo(Size, 4); // Pad to multiple of 4. 166 167 // The first byte in an ELF string table must be null, according to the ELF 168 // specification. In 'initSize()' we reserved the first byte to hold null for 169 // this purpose and here we actually add the string to allow 'getOffset()' to 170 // be called on an empty string. 171 if (K == ELF) 172 StringIndexMap[CachedHashStringRef("")] = 0; 173 } 174 175 void StringTableBuilder::clear() { 176 Finalized = false; 177 StringIndexMap.clear(); 178 } 179 180 size_t StringTableBuilder::getOffset(CachedHashStringRef S) const { 181 assert(isFinalized()); 182 auto I = StringIndexMap.find(S); 183 assert(I != StringIndexMap.end() && "String is not in table!"); 184 return I->second; 185 } 186 187 size_t StringTableBuilder::add(CachedHashStringRef S) { 188 if (K == WinCOFF) 189 assert(S.size() > COFF::NameSize && "Short string in COFF string table!"); 190 191 assert(!isFinalized()); 192 auto P = StringIndexMap.insert(std::make_pair(S, 0)); 193 if (P.second) { 194 size_t Start = alignTo(Size, Alignment); 195 P.first->second = Start; 196 Size = Start + S.size() + (K != RAW); 197 } 198 return P.first->second; 199 } 200