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 #include "llvm/Support/TargetRegistry.h"
24 using namespace llvm;
25 
26 MCObjectStreamer::MCObjectStreamer(MCContext &Context, MCAsmBackend &TAB,
27                                    raw_pwrite_stream &OS,
28                                    MCCodeEmitter *Emitter_)
29     : MCStreamer(Context),
30       Assembler(new MCAssembler(Context, TAB, *Emitter_,
31                                 *TAB.createObjectWriter(OS), OS)),
32       EmitEHFrame(true), EmitDebugFrame(false) {}
33 
34 MCObjectStreamer::~MCObjectStreamer() {
35   delete &Assembler->getBackend();
36   delete &Assembler->getEmitter();
37   delete &Assembler->getWriter();
38   delete Assembler;
39 }
40 
41 void MCObjectStreamer::flushPendingLabels(MCFragment *F, uint64_t FOffset) {
42   if (PendingLabels.size()) {
43     if (!F) {
44       F = new MCDataFragment();
45       MCSection *CurSection = getCurrentSectionOnly();
46       CurSection->getFragmentList().insert(CurInsertionPoint, F);
47       F->setParent(CurSection);
48     }
49     for (MCSymbol *Sym : PendingLabels) {
50       Sym->setFragment(F);
51       Sym->setOffset(FOffset);
52     }
53     PendingLabels.clear();
54   }
55 }
56 
57 void MCObjectStreamer::emitAbsoluteSymbolDiff(const MCSymbol *Hi,
58                                               const MCSymbol *Lo,
59                                               unsigned Size) {
60   // If not assigned to the same (valid) fragment, fallback.
61   if (!Hi->getFragment() || Hi->getFragment() != Lo->getFragment()) {
62     MCStreamer::emitAbsoluteSymbolDiff(Hi, Lo, Size);
63     return;
64   }
65 
66   assert(Hi->getOffset() >= Lo->getOffset() &&
67          "Expected Hi to be greater than Lo");
68   EmitIntValue(Hi->getOffset() - Lo->getOffset(), Size);
69 }
70 
71 void MCObjectStreamer::reset() {
72   if (Assembler)
73     Assembler->reset();
74   CurInsertionPoint = MCSection::iterator();
75   EmitEHFrame = true;
76   EmitDebugFrame = false;
77   PendingLabels.clear();
78   MCStreamer::reset();
79 }
80 
81 void MCObjectStreamer::EmitFrames(MCAsmBackend *MAB) {
82   if (!getNumFrameInfos())
83     return;
84 
85   if (EmitEHFrame)
86     MCDwarfFrameEmitter::Emit(*this, MAB, true);
87 
88   if (EmitDebugFrame)
89     MCDwarfFrameEmitter::Emit(*this, MAB, false);
90 }
91 
92 MCFragment *MCObjectStreamer::getCurrentFragment() const {
93   assert(getCurrentSectionOnly() && "No current section!");
94 
95   if (CurInsertionPoint != getCurrentSectionOnly()->getFragmentList().begin())
96     return std::prev(CurInsertionPoint);
97 
98   return nullptr;
99 }
100 
101 MCDataFragment *MCObjectStreamer::getOrCreateDataFragment() {
102   MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
103   // When bundling is enabled, we don't want to add data to a fragment that
104   // already has instructions (see MCELFStreamer::EmitInstToData for details)
105   if (!F || (Assembler->isBundlingEnabled() && !Assembler->getRelaxAll() &&
106              F->hasInstructions())) {
107     F = new MCDataFragment();
108     insert(F);
109   }
110   return F;
111 }
112 
113 void MCObjectStreamer::visitUsedSymbol(const MCSymbol &Sym) {
114   Assembler->registerSymbol(Sym);
115 }
116 
117 void MCObjectStreamer::EmitCFISections(bool EH, bool Debug) {
118   MCStreamer::EmitCFISections(EH, Debug);
119   EmitEHFrame = EH;
120   EmitDebugFrame = Debug;
121 }
122 
123 void MCObjectStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
124                                      const SMLoc &Loc) {
125   MCStreamer::EmitValueImpl(Value, Size, Loc);
126   MCDataFragment *DF = getOrCreateDataFragment();
127 
128   MCLineEntry::Make(this, getCurrentSection().first);
129 
130   // Avoid fixups when possible.
