1 //===- lib/MC/MCObjectStreamer.cpp - Object File MCStreamer Interface -----===//
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 #include "llvm/MC/MCObjectStreamer.h"
11 #include "llvm/ADT/STLExtras.h"
12 #include "llvm/MC/MCAsmBackend.h"
13 #include "llvm/MC/MCAsmInfo.h"
14 #include "llvm/MC/MCAssembler.h"
15 #include "llvm/MC/MCCodeEmitter.h"
16 #include "llvm/MC/MCContext.h"
17 #include "llvm/MC/MCDwarf.h"
18 #include "llvm/MC/MCExpr.h"
19 #include "llvm/MC/MCObjectWriter.h"
20 #include "llvm/MC/MCSection.h"
21 #include "llvm/MC/MCSymbol.h"
22 #include "llvm/Support/ErrorHandling.h"
23 using namespace llvm;
24 
25 MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
26                                    raw_ostream &OS, MCCodeEmitter *Emitter_)
27     : MCStreamer(Context),
28       Assembler(new MCAssembler(Context, TAB, *Emitter_,
29                                 *TAB.createObjectWriter(OS), OS)),
30       CurSectionData(nullptr) {}
31 
32 MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
33                                    raw_ostream &OS, MCCodeEmitter *Emitter_,
34                                    MCAssembler *_Assembler)
35     : MCStreamer(Context), Assembler(_Assembler), CurSectionData(nullptr) {}
36 
37 MCObjectStreamer::~MCObjectStreamer() {
38   delete &Assembler->getBackend();
39   delete &Assembler->getEmitter();
40   delete &Assembler->getWriter();
41   delete Assembler;
42 }
43 
44 void MCObjectStreamer::reset() {
45   if (Assembler)
46     Assembler->reset();
47   CurSectionData = nullptr;
48   CurInsertionPoint = MCSectionData::iterator();
49   MCStreamer::reset();
50 }
51 
52 MCFragment *MCObjectStreamer::getCurrentFragment() const {
53   assert(getCurrentSectionData() && "No current section!");
54 
55   if (CurInsertionPoint != getCurrentSectionData()->getFragmentList().begin())
56     return std::prev(CurInsertionPoint);
57 
58   return nullptr;
59 }
60 
61 MCDataFragment *MCObjectStreamer::getOrCreateDataFragment() const {
62   MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
63   // When bundling is enabled, we don't want to add data to a fragment that
64   // already has instructions (see MCELFStreamer::EmitInstToData for details)
65   if (!F || (Assembler->isBundlingEnabled() && F->hasInstructions())) {
66     F = new MCDataFragment();
67     insert(F);
68   }
69   return F;
70 }
71 
72 const MCExpr *MCObjectStreamer::AddValueSymbols(const MCExpr *Value) {
73   switch (Value->getKind()) {
74   case MCExpr::Target:
75     cast<MCTargetExpr>(Value)->AddValueSymbols(Assembler);
76     break;
77 
78   case MCExpr::Constant:
79     break;
80 
81   case MCExpr::Binary: {
82     const MCBinaryExpr *BE = cast<MCBinaryExpr>(Value);
83     AddValueSymbols(BE->getLHS());
84     AddValueSymbols(BE->getRHS());
85     break;
86   }
87 
88   case MCExpr::SymbolRef:
89     Assembler->getOrCreateSymbolData(cast<MCSymbolRefExpr>(Value)->getSymbol());
90     break;
91 
92   case MCExpr::Unary:
93     AddValueSymbols(cast<MCUnaryExpr>(Value)->getSubExpr());
94     break;
95   }
96 
97   return Value;
98 }
99 
100 void MCObjectStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size) {
101   MCDataFragment *DF = getOrCreateDataFragment();
102 
103   MCLineEntry::Make(this, getCurrentSection().first);
104 
105   // Avoid fixups when possible.
106   int64_t AbsValue;
107   if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue, getAssembler())) {
108     EmitIntValue(AbsValue, Size);
109     return;
110   }
111   DF->getFixups().push_back(
112       MCFixup::Create(DF->getContents().size(), Value,
113                       MCFixup::getKindForSize(Size, false)));
114   DF->getContents().resize(DF->getContents().size() + Size, 0);
115 }
116 
117 void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame) {
118   RecordProcStart(Frame);
119 }
120 
121 void MCObjectStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {
122   RecordProcEnd(Frame);
123 }
124 
125 void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
126   MCStreamer::EmitLabel(Symbol);
127 
128   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
129 
130   // FIXME: This is wasteful, we don't necessarily need to create a data
131   // fragment. Instead, we should mark the symbol as pointing into the data
132   // fragment if it exists, otherwise we should just queue the label and set its
133   // fragment pointer when we emit the next fragment.
