lib/CodeGen/AsmPrinter/DIEHash.cpp

   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 "DwarfDebug.h"
  16 #include "llvm/ADT/ArrayRef.h"
  17 #include "llvm/ADT/StringRef.h"
  18 #include "llvm/BinaryFormat/Dwarf.h"
  19 #include "llvm/CodeGen/AsmPrinter.h"
  20 #include "llvm/CodeGen/DIE.h"
  21 #include "llvm/Support/Debug.h"
  22 #include "llvm/Support/Endian.h"
  23 #include "llvm/Support/MD5.h"
  24 #include "llvm/Support/raw_ostream.h"
  25
  26 using namespace llvm;
  27
  28 #define DEBUG_TYPE "dwarfdebug"
  29
  30 /// Grabs the string in whichever attribute is passed in and returns
  31 /// a reference to it.
  32 static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) {
  33   // Iterate through all the attributes until we find the one we're
  34   // looking for, if we can't find it return an empty string.
  35   for (const auto &V : Die.values())
  36     if (V.getAttribute() == Attr)
  37       return V.getDIEString().getString();
  38
  39   return StringRef("");
  40 }
  41
  42 /// Adds the string in \p Str to the hash. This also hashes
  43 /// a trailing NULL with the string.
  44 void DIEHash::addString(StringRef Str) {
  45   LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");
  46   Hash.update(Str);
  47   Hash.update(makeArrayRef((uint8_t)'\0'));
  48 }
  49
  50 // FIXME: The LEB128 routines are copied and only slightly modified out of
  51 // LEB128.h.
  52
  53 /// Adds the unsigned in \p Value to the hash encoded as a ULEB128.
  54 void DIEHash::addULEB128(uint64_t Value) {
  55   LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
  56   do {
  57     uint8_t Byte = Value & 0x7f;
  58     Value >>= 7;
  59     if (Value != 0)
  60       Byte |= 0x80; // Mark this byte to show that more bytes will follow.
  61     Hash.update(Byte);
  62   } while (Value != 0);
  63 }
  64
  65 void DIEHash::addSLEB128(int64_t Value) {
  66   LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");
  67   bool More;
  68   do {
  69     uint8_t Byte = Value & 0x7f;
  70     Value >>= 7;
  71     More = !((((Value == 0) && ((Byte & 0x40) == 0)) ||
  72               ((Value == -1) && ((Byte & 0x40) != 0))));
  73     if (More)
  74       Byte |= 0x80; // Mark this byte to show that more bytes will follow.
  75     Hash.update(Byte);
  76   } while (More);
  77 }
  78
  79 /// Including \p Parent adds the context of Parent to the hash..
  80 void DIEHash::addParentContext(const DIE &Parent) {
  81
  82   LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");
  83
  84   // [7.27.2] For each surrounding type or namespace beginning with the
  85   // outermost such construct...
  86   SmallVector<const DIE *, 1> Parents;
  87   const DIE *Cur = &Parent;
  88   while (Cur->getParent()) {
  89     Parents.push_back(Cur);
  90     Cur = Cur->getParent();
  91   }
  92   assert(Cur->getTag() == dwarf::DW_TAG_compile_unit ||
  93          Cur->getTag() == dwarf::DW_TAG_type_unit);
  94
  95   // Reverse iterate over our list to go from the outermost construct to the
  96   // innermost.
  97   for (SmallVectorImpl<const DIE *>::reverse_iterator I = Parents.rbegin(),
  98                                                       E = Parents.rend();
  99        I != E; ++I) {
 100     const DIE &Die = **I;
 101
 102     // ... Append the letter "C" to the sequence...
 103     addULEB128('C');
 104
 105     // ... Followed by the DWARF tag of the construct...
 106     addULEB128(Die.getTag());
 107
 108     // ... Then the name, taken from the DW_AT_name attribute.
 109     StringRef Name = getDIEStringAttr(Die, dwarf::DW_AT_name);
 110     LLVM_DEBUG(dbgs() << "... adding context: " << Name << "\n");
 111     if (!Name.empty())
 112       addString(Name);
 113   }
 114 }
 115
 116 // Collect all of the attributes for a particular DIE in single structure.
