//===- llvm/CodeGen/DwarfExpression.h - Dwarf Compile Unit ------*- 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
//
//===----------------------------------------------------------------------===//
//
// This file contains support for writing dwarf compile unit.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
#define LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
#include "ByteStreamer.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include <cassert>
#include <cstdint>
#include <iterator>
namespace llvm {
class AsmPrinter;
class APInt;
class DwarfCompileUnit;
class DIELoc;
class TargetRegisterInfo;
class MachineLocation;
/// Holds a DIExpression and keeps track of how many operands have been consumed
/// so far.
class DIExpressionCursor {
DIExpression::expr_op_iterator Start, End;
public:
DIExpressionCursor(const DIExpression *Expr) {
if (!Expr) {
assert(Start == End);
return;
}
Start = Expr->expr_op_begin();
End = Expr->expr_op_end();
}
DIExpressionCursor(ArrayRef<uint64_t> Expr)
: Start(Expr.begin()), End(Expr.end()) {}
DIExpressionCursor(const DIExpressionCursor &) = default;
/// Consume one operation.
Optional<DIExpression::ExprOperand> take() {
if (Start == End)
return None;
return *(Start++);
}
/// Consume N operations.
void consume(unsigned N) { std::advance(Start, N); }
/// Return the current operation.
Optional<DIExpression::ExprOperand> peek() const {
if (Start == End)
return None;
return *(Start);
}
/// Return the next operation.
Optional<DIExpression::ExprOperand> peekNext() const {
if (Start == End)
return None;
auto Next = Start.getNext();
if (Next == End)
return None;
return *Next;
}
/// Determine whether there are any operations left in this expression.
operator bool() const { return Start != End; }
DIExpression::expr_op_iterator begin() const { return Start; }
DIExpression::expr_op_iterator end() const { return End; }
/// Retrieve the fragment information, if any.
Optional<DIExpression::FragmentInfo> getFragmentInfo() const {
return DIExpression::getFragmentInfo(Start, End);
}
};
/// Base class containing the logic for constructing DWARF expressions
/// independently of whether they are emitted into a DIE or into a .debug_loc
/// entry.
///
/// Some DWARF operations, e.g. DW_OP_entry_value, need to calculate the size
/// of a succeeding DWARF block before the latter is emitted to the output.
/// To handle such cases, data can conditionally be emitted to a temporary
/// buffer, which can later on be committed to the main output. The size of the
/// temporary buffer is queryable, allowing for the size of the data to be
/// emitted before the data is committed.
class DwarfExpression {
protected:
/// Holds information about all subregisters comprising a register location.
struct Register {
int DwarfRegNo;
unsigned SubRegSize;
const char *Comment;
/// Create a full register, no extra DW_OP_piece operators necessary.
static Register createRegister(int RegNo, const char *Comment) {
return {RegNo, 0, Comment};
}
/// Create a subregister that needs a DW_OP_piece operator with SizeInBits.
static Register createSubRegister(int RegNo, unsigned SizeInBits,
const char *Comment) {
return {RegNo, SizeInBits, Comment};
}
bool isSubRegister() const { return SubRegSize; }
};
/// Whether we are currently emitting an entry value operation.
bool IsEmittingEntryValue = false;
DwarfCompileUnit &CU;
/// The register location, if any.
SmallVector<Register, 2> DwarfRegs;
/// Current Fragment Offset in Bits.
uint64_t OffsetInBits = 0;
/// Sometimes we need to add a DW_OP_bit_piece to describe a subregister.
unsigned SubRegisterSizeInBits : 16;
unsigned SubRegisterOffsetInBits : 16;
/// The kind of location description being produced.
enum { Unknown = 0, Register, Memory, Implicit };
/// Additional location flags which may be combined with any location kind.
/// Currently, entry values are not supported for the Memory location kind.
enum { EntryValue = 1 << 0, Indirect = 1 << 1, CallSiteParamValue = 1 << 2 };
unsigned LocationKind : 3;
unsigned LocationFlags : 3;
unsigned DwarfVersion : 4;
public:
/// Set the location (\p Loc) and \ref DIExpression (\p DIExpr) to describe.
void setLocation(const MachineLocation &Loc, const DIExpression *DIExpr);
bool isUnknownLocation() const { return LocationKind == Unknown; }
bool isMemoryLocation() const { return LocationKind == Memory; }
bool isRegisterLocation() const { return LocationKind == Register; }
bool isImplicitLocation() const { return LocationKind == Implicit; }
bool isEntryValue() const { return LocationFlags & EntryValue; }
bool isIndirect() const { return LocationFlags & Indirect; }
bool isParameterValue() { return LocationFlags & CallSiteParamValue; }
Optional<uint8_t> TagOffset;
protected:
/// Push a DW_OP_piece / DW_OP_bit_piece for emitting later, if one is needed
/// to represent a subregister.
