xref: /llvm-project/llvm/lib/MC/MCObjectStreamer.cpp (revision 652ec6ee895fb9f5cf7a1e3c9d7f6996f68be132) 
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), EmitEHFrame(true), EmitDebugFrame(false) {}
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       EmitEHFrame(true), EmitDebugFrame(false) {}
37 
38 MCObjectStreamer::~MCObjectStreamer() {
39   delete &Assembler->getBackend();
40   delete &Assembler->getEmitter();
41   delete &Assembler->getWriter();
42   delete Assembler;
43 }
44 
45 void MCObjectStreamer::flushPendingLabels(MCFragment *F) {
46   if (PendingLabels.size()) {
47     if (!F) {
48       F = new MCDataFragment();
49       CurSectionData->getFragmentList().insert(CurInsertionPoint, F);
50       F->setParent(CurSectionData);
51     }
52     for (MCSymbolData *SD : PendingLabels) {
53       SD->setFragment(F);
54       SD->setOffset(0);
55     }
56     PendingLabels.clear();
57   }
58 }
59 
60 void MCObjectStreamer::reset() {
61   if (Assembler)
62     Assembler->reset();
63   CurSectionData = nullptr;
64   CurInsertionPoint = MCSectionData::iterator();
65   EmitEHFrame = true;
66   EmitDebugFrame = false;
67   PendingLabels.clear();
68   MCStreamer::reset();
69 }
70 
71 void MCObjectStreamer::EmitFrames(MCAsmBackend *MAB) {
72   if (!getNumFrameInfos())
73     return;
74 
75   if (EmitEHFrame)
76     MCDwarfFrameEmitter::Emit(*this, MAB, true);
77 
78   if (EmitDebugFrame)
79     MCDwarfFrameEmitter::Emit(*this, MAB, false);
80 }
81 
82 MCFragment *MCObjectStreamer::getCurrentFragment() const {
83   assert(getCurrentSectionData() && "No current section!");
84 
85   if (CurInsertionPoint != getCurrentSectionData()->getFragmentList().begin())
86     return std::prev(CurInsertionPoint);
87 
88   return nullptr;
89 }
90 
91 MCDataFragment *MCObjectStreamer::getOrCreateDataFragment() {
92   MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
93   // When bundling is enabled, we don't want to add data to a fragment that
94   // already has instructions (see MCELFStreamer::EmitInstToData for details)
95   if (!F || (Assembler->isBundlingEnabled() && F->hasInstructions())) {
96     F = new MCDataFragment();
97     insert(F);
98   }
99   return F;
100 }
101 
102 void MCObjectStreamer::visitUsedSymbol(const MCSymbol &Sym) {
103   Assembler->getOrCreateSymbolData(Sym);
104 }
105 
106 void MCObjectStreamer::EmitCFISections(bool EH, bool Debug) {
107   MCStreamer::EmitCFISections(EH, Debug);
108   EmitEHFrame = EH;
109   EmitDebugFrame = Debug;
110 }
111 
112 void MCObjectStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
113                                      const SMLoc &Loc) {
114   MCStreamer::EmitValueImpl(Value, Size, Loc);
115   MCDataFragment *DF = getOrCreateDataFragment();
116 
117   MCLineEntry::Make(this, getCurrentSection().first);
118 
119   // Avoid fixups when possible.
120   int64_t AbsValue;
121   if (Value->EvaluateAsAbsolute(AbsValue, getAssembler())) {
122     EmitIntValue(AbsValue, Size);
123     return;
124   }
125   DF->getFixups().push_back(
126       MCFixup::Create(DF->getContents().size(), Value,
127                       MCFixup::getKindForSize(Size, false), Loc));
128   DF->getContents().resize(DF->getContents().size() + Size, 0);
129 }
130 
131 void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame,
132                                             MCSymbol *FuncSym) {
133   if (!FuncSym) {
134     FuncSym = getContext().CreateTempSymbol();
135     EmitLabel(FuncSym);
136   }
137   Frame.Begin = FuncSym;
138 }
139 
140 void MCObjectStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {
141   Frame.End = getContext().CreateTempSymbol();
142   EmitLabel(Frame.End);
143 }
144 
145 void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
146   MCStreamer::EmitLabel(Symbol);
147 
148   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
149   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
150 
151   // If there is a current fragment, mark the symbol as pointing into it.
152   // Otherwise queue the label and set its fragment pointer when we emit the
153   // next fragment.
