clang  3.7.0
HeaderMap.cpp
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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/Basic/CharInfo.h"
17 #include "llvm/ADT/SmallString.h"
18 #include "llvm/Support/DataTypes.h"
19 #include "llvm/Support/MathExtras.h"
20 #include "llvm/Support/MemoryBuffer.h"
21 #include <cstdio>
22 #include <memory>
23 using namespace clang;
24 
25 //===----------------------------------------------------------------------===//
26 // Data Structures and Manifest Constants
27 //===----------------------------------------------------------------------===//
28 
29 enum {
30  HMAP_HeaderMagicNumber = ('h' << 24) | ('m' << 16) | ('a' << 8) | 'p',
32 
34 };
35 
36 namespace clang {
37 struct HMapBucket {
38  uint32_t Key; // Offset (into strings) of key.
39 
40  uint32_t Prefix; // Offset (into strings) of value prefix.
41  uint32_t Suffix; // Offset (into strings) of value suffix.
42 };
43 
44 struct HMapHeader {
45  uint32_t Magic; // Magic word, also indicates byte order.
46  uint16_t Version; // Version number -- currently 1.
47  uint16_t Reserved; // Reserved for future use - zero for now.
48  uint32_t StringsOffset; // Offset to start of string pool.
49  uint32_t NumEntries; // Number of entries in the string table.
50  uint32_t NumBuckets; // Number of buckets (always a power of 2).
51  uint32_t MaxValueLength; // Length of longest result path (excluding nul).
52  // An array of 'NumBuckets' HMapBucket objects follows this header.
53  // Strings follow the buckets, at StringsOffset.
54 };
55 } // end namespace clang.
56 
57 /// HashHMapKey - This is the 'well known' hash function required by the file
58 /// format, used to look up keys in the hash table. The hash table uses simple
59 /// linear probing based on this function.
60 static inline unsigned HashHMapKey(StringRef Str) {
61  unsigned Result = 0;
62  const char *S = Str.begin(), *End = Str.end();
63 
64  for (; S != End; S++)
65  Result += toLowercase(*S) * 13;
66  return Result;
67 }
68 
69 
70 
71 //===----------------------------------------------------------------------===//
72 // Verification and Construction
73 //===----------------------------------------------------------------------===//
74 
75 /// HeaderMap::Create - This attempts to load the specified file as a header
76 /// map. If it doesn't look like a HeaderMap, it gives up and returns null.
77 /// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
78 /// into the string error argument and returns null.
80  // If the file is too small to be a header map, ignore it.
81  unsigned FileSize = FE->getSize();
82  if (FileSize <= sizeof(HMapHeader)) return nullptr;
83 
84  auto FileBuffer = FM.getBufferForFile(FE);
85  if (!FileBuffer) return nullptr; // Unreadable file?
86  const char *FileStart = (*FileBuffer)->getBufferStart();
87 
88  // We know the file is at least as big as the header, check it now.
89  const HMapHeader *Header = reinterpret_cast<const HMapHeader*>(FileStart);
90 
91  // Sniff it to see if it's a headermap by checking the magic number and
92  // version.
93  bool NeedsByteSwap;
94  if (Header->Magic == HMAP_HeaderMagicNumber &&
95  Header->Version == HMAP_HeaderVersion)
96  NeedsByteSwap = false;
97  else if (Header->Magic == llvm::ByteSwap_32(HMAP_HeaderMagicNumber) &&
98  Header->Version == llvm::ByteSwap_16(HMAP_HeaderVersion))
99  NeedsByteSwap = true; // Mixed endianness headermap.
100  else
101  return nullptr; // Not a header map.
102 
103  if (Header->Reserved != 0) return nullptr;
104 
105  // Okay, everything looks good, create the header map.
106  return new HeaderMap(std::move(*FileBuffer), NeedsByteSwap);
107 }
108 
109 //===----------------------------------------------------------------------===//
110 // Utility Methods
111 //===----------------------------------------------------------------------===//
112 
113 
114 /// getFileName - Return the filename of the headermap.
115 const char *HeaderMap::getFileName() const {
116  return FileBuffer->getBufferIdentifier();
117 }
118 
119 unsigned HeaderMap::getEndianAdjustedWord(unsigned X) const {
120  if (!NeedsBSwap) return X;
121  return llvm::ByteSwap_32(X);
122 }
123 
124 /// getHeader - Return a reference to the file header, in unbyte-swapped form.
125 /// This method cannot fail.
126 const HMapHeader &HeaderMap::getHeader() const {
127  // We know the file is at least as big as the header. Return it.
128  return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
129 }
130 
131 /// getBucket - Return the specified hash table bucket from the header map,
132 /// bswap'ing its fields as appropriate. If the bucket number is not valid,
133 /// this return a bucket with an empty key (0).
134 HMapBucket HeaderMap::getBucket(unsigned BucketNo) const {
136  Result.Key = HMAP_EmptyBucketKey;
137 
138  const HMapBucket *BucketArray =
139  reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
140  sizeof(HMapHeader));
141 
142  const HMapBucket *BucketPtr = BucketArray+BucketNo;
143  if ((const char*)(BucketPtr+1) > FileBuffer->getBufferEnd()) {
144  Result.Prefix = 0;
145  Result.Suffix = 0;
146  return Result; // Invalid buffer, corrupt hmap.