134   MCDataFragment *F = getOrCreateDataFragment();
135   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
136   SD.setFragment(F);
137   SD.setOffset(F->getContents().size());
138 }
139 
140 void MCObjectStreamer::EmitDebugLabel(MCSymbol *Symbol) {
141   EmitLabel(Symbol);
142 }
143 
144 void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
145   int64_t IntValue;
146   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
147     EmitULEB128IntValue(IntValue);
148     return;
149   }
150   Value = ForceExpAbs(Value);
151   insert(new MCLEBFragment(*Value, false));
152 }
153 
154 void MCObjectStreamer::EmitSLEB128Value(const MCExpr *Value) {
155   int64_t IntValue;
156   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
157     EmitSLEB128IntValue(IntValue);
158     return;
159   }
160   Value = ForceExpAbs(Value);
161   insert(new MCLEBFragment(*Value, true));
162 }
163 
164 void MCObjectStreamer::EmitWeakReference(MCSymbol *Alias,
165                                          const MCSymbol *Symbol) {
166   report_fatal_error("This file format doesn't support weak aliases.");
167 }
168 
169 void MCObjectStreamer::ChangeSection(const MCSection *Section,
170                                      const MCExpr *Subsection) {
171   assert(Section && "Cannot switch to a null section!");
172 
173   CurSectionData = &getAssembler().getOrCreateSectionData(*Section);
174 
175   int64_t IntSubsection = 0;
176   if (Subsection &&
177       !Subsection->EvaluateAsAbsolute(IntSubsection, getAssembler()))
178     report_fatal_error("Cannot evaluate subsection number");
179   if (IntSubsection < 0 || IntSubsection > 8192)
180     report_fatal_error("Subsection number out of range");
181   CurInsertionPoint =
182     CurSectionData->getSubsectionInsertionPoint(unsigned(IntSubsection));
183 }
184 
185 void MCObjectStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
186   getAssembler().getOrCreateSymbolData(*Symbol);
187   AddValueSymbols(Value);
188   MCStreamer::EmitAssignment(Symbol, Value);
189 }
190 
191 void MCObjectStreamer::EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI) {
192   // Scan for values.
193   for (unsigned i = Inst.getNumOperands(); i--; )
194     if (Inst.getOperand(i).isExpr())
195       AddValueSymbols(Inst.getOperand(i).getExpr());
196 
197   MCSectionData *SD = getCurrentSectionData();
198   SD->setHasInstructions(true);
199 
200   // Now that a machine instruction has been assembled into this section, make
201   // a line entry for any .loc directive that has been seen.
202   MCLineEntry::Make(this, getCurrentSection().first);
203 
204   // If this instruction doesn't need relaxation, just emit it as data.
205   MCAssembler &Assembler = getAssembler();
206   if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
207     EmitInstToData(Inst, STI);
208     return;
209   }
210 
211   // Otherwise, relax and emit it as data if either:
212   // - The RelaxAll flag was passed
213   // - Bundling is enabled and this instruction is inside a bundle-locked
214   //   group. We want to emit all such instructions into the same data
215   //   fragment.
216   if (Assembler.getRelaxAll() ||
217       (Assembler.isBundlingEnabled() && SD->isBundleLocked())) {
218     MCInst Relaxed;
219     getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
220     while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
221       getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
222     EmitInstToData(Relaxed, STI);
223     return;
224   }
225 
226   // Otherwise emit to a separate fragment.
227   EmitInstToFragment(Inst, STI);
228 }
229 
230 void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
231                                           const MCSubtargetInfo &STI) {
232   // Always create a new, separate fragment here, because its size can change
233   // during relaxation.
234   MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
235   insert(IF);
236 
237   SmallString<128> Code;
238   raw_svector_ostream VecOS(Code);
239   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, IF->getFixups(),
240                                                 STI);
241   VecOS.flush();
242   IF->getContents().append(Code.begin(), Code.end());
243 }
244 
245 #ifndef NDEBUG
246 static const char *const BundlingNotImplementedMsg =
247   "Aligned bundling is not implemented for this object format";
248 #endif
249 
250 void MCObjectStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
251   llvm_unreachable(BundlingNotImplementedMsg);
252 }
253 
254 void MCObjectStreamer::EmitBundleLock(bool AlignToEnd) {
255   llvm_unreachable(BundlingNotImplementedMsg);
256 }
257 
258 void MCObjectStreamer::EmitBundleUnlock() {
259   llvm_unreachable(BundlingNotImplementedMsg);
260 }
261 
262 void MCObjectStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
263                                              unsigned Column, unsigned Flags,
264                                              unsigned Isa,
265                                              unsigned Discriminator,
266                                              StringRef FileName) {
267   // In case we see two .loc directives in a row, make sure the
268   // first one gets a line entry.
