DWARFUnwindTable.h

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//===----------------------------------------------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_DEBUGINFO_DWARF_LOWLEVEL_DWARFUNWINDTABLE_H
#define LLVM_DEBUGINFO_DWARF_LOWLEVEL_DWARFUNWINDTABLE_H
 
#include "llvm/ADT/SmallVector.h"
#include "llvm/DebugInfo/DWARF/LowLevel/DWARFCFIProgram.h"
#include "llvm/DebugInfo/DWARF/LowLevel/DWARFExpression.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Error.h"
#include <map>
#include <vector>
 
namespace llvm {
 
namespace dwarf {
constexpr uint32_t InvalidRegisterNumber = UINT32_MAX;
 
/// A class that represents a location for the Call Frame Address (CFA) or a
/// register. This is decoded from the DWARF Call Frame Information
/// instructions and put into an UnwindRow.
class UnwindLocation {
public:
  enum Location {
    /// Not specified.
    Unspecified,
    /// Register is not available and can't be recovered.
    Undefined,
    /// Register value is in the register, nothing needs to be done to unwind
    /// it:
    ///   reg = reg
    Same,
    /// Register is in or at the CFA plus an offset:
    ///   reg = CFA + offset
    ///   reg = defef(CFA + offset)
    CFAPlusOffset,
    /// Register or CFA is in or at a register plus offset, optionally in
    /// an address space:
    ///   reg = reg + offset [in addrspace]
    ///   reg = deref(reg + offset [in addrspace])
    RegPlusOffset,
    /// Register or CFA value is in or at a value found by evaluating a DWARF
    /// expression:
    ///   reg = eval(dwarf_expr)
    ///   reg = deref(eval(dwarf_expr))
    DWARFExpr,
    /// Value is a constant value contained in "Offset":
    ///   reg = Offset
    Constant,
  };
 
private:
  Location Kind;   /// The type of the location that describes how to unwind it.
  uint32_t RegNum; /// The register number for Kind == RegPlusOffset.
  int32_t Offset;  /// The offset for Kind == CFAPlusOffset or RegPlusOffset.
  std::optional<uint32_t> AddrSpace;   /// The address space for Kind ==
                                       /// RegPlusOffset for CFA.
  std::optional<DWARFExpression> Expr; /// The DWARF expression for Kind ==
                                       /// DWARFExpression.
  bool Dereference; /// If true, the resulting location must be dereferenced
                    /// after the location value is computed.
 
  // Constructors are private to force people to use the create static
  // functions.
  UnwindLocation(Location K)
      : Kind(K), RegNum(InvalidRegisterNumber), Offset(0),
        AddrSpace(std::nullopt), Dereference(false) {}
 
  UnwindLocation(Location K, uint32_t Reg, int32_t Off,
                 std::optional<uint32_t> AS, bool Deref)
      : Kind(K), RegNum(Reg), Offset(Off), AddrSpace(AS), Dereference(Deref) {}
 
  UnwindLocation(DWARFExpression E, bool Deref)
      : Kind(DWARFExpr), RegNum(InvalidRegisterNumber), Offset(0), Expr(E),
        Dereference(Deref) {}
 
public:
  /// Create a location whose rule is set to Unspecified. This means the
  /// register value might be in the same register but it wasn't specified in
  /// the unwind opcodes.
  LLVM_ABI static UnwindLocation createUnspecified();
  /// Create a location where the value is undefined and not available. This can
  /// happen when a register is volatile and can't be recovered.
  LLVM_ABI static UnwindLocation createUndefined();
  /// Create a location where the value is known to be in the register itself.
  LLVM_ABI static UnwindLocation createSame();
  /// Create a location that is in (Deref == false) or at (Deref == true) the
  /// CFA plus an offset. Most registers that are spilled onto the stack use
  /// this rule. The rule for the register will use this rule and specify a
  /// unique offset from the CFA with \a Deref set to true. This value will be
  /// relative to a CFA value which is typically defined using the register
  /// plus offset location. \see createRegisterPlusOffset(...) for more
  /// information.
  LLVM_ABI static UnwindLocation createIsCFAPlusOffset(int32_t Off);
  LLVM_ABI static UnwindLocation createAtCFAPlusOffset(int32_t Off);
  /// Create a location where the saved value is in (Deref == false) or at
  /// (Deref == true) a regiser plus an offset and, optionally, in the specified
  /// address space (used mostly for the CFA).
  ///
  /// The CFA is usually defined using this rule by using the stack pointer or
  /// frame pointer as the register, with an offset that accounts for all
  /// spilled registers and all local variables in a function, and Deref ==
  /// false.
  LLVM_ABI static UnwindLocation
  createIsRegisterPlusOffset(uint32_t Reg, int32_t Off,
                             std::optional<uint32_t> AddrSpace = std::nullopt);
  LLVM_ABI static UnwindLocation
  createAtRegisterPlusOffset(uint32_t Reg, int32_t Off,
                             std::optional<uint32_t> AddrSpace = std::nullopt);
  /// Create a location whose value is the result of evaluating a DWARF
  /// expression. This allows complex expressions to be evaluated in order to
  /// unwind a register or CFA value.
  LLVM_ABI static UnwindLocation createIsDWARFExpression(DWARFExpression Expr);
  LLVM_ABI static UnwindLocation createAtDWARFExpression(DWARFExpression Expr);
  LLVM_ABI static UnwindLocation createIsConstant(int32_t Value);
 
