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llvm-project/llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp

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//===- llvm/CodeGen/DwarfExpression.cpp - Dwarf Debug 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 writing dwarf debug info into asm files.
//
//===----------------------------------------------------------------------===//
#include "DwarfExpression.h"
#include "DwarfCompileUnit.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/SmallBitVector.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
#include <cassert>
#include <cstdint>
using namespace llvm;
void DwarfExpression::emitConstu(uint64_t Value) {
if (Value < 32)
emitOp(dwarf::DW_OP_lit0 + Value);
else if (Value == std::numeric_limits<uint64_t>::max()) {
// Only do this for 64-bit values as the DWARF expression stack uses
// target-address-size values.
emitOp(dwarf::DW_OP_lit0);
emitOp(dwarf::DW_OP_not);
} else {
emitOp(dwarf::DW_OP_constu);
emitUnsigned(Value);
}
}
void DwarfExpression::addReg(int DwarfReg, const char *Comment) {
assert(DwarfReg >= 0 && "invalid negative dwarf register number");
assert((LocationKind == Unknown || LocationKind == Register) &&
"location description already locked down");
LocationKind = Register;
if (DwarfReg < 32) {
emitOp(dwarf::DW_OP_reg0 + DwarfReg, Comment);
} else {
emitOp(dwarf::DW_OP_regx, Comment);
emitUnsigned(DwarfReg);
}
}
void DwarfExpression::addBReg(int DwarfReg, int Offset) {
assert(DwarfReg >= 0 && "invalid negative dwarf register number");
assert(LocationKind != Register && "location description already locked down");
if (DwarfReg < 32) {
emitOp(dwarf::DW_OP_breg0 + DwarfReg);
} else {
emitOp(dwarf::DW_OP_bregx);
emitUnsigned(DwarfReg);
}
emitSigned(Offset);
}
void DwarfExpression::addFBReg(int Offset) {
emitOp(dwarf::DW_OP_fbreg);
emitSigned(Offset);
}
void DwarfExpression::addOpPiece(unsigned SizeInBits, unsigned OffsetInBits) {
if (!SizeInBits)
return;
const unsigned SizeOfByte = 8;
if (OffsetInBits > 0 || SizeInBits % SizeOfByte) {
emitOp(dwarf::DW_OP_bit_piece);
emitUnsigned(SizeInBits);
emitUnsigned(OffsetInBits);
} else {
emitOp(dwarf::DW_OP_piece);
unsigned ByteSize = SizeInBits / SizeOfByte;
emitUnsigned(ByteSize);
}
this->OffsetInBits += SizeInBits;
}
void DwarfExpression::addShr(unsigned ShiftBy) {
emitConstu(ShiftBy);
emitOp(dwarf::DW_OP_shr);
}
void DwarfExpression::addAnd(unsigned Mask) {
emitConstu(Mask);
emitOp(dwarf::DW_OP_and);
}
bool DwarfExpression::addMachineReg(const TargetRegisterInfo &TRI,
unsigned MachineReg, unsigned MaxSize) {
if (!TRI.isPhysicalRegister(MachineReg)) {
if (isFrameRegister(TRI, MachineReg)) {
DwarfRegs.push_back({-1, 0, nullptr});
return true;
}
return false;
}
int Reg = TRI.getDwarfRegNum(MachineReg, false);
// If this is a valid register number, emit it.
if (Reg >= 0) {
DwarfRegs.push_back({Reg, 0, nullptr});
return true;
}
// Walk up the super-register chain until we find a valid number.
// For example, EAX on x86_64 is a 32-bit fragment of RAX with offset 0.
for (MCSuperRegIterator SR(MachineReg, &TRI); SR.isValid(); ++SR) {
Reg = TRI.getDwarfRegNum(*SR, false);
if (Reg >= 0) {
unsigned Idx = TRI.getSubRegIndex(*SR, MachineReg);
unsigned Size = TRI.getSubRegIdxSize(Idx);
unsigned RegOffset = TRI.getSubRegIdxOffset(Idx);
DwarfRegs.push_back({Reg, 0, "super-register"});
// Use a DW_OP_bit_piece to describe the sub-register.
setSubRegisterPiece(Size, RegOffset);
return true;
}
}
// Otherwise, attempt to find a covering set of sub-register numbers.
// For example, Q0 on ARM is a composition of D0+D1.
unsigned CurPos = 0;
// The size of the register in bits.
const TargetRegisterClass *RC = TRI.getMinimalPhysRegClass(MachineReg);
unsigned RegSize = TRI.getRegSizeInBits(*RC);
// Keep track of the bits in the register we already emitted, so we
// can avoid emitting redundant aliasing subregs. Because this is
// just doing a greedy scan of all subregisters, it is possible that
// this doesn't find a combination of subregisters that fully cover
// the register (even though one may exist).