147  }
148 
149  // Otherwise, the bucket is valid. Load the values, bswapping as needed.
150  Result.Key = getEndianAdjustedWord(BucketPtr->Key);
151  Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
152  Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
153  return Result;
154 }
155 
156 /// getString - Look up the specified string in the string table. If the string
157 /// index is not valid, it returns an empty string.
158 const char *HeaderMap::getString(unsigned StrTabIdx) const {
159  // Add the start of the string table to the idx.
160  StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
161 
162  // Check for invalid index.
163  if (StrTabIdx >= FileBuffer->getBufferSize())
164  return nullptr;
165 
166  // Otherwise, we have a valid pointer into the file. Just return it. We know
167  // that the "string" can not overrun the end of the file, because the buffer
168  // is nul terminated by virtue of being a MemoryBuffer.
169  return FileBuffer->getBufferStart()+StrTabIdx;
170 }
171 
172 //===----------------------------------------------------------------------===//
173 // The Main Drivers
174 //===----------------------------------------------------------------------===//
175 
176 /// dump - Print the contents of this headermap to stderr.
177 void HeaderMap::dump() const {
178  const HMapHeader &Hdr = getHeader();
179  unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
180 
181  fprintf(stderr, "Header Map %s:\n %d buckets, %d entries\n",
182  getFileName(), NumBuckets,
183  getEndianAdjustedWord(Hdr.NumEntries));
184 
185  for (unsigned i = 0; i != NumBuckets; ++i) {
186  HMapBucket B = getBucket(i);
187  if (B.Key == HMAP_EmptyBucketKey) continue;
188 
189  const char *Key = getString(B.Key);
190  const char *Prefix = getString(B.Prefix);
191  const char *Suffix = getString(B.Suffix);
192  fprintf(stderr, " %d. %s -> '%s' '%s'\n", i, Key, Prefix, Suffix);
193  }
194 }
195 
196 /// LookupFile - Check to see if the specified relative filename is located in
197 /// this HeaderMap. If so, open it and return its FileEntry.
199  StringRef Filename, FileManager &FM) const {
200 
201  SmallString<1024> Path;
202  StringRef Dest = lookupFilename(Filename, Path);
203  if (Dest.empty())
204  return nullptr;
205 
206  return FM.getFile(Dest);
207 }
208 
209 StringRef HeaderMap::lookupFilename(StringRef Filename,
210  SmallVectorImpl<char> &DestPath) const {
211  const HMapHeader &Hdr = getHeader();
212  unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
213 
214  // If the number of buckets is not a power of two, the headermap is corrupt.
215  // Don't probe infinitely.
216  if (NumBuckets & (NumBuckets-1))
217  return StringRef();
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  if (!Filename.equals_lower(getString(B.Key)))
226  continue;
227 
228  // If so, we have a match in the hash table. Construct the destination
229  // path.
230  StringRef Prefix = getString(B.Prefix);
231  StringRef Suffix = getString(B.Suffix);
232  DestPath.clear();
233  DestPath.append(Prefix.begin(), Prefix.end());
234  DestPath.append(Suffix.begin(), Suffix.end());
235  return StringRef(DestPath.begin(), DestPath.size());
236  }
237 }
Implements support for file system lookup, file system caching, and directory search management...
Definition: FileManager.h:115
Defines the clang::FileManager interface and associated types.
const char * getFileName() const
getFileName - Return the filename of the headermap.
Definition: HeaderMap.cpp:115
const FileEntry * LookupFile(StringRef Filename, FileManager &FM) const
Definition: HeaderMap.cpp:198
off_t getSize() const
Definition: FileManager.h:86
uint16_t Reserved
Definition: HeaderMap.cpp:47
uint32_t StringsOffset
Definition: HeaderMap.cpp:48
static const HeaderMap * Create(const FileEntry *FE, FileManager &FM)
Definition: HeaderMap.cpp:79
uint32_t MaxValueLength
Definition: HeaderMap.cpp:51
void dump() const
dump - Print the contents of this headermap to stderr.
Definition: HeaderMap.cpp:177
const FileEntry * getFile(StringRef Filename, bool OpenFile=false, bool CacheFailure=true)
Lookup, cache, and verify the specified file (real or virtual).
const SmallVectorImpl< AnnotatedLine * >::const_iterator End
The result type of a method or function.
Cached information about one file (either on disk or in the virtual file system). ...
Definition: FileManager.h:53
llvm::ErrorOr< std::unique_ptr< llvm::MemoryBuffer > > getBufferForFile(const FileEntry *Entry, bool isVolatile=false, bool ShouldCloseOpenFile=true)
Open the specified file as a MemoryBuffer, returning a new MemoryBuffer if successful, otherwise returning null.
uint16_t Version
Definition: HeaderMap.cpp:46
uint32_t NumEntries
Definition: HeaderMap.cpp:49
X
Definition: SemaDecl.cpp:11429
static LLVM_READONLY char toLowercase(char c)
Definition: CharInfo.h:165
static unsigned HashHMapKey(StringRef Str)
Definition: HeaderMap.cpp:60
StringRef lookupFilename(StringRef Filename, SmallVectorImpl< char > &DestPath) const
Definition: HeaderMap.cpp:209
uint32_t NumBuckets
Definition: HeaderMap.cpp:50
llvm::TimeRecord * Bucket