  Location getLocation() const { return Kind; }
  uint32_t getRegister() const { return RegNum; }
  int32_t getOffset() const { return Offset; }
  bool hasAddressSpace() const {
    if (AddrSpace)
      return true;
    return false;
  }
  uint32_t getAddressSpace() const {
    assert(Kind == RegPlusOffset && AddrSpace);
    return *AddrSpace;
  }
  int32_t getConstant() const { return Offset; }
  bool getDereference() const { return Dereference; }
 
  /// Some opcodes will modify the CFA location's register only, so we need
  /// to be able to modify the CFA register when evaluating DWARF Call Frame
  /// Information opcodes.
  void setRegister(uint32_t NewRegNum) { RegNum = NewRegNum; }
  /// Some opcodes will modify the CFA location's offset only, so we need
  /// to be able to modify the CFA offset when evaluating DWARF Call Frame
  /// Information opcodes.
  void setOffset(int32_t NewOffset) { Offset = NewOffset; }
  /// Some opcodes modify a constant value and we need to be able to update
  /// the constant value (DW_CFA_GNU_window_save which is also known as
  // DW_CFA_AARCH64_negate_ra_state).
  void setConstant(int32_t Value) { Offset = Value; }
 
  std::optional<DWARFExpression> getDWARFExpressionBytes() const {
    return Expr;
  }
 
  LLVM_ABI bool operator==(const UnwindLocation &RHS) const;
};
 
/// A class that can track all registers with locations in a UnwindRow object.
///
/// Register locations use a map where the key is the register number and the
/// the value is a UnwindLocation.
///
/// The register maps are put into a class so that all register locations can
/// be copied when parsing the unwind opcodes DW_CFA_remember_state and
/// DW_CFA_restore_state.
class RegisterLocations {
  std::map<uint32_t, UnwindLocation> Locations;
 
public:
  /// Return the location for the register in \a RegNum if there is a location.
  ///
  /// \param RegNum the register number to find a location for.
  ///
  /// \returns A location if one is available for \a RegNum, or std::nullopt
  /// otherwise.
  std::optional<UnwindLocation> getRegisterLocation(uint32_t RegNum) const {
    auto Pos = Locations.find(RegNum);
    if (Pos == Locations.end())
      return std::nullopt;
    return Pos->second;
  }
 
  SmallVector<uint32_t, 4> getRegisters() const {
    SmallVector<uint32_t, 4> Registers;
    for (auto &&[Register, _] : Locations)
      Registers.push_back(Register);
    return Registers;
  }
 
  /// Set the location for the register in \a RegNum to \a Location.
  ///
  /// \param RegNum the register number to set the location for.
  ///
  /// \param Location the UnwindLocation that describes how to unwind the value.
  void setRegisterLocation(uint32_t RegNum, const UnwindLocation &Location) {
    Locations.erase(RegNum);
    Locations.insert(std::make_pair(RegNum, Location));
  }
 
  /// Removes any rule for the register in \a RegNum.
  ///
  /// \param RegNum the register number to remove the location for.
  void removeRegisterLocation(uint32_t RegNum) { Locations.erase(RegNum); }
 
  /// Returns true if we have any register locations in this object.
  bool hasLocations() const { return !Locations.empty(); }
 
  size_t size() const { return Locations.size(); }
 
  bool operator==(const RegisterLocations &RHS) const {
    return Locations == RHS.Locations;
  }
};
 
