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 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
153 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
155 // FIXME: This is wasteful, we don't necessarily need to create a data
156 // fragment. Instead, we should mark the symbol as pointing into the data
157 // fragment if it exists, otherwise we should just queue the label and set its
158 // fragment pointer when we emit the next fragment.
159 MCDataFragment *F = getOrCreateDataFragment();
160 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
161 assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
163 SD.setOffset(F->getContents().size());
165 Symbol->setSection(*CurSection);
168 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
170 case MCAF_SubsectionsViaSymbols:
171 getAssembler().setSubsectionsViaSymbols(true);
175 assert(0 && "invalid assembler flag!");
178 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
179 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
181 // FIXME: Lift context changes into super class.
182 getAssembler().getOrCreateSymbolData(*Symbol);
183 Symbol->setVariableValue(AddValueSymbols(Value));
186 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
187 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
188 Binding == ELF::STB_WEAK);
189 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
190 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
193 static unsigned GetBinding(const MCSymbolData &SD) {
194 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
195 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
196 Binding == ELF::STB_WEAK);
200 static void SetType(MCSymbolData &SD, unsigned Type) {
201 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
202 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
203 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
204 Type == ELF::STT_TLS);
206 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
207 SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
210 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
211 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
212 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
214 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
215 SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
218 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
219 MCSymbolAttr Attribute) {
220 // Indirect symbols are handled differently, to match how 'as' handles
221 // them. This makes writing matching .o files easier.
222 if (Attribute == MCSA_IndirectSymbol) {
223 // Note that we intentionally cannot use the symbol data here; this is
224 // important for matching the string table that 'as' generates.
225 IndirectSymbolData ISD;
227 ISD.SectionData = getCurrentSectionData();
228 getAssembler().getIndirectSymbols().push_back(ISD);
232 // Adding a symbol attribute always introduces the symbol, note that an
233 // important side effect of calling getOrCreateSymbolData here is to register
234 // the symbol with the assembler.
235 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
237 // The implementation of symbol attributes is designed to match 'as', but it
238 // leaves much to desired. It doesn't really make sense to arbitrarily add and
239 // remove flags, but 'as' allows this (in particular, see .desc).
241 // In the future it might be worth trying to make these operations more well
244 case MCSA_LazyReference:
246 case MCSA_NoDeadStrip:
247 case MCSA_PrivateExtern:
248 case MCSA_WeakDefinition:
249 case MCSA_WeakDefAutoPrivate:
251 case MCSA_ELF_TypeIndFunction:
252 case MCSA_IndirectSymbol:
253 assert(0 && "Invalid symbol attribute for ELF!");
257 SetBinding(SD, ELF::STB_GLOBAL);
258 SD.setExternal(true);
259 BindingExplicitlySet.insert(Symbol);
262 case MCSA_WeakReference:
264 SetBinding(SD, ELF::STB_WEAK);
265 BindingExplicitlySet.insert(Symbol);
269 SetBinding(SD, ELF::STB_LOCAL);
270 SD.setExternal(false);
271 BindingExplicitlySet.insert(Symbol);
274 case MCSA_ELF_TypeFunction:
275 SetType(SD, ELF::STT_FUNC);
278 case MCSA_ELF_TypeObject:
279 SetType(SD, ELF::STT_OBJECT);
282 case MCSA_ELF_TypeTLS:
283 SetType(SD, ELF::STT_TLS);
286 case MCSA_ELF_TypeCommon:
287 SetType(SD, ELF::STT_COMMON);
290 case MCSA_ELF_TypeNoType:
291 SetType(SD, ELF::STT_NOTYPE);
295 SetVisibility(SD, ELF::STV_PROTECTED);
299 SetVisibility(SD, ELF::STV_HIDDEN);
303 SetVisibility(SD, ELF::STV_INTERNAL);
308 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
309 unsigned ByteAlignment) {
310 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
312 if (!BindingExplicitlySet.count(Symbol)) {
313 SetBinding(SD, ELF::STB_GLOBAL);
314 SD.setExternal(true);
317 if (GetBinding(SD) == ELF_STB_Local) {
318 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
319 MCSectionELF::SHT_NOBITS,
320 MCSectionELF::SHF_WRITE |
321 MCSectionELF::SHF_ALLOC,
322 SectionKind::getBSS());
324 MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
325 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
327 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
329 Symbol->setSection(*Section);
331 // Update the maximum alignment of the section if necessary.
