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>
23using namespace clang;
24
25//===----------------------------------------------------------------------===//
26// Data Structures and Manifest Constants
27//===----------------------------------------------------------------------===//
28
29enum {
30  HMAP_HeaderMagicNumber = ('h' << 24) | ('m' << 16) | ('a' << 8) | 'p',
31  HMAP_HeaderVersion = 1,
32
33  HMAP_EmptyBucketKey = 0
34};
35
36namespace clang {
37struct 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
44struct 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.
60static 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.
79const 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  std::unique_ptr<const llvm::MemoryBuffer> 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(FileBuffer.release(), NeedsByteSwap);
107}
108
109HeaderMap::~HeaderMap() {
110  delete FileBuffer;
111}
112
113//===----------------------------------------------------------------------===//
114//  Utility Methods
115//===----------------------------------------------------------------------===//
116
117
118/// getFileName - Return the filename of the headermap.
119const char *HeaderMap::getFileName() const {
120  return FileBuffer->getBufferIdentifier();
121}
122
123unsigned HeaderMap::getEndianAdjustedWord(unsigned X) const {
124  if (!NeedsBSwap) return X;
125  return llvm::ByteSwap_32(X);
126}
127
128/// getHeader - Return a reference to the file header, in unbyte-swapped form.
129/// This method cannot fail.
130const HMapHeader &HeaderMap::getHeader() const {
131  // We know the file is at least as big as the header.  Return it.
132  return *reinterpret_cast<const HMapHeader*>(FileBuffer->getBufferStart());
133}
134
135/// getBucket - Return the specified hash table bucket from the header map,
136/// bswap'ing its fields as appropriate.  If the bucket number is not valid,
137/// this return a bucket with an empty key (0).
138HMapBucket HeaderMap::getBucket(unsigned BucketNo) const {
139  HMapBucket Result;
140  Result.Key = HMAP_EmptyBucketKey;
141
142  const HMapBucket *BucketArray =
143    reinterpret_cast<const HMapBucket*>(FileBuffer->getBufferStart() +
144                                        sizeof(HMapHeader));
145
146  const HMapBucket *BucketPtr = BucketArray+BucketNo;
147  if ((const char*)(BucketPtr+1) > FileBuffer->getBufferEnd()) {
148    Result.Prefix = 0;
149    Result.Suffix = 0;
150    return Result;  // Invalid buffer, corrupt hmap.
151  }
152
153  // Otherwise, the bucket is valid.  Load the values, bswapping as needed.
154  Result.Key    = getEndianAdjustedWord(BucketPtr->Key);
155  Result.Prefix = getEndianAdjustedWord(BucketPtr->Prefix);
156  Result.Suffix = getEndianAdjustedWord(BucketPtr->Suffix);
157  return Result;
158}
159
160/// getString - Look up the specified string in the string table.  If the string
161/// index is not valid, it returns an empty string.
162const char *HeaderMap::getString(unsigned StrTabIdx) const {
163  // Add the start of the string table to the idx.
164  StrTabIdx += getEndianAdjustedWord(getHeader().StringsOffset);
165
166  // Check for invalid index.
167  if (StrTabIdx >= FileBuffer->getBufferSize())
168    return nullptr;
169
170  // Otherwise, we have a valid pointer into the file.  Just return it.  We know
171  // that the "string" can not overrun the end of the file, because the buffer
172  // is nul terminated by virtue of being a MemoryBuffer.
173  return FileBuffer->getBufferStart()+StrTabIdx;
174}
175
176//===----------------------------------------------------------------------===//
177// The Main Drivers
178//===----------------------------------------------------------------------===//
179
180/// dump - Print the contents of this headermap to stderr.
181void HeaderMap::dump() const {
182  const HMapHeader &Hdr = getHeader();
183  unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
184
185  fprintf(stderr, "Header Map %s:\n  %d buckets, %d entries\n",
186          getFileName(), NumBuckets,
187          getEndianAdjustedWord(Hdr.NumEntries));
188
189  for (unsigned i = 0; i != NumBuckets; ++i) {
190    HMapBucket B = getBucket(i);
191    if (B.Key == HMAP_EmptyBucketKey) continue;
192
193    const char *Key    = getString(B.Key);
194    const char *Prefix = getString(B.Prefix);
195    const char *Suffix = getString(B.Suffix);
196    fprintf(stderr, "  %d. %s -> '%s' '%s'\n", i, Key, Prefix, Suffix);
197  }
198}
199
200/// LookupFile - Check to see if the specified relative filename is located in
201/// this HeaderMap.  If so, open it and return its FileEntry.
202const FileEntry *HeaderMap::LookupFile(
203    StringRef Filename, FileManager &FM) const {
204
205  SmallString<1024> Path;
206  StringRef Dest = lookupFilename(Filename, Path);
207  if (Dest.empty())
208    return nullptr;
209
210  return FM.getFile(Dest);
211}
212
213StringRef HeaderMap::lookupFilename(StringRef Filename,
214                                    SmallVectorImpl<char> &DestPath) const {
215  const HMapHeader &Hdr = getHeader();
216  unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
217
218  // If the number of buckets is not a power of two, the headermap is corrupt.
219  // Don't probe infinitely.
220  if (NumBuckets & (NumBuckets-1))
221    return StringRef();
222
223  // Linearly probe the hash table.
224  for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
225    HMapBucket B = getBucket(Bucket & (NumBuckets-1));
226    if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
227
228    // See if the key matches.  If not, probe on.
229    if (!Filename.equals_lower(getString(B.Key)))
230      continue;
231
232    // If so, we have a match in the hash table.  Construct the destination
233    // path.
234    StringRef Prefix = getString(B.Prefix);
235    StringRef Suffix = getString(B.Suffix);
236    DestPath.clear();
237    DestPath.append(Prefix.begin(), Prefix.end());
238    DestPath.append(Suffix.begin(), Suffix.end());
239    return StringRef(DestPath.begin(), DestPath.size());
240  }
241}
242