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(0) {}
31 
32 MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
33                                    raw_ostream &OS, MCCodeEmitter *Emitter_,
34                                    MCAssembler *_Assembler)
35     : MCStreamer(Context), Assembler(_Assembler), CurSectionData(0) {}
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 = 0;
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 prior(CurInsertionPoint);
57 
58   return 0;
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   Symbol->setVariableValue(AddValueSymbols(Value));
188 }
189 
190 void MCObjectStreamer::EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI) {
191   // Scan for values.
192   for (unsigned i = Inst.getNumOperands(); i--; )
193     if (Inst.getOperand(i).isExpr())
194       AddValueSymbols(Inst.getOperand(i).getExpr());
195 
196   MCSectionData *SD = getCurrentSectionData();
197   SD->setHasInstructions(true);
198 
199   // Now that a machine instruction has been assembled into this section, make
200   // a line entry for any .loc directive that has been seen.
201   MCLineEntry::Make(this, getCurrentSection().first);
202 
203   // If this instruction doesn't need relaxation, just emit it as data.
204   MCAssembler &Assembler = getAssembler();
205   if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
206     EmitInstToData(Inst, STI);
207     return;
208   }
209 
210   // Otherwise, relax and emit it as data if either:
211   // - The RelaxAll flag was passed
212   // - Bundling is enabled and this instruction is inside a bundle-locked
213   //   group. We want to emit all such instructions into the same data
214   //   fragment.
215   if (Assembler.getRelaxAll() ||
216       (Assembler.isBundlingEnabled() && SD->isBundleLocked())) {
217     MCInst Relaxed;
218     getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
219     while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
220       getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
221     EmitInstToData(Relaxed, STI);
222     return;
223   }
224 
225   // Otherwise emit to a separate fragment.
226   EmitInstToFragment(Inst, STI);
227 }
228 
229 void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
230                                           const MCSubtargetInfo &STI) {
231   // Always create a new, separate fragment here, because its size can change
232   // during relaxation.
233   MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
234   insert(IF);
235 
236   SmallString<128> Code;
237   raw_svector_ostream VecOS(Code);
238   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, IF->getFixups(),
239                                                 STI);
240   VecOS.flush();
241   IF->getContents().append(Code.begin(), Code.end());
242 }
243 
244 #ifndef NDEBUG
245 static const char *const BundlingNotImplementedMsg =
246   "Aligned bundling is not implemented for this object format";
247 #endif
248 
249 void MCObjectStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
250   llvm_unreachable(BundlingNotImplementedMsg);
251 }
252 
253 void MCObjectStreamer::EmitBundleLock(bool AlignToEnd) {
254   llvm_unreachable(BundlingNotImplementedMsg);
255 }
256 
257 void MCObjectStreamer::EmitBundleUnlock() {
258   llvm_unreachable(BundlingNotImplementedMsg);
259 }
260 
261 void MCObjectStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
262                                              unsigned Column, unsigned Flags,
263                                              unsigned Isa,
264                                              unsigned Discriminator,
265                                              StringRef FileName) {
266   // In case we see two .loc directives in a row, make sure the
267   // first one gets a line entry.
