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      1 //===--- HeaderMap.cpp - A file that acts like dir of symlinks ------------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file implements the HeaderMap interface.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "clang/Lex/HeaderMap.h"
     15 #include "clang/Lex/HeaderMapTypes.h"
     16 #include "clang/Basic/CharInfo.h"
     17 #include "clang/Basic/FileManager.h"
     18 #include "llvm/ADT/SmallString.h"
     19 #include "llvm/Support/Compiler.h"
     20 #include "llvm/Support/DataTypes.h"
     21 #include "llvm/Support/MathExtras.h"
     22 #include "llvm/Support/MemoryBuffer.h"
     23 #include "llvm/Support/SwapByteOrder.h"
     24 #include "llvm/Support/Debug.h"
     25 #include <cstring>
     26 #include <memory>
     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 const HeaderMap *HeaderMap::Create(const FileEntry *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 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 const char *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 /// LookupFile - Check to see if the specified relative filename is located in
    198 /// this HeaderMap.  If so, open it and return its FileEntry.
    199 const FileEntry *HeaderMap::LookupFile(
    200     StringRef Filename, FileManager &FM) const {
    201 
    202   SmallString<1024> Path;
    203   StringRef Dest = HeaderMapImpl::lookupFilename(Filename, Path);
    204   if (Dest.empty())
    205     return nullptr;
    206 
    207   return FM.getFile(Dest);
    208 }
    209 
    210 StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
    211                                         SmallVectorImpl<char> &DestPath) const {
    212   const HMapHeader &Hdr = getHeader();
    213   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
    214 
    215   // Don't probe infinitely.  This should be checked before constructing.
    216   assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
    217 
    218   // Linearly probe the hash table.
    219   for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
    220     HMapBucket B = getBucket(Bucket & (NumBuckets-1));
    221     if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
    222 
    223     // See if the key matches.  If not, probe on.
    224     Optional<StringRef> Key = getString(B.Key);
    225     if (LLVM_UNLIKELY(!Key))
    226       continue;
    227     if (!Filename.equals_lower(*Key))
    228       continue;
    229 
    230     // If so, we have a match in the hash table.  Construct the destination
    231     // path.
    232     Optional<StringRef> Prefix = getString(B.Prefix);
    233     Optional<StringRef> Suffix = getString(B.Suffix);
    234 
    235     DestPath.clear();
    236     if (LLVM_LIKELY(Prefix && Suffix)) {
    237       DestPath.append(Prefix->begin(), Prefix->end());
    238       DestPath.append(Suffix->begin(), Suffix->end());
    239     }
    240     return StringRef(DestPath.begin(), DestPath.size());
    241   }
    242 }
    243