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   case DXContainer:
  45     // Start the table with a NUL byte.
  46     Size = 1;
  47     break;
  48   case XCOFF:
  49   case WinCOFF:
  50     // Make room to write the table size later.
  51     Size = 4;
  52     break;
  53   }
  54 }
  55
  56 StringTableBuilder::StringTableBuilder(Kind K, Align Alignment)
  57     : K(K), Alignment(Alignment) {
  58   initSize();
  59 }
  60
  61 void StringTableBuilder::write(raw_ostream &OS) const {
  62   assert(isFinalized());
  63   SmallString<0> Data;
  64   Data.resize(getSize());
  65   write((uint8_t *)Data.data());
  66   OS << Data;
  67 }
  68
  69 using StringPair = std::pair<CachedHashStringRef, size_t>;
  70
  71 void StringTableBuilder::write(uint8_t *Buf) const {
  72   assert(isFinalized());
  73   for (const StringPair &P : StringIndexMap) {
  74     StringRef Data = P.first.val();
  75     if (!Data.empty())
  76       memcpy(Buf + P.second, Data.data(), Data.size());
  77   }
  78   // The COFF formats store the size of the string table in the first 4 bytes.
  79   // For Windows, the format is little-endian; for AIX, it is big-endian.
  80   if (K == WinCOFF)
  81     support::endian::write32le(Buf, Size);
  82   else if (K == XCOFF)
  83     support::endian::write32be(Buf, Size);
  84 }
  85
  86 // Returns the character at Pos from end of a string.
  87 static int charTailAt(StringPair *P, size_t Pos) {
  88   StringRef S = P->first.val();
  89   if (Pos >= S.size())
  90     return -1;
  91   return (unsigned char)S[S.size() - Pos - 1];
  92 }
  93
  94 // Three-way radix quicksort. This is much faster than std::sort with strcmp
  95 // because it does not compare characters that we already know the same.
  96 static void multikeySort(MutableArrayRef<StringPair *> Vec, int Pos) {
  97 tailcall:
  98   if (Vec.size() <= 1)
  99     return;
 100
 101   // Partition items so that items in [0, I) are greater than the pivot,
 102   // [I, J) are the same as the pivot, and [J, Vec.size()) are less than
 103   // the pivot.
 104   int Pivot = charTailAt(Vec[0], Pos);
 105   size_t I = 0;
 106   size_t J = Vec.size();
 107   for (size_t K = 1; K < J;) {
 108     int C = charTailAt(Vec[K], Pos);
 109     if (C > Pivot)
 110       std::swap(Vec[I++], Vec[K++]);
 111     else if (C < Pivot)
 112       std::swap(Vec[--J], Vec[K]);
 113     else
 114       K++;
 115   }
 116
 117   multikeySort(Vec.slice(0, I), Pos);
 118   multikeySort(Vec.slice(J), Pos);
 119
 120   // multikeySort(Vec.slice(I, J - I), Pos + 1), but with
 121   // tail call optimization.
 122   if (Pivot != -1) {
 123     Vec = Vec.slice(I, J - I);
 124     ++Pos;
 125     goto tailcall;
 126   }
 127 }
 128
 129 void StringTableBuilder::finalize() {
 130   assert(K != DWARF);
 131   finalizeStringTable(/*Optimize=*/true);
 132 }
 133
 134 void StringTableBuilder::finalizeInOrder() {
 135   finalizeStringTable(/*Optimize=*/false);
 136 }
 137
 138 void StringTableBuilder::finalizeStringTable(bool Optimize) {
 139   Finalized = true;
 140
 141   if (Optimize) {
 142     std::vector<StringPair *> Strings;
 143     Strings.reserve(StringIndexMap.size());
 144     for (StringPair &P : StringIndexMap)
 145       Strings.push_back(&P);
 146
 147     multikeySort(Strings, 0);
 148     initSize();
 149
 150     StringRef Previous;
 151     for (StringPair *P : Strings) {
 152       StringRef S = P->first.val();
 153       if (Previous.ends_with(S)) {
 154         size_t Pos = Size - S.size() - (K != RAW);
 155         if (isAligned(Alignment, Pos)) {
 156           P->second = Pos;
 157           continue;
 158         }
 159       }
 160
 161       Size = alignTo(Size, Alignment);
 162       P->second = Size;
 163
 164       Size += S.size();
 165       if (K != RAW)
 166         ++Size;
 167       Previous = S;
 168     }
 169   }
 170
 171   if (K == MachO || K == MachOLinked || K == DXContainer)
 172     Size = alignTo(Size, 4); // Pad to multiple of 4.
 173   if (K == MachO64 || K == MachO64Linked)
 174     Size = alignTo(Size, 8); // Pad to multiple of 8.
 175
 176   // According to ld64 the string table of a final linked Mach-O binary starts
 177   // with " ", i.e. the first byte is ' ' and the second byte is zero. In
 178   // 'initSize()' we reserved the first two bytes for holding this string.
 179   if (K == MachOLinked || K == MachO64Linked)
 180     StringIndexMap[CachedHashStringRef(" ")] = 0;
 181
 182   // The first byte in an ELF string table must be null, according to the ELF
 183   // specification. In 'initSize()' we reserved the first byte to hold null for
 184   // this purpose and here we actually add the string to allow 'getOffset()' to
 185   // be called on an empty string.
 186   if (K == ELF)
 187     StringIndexMap[CachedHashStringRef("")] = 0;
 188 }
 189
 190 void StringTableBuilder::clear() {
 191   Finalized = false;
 192   StringIndexMap.clear();
 193 }
 194
 195 size_t StringTableBuilder::getOffset(CachedHashStringRef S) const {
 196   assert(isFinalized());
 197   auto I = StringIndexMap.find(S);
 198   assert(I != StringIndexMap.end() && "String is not in table!");
 199   return I->second;
 200 }
 201
 202 size_t StringTableBuilder::add(CachedHashStringRef S) {
 203   if (K == WinCOFF)
 204     assert(S.size() > COFF::NameSize && "Short string in COFF string table!");
 205
 206   assert(!isFinalized());
 207   auto P = StringIndexMap.insert(std::make_pair(S, 0));
 208   if (P.second) {
 209     size_t Start = alignTo(Size, Alignment);
 210     P.first->second = Start;
 211     Size = Start + S.size() + (K != RAW);
 212   }
 213   return P.first->second;
 214 }