441 lines · 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-exception6//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"19#include "llvm/BinaryFormat/Dwarf.h"20#include "llvm/CodeGen/AsmPrinter.h"21#include "llvm/Support/Debug.h"22#include "llvm/Support/raw_ostream.h"23 24using namespace llvm;25 26#define DEBUG_TYPE "dwarfdebug"27 28/// Grabs the string in whichever attribute is passed in and returns29/// a reference to it.30static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) {31 // Iterate through all the attributes until we find the one we're32 // looking for, if we can't find it return an empty string.33 for (const auto &V : Die.values())34 if (V.getAttribute() == Attr)35 return V.getDIEString().getString();36 37 return StringRef("");38}39 40/// Adds the string in \p Str to the hash. This also hashes41/// a trailing NULL with the string.42void DIEHash::addString(StringRef Str) {43 LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");44 Hash.update(Str);45 Hash.update(ArrayRef((uint8_t)'\0'));46}47 48// FIXME: The LEB128 routines are copied and only slightly modified out of49// LEB128.h.50 51/// Adds the unsigned in \p Value to the hash encoded as a ULEB128.52void DIEHash::addULEB128(uint64_t Value) {53 LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");54 do {55 uint8_t Byte = Value & 0x7f;56 Value >>= 7;57 if (Value != 0)58 Byte |= 0x80; // Mark this byte to show that more bytes will follow.59 Hash.update(Byte);60 } while (Value != 0);61}62 63void DIEHash::addSLEB128(int64_t Value) {64 LLVM_DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n");65 bool More;66 do {67 uint8_t Byte = Value & 0x7f;68 Value >>= 7;69 More = !((((Value == 0) && ((Byte & 0x40) == 0)) ||70 ((Value == -1) && ((Byte & 0x40) != 0))));71 if (More)72 Byte |= 0x80; // Mark this byte to show that more bytes will follow.73 Hash.update(Byte);74 } while (More);75}76 77/// Including \p Parent adds the context of Parent to the hash..78void DIEHash::addParentContext(const DIE &Parent) {79 80 LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");81 82 // [7.27.2] For each surrounding type or namespace beginning with the83 // outermost such construct...84 SmallVector<const DIE *, 1> Parents;85 const DIE *Cur = &Parent;86 while (Cur->getParent()) {87 Parents.push_back(Cur);88 Cur = Cur->getParent();89 }90 assert(Cur->getTag() == dwarf::DW_TAG_compile_unit ||91 Cur->getTag() == dwarf::DW_TAG_type_unit);92 93 // Reverse iterate over our list to go from the outermost construct to the94 // innermost.95 for (const DIE *Die : llvm::reverse(Parents)) {96 // ... Append the letter "C" to the sequence...97 addULEB128('C');98 99 // ... Followed by the DWARF tag of the construct...100 addULEB128(Die->getTag());101 102 // ... Then the name, taken from the DW_AT_name attribute.103 StringRef Name = getDIEStringAttr(*Die, dwarf::DW_AT_name);104 LLVM_DEBUG(dbgs() << "... adding context: " << Name << "\n");105 if (!Name.empty())106 addString(Name);107 }108}109 110// Collect all of the attributes for a particular DIE in single structure.111void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) {112 113 for (const auto &V : Die.values()) {114 LLVM_DEBUG(dbgs() << "Attribute: "115 << dwarf::AttributeString(V.getAttribute())116 << " added.\n");117 switch (V.getAttribute()) {118#define HANDLE_DIE_HASH_ATTR(NAME) \119 case dwarf::NAME: \120 Attrs.NAME = V; \121 break;122#include "DIEHashAttributes.def"123 default:124 break;125 }126 }127}128 129void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute,130 const DIE &Entry, StringRef Name) {131 // append the letter 'N'132 addULEB128('N');133 134 // the DWARF attribute code (DW_AT_type or DW_AT_friend),135 addULEB128(Attribute);136 137 // the context of the tag,138 if (const DIE *Parent = Entry.getParent())139 addParentContext(*Parent);140 141 // the letter 'E',142 addULEB128('E');143 144 // and the name of the type.145 addString(Name);146 147 // Currently DW_TAG_friends are not used by Clang, but if they do become so,148 // here's the relevant spec text to implement:149 //150 // For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram,151 // the context is omitted and the name to be used is the ABI-specific name152 // of the subprogram (e.g., the mangled linker name).153}154 155void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute,156 unsigned DieNumber) {157 // a) If T is in the list of [previously hashed types], use the letter158 // 'R' as the marker159 addULEB128('R');160 161 addULEB128(Attribute);162 163 // and use the unsigned LEB128 encoding of [the index of T in the164 // list] as the attribute value;165 