//===-- llvm/CodeGen/DIEHash.cpp - Dwarf Hashing Framework ----------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file contains support for DWARF4 hashing of DIEs. // //===----------------------------------------------------------------------===// #include "ByteStreamer.h" #include "DIEHash.h" #include "DwarfDebug.h" #include "llvm/ADT/ArrayRef.h" #include "llvm/ADT/StringRef.h" #include "llvm/CodeGen/AsmPrinter.h" #include "llvm/CodeGen/DIE.h" #include "llvm/Support/Debug.h" #include "llvm/Support/Dwarf.h" #include "llvm/Support/Endian.h" #include "llvm/Support/MD5.h" #include "llvm/Support/raw_ostream.h" using namespace llvm; #define DEBUG_TYPE "dwarfdebug" /// \brief Grabs the string in whichever attribute is passed in and returns /// a reference to it. static StringRef getDIEStringAttr(const DIE &Die, uint16_t Attr) { // Iterate through all the attributes until we find the one we're // looking for, if we can't find it return an empty string. for (const auto &V : Die.values()) if (V.getAttribute() == Attr) return V.getDIEString().getString(); return StringRef(""); } /// \brief Adds the string in \p Str to the hash. This also hashes /// a trailing NULL with the string. void DIEHash::addString(StringRef Str) { DEBUG(dbgs() << "Adding string " << Str << " to hash.\n"); Hash.update(Str); Hash.update(makeArrayRef((uint8_t)'\0')); } // FIXME: The LEB128 routines are copied and only slightly modified out of // LEB128.h. /// \brief Adds the unsigned in \p Value to the hash encoded as a ULEB128. void DIEHash::addULEB128(uint64_t Value) { DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n"); do { uint8_t Byte = Value & 0x7f; Value >>= 7; if (Value != 0) Byte |= 0x80; // Mark this byte to show that more bytes will follow. Hash.update(Byte); } while (Value != 0); } void DIEHash::addSLEB128(int64_t Value) { DEBUG(dbgs() << "Adding ULEB128 " << Value << " to hash.\n"); bool More; do { uint8_t Byte = Value & 0x7f; Value >>= 7; More = !((((Value == 0) && ((Byte & 0x40) == 0)) || ((Value == -1) && ((Byte & 0x40) != 0)))); if (More) Byte |= 0x80; // Mark this byte to show that more bytes will follow. Hash.update(Byte); } while (More); } /// \brief Including \p Parent adds the context of Parent to the hash.. void DIEHash::addParentContext(const DIE &Parent) { DEBUG(dbgs() << "Adding parent context to hash...\n"); // [7.27.2] For each surrounding type or namespace beginning with the // outermost such construct... SmallVector Parents; const DIE *Cur = &Parent; while (Cur->getParent()) { Parents.push_back(Cur); Cur = Cur->getParent(); } assert(Cur->getTag() == dwarf::DW_TAG_compile_unit || Cur->getTag() == dwarf::DW_TAG_type_unit); // Reverse iterate over our list to go from the outermost construct to the // innermost. for (SmallVectorImpl::reverse_iterator I = Parents.rbegin(), E = Parents.rend(); I != E; ++I) { const DIE &Die = **I; // ... Append the letter "C" to the sequence... addULEB128('C'); // ... Followed by the DWARF tag of the construct... addULEB128(Die.getTag()); // ... Then the name, taken from the DW_AT_name attribute. StringRef Name = getDIEStringAttr(Die, dwarf::DW_AT_name); DEBUG(dbgs() << "... adding context: " << Name << "\n"); if (!Name.empty()) addString(Name); } } // Collect all of the attributes for a particular DIE in single structure. void DIEHash::collectAttributes(const DIE &Die, DIEAttrs &Attrs) { for (const auto &V : Die.values()) { DEBUG(dbgs() << "Attribute: " << dwarf::AttributeString(V.getAttribute()) << " added.\n"); switch (V.getAttribute()) { #define HANDLE_DIE_HASH_ATTR(NAME) \ case dwarf::NAME: \ Attrs.NAME = V; \ break; #include "DIEHashAttributes.def" default: break; } } } void DIEHash::hashShallowTypeReference(dwarf::Attribute Attribute, const DIE &Entry, StringRef Name) { // append the letter 'N' addULEB128('N'); // the DWARF attribute code (DW_AT_type or DW_AT_friend), addULEB128(Attribute); // the context of the tag, if (const DIE *Parent = Entry.getParent()) addParentContext(*Parent); // the letter 'E', addULEB128('E'); // and the name of the type. addString(Name); // Currently DW_TAG_friends are not used by Clang, but if they do become so, // here's the