/// A class that represents a single row in the unwind table that is decoded by
/// parsing the DWARF Call Frame Information opcodes.
///
/// The row consists of an optional address, the rule to unwind the CFA and all
/// rules to unwind any registers. If the address doesn't have a value, this
/// row represents the initial instructions for a CIE. If the address has a
/// value the UnwindRow represents a row in the UnwindTable for a FDE. The
/// address is the first address for which the CFA location and register rules
/// are valid within a function.
///
/// UnwindRow objects are created by parsing opcodes in the DWARF Call Frame
/// Information and UnwindRow objects are lazily populated and pushed onto a
/// stack in the UnwindTable when evaluating this state machine. Accessors are
/// needed for the address, CFA value, and register locations as the opcodes
/// encode a state machine that produces a sorted array of UnwindRow objects
/// \see UnwindTable.
class UnwindRow {
  /// The address will be valid when parsing the instructions in a FDE. If
  /// invalid, this object represents the initial instructions of a CIE.
  std::optional<uint64_t> Address; ///< Address for row in FDE, invalid for CIE.
  UnwindLocation CFAValue;   ///< How to unwind the Call Frame Address (CFA).
  RegisterLocations RegLocs; ///< How to unwind all registers in this list.
 
public:
  UnwindRow() : CFAValue(UnwindLocation::createUnspecified()) {}
 
  /// Returns true if the address is valid in this object.
  bool hasAddress() const { return Address.has_value(); }
 
  /// Get the address for this row.
  ///
  /// Clients should only call this function after verifying it has a valid
  /// address with a call to \see hasAddress().
  uint64_t getAddress() const { return *Address; }
 
  /// Set the address for this UnwindRow.
  ///
  /// The address represents the first address for which the CFAValue and
  /// RegLocs are valid within a function.
  void setAddress(uint64_t Addr) { Address = Addr; }
 
  /// Offset the address for this UnwindRow.
  ///
  /// The address represents the first address for which the CFAValue and
  /// RegLocs are valid within a function. Clients must ensure that this object
  /// already has an address (\see hasAddress()) prior to calling this
  /// function.
  void slideAddress(uint64_t Offset) { *Address += Offset; }
  UnwindLocation &getCFAValue() { return CFAValue; }
  const UnwindLocation &getCFAValue() const { return CFAValue; }
  RegisterLocations &getRegisterLocations() { return RegLocs; }
  const RegisterLocations &getRegisterLocations() const { return RegLocs; }
};
 
/// A class that contains all UnwindRow objects for an FDE or a single unwind
/// row for a CIE. To unwind an address the rows, which are sorted by start
/// address, can be searched to find the UnwindRow with the lowest starting
/// address that is greater than or equal to the address that is being looked
/// up.
class UnwindTable {
public:
  using RowContainer = std::vector<UnwindRow>;
  using iterator = RowContainer::iterator;
  using const_iterator = RowContainer::const_iterator;
 
  UnwindTable(RowContainer &&Rows) : Rows(std::move(Rows)) {}
 
  size_t size() const { return Rows.size(); }
  iterator begin() { return Rows.begin(); }
  const_iterator begin() const { return Rows.begin(); }
  iterator end() { return Rows.end(); }
  const_iterator end() const { return Rows.end(); }
  const UnwindRow &operator[](size_t Index) const {
    assert(Index < size());
    return Rows[Index];
  }
 
private:
  RowContainer Rows;
};
 
/// Parse the information in the CFIProgram and update the CurrRow object
/// that the state machine describes.
///
/// This function emulates the state machine described in the DWARF Call Frame
/// Information opcodes and will push CurrRow onto a RowContainer when needed.
///
/// \param CFIP the CFI program that contains the opcodes from a CIE or FDE.
///
/// \param CurrRow the current row to modify while parsing the state machine.
///
/// \param InitialLocs If non-NULL, we are parsing a FDE and this contains
/// the initial register locations from the CIE. If NULL, then a CIE's
/// opcodes are being parsed and this is not needed. This is used for the
/// DW_CFA_restore and DW_CFA_restore_extended opcodes.
///
/// \returns An error if the DWARF Call Frame Information opcodes have state
/// machine errors, or the accumulated rows otherwise.
LLVM_ABI Expected<UnwindTable::RowContainer>
parseRows(const CFIProgram &CFIP, UnwindRow &CurrRow,
          const RegisterLocations *InitialLocs);
 
} // end namespace dwarf
 
} // end namespace llvm
 
#endif // LLVM_DEBUGINFO_DWARF_LOWLEVEL_DWARFUNWINDTABLE_H