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 std::unique_ptr<HeaderMap> HeaderMap::Create(const FileEntry *FE,
52                                              FileManager &FM) {
53   // If the file is too small to be a header map, ignore it.
54   unsigned FileSize = FE->getSize();
55   if (FileSize <= sizeof(HMapHeader)) return nullptr;
56 
57   auto FileBuffer = FM.getBufferForFile(FE);
58   if (!FileBuffer || !*FileBuffer)
59     return nullptr;
60   bool NeedsByteSwap;
61   if (!checkHeader(**FileBuffer, NeedsByteSwap))
62     return nullptr;
63   return std::unique_ptr<HeaderMap>(new HeaderMap(std::move(*FileBuffer), NeedsByteSwap));
64 }
65 
66 bool HeaderMapImpl::checkHeader(const llvm::MemoryBuffer &File,
67                                 bool &NeedsByteSwap) {
68   if (File.getBufferSize() <= sizeof(HMapHeader))
69     return false;
70   const char *FileStart = File.getBufferStart();
71 
72   // We know the file is at least as big as the header, check it now.
73   const HMapHeader *Header = reinterpret_cast<const HMapHeader*>(FileStart);
74 
75   // Sniff it to see if it's a headermap by checking the magic number and
76   // version.
77   if (Header->Magic == HMAP_HeaderMagicNumber &&
78       Header->Version == HMAP_HeaderVersion)
79     NeedsByteSwap = false;
80   else if (Header->Magic == llvm::ByteSwap_32(HMAP_HeaderMagicNumber) &&
81            Header->Version == llvm::ByteSwap_16(HMAP_HeaderVersion))
82     NeedsByteSwap = true;  // Mixed endianness headermap.
83   else
84     return false;  // Not a header map.
85 
86   if (Header->Reserved != 0)
87     return false;
88 
89   // Check the number of buckets.  It should be a power of two, and there
90   // should be enough space in the file for all of them.
91   uint32_t NumBuckets = NeedsByteSwap
92                             ? llvm::sys::getSwappedBytes(Header->NumBuckets)
93                             : Header->NumBuckets;
94   if (!llvm::isPowerOf2_32(NumBuckets))
95     return false;
96   if (File.getBufferSize() <
97       sizeof(HMapHeader) + sizeof(HMapBucket) * NumBuckets)
98     return false;
99 
100   // Okay, everything looks good.
101   return true;
102 }
103 
104 //===----------------------------------------------------------------------===//
105 //  Utility Methods
106 //===----------------------------------------------------------------------===//
107 
108 
109 /// getFileName - Return the filename of the headermap.
110 StringRef HeaderMapImpl::getFileName() const {
111   return FileBuffer->getBufferIdentifier();
112 }
113 
114 unsigned HeaderMapImpl::getEndianAdjustedWord(unsigned X) const {
115   if (!NeedsBSwap) return X;
116   return llvm::ByteSwap_32(X);
117 }
118 
119 /// getHeader - Return a reference to the file header, in unbyte-swapped form.
120 /// This method cannot fail.
121 const HMapHeader &HeaderMapImpl::getHeader() const {
122   // We know the file is at least as big as the header.  Return it.
123   return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
124 }
125 
126 /// getBucket - Return the specified hash table bucket from the header map,
127 /// bswap'ing its fields as appropriate.  If the bucket number is not valid,
128 /// this return a bucket with an empty key (0).
129 HMapBucket HeaderMapImpl::getBucket(unsigned BucketNo) const {
130   assert(FileBuffer->getBufferSize() >=
131              sizeof(HMapHeader) + sizeof(HMapBucket) * BucketNo &&
132          "Expected bucket to be in range");
133 
134   HMapBucket Result;
135   Result.Key = HMAP_EmptyBucketKey;
136 
137   const HMapBucket *BucketArray =
138     reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
139                                         sizeof(HMapHeader));
140   const HMapBucket *BucketPtr = BucketArray+BucketNo;
141 
142   // Load the values, bswapping as needed.