SmallBitVector Coverage(RegSize, false);
for (MCSubRegIterator SR(MachineReg, &TRI); SR.isValid(); ++SR) {
unsigned Idx = TRI.getSubRegIndex(MachineReg, *SR);
unsigned Size = TRI.getSubRegIdxSize(Idx);
unsigned Offset = TRI.getSubRegIdxOffset(Idx);
Reg = TRI.getDwarfRegNum(*SR, false);
if (Reg < 0)
continue;
// Intersection between the bits we already emitted and the bits
// covered by this subregister.
SmallBitVector CurSubReg(RegSize, false);
CurSubReg.set(Offset, Offset + Size);
// If this sub-register has a DWARF number and we haven't covered
// its range, emit a DWARF piece for it.
if (CurSubReg.test(Coverage)) {
// Emit a piece for any gap in the coverage.
if (Offset > CurPos)
DwarfRegs.push_back({-1, Offset - CurPos, "no DWARF register encoding"});
DwarfRegs.push_back(
{Reg, std::min<unsigned>(Size, MaxSize - Offset), "sub-register"});
if (Offset >= MaxSize)
break;
// Mark it as emitted.
Coverage.set(Offset, Offset + Size);
CurPos = Offset + Size;
}
}
// Failed to find any DWARF encoding.
if (CurPos == 0)
return false;
// Found a partial or complete DWARF encoding.
if (CurPos < RegSize)
DwarfRegs.push_back({-1, RegSize - CurPos, "no DWARF register encoding"});
return true;
}
void DwarfExpression::addStackValue() {
if (DwarfVersion >= 4)
emitOp(dwarf::DW_OP_stack_value);
}
void DwarfExpression::addSignedConstant(int64_t Value) {
assert(LocationKind == Implicit || LocationKind == Unknown);
LocationKind = Implicit;
emitOp(dwarf::DW_OP_consts);
emitSigned(Value);
}
void DwarfExpression::addUnsignedConstant(uint64_t Value) {
assert(LocationKind == Implicit || LocationKind == Unknown);
LocationKind = Implicit;
emitConstu(Value);
}
void DwarfExpression::addUnsignedConstant(const APInt &Value) {
assert(LocationKind == Implicit || LocationKind == Unknown);
LocationKind = Implicit;
unsigned Size = Value.getBitWidth();
const uint64_t *Data = Value.getRawData();
// Chop it up into 64-bit pieces, because that's the maximum that
// addUnsignedConstant takes.
unsigned Offset = 0;
while (Offset < Size) {
addUnsignedConstant(*Data++);
if (Offset == 0 && Size <= 64)
break;
addStackValue();
addOpPiece(std::min(Size - Offset, 64u), Offset);
Offset += 64;
}
}
bool DwarfExpression::addMachineRegExpression(const TargetRegisterInfo &TRI,
DIExpressionCursor &ExprCursor,
unsigned MachineReg,
unsigned FragmentOffsetInBits) {
auto Fragment = ExprCursor.getFragmentInfo();
if (!addMachineReg(TRI, MachineReg, Fragment ? Fragment->SizeInBits : ~1U)) {
LocationKind = Unknown;
return false;
}
bool HasComplexExpression = false;
auto Op = ExprCursor.peek();
if (Op && Op->getOp() != dwarf::DW_OP_LLVM_fragment)
HasComplexExpression = true;
// If the register can only be described by a complex expression (i.e.,
// multiple subregisters) it doesn't safely compose with another complex
// expression. For example, it is not possible to apply a DW_OP_deref
// operation to multiple DW_OP_pieces.
if (HasComplexExpression && DwarfRegs.size() > 1) {
DwarfRegs.clear();
LocationKind = Unknown;
return false;
}
// Handle simple register locations.
if (LocationKind != Memory && !HasComplexExpression) {
for (auto &Reg : DwarfRegs) {
if (Reg.DwarfRegNo >= 0)
addReg(Reg.DwarfRegNo, Reg.Comment);
addOpPiece(Reg.Size);
}
DwarfRegs.clear();
return true;
}
// Don't emit locations that cannot be expressed without DW_OP_stack_value.
if (DwarfVersion < 4)
if (any_of(ExprCursor, [](DIExpression::ExprOperand Op) -> bool {
return Op.getOp() == dwarf::DW_OP_stack_value;
})) {
DwarfRegs.clear();
LocationKind = Unknown;
return false;
}
assert(DwarfRegs.size() == 1);
auto Reg = DwarfRegs[0];
bool FBReg = isFrameRegister(TRI, MachineReg);
int SignedOffset = 0;
assert(Reg.Size == 0 && "subregister has same size as superregister");
// Pattern-match combinations for which more efficient representations exist.
