clang/lib/Lex/HeaderMap.cpp

   1 //===--- HeaderMap.cpp - A file that acts like dir of symlinks ------------===//
   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 // This file implements the HeaderMap interface.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "clang/Lex/HeaderMap.h"
  14 #include "clang/Lex/HeaderMapTypes.h"
  15 #include "clang/Basic/CharInfo.h"
  16 #include "clang/Basic/FileManager.h"
  17 #include "llvm/ADT/SmallString.h"
  18 #include "llvm/Support/Compiler.h"
  19 #include "llvm/Support/DataTypes.h"
  20 #include "llvm/Support/MathExtras.h"
  21 #include "llvm/Support/MemoryBuffer.h"
  22 #include "llvm/Support/SwapByteOrder.h"
  23 #include "llvm/Support/Debug.h"
  24 #include <cstring>
  25 #include <memory>
  26 using namespace clang;
  27
  28 /// HashHMapKey - This is the 'well known' hash function required by the file
  29 /// format, used to look up keys in the hash table.  The hash table uses simple
  30 /// linear probing based on this function.
  31 static inline unsigned HashHMapKey(StringRef Str) {
  32   unsigned Result = 0;
  33   const char *S = Str.begin(), *End = Str.end();
  34
  35   for (; S != End; S++)
  36     Result += toLowercase(*S) * 13;
  37   return Result;
  38 }
  39
  40
  41
  42 //===----------------------------------------------------------------------===//
  43 // Verification and Construction
  44 //===----------------------------------------------------------------------===//
  45
  46 /// HeaderMap::Create - This attempts to load the specified file as a header
  47 /// map.  If it doesn't look like a HeaderMap, it gives up and returns null.
  48 /// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
  49 /// into the string error argument and returns null.
  50 std::unique_ptr<HeaderMap> HeaderMap::Create(const FileEntry *FE,
  51                                              FileManager &FM) {
  52   // If the file is too small to be a header map, ignore it.
  53   unsigned FileSize = FE->getSize();
  54   if (FileSize <= sizeof(HMapHeader)) return nullptr;
  55
  56   auto FileBuffer = FM.getBufferForFile(FE);
  57   if (!FileBuffer || !*FileBuffer)
  58     return nullptr;
  59   bool NeedsByteSwap;
  60   if (!checkHeader(**FileBuffer, NeedsByteSwap))
  61     return nullptr;
  62   return std::unique_ptr<HeaderMap>(new HeaderMap(std::move(*FileBuffer), NeedsByteSwap));
  63 }
  64
  65 bool HeaderMapImpl::checkHeader(const llvm::MemoryBuffer &File,
  66                                 bool &NeedsByteSwap) {
  67   if (File.getBufferSize() <= sizeof(HMapHeader))
  68     return false;
  69   const char *FileStart = File.getBufferStart();
  70
  71   // We know the file is at least as big as the header, check it now.
  72   const HMapHeader *Header = reinterpret_cast<const HMapHeader*>(FileStart);
  73
  74   // Sniff it to see if it's a headermap by checking the magic number and
  75   // version.
  76   if (Header->Magic == HMAP_HeaderMagicNumber &&
  77       Header->Version == HMAP_HeaderVersion)
  78     NeedsByteSwap = false;
  79   else if (Header->Magic == llvm::ByteSwap_32(HMAP_HeaderMagicNumber) &&
  80            Header->Version == llvm::ByteSwap_16(HMAP_HeaderVersion))
  81     NeedsByteSwap = true;  // Mixed endianness headermap.
  82   else
  83     return false;  // Not a header map.
  84
  85   if (Header->Reserved != 0)
  86     return false;
  87
  88   // Check the number of buckets.  It should be a power of two, and there
  89   // should be enough space in the file for all of them.
  90   uint32_t NumBuckets = NeedsByteSwap
  91                             ? llvm::sys::getSwappedBytes(Header->NumBuckets)
  92                             : Header->NumBuckets;
  93   if (!llvm::isPowerOf2_32(NumBuckets))
  94     return false;
  95   if (File.getBufferSize() <
  96       sizeof(HMapHeader) + sizeof(HMapBucket) * NumBuckets)
  97     return false;
  98
  99   // Okay, everything looks good.
 100   return true;
 101 }
 102
 103 //===----------------------------------------------------------------------===//
 104 //  Utility Methods
 105 //===----------------------------------------------------------------------===//
 106
 107
 108 /// getFileName - Return the filename of the headermap.
 109 StringRef HeaderMapImpl::getFileName() const {
 110   return FileBuffer->getBufferIdentifier();
 111 }
 112
 113 unsigned HeaderMapImpl::getEndianAdjustedWord(unsigned X) const {
 114   if (!NeedsBSwap) return X;
 115   return llvm::ByteSwap_32(X);
 116 }
 117
 118 /// getHeader - Return a reference to the file header, in unbyte-swapped form.
 119 /// This method cannot fail.
 120 const HMapHeader &HeaderMapImpl::getHeader() const {
 121   // We know the file is at least as big as the header.  Return it.
 122   return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
 123 }
 124
 125 /// getBucket - Return the specified hash table bucket from the header map,
 126 /// bswap'ing its fields as appropriate.  If the bucket number is not valid,
 127 /// this return a bucket with an empty key (0).
 128 HMapBucket HeaderMapImpl::getBucket(unsigned BucketNo) const {
 129   assert(FileBuffer->getBufferSize() >=
 130              sizeof(HMapHeader) + sizeof(HMapBucket) * BucketNo &&
 131          "Expected bucket to be in range");
 132
 133   HMapBucket Result;
 134   Result.Key = HMAP_EmptyBucketKey;
 135
 136   const HMapBucket *BucketArray =
 137     reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
 138                                         sizeof(HMapHeader));
 139   const HMapBucket *BucketPtr = BucketArray+BucketNo;
 140
 141   // Load the values, bswapping as needed.
 142   Result.Key    = getEndianAdjustedWord(BucketPtr->Key);
 143   Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
 144   Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
 145   return Result;
 146 }
 147
 148 Optional<StringRef> HeaderMapImpl::getString(unsigned StrTabIdx) const {
 149   // Add the start of the string table to the idx.
 150   StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
 151
 152   // Check for invalid index.
 153   if (StrTabIdx >= FileBuffer->getBufferSize())
 154     return None;
 155
 156   const char *Data = FileBuffer->getBufferStart() + StrTabIdx;
 157   unsigned MaxLen = FileBuffer->getBufferSize() - StrTabIdx;
 158   unsigned Len = strnlen(Data, MaxLen);
 159
 160   // Check whether the buffer is null-terminated.
 161   if (Len == MaxLen && Data[Len - 1])
 162     return None;
 163
 164   return StringRef(Data, Len);
 165 }
 166
 167 //===----------------------------------------------------------------------===//
 168 // The Main Drivers
 169 //===----------------------------------------------------------------------===//
 170
 171 /// dump - Print the contents of this headermap to stderr.
 172 LLVM_DUMP_METHOD void HeaderMapImpl::dump() const {
 173   const HMapHeader &Hdr = getHeader();
 174   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 175
 176   llvm::dbgs() << "Header Map " << getFileName() << ":\n  " << NumBuckets
 177                << ", " << getEndianAdjustedWord(Hdr.NumEntries) << "\n";
 178
 179   auto getStringOrInvalid = [this](unsigned Id) -> StringRef {
 180     if (Optional<StringRef> S = getString(Id))
 181       return *S;
 182     return "<invalid>";
 183   };
 184
 185   for (unsigned i = 0; i != NumBuckets; ++i) {
 186     HMapBucket B = getBucket(i);
 187     if (B.Key == HMAP_EmptyBucketKey) continue;
 188
 189     StringRef Key = getStringOrInvalid(B.Key);
 190     StringRef Prefix = getStringOrInvalid(B.Prefix);
 191     StringRef Suffix = getStringOrInvalid(B.Suffix);
 192     llvm::dbgs() << "  " << i << ". " << Key << " -> '" << Prefix << "' '"
 193                  << Suffix << "'\n";
 194   }
 195 }
 196
 197 StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
 198                                         SmallVectorImpl<char> &DestPath) const {
 199   const HMapHeader &Hdr = getHeader();
 200   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 201
 202   // Don't probe infinitely.  This should be checked before constructing.
 203   assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
 204
 205   // Linearly probe the hash table.
 206   for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
 207     HMapBucket B = getBucket(Bucket & (NumBuckets-1));
 208     if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
 209
 210     // See if the key matches.  If not, probe on.
 211     Optional<StringRef> Key = getString(B.Key);
 212     if (LLVM_UNLIKELY(!Key))
 213       continue;
 214     if (!Filename.equals_insensitive(*Key))
 215       continue;
 216
 217     // If so, we have a match in the hash table.  Construct the destination
 218     // path.
 219     Optional<StringRef> Prefix = getString(B.Prefix);
 220     Optional<StringRef> Suffix = getString(B.Suffix);
 221
 222     DestPath.clear();
 223     if (LLVM_LIKELY(Prefix && Suffix)) {
 224       DestPath.append(Prefix->begin(), Prefix->end());
 225       DestPath.append(Suffix->begin(), Suffix->end());
 226     }
 227     return StringRef(DestPath.begin(), DestPath.size());
 228   }
 229 }
 230
 231 StringRef HeaderMapImpl::reverseLookupFilename(StringRef DestPath) const {
 232   if (!ReverseMap.empty())
 233     return ReverseMap.lookup(DestPath);
 234
 235   const HMapHeader &Hdr = getHeader();
 236   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 237   StringRef RetKey;
 238   for (unsigned i = 0; i != NumBuckets; ++i) {
 239     HMapBucket B = getBucket(i);
 240     if (B.Key == HMAP_EmptyBucketKey)
 241       continue;
 242
 243     Optional<StringRef> Key = getString(B.Key);
 244     Optional<StringRef> Prefix = getString(B.Prefix);
 245     Optional<StringRef> Suffix = getString(B.Suffix);
 246     if (LLVM_LIKELY(Key && Prefix && Suffix)) {
 247       SmallVector<char, 1024> Buf;
 248       Buf.append(Prefix->begin(), Prefix->end());
 249       Buf.append(Suffix->begin(), Suffix->end());
 250       StringRef Value(Buf.begin(), Buf.size());
 251       ReverseMap[Value] = *Key;
 252
 253       if (DestPath == Value)
 254         RetKey = *Key;
 255     }
 256   }
 257   return RetKey;
 258 }