1 //===-- AsmPrinterDwarf.cpp - AsmPrinter Dwarf Support --------------------===//
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 implements the Dwarf emissions parts of AsmPrinter.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #define DEBUG_TYPE "asm-printer"
15 #include "llvm/CodeGen/AsmPrinter.h"
16 #include "llvm/CodeGen/MachineLocation.h"
17 #include "llvm/MC/MCAsmInfo.h"
18 #include "llvm/MC/MCSection.h"
19 #include "llvm/MC/MCStreamer.h"
20 #include "llvm/MC/MCSymbol.h"
21 #include "llvm/Target/TargetData.h"
22 #include "llvm/Target/TargetFrameInfo.h"
23 #include "llvm/Target/TargetLoweringObjectFile.h"
24 #include "llvm/Target/TargetMachine.h"
25 #include "llvm/Target/TargetRegisterInfo.h"
26 #include "llvm/ADT/Twine.h"
27 #include "llvm/Support/Dwarf.h"
28 using namespace llvm;
29 
30 //===----------------------------------------------------------------------===//
31 // Dwarf Emission Helper Routines
32 //===----------------------------------------------------------------------===//
33 
34 /// EmitSLEB128 - emit the specified signed leb128 value.
35 void AsmPrinter::EmitSLEB128(int Value, const char *Desc) const {
36   if (isVerbose() && Desc)
37     OutStreamer.AddComment(Desc);
38 
39   if (MAI->hasLEB128()) {
40     // FIXME: MCize.
41     OutStreamer.EmitRawText("\t.sleb128\t" + Twine(Value));
42     return;
43   }
44 
45   // If we don't have .sleb128, emit as .bytes.
46   int Sign = Value >> (8 * sizeof(Value) - 1);
47   bool IsMore;
48 
49   do {
50     unsigned char Byte = static_cast<unsigned char>(Value & 0x7f);
51     Value >>= 7;
52     IsMore = Value != Sign || ((Byte ^ Sign) & 0x40) != 0;
53     if (IsMore) Byte |= 0x80;
54     OutStreamer.EmitIntValue(Byte, 1, /*addrspace*/0);
55   } while (IsMore);
56 }
57 
58 /// EmitULEB128 - emit the specified signed leb128 value.
59 void AsmPrinter::EmitULEB128(unsigned Value, const char *Desc,
60                              unsigned PadTo) const {
61   if (isVerbose() && Desc)
62     OutStreamer.AddComment(Desc);
63 
64   if (MAI->hasLEB128() && PadTo == 0) {
65     // FIXME: MCize.
66     OutStreamer.EmitRawText("\t.uleb128\t" + Twine(Value));
67     return;
68   }
69 
70   // If we don't have .uleb128 or we want to emit padding, emit as .bytes.
71   do {
72     unsigned char Byte = static_cast<unsigned char>(Value & 0x7f);
73     Value >>= 7;
74     if (Value || PadTo != 0) Byte |= 0x80;
75     OutStreamer.EmitIntValue(Byte, 1, /*addrspace*/0);
76   } while (Value);
77 
78   if (PadTo) {
79     if (PadTo > 1)
80       OutStreamer.EmitFill(PadTo - 1, 0x80/*fillval*/, 0/*addrspace*/);
81     OutStreamer.EmitFill(1, 0/*fillval*/, 0/*addrspace*/);
82   }
83 }
84 
85 /// EmitCFAByte - Emit a .byte 42 directive for a DW_CFA_xxx value.
