1 //===-- llvm/CodeGen/DwarfExpression.cpp - Dwarf Debug Framework ----------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains support for writing dwarf debug info into asm files.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "DwarfExpression.h"
15 #include "DwarfDebug.h"
16 #include "llvm/ADT/SmallBitVector.h"
17 #include "llvm/CodeGen/AsmPrinter.h"
18 #include "llvm/Support/Dwarf.h"
19 #include "llvm/Target/TargetMachine.h"
20 #include "llvm/Target/TargetRegisterInfo.h"
21 #include "llvm/Target/TargetSubtargetInfo.h"
22
23 using namespace llvm;
24
getTRI() const25 const TargetRegisterInfo *DwarfExpression::getTRI() const {
26 return AP.TM.getSubtargetImpl()->getRegisterInfo();
27 }
28
getDwarfVersion() const29 unsigned DwarfExpression::getDwarfVersion() const {
30 return AP.getDwarfDebug()->getDwarfVersion();
31 }
32
AddReg(int DwarfReg,const char * Comment)33 void DwarfExpression::AddReg(int DwarfReg, const char *Comment) {
34 assert(DwarfReg >= 0 && "invalid negative dwarf register number");
35 if (DwarfReg < 32) {
36 EmitOp(dwarf::DW_OP_reg0 + DwarfReg, Comment);
37 } else {
38 EmitOp(dwarf::DW_OP_regx, Comment);
39 EmitUnsigned(DwarfReg);
40 }
41 }
42
AddRegIndirect(int DwarfReg,int Offset,bool Deref)43 void DwarfExpression::AddRegIndirect(int DwarfReg, int Offset, bool Deref) {
44 assert(DwarfReg >= 0 && "invalid negative dwarf register number");
45 if (DwarfReg < 32) {
46 EmitOp(dwarf::DW_OP_breg0 + DwarfReg);
47 } else {
48 EmitOp(dwarf::DW_OP_bregx);
49 EmitUnsigned(DwarfReg);
50 }
51 EmitSigned(Offset);
52 if (Deref)
53 EmitOp(dwarf::DW_OP_deref);
54 }
55
AddOpPiece(unsigned SizeInBits,unsigned OffsetInBits)56 void DwarfExpression::AddOpPiece(unsigned SizeInBits, unsigned OffsetInBits) {
57 assert(SizeInBits > 0 && "piece has size zero");
58 const unsigned SizeOfByte = 8;
59 if (OffsetInBits > 0 || SizeInBits % SizeOfByte) {
60 EmitOp(dwarf::DW_OP_bit_piece);
61 EmitUnsigned(SizeInBits);
62 EmitUnsigned(OffsetInBits);
63 } else {
64 EmitOp(dwarf::DW_OP_piece);
65 unsigned ByteSize = SizeInBits / SizeOfByte;
66 EmitUnsigned(ByteSize);
67 }
68 }
69
AddShr(unsigned ShiftBy)70 void DwarfExpression::AddShr(unsigned ShiftBy) {
71 EmitOp(dwarf::DW_OP_constu);
72 EmitUnsigned(ShiftBy);
73 EmitOp(dwarf::DW_OP_shr);
74 }
75
AddMachineRegIndirect(unsigned MachineReg,int Offset)76 bool DwarfExpression::AddMachineRegIndirect(unsigned MachineReg, int Offset) {
77 int DwarfReg = getTRI()->getDwarfRegNum(MachineReg, false);
78 if (DwarfReg < 0)
79 return false;
80
81 if (isFrameRegister(MachineReg)) {
82 // If variable offset is based in frame register then use fbreg.
83 EmitOp(dwarf::DW_OP_fbreg);
84 EmitSigned(Offset);
85 } else {
86 AddRegIndirect(DwarfReg, Offset);
87 }
88 return true;
89 }
90
AddMachineRegPiece(unsigned MachineReg,unsigned PieceSizeInBits,unsigned PieceOffsetInBits)91 bool DwarfExpression::AddMachineRegPiece(unsigned MachineReg,
92 unsigned PieceSizeInBits,
93 unsigned PieceOffsetInBits) {
94 const TargetRegisterInfo *TRI = getTRI();
95 int Reg = TRI->getDwarfRegNum(MachineReg, false);
96
97 // If this is a valid register number, emit it.
