xref: /freebsd/contrib/llvm-project/clang/lib/Lex/HeaderMap.cpp (revision e6bfd18d21b225af6a0ed67ceeaf1293b7b9eba5)
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 using namespace clang;
27 
28 /// HashHMapKey - This is the 'well known' hash function required by the file
29 /// format, used to look up keys in the hash table.  The hash table uses simple
30 /// linear probing based on this function.
31 static inline unsigned HashHMapKey(StringRef Str) {
32   unsigned Result = 0;
33   const char *S = Str.begin(), *End = Str.end();
34 
35   for (; S != End; S++)
36     Result += toLowercase(*S) * 13;
37   return Result;
38 }
39 
40 
41 
42 //===----------------------------------------------------------------------===//
43 // Verification and Construction
44 //===----------------------------------------------------------------------===//
45 
46 /// HeaderMap::Create - This attempts to load the specified file as a header
47 /// map.  If it doesn't look like a HeaderMap, it gives up and returns null.
48 /// If it looks like a HeaderMap but is obviously corrupted, it puts a reason
49 /// into the string error argument and returns null.
50 std::unique_ptr<HeaderMap> HeaderMap::Create(const FileEntry *FE,
51                                              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_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 StringRef 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 StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
198                                         SmallVectorImpl<char> &DestPath) const {
199   const HMapHeader &Hdr = getHeader();
200   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
201 
202   // Don't probe infinitely.  This should be checked before constructing.
203   assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
204 
205   // Linearly probe the hash table.
206   for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
207     HMapBucket B = getBucket(Bucket & (NumBuckets-1));
208     if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
209 
210     // See if the key matches.  If not, probe on.
211     Optional<StringRef> Key = getString(B.Key);
212     if (LLVM_UNLIKELY(!Key))
213       continue;
214     if (!Filename.equals_insensitive(*Key))
215       continue;
216 
217     // If so, we have a match in the hash table.  Construct the destination
218     // path.
219     Optional<StringRef> Prefix = getString(B.Prefix);
220     Optional<StringRef> Suffix = getString(B.Suffix);
221 
222     DestPath.clear();
223     if (LLVM_LIKELY(Prefix && Suffix)) {
224       DestPath.append(Prefix->begin(), Prefix->end());
225       DestPath.append(Suffix->begin(), Suffix->end());
226     }
227     return StringRef(DestPath.begin(), DestPath.size());
228   }
229 }
230 
231 StringRef HeaderMapImpl::reverseLookupFilename(StringRef DestPath) const {
232   if (!ReverseMap.empty())
233     return ReverseMap.lookup(DestPath);
234 
235   const HMapHeader &Hdr = getHeader();
236   unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
237   StringRef RetKey;
238   for (unsigned i = 0; i != NumBuckets; ++i) {
239     HMapBucket B = getBucket(i);
240     if (B.Key == HMAP_EmptyBucketKey)
241       continue;
242 
243     Optional<StringRef> Key = getString(B.Key);
244     Optional<StringRef> Prefix = getString(B.Prefix);
245     Optional<StringRef> Suffix = getString(B.Suffix);
246     if (LLVM_LIKELY(Key && Prefix && Suffix)) {
247       SmallVector<char, 1024> Buf;
248       Buf.append(Prefix->begin(), Prefix->end());
249       Buf.append(Suffix->begin(), Suffix->end());
250       StringRef Value(Buf.begin(), Buf.size());
251       ReverseMap[Value] = *Key;
252 
253       if (DestPath == Value)
254         RetKey = *Key;
255     }
256   }
257   return RetKey;
258 }
259