 117 void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) {
 118
 119   for (const auto &V : Die.values()) {
 120     LLVM_DEBUG(dbgs() << "Attribute: "
 121                       << dwarf::AttributeString(V.getAttribute())
 122                       << " added.\n");
 123     switch (V.getAttribute()) {
 124 #define HANDLE_DIE_HASH_ATTR(NAME)                                             \
 125   case dwarf::NAME:                                                            \
 126     Attrs.NAME = V;                                                            \
 127     break;
 128 #include "DIEHashAttributes.def"
 129     default:
 130       break;
 131     }
 132   }
 133 }
 134
 135 void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute,
 136                                        const DIE &Entry, StringRef Name) {
 137   // append the letter 'N'
 138   addULEB128('N');
 139
 140   // the DWARF attribute code (DW_AT_type or DW_AT_friend),
 141   addULEB128(Attribute);
 142
 143   // the context of the tag,
 144   if (const DIE *Parent = Entry.getParent())
 145     addParentContext(*Parent);
 146
 147   // the letter 'E',
 148   addULEB128('E');
 149
 150   // and the name of the type.
 151   addString(Name);
 152
 153   // Currently DW_TAG_friends are not used by Clang, but if they do become so,
 154   // here's the relevant spec text to implement:
 155   //
 156   // For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram,
 157   // the context is omitted and the name to be used is the ABI-specific name
 158   // of the subprogram (e.g., the mangled linker name).
 159 }
 160
 161 void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute,
 162                                         unsigned DieNumber) {
 163   // a) If T is in the list of [previously hashed types], use the letter
 164   // 'R' as the marker
 165   addULEB128('R');
 166
 167   addULEB128(Attribute);
 168
 169   // and use the unsigned LEB128 encoding of [the index of T in the
 170   // list] as the attribute value;
 171   addULEB128(DieNumber);
 172 }
 173
 174 void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag,
 175                            const DIE &Entry) {
 176   assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend "
 177                                         "tags. Add support here when there's "
 178                                         "a use case");
 179   // Step 5
 180   // If the tag in Step 3 is one of [the below tags]
 181   if ((Tag == dwarf::DW_TAG_pointer_type ||
 182        Tag == dwarf::DW_TAG_reference_type ||
 183        Tag == dwarf::DW_TAG_rvalue_reference_type ||
 184        Tag == dwarf::DW_TAG_ptr_to_member_type) &&
 185       // and the referenced type (via the [below attributes])
 186       // FIXME: This seems overly restrictive, and causes hash mismatches
 187       // there's a decl/def difference in the containing type of a
 188       // ptr_to_member_type, but it's what DWARF says, for some reason.
 189       Attribute == dwarf::DW_AT_type) {
 190     // ... has a DW_AT_name attribute,
 191     StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name);
 192     if (!Name.empty()) {
 193       hashShallowTypeReference(Attribute, Entry, Name);
 194       return;
 195     }
 196   }
 197
 198   unsigned &DieNumber = Numbering[&Entry];
 199   if (DieNumber) {
 200     hashRepeatedTypeReference(Attribute, DieNumber);
 201     return;
 202   }
 203
 204   // otherwise, b) use the letter 'T' as the marker, ...
 205   addULEB128('T');
 206
 207   addULEB128(Attribute);
 208
 209   // ... process the type T recursively by performing Steps 2 through 7, and
 210   // use the result as the attribute value.
 211   DieNumber = Numbering.size();
 212   computeHash(Entry);
 213 }
 214
 215 // Hash all of the values in a block like set of values. This assumes that
 216 // all of the data is going to be added as integers.
 217 void DIEHash::hashBlockData(const DIE::const_value_range &Values) {
 218   for (const auto &V : Values)
 219     Hash.update((uint64_t)V.getDIEInteger().getValue());
 220 }
 221
 222 // Hash the contents of a loclistptr class.