98 if (Reg >= 0) {
99 AddReg(Reg);
100 if (PieceSizeInBits)
101 AddOpPiece(PieceSizeInBits, PieceOffsetInBits);
102 return true;
103 }
104
105 // Walk up the super-register chain until we find a valid number.
106 // For example, EAX on x86_64 is a 32-bit piece of RAX with offset 0.
107 for (MCSuperRegIterator SR(MachineReg, TRI); SR.isValid(); ++SR) {
108 Reg = TRI->getDwarfRegNum(*SR, false);
109 if (Reg >= 0) {
110 unsigned Idx = TRI->getSubRegIndex(*SR, MachineReg);
111 unsigned Size = TRI->getSubRegIdxSize(Idx);
112 unsigned RegOffset = TRI->getSubRegIdxOffset(Idx);
113 AddReg(Reg, "super-register");
114 if (PieceOffsetInBits == RegOffset) {
115 AddOpPiece(Size, RegOffset);
116 } else {
117 // If this is part of a variable in a sub-register at a
118 // non-zero offset, we need to manually shift the value into
119 // place, since the DW_OP_piece describes the part of the
120 // variable, not the position of the subregister.
121 if (RegOffset)
122 AddShr(RegOffset);
123 AddOpPiece(Size, PieceOffsetInBits);
124 }
125 return true;
126 }
127 }
128
129 // Otherwise, attempt to find a covering set of sub-register numbers.
130 // For example, Q0 on ARM is a composition of D0+D1.
131 //
132 // Keep track of the current position so we can emit the more
133 // efficient DW_OP_piece.
134 unsigned CurPos = PieceOffsetInBits;
135 // The size of the register in bits, assuming 8 bits per byte.
136 unsigned RegSize = TRI->getMinimalPhysRegClass(MachineReg)->getSize() * 8;
137 // Keep track of the bits in the register we already emitted, so we
138 // can avoid emitting redundant aliasing subregs.
139 SmallBitVector Coverage(RegSize, false);
140 for (MCSubRegIterator SR(MachineReg, TRI); SR.isValid(); ++SR) {
141 unsigned Idx = TRI->getSubRegIndex(MachineReg, *SR);
142 unsigned Size = TRI->getSubRegIdxSize(Idx);
143 unsigned Offset = TRI->getSubRegIdxOffset(Idx);
144 Reg = TRI->getDwarfRegNum(*SR, false);
145
146 // Intersection between the bits we already emitted and the bits
147 // covered by this subregister.
148 SmallBitVector Intersection(RegSize, false);
149 Intersection.set(Offset, Offset + Size);
150 Intersection ^= Coverage;
151
152 // If this sub-register has a DWARF number and we haven't covered
153 // its range, emit a DWARF piece for it.
154 if (Reg >= 0 && Intersection.any()) {
155 AddReg(Reg, "sub-register");
156 AddOpPiece(Size, Offset == CurPos ? 0 : Offset);
157 CurPos = Offset + Size;
158
159 // Mark it as emitted.
160 Coverage.set(Offset, Offset + Size);
161 }
162 }
163
164 return CurPos > PieceOffsetInBits;
165 }
166
AddSignedConstant(int Value)167 void DwarfExpression::AddSignedConstant(int Value) {
168 EmitOp(dwarf::DW_OP_consts);
169 EmitSigned(Value);
170 // The proper way to describe a constant value is
171 // DW_OP_constu <const>, DW_OP_stack_value.
172 // Unfortunately, DW_OP_stack_value was not available until DWARF-4,
173 // so we will continue to generate DW_OP_constu <const> for DWARF-2
174 // and DWARF-3. Technically, this is incorrect since DW_OP_const <const>
175 // actually describes a value at a constant addess, not a constant value.
176 // However, in the past there was no better way to describe a constant
177 // value, so the producers and consumers started to rely on heuristics
178 // to disambiguate the value vs. location status of the expression.