void setSubRegisterPiece(unsigned SizeInBits, unsigned OffsetInBits) {
assert(SizeInBits < 65536 && OffsetInBits < 65536);
SubRegisterSizeInBits = SizeInBits;
SubRegisterOffsetInBits = OffsetInBits;
}
/// Add masking operations to stencil out a subregister.
void maskSubRegister();
/// Output a dwarf operand and an optional assembler comment.
virtual void emitOp(uint8_t Op, const char *Comment = nullptr) = 0;
/// Emit a raw signed value.
virtual void emitSigned(int64_t Value) = 0;
/// Emit a raw unsigned value.
virtual void emitUnsigned(uint64_t Value) = 0;
virtual void emitData1(uint8_t Value) = 0;
virtual void emitBaseTypeRef(uint64_t Idx) = 0;
/// Start emitting data to the temporary buffer. The data stored in the
/// temporary buffer can be committed to the main output using
/// commitTemporaryBuffer().
virtual void enableTemporaryBuffer() = 0;
/// Disable emission to the temporary buffer. This does not commit data
/// in the temporary buffer to the main output.
virtual void disableTemporaryBuffer() = 0;
/// Return the emitted size, in number of bytes, for the data stored in the
/// temporary buffer.
virtual unsigned getTemporaryBufferSize() = 0;
/// Commit the data stored in the temporary buffer to the main output.
virtual void commitTemporaryBuffer() = 0;
/// Emit a normalized unsigned constant.
void emitConstu(uint64_t Value);
/// Return whether the given machine register is the frame register in the
/// current function.
virtual bool isFrameRegister(const TargetRegisterInfo &TRI,
unsigned MachineReg) = 0;
/// Emit a DW_OP_reg operation. Note that this is only legal inside a DWARF
/// register location description.
void addReg(int DwarfReg, const char *Comment = nullptr);
/// Emit a DW_OP_breg operation.
void addBReg(int DwarfReg, int Offset);
/// Emit DW_OP_fbreg <Offset>.
void addFBReg(int Offset);
/// Emit a partial DWARF register operation.
///
/// \param MachineReg The register number.
/// \param MaxSize If the register must be composed from
/// sub-registers this is an upper bound
/// for how many bits the emitted DW_OP_piece
/// may cover.
///
/// If size and offset is zero an operation for the entire register is
/// emitted: Some targets do not provide a DWARF register number for every
/// register. If this is the case, this function will attempt to emit a DWARF
/// register by emitting a fragment of a super-register or by piecing together
/// multiple subregisters that alias the register.
///
/// \return false if no DWARF register exists for MachineReg.
bool addMachineReg(const TargetRegisterInfo &TRI, unsigned MachineReg,
unsigned MaxSize = ~1U);
/// Emit a DW_OP_piece or DW_OP_bit_piece operation for a variable fragment.
/// \param OffsetInBits This is an optional offset into the location that
/// is at the top of the DWARF stack.
void addOpPiece(unsigned SizeInBits, unsigned OffsetInBits = 0);
/// Emit a shift-right dwarf operation.
void addShr(unsigned ShiftBy);
/// Emit a bitwise and dwarf operation.
void addAnd(unsigned Mask);
/// Emit a DW_OP_stack_value, if supported.
///
/// The proper way to describe a constant value is DW_OP_constu <const>,
/// DW_OP_stack_value. Unfortunately, DW_OP_stack_value was not available
/// until DWARF 4, so we will continue to generate DW_OP_constu <const> for
/// DWARF 2 and DWARF 3. Technically, this is incorrect since DW_OP_const
/// <const> actually describes a value at a constant address, not a constant
/// value. However, in the past there was no better way to describe a
/// constant value, so the producers and consumers started to rely on
/// heuristics to disambiguate the value vs. location status of the
/// expression. See PR21176 for more details.
void addStackValue();
/// Finalize an entry value by emitting its size operand, and committing the
/// DWARF block which has been emitted to the temporary buffer.
void finalizeEntryValue();
/// Cancel the emission of an entry value.
void cancelEntryValue();
~DwarfExpression() = default;
public:
DwarfExpression(unsigned DwarfVersion, DwarfCompileUnit &CU)
: CU(CU), SubRegisterSizeInBits(0), SubRegisterOffsetInBits(0),
LocationKind(Unknown), LocationFlags(Unknown),
DwarfVersion(DwarfVersion) {}
/// This needs to be called last to commit any pending changes.
void finalize();
/// Emit a signed constant.
void addSignedConstant(int64_t Value);
/// Emit an unsigned constant.
void addUnsignedConstant(uint64_t Value);
/// Emit an unsigned constant.
void addUnsignedConstant(const APInt &Value);
/// Lock this down to become a memory location description.
void setMemoryLocationKind() {
assert(isUnknownLocation());
LocationKind = Memory;
}
/// Lock this down to become an entry value location.
void setEntryValueFlags(const MachineLocation &Loc);
/// Lock this down to become a call site parameter location.
void setCallSiteParamValueFlag() { LocationFlags |= CallSiteParamValue; }
/// Emit a machine register location. As an optimization this may also consume
/// the prefix of a DwarfExpression if a more efficient representation for
/// combining the register location and the first operation exists.