addULEB128(DieNumber);166}167 168void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag,169 const DIE &Entry) {170 assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend "171 "tags. Add support here when there's "172 "a use case");173 // Step 5174 // If the tag in Step 3 is one of [the below tags]175 if ((Tag == dwarf::DW_TAG_pointer_type ||176 Tag == dwarf::DW_TAG_reference_type ||177 Tag == dwarf::DW_TAG_rvalue_reference_type ||178 Tag == dwarf::DW_TAG_ptr_to_member_type) &&179 // and the referenced type (via the [below attributes])180 // FIXME: This seems overly restrictive, and causes hash mismatches181 // there's a decl/def difference in the containing type of a182 // ptr_to_member_type, but it's what DWARF says, for some reason.183 Attribute == dwarf::DW_AT_type) {184 // ... has a DW_AT_name attribute,185 StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name);186 if (!Name.empty()) {187 hashShallowTypeReference(Attribute, Entry, Name);188 return;189 }190 }191 192 unsigned &DieNumber = Numbering[&Entry];193 if (DieNumber) {194 hashRepeatedTypeReference(Attribute, DieNumber);195 return;196 }197 198 // otherwise, b) use the letter 'T' as the marker, ...199 addULEB128('T');200 201 addULEB128(Attribute);202 203 // ... process the type T recursively by performing Steps 2 through 7, and204 // use the result as the attribute value.205 DieNumber = Numbering.size();206 computeHash(Entry);207}208 209void DIEHash::hashRawTypeReference(const DIE &Entry) {210 unsigned &DieNumber = Numbering[&Entry];211 if (DieNumber) {212 addULEB128('R');213 addULEB128(DieNumber);214 return;215 }216 DieNumber = Numbering.size();217 addULEB128('T');218 computeHash(Entry);219}220 221// Hash all of the values in a block like set of values. This assumes that222// all of the data is going to be added as integers.223void DIEHash::hashBlockData(const DIE::const_value_range &Values) {224 for (const auto &V : Values)225 if (V.getType() == DIEValue::isBaseTypeRef) {226 const DIE &C =227 *CU->ExprRefedBaseTypes[V.getDIEBaseTypeRef().getIndex()].Die;228 StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);229 assert(!Name.empty() &&230 "Base types referenced from DW_OP_convert should have a name");231 hashNestedType(C, Name);232 } else233 Hash.update(V.getDIEInteger().getValue());234}235 236// Hash the contents of a loclistptr class.237void DIEHash::hashLocList(const DIELocList &LocList) {238 HashingByteStreamer Streamer(*this);239 DwarfDebug &DD = *AP->getDwarfDebug();240 const DebugLocStream &Locs = DD.getDebugLocs();241 const DebugLocStream::List &List = Locs.getList(LocList.getValue());242 for (const DebugLocStream::Entry &Entry : Locs.getEntries(List))243 DD.emitDebugLocEntry(Streamer, Entry, List.CU);244}245 246// Hash an individual attribute \param Attr based on the type of attribute and247// the form.248void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) {249 dwarf::Attribute Attribute = Value.getAttribute();250 251 // Other attribute values use the letter 'A' as the marker, and the value252 // consists of the form code (encoded as an unsigned LEB128 value) followed by253 // the encoding of the value according to the form code. To ensure254 // reproducibility of the signature, the set of forms used in the signature255 // computation is limited to the following: DW_FORM_sdata, DW_FORM_flag,256 // DW_FORM_string, and DW_FORM_block.257 258 switch (Value.getType()) {259 case DIEValue::isNone:260 llvm_unreachable("Expected valid DIEValue");261 262 // 7.27 Step 3263 // ... An attribute that refers to another type entry T is processed as264 // follows:265 case DIEValue::isEntry:266 hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry());267 break;268 case DIEValue::isInteger: {269 addULEB128('A');270 addULEB128(Attribute);271 switch (Value.getForm()) {272 case dwarf::DW_FORM_data1:273 case dwarf::DW_FORM_data2:274 case dwarf::DW_FORM_data4:275 case dwarf::DW_FORM_data8:276 case dwarf::DW_FORM_udata:277 case dwarf::DW_FORM_sdata:278 addULEB128(dwarf::DW_FORM_sdata);279 addSLEB128((int64_t)Value.getDIEInteger().getValue());280 break;281 // DW_FORM_flag_present is just flag with a value of one. We still give it a282 // value so just use the value.283 case dwarf::DW_FORM_flag_present:284 case dwarf::DW_FORM_flag:285 addULEB128(dwarf::DW_FORM_flag);286 addULEB128((int64_t)Value.getDIEInteger().getValue());287 break;288 default:289 llvm_unreachable("Unknown integer form!");290 }291 break;292 }293 case DIEValue::isString:294 addULEB128('A');295 addULEB128(Attribute);296 addULEB128(dwarf::DW_FORM_string);297 addString(Value.getDIEString().getString());298 break;299 case