xref: /llvm-project/llvm/lib/MC/MCObjectStreamer.cpp (revision 9f380a3ca0eb7fe88e315fc9af684db81456fd86) 
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   // We need to create a local symbol to avoid relocations.
133   Frame.Begin = getContext().CreateTempSymbol();
134   EmitLabel(Frame.Begin);
135 }
136 
137 void MCObjectStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {
138   Frame.End = getContext().CreateTempSymbol();
139   EmitLabel(Frame.End);
140 }
141 
142 void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
143   MCStreamer::EmitLabel(Symbol);
144 
145   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
146   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
147 
148   // If there is a current fragment, mark the symbol as pointing into it.
149   // Otherwise queue the label and set its fragment pointer when we emit the
150   // next fragment.
151   if (auto *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment())) {
152     SD.setFragment(F);
153     SD.setOffset(F->getContents().size());
154   } else {
155     PendingLabels.push_back(&SD);
156   }
157 }
158 
159 void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
160   int64_t IntValue;
161   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
162     EmitULEB128IntValue(IntValue);
163     return;
164   }
165   insert(new MCLEBFragment(*Value, false));
166 }
167 
168 void MCObjectStreamer::EmitSLEB128Value(const MCExpr *Value) {
169   int64_t IntValue;
170   if (Value->EvaluateAsAbsolute(IntValue, getAssembler())) {
171     EmitSLEB128IntValue(IntValue);
172     return;
173   }
174   insert(new MCLEBFragment(*Value, true));
175 }
176 
177 void MCObjectStreamer::EmitWeakReference(MCSymbol *Alias,
178                                          const MCSymbol *Symbol) {
179   report_fatal_error("This file format doesn't support weak aliases.");
180 }
181 
182 void MCObjectStreamer::ChangeSection(const MCSection *Section,
183                                      const MCExpr *Subsection) {
184   assert(Section && "Cannot switch to a null section!");
185   flushPendingLabels(nullptr);
186 
187   CurSectionData = &getAssembler().getOrCreateSectionData(*Section);
188 
189   int64_t IntSubsection = 0;
190   if (Subsection &&
191       !Subsection->EvaluateAsAbsolute(IntSubsection, getAssembler()))
192     report_fatal_error("Cannot evaluate subsection number");
193   if (IntSubsection < 0 || IntSubsection > 8192)
194     report_fatal_error("Subsection number out of range");
195   CurInsertionPoint =
196     CurSectionData->getSubsectionInsertionPoint(unsigned(IntSubsection));
197 }
198 
199 void MCObjectStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
200   getAssembler().getOrCreateSymbolData(*Symbol);
201   MCStreamer::EmitAssignment(Symbol, Value);
202 }
203 
204 void MCObjectStreamer::EmitInstruction(const MCInst &Inst,
205                                        const MCSubtargetInfo &STI) {
206   MCStreamer::EmitInstruction(Inst, STI);
207 
208   MCSectionData *SD = getCurrentSectionData();
209   SD->setHasInstructions(true);
210 
211   // Now that a machine instruction has been assembled into this section, make
212   // a line entry for any .loc directive that has been seen.
213   MCLineEntry::Make(this, getCurrentSection().first);
214 
215   // If this instruction doesn't need relaxation, just emit it as data.
216   MCAssembler &Assembler = getAssembler();
217   if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
218     EmitInstToData(Inst, STI);
219     return;
220   }
221 
222   // Otherwise, relax and emit it as data if either:
223   // - The RelaxAll flag was passed
224   // - Bundling is enabled and this instruction is inside a bundle-locked
225   //   group. We want to emit all such instructions into the same data
226   //   fragment.
227   if (Assembler.getRelaxAll() ||
228       (Assembler.isBundlingEnabled() && SD->isBundleLocked())) {
229     MCInst Relaxed;
230     getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
231     while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
232       getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
233     EmitInstToData(Relaxed, STI);
234     return;
235   }
236 
237   // Otherwise emit to a separate fragment.
238   EmitInstToFragment(Inst, STI);
239 }
240 
241 void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
242                                           const MCSubtargetInfo &STI) {
243   // Always create a new, separate fragment here, because its size can change
244   // during relaxation.
245   MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
246   insert(IF);
247 
248   SmallString<128> Code;
249   raw_svector_ostream VecOS(Code);
250   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, IF->getFixups(),
251                                                 STI);
252   VecOS.flush();
253   IF->getContents().append(Code.begin(), Code.end());
254 }
255 
256 #ifndef NDEBUG
257 static const char *const BundlingNotImplementedMsg =
258   "Aligned bundling is not implemented for this object format";
259 #endif
260 
261 void MCObjectStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
262   llvm_unreachable(BundlingNotImplementedMsg);
263 }
264 
265 void MCObjectStreamer::EmitBundleLock(bool AlignToEnd) {
266   llvm_unreachable(BundlingNotImplementedMsg);
267 }
268 
269 void MCObjectStreamer::EmitBundleUnlock() {
270   llvm_unreachable(BundlingNotImplementedMsg);
271 }
272 
273 void MCObjectStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
274                                              unsigned Column, unsigned Flags,
275                                              unsigned Isa,
276                                              unsigned Discriminator,
277                                              StringRef FileName) {
278   // In case we see two .loc directives in a row, make sure the
279   // first one gets a line entry.
