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  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.
115const char *HeaderMap::getFileName() const {
116  return FileBuffer->getBufferIdentifier();
117}
118
119unsigned 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.
126const 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).
134HMapBucket 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.
158const 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.
177void 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.
198const 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
209StringRef 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