154   if (auto *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment())) {
155     SD.setFragment(F);
156     SD.setOffset(F->getContents().size());
157   } else {
158     PendingLabels.push_back(&SD);
159   }
160 }
161 
162 void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
163   int64_t IntValue;
164   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
165     EmitULEB128IntValue(IntValue);
166     return;
167   }
168   insert(new MCLEBFragment(*Value, false));
169 }
170 
171 void MCObjectStreamer::EmitSLEB128Value(const MCExpr *Value) {
172   int64_t IntValue;
173   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
174     EmitSLEB128IntValue(IntValue);
175     return;
176   }
177   insert(new MCLEBFragment(*Value, true));
178 }
179 
180 void MCObjectStreamer::EmitWeakReference(MCSymbol *Alias,
181                                          const MCSymbol *Symbol) {
182   report_fatal_error("This file format doesn't support weak aliases.");
183 }
184 
185 void MCObjectStreamer::ChangeSection(const MCSection *Section,
186                                      const MCExpr *Subsection) {
187   assert(Section && "Cannot switch to a null section!");
188   flushPendingLabels(nullptr);
189 
190   CurSectionData = &getAssembler().getOrCreateSectionData(*Section);
191 
192   int64_t IntSubsection = 0;
193   if (Subsection &&
194       !Subsection->EvaluateAsAbsolute(IntSubsection, getAssembler()))
195     report_fatal_error("Cannot evaluate subsection number");
196   if (IntSubsection < 0 || IntSubsection > 8192)
197     report_fatal_error("Subsection number out of range");
198   CurInsertionPoint =
199     CurSectionData->getSubsectionInsertionPoint(unsigned(IntSubsection));
200 }
201 
202 void MCObjectStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
203   getAssembler().getOrCreateSymbolData(*Symbol);
204   MCStreamer::EmitAssignment(Symbol, Value);
205 }
206 
207 void MCObjectStreamer::EmitInstruction(const MCInst &Inst,
208                                        const MCSubtargetInfo &STI) {
209   MCStreamer::EmitInstruction(Inst, STI);
210 
211   MCSectionData *SD = getCurrentSectionData();
212   SD->setHasInstructions(true);
213 
214   // Now that a machine instruction has been assembled into this section, make
215   // a line entry for any .loc directive that has been seen.
216   MCLineEntry::Make(this, getCurrentSection().first);
217 
218   // If this instruction doesn't need relaxation, just emit it as data.
219   MCAssembler &Assembler = getAssembler();
220   if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
221     EmitInstToData(Inst, STI);
222     return;
223   }
224 
225   // Otherwise, relax and emit it as data if either:
226   // - The RelaxAll flag was passed
227   // - Bundling is enabled and this instruction is inside a bundle-locked
228   //   group. We want to emit all such instructions into the same data
229   //   fragment.
230   if (Assembler.getRelaxAll() ||
231       (Assembler.isBundlingEnabled() && SD->isBundleLocked())) {
232     MCInst Relaxed;
233     getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
234     while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
235       getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
236     EmitInstToData(Relaxed, STI);
237     return;
238   }
239 
240   // Otherwise emit to a separate fragment.
241   EmitInstToFragment(Inst, STI);
242 }
243 
244 void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
245                                           const MCSubtargetInfo &STI) {
246   // Always create a new, separate fragment here, because its size can change
247   // during relaxation.
248   MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
249   insert(IF);
250 
251   SmallString<128> Code;
252   raw_svector_ostream VecOS(Code);
253   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, IF->getFixups(),
254                                                 STI);
255   VecOS.flush();
256   IF->getContents().append(Code.begin(), Code.end());
257 }
258 
259 #ifndef NDEBUG
260 static const char *const BundlingNotImplementedMsg =
261   "Aligned bundling is not implemented for this object format";
262 #endif
263 
264 void MCObjectStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
265   llvm_unreachable(BundlingNotImplementedMsg);
266 }
267 
268 void MCObjectStreamer::EmitBundleLock(bool AlignToEnd) {
269   llvm_unreachable(BundlingNotImplementedMsg);
270 }
271 
272 void MCObjectStreamer::EmitBundleUnlock() {
273   llvm_unreachable(BundlingNotImplementedMsg);
274 }
275 
276 void MCObjectStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
277                                              unsigned Column, unsigned Flags,
278                                              unsigned Isa,
279                                              unsigned Discriminator,
280                                              StringRef FileName) {
281   // In case we see two .loc directives in a row, make sure the
282   // first one gets a line entry.
283   MCLineEntry::Make(this, getCurrentSection().first);
284 
285   this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,
286                                           Isa, Discriminator, FileName);
287 }
288 
289 static const MCExpr *buildSymbolDiff(MCObjectStreamer &OS, const MCSymbol *A,
290                                      const MCSymbol *B) {
291   MCContext &Context = OS.getContext();
292   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
293   const MCExpr *ARef = MCSymbolRefExpr::Create(A, Variant, Context);
294   const MCExpr *BRef = MCSymbolRefExpr::Create(B, Variant, Context);
295   const MCExpr *AddrDelta =
296       MCBinaryExpr::Create(MCBinaryExpr::Sub, ARef, BRef, Context);
297   return AddrDelta;
298 }
299 
300 static void emitDwarfSetLineAddr(MCObjectStreamer &OS, int64_t LineDelta,
301                                  const MCSymbol *Label, int PointerSize) {
302   // emit the sequence to set the address
303   OS.EmitIntValue(dwarf::DW_LNS_extended_op, 1);
304   OS.EmitULEB128IntValue(PointerSize + 1);
305   OS.EmitIntValue(dwarf::DW_LNE_set_address, 1);
306   OS.EmitSymbolValue(Label, PointerSize);
307 
308   // emit the sequence for the LineDelta (from 1) and a zero address delta.
