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/MCELFStreamer.h"
15 #include "llvm/ADT/STLExtras.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/MC/MCAsmBackend.h"
18 #include "llvm/MC/MCAsmInfo.h"
19 #include "llvm/MC/MCAssembler.h"
20 #include "llvm/MC/MCCodeEmitter.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCELF.h"
23 #include "llvm/MC/MCELFSymbolFlags.h"
24 #include "llvm/MC/MCExpr.h"
25 #include "llvm/MC/MCInst.h"
26 #include "llvm/MC/MCObjectFileInfo.h"
27 #include "llvm/MC/MCObjectStreamer.h"
28 #include "llvm/MC/MCSection.h"
29 #include "llvm/MC/MCSectionELF.h"
30 #include "llvm/MC/MCSymbol.h"
31 #include "llvm/MC/MCValue.h"
32 #include "llvm/Support/Debug.h"
33 #include "llvm/Support/ELF.h"
34 #include "llvm/Support/ErrorHandling.h"
35 #include "llvm/Support/raw_ostream.h"
39 MCELFStreamer::~MCELFStreamer() {
42 void MCELFStreamer::InitSections(bool NoExecStack) {
43 // This emulates the same behavior of GNU as. This makes it easier
44 // to compare the output as the major sections are in the same order.
45 MCContext &Ctx = getContext();
46 SwitchSection(Ctx.getObjectFileInfo()->getTextSection());
49 SwitchSection(Ctx.getObjectFileInfo()->getDataSection());
52 SwitchSection(Ctx.getObjectFileInfo()->getBSSSection());
55 SwitchSection(Ctx.getObjectFileInfo()->getTextSection());
58 SwitchSection(Ctx.getAsmInfo()->getNonexecutableStackSection(Ctx));
61 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
62 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
64 MCObjectStreamer::EmitLabel(Symbol);
66 const MCSectionELF &Section =
67 static_cast<const MCSectionELF&>(Symbol->getSection());
68 MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
69 if (Section.getFlags() & ELF::SHF_TLS)
70 MCELF::SetType(SD, ELF::STT_TLS);
73 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
74 // Let the target do whatever target specific stuff it needs to do.
75 getAssembler().getBackend().handleAssemblerFlag(Flag);
76 // Do any generic stuff we need to do.
78 case MCAF_SyntaxUnified: return; // no-op here.
79 case MCAF_Code16: return; // Change parsing mode; no-op here.
80 case MCAF_Code32: return; // Change parsing mode; no-op here.
81 case MCAF_Code64: return; // Change parsing mode; no-op here.
82 case MCAF_SubsectionsViaSymbols:
83 getAssembler().setSubsectionsViaSymbols(true);
87 llvm_unreachable("invalid assembler flag!");
90 void MCELFStreamer::ChangeSection(const MCSection *Section,
91 const MCExpr *Subsection) {
92 MCSectionData *CurSection = getCurrentSectionData();
93 if (CurSection && CurSection->isBundleLocked())
94 report_fatal_error("Unterminated .bundle_lock when changing a section");
96 MCAssembler &Asm = getAssembler();
97 auto *SectionELF = static_cast<const MCSectionELF *>(Section);
98 const MCSymbol *Grp = SectionELF->getGroup();
100 Asm.getOrCreateSymbolData(*Grp);
102 this->MCObjectStreamer::ChangeSection(Section, Subsection);
103 MCSymbol *SectionSymbol = getContext().getOrCreateSectionSymbol(*SectionELF);
104 if (SectionSymbol->isUndefined()) {
105 EmitLabel(SectionSymbol);
106 MCELF::SetType(Asm.getSymbolData(*SectionSymbol), ELF::STT_SECTION);
110 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
111 getAssembler().getOrCreateSymbolData(*Symbol);
112 const MCExpr *Value = MCSymbolRefExpr::Create(
113 Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
114 Alias->setVariableValue(Value);
117 // When GNU as encounters more than one .type declaration for an object it seems
118 // to use a mechanism similar to the one below to decide which type is actually
119 // used in the object file. The greater of T1 and T2 is selected based on the
120 // following ordering:
121 // STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
122 // If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
124 static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
125 for (unsigned Type : {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
126 ELF::STT_GNU_IFUNC, ELF::STT_TLS}) {
136 bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
137 MCSymbolAttr Attribute) {
138 // Indirect symbols are handled differently, to match how 'as' handles
139 // them. This makes writing matching .o files easier.
140 if (Attribute == MCSA_IndirectSymbol) {
141 // Note that we intentionally cannot use the symbol data here; this is
142 // important for matching the string table that 'as' generates.
143 IndirectSymbolData ISD;
145 ISD.SectionData = getCurrentSectionData();
146 getAssembler().getIndirectSymbols().push_back(ISD);
150 // Adding a symbol attribute always introduces the symbol, note that an
151 // important side effect of calling getOrCreateSymbolData here is to register
152 // the symbol with the assembler.
153 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
155 // The implementation of symbol attributes is designed to match 'as', but it
156 // leaves much to desired. It doesn't really make sense to arbitrarily add and
157 // remove flags, but 'as' allows this (in particular, see .desc).
159 // In the future it might be worth trying to make these operations more well
162 case MCSA_LazyReference:
164 case MCSA_SymbolResolver:
165 case MCSA_PrivateExtern:
166 case MCSA_WeakDefinition:
167 case MCSA_WeakDefAutoPrivate:
169 case MCSA_IndirectSymbol:
172 case MCSA_NoDeadStrip:
176 case MCSA_ELF_TypeGnuUniqueObject:
177 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD), ELF::STT_OBJECT));
178 MCELF::SetBinding(SD, ELF::STB_GNU_UNIQUE);
179 SD.setExternal(true);
180 BindingExplicitlySet.insert(Symbol);
184 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
185 SD.setExternal(true);
186 BindingExplicitlySet.insert(Symbol);
189 case MCSA_WeakReference:
191 MCELF::SetBinding(SD, ELF::STB_WEAK);
192 SD.setExternal(true);
193 BindingExplicitlySet.insert(Symbol);
197 MCELF::SetBinding(SD, ELF::STB_LOCAL);
198 SD.setExternal(false);
199 BindingExplicitlySet.insert(Symbol);
202 case MCSA_ELF_TypeFunction:
203 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
207 case MCSA_ELF_TypeIndFunction:
208 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
209 ELF::STT_GNU_IFUNC));
212 case MCSA_ELF_TypeObject:
213 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
217 case MCSA_ELF_TypