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 #include <optional>
  27 using namespace clang;
  28
  29 /// HashHMapKey - This is the 'well known' hash function required by the file
  30 /// format, used to look up keys in the hash table.  The hash table uses simple
  31 /// linear probing based on this function.
  32 static inline unsigned HashHMapKey(StringRef Str) {
  33   unsigned Result = 0;
  34   const char *S = Str.begin(), *End = Str.end();
  35
  36   for (; S != End; S++)
  37     Result += toLowercase(*S) * 13;
  38   return Result;
  39 }
  40
  41
  42
  43 //===----------------------------------------------------------------------===//
  44 // Verification and Construction
  45 //===----------------------------------------------------------------------===//
  46
  47 /// HeaderMap::Create - This attempts to load the specified file as a header
  48 /// map.  If it doesn't look like a HeaderMap, it gives up and returns null.
  49 /// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
  50 /// into the string error argument and returns null.
  51 std::unique_ptr<HeaderMap> HeaderMap::Create(FileEntryRef FE, 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<uint32_t>(HMAP_HeaderMagicNumber) &&
  80            Header->Version == llvm::byteswap<uint16_t>(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 =
  91       NeedsByteSwap ? llvm::byteswap(Header->NumBuckets) : Header->NumBuckets;
  92   if (!llvm::isPowerOf2_32(NumBuckets))
  93     return false;
  94   if (File.getBufferSize() <
  95       sizeof(HMapHeader) + sizeof(HMapBucket) * NumBuckets)
  96     return false;
  97
  98   // Okay, everything looks good.
  99   return true;
 100 }
 101
 102 //===----------------------------------------------------------------------===//
 103 //  Utility Methods
 104 //===----------------------------------------------------------------------===//
 105
 106
 107 /// getFileName - Return the filename of the headermap.
 108 StringRef HeaderMapImpl::getFileName() const {
 109   return FileBuffer->getBufferIdentifier();
 110 }
 111
 112 unsigned HeaderMapImpl::getEndianAdjustedWord(unsigned X) const {
 113   if (!NeedsBSwap) return X;
 114   return llvm::byteswap<uint32_t>(X);
 115 }
 116
 117 /// getHeader - Return a reference to the file header, in unbyte-swapped form.
 118 /// This method cannot fail.
 119 const HMapHeader &HeaderMapImpl::getHeader() const {
 120   // We know the file is at least as big as the header.  Return it.
 121   return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
 122 }
 123
 124 /// getBucket - Return the specified hash table bucket from the header map,
 125 /// bswap'ing its fields as appropriate.  If the bucket number is not valid,
 126 /// this return a bucket with an empty key (0).
 127 HMapBucket HeaderMapImpl::getBucket(unsigned BucketNo) const {
 128   assert(FileBuffer->getBufferSize() >=
 129              sizeof(HMapHeader) + sizeof(HMapBucket) * BucketNo &&
 130          "Expected bucket to be in range");
 131
 132   HMapBucket Result;
 133   Result.Key = HMAP_EmptyBucketKey;
 134
 135   const HMapBucket *BucketArray =
 136     reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
 137                                         sizeof(HMapHeader));
 138   const HMapBucket *BucketPtr = BucketArray+BucketNo;
 139
 140   // Load the values, bswapping as needed.
 141   Result.Key    = getEndianAdjustedWord(BucketPtr->Key);
 142   Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
 143   Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
 144   return Result;
 145 }
 146
 147 std::optional<StringRef> HeaderMapImpl::getString(unsigned StrTabIdx) const {
 148   // Add the start of the string table to the idx.
 149   StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
 150
 151   // Check for invalid index.
 152   if (StrTabIdx >= FileBuffer->getBufferSize())
 153     return std::nullopt;
 154
 155   const char *Data = FileBuffer->getBufferStart() + StrTabIdx;
 156   unsigned MaxLen = FileBuffer->getBufferSize() - StrTabIdx;
 157   unsigned Len = strnlen(Data, MaxLen);
 158
 159   // Check whether the buffer is null-terminated.
