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"
16 #include "clang/Basic/FileManager.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',
31 HMAP_HeaderVersion = 1,
32
33 HMAP_EmptyBucketKey = 0
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.
HashHMapKey(StringRef Str)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.
Create(const FileEntry * FE,FileManager & FM)79 const HeaderMap *HeaderMap::Create(const FileEntry *FE, FileManager &FM) {
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.
getFileName() const115 const char *HeaderMap::getFileName() const {
116 return FileBuffer->getBufferIdentifier();
117 }
118
getEndianAdjustedWord(unsigned X) const119 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.
getHeader() const126 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).
getBucket(unsigned BucketNo) const134 HMapBucket HeaderMap::getBucket(unsigned BucketNo) const {
135 HMapBucket Result;
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.
getString(unsigned StrTabIdx) const158 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.
dump() const177 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.
LookupFile(StringRef Filename,FileManager & FM) const198 const FileEntry *HeaderMap::LookupFile(
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
lookupFilename(StringRef Filename,SmallVectorImpl<char> & DestPath) const209 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 }
238