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/MC/MCValue.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ELF.h"
30 #include "llvm/Support/ErrorHandling.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include "llvm/Target/TargetAsmBackend.h"
38 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
39 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
40 Binding == ELF::STB_WEAK);
41 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
42 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
45 static unsigned GetBinding(const MCSymbolData &SD) {
46 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
47 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
48 Binding == ELF::STB_WEAK);
52 static void SetType(MCSymbolData &SD, unsigned Type) {
53 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
54 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
55 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
56 Type == ELF::STT_TLS);
58 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
59 SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
62 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
63 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
64 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
66 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
67 SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
70 class MCELFStreamer : public MCObjectStreamer {
72 MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
73 raw_ostream &OS, MCCodeEmitter *Emitter)
74 : MCObjectStreamer(Context, TAB, OS, Emitter, false) {}
78 /// @name MCStreamer Interface
81 virtual void InitSections();
82 virtual void EmitLabel(MCSymbol *Symbol);
83 virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
84 virtual void EmitThumbFunc(MCSymbol *Func);
85 virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
86 virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
87 virtual void SwitchSection(const MCSection *Section);
88 virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
89 virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
90 assert(0 && "ELF doesn't support this directive");
92 virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
93 unsigned ByteAlignment);
94 virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
95 assert(0 && "ELF doesn't support this directive");
98 virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
99 assert(0 && "ELF doesn't support this directive");
102 virtual void EmitCOFFSymbolType(int Type) {
103 assert(0 && "ELF doesn't support this directive");
106 virtual void EndCOFFSymbolDef() {
107 assert(0 && "ELF doesn't support this directive");
110 virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
111 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
115 virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
116 assert(0 && "ELF doesn't support this directive");
118 virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
119 unsigned Size = 0, unsigned ByteAlignment = 0) {
120 assert(0 && "ELF doesn't support this directive");
122 virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
123 uint64_t Size, unsigned ByteAlignment = 0) {
124 assert(0 && "ELF doesn't support this directive");
126 virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
127 virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
128 virtual void EmitGPRel32Value(const MCExpr *Value) {
129 assert(0 && "ELF doesn't support this directive");
131 virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
132 unsigned ValueSize = 1,
133 unsigned MaxBytesToEmit = 0);
134 virtual void EmitCodeAlignment(unsigned ByteAlignment,
135 unsigned MaxBytesToEmit = 0);
136 virtual void EmitValueToOffset(const MCExpr *Offset,
137 unsigned char Value = 0);
139 virtual void EmitFileDirective(StringRef Filename);
141 virtual void Finish();
144 virtual void EmitInstToFragment(const MCInst &Inst);
145 virtual void EmitInstToData(const MCInst &Inst);
147 void fixSymbolsInTLSFixups(const MCExpr *expr);
152 unsigned ByteAlignment;
154 std::vector<LocalCommon> LocalCommons;
156 SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
158 void SetSection(StringRef Section, unsigned Type, unsigned Flags,
160 SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
163 void SetSectionData() {
164 SetSection(".data", MCSectionELF::SHT_PROGBITS,
165 MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
166 SectionKind::getDataRel());
167 EmitCodeAlignment(4, 0);
169 void SetSectionText() {
170 SetSection(".text", MCSectionELF::SHT_PROGBITS,
171 MCSectionELF::SHF_EXECINSTR |
172 MCSectionELF::SHF_ALLOC, SectionKind::getText());
173 EmitCodeAlignment(4, 0);
175 void SetSectionBss() {
176 SetSection(".bss", MCSectionELF::SHT_NOBITS,
177 MCSectionELF::SHF_WRITE |
178 MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
179 EmitCodeAlignment(4, 0);
183 } // end anonymous namespace.
185 void MCELFStreamer::InitSections() {
186 // This emulates the same behavior of GNU as. This makes it easier
187 // to compare the output as the major sections are in the same order.
194 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
195 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
197 Symbol->setSection(*CurSection);
199 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
201 const MCSectionELF &Section =
202 static_cast<const MCSectionELF&>(Symbol->getSection());
203 if (Section.getFlags() & MCSectionELF::SHF_TLS)
204 SetType(SD, ELF::STT_TLS);
206 // FIXME: This is wasteful, we don't necessarily need to create a data
207 // fragment. Instead, we should mark the symbol as pointing into the data
208 // fragment if it exists, otherwise we should just queue the label and set its
209 // fragment pointer when we emit the next fragment.
210 MCDataFragment *F = getOrCreateDataFragment();
212 assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
214 SD.setOffset(F->getContents().size());
217 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
219 case MCAF_SyntaxUnified: return; // no-op here.