DIEValue::isInlineString:300 addULEB128('A');301 addULEB128(Attribute);302 addULEB128(dwarf::DW_FORM_string);303 addString(Value.getDIEInlineString().getString());304 break;305 case DIEValue::isBlock:306 case DIEValue::isLoc:307 case DIEValue::isLocList:308 addULEB128('A');309 addULEB128(Attribute);310 addULEB128(dwarf::DW_FORM_block);311 if (Value.getType() == DIEValue::isBlock) {312 addULEB128(Value.getDIEBlock().computeSize(AP->getDwarfFormParams()));313 hashBlockData(Value.getDIEBlock().values());314 } else if (Value.getType() == DIEValue::isLoc) {315 addULEB128(Value.getDIELoc().computeSize(AP->getDwarfFormParams()));316 hashBlockData(Value.getDIELoc().values());317 } else {318 // We could add the block length, but that would take319 // a bit of work and not add a lot of uniqueness320 // to the hash in some way we could test.321 hashLocList(Value.getDIELocList());322 }323 break;324 // FIXME: It's uncertain whether or not we should handle this at the moment.325 case DIEValue::isExpr:326 case DIEValue::isLabel:327 case DIEValue::isBaseTypeRef:328 case DIEValue::isDelta:329 case DIEValue::isAddrOffset:330 llvm_unreachable("Add support for additional value types.");331 }332}333 334// Go through the attributes from \param Attrs in the order specified in 7.27.4335// and hash them.336void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) {337#define HANDLE_DIE_HASH_ATTR(NAME) \338 { \339 if (Attrs.NAME) \340 hashAttribute(Attrs.NAME, Tag); \341 }342#include "DIEHashAttributes.def"343 // FIXME: Add the extended attributes.344}345 346// Add all of the attributes for \param Die to the hash.347void DIEHash::addAttributes(const DIE &Die) {348 DIEAttrs Attrs = {};349 collectAttributes(Die, Attrs);350 hashAttributes(Attrs, Die.getTag());351}352 353void DIEHash::hashNestedType(const DIE &Die, StringRef Name) {354 // 7.27 Step 7355 // ... append the letter 'S',356 addULEB128('S');357 358 // the tag of C,359 addULEB128(Die.getTag());360 361 // and the name.362 addString(Name);363}364 365// Compute the hash of a DIE. This is based on the type signature computation366// given in section 7.27 of the DWARF4 standard. It is the md5 hash of a367// flattened description of the DIE.368void DIEHash::computeHash(const DIE &Die) {369 // Append the letter 'D', followed by the DWARF tag of the DIE.370 addULEB128('D');371 addULEB128(Die.getTag());372 373 // Add each of the attributes of the DIE.374 addAttributes(Die);375 376 // Then hash each of the children of the DIE.377 for (const auto &C : Die.children()) {378 // 7.27 Step 7379 // If C is a nested type entry or a member function entry, ...380 if (isType(C.getTag()) || (C.getTag() == dwarf::DW_TAG_subprogram && isType(C.getParent()->getTag()))) {381 StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);382 // ... and has a DW_AT_name attribute383 if (!Name.empty()) {384 hashNestedType(C, Name);385 continue;386 }387 }388 computeHash(C);389 }390 391 // Following the last (or if there are no children), append a zero byte.392 Hash.update(ArrayRef((uint8_t)'\0'));393}394 395/// This is based on the type signature computation given in section 7.27 of the396/// DWARF4 standard. It is an md5 hash of the flattened description of the DIE397/// with the inclusion of the full CU and all top level CU entities.398// TODO: Initialize the type chain at 0 instead of 1 for CU signatures.399uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) {400 Numbering.clear();401 Numbering[&Die] = 1;402 403 if (!DWOName.empty())404 Hash.update(DWOName);405 // Hash the DIE.406 computeHash(Die);407 408 // Now return the result.409 MD5::MD5Result Result;410 Hash.final(Result);411 412 // ... take the least significant 8 bytes and return those. Our MD5413 // implementation always returns its results in little endian, so we actually414 // need the "high" word.415 return Result.high();416}417 418/// This is based on the type signature computation given in section 7.27 of the419/// DWARF4 standard. It is an md5 hash of the flattened description of the DIE420/// with the inclusion of additional forms not specifically called out in the421/// standard.422uint64_t DIEHash::computeTypeSignature(const DIE &Die) {423 Numbering.clear();424 Numbering[&Die] = 1;425 426 if (const DIE *Parent = Die.getParent())427 addParentContext(*Parent);428 429 // Hash the DIE.430 computeHash(Die);431 432 // Now return the result.433 MD5::MD5Result Result;434 Hash.final(Result);435 436 // ... take the least significant 8 bytes and return those. Our MD5437 // implementation always returns its results in little endian, so we actually438 // need the "high" word.439 return Result.high();440}441