268   MCLineEntry::Make(this, getCurrentSection().first);
269 
270   this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,
271                                           Isa, Discriminator, FileName);
272 }
273 
274 void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
275                                                 const MCSymbol *LastLabel,
276                                                 const MCSymbol *Label,
277                                                 unsigned PointerSize) {
278   if (!LastLabel) {
279     EmitDwarfSetLineAddr(LineDelta, Label, PointerSize);
280     return;
281   }
282   const MCExpr *AddrDelta = BuildSymbolDiff(getContext(), Label, LastLabel);
283   int64_t Res;
284   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
285     MCDwarfLineAddr::Emit(this, LineDelta, Res);
286     return;
287   }
288   AddrDelta = ForceExpAbs(AddrDelta);
289   insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
290 }
291 
292 void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
293                                                  const MCSymbol *Label) {
294   const MCExpr *AddrDelta = BuildSymbolDiff(getContext(), Label, LastLabel);
295   int64_t Res;
296   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
297     MCDwarfFrameEmitter::EmitAdvanceLoc(*this, Res);
298     return;
299   }
300   AddrDelta = ForceExpAbs(AddrDelta);
301   insert(new MCDwarfCallFrameFragment(*AddrDelta));
302 }
303 
304 void MCObjectStreamer::EmitBytes(StringRef Data) {
305   MCLineEntry::Make(this, getCurrentSection().first);
306   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
307 }
308 
309 void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment,
310                                             int64_t Value,
311                                             unsigned ValueSize,
312                                             unsigned MaxBytesToEmit) {
313   if (MaxBytesToEmit == 0)
314     MaxBytesToEmit = ByteAlignment;
315   insert(new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit));
316 
317   // Update the maximum alignment on the current section if necessary.
318   if (ByteAlignment > getCurrentSectionData()->getAlignment())
319     getCurrentSectionData()->setAlignment(ByteAlignment);
320 }
321 
322 void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
323                                          unsigned MaxBytesToEmit) {
324   EmitValueToAlignment(ByteAlignment, 0, 1, MaxBytesToEmit);
325   cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
326 }
327 
328 bool MCObjectStreamer::EmitValueToOffset(const MCExpr *Offset,
329                                          unsigned char Value) {
330   int64_t Res;
331   if (Offset->EvaluateAsAbsolute(Res, getAssembler())) {
332     insert(new MCOrgFragment(*Offset, Value));
333     return false;
334   }
335 
336   MCSymbol *CurrentPos = getContext().CreateTempSymbol();
337   EmitLabel(CurrentPos);
338   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
339   const MCExpr *Ref =
340     MCSymbolRefExpr::Create(CurrentPos, Variant, getContext());
341   const MCExpr *Delta =
342     MCBinaryExpr::Create(MCBinaryExpr::Sub, Offset, Ref, getContext());
343 
344   if (!Delta->EvaluateAsAbsolute(Res, getAssembler()))
345     return true;
346   EmitFill(Res, Value);
347   return false;
348 }
349 
350 // Associate GPRel32 fixup with data and resize data area
351 void MCObjectStreamer::EmitGPRel32Value(const MCExpr *Value) {
352   MCDataFragment *DF = getOrCreateDataFragment();
353 
354   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
355                                             Value, FK_GPRel_4));
356   DF->getContents().resize(DF->getContents().size() + 4, 0);
357 }
358 
359 // Associate GPRel32 fixup with data and resize data area
360 void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
361   MCDataFragment *DF = getOrCreateDataFragment();
362 
363   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
364                                             Value, FK_GPRel_4));
365   DF->getContents().resize(DF->getContents().size() + 8, 0);
366 }
367 
368 void MCObjectStreamer::EmitFill(uint64_t NumBytes, uint8_t FillValue) {
369   // FIXME: A MCFillFragment would be more memory efficient but MCExpr has
370   //        problems evaluating expressions across multiple fragments.
371   getOrCreateDataFragment()->getContents().append(NumBytes, FillValue);
372 }
373 
374 void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
375   unsigned ItemSize = getCurrentSection().first->isVirtualSection() ? 0 : 1;
376   insert(new MCFillFragment(0, ItemSize, NumBytes));
377 }
378 
379 void MCObjectStreamer::FinishImpl() {
380   // Dump out the dwarf file & directory tables and line tables.
381   const MCSymbol *LineSectionSymbol = NULL;
382   if (!getContext().getMCLineTableSymbols().empty() ||
383       getContext().hasDwarfFiles())
384     LineSectionSymbol = MCDwarfFileTable::Emit(this);
385 
386   // If we are generating dwarf for assembly source files dump out the sections.
387   if (getContext().getGenDwarfForAssembly())
388     MCGenDwarfInfo::Emit(this, LineSectionSymbol);
389 
390   getAssembler().Finish();
391 }
392