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>
26using 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.
31static 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.
50std::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
65bool 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.
109StringRef HeaderMapImpl::getFileName() const {
110  return FileBuffer->getBufferIdentifier();
111}
112
113unsigned 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.
120const 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).
128HMapBucket 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
148Optional<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.
172LLVM_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/// LookupFile - Check to see if the specified relative filename is located in
198/// this HeaderMap.  If so, open it and return its FileEntry.
199Optional<FileEntryRef> HeaderMap::LookupFile(StringRef Filename,
200                                             FileManager &FM) const {
201
202  SmallString<1024> Path;
203  StringRef Dest = HeaderMapImpl::lookupFilename(Filename, Path);
204  if (Dest.empty())
205    return None;
206
207  return FM.getOptionalFileRef(Dest);
208}
209
210StringRef HeaderMapImpl::lookupFilename(StringRef Filename,
211                                        SmallVectorImpl<char> &DestPath) const {
212  const HMapHeader &Hdr = getHeader();
213  unsigned NumBuckets = getEndianAdjustedWord(Hdr.NumBuckets);
214
215  // Don't probe infinitely.  This should be checked before constructing.
216  assert(llvm::isPowerOf2_32(NumBuckets) && "Expected power of 2");
217
218  // Linearly probe the hash table.
219  for (unsigned Bucket = HashHMapKey(Filename);; ++Bucket) {
220    HMapBucket B = getBucket(Bucket & (NumBuckets-1));
221    if (B.Key == HMAP_EmptyBucketKey) return StringRef(); // Hash miss.
222
223    // See if the key matches.  If not, probe on.
224    Optional<StringRef> Key = getString(B.Key);
225    if (LLVM_UNLIKELY(!Key))
226      continue;
227    if (!Filename.equals_lower(*Key))
228      continue;
229
230    // If so, we have a match in the hash table.  Construct the destination
231    // path.
232    Optional<StringRef> Prefix = getString(B.Prefix);
233    Optional<StringRef> Suffix = getString(B.Suffix);
234
235    DestPath.clear();
236    if (LLVM_LIKELY(Prefix && Suffix)) {
237      DestPath.append(Prefix->begin(), Prefix->end());
238      DestPath.append(Suffix->begin(), Suffix->end());
239    }
240    return StringRef(DestPath.begin(), DestPath.size());
241  }
242}
243