1 //===- lib/MC/MCELFStreamer.cpp - ELF Object Output ------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file assembles .s files and emits ELF .o object files.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/MC/MCStreamer.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/MC/MCAssembler.h"
18 #include "llvm/MC/MCContext.h"
19 #include "llvm/MC/MCCodeEmitter.h"
20 #include "llvm/MC/MCELFSymbolFlags.h"
21 #include "llvm/MC/MCExpr.h"
22 #include "llvm/MC/MCInst.h"
23 #include "llvm/MC/MCObjectStreamer.h"
24 #include "llvm/MC/MCSection.h"
25 #include "llvm/MC/MCSectionELF.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ELF.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/Target/TargetAsmBackend.h"
37 class MCELFStreamer : public MCObjectStreamer {
38 void EmitInstToFragment(const MCInst &Inst);
39 void EmitInstToData(const MCInst &Inst);
41 MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
42 raw_ostream &OS, MCCodeEmitter *Emitter)
43 : MCObjectStreamer(Context, TAB, OS, Emitter, false) {}
47 /// @name MCStreamer Interface
50 virtual void InitSections();
51 virtual void EmitLabel(MCSymbol *Symbol);
52 virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
53 virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
54 virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
55 virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
56 assert(0 && "ELF doesn't support this directive");
58 virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
59 unsigned ByteAlignment);
60 virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
61 assert(0 && "ELF doesn't support this directive");
64 virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
65 assert(0 && "ELF doesn't support this directive");
68 virtual void EmitCOFFSymbolType(int Type) {
69 assert(0 && "ELF doesn't support this directive");
72 virtual void EndCOFFSymbolDef() {
73 assert(0 && "ELF doesn't support this directive");
76 virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
77 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
81 virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
82 assert(0 && "ELF doesn't support this directive");
84 virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
85 unsigned Size = 0, unsigned ByteAlignment = 0) {
86 assert(0 && "ELF doesn't support this directive");
88 virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
89 uint64_t Size, unsigned ByteAlignment = 0) {
90 assert(0 && "ELF doesn't support this directive");
92 virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
93 virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
94 virtual void EmitGPRel32Value(const MCExpr *Value) {
95 assert(0 && "ELF doesn't support this directive");
97 virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
98 unsigned ValueSize = 1,
99 unsigned MaxBytesToEmit = 0);
100 virtual void EmitCodeAlignment(unsigned ByteAlignment,
101 unsigned MaxBytesToEmit = 0);
102 virtual void EmitValueToOffset(const MCExpr *Offset,
103 unsigned char Value = 0);
105 virtual void EmitFileDirective(StringRef Filename);
106 virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
107 DEBUG(dbgs() << "FIXME: MCELFStreamer:EmitDwarfFileDirective not implemented\n");
110 virtual void EmitInstruction(const MCInst &Inst);
111 virtual void Finish();
117 unsigned ByteAlignment;
119 std::vector<LocalCommon> LocalCommons;
121 SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
123 void SetSection(StringRef Section, unsigned Type, unsigned Flags,
125 SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
128 void SetSectionData() {
129 SetSection(".data", MCSectionELF::SHT_PROGBITS,
130 MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
131 SectionKind::getDataRel());
132 EmitCodeAlignment(4, 0);
134 void SetSectionText() {
135 SetSection(".text", MCSectionELF::SHT_PROGBITS,
136 MCSectionELF::SHF_EXECINSTR |
137 MCSectionELF::SHF_ALLOC, SectionKind::getText());
138 EmitCodeAlignment(4, 0);
140 void SetSectionBss() {
141 SetSection(".bss", MCSectionELF::SHT_NOBITS,
142 MCSectionELF::SHF_WRITE |
143 MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
144 EmitCodeAlignment(4, 0);
148 } // end anonymous namespace.
150 void MCELFStreamer::InitSections() {
151 // This emulates the same behavior of GNU as. This makes it easier
152 // to compare the output as the major sections are in the same order.
159 static bool isSymbolLinkerVisible(const MCAssembler &Asm,
160 const MCSymbolData &Data) {
161 const MCSymbol &Symbol = Data.getSymbol();
162 // Absolute temporary labels are never visible.
163 if (!Symbol.isInSection())
166 if (Asm.getBackend().doesSectionRequireSymbols(Symbol.getSection()))
169 if (!Data.isExternal())
172 return Asm.isSymbolLinkerVisible(Symbol);
175 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
176 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
178 Symbol->setSection(*CurSection);
180 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
182 // We have to create a new fragment if this is an atom defining symbol,
183 // fragments cannot span atoms.
184 if (isSymbolLinkerVisible(getAssembler(), SD))
185 new MCDataFragment(getCurrentSectionData());
187 // FIXME: This is wasteful, we don't necessarily need to create a data
188 // fragment. Instead, we should mark the symbol as pointing into the data
189 // fragment if it exists, otherwise we should just queue the label and set its
190 // fragment pointer when we emit the next fragment.