131   int64_t AbsValue;
132   if (Value->evaluateAsAbsolute(AbsValue, getAssembler())) {
133     EmitIntValue(AbsValue, Size);
134     return;
135   }
136   DF->getFixups().push_back(
137       MCFixup::create(DF->getContents().size(), Value,
138                       MCFixup::getKindForSize(Size, false), Loc));
139   DF->getContents().resize(DF->getContents().size() + Size, 0);
140 }
141 
142 void MCObjectStreamer::EmitCFIStartProcImpl(MCDwarfFrameInfo &Frame) {
143   // We need to create a local symbol to avoid relocations.
144   Frame.Begin = getContext().createTempSymbol();
145   EmitLabel(Frame.Begin);
146 }
147 
148 void MCObjectStreamer::EmitCFIEndProcImpl(MCDwarfFrameInfo &Frame) {
149   Frame.End = getContext().createTempSymbol();
150   EmitLabel(Frame.End);
151 }
152 
153 void MCObjectStreamer::EmitLabel(MCSymbol *Symbol) {
154   MCStreamer::EmitLabel(Symbol);
155 
156   getAssembler().registerSymbol(*Symbol);
157   assert(!Symbol->getFragment() && "Unexpected fragment on symbol data!");
158 
159   // If there is a current fragment, mark the symbol as pointing into it.
160   // Otherwise queue the label and set its fragment pointer when we emit the
161   // next fragment.
162   auto *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
163   if (F && !(getAssembler().isBundlingEnabled() &&
164              getAssembler().getRelaxAll())) {
165     Symbol->setFragment(F);
166     Symbol->setOffset(F->getContents().size());
167   } else {
168     PendingLabels.push_back(Symbol);
169   }
170 }
171 
172 void MCObjectStreamer::EmitULEB128Value(const MCExpr *Value) {
173   int64_t IntValue;
174   if (Value->evaluateAsAbsolute(IntValue, getAssembler())) {
175     EmitULEB128IntValue(IntValue);
176     return;
177   }
178   insert(new MCLEBFragment(*Value, false));
179 }
180 
181 void MCObjectStreamer::EmitSLEB128Value(const MCExpr *Value) {
182   int64_t IntValue;
183   if (Value->evaluateAsAbsolute(IntValue, getAssembler())) {
184     EmitSLEB128IntValue(IntValue);
185     return;
186   }
187   insert(new MCLEBFragment(*Value, true));
188 }
189 
190 void MCObjectStreamer::EmitWeakReference(MCSymbol *Alias,
191                                          const MCSymbol *Symbol) {
192   report_fatal_error("This file format doesn't support weak aliases.");
193 }
194 
195 void MCObjectStreamer::ChangeSection(MCSection *Section,
196                                      const MCExpr *Subsection) {
197   changeSectionImpl(Section, Subsection);
198 }
199 
200 bool MCObjectStreamer::changeSectionImpl(MCSection *Section,
201                                          const MCExpr *Subsection) {
202   assert(Section && "Cannot switch to a null section!");
203   flushPendingLabels(nullptr);
204 
205   bool Created = getAssembler().registerSection(*Section);
206 
207   int64_t IntSubsection = 0;
208   if (Subsection &&
209       !Subsection->evaluateAsAbsolute(IntSubsection, getAssembler()))
210     report_fatal_error("Cannot evaluate subsection number");
211   if (IntSubsection < 0 || IntSubsection > 8192)
212     report_fatal_error("Subsection number out of range");
213   CurInsertionPoint =
214       Section->getSubsectionInsertionPoint(unsigned(IntSubsection));
215   return Created;
216 }
217 
218 void MCObjectStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
219   getAssembler().registerSymbol(*Symbol);
220   MCStreamer::EmitAssignment(Symbol, Value);
221 }
222 
223 bool MCObjectStreamer::mayHaveInstructions(MCSection &Sec) const {
224   return Sec.hasInstructions();
225 }
226 
227 void MCObjectStreamer::EmitInstruction(const MCInst &Inst,
228                                        const MCSubtargetInfo &STI) {
229   MCStreamer::EmitInstruction(Inst, STI);
230 
231   MCSection *Sec = getCurrentSectionOnly();
232   Sec->setHasInstructions(true);
233 
234   // Now that a machine instruction has been assembled into this section, make
235   // a line entry for any .loc directive that has been seen.
236   MCLineEntry::Make(this, getCurrentSection().first);
237 
238   // If this instruction doesn't need relaxation, just emit it as data.
239   MCAssembler &Assembler = getAssembler();
240   if (!Assembler.getBackend().mayNeedRelaxation(Inst)) {
241     EmitInstToData(Inst, STI);
242     return;
243   }
244 
245   // Otherwise, relax and emit it as data if either:
246   // - The RelaxAll flag was passed
247   // - Bundling is enabled and this instruction is inside a bundle-locked
248   //   group. We want to emit all such instructions into the same data
249   //   fragment.