86 void AsmPrinter::EmitCFAByte(unsigned Val) const {
87   if (isVerbose()) {
88     if (Val >= dwarf::DW_CFA_offset && Val < dwarf::DW_CFA_offset+64)
89       OutStreamer.AddComment("DW_CFA_offset + Reg (" +
90                              Twine(Val-dwarf::DW_CFA_offset) + ")");
91     else
92       OutStreamer.AddComment(dwarf::CallFrameString(Val));
93   }
94   OutStreamer.EmitIntValue(Val, 1, 0/*addrspace*/);
95 }
96 
97 static const char *DecodeDWARFEncoding(unsigned Encoding) {
98   switch (Encoding) {
99   case dwarf::DW_EH_PE_absptr: return "absptr";
100   case dwarf::DW_EH_PE_omit:   return "omit";
101   case dwarf::DW_EH_PE_pcrel:  return "pcrel";
102   case dwarf::DW_EH_PE_udata4: return "udata4";
103   case dwarf::DW_EH_PE_udata8: return "udata8";
104   case dwarf::DW_EH_PE_sdata4: return "sdata4";
105   case dwarf::DW_EH_PE_sdata8: return "sdata8";
106   case dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_udata4: return "pcrel udata4";
107   case dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata4: return "pcrel sdata4";
108   case dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_udata8: return "pcrel udata8";
109   case dwarf::DW_EH_PE_pcrel | dwarf::DW_EH_PE_sdata8: return "pcrel sdata8";
110   case dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |dwarf::DW_EH_PE_udata4:
111     return "indirect pcrel udata4";
112   case dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |dwarf::DW_EH_PE_sdata4:
113     return "indirect pcrel sdata4";
114   case dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |dwarf::DW_EH_PE_udata8:
115     return "indirect pcrel udata8";
116   case dwarf::DW_EH_PE_indirect | dwarf::DW_EH_PE_pcrel |dwarf::DW_EH_PE_sdata8:
117     return "indirect pcrel sdata8";
118   }
119 
120   return "<unknown encoding>";
121 }
122 
123 
124 /// EmitEncodingByte - Emit a .byte 42 directive that corresponds to an
125 /// encoding.  If verbose assembly output is enabled, we output comments
126 /// describing the encoding.  Desc is an optional string saying what the
127 /// encoding is specifying (e.g. "LSDA").
128 void AsmPrinter::EmitEncodingByte(unsigned Val, const char *Desc) const {
129   if (isVerbose()) {
130     if (Desc != 0)
131       OutStreamer.AddComment(Twine(Desc)+" Encoding = " +
132                              Twine(DecodeDWARFEncoding(Val)));
133     else
134       OutStreamer.AddComment(Twine("Encoding = ") +
135                              DecodeDWARFEncoding(Val));
136   }
137 
138   OutStreamer.EmitIntValue(Val, 1, 0/*addrspace*/);
139 }
140 
141 /// GetSizeOfEncodedValue - Return the size of the encoding in bytes.
142 unsigned AsmPrinter::GetSizeOfEncodedValue(unsigned Encoding) const {
143   if (Encoding == dwarf::DW_EH_PE_omit)
144     return 0;
145 
146   switch (Encoding & 0x07) {
147   default: assert(0 && "Invalid encoded value.");
148   case dwarf::DW_EH_PE_absptr: return TM.getTargetData()->getPointerSize();
149   case dwarf::DW_EH_PE_udata2: return 2;
150   case dwarf::DW_EH_PE_udata4: return 4;
151   case dwarf::DW_EH_PE_udata8: return 8;
152   }
153 }
154 
155 void AsmPrinter::EmitReference(const MCSymbol *Sym, unsigned Encoding) const {
156   const TargetLoweringObjectFile &TLOF = getObjFileLowering();
157 
158   const MCExpr *Exp =
159     TLOF.getExprForDwarfReference(Sym, Mang, MMI, Encoding, OutStreamer);
160   OutStreamer.EmitValue(Exp, GetSizeOfEncodedValue(Encoding), /*addrspace*/0);
161 }
162 
163 void AsmPrinter::EmitReference(const GlobalValue *GV, unsigned Encoding)const{
164   const TargetLoweringObjectFile &TLOF = getObjFileLowering();
165 
166   const MCExpr *Exp =
167     TLOF.getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, OutStreamer);
168   OutStreamer.EmitValue(Exp, GetSizeOfEncodedValue(Encoding), /*addrspace*/0);
169 }
170 
171 /// EmitSectionOffset - Emit the 4-byte offset of Label from the start of its
172 /// section.  This can be done with a special directive if the target supports
173 /// it (e.g. cygwin) or by emitting it as an offset from a label at the start
174 /// of the section.
175 ///
176 /// SectionLabel is a temporary label emitted at the start of the section that
177 /// Label lives in.
178 void AsmPrinter::EmitSectionOffset(const MCSymbol *Label,
179                                    const MCSymbol *SectionLabel) const {
180   // On COFF targets, we have to emit the special .secrel32 directive.
181   if (const char *SecOffDir = MAI->getDwarfSectionOffsetDirective()) {
182     // FIXME: MCize.