191 MCDataFragment *F = getOrCreateDataFragment();
193 assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
195 SD.setOffset(F->getContents().size());
198 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
200 case MCAF_SyntaxUnified: return; // no-op here?
201 case MCAF_SubsectionsViaSymbols:
202 getAssembler().setSubsectionsViaSymbols(true);
206 assert(0 && "invalid assembler flag!");
209 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
210 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
212 // FIXME: Lift context changes into super class.
213 getAssembler().getOrCreateSymbolData(*Symbol);
214 Symbol->setVariableValue(AddValueSymbols(Value));
217 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
218 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
219 Binding == ELF::STB_WEAK);
220 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
221 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
224 static unsigned GetBinding(const MCSymbolData &SD) {
225 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
226 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
227 Binding == ELF::STB_WEAK);
231 static void SetType(MCSymbolData &SD, unsigned Type) {
232 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
233 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
234 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
235 Type == ELF::STT_TLS);
237 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
238 SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
241 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
242 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
243 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
245 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
246 SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
249 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
250 MCSymbolAttr Attribute) {
251 // Indirect symbols are handled differently, to match how 'as' handles
252 // them. This makes writing matching .o files easier.
253 if (Attribute == MCSA_IndirectSymbol) {
254 // Note that we intentionally cannot use the symbol data here; this is
255 // important for matching the string table that 'as' generates.
256 IndirectSymbolData ISD;
258 ISD.SectionData = getCurrentSectionData();
259 getAssembler().getIndirectSymbols().push_back(ISD);
263 // Adding a symbol attribute always introduces the symbol, note that an
264 // important side effect of calling getOrCreateSymbolData here is to register
265 // the symbol with the assembler.
266 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
268 // The implementation of symbol attributes is designed to match 'as', but it
269 // leaves much to desired. It doesn't really make sense to arbitrarily add and
270 // remove flags, but 'as' allows this (in particular, see .desc).
272 // In the future it might be worth trying to make these operations more well
275 case MCSA_LazyReference:
277 case MCSA_NoDeadStrip:
278 case MCSA_PrivateExtern:
279 case MCSA_WeakDefinition:
280 case MCSA_WeakDefAutoPrivate:
282 case MCSA_ELF_TypeIndFunction:
283 case MCSA_IndirectSymbol:
284 assert(0 && "Invalid symbol attribute for ELF!");
288 SetBinding(SD, ELF::STB_GLOBAL);
289 SD.setExternal(true);
290 BindingExplicitlySet.insert(Symbol);
293 case MCSA_WeakReference:
295 SetBinding(SD, ELF::STB_WEAK);
296 BindingExplicitlySet.insert(Symbol);
300 SetBinding(SD, ELF::STB_LOCAL);
301 SD.setExternal(false);
302 BindingExplicitlySet.insert(Symbol);
305 case MCSA_ELF_TypeFunction:
306 SetType(SD, ELF::STT_FUNC);
309 case MCSA_ELF_TypeObject:
310 SetType(SD, ELF::STT_OBJECT);
313 case MCSA_ELF_TypeTLS:
314 SetType(SD, ELF::STT_TLS);
317 case MCSA_ELF_TypeCommon:
318 SetType(SD, ELF::STT_COMMON);
321 case MCSA_ELF_TypeNoType:
322 SetType(SD, ELF::STT_NOTYPE);
326 SetVisibility(SD, ELF::STV_PROTECTED);
330 SetVisibility(SD, ELF::STV_HIDDEN);
334 SetVisibility(SD, ELF::STV_INTERNAL);
339 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
340 unsigned ByteAlignment) {
341 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
343 if (!BindingExplicitlySet.count(Symbol)) {
344 SetBinding(SD, ELF::STB_GLOBAL);
345 SD.setExternal(true);
348 if (GetBinding(SD) == ELF_STB_Local) {
349 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
350 MCSectionELF::SHT_NOBITS,
351 MCSectionELF::SHF_WRITE |
352 MCSectionELF::SHF_ALLOC,
353 SectionKind::getBSS());
354 Symbol->setSection(*Section);
356 struct LocalCommon L = {&SD, Size, ByteAlignment};
357 LocalCommons.push_back(L);
359 SD.setCommon(Size, ByteAlignment);
362 SD.setSize(MCConstantExpr::Create(Size, getContext()));
365 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
366 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
368 getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
371 void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
372 unsigned AddrSpace) {
373 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
375 MCDataFragment *DF = getOrCreateDataFragment();
377 // Avoid fixups when possible.
379 if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
380 // FIXME: Endianness assumption.