250   if (Assembler.getRelaxAll() ||
251       (Assembler.isBundlingEnabled() && Sec->isBundleLocked())) {
252     MCInst Relaxed;
253     getAssembler().getBackend().relaxInstruction(Inst, Relaxed);
254     while (getAssembler().getBackend().mayNeedRelaxation(Relaxed))
255       getAssembler().getBackend().relaxInstruction(Relaxed, Relaxed);
256     EmitInstToData(Relaxed, STI);
257     return;
258   }
259 
260   // Otherwise emit to a separate fragment.
261   EmitInstToFragment(Inst, STI);
262 }
263 
264 void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
265                                           const MCSubtargetInfo &STI) {
266   if (getAssembler().getRelaxAll() && getAssembler().isBundlingEnabled())
267     llvm_unreachable("All instructions should have already been relaxed");
268 
269   // Always create a new, separate fragment here, because its size can change
270   // during relaxation.
271   MCRelaxableFragment *IF = new MCRelaxableFragment(Inst, STI);
272   insert(IF);
273 
274   SmallString<128> Code;
275   raw_svector_ostream VecOS(Code);
276   getAssembler().getEmitter().encodeInstruction(Inst, VecOS, IF->getFixups(),
277                                                 STI);
278   VecOS.flush();
279   IF->getContents().append(Code.begin(), Code.end());
280 }
281 
282 #ifndef NDEBUG
283 static const char *const BundlingNotImplementedMsg =
284   "Aligned bundling is not implemented for this object format";
285 #endif
286 
287 void MCObjectStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
288   llvm_unreachable(BundlingNotImplementedMsg);
289 }
290 
291 void MCObjectStreamer::EmitBundleLock(bool AlignToEnd) {
292   llvm_unreachable(BundlingNotImplementedMsg);
293 }
294 
295 void MCObjectStreamer::EmitBundleUnlock() {
296   llvm_unreachable(BundlingNotImplementedMsg);
297 }
298 
299 void MCObjectStreamer::EmitDwarfLocDirective(unsigned FileNo, unsigned Line,
300                                              unsigned Column, unsigned Flags,
301                                              unsigned Isa,
302                                              unsigned Discriminator,
303                                              StringRef FileName) {
304   // In case we see two .loc directives in a row, make sure the
305   // first one gets a line entry.
306   MCLineEntry::Make(this, getCurrentSection().first);
307 
308   this->MCStreamer::EmitDwarfLocDirective(FileNo, Line, Column, Flags,
309                                           Isa, Discriminator, FileName);
310 }
311 
312 static const MCExpr *buildSymbolDiff(MCObjectStreamer &OS, const MCSymbol *A,
313                                      const MCSymbol *B) {
314   MCContext &Context = OS.getContext();
315   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
316   const MCExpr *ARef = MCSymbolRefExpr::create(A, Variant, Context);
317   const MCExpr *BRef = MCSymbolRefExpr::create(B, Variant, Context);
318   const MCExpr *AddrDelta =
319       MCBinaryExpr::create(MCBinaryExpr::Sub, ARef, BRef, Context);
320   return AddrDelta;
321 }
322 
323 static void emitDwarfSetLineAddr(MCObjectStreamer &OS, int64_t LineDelta,
324                                  const MCSymbol *Label, int PointerSize) {
325   // emit the sequence to set the address
326   OS.EmitIntValue(dwarf::DW_LNS_extended_op, 1);
327   OS.EmitULEB128IntValue(PointerSize + 1);
328   OS.EmitIntValue(dwarf::DW_LNE_set_address, 1);
329   OS.EmitSymbolValue(Label, PointerSize);
330 
331   // emit the sequence for the LineDelta (from 1) and a zero address delta.
