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();
114 SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
116 void SetSection(StringRef Section, unsigned Type, unsigned Flags,
118 SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
121 void SetSectionData() {
122 SetSection(".data", MCSectionELF::SHT_PROGBITS,
123 MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
124 SectionKind::getDataRel());
125 EmitCodeAlignment(4, 0);
127 void SetSectionText() {
128 SetSection(".text", MCSectionELF::SHT_PROGBITS,
129 MCSectionELF::SHF_EXECINSTR |
130 MCSectionELF::SHF_ALLOC, SectionKind::getText());
131 EmitCodeAlignment(4, 0);
133 void SetSectionBss() {
134 SetSection(".bss", MCSectionELF::SHT_NOBITS,
135 MCSectionELF::SHF_WRITE |
136 MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
137 EmitCodeAlignment(4, 0);
141 } // end anonymous namespace.
143 void MCELFStreamer::InitSections() {
144 // This emulates the same behavior of GNU as. This makes it easier
145 // to compare the output as the major sections are in the same order.
152 static bool isSymbolLinkerVisible(const MCAssembler &Asm,
153 const MCSymbolData &Data) {
154 const MCSymbol &Symbol = Data.getSymbol();
155 // Absolute temporary labels are never visible.
156 if (!Symbol.isInSection())
159 if (Asm.getBackend().doesSectionRequireSymbols(Symbol.getSection()))
162 if (!Data.isExternal())
165 return Asm.isSymbolLinkerVisible(Symbol);
168 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
169 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
171 Symbol->setSection(*CurSection);
173 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
175 // We have to create a new fragment if this is an atom defining symbol,
176 // fragments cannot span atoms.
177 if (isSymbolLinkerVisible(getAssembler(), SD))
178 new MCDataFragment(getCurrentSectionData());
180 // FIXME: This is wasteful, we don't necessarily need to create a data
181 // fragment. Instead, we should mark the symbol as pointing into the data
182 // fragment if it exists, otherwise we should just queue the label and set its
183 // fragment pointer when we emit the next fragment.
184 MCDataFragment *F = getOrCreateDataFragment();
186 assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
188 SD.setOffset(F->getContents().size());
191 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
193 case MCAF_SubsectionsViaSymbols:
194 getAssembler().setSubsectionsViaSymbols(true);
198 assert(0 && "invalid assembler flag!");
201 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
202 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
204 // FIXME: Lift context changes into super class.
205 getAssembler().getOrCreateSymbolData(*Symbol);
206 Symbol->setVariableValue(AddValueSymbols(Value));
209 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
210 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
211 Binding == ELF::STB_WEAK);
212 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
213 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
216 static unsigned GetBinding(const MCSymbolData &SD) {
217 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
218 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
219 Binding == ELF::STB_WEAK);
223 static void SetType(MCSymbolData &SD, unsigned Type) {
224 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
225 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
226 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
227 Type == ELF::STT_TLS);
229 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
230 SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
233 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
234 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
235 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
237 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
238 SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
241 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
242 MCSymbolAttr Attribute) {
243 // Indirect symbols are handled differently, to match how 'as' handles
244 // them. This makes writing matching .o files easier.
245 if (Attribute == MCSA_IndirectSymbol) {
246 // Note that we intentionally cannot use the symbol data here; this is
247 // important for matching the string table that 'as' generates.
248 IndirectSymbolData ISD;
250 ISD.SectionData = getCurrentSectionData();
251 getAssembler().getIndirectSymbols().push_back(ISD);
255 // Adding a symbol attribute always introduces the symbol, note that an
256 // important side effect of calling getOrCreateSymbolData here is to register
257 // the symbol with the assembler.
258 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
260 // The implementation of symbol attributes is designed to match 'as', but it
261 // leaves much to desired. It doesn't really make sense to arbitrarily add and
262 // remove flags, but 'as' allows this (in particular, see .desc).
264 // In the future it might be worth trying to make these operations more well
267 case MCSA_LazyReference:
269 case MCSA_NoDeadStrip:
270 case MCSA_PrivateExtern:
271 case MCSA_WeakDefinition:
272 case MCSA_WeakDefAutoPrivate:
274 case MCSA_ELF_TypeIndFunction:
275 case MCSA_IndirectSymbol:
276 assert(0 && "Invalid symbol attribute for ELF!");
280 SetBinding(SD, ELF::STB_GLOBAL);
281 SD.setExternal(true);
282 BindingExplicitlySet.insert(Symbol);
285 case MCSA_WeakReference:
287 SetBinding(SD, ELF::STB_WEAK);
288 BindingExplicitlySet.insert(Symbol);
292 SetBinding(SD, ELF::STB_LOCAL);
293 SD.setExternal(false);
294 BindingExplicitlySet.insert(Symbol);
297 case MCSA_ELF_TypeFunction:
298 SetType(SD, ELF::STT_FUNC);
301 case MCSA_ELF_TypeObject:
302 SetType(SD, ELF::STT_OBJECT);
305 case MCSA_ELF_TypeTLS:
306 SetType(SD, ELF::STT_TLS);
309 case MCSA_ELF_TypeCommon:
310 SetType(SD, ELF::STT_COMMON);
313 case MCSA_ELF_TypeNoType:
314 SetType(SD, ELF::STT_NOTYPE);
318 SetVisibility(SD, ELF::STV_PROTECTED);
322 SetVisibility(SD, ELF::STV_HIDDEN);
326 SetVisibility(SD, ELF::STV_INTERNAL);
331 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
332 unsigned ByteAlignment) {
333 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
335 if (!BindingExplicitlySet.count(Symbol)) {
336 SetBinding(SD, ELF::STB_GLOBAL);
337 SD.setExternal(true);
340 if (GetBinding(SD) == ELF_STB_Local) {
341 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
342 MCSectionELF::SHT_NOBITS,
343 MCSectionELF::SHF_WRITE |
344 MCSectionELF::SHF_ALLOC,
345 SectionKind::getBSS());
347 MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
348 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
350 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
352 Symbol->setSection(*Section);
354 // Update the maximum alignment of the section if necessary.
