LLVM  14.0.0git
DIEHash.cpp
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1 //===-- llvm/CodeGen/DIEHash.cpp - Dwarf Hashing Framework ----------------===//
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 contains support for DWARF4 hashing of DIEs.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "DIEHash.h"
14 #include "ByteStreamer.h"
15 #include "DwarfCompileUnit.h"
16 #include "DwarfDebug.h"
17 #include "llvm/ADT/ArrayRef.h"
18 #include "llvm/ADT/StringRef.h"
21 #include "llvm/Support/Debug.h"
22 #include "llvm/Support/Endian.h"
24 
25 using namespace llvm;
26 
27 #define DEBUG_TYPE "dwarfdebug"
28 
29 /// Grabs the string in whichever attribute is passed in and returns
30 /// a reference to it.
31 static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) {
32  // Iterate through all the attributes until we find the one we're
33  // looking for, if we can't find it return an empty string.
34  for (const auto &V : Die.values())
35  if (V.getAttribute() == Attr)
36  return V.getDIEString().getString();
37 
38  return StringRef("");
39 }
40 
41 /// Adds the string in \p Str to the hash. This also hashes
42 /// a trailing NULL with the string.
43 void DIEHash::addString(StringRef Str) {
44  LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");
45  Hash.update(Str);
46  Hash.update(makeArrayRef((uint8_t)'\0'));
47 }
48 
49 // FIXME: The LEB128 routines are copied and only slightly modified out of
50 // LEB128.h.
51 
52 /// Adds the unsigned in \p Value to the hash encoded as a ULEB128.
54  LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
55  do {
56  uint8_t Byte = Value & 0x7f;
57  Value >>= 7;
58  if (Value != 0)
59  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
60  Hash.update(Byte);
61  } while (Value != 0);
62 }
63 
64 void DIEHash::addSLEB128(int64_t Value) {
65  LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
66  bool More;
67  do {
68  uint8_t Byte = Value & 0x7f;
69  Value >>= 7;
70  More = !((((Value == 0) && ((Byte & 0x40) == 0)) ||
71  ((Value == -1) && ((Byte & 0x40) != 0))));
72  if (More)
73  Byte |= 0x80; // Mark this byte to show that more bytes will follow.
74  Hash.update(Byte);
75  } while (More);
76 }
77 
78 /// Including \p Parent adds the context of Parent to the hash..
79 void DIEHash::addParentContext(const DIE &Parent) {
80 
81  LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");
82 
83  // [7.27.2] For each surrounding type or namespace beginning with the
84  // outermost such construct...
86  const DIE *Cur = &Parent;
87  while (Cur->getParent()) {
88  Parents.push_back(Cur);
89  Cur = Cur->getParent();
90  }
91  assert(Cur->getTag() == dwarf::DW_TAG_compile_unit ||
92  Cur->getTag() == dwarf::DW_TAG_type_unit);
93 
94  // Reverse iterate over our list to go from the outermost construct to the
95  // innermost.
96  for (const DIE *Die : llvm::reverse(Parents)) {
97  // ... Append the letter "C" to the sequence...
98  addULEB128('C');
99 
100  // ... Followed by the DWARF tag of the construct...
101  addULEB128(Die->getTag());
102 
103  // ... Then the name, taken from the DW_AT_name attribute.
104  StringRef Name = getDIEStringAttr(*Die, dwarf::DW_AT_name);
105  LLVM_DEBUG(dbgs() << "... adding context: " << Name << "\n");
106  if (!Name.empty())
107  addString(Name);
108  }
109 }
110 
111 // Collect all of the attributes for a particular DIE in single structure.