 223 void DIEHash::hashLocList(const DIELocList &LocList) {
 224   HashingByteStreamer Streamer(*this);
 225   DwarfDebug &DD = *AP->getDwarfDebug();
 226   const DebugLocStream &Locs = DD.getDebugLocs();
 227   for (const auto &Entry : Locs.getEntries(Locs.getList(LocList.getValue())))
 228     DD.emitDebugLocEntry(Streamer, Entry, nullptr);
 229 }
 230
 231 // Hash an individual attribute \param Attr based on the type of attribute and
 232 // the form.
 233 void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {
 234   dwarf::Attribute Attribute = Value.getAttribute();
 235
 236   // Other attribute values use the letter 'A' as the marker, and the value
 237   // consists of the form code (encoded as an unsigned LEB128 value) followed by
 238   // the encoding of the value according to the form code. To ensure
 239   // reproducibility of the signature, the set of forms used in the signature
 240   // computation is limited to the following: DW_FORM_sdata, DW_FORM_flag,
 241   // DW_FORM_string, and DW_FORM_block.
 242
 243   switch (Value.getType()) {
 244   case DIEValue::isNone:
 245     llvm_unreachable("Expected valid DIEValue");
 246
 247     // 7.27 Step 3
 248     // ... An attribute that refers to another type entry T is processed as
 249     // follows:
 250   case DIEValue::isEntry:
 251     hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry());
 252     break;
 253   case DIEValue::isInteger: {
 254     addULEB128('A');
 255     addULEB128(Attribute);
 256     switch (Value.getForm()) {
 257     case dwarf::DW_FORM_data1:
 258     case dwarf::DW_FORM_data2:
 259     case dwarf::DW_FORM_data4:
 260     case dwarf::DW_FORM_data8:
 261     case dwarf::DW_FORM_udata:
 262     case dwarf::DW_FORM_sdata:
 263       addULEB128(dwarf::DW_FORM_sdata);
 264       addSLEB128((int64_t)Value.getDIEInteger().getValue());
 265       break;
 266     // DW_FORM_flag_present is just flag with a value of one. We still give it a
 267     // value so just use the value.
 268     case dwarf::DW_FORM_flag_present:
 269     case dwarf::DW_FORM_flag:
 270       addULEB128(dwarf::DW_FORM_flag);
 271       addULEB128((int64_t)Value.getDIEInteger().getValue());
 272       break;
 273     default:
 274       llvm_unreachable("Unknown integer form!");
 275     }
 276     break;
 277   }
 278   case DIEValue::isString:
 279     addULEB128('A');
 280     addULEB128(Attribute);
 281     addULEB128(dwarf::DW_FORM_string);
 282     addString(Value.getDIEString().getString());
 283     break;
 284   case DIEValue::isInlineString:
 285     addULEB128('A');
 286     addULEB128(Attribute);
 287     addULEB128(dwarf::DW_FORM_string);
 288     addString(Value.getDIEInlineString().getString());
 289     break;
 290   case DIEValue::isBlock:
 291   case DIEValue::isLoc:
 292   case DIEValue::isLocList:
 293     addULEB128('A');
 294     addULEB128(Attribute);
 295     addULEB128(dwarf::DW_FORM_block);
 296     if (Value.getType() == DIEValue::isBlock) {
 297       addULEB128(Value.getDIEBlock().ComputeSize(AP));
 298       hashBlockData(Value.getDIEBlock().values());
 299     } else if (Value.getType() == DIEValue::isLoc) {
 300       addULEB128(Value.getDIELoc().ComputeSize(AP));
 301       hashBlockData(Value.getDIELoc().values());
 302     } else {
 303       // We could add the block length, but that would take
 304       // a bit of work and not add a lot of uniqueness
 305       // to the hash in some way we could test.
 306       hashLocList(Value.getDIELocList());
 307     }
 308     break;
 309     // FIXME: It's uncertain whether or not we should handle this at the moment.