// [Reg, DW_OP_plus_uconst, Offset] --> [DW_OP_breg, Offset].
if (Op && (Op->getOp() == dwarf::DW_OP_plus_uconst)) {
SignedOffset = Op->getArg(0);
ExprCursor.take();
}
// [Reg, DW_OP_constu, Offset, DW_OP_plus] --> [DW_OP_breg, Offset]
// [Reg, DW_OP_constu, Offset, DW_OP_minus] --> [DW_OP_breg,-Offset]
// If Reg is a subregister we need to mask it out before subtracting.
if (Op && Op->getOp() == dwarf::DW_OP_constu) {
auto N = ExprCursor.peekNext();
if (N && (N->getOp() == dwarf::DW_OP_plus ||
(N->getOp() == dwarf::DW_OP_minus && !SubRegisterSizeInBits))) {
int Offset = Op->getArg(0);
SignedOffset = (N->getOp() == dwarf::DW_OP_minus) ? -Offset : Offset;
ExprCursor.consume(2);
}
}
if (FBReg)
addFBReg(SignedOffset);
else
addBReg(Reg.DwarfRegNo, SignedOffset);
DwarfRegs.clear();
return true;
}
/// Assuming a well-formed expression, match "DW_OP_deref* DW_OP_LLVM_fragment?".
static bool isMemoryLocation(DIExpressionCursor ExprCursor) {
while (ExprCursor) {
auto Op = ExprCursor.take();
switch (Op->getOp()) {
case dwarf::DW_OP_deref:
case dwarf::DW_OP_LLVM_fragment:
break;
default:
return false;
}
}
return true;
}
void DwarfExpression::addExpression(DIExpressionCursor &&ExprCursor,
unsigned FragmentOffsetInBits) {
// If we need to mask out a subregister, do it now, unless the next
// operation would emit an OpPiece anyway.
auto N = ExprCursor.peek();
if (SubRegisterSizeInBits && N && (N->getOp() != dwarf::DW_OP_LLVM_fragment))
maskSubRegister();
Optional<DIExpression::ExprOperand> PrevConvertOp = None;
while (ExprCursor) {
auto Op = ExprCursor.take();
switch (Op->getOp()) {
case dwarf::DW_OP_LLVM_fragment: {
unsigned SizeInBits = Op->getArg(1);
unsigned FragmentOffset = Op->getArg(0);
// The fragment offset must have already been adjusted by emitting an
// empty DW_OP_piece / DW_OP_bit_piece before we emitted the base
// location.
assert(OffsetInBits >= FragmentOffset && "fragment offset not added?");
// If addMachineReg already emitted DW_OP_piece operations to represent
// a super-register by splicing together sub-registers, subtract the size
// of the pieces that was already emitted.
SizeInBits -= OffsetInBits - FragmentOffset;
// If addMachineReg requested a DW_OP_bit_piece to stencil out a
// sub-register that is smaller than the current fragment's size, use it.
if (SubRegisterSizeInBits)
SizeInBits = std::min<unsigned>(SizeInBits, SubRegisterSizeInBits);
// Emit a DW_OP_stack_value for implicit location descriptions.
if (LocationKind == Implicit)
addStackValue();
// Emit the DW_OP_piece.
addOpPiece(SizeInBits, SubRegisterOffsetInBits);
setSubRegisterPiece(0, 0);
// Reset the location description kind.
LocationKind = Unknown;
return;
}
case dwarf::DW_OP_plus_uconst:
assert(LocationKind != Register);
emitOp(dwarf::DW_OP_plus_uconst);
emitUnsigned(Op->getArg(0));
break;
case dwarf::DW_OP_plus:
case dwarf::DW_OP_minus:
case dwarf::DW_OP_mul:
case dwarf::DW_OP_div:
case dwarf::DW_OP_mod:
case dwarf::DW_OP_or:
case dwarf::DW_OP_and:
case dwarf::DW_OP_xor:
case dwarf::DW_OP_shl:
case dwarf::DW_OP_shr:
case dwarf::DW_OP_shra:
case dwarf::DW_OP_lit0:
case dwarf::DW_OP_not:
case dwarf::DW_OP_dup:
emitOp(Op->getOp());
break;
case dwarf::DW_OP_deref:
assert(LocationKind != Register);
if (LocationKind != Memory && ::isMemoryLocation(ExprCursor))
// Turning this into a memory location description makes the deref
// implicit.