relevant spec text to implement: // // For DW_TAG_friend, if the referenced entry is the DW_TAG_subprogram, // the context is omitted and the name to be used is the ABI-specific name // of the subprogram (e.g., the mangled linker name). } void DIEHash::hashRepeatedTypeReference(dwarf::Attribute Attribute, unsigned DieNumber) { // a) If T is in the list of [previously hashed types], use the letter // 'R' as the marker addULEB128('R'); addULEB128(Attribute); // and use the unsigned LEB128 encoding of [the index of T in the // list] as the attribute value; addULEB128(DieNumber); } void DIEHash::hashDIEEntry(dwarf::Attribute Attribute, dwarf::Tag Tag, const DIE &Entry) { assert(Tag != dwarf::DW_TAG_friend && "No current LLVM clients emit friend " "tags. Add support here when there's " "a use case"); // Step 5 // If the tag in Step 3 is one of [the below tags] if ((Tag == dwarf::DW_TAG_pointer_type || Tag == dwarf::DW_TAG_reference_type || Tag == dwarf::DW_TAG_rvalue_reference_type || Tag == dwarf::DW_TAG_ptr_to_member_type) && // and the referenced type (via the [below attributes]) // FIXME: This seems overly restrictive, and causes hash mismatches // there's a decl/def difference in the containing type of a // ptr_to_member_type, but it's what DWARF says, for some reason. Attribute == dwarf::DW_AT_type) { // ... has a DW_AT_name attribute, StringRef Name = getDIEStringAttr(Entry, dwarf::DW_AT_name); if (!Name.empty()) { hashShallowTypeReference(Attribute, Entry, Name); return; } } unsigned &DieNumber = Numbering[&Entry]; if (DieNumber) { hashRepeatedTypeReference(Attribute, DieNumber); return; } // otherwise, b) use the letter 'T' as the marker, ... addULEB128('T'); addULEB128(Attribute); // ... process the type T recursively by performing Steps 2 through 7, and // use the result as the attribute value. DieNumber = Numbering.size(); computeHash(Entry); } // Hash all of the values in a block like set of values. This assumes that // all of the data is going to be added as integers. void DIEHash::hashBlockData(const DIE::const_value_range &Values) { for (const auto &V : Values) Hash.update((uint64_t)V.getDIEInteger().getValue()); } // Hash the contents of a loclistptr class. void DIEHash::hashLocList(const DIELocList &LocList) { HashingByteStreamer Streamer(*this); DwarfDebug &DD = *AP->getDwarfDebug(); const DebugLocStream &Locs = DD.getDebugLocs(); for (const auto &Entry : Locs.getEntries(Locs.getList(LocList.getValue()))) DD.emitDebugLocEntry(Streamer, Entry); } // Hash an individual attribute \param Attr based on the type of attribute and // the form. void DIEHash::hashAttribute(const DIEValue &Value, dwarf::Tag Tag) { dwarf::Attribute Attribute = Value.getAttribute(); // Other attribute values use the letter 'A' as the marker, and the value // consists of the form code (encoded as an unsigned LEB128 value) followed by // the encoding of the value according to the form code. To ensure // reproducibility of the signature, the set of forms used in the signature // computation is limited to the following: DW_FORM_sdata, DW_FORM_flag, // DW_FORM_string, and DW_FORM_block. switch (Value.getType()) { case DIEValue::isNone: llvm_unreachable("Expected valid DIEValue"); // 7.27 Step 3 // ... An attribute that refers to another type entry T is processed as // follows: case DIEValue::isEntry: hashDIEEntry(Attribute, Tag, Value.getDIEEntry().getEntry()); break; case DIEValue::isInteger: { addULEB128('A'); addULEB128(Attribute); switch (Value.getForm()) { case dwarf::DW_FORM_data1: case dwarf::DW_FORM_data2: case dwarf::DW_FORM_data4: case dwarf::DW_FORM_data8: case dwarf::DW_FORM_udata: case dwarf::DW_FORM_sdata: addULEB128(dwarf::DW_FORM_sdata); addSLEB128((int64_t)Value.getDIEInteger().getValue()); break; // DW_FORM_flag_present is just flag with a value of one. We still give it a // value so just use the value. case dwarf::DW_FORM_flag_present: case dwarf::DW_FORM_flag: addULEB128(dwarf::DW_FORM_flag); addULEB128((int64_t)Value.getDIEInteger().getValue()); break; default: llvm_unreachable("Unknown integer form!"); } break; } case DIEValue::isString: addULEB128('A'); addULEB128(Attribute); addULEB128(dwarf::DW_FORM_string); addString(Value.getDIEString().getString()); break; case DIEValue::isInlineString: addULEB128('A'); addULEB128(Attribute); addULEB128(dwarf::DW_FORM_string); addString(Value.getDIEInlineString().getString()); break; case DIEValue::isBlock: case DIEValue::isLoc: case DIEValue::isLocList: addULEB128('A'); addULEB128(Attribute); addULEB128(dwarf::DW_FORM_block); if (Value.getType() == DIEValue::isBlock) { addULEB128(Value.getDIEBlock().ComputeSize(AP)); hashBlockData(Value.getDIEBlock().values()); } else if (Value.getType() == DIEValue::isLoc) { addULEB128(Value.getDIELoc().ComputeSize(AP)); hashBlockData(Value.getDIELoc().values()); } else { // We could add the block length, but that would take // a bit of work and not add a lot of uniqueness // to the hash in some way we could test. hashLocList(Value.getDIELocList()); } break; // FIXME: It's uncertain whether or not we should handle this at the moment. case DIEValue::isExpr: case DIEValue::isLabel: case DIEValue::isDelta: llvm_unreachable("Add support for additional value types."); } } // Go through the attributes from \param Attrs in the order specified in 7.27.4 // and hash them. void DIEHash::hashAttributes(const DIEAttrs &Attrs, dwarf::Tag Tag) { #define HANDLE_DIE_HASH_ATTR(NAME) \ { \ if (Attrs.NAME) \ hashAttribute(Attrs.NAME, Tag); \ } #include "DIEHashAttributes.def" // FIXME: Add the extended attributes. } // Add all of the attributes for \param Die to the hash. void DIEHash::addAttributes(const DIE &Die) { DIEAttrs Attrs = {}; collectAttributes(Die, Attrs); hashAttributes(Attrs, Die.getTag()); } void DIEHash::hashNestedType(const DIE &Die, StringRef Name) { // 7.27 Step 7 // ... append the letter 'S', addULEB128('S'); // the tag of C, addULEB128(Die.getTag()); // and the name. addString(Name); } // Compute the hash of a DIE. This is based on the type signature computation // given in section 7.27 of the DWARF4 standard. It is the md5 hash of a // flattened description of the DIE. void DIEHash::computeHash(const DIE &Die) { // Append the letter 'D', followed by the DWARF tag of the DIE. addULEB128('D'); addULEB128(Die.getTag()); // Add each of the attributes of the DIE. addAttributes(Die); // Then hash each of the children of the DIE. for (auto &C : Die.children()) { // 7.27 Step 7 // If C is a nested type entry or a member function entry, ... if (isType(C.getTag()) || C.getTag() == dwarf::DW_TAG_subprogram) { StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name); // ... and has a DW_AT_name attribute if (!Name.empty()) { hashNestedType(C, Name); continue; } } computeHash(C); } // Following the last (or if there are no children), append a zero byte. Hash.update(makeArrayRef((uint8_t)'\0')); } /// This is based on the type signature computation given in section 7.27 of the /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE /// with the inclusion of the full CU and all top level CU entities. // TODO: Initialize the type chain at 0 instead of 1 for CU signatures. uint64_t DIEHash::computeCUSignature(StringRef DWOName, const DIE &Die) { Numbering.clear(); Numbering[&Die] = 1; if (!DWOName.empty()) Hash.update(DWOName); // Hash the DIE. computeHash(Die); // Now return the result. MD5::MD5Result Result; Hash.final(Result); // ... take the least significant 8 bytes and return those. Our MD5 // implementation always returns its results in little endian, so we actually // need the "high" word. return Result.high(); } /// This is based on the type signature computation given in section 7.27 of the /// DWARF4 standard. It is an md5 hash of the flattened description of the DIE /// with the inclusion of additional forms not specifically called out in the /// standard. uint64_t DIEHash::computeTypeSignature(const DIE &Die) { Numbering.clear(); Numbering[&Die] = 1; if (const DIE *Parent = Die.getParent()) addParentContext(*Parent); // Hash the DIE. computeHash(Die); // Now return the result. MD5::MD5Result Result; Hash.final(Result); // ... take the least significant 8 bytes and return those. Our MD5 // implementation always returns its results in little endian, so we actually // need the "high" word. return Result.high(); }