112 void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) {
113 
114  for (const auto &V : Die.values()) {
115  LLVM_DEBUG(dbgs() << "Attribute: "
116  << dwarf::AttributeString(V.getAttribute())
117  << " added.\n");
118  switch (V.getAttribute()) {
119 #define HANDLE_DIE_HASH_ATTR(NAME) \
120  case dwarf::NAME: \
121  Attrs.NAME = V; \
122  break;
123 #include "DIEHashAttributes.def"
124  default:
125  break;
126  }
127  }
128 }
129 
130 void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute,
131  const DIE &Entry, StringRef Name) {
132  // append the letter 'N'
133  addULEB128('N');
134 
135  // the DWARF attribute code (DW_AT_type or DW_AT_friend),
137 
138  // the context of the tag,
139  if (const DIE *Parent = Entry.getParent())
140  addParentContext(*Parent);
141 
142  // the letter 'E',
143  addULEB128('E');
144 
145  // and the name of the type.
146  addString(Name);
147 
148  // Currently DW_TAG_friends are not used by Clang, but if they do become so,
149  // here's the relevant spec text to implement:
150  //
151  // For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram,
152  // the context is omitted and the name to be used is the ABI-specific name
153  // of the subprogram (e.g., the mangled linker name).
154 }
155 
156 void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute,
157  unsigned DieNumber) {
158  // a) If T is in the list of [previously hashed types], use the letter
159  // 'R' as the marker
160  addULEB128('R');
161 
163 
164  // and use the unsigned LEB128 encoding of [the index of T in the
165  // list] as the attribute value;
166  addULEB128(DieNumber);
167 }
168 
169 void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag,
170  const DIE &Entry) {
171  assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend "
172  "tags. Add support here when there's "
173  "a use case");
174  // Step 5
175  // If the tag in Step 3 is one of [the below tags]
176  if ((Tag == dwarf::DW_TAG_pointer_type ||
177  Tag == dwarf::DW_TAG_reference_type ||
178  Tag == dwarf::DW_TAG_rvalue_reference_type ||
179  Tag == dwarf::DW_TAG_ptr_to_member_type) &&
180  // and the referenced type (via the [below attributes])
181  // FIXME: This seems overly restrictive, and causes hash mismatches
182  // there's a decl/def difference in the containing type of a
183  // ptr_to_member_type, but it's what DWARF says, for some reason.
184  Attribute == dwarf::DW_AT_type) {
185  // ... has a DW_AT_name attribute,
186  StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name);
187  if (!Name.empty()) {
188  hashShallowTypeReference(Attribute, Entry, Name);
189  return;
190  }
191  }
192 
193  unsigned &DieNumber = Numbering[&Entry];
194  if (DieNumber) {
195  hashRepeatedTypeReference(Attribute, DieNumber);
196  return;
197  }
198 
199  // otherwise, b) use the letter 'T' as the marker, ...
200  addULEB128('T');
201 
203 
204  // ... process the type T recursively by performing Steps 2 through 7, and
205  // use the result as the attribute value.
206  DieNumber = Numbering.size();
207  computeHash(Entry);
208 }
209 
210 void DIEHash::hashRawTypeReference(const DIE &Entry) {
211  unsigned &DieNumber = Numbering[&Entry];
212  if (DieNumber) {
213  addULEB128('R');
214  addULEB128(DieNumber);
215  return;
216  }
217  DieNumber = Numbering.size();
218  addULEB128('T');
219  computeHash(Entry);
220 }
221 
222 // Hash all of the values in a block like set of values. This assumes that
223 // all of the data is going to be added as integers.
224 void DIEHash::hashBlockData(const DIE::const_value_range &Values) {
225  for (const auto &V : Values)
226  if (V.getType() == DIEValue::isBaseTypeRef) {
227  const DIE &C =
228  *CU->ExprRefedBaseTypes[V.getDIEBaseTypeRef().getIndex()].Die;
229  StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);
230  assert(!Name.empty() &&
231  "Base types referenced from DW_OP_convert should have a name");
232  hashNestedType(C, Name);
233  } else
234  Hash.update((uint64_t)V.getDIEInteger().getValue());
235 }
236 
237 // Hash the contents of a loclistptr class.
238 void DIEHash::hashLocList(const DIELocList &LocList) {
239  HashingByteStreamer Streamer(*this);
240  DwarfDebug &DD = *AP->getDwarfDebug();
241  const DebugLocStream &Locs = DD.getDebugLocs();
242  const DebugLocStream::List &List = Locs.getList(LocList.getValue());
243  for (const DebugLocStream::Entry &Entry : Locs.getEntries(List))
244  DD.emitDebugLocEntry(Streamer, Entry, List.CU);
245 }
246 
247 // Hash an individual attribute \param Attr based on the type of attribute and
248 // the form.
249 void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {
250  dwarf::Attribute Attribute = Value.getAttribute();
251 
252  // Other attribute values use the letter 'A' as the marker, and the value
253  // consists of the form code (encoded as an unsigned LEB128 value) followed by
254  // the encoding of the value according to the form code. To ensure
255  // reproducibility of the signature, the set of forms used in the signature
256  // computation is limited to the following: DW_FORM_sdata, DW_FORM_flag,
257  // DW_FORM_string, and DW_FORM_block.
258 
259  switch (Value.getType()) {
260  case DIEValue::isNone:
261  llvm_unreachable("Expected valid DIEValue");
262 
263  // 7.27 Step 3
264  // ... An attribute that refers to another type entry T is processed as
265  // follows:
266  case DIEValue::isEntry:
267  hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry());
268  break;
269  case DIEValue::isInteger: {
270  addULEB128('A');
272  switch (Value.getForm()) {
273  case dwarf::DW_FORM_data1:
274  case dwarf::DW_FORM_data2:
275  case dwarf::DW_FORM_data4:
276  case dwarf::DW_FORM_data8:
277  case dwarf::DW_FORM_udata:
278  case dwarf::DW_FORM_sdata:
279  addULEB128(dwarf::DW_FORM_sdata);
280  addSLEB128((int64_t)Value.getDIEInteger().getValue());
281  break;
282  // DW_FORM_flag_present is just flag with a value of one. We still give it a
283  // value so just use the value.
284  case dwarf::DW_FORM_flag_present:
285  case dwarf::DW_FORM_flag:
286  addULEB128(dwarf::DW_FORM_flag);
287  addULEB128((int64_t)Value.getDIEInteger().getValue());
288  break;
289  default:
290  llvm_unreachable("Unknown integer form!");
291  }
292  break;
293  }
294  case DIEValue::isString:
295  addULEB128('A');
297  addULEB128(dwarf::DW_FORM_string);
298  addString(Value.getDIEString().getString());
299  break;
300  case DIEValue::isInlineString:
301  addULEB128('A');
303  addULEB128(dwarf::DW_FORM_string);
304  addString(Value.getDIEInlineString().getString());
305  break;
306  case DIEValue::isBlock:
307  case DIEValue::isLoc:
308  case DIEValue::isLocList:
309  addULEB128('A');
311  addULEB128(dwarf::DW_FORM_block);
312  if (Value.getType() == DIEValue::isBlock) {
313  addULEB128(Value.getDIEBlock().computeSize(AP->getDwarfFormParams()));
314  hashBlockData(Value.getDIEBlock().values());
315  } else if (Value.getType() == DIEValue::isLoc) {
316  addULEB128(Value.getDIELoc().computeSize(AP->getDwarfFormParams()));
317  hashBlockData(Value.getDIELoc().values());
318  } else {
319  // We could add the block length, but that would take
320  // a bit of work and not add a lot of uniqueness
321  // to the hash in some way we could test.
322  hashLocList(Value.getDIELocList());
323  }
324  break;
325  // FIXME: It's uncertain whether or not we should handle this at the moment.
326  case DIEValue::isExpr:
327  case DIEValue::isLabel:
328  case DIEValue::isBaseTypeRef:
329  case DIEValue::isDelta:
330  case DIEValue::isAddrOffset:
331  llvm_unreachable("Add support for additional value types.");
332  }
333 }
334 
335 // Go through the attributes from \param Attrs in the order specified in 7.27.4
336 // and hash them.
337 void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) {
338 #define HANDLE_DIE_HASH_ATTR(NAME) \
339  { \
340  if (Attrs.NAME) \
341  hashAttribute(Attrs.NAME, Tag); \
342  }
343 #include "DIEHashAttributes.def"
344  // FIXME: Add the extended attributes.
345 }
346 
347 // Add all of the attributes for \param Die to the hash.
348 void DIEHash::addAttributes(const DIE &Die) {
349  DIEAttrs Attrs = {};
350  collectAttributes(Die, Attrs);
351  hashAttributes(Attrs, Die.getTag());
352 }
353 
354 void DIEHash::hashNestedType(const DIE &Die, StringRef Name) {
355  // 7.27 Step 7
356  // ... append the letter 'S',
357  addULEB128('S');
358 
359  // the tag of C,
360  addULEB128(Die.getTag());
361 
362  // and the name.
363  addString(Name);
364 }
365 
366 // Compute the hash of a DIE. This is based on the type signature computation
367 // given in section 7.27 of the DWARF4 standard. It is the md5 hash of a
368 // flattened description of the DIE.
369 void DIEHash::computeHash(const DIE &Die) {
370  // Append the letter 'D', followed by the DWARF tag of the DIE.
371  addULEB128('D');
372  addULEB128(Die.getTag());
373 
374  // Add each of the attributes of the DIE.
375  addAttributes(Die);
376 
377  // Then hash each of the children of the DIE.
378  for (auto &C : Die.children()) {
379  // 7.27 Step 7
380  // If C is a nested type entry or a member function entry, ...
381  if (isType(C.getTag()) || (C.getTag() == dwarf::DW_TAG_subprogram && isType(C.getParent()->getTag()))) {
382  StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);
383  // ... and has a DW_AT_name attribute
384  if (!Name.empty()) {
385  hashNestedType(C, Name);
386  continue;
387  }
388  }
389  computeHash(C);
390  }
391 
392  // Following the last (or if there are no children), append a zero byte.
393  Hash.update(makeArrayRef((uint8_t)'\0'));
394 }
395 
396 /// This is based on the type signature computation given in section 7.27 of the
397 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
398 /// with the inclusion of the full CU and all top level CU entities.
399 // TODO: Initialize the type chain at 0 instead of 1 for CU signatures.
401  Numbering.clear();
402  Numbering[&Die] = 1;
403 
404  if (!DWOName.empty())
405  Hash.update(DWOName);
406  // Hash the DIE.
407  computeHash(Die);
408 
409  // Now return the result.
410  MD5::MD5Result Result;
411  Hash.final(Result);
412 
413  // ... take the least significant 8 bytes and return those. Our MD5
414  // implementation always returns its results in little endian, so we actually
415  // need the "high" word.
416  return Result.high();
417 }
418 
419 /// This is based on the type signature computation given in section 7.27 of the
420 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
421 /// with the inclusion of additional forms not specifically called out in the
422 /// standard.
424  Numbering.clear();
425  Numbering[&Die] = 1;
426 
427  if (const DIE *Parent = Die.getParent())
428  addParentContext(*Parent);
429 
430  // Hash the DIE.
431  computeHash(Die);
432 
433  // Now return the result.
434  MD5::MD5Result Result;
435  Hash.final(Result);
436 
437  // ... take the least significant 8 bytes and return those. Our MD5
438  // implementation always returns its results in little endian, so we actually
439  // need the "high" word.
440  return Result.high();
441 }
AsmPrinter.h
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Definition: DebugLocStream.h:31
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Definition: DIEHash.cpp:53
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Definition: DIEHash.cpp:64
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