381 for (unsigned i = 0; i != Size; ++i)
382 DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
384 DF->addFixup(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
385 MCFixup::getKindForSize(Size)));
386 DF->getContents().resize(DF->getContents().size() + Size, 0);
390 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
391 int64_t Value, unsigned ValueSize,
392 unsigned MaxBytesToEmit) {
393 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
395 if (MaxBytesToEmit == 0)
396 MaxBytesToEmit = ByteAlignment;
397 new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
398 getCurrentSectionData());
400 // Update the maximum alignment on the current section if necessary.
401 if (ByteAlignment > getCurrentSectionData()->getAlignment())
402 getCurrentSectionData()->setAlignment(ByteAlignment);
405 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
406 unsigned MaxBytesToEmit) {
407 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
409 if (MaxBytesToEmit == 0)
410 MaxBytesToEmit = ByteAlignment;
411 MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
412 getCurrentSectionData());
413 F->setEmitNops(true);
415 // Update the maximum alignment on the current section if necessary.
416 if (ByteAlignment > getCurrentSectionData()->getAlignment())
417 getCurrentSectionData()->setAlignment(ByteAlignment);
420 void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
421 unsigned char Value) {
422 // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
424 new MCOrgFragment(*Offset, Value, getCurrentSectionData());
427 // Add a symbol for the file name of this module. This is the second
428 // entry in the module's symbol table (the first being the null symbol).
429 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
430 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
431 Symbol->setSection(*CurSection);
432 Symbol->setAbsolute();
434 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
436 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
439 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
440 MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
442 // Add the fixups and data.
444 // FIXME: Revisit this design decision when relaxation is done, we may be
445 // able to get away with not storing any extra data in the MCInst.
446 SmallVector<MCFixup, 4> Fixups;
447 SmallString<256> Code;
448 raw_svector_ostream VecOS(Code);
449 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
452 IF->getCode() = Code;
453 IF->getFixups() = Fixups;
456 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
457 MCDataFragment *DF = getOrCreateDataFragment();
459 SmallVector<MCFixup, 4> Fixups;
460 SmallString<256> Code;
461 raw_svector_ostream VecOS(Code);
462 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
465 // Add the fixups and data.
466 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
467 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
468 DF->addFixup(Fixups[i]);
470 DF->getContents().append(Code.begin(), Code.end());
473 void MCELFStreamer::EmitInstruction(const MCInst &Inst) {
475 for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
476 if (Inst.getOperand(i).isExpr())
477 AddValueSymbols(Inst.getOperand(i).getExpr());
479 getCurrentSectionData()->setHasInstructions(true);
481 // If this instruction doesn't need relaxation, just emit it as data.
482 if (!getAssembler().getBackend().MayNeedRelaxation(Inst)) {
483 EmitInstToData(Inst);
487 // Otherwise, if we are relaxing everything, relax the instruction as much as
488 // possible and emit it as data.
489 if (getAssembler().getRelaxAll()) {
491 getAssembler().getBackend().RelaxInstruction(Inst, Relaxed);
492 while (getAssembler().getBackend().MayNeedRelaxation(Relaxed))
493 getAssembler().getBackend().RelaxInstruction(Relaxed, Relaxed);
494 EmitInstToData(Relaxed);
498 // Otherwise emit to a separate fragment.
499 EmitInstToFragment(Inst);
502 void MCELFStreamer::Finish() {
503 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
504 e = LocalCommons.end();
506 MCSymbolData *SD = i->SD;
507 uint64_t Size = i->Size;
508 unsigned ByteAlignment = i->ByteAlignment;
509 const MCSymbol &Symbol = SD->getSymbol();
510 const MCSection &Section = Symbol.getSection();
512 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
513 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
515 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
518 // Update the maximum alignment of the section if necessary.
519 if (ByteAlignment > SectData.getAlignment())
520 SectData.setAlignment(ByteAlignment);
523 // FIXME: We create more atoms than it is necessary. Some relocations to
524 // merge sections can be implemented with section address + offset,
525 // figure out which ones and why.
527 // First, scan the symbol table to build a lookup table from fragments to
529 DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
530 for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
531 ie = getAssembler().symbol_end(); it != ie; ++it) {
532 if (isSymbolLinkerVisible(getAssembler(), *it) &&
534 // An atom defining symbol should never be internal to a fragment.
535 assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
536 DefiningSymbolMap[it->getFragment()] = it;
540 // Set the fragment atom associations by tracking the last seen atom defining
542 for (MCAssembler::iterator it = getAssembler().begin(),
543 ie = getAssembler().end(); it != ie; ++it) {
544 MCSymbolData *CurrentAtom = 0;
545 for (MCSectionData::iterator it2 = it->begin(),
546 ie2 = it->end(); it2 != ie2; ++it2) {
547 if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
549 it2->setAtom(CurrentAtom);
553 this->MCObjectStreamer::Finish();
556 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
557 raw_ostream &OS, MCCodeEmitter *CE,
559 MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
561 S->getAssembler().setRelaxAll(true);