220 case MCAF_Code16: return; // no-op here.
221 case MCAF_Code32: return; // no-op here.
222 case MCAF_SubsectionsViaSymbols:
223 getAssembler().setSubsectionsViaSymbols(true);
227 assert(0 && "invalid assembler flag!");
230 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
231 // FIXME: Anything needed here to flag the function as thumb?
234 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
235 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
237 // FIXME: Lift context changes into super class.
238 getAssembler().getOrCreateSymbolData(*Symbol);
239 Symbol->setVariableValue(AddValueSymbols(Value));
242 void MCELFStreamer::SwitchSection(const MCSection *Section) {
243 const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
245 getAssembler().getOrCreateSymbolData(*Grp);
246 this->MCObjectStreamer::SwitchSection(Section);
249 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
250 getAssembler().getOrCreateSymbolData(*Symbol);
251 MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
252 AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
253 const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
254 Alias->setVariableValue(Value);
257 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
258 MCSymbolAttr Attribute) {
259 // Indirect symbols are handled differently, to match how 'as' handles
260 // them. This makes writing matching .o files easier.
261 if (Attribute == MCSA_IndirectSymbol) {
262 // Note that we intentionally cannot use the symbol data here; this is
263 // important for matching the string table that 'as' generates.
264 IndirectSymbolData ISD;
266 ISD.SectionData = getCurrentSectionData();
267 getAssembler().getIndirectSymbols().push_back(ISD);
271 // Adding a symbol attribute always introduces the symbol, note that an
272 // important side effect of calling getOrCreateSymbolData here is to register
273 // the symbol with the assembler.
274 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
276 // The implementation of symbol attributes is designed to match 'as', but it
277 // leaves much to desired. It doesn't really make sense to arbitrarily add and
278 // remove flags, but 'as' allows this (in particular, see .desc).
280 // In the future it might be worth trying to make these operations more well
283 case MCSA_LazyReference:
285 case MCSA_NoDeadStrip:
286 case MCSA_SymbolResolver:
287 case MCSA_PrivateExtern:
288 case MCSA_WeakDefinition:
289 case MCSA_WeakDefAutoPrivate:
291 case MCSA_ELF_TypeIndFunction:
292 case MCSA_IndirectSymbol:
293 assert(0 && "Invalid symbol attribute for ELF!");
296 case MCSA_ELF_TypeGnuUniqueObject:
301 SetBinding(SD, ELF::STB_GLOBAL);
302 SD.setExternal(true);
303 BindingExplicitlySet.insert(Symbol);
306 case MCSA_WeakReference:
308 SetBinding(SD, ELF::STB_WEAK);
309 SD.setExternal(true);
310 BindingExplicitlySet.insert(Symbol);
314 SetBinding(SD, ELF::STB_LOCAL);
315 SD.setExternal(false);
316 BindingExplicitlySet.insert(Symbol);
319 case MCSA_ELF_TypeFunction:
320 SetType(SD, ELF::STT_FUNC);
323 case MCSA_ELF_TypeObject:
324 SetType(SD, ELF::STT_OBJECT);
327 case MCSA_ELF_TypeTLS:
328 SetType(SD, ELF::STT_TLS);
331 case MCSA_ELF_TypeCommon:
332 SetType(SD, ELF::STT_COMMON);
335 case MCSA_ELF_TypeNoType:
336 SetType(SD, ELF::STT_NOTYPE);
340 SetVisibility(SD, ELF::STV_PROTECTED);
344 SetVisibility(SD, ELF::STV_HIDDEN);
348 SetVisibility(SD, ELF::STV_INTERNAL);
353 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
354 unsigned ByteAlignment) {
355 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
357 if (!BindingExplicitlySet.count(Symbol)) {
358 SetBinding(SD, ELF::STB_GLOBAL);
359 SD.setExternal(true);
362 SetType(SD, ELF::STT_OBJECT);
364 if (GetBinding(SD) == ELF_STB_Local) {
365 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
366 MCSectionELF::SHT_NOBITS,
367 MCSectionELF::SHF_WRITE |
368 MCSectionELF::SHF_ALLOC,
369 SectionKind::getBSS());
370 Symbol->setSection(*Section);
372 struct LocalCommon L = {&SD, Size, ByteAlignment};
373 LocalCommons.push_back(L);
375 SD.setCommon(Size, ByteAlignment);
378 SD.setSize(MCConstantExpr::Create(Size, getContext()));
381 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
382 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
384 getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
387 void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
388 unsigned AddrSpace) {
389 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
391 MCDataFragment *DF = getOrCreateDataFragment();
393 // Avoid fixups when possible.