269   MCLineEntry::Make(this, getCurrentSection().first);
270 
271   this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,
272                                           Isa, Discriminator, FileName);
273 }
274 
275 void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
276                                                 const MCSymbol *LastLabel,
277                                                 const MCSymbol *Label,
278                                                 unsigned PointerSize) {
279   if (!LastLabel) {
280     EmitDwarfSetLineAddr(LineDelta, Label, PointerSize);
281     return;
282   }
283   const MCExpr *AddrDelta = BuildSymbolDiff(getContext(), Label, LastLabel);
284   int64_t Res;
285   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
286     MCDwarfLineAddr::Emit(this, LineDelta, Res);
287     return;
288   }
289   AddrDelta = ForceExpAbs(AddrDelta);
290   insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
291 }
292 
293 void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
294                                                  const MCSymbol *Label) {
295   const MCExpr *AddrDelta = BuildSymbolDiff(getContext(), Label, LastLabel);
296   int64_t Res;
297   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
298     MCDwarfFrameEmitter::EmitAdvanceLoc(*this, Res);
299     return;
300   }
301   AddrDelta = ForceExpAbs(AddrDelta);
302   insert(new MCDwarfCallFrameFragment(*AddrDelta));
303 }
304 
305 void MCObjectStreamer::EmitBytes(StringRef Data) {
306   MCLineEntry::Make(this, getCurrentSection().first);
307   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
308 }
309 
310 void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment,
311                                             int64_t Value,
312                                             unsigned ValueSize,
313                                             unsigned MaxBytesToEmit) {
314   if (MaxBytesToEmit == 0)
315     MaxBytesToEmit = ByteAlignment;
316   insert(new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit));
317 
318   // Update the maximum alignment on the current section if necessary.
319   if (ByteAlignment > getCurrentSectionData()->getAlignment())
320     getCurrentSectionData()->setAlignment(ByteAlignment);
321 }
322 
323 void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
324                                          unsigned MaxBytesToEmit) {
325   EmitValueToAlignment(ByteAlignment, 0, 1, MaxBytesToEmit);
326   cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
327 }
328 
329 bool MCObjectStreamer::EmitValueToOffset(const MCExpr *Offset,
330                                          unsigned char Value) {
331   int64_t Res;
332   if (Offset->EvaluateAsAbsolute(Res, getAssembler())) {
333     insert(new MCOrgFragment(*Offset, Value));
334     return false;
335   }
336 
337   MCSymbol *CurrentPos = getContext().CreateTempSymbol();
338   EmitLabel(CurrentPos);
339   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
340   const MCExpr *Ref =
341     MCSymbolRefExpr::Create(CurrentPos, Variant, getContext());
342   const MCExpr *Delta =
343     MCBinaryExpr::Create(MCBinaryExpr::Sub, Offset, Ref, getContext());
344 
345   if (!Delta->EvaluateAsAbsolute(Res, getAssembler()))
346     return true;
347   EmitFill(Res, Value);
348   return false;
349 }
350 
351 // Associate GPRel32 fixup with data and resize data area
352 void MCObjectStreamer::EmitGPRel32Value(const MCExpr *Value) {
353   MCDataFragment *DF = getOrCreateDataFragment();
354 
355   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
356                                             Value, FK_GPRel_4));
357   DF->getContents().resize(DF->getContents().size() + 4, 0);
358 }
359 
360 // Associate GPRel32 fixup with data and resize data area
361 void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
362   MCDataFragment *DF = getOrCreateDataFragment();
363 
364   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
365                                             Value, FK_GPRel_4));
366   DF->getContents().resize(DF->getContents().size() + 8, 0);
367 }
368 
369 void MCObjectStreamer::EmitFill(uint64_t NumBytes, uint8_t FillValue) {
370   // FIXME: A MCFillFragment would be more memory efficient but MCExpr has
371   //        problems evaluating expressions across multiple fragments.
372   getOrCreateDataFragment()->getContents().append(NumBytes, FillValue);
373 }
374 
375 void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
376   unsigned ItemSize = getCurrentSection().first->isVirtualSection() ? 0 : 1;
377   insert(new MCFillFragment(0, ItemSize, NumBytes));
378 }
379 
380 void MCObjectStreamer::FinishImpl() {
381   // If we are generating dwarf for assembly source files dump out the sections.
382   if (getContext().getGenDwarfForAssembly())
383     MCGenDwarfInfo::Emit(this);
384 
385   // Dump out the dwarf file & directory tables and line tables.
386   MCDwarfLineTable::Emit(this);
387 
388   getAssembler().Finish();
389 }
390