//===-- llvm/CodeGen/DIEHash.cpp - Dwarf Hashing Framework ----------------===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file contains support for DWARF4 hashing of DIEs.

//

//===----------------------------------------------------------------------===//

#include "DIEHash.h"

#include "ByteStreamer.h"

#include "DwarfCompileUnit.h"

#include "DwarfDebug.h"

#include "llvm/ADT/ArrayRef.h"

#include "llvm/ADT/StringRef.h"

#include "llvm/BinaryFormat/Dwarf.h"

#include "llvm/CodeGen/AsmPrinter.h"

#include "llvm/Support/Debug.h"

#include "llvm/Support/raw_ostream.h"

using namespace llvm;

#define DEBUG_TYPE "dwarfdebug"

/// 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("");

}

/// Adds the string in \p Str to the hash. This also hashes

/// a trailing NULL with the string.

void DIEHash::addString(StringRef Str) {

  LLVM_DEBUG(dbgs() << "Adding string " << Str << " to hash.\n");

  Hash.update(Str);

  Hash.update(ArrayRef((uint8_t)'\0'));

}

// FIXME: The LEB128 routines are copied and only slightly modified out of

// LEB128.h.

/// Adds the unsigned in \p Value to the hash encoded as a ULEB128.

void DIEHash::addULEB128(uint64_t Value) {

  LLVM_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) {

  LLVM_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);

}

/// Including \p Parent adds the context of Parent to the hash..

void DIEHash::addParentContext(const DIE &Parent) {

  LLVM_DEBUG(dbgs() << "Adding parent context to hash...\n");

  // [7.27.2] For each surrounding type or namespace beginning with the

  // outermost such construct...

  SmallVector<const DIE *, 1> 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 (const DIE *Die : llvm::reverse(Parents)) {

    // ... 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);

    LLVM_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()) {

    LLVM_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);

}

void DIEHash::hashRawTypeReference(const DIE &Entry) {

  unsigned &DieNumber = Numbering[&Entry];

  if (DieNumber) {

    addULEB128('R');

    addULEB128(DieNumber);

    return;

  }

  DieNumber = Numbering.size();

  addULEB128('T');

  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)

    if (V.getType() == DIEValue::isBaseTypeRef) {

      const DIE &C =

          *CU->ExprRefedBaseTypes[V.getDIEBaseTypeRef().getIndex()].Die;

      StringRef Name = getDIEStringAttr(C, dwarf::DW_AT_name);

      assert(!Name.empty() &&

             "Base types referenced from DW_OP_convert should have a name");

      hashNestedType(C, Name);

    } else

      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();

  const DebugLocStream::List &List = Locs.getList(LocList.getValue());

  for (const DebugLocStream::Entry &Entry : Locs.getEntries(List))

    DD.emitDebugLocEntry(Streamer, Entry, List.CU);

}

// 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->getDwarfFormParams()));

      hashBlockData(Value.getDIEBlock().values());

    } else if (Value.getType() == DIEValue::isLoc) {

      addULEB128(Value.getDIELoc().computeSize(AP->getDwarfFormParams()));

      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::isBaseTypeRef:

  case DIEValue::isDelta:

  case DIEValue::isAddrOffset:

    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 (const 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 && isType(C.getParent()->getTag()))) {

      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(ArrayRef((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();

}