332   MCDwarfLineAddr::Emit(&OS, LineDelta, 0);
333 }
334 
335 void MCObjectStreamer::EmitDwarfAdvanceLineAddr(int64_t LineDelta,
336                                                 const MCSymbol *LastLabel,
337                                                 const MCSymbol *Label,
338                                                 unsigned PointerSize) {
339   if (!LastLabel) {
340     emitDwarfSetLineAddr(*this, LineDelta, Label, PointerSize);
341     return;
342   }
343   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
344   int64_t Res;
345   if (AddrDelta->evaluateAsAbsolute(Res, getAssembler())) {
346     MCDwarfLineAddr::Emit(this, LineDelta, Res);
347     return;
348   }
349   insert(new MCDwarfLineAddrFragment(LineDelta, *AddrDelta));
350 }
351 
352 void MCObjectStreamer::EmitDwarfAdvanceFrameAddr(const MCSymbol *LastLabel,
353                                                  const MCSymbol *Label) {
354   const MCExpr *AddrDelta = buildSymbolDiff(*this, Label, LastLabel);
355   int64_t Res;
356   if (AddrDelta->evaluateAsAbsolute(Res, getAssembler())) {
357     MCDwarfFrameEmitter::EmitAdvanceLoc(*this, Res);
358     return;
359   }
360   insert(new MCDwarfCallFrameFragment(*AddrDelta));
361 }
362 
363 void MCObjectStreamer::EmitBytes(StringRef Data) {
364   MCLineEntry::Make(this, getCurrentSection().first);
365   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
366 }
367 
368 void MCObjectStreamer::EmitValueToAlignment(unsigned ByteAlignment,
369                                             int64_t Value,
370                                             unsigned ValueSize,
371                                             unsigned MaxBytesToEmit) {
372   if (MaxBytesToEmit == 0)
373     MaxBytesToEmit = ByteAlignment;
374   insert(new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit));
375 
376   // Update the maximum alignment on the current section if necessary.
377   MCSection *CurSec = getCurrentSection().first;
378   if (ByteAlignment > CurSec->getAlignment())
379     CurSec->setAlignment(ByteAlignment);
380 }
381 
382 void MCObjectStreamer::EmitCodeAlignment(unsigned ByteAlignment,
383                                          unsigned MaxBytesToEmit) {
384   EmitValueToAlignment(ByteAlignment, 0, 1, MaxBytesToEmit);
385   cast<MCAlignFragment>(getCurrentFragment())->setEmitNops(true);
386 }
387 
388 bool MCObjectStreamer::EmitValueToOffset(const MCExpr *Offset,
389                                          unsigned char Value) {
390   int64_t Res;
391   if (Offset->evaluateAsAbsolute(Res, getAssembler())) {
392     insert(new MCOrgFragment(*Offset, Value));
393     return false;
394   }
395 
396   MCSymbol *CurrentPos = getContext().createTempSymbol();
397   EmitLabel(CurrentPos);
398   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
399   const MCExpr *Ref =
400     MCSymbolRefExpr::create(CurrentPos, Variant, getContext());
401   const MCExpr *Delta =
402     MCBinaryExpr::create(MCBinaryExpr::Sub, Offset, Ref, getContext());
403 
404   if (!Delta->evaluateAsAbsolute(Res, getAssembler()))
405     return true;
406   EmitFill(Res, Value);
407   return false;
408 }
409 
410 // Associate GPRel32 fixup with data and resize data area
411 void MCObjectStreamer::EmitGPRel32Value(const MCExpr *Value) {
412   MCDataFragment *DF = getOrCreateDataFragment();
413 
414   DF->getFixups().push_back(MCFixup::create(DF->getContents().size(),
415                                             Value, FK_GPRel_4));
416   DF->getContents().resize(DF->getContents().size() + 4, 0);
417 }
418 
419 // Associate GPRel32 fixup with data and resize data area
420 void MCObjectStreamer::EmitGPRel64Value(const MCExpr *Value) {
421   MCDataFragment *DF = getOrCreateDataFragment();
422 
423   DF->getFixups().push_back(MCFixup::create(DF->getContents().size(),
424                                             Value, FK_GPRel_4));
425   DF->getContents().resize(DF->getContents().size() + 8, 0);
426 }
427 
428 void MCObjectStreamer::EmitFill(uint64_t NumBytes, uint8_t FillValue) {
429   // FIXME: A MCFillFragment would be more memory efficient but MCExpr has
430   //        problems evaluating expressions across multiple fragments.
431   getOrCreateDataFragment()->getContents().append(NumBytes, FillValue);
432 }
433 
434 void MCObjectStreamer::EmitZeros(uint64_t NumBytes) {
435   const MCSection *Sec = getCurrentSection().first;
436   assert(Sec && "need a section");
437   unsigned ItemSize = Sec->isVirtualSection() ? 0 : 1;
438   insert(new MCFillFragment(0, ItemSize, NumBytes));
439 }
440 
441 void MCObjectStreamer::FinishImpl() {
442   // If we are generating dwarf for assembly source files dump out the sections.
443   if (getContext().getGenDwarfForAssembly())
444     MCGenDwarfInfo::Emit(this);
445 
446   // Dump out the dwarf file & directory tables and line tables.
447   MCDwarfLineTable::Emit(this);
448 
449   flushPendingLabels(nullptr);
450   getAssembler().Finish();
451 }
452