LocationKind = Memory;
else
emitOp(dwarf::DW_OP_deref);
break;
case dwarf::DW_OP_constu:
assert(LocationKind != Register);
emitConstu(Op->getArg(0));
break;
case dwarf::DW_OP_LLVM_convert: {
unsigned BitSize = Op->getArg(0);
dwarf::TypeKind Encoding = static_cast<dwarf::TypeKind>(Op->getArg(1));
if (DwarfVersion >= 5) {
emitOp(dwarf::DW_OP_convert);
// Reuse the base_type if we already have one in this CU otherwise we
// create a new one.
unsigned I = 0, E = CU.ExprRefedBaseTypes.size();
for (; I != E; ++I)
if (CU.ExprRefedBaseTypes[I].BitSize == BitSize &&
CU.ExprRefedBaseTypes[I].Encoding == Encoding)
break;
if (I == E)
CU.ExprRefedBaseTypes.emplace_back(BitSize, Encoding);
// If targeting a location-list; simply emit the index into the raw
// byte stream as ULEB128, DwarfDebug::emitDebugLocEntry has been
// fitted with means to extract it later.
// If targeting a inlined DW_AT_location; insert a DIEBaseTypeRef
// (containing the index and a resolve mechanism during emit) into the
// DIE value list.
emitBaseTypeRef(I);
} else {
if (PrevConvertOp && PrevConvertOp->getArg(0) < BitSize) {
if (Encoding == dwarf::DW_ATE_signed)
emitLegacySExt(PrevConvertOp->getArg(0));
else if (Encoding == dwarf::DW_ATE_unsigned)
emitLegacyZExt(PrevConvertOp->getArg(0));
PrevConvertOp = None;
} else {
PrevConvertOp = Op;
}
}
break;
}
case dwarf::DW_OP_stack_value:
LocationKind = Implicit;
break;
case dwarf::DW_OP_swap:
assert(LocationKind != Register);
emitOp(dwarf::DW_OP_swap);
break;
case dwarf::DW_OP_xderef:
assert(LocationKind != Register);
emitOp(dwarf::DW_OP_xderef);
break;
default:
llvm_unreachable("unhandled opcode found in expression");
}
}
if (LocationKind == Implicit)
// Turn this into an implicit location description.
addStackValue();
}
/// add masking operations to stencil out a subregister.
void DwarfExpression::maskSubRegister() {
assert(SubRegisterSizeInBits && "no subregister was registered");
if (SubRegisterOffsetInBits > 0)
addShr(SubRegisterOffsetInBits);
uint64_t Mask = (1ULL << (uint64_t)SubRegisterSizeInBits) - 1ULL;
addAnd(Mask);
}
void DwarfExpression::finalize() {
assert(DwarfRegs.size() == 0 && "dwarf registers not emitted");
// Emit any outstanding DW_OP_piece operations to mask out subregisters.
if (SubRegisterSizeInBits == 0)
return;
// Don't emit a DW_OP_piece for a subregister at offset 0.
if (SubRegisterOffsetInBits == 0)
return;
addOpPiece(SubRegisterSizeInBits, SubRegisterOffsetInBits);
}
void DwarfExpression::addFragmentOffset(const DIExpression *Expr) {
if (!Expr || !Expr->isFragment())
return;
uint64_t FragmentOffset = Expr->getFragmentInfo()->OffsetInBits;
assert(FragmentOffset >= OffsetInBits &&
"overlapping or duplicate fragments");
if (FragmentOffset > OffsetInBits)
addOpPiece(FragmentOffset - OffsetInBits);
OffsetInBits = FragmentOffset;
}
void DwarfExpression::emitLegacySExt(unsigned FromBits) {
// (((X >> (FromBits - 1)) * (~0)) << FromBits) | X
emitOp(dwarf::DW_OP_dup);
emitOp(dwarf::DW_OP_constu);
emitUnsigned(FromBits - 1);
emitOp(dwarf::DW_OP_shr);
emitOp(dwarf::DW_OP_lit0);
emitOp(dwarf::DW_OP_not);
emitOp(dwarf::DW_OP_mul);
emitOp(dwarf::DW_OP_constu);
emitUnsigned(FromBits);
emitOp(dwarf::DW_OP_shl);
emitOp(dwarf::DW_OP_or);
}
void DwarfExpression::emitLegacyZExt(unsigned FromBits) {
// (X & (1 << FromBits - 1))
emitOp(dwarf::DW_OP_constu);
emitUnsigned((1ULL << FromBits) - 1);
emitOp(dwarf::DW_OP_and);
}
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