143   Result.Key    = getEndianAdjustedWord(BucketPtr->Key);
144   Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
145   Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
146   return Result;
147 }
148 
149 Optional<StringRef> HeaderMapImpl::getString(unsigned StrTabIdx) const {
150   // Add the start of the string table to the idx.
151   StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
152 
153   // Check for invalid index.
154   if (StrTabIdx >= FileBuffer->getBufferSize())
155     return None;
156 
157   const char *Data = FileBuffer->getBufferStart() + StrTabIdx;
158   unsigned MaxLen = FileBuffer->getBufferSize() - StrTabIdx;
159   unsigned Len = strnlen(Data, MaxLen);
160 
161   // Check whether the buffer is null-terminated.
162   if (Len == MaxLen && Data[Len - 1])
163     return None;
164 
165   return StringRef(Data, Len);
166 }
167 
168 //===----------------------------------------------------------------------===//
169 // The Main Drivers
170 //===----------------------------------------------------------------------===//
171 
172 /// dump - Print the contents of this headermap to stderr.
173 LLVM_DUMP_METHOD void HeaderMapImpl::dump() const {
174   const HMapHeader &Hdr = getHeader();
175   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
176 
177   llvm::dbgs() << "Header Map " << getFileName() << ":\n  " << NumBuckets
178                << ", " << getEndianAdjustedWord(Hdr.NumEntries) << "\n";
179 
180   auto getStringOrInvalid = [this](unsigned Id) -> StringRef {
181     if (Optional<StringRef> S = getString(Id))
182       return *S;
183     return "<invalid>";
184   };
185 
186   for (unsigned i = 0; i != NumBuckets; ++i) {
187     HMapBucket B = getBucket(i);
188     if (B.Key == HMAP_EmptyBucketKey) continue;
189 
190     StringRef Key = getStringOrInvalid(B.Key);
191     StringRef Prefix = getStringOrInvalid(B.Prefix);
192     StringRef Suffix = getStringOrInvalid(B.Suffix);
193     llvm::dbgs() << "  " << i << ". " << Key << " -> '" << Prefix << "' '"
194                  << Suffix << "'\n";
195   }
196 }
197 
198 /// LookupFile - Check to see if the specified relative filename is located in
199 /// this HeaderMap.  If so, open it and return its FileEntry.
200 const FileEntry *HeaderMap::LookupFile(
201     StringRef Filename, FileManager &FM) const {
202 
203   SmallString<1024> Path;
204   StringRef Dest = HeaderMapImpl::lookupFilename(Filename, Path);
205   if (Dest.empty())
206     return nullptr;
207 
208   return FM.getFile(Dest);
209 }
210 
211 StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
212                                         SmallVectorImpl<char> &DestPath) const {
213   const HMapHeader &Hdr = getHeader();
214   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
215 
216   // Don't probe infinitely.  This should be checked before constructing.
217   assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
218 
219   // Linearly probe the hash table.
220   for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
221     HMapBucket B = getBucket(Bucket & (NumBuckets-1));
222     if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
223 
224     // See if the key matches.  If not, probe on.
225     Optional<StringRef> Key = getString(B.Key);
226     if (LLVM_UNLIKELY(!Key))
227       continue;
228     if (!Filename.equals_lower(*Key))
229       continue;
230 
231     // If so, we have a match in the hash table.  Construct the destination
232     // path.
233     Optional<StringRef> Prefix = getString(B.Prefix);
234     Optional<StringRef> Suffix = getString(B.Suffix);
235 
236     DestPath.clear();
237     if (LLVM_LIKELY(Prefix && Suffix)) {
238       DestPath.append(Prefix->begin(), Prefix->end());
239       DestPath.append(Suffix->begin(), Suffix->end());
240     }
241     return StringRef(DestPath.begin(), DestPath.size());
242   }
243 }
244