355 if (ByteAlignment > SectData.getAlignment())
356 SectData.setAlignment(ByteAlignment);
358 SD.setCommon(Size, ByteAlignment);
361 SD.setSize(MCConstantExpr::Create(Size, getContext()));
364 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
365 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
367 getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
370 void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
371 unsigned AddrSpace) {
372 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
374 MCDataFragment *DF = getOrCreateDataFragment();
376 // Avoid fixups when possible.
378 if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
379 // FIXME: Endianness assumption.
380 for (unsigned i = 0; i != Size; ++i)
381 DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
383 DF->addFixup(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
384 MCFixup::getKindForSize(Size)));
385 DF->getContents().resize(DF->getContents().size() + Size, 0);
389 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
390 int64_t Value, unsigned ValueSize,
391 unsigned MaxBytesToEmit) {
392 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
394 if (MaxBytesToEmit == 0)
395 MaxBytesToEmit = ByteAlignment;
396 new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
397 getCurrentSectionData());
399 // Update the maximum alignment on the current section if necessary.
400 if (ByteAlignment > getCurrentSectionData()->getAlignment())
401 getCurrentSectionData()->setAlignment(ByteAlignment);
404 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
405 unsigned MaxBytesToEmit) {
406 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
408 if (MaxBytesToEmit == 0)
409 MaxBytesToEmit = ByteAlignment;
410 MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
411 getCurrentSectionData());
412 F->setEmitNops(true);
414 // Update the maximum alignment on the current section if necessary.
415 if (ByteAlignment > getCurrentSectionData()->getAlignment())
416 getCurrentSectionData()->setAlignment(ByteAlignment);
419 void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
420 unsigned char Value) {
421 // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
423 new MCOrgFragment(*Offset, Value, getCurrentSectionData());
426 // Add a symbol for the file name of this module. This is the second
427 // entry in the module's symbol table (the first being the null symbol).
428 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
429 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
430 Symbol->setSection(*CurSection);
431 Symbol->setAbsolute();
433 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
435 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
438 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
439 MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
441 // Add the fixups and data.
443 // FIXME: Revisit this design decision when relaxation is done, we may be
444 // able to get away with not storing any extra data in the MCInst.
445 SmallVector<MCFixup, 4> Fixups;
446 SmallString<256> Code;
447 raw_svector_ostream VecOS(Code);
448 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
451 IF->getCode() = Code;
452 IF->getFixups() = Fixups;
455 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
456 MCDataFragment *DF = getOrCreateDataFragment();
458 SmallVector<MCFixup, 4> Fixups;
459 SmallString<256> Code;
460 raw_svector_ostream VecOS(Code);
461 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
464 // Add the fixups and data.
465 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
466 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
467 DF->addFixup(Fixups[i]);
469 DF->getContents().append(Code.begin(), Code.end());
472 void MCELFStreamer::EmitInstruction(const MCInst &Inst) {
474 for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
475 if (Inst.getOperand(i).isExpr())
476 AddValueSymbols(Inst.getOperand(i).getExpr());
478 getCurrentSectionData()->setHasInstructions(true);
480 // If this instruction doesn't need relaxation, just emit it as data.
481 if (!getAssembler().getBackend().MayNeedRelaxation(Inst)) {
482 EmitInstToData(Inst);
486 // Otherwise, if we are relaxing everything, relax the instruction as much as
487 // possible and emit it as data.
488 if (getAssembler().getRelaxAll()) {
490 getAssembler().getBackend().RelaxInstruction(Inst, Relaxed);
491 while (getAssembler().getBackend().MayNeedRelaxation(Relaxed))
492 getAssembler().getBackend().RelaxInstruction(Relaxed, Relaxed);
493 EmitInstToData(Relaxed);
497 // Otherwise emit to a separate fragment.
498 EmitInstToFragment(Inst);
501 void MCELFStreamer::Finish() {
502 // FIXME: We create more atoms than it is necessary. Some relocations to
503 // merge sections can be implemented with section address + offset,
504 // figure out which ones and why.
506 // First, scan the symbol table to build a lookup table from fragments to
508 DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
509 for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
510 ie = getAssembler().symbol_end(); it != ie; ++it) {
511 if (isSymbolLinkerVisible(getAssembler(), *it) &&
513 // An atom defining symbol should never be internal to a fragment.
514 assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
515 DefiningSymbolMap[it->getFragment()] = it;
519 // Set the fragment atom associations by tracking the last seen atom defining
521 for (MCAssembler::iterator it = getAssembler().begin(),
522 ie = getAssembler().end(); it != ie; ++it) {
523 MCSymbolData *CurrentAtom = 0;
524 for (MCSectionData::iterator it2 = it->begin(),
525 ie2 = it->end(); it2 != ie2; ++it2) {
526 if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
528 it2->setAtom(CurrentAtom);
532 this->MCObjectStreamer::Finish();
535 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
536 raw_ostream &OS, MCCodeEmitter *CE,
538 MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
540 S->getAssembler().setRelaxAll(true);