183     OutStreamer.EmitRawText(SecOffDir + Twine(Label->getName()));
184     return;
185   }
186 
187   // Get the section that we're referring to, based on SectionLabel.
188   const MCSection &Section = SectionLabel->getSection();
189 
190   // If Label has already been emitted, verify that it is in the same section as
191   // section label for sanity.
192   assert((!Label->isInSection() || &Label->getSection() == &Section) &&
193          "Section offset using wrong section base for label");
194 
195   // If the section in question will end up with an address of 0 anyway, we can
196   // just emit an absolute reference to save a relocation.
197   if (Section.isBaseAddressKnownZero()) {
198     OutStreamer.EmitSymbolValue(Label, 4, 0/*AddrSpace*/);
199     return;
200   }
201 
202   // Otherwise, emit it as a label difference from the start of the section.
203   EmitLabelDifference(Label, SectionLabel, 4);
204 }
205 
206 //===----------------------------------------------------------------------===//
207 // Dwarf Lowering Routines
208 //===----------------------------------------------------------------------===//
209 
210 
211 /// EmitFrameMoves - Emit frame instructions to describe the layout of the
212 /// frame.
213 void AsmPrinter::EmitFrameMoves(const std::vector<MachineMove> &Moves,
214                                 MCSymbol *BaseLabel, bool isEH) const {
215   const TargetRegisterInfo *RI = TM.getRegisterInfo();
216 
217   int stackGrowth = TM.getTargetData()->getPointerSize();
218   if (TM.getFrameInfo()->getStackGrowthDirection() !=
219       TargetFrameInfo::StackGrowsUp)
220     stackGrowth *= -1;
221 
222   for (unsigned i = 0, N = Moves.size(); i < N; ++i) {
223     const MachineMove &Move = Moves[i];
224     MCSymbol *Label = Move.getLabel();
225     // Throw out move if the label is invalid.
226     if (Label && !Label->isDefined()) continue; // Not emitted, in dead code.
227 
228     const MachineLocation &Dst = Move.getDestination();
229     const MachineLocation &Src = Move.getSource();
230 
231     // Advance row if new location.
232     if (BaseLabel && Label) {
233       MCSymbol *ThisSym = Label;
234       if (ThisSym != BaseLabel) {
235         EmitCFAByte(dwarf::DW_CFA_advance_loc4);
236         EmitLabelDifference(ThisSym, BaseLabel, 4);
237         BaseLabel = ThisSym;
238       }
239     }
240 
241     // If advancing cfa.
242     if (Dst.isReg() && Dst.getReg() == MachineLocation::VirtualFP) {
243       assert(!Src.isReg() && "Machine move not supported yet.");
244 
245       if (Src.getReg() == MachineLocation::VirtualFP) {
246         EmitCFAByte(dwarf::DW_CFA_def_cfa_offset);
247       } else {
248         EmitCFAByte(dwarf::DW_CFA_def_cfa);
249         EmitULEB128(RI->getDwarfRegNum(Src.getReg(), isEH), "Register");
250       }
251 
252       EmitULEB128(-Src.getOffset(), "Offset");
253       continue;
254     }
255 
256     if (Src.isReg() && Src.getReg() == MachineLocation::VirtualFP) {
257       assert(Dst.isReg() && "Machine move not supported yet.");
258       EmitCFAByte(dwarf::DW_CFA_def_cfa_register);
259       EmitULEB128(RI->getDwarfRegNum(Dst.getReg(), isEH), "Register");
260       continue;
261     }
262 
263     unsigned Reg = RI->getDwarfRegNum(Src.getReg(), isEH);
264     int Offset = Dst.getOffset() / stackGrowth;
265 
266     if (Offset < 0) {
267       EmitCFAByte(dwarf::DW_CFA_offset_extended_sf);
268       EmitULEB128(Reg, "Reg");
269       EmitSLEB128(Offset, "Offset");
270     } else if (Reg < 64) {
271       EmitCFAByte(dwarf::DW_CFA_offset + Reg);
272       EmitULEB128(Offset, "Offset");
273     } else {
274       EmitCFAByte(dwarf::DW_CFA_offset_extended);
275       EmitULEB128(Reg, "Reg");
276       EmitULEB128(Offset, "Offset");
277     }
278   }
279 }
280