 160   if (Len == MaxLen && Data[Len - 1])
 161     return std::nullopt;
 162
 163   return StringRef(Data, Len);
 164 }
 165
 166 //===----------------------------------------------------------------------===//
 167 // The Main Drivers
 168 //===----------------------------------------------------------------------===//
 169
 170 /// dump - Print the contents of this headermap to stderr.
 171 LLVM_DUMP_METHOD void HeaderMapImpl::dump() const {
 172   const HMapHeader &Hdr = getHeader();
 173   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 174
 175   llvm::dbgs() << "Header Map " << getFileName() << ":\n  " << NumBuckets
 176                << ", " << getEndianAdjustedWord(Hdr.NumEntries) << "\n";
 177
 178   auto getStringOrInvalid = [this](unsigned Id) -> StringRef {
 179     if (std::optional<StringRef> S = getString(Id))
 180       return *S;
 181     return "<invalid>";
 182   };
 183
 184   for (unsigned i = 0; i != NumBuckets; ++i) {
 185     HMapBucket B = getBucket(i);
 186     if (B.Key == HMAP_EmptyBucketKey) continue;
 187
 188     StringRef Key = getStringOrInvalid(B.Key);
 189     StringRef Prefix = getStringOrInvalid(B.Prefix);
 190     StringRef Suffix = getStringOrInvalid(B.Suffix);
 191     llvm::dbgs() << "  " << i << ". " << Key << " -> '" << Prefix << "' '"
 192                  << Suffix << "'\n";
 193   }
 194 }
 195
 196 StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
 197                                         SmallVectorImpl<char> &DestPath) const {
 198   const HMapHeader &Hdr = getHeader();
 199   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 200
 201   // Don't probe infinitely.  This should be checked before constructing.
 202   assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
 203
 204   // Linearly probe the hash table.
 205   for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
 206     HMapBucket B = getBucket(Bucket & (NumBuckets-1));
 207     if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
 208
 209     // See if the key matches.  If not, probe on.
 210     std::optional<StringRef> Key = getString(B.Key);
 211     if (LLVM_UNLIKELY(!Key))
 212       continue;
 213     if (!Filename.equals_insensitive(*Key))
 214       continue;
 215
 216     // If so, we have a match in the hash table.  Construct the destination
 217     // path.
 218     std::optional<StringRef> Prefix = getString(B.Prefix);
 219     std::optional<StringRef> Suffix = getString(B.Suffix);
 220
 221     DestPath.clear();
 222     if (LLVM_LIKELY(Prefix && Suffix)) {
 223       DestPath.append(Prefix->begin(), Prefix->end());
 224       DestPath.append(Suffix->begin(), Suffix->end());
 225     }
 226     return StringRef(DestPath.begin(), DestPath.size());
 227   }
 228 }
 229
 230 StringRef HeaderMapImpl::reverseLookupFilename(StringRef DestPath) const {
 231   if (!ReverseMap.empty())
 232     return ReverseMap.lookup(DestPath);
 233
 234   const HMapHeader &Hdr = getHeader();
 235   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
 236   StringRef RetKey;
 237   for (unsigned i = 0; i != NumBuckets; ++i) {
 238     HMapBucket B = getBucket(i);
 239     if (B.Key == HMAP_EmptyBucketKey)
 240       continue;
 241
 242     std::optional<StringRef> Key = getString(B.Key);
 243     std::optional<StringRef> Prefix = getString(B.Prefix);
 244     std::optional<StringRef> Suffix = getString(B.Suffix);
 245     if (LLVM_LIKELY(Key && Prefix && Suffix)) {
 246       SmallVector<char, 1024> Buf;
 247       Buf.append(Prefix->begin(), Prefix->end());
 248       Buf.append(Suffix->begin(), Suffix->end());
 249       StringRef Value(Buf.begin(), Buf.size());
 250       ReverseMap[Value] = *Key;
 251
 252       if (DestPath == Value)
 253         RetKey = *Key;
 254     }
 255   }
 256   return RetKey;
 257 }