///
/// \param FragmentOffsetInBits If this is one fragment out of a
/// fragmented
/// location, this is the offset of the
/// fragment inside the entire variable.
/// \return false if no DWARF register exists
/// for MachineReg.
bool addMachineRegExpression(const TargetRegisterInfo &TRI,
DIExpressionCursor &Expr, unsigned MachineReg,
unsigned FragmentOffsetInBits = 0);
/// Begin emission of an entry value dwarf operation. The entry value's
/// first operand is the size of the DWARF block (its second operand),
/// which needs to be calculated at time of emission, so we don't emit
/// any operands here.
void beginEntryValueExpression(DIExpressionCursor &ExprCursor);
/// Return the index of a base type with the given properties and
/// create one if necessary.
unsigned getOrCreateBaseType(unsigned BitSize, dwarf::TypeKind Encoding);
/// Emit all remaining operations in the DIExpressionCursor.
///
/// \param FragmentOffsetInBits If this is one fragment out of multiple
/// locations, this is the offset of the
/// fragment inside the entire variable.
void addExpression(DIExpressionCursor &&Expr,
unsigned FragmentOffsetInBits = 0);
/// If applicable, emit an empty DW_OP_piece / DW_OP_bit_piece to advance to
/// the fragment described by \c Expr.
void addFragmentOffset(const DIExpression *Expr);
void emitLegacySExt(unsigned FromBits);
void emitLegacyZExt(unsigned FromBits);
/// Emit location information expressed via WebAssembly location + offset
/// The Index is an identifier for locals, globals or operand stack.
void addWasmLocation(unsigned Index, uint64_t Offset);
};
/// DwarfExpression implementation for .debug_loc entries.
class DebugLocDwarfExpression final : public DwarfExpression {
struct TempBuffer {
SmallString<32> Bytes;
std::vector<std::string> Comments;
BufferByteStreamer BS;
TempBuffer(bool GenerateComments) : BS(Bytes, Comments, GenerateComments) {}
};
std::unique_ptr<TempBuffer> TmpBuf;
BufferByteStreamer &OutBS;
bool IsBuffering = false;
/// Return the byte streamer that currently is being emitted to.
ByteStreamer &getActiveStreamer() { return IsBuffering ? TmpBuf->BS : OutBS; }
void emitOp(uint8_t Op, const char *Comment = nullptr) override;
void emitSigned(int64_t Value) override;
void emitUnsigned(uint64_t Value) override;
void emitData1(uint8_t Value) override;
void emitBaseTypeRef(uint64_t Idx) override;
void enableTemporaryBuffer() override;
void disableTemporaryBuffer() override;
unsigned getTemporaryBufferSize() override;
void commitTemporaryBuffer() override;
bool isFrameRegister(const TargetRegisterInfo &TRI,
unsigned MachineReg) override;
public:
DebugLocDwarfExpression(unsigned DwarfVersion, BufferByteStreamer &BS,
DwarfCompileUnit &CU)
: DwarfExpression(DwarfVersion, CU), OutBS(BS) {}
};
/// DwarfExpression implementation for singular DW_AT_location.
class DIEDwarfExpression final : public DwarfExpression {
const AsmPrinter &AP;
DIELoc &OutDIE;
DIELoc TmpDIE;
bool IsBuffering = false;
/// Return the DIE that currently is being emitted to.
DIELoc &getActiveDIE() { return IsBuffering ? TmpDIE : OutDIE; }
void emitOp(uint8_t Op, const char *Comment = nullptr) override;
void emitSigned(int64_t Value) override;
void emitUnsigned(uint64_t Value) override;
void emitData1(uint8_t Value) override;
void emitBaseTypeRef(uint64_t Idx) override;
void enableTemporaryBuffer() override;
void disableTemporaryBuffer() override;
unsigned getTemporaryBufferSize() override;
void commitTemporaryBuffer() override;
bool isFrameRegister(const TargetRegisterInfo &TRI,
unsigned MachineReg) override;
public:
DIEDwarfExpression(const AsmPrinter &AP, DwarfCompileUnit &CU, DIELoc &DIE);
DIELoc *finalize() {
DwarfExpression::finalize();
return &OutDIE;
}
};
} // end namespace llvm
#endif // LLVM_LIB_CODEGEN_ASMPRINTER_DWARFEXPRESSION_H