309   MCDwarfLineAddr::Emit(&OS, LineDelta, 0);
310 }
311 
312 void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
313                                                 const MCSymbol *LastLabel,
314                                                 const MCSymbol *Label,
315                                                 unsigned PointerSize) {
316   if (!LastLabel) {
317     emitDwarfSetLineAddr(*this, LineDelta, Label, PointerSize);
318     return;
319   }
320   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
321   int64_t Res;
322   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
323     MCDwarfLineAddr::Emit(this, LineDelta, Res);
324     return;
325   }
326   insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
327 }
328 
329 void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
330                                                  const MCSymbol *Label) {
331   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
332   int64_t Res;
333   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
334     MCDwarfFrameEmitter::EmitAdvanceLoc(*this, Res);
335     return;
336   }
337   insert(new MCDwarfCallFrameFragment(*AddrDelta));
338 }
339 
340 void MCObjectStreamer::EmitBytes(StringRef Data) {
341   MCLineEntry::Make(this, getCurrentSection().first);
342   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
343 }
344 
345 void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment,
346                                             int64_t Value,
347                                             unsigned ValueSize,
348                                             unsigned MaxBytesToEmit) {
349   if (MaxBytesToEmit == 0)
350     MaxBytesToEmit = ByteAlignment;
351   insert(new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit));
352 
353   // Update the maximum alignment on the current section if necessary.
354   if (ByteAlignment > getCurrentSectionData()->getAlignment())
355     getCurrentSectionData()->setAlignment(ByteAlignment);
356 }
357 
358 void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
359                                          unsigned MaxBytesToEmit) {
360   EmitValueToAlignment(ByteAlignment, 0, 1, MaxBytesToEmit);
361   cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
362 }
363 
364 bool MCObjectStreamer::EmitValueToOffset(const MCExpr *Offset,
365                                          unsigned char Value) {
366   int64_t Res;
367   if (Offset->EvaluateAsAbsolute(Res, getAssembler())) {
368     insert(new MCOrgFragment(*Offset, Value));
369     return false;
370   }
371 
372   MCSymbol *CurrentPos = getContext().CreateTempSymbol();
373   EmitLabel(CurrentPos);
374   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
375   const MCExpr *Ref =
376     MCSymbolRefExpr::Create(CurrentPos, Variant, getContext());
377   const MCExpr *Delta =
378     MCBinaryExpr::Create(MCBinaryExpr::Sub, Offset, Ref, getContext());
379 
380   if (!Delta->EvaluateAsAbsolute(Res, getAssembler()))
381     return true;
382   EmitFill(Res, Value);
383   return false;
384 }
385 
386 // Associate GPRel32 fixup with data and resize data area
387 void MCObjectStreamer::EmitGPRel32Value(const MCExpr *Value) {
388   MCDataFragment *DF = getOrCreateDataFragment();
389 
390   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
391                                             Value, FK_GPRel_4));
392   DF->getContents().resize(DF->getContents().size() + 4, 0);
393 }
394 
395 // Associate GPRel32 fixup with data and resize data area
396 void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
397   MCDataFragment *DF = getOrCreateDataFragment();
398 
399   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
400                                             Value, FK_GPRel_4));
401   DF->getContents().resize(DF->getContents().size() + 8, 0);
402 }
403 
404 void MCObjectStreamer::EmitFill(uint64_t NumBytes, uint8_t FillValue) {
405   // FIXME: A MCFillFragment would be more memory efficient but MCExpr has
406   //        problems evaluating expressions across multiple fragments.
407   getOrCreateDataFragment()->getContents().append(NumBytes, FillValue);
408 }
409 
410 void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
411   unsigned ItemSize = getCurrentSection().first->isVirtualSection() ? 0 : 1;
412   insert(new MCFillFragment(0, ItemSize, NumBytes));
413 }
414 
415 void MCObjectStreamer::FinishImpl() {
416   // If we are generating dwarf for assembly source files dump out the sections.
417   if (getContext().getGenDwarfForAssembly())
418     MCGenDwarfInfo::Emit(this);
419 
420   // Dump out the dwarf file & directory tables and line tables.
421   MCDwarfLineTable::Emit(this);
422 
423   flushPendingLabels(nullptr);
424   getAssembler().Finish();
425 }
426