280   MCLineEntry::Make(this, getCurrentSection().first);
281 
282   this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,
283                                           Isa, Discriminator, FileName);
284 }
285 
286 static const MCExpr *buildSymbolDiff(MCObjectStreamer &OS, const MCSymbol *A,
287                                      const MCSymbol *B) {
288   MCContext &Context = OS.getContext();
289   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
290   const MCExpr *ARef = MCSymbolRefExpr::Create(A, Variant, Context);
291   const MCExpr *BRef = MCSymbolRefExpr::Create(B, Variant, Context);
292   const MCExpr *AddrDelta =
293       MCBinaryExpr::Create(MCBinaryExpr::Sub, ARef, BRef, Context);
294   return AddrDelta;
295 }
296 
297 static void emitDwarfSetLineAddr(MCObjectStreamer &OS, int64_t LineDelta,
298                                  const MCSymbol *Label, int PointerSize) {
299   // emit the sequence to set the address
300   OS.EmitIntValue(dwarf::DW_LNS_extended_op, 1);
301   OS.EmitULEB128IntValue(PointerSize + 1);
302   OS.EmitIntValue(dwarf::DW_LNE_set_address, 1);
303   OS.EmitSymbolValue(Label, PointerSize);
304 
305   // emit the sequence for the LineDelta (from 1) and a zero address delta.
306   MCDwarfLineAddr::Emit(&OS, LineDelta, 0);
307 }
308 
309 void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
310                                                 const MCSymbol *LastLabel,
311                                                 const MCSymbol *Label,
312                                                 unsigned PointerSize) {
313   if (!LastLabel) {
314     emitDwarfSetLineAddr(*this, LineDelta, Label, PointerSize);
315     return;
316   }
317   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
318   int64_t Res;
319   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
320     MCDwarfLineAddr::Emit(this, LineDelta, Res);
321     return;
322   }
323   insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
324 }
325 
326 void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
327                                                  const MCSymbol *Label) {
328   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
329   int64_t Res;
330   if (AddrDelta->EvaluateAsAbsolute(Res, getAssembler())) {
331     MCDwarfFrameEmitter::EmitAdvanceLoc(*this, Res);
332     return;
333   }
334   insert(new MCDwarfCallFrameFragment(*AddrDelta));
335 }
336 
337 void MCObjectStreamer::EmitBytes(StringRef Data) {
338   MCLineEntry::Make(this, getCurrentSection().first);
339   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
340 }
341 
342 void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment,
343                                             int64_t Value,
344                                             unsigned ValueSize,
345                                             unsigned MaxBytesToEmit) {
346   if (MaxBytesToEmit == 0)
347     MaxBytesToEmit = ByteAlignment;
348   insert(new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit));
349 
350   // Update the maximum alignment on the current section if necessary.
351   if (ByteAlignment > getCurrentSectionData()->getAlignment())
352     getCurrentSectionData()->setAlignment(ByteAlignment);
353 }
354 
355 void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
356                                          unsigned MaxBytesToEmit) {
357   EmitValueToAlignment(ByteAlignment, 0, 1, MaxBytesToEmit);
358   cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
359 }
360 
361 bool MCObjectStreamer::EmitValueToOffset(const MCExpr *Offset,
362                                          unsigned char Value) {
363   int64_t Res;
364   if (Offset->EvaluateAsAbsolute(Res, getAssembler())) {
365     insert(new MCOrgFragment(*Offset, Value));
366     return false;
367   }
368 
369   MCSymbol *CurrentPos = getContext().CreateTempSymbol();
370   EmitLabel(CurrentPos);
371   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
372   const MCExpr *Ref =
373     MCSymbolRefExpr::Create(CurrentPos, Variant, getContext());
374   const MCExpr *Delta =
375     MCBinaryExpr::Create(MCBinaryExpr::Sub, Offset, Ref, getContext());
376 
377   if (!Delta->EvaluateAsAbsolute(Res, getAssembler()))
378     return true;
379   EmitFill(Res, Value);
380   return false;
381 }
382 
383 // Associate GPRel32 fixup with data and resize data area
384 void MCObjectStreamer::EmitGPRel32Value(const MCExpr *Value) {
385   MCDataFragment *DF = getOrCreateDataFragment();
386 
387   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
388                                             Value, FK_GPRel_4));
389   DF->getContents().resize(DF->getContents().size() + 4, 0);
390 }
391 
392 // Associate GPRel32 fixup with data and resize data area
393 void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
394   MCDataFragment *DF = getOrCreateDataFragment();
395 
396   DF->getFixups().push_back(MCFixup::Create(DF->getContents().size(),
397                                             Value, FK_GPRel_4));
398   DF->getContents().resize(DF->getContents().size() + 8, 0);
399 }
400 
401 void MCObjectStreamer::EmitFill(uint64_t NumBytes, uint8_t FillValue) {
402   // FIXME: A MCFillFragment would be more memory efficient but MCExpr has
403   //        problems evaluating expressions across multiple fragments.
404   getOrCreateDataFragment()->getContents().append(NumBytes, FillValue);
405 }
406 
407 void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
408   const MCSection *Sec = getCurrentSection().first;
409   assert(Sec && "need a section");
410   unsigned ItemSize = Sec->isVirtualSection() ? 0 : 1;
411   insert(new MCFillFragment(0, ItemSize, NumBytes));
412 }
413 
414 void MCObjectStreamer::FinishImpl() {
415   // If we are generating dwarf for assembly source files dump out the sections.
416   if (getContext().getGenDwarfForAssembly())
417     MCGenDwarfInfo::Emit(this);
418 
419   // Dump out the dwarf file & directory tables and line tables.
420   MCDwarfLineTable::Emit(this);
421 
422   flushPendingLabels(nullptr);
423   getAssembler().Finish();
424 }
425