332 if (ByteAlignment > SectData.getAlignment())
333 SectData.setAlignment(ByteAlignment);
335 SD.setCommon(Size, ByteAlignment);
338 SD.setSize(MCConstantExpr::Create(Size, getContext()));
341 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
342 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
344 getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
347 void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
348 unsigned AddrSpace) {
349 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
351 MCDataFragment *DF = getOrCreateDataFragment();
353 // Avoid fixups when possible.
355 if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
356 // FIXME: Endianness assumption.
357 for (unsigned i = 0; i != Size; ++i)
358 DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
360 DF->addFixup(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
361 MCFixup::getKindForSize(Size)));
362 DF->getContents().resize(DF->getContents().size() + Size, 0);
366 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
367 int64_t Value, unsigned ValueSize,
368 unsigned MaxBytesToEmit) {
369 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
371 if (MaxBytesToEmit == 0)
372 MaxBytesToEmit = ByteAlignment;
373 new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
374 getCurrentSectionData());
376 // Update the maximum alignment on the current section if necessary.
377 if (ByteAlignment > getCurrentSectionData()->getAlignment())
378 getCurrentSectionData()->setAlignment(ByteAlignment);
381 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
382 unsigned MaxBytesToEmit) {
383 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
385 if (MaxBytesToEmit == 0)
386 MaxBytesToEmit = ByteAlignment;
387 MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
388 getCurrentSectionData());
389 F->setEmitNops(true);
391 // Update the maximum alignment on the current section if necessary.
392 if (ByteAlignment > getCurrentSectionData()->getAlignment())
393 getCurrentSectionData()->setAlignment(ByteAlignment);
396 void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
397 unsigned char Value) {
398 // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
400 new MCOrgFragment(*Offset, Value, getCurrentSectionData());
403 // Add a symbol for the file name of this module. This is the second
404 // entry in the module's symbol table (the first being the null symbol).
405 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
406 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
407 Symbol->setSection(*CurSection);
408 Symbol->setAbsolute();
410 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
412 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
415 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
416 MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
418 // Add the fixups and data.
420 // FIXME: Revisit this design decision when relaxation is done, we may be
421 // able to get away with not storing any extra data in the MCInst.
422 SmallVector<MCFixup, 4> Fixups;
423 SmallString<256> Code;
424 raw_svector_ostream VecOS(Code);
425 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
428 IF->getCode() = Code;
429 IF->getFixups() = Fixups;
432 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
433 MCDataFragment *DF = getOrCreateDataFragment();
435 SmallVector<MCFixup, 4> Fixups;
436 SmallString<256> Code;
437 raw_svector_ostream VecOS(Code);
438 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
441 // Add the fixups and data.
442 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
443 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
444 DF->addFixup(Fixups[i]);
446 DF->getContents().append(Code.begin(), Code.end());
449 void MCELFStreamer::EmitInstruction(const MCInst &Inst) {
451 for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
452 if (Inst.getOperand(i).isExpr())
453 AddValueSymbols(Inst.getOperand(i).getExpr());
455 getCurrentSectionData()->setHasInstructions(true);
457 // If this instruction doesn't need relaxation, just emit it as data.
458 if (!getAssembler().getBackend().MayNeedRelaxation(Inst)) {
459 EmitInstToData(Inst);
463 // Otherwise, if we are relaxing everything, relax the instruction as much as
464 // possible and emit it as data.
465 if (getAssembler().getRelaxAll()) {
467 getAssembler().getBackend().RelaxInstruction(Inst, Relaxed);
468 while (getAssembler().getBackend().MayNeedRelaxation(Relaxed))
469 getAssembler().getBackend().RelaxInstruction(Relaxed, Relaxed);
470 EmitInstToData(Relaxed);
474 // Otherwise emit to a separate fragment.
475 EmitInstToFragment(Inst);
478 void MCELFStreamer::Finish() {
479 getAssembler().Finish();
482 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
483 raw_ostream &OS, MCCodeEmitter *CE,
485 MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
487 S->getAssembler().setRelaxAll(true);