179 // See PR21176 for more details.
180 if (getDwarfVersion() >= 4)
181 EmitOp(dwarf::DW_OP_stack_value);
182 }
183
AddUnsignedConstant(unsigned Value)184 void DwarfExpression::AddUnsignedConstant(unsigned Value) {
185 EmitOp(dwarf::DW_OP_constu);
186 EmitUnsigned(Value);
187 // cf. comment in DwarfExpression::AddSignedConstant().
188 if (getDwarfVersion() >= 4)
189 EmitOp(dwarf::DW_OP_stack_value);
190 }
191
getOffsetOrZero(unsigned OffsetInBits,unsigned PieceOffsetInBits)192 static unsigned getOffsetOrZero(unsigned OffsetInBits,
193 unsigned PieceOffsetInBits) {
194 if (OffsetInBits == PieceOffsetInBits)
195 return 0;
196 assert(OffsetInBits >= PieceOffsetInBits && "overlapping pieces");
197 return OffsetInBits;
198 }
199
AddMachineRegExpression(DIExpression Expr,unsigned MachineReg,unsigned PieceOffsetInBits)200 bool DwarfExpression::AddMachineRegExpression(DIExpression Expr,
201 unsigned MachineReg,
202 unsigned PieceOffsetInBits) {
203 unsigned N = Expr.getNumElements();
204 unsigned I = 0;
205 bool ValidReg = false;
206 // Pattern-match combinations for which more efficient representations exist
207 // first.
208 if (N >= 3 && Expr.getElement(0) == dwarf::DW_OP_piece) {
209 unsigned SizeOfByte = 8;
210 unsigned OffsetInBits = Expr.getElement(1) * SizeOfByte;
211 unsigned SizeInBits = Expr.getElement(2) * SizeOfByte;
212 ValidReg =
213 AddMachineRegPiece(MachineReg, SizeInBits,
214 getOffsetOrZero(OffsetInBits, PieceOffsetInBits));
215 I = 3;
216 } else if (N >= 3 && Expr.getElement(0) == dwarf::DW_OP_plus &&
217 Expr.getElement(2) == dwarf::DW_OP_deref) {
218 // [DW_OP_reg,Offset,DW_OP_plus,DW_OP_deref] --> [DW_OP_breg,Offset].
219 unsigned Offset = Expr.getElement(1);
220 ValidReg = AddMachineRegIndirect(MachineReg, Offset);
221 I = 3;
222 } else if (N >= 1 && Expr.getElement(0) == dwarf::DW_OP_deref) {
223 // [DW_OP_reg,DW_OP_deref] --> [DW_OP_breg].
224 ValidReg = AddMachineRegIndirect(MachineReg);
225 I = 1;
226 } else
227 ValidReg = AddMachineRegPiece(MachineReg);
228
229 if (!ValidReg)
230 return false;
231
232 // Emit remaining elements of the expression.
233 AddExpression(Expr, I);
234 return true;
235 }
236
AddExpression(DIExpression Expr,unsigned I,unsigned PieceOffsetInBits)237 void DwarfExpression::AddExpression(DIExpression Expr, unsigned I,
238 unsigned PieceOffsetInBits) {
239 unsigned N = Expr.getNumElements();
240 for (; I < N; ++I) {
241 switch (Expr.getElement(I)) {
242 case dwarf::DW_OP_piece: {
243 unsigned SizeOfByte = 8;
244 unsigned OffsetInBits = Expr.getElement(++I) * SizeOfByte;
245 unsigned SizeInBits = Expr.getElement(++I) * SizeOfByte;
246 AddOpPiece(SizeInBits, getOffsetOrZero(OffsetInBits, PieceOffsetInBits));
247 break;
248 }
249 case dwarf::DW_OP_plus:
250 EmitOp(dwarf::DW_OP_plus_uconst);
251 EmitUnsigned(Expr.getElement(++I));
252 break;
253 case dwarf::DW_OP_deref:
254 EmitOp(dwarf::DW_OP_deref);
255 break;
256 default:
257 llvm_unreachable("unhandled opcode found in DIExpression");
258 }
259 }
260 }
261