llvm/lib/MC/StringTableBuilder.cpp

   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/ArrayRef.h"
  11 #include "llvm/ADT/CachedHashString.h"
  12 #include "llvm/ADT/SmallString.h"
  13 #include "llvm/ADT/StringRef.h"
  14 #include "llvm/BinaryFormat/COFF.h"
  15 #include "llvm/Support/Endian.h"
  16 #include "llvm/Support/MathExtras.h"
  17 #include "llvm/Support/raw_ostream.h"
  18 #include <cassert>
  19 #include <cstddef>
  20 #include <cstdint>
  21 #include <cstring>
  22 #include <utility>
  23 #include <vector>
  24
  25 using namespace llvm;
  26
  27 StringTableBuilder::~StringTableBuilder() = default;
  28
  29 void StringTableBuilder::initSize() {
  30   // Account for leading bytes in table so that offsets returned from add are
  31   // correct.
  32   switch (K) {
  33   case RAW:
  34   case DWARF:
  35     Size = 0;
  36     break;
  37   case MachOLinked:
  38   case MachO64Linked:
  39     Size = 2;
  40     break;
  41   case MachO:
  42   case MachO64:
  43   case ELF:
  44     // Start the table with a NUL byte.
  45     Size = 1;
  46     break;
  47   case XCOFF:
  48   case WinCOFF:
  49     // Make room to write the table size later.
  50     Size = 4;
  51     break;
  52   }
  53 }
  54
  55 StringTableBuilder::StringTableBuilder(Kind K, unsigned Alignment)
  56     : K(K), Alignment(Alignment) {
  57   initSize();
  58 }
  59
  60 void StringTableBuilder::write(raw_ostream &OS) const {
  61   assert(isFinalized());
  62   SmallString<0> Data;
  63   Data.resize(getSize());
  64   write((uint8_t *)Data.data());
  65   OS << Data;
  66 }
  67
  68 using StringPair = std::pair<CachedHashStringRef, size_t>;
  69
  70 void StringTableBuilder::write(uint8_t *Buf) const {
  71   assert(isFinalized());
  72   for (const StringPair &P : StringIndexMap) {
  73     StringRef Data = P.first.val();
  74     if (!Data.empty())
  75       memcpy(Buf + P.second, Data.data(), Data.size());
  76   }
  77   // The COFF formats store the size of the string table in the first 4 bytes.
  78   // For Windows, the format is little-endian; for AIX, it is big-endian.
  79   if (K == WinCOFF)
  80     support::endian::write32le(Buf, Size);
  81   else if (K == XCOFF)
  82     support::endian::write32be(Buf, Size);
  83 }
  84
  85 // Returns the character at Pos from end of a string.
  86 static int charTailAt(StringPair *P, size_t Pos) {
  87   StringRef S = P->first.val();
  88   if (Pos >= S.size())
  89     return -1;
  90   return (unsigned char)S[S.size() - Pos - 1];
  91 }
  92
  93 // Three-way radix quicksort. This is much faster than std::sort with strcmp
  94 // because it does not compare characters that we already know the same.
  95 static void multikeySort(MutableArrayRef<StringPair *> Vec, int Pos) {
  96 tailcall:
  97   if (Vec.size() <= 1)
  98     return;
  99
 100   // Partition items so that items in [0, I) are greater than the pivot,
 101   // [I, J) are the same as the pivot, and [J, Vec.size()) are less than
 102   // the pivot.
 103   int Pivot = charTailAt(Vec[0], Pos);
 104   size_t I = 0;
 105   size_t J = Vec.size();
 106   for (size_t K = 1; K < J;) {
 107     int C = charTailAt(Vec[K], Pos);
 108     if (C > Pivot)
 109       std::swap(Vec[I++], Vec[K++]);
 110     else if (C < Pivot)
 111       std::swap(Vec[--J], Vec[K]);
 112     else
 113       K++;
 114   }
 115
 116   multikeySort(Vec.slice(0, I), Pos);
 117   multikeySort(Vec.slice(J), Pos);
 118
 119   // multikeySort(Vec.slice(I, J - I), Pos + 1), but with
 120   // tail call optimization.
 121   if (Pivot != -1) {
 122     Vec = Vec.slice(I, J - I);
 123     ++Pos;
 124     goto tailcall;
 125   }
 126 }
 127
 128 void StringTableBuilder::finalize() {
 129   assert(K != DWARF);
 130   finalizeStringTable(/*Optimize=*/true);
 131 }
 132
 133 void StringTableBuilder::finalizeInOrder() {
 134   finalizeStringTable(/*Optimize=*/false);
 135 }
 136
 137 void StringTableBuilder::finalizeStringTable(bool Optimize) {
 138   Finalized = true;
 139
 140   if (Optimize) {
 141     std::vector<StringPair *> Strings;
 142     Strings.reserve(StringIndexMap.size());
 143     for (StringPair &P : StringIndexMap)
 144       Strings.push_back(&P);
 145
 146     multikeySort(Strings, 0);
 147     initSize();
 148
 149     StringRef Previous;
 150     for (StringPair *P : Strings) {
 151       StringRef S = P->first.val();
 152       if (Previous.endswith(S)) {
 153         size_t Pos = Size - S.size() - (K != RAW);
 154         if (!(Pos & (Alignment - 1))) {
 155           P->second = Pos;
 156           continue;
 157         }
 158       }
 159
 160       Size = alignTo(Size, Alignment);
 161       P->second = Size;
 162
 163       Size += S.size();
 164       if (K != RAW)
 165         ++Size;
 166       Previous = S;
 167     }
 168   }
 169
 170   if (K == MachO || K == MachOLinked)
 171     Size = alignTo(Size, 4); // Pad to multiple of 4.
 172   if (K == MachO64 || K == MachO64Linked)
 173     Size = alignTo(Size, 8); // Pad to multiple of 8.
 174
 175   // According to ld64 the string table of a final linked Mach-O binary starts
 176   // with " ", i.e. the first byte is ' ' and the second byte is zero. In
 177   // 'initSize()' we reserved the first two bytes for holding this string.
 178   if (K == MachOLinked || K == MachO64Linked)
 179     StringIndexMap[CachedHashStringRef(" ")] = 0;
 180
 181   // The first byte in an ELF string table must be null, according to the ELF
 182   // specification. In 'initSize()' we reserved the first byte to hold null for
 183   // this purpose and here we actually add the string to allow 'getOffset()' to
 184   // be called on an empty string.
 185   if (K == ELF)
 186     StringIndexMap[CachedHashStringRef("")] = 0;
 187 }
 188
 189 void StringTableBuilder::clear() {
 190   Finalized = false;
 191   StringIndexMap.clear();
 192 }
 193
 194 size_t StringTableBuilder::getOffset(CachedHashStringRef S) const {
 195   assert(isFinalized());
 196   auto I = StringIndexMap.find(S);
 197   assert(I != StringIndexMap.end() && "String is not in table!");
 198   return I->second;
 199 }
 200
 201 size_t StringTableBuilder::add(CachedHashStringRef S) {
 202   if (K == WinCOFF)
 203     assert(S.size() > COFF::NameSize && "Short string in COFF string table!");
 204
 205   assert(!isFinalized());
 206   auto P = StringIndexMap.insert(std::make_pair(S, 0));
 207   if (P.second) {
 208     size_t Start = alignTo(Size, Alignment);
 209     P.first->second = Start;
 210     Size = Start + S.size() + (K != RAW);
 211   }
 212   return P.first->second;
 213 }