395 if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
396 // FIXME: Endianness assumption.
397 for (unsigned i = 0; i != Size; ++i)
398 DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
400 DF->addFixup(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
401 MCFixup::getKindForSize(Size)));
402 DF->getContents().resize(DF->getContents().size() + Size, 0);
406 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
407 int64_t Value, unsigned ValueSize,
408 unsigned MaxBytesToEmit) {
409 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
411 if (MaxBytesToEmit == 0)
412 MaxBytesToEmit = ByteAlignment;
413 new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
414 getCurrentSectionData());
416 // Update the maximum alignment on the current section if necessary.
417 if (ByteAlignment > getCurrentSectionData()->getAlignment())
418 getCurrentSectionData()->setAlignment(ByteAlignment);
421 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
422 unsigned MaxBytesToEmit) {
423 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
425 if (MaxBytesToEmit == 0)
426 MaxBytesToEmit = ByteAlignment;
427 MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
428 getCurrentSectionData());
429 F->setEmitNops(true);
431 // Update the maximum alignment on the current section if necessary.
432 if (ByteAlignment > getCurrentSectionData()->getAlignment())
433 getCurrentSectionData()->setAlignment(ByteAlignment);
436 void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
437 unsigned char Value) {
438 // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
440 new MCOrgFragment(*Offset, Value, getCurrentSectionData());
443 // Add a symbol for the file name of this module. This is the second
444 // entry in the module's symbol table (the first being the null symbol).
445 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
446 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
447 Symbol->setSection(*CurSection);
448 Symbol->setAbsolute();
450 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
452 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
455 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
456 switch (expr->getKind()) {
457 case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
458 case MCExpr::Constant:
461 case MCExpr::Binary: {
462 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
463 fixSymbolsInTLSFixups(be->getLHS());
464 fixSymbolsInTLSFixups(be->getRHS());
468 case MCExpr::SymbolRef: {
469 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
470 MCSymbolRefExpr::VariantKind kind = symRef.getKind();
471 if (kind != MCSymbolRefExpr::VK_TLSGD &&
472 kind != MCSymbolRefExpr::VK_TLSLD &&
473 kind != MCSymbolRefExpr::VK_TLSLDM &&
474 kind != MCSymbolRefExpr::VK_ARM_TLSGD)
476 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
477 SetType(SD, ELF::STT_TLS);
482 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
487 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
488 MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
490 // Add the fixups and data.
492 // FIXME: Revisit this design decision when relaxation is done, we may be
493 // able to get away with not storing any extra data in the MCInst.
494 SmallVector<MCFixup, 4> Fixups;
495 SmallString<256> Code;
496 raw_svector_ostream VecOS(Code);
497 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
500 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
501 fixSymbolsInTLSFixups(Fixups[i].getValue());
503 IF->getCode() = Code;
504 IF->getFixups() = Fixups;
507 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
508 MCDataFragment *DF = getOrCreateDataFragment();
510 SmallVector<MCFixup, 4> Fixups;
511 SmallString<256> Code;
512 raw_svector_ostream VecOS(Code);
513 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
516 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
517 fixSymbolsInTLSFixups(Fixups[i].getValue());
519 // Add the fixups and data.
520 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
521 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
522 DF->addFixup(Fixups[i]);
524 DF->getContents().append(Code.begin(), Code.end());
527 void MCELFStreamer::Finish() {
528 // FIXME: duplicated code with the MachO streamer.
529 // Dump out the dwarf file & directory tables and line tables.
530 if (getContext().hasDwarfFiles()) {
531 const MCSection *DwarfLineSection =
532 getContext().getELFSection(".debug_line", 0, 0,
533 SectionKind::getDataRelLocal());
535 getAssembler().getOrCreateSectionData(*DwarfLineSection);
536 int PointerSize = getAssembler().getBackend().getPointerSize();
537 MCDwarfFileTable::Emit(this, DwarfLineSection, &DLS, PointerSize);
540 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
541 e = LocalCommons.end();
543 MCSymbolData *SD = i->SD;
544 uint64_t Size = i->Size;
545 unsigned ByteAlignment = i->ByteAlignment;
546 const MCSymbol &Symbol = SD->getSymbol();
547 const MCSection &Section = Symbol.getSection();
549 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
550 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
552 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
555 // Update the maximum alignment of the section if necessary.
556 if (ByteAlignment > SectData.getAlignment())
557 SectData.setAlignment(ByteAlignment);
560 this->MCObjectStreamer::Finish();
563 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
564 raw_ostream &OS, MCCodeEmitter *CE,
566 MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
568 S->getAssembler().setRelaxAll(true);