Utils.cpp

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//===- Utils.cpp ------------------------------------------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#include "llvm/DWARFLinker/Utils.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFDie.h"
#include "llvm/DebugInfo/DWARF/DWARFUnit.h"
#include "llvm/DebugInfo/DWARF/LowLevel/DWARFExpression.h"
#include <limits>
#include <map>
 
namespace llvm {
namespace dwarf_linker {
 
bool hasImplicitAddressLocation(const DWARFDie &Die) {
  std::optional<DWARFFormValue> Location = Die.find(dwarf::DW_AT_location);
  if (!Location)
    return false;
 
  std::optional<ArrayRef<uint8_t>> Block = Location->getAsBlock();
  if (!Block)
    return false;
 
  DWARFUnit *U = Die.getDwarfUnit();
  DataExtractor Data(*Block, U->getContext().isLittleEndian());
  DWARFExpression Expression(Data, U->getAddressByteSize(),
                             U->getFormParams().Format);
  return !Expression.isMemoryLocation() &&
         any_of(Expression, [](const DWARFExpression::Operation &Op) {
           return !Op.isError() && (Op.getCode() == dwarf::DW_OP_addr ||
                                    Op.getCode() == dwarf::DW_OP_addrx);
         });
}
 
bool isStaticDataMember(const DWARFDie &Die) {
  assert(Die.getTag() == dwarf::DW_TAG_member && "expected a DW_TAG_member");
 
  if (!dwarf::toUnsigned(Die.find(dwarf::DW_AT_declaration), 0))
    return false;
 
  // A member that has a location occupies storage in the record regardless of
  // how else it is marked, so it is the absence of a location that makes this a
  // pure declaration. Zero is a valid offset, so only the attribute's presence
  // matters, not its value.
  return !Die.find(
      {dwarf::DW_AT_data_member_location, dwarf::DW_AT_data_bit_offset});
}
 
bool isIdentifiedByChildren(dwarf::Tag Tag) {
  switch (Tag) {
  case dwarf::DW_TAG_class_type:
  case dwarf::DW_TAG_enumeration_type:
  case dwarf::DW_TAG_interface_type:
  case dwarf::DW_TAG_structure_type:
  case dwarf::DW_TAG_union_type:
    return true;
  default:
    return false;
  }
}
 
bool isIdentifyingChild(const DWARFDie &Die) {
  // Units disagree on implicit member functions and on how static data
  // members are spelled.
  switch (Die.getTag()) {
  case dwarf::DW_TAG_member:
    return !isStaticDataMember(Die);
  case dwarf::DW_TAG_enumerator:
  case dwarf::DW_TAG_inheritance:
    return true;
  default:
    return false;
  }
}
 
void buildStmtSeqOffsetToFirstRowIndex(
    const DWARFDebugLine::LineTable &LT,
    ArrayRef<uint64_t> SortedStmtSeqOffsets,
    DenseMap<uint64_t, uint64_t> &SeqOffToFirstRow) {
  // Use std::map for ordered iteration by input stmt-sequence offset.
  std::map<uint64_t, uint64_t> LineTableMapping;
  for (const DWARFDebugLine::Sequence &Seq : LT.Sequences)
    LineTableMapping[Seq.StmtSeqOffset] = Seq.FirstRowIndex;
 
  if (LT.Rows.empty()) {
    for (const auto &[Off, Row] : LineTableMapping)
      SeqOffToFirstRow[Off] = Row;
    return;
  }
 
  // Row indices that look like sequence starts: row 0, plus every row
  // immediately following an end_sequence marker.
  SmallVector<uint64_t> SeqStartRows;
  SeqStartRows.push_back(0);
  for (auto [I, Row] : llvm::enumerate(ArrayRef(LT.Rows).drop_back()))
    if (Row.EndSequence)
      SeqStartRows.push_back(I + 1);
 
  ArrayRef<uint64_t> StmtAttrsRef(SortedStmtSeqOffsets);
  ArrayRef<uint64_t> SeqStartRowsRef(SeqStartRows);
 
  // While SeqOffToFirstRow parsed from LT could be the ground truth, e.g.
  //
  // SeqOff     Row
  // 0x08        9
  // 0x14       15
  //
  // The StmtAttrs and SeqStartRows may not match perfectly, e.g.
  //
  // StmtAttrs  SeqStartRows
  // 0x04        3
  // 0x08        5
  // 0x10        9
  // 0x12       11
  // 0x14       15
  //
  // In this case, we don't want to assign 5 to 0x08, since we know 0x08
  // maps to 9. If we do a dummy 1:1 mapping 0x10 will be mapped to 9
  // which is incorrect. The expected behavior is ignore 5, realign the
  // table based on the result from the line table:
  //
  // StmtAttrs  SeqStartRows
  // 0x04        3
  //   --        5
  // 0x08        9 <- LineTableMapping ground truth
  // 0x10       11
  // 0x12       --
  // 0x14       15 <- LineTableMapping ground truth
 
  // Dummy trailing anchor so both refs always drain before we run out
  // of map entries to walk.
  constexpr uint64_t DummyKey = std::numeric_limits<uint64_t>::max();
  constexpr uint64_t DummyVal = std::numeric_limits<uint64_t>::max();
  LineTableMapping[DummyKey] = DummyVal;
 
  for (auto [NextSeqOff, NextRow] : LineTableMapping) {
    auto StmtAttrSmallerThanNext = [N = NextSeqOff](uint64_t SA) {
      return SA < N;
    };
    auto SeqStartSmallerThanNext = [N = NextRow](uint64_t Row) {
      return Row < N;
    };
    // While both lists still point strictly before the next anchor,
    // pair them up 1:1 — this captures sequences the parser missed.
    while (!StmtAttrsRef.empty() && !SeqStartRowsRef.empty() &&
           StmtAttrSmallerThanNext(StmtAttrsRef.front()) &&
           SeqStartSmallerThanNext(SeqStartRowsRef.front())) {
      SeqOffToFirstRow[StmtAttrsRef.consume_front()] =
          SeqStartRowsRef.consume_front();
    }
    // Either list may now be ahead of or at the anchor: drop entries we
    // can't safely pair, then use the parser's (NextSeqOff,NextRow)
    // mapping as ground truth.
    StmtAttrsRef = StmtAttrsRef.drop_while(StmtAttrSmallerThanNext);
    SeqStartRowsRef = SeqStartRowsRef.drop_while(SeqStartSmallerThanNext);
    if (NextSeqOff != DummyKey)
      SeqOffToFirstRow[NextSeqOff] = NextRow;
    // Advance each list past the anchor only if it was pointing exactly
    // at it.
    if (!StmtAttrsRef.empty() && StmtAttrsRef.front() == NextSeqOff)
      StmtAttrsRef = StmtAttrsRef.drop_front();
    if (!SeqStartRowsRef.empty() && SeqStartRowsRef.front() == NextRow)
      SeqStartRowsRef = SeqStartRowsRef.drop_front();
  }
}
 
} // namespace dwarf_linker
} // namespace llvm