 310   case DIEValue::isExpr:
 311   case DIEValue::isLabel:
 312   case DIEValue::isBaseTypeRef:
 313   case DIEValue::isDelta:
 314     llvm_unreachable("Add support for additional value types.");
 315   }
 316 }
 317
 318 // Go through the attributes from \param Attrs in the order specified in 7.27.4
 319 // and hash them.
 320 void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) {
 321 #define HANDLE_DIE_HASH_ATTR(NAME)                                             \
 322   {                                                                            \
 323     if (Attrs.NAME)                                                           \
 324       hashAttribute(Attrs.NAME, Tag);                                         \
 325   }
 326 #include "DIEHashAttributes.def"
 327   // FIXME: Add the extended attributes.
 328 }
 329
 330 // Add all of the attributes for \param Die to the hash.
 331 void DIEHash::addAttributes(const DIE &Die) {
 332   DIEAttrs Attrs = {};
 333   collectAttributes(Die, Attrs);
 334   hashAttributes(Attrs, Die.getTag());
 335 }
 336
 337 void DIEHash::hashNestedType(const DIE &Die, StringRef Name) {
 338   // 7.27 Step 7
 339   // ... append the letter 'S',
 340   addULEB128('S');
 341
 342   // the tag of C,
 343   addULEB128(Die.getTag());
 344
 345   // and the name.
 346   addString(Name);
 347 }
 348
 349 // Compute the hash of a DIE. This is based on the type signature computation
 350 // given in section 7.27 of the DWARF4 standard. It is the md5 hash of a
 351 // flattened description of the DIE.
 352 void DIEHash::computeHash(const DIE &Die) {
 353   // Append the letter 'D', followed by the DWARF tag of the DIE.
 354   addULEB128('D');
 355   addULEB128(Die.getTag());
 356
 357   // Add each of the attributes of the DIE.
 358   addAttributes(Die);
 359
 360   // Then hash each of the children of the DIE.
 361   for (auto &C : Die.children()) {
 362     // 7.27 Step 7
 363     // If C is a nested type entry or a member function entry, ...
 364     if (isType(C.getTag()) || C.getTag() == dwarf::DW_TAG_subprogram) {
 365       StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);
 366       // ... and has a DW_AT_name attribute
 367       if (!Name.empty()) {
 368         hashNestedType(C, Name);
 369         continue;
 370       }
 371     }
 372     computeHash(C);
 373   }
 374
 375   // Following the last (or if there are no children), append a zero byte.
 376   Hash.update(makeArrayRef((uint8_t)'\0'));
 377 }
 378
 379 /// This is based on the type signature computation given in section 7.27 of the
 380 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
 381 /// with the inclusion of the full CU and all top level CU entities.
 382 // TODO: Initialize the type chain at 0 instead of 1 for CU signatures.
 383 uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) {
 384   Numbering.clear();
 385   Numbering[&Die] = 1;
 386
 387   if (!DWOName.empty())
 388     Hash.update(DWOName);
 389   // Hash the DIE.
 390   computeHash(Die);
 391
 392   // Now return the result.
 393   MD5::MD5Result Result;
 394   Hash.final(Result);
 395
 396   // ... take the least significant 8 bytes and return those. Our MD5
 397   // implementation always returns its results in little endian, so we actually
 398   // need the "high" word.
 399   return Result.high();
 400 }
 401
 402 /// This is based on the type signature computation given in section 7.27 of the
 403 /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE
 404 /// with the inclusion of additional forms not specifically called out in the
 405 /// standard.
 406 uint64_t DIEHash::computeTypeSignature(const DIE &Die) {
 407   Numbering.clear();
 408   Numbering[&Die] = 1;
 409
 410   if (const DIE *Parent = Die.getParent())
 411     addParentContext(*Parent);
 412
 413   // Hash the DIE.
 414   computeHash(Die);
 415
 416   // Now return the result.
 417   MD5::MD5Result Result;
 418   Hash.final(Result);
 419
 420   // ... take the least significant 8 bytes and return those. Our MD5
 421   // implementation always returns its results in little endian, so we actually
 422   // need the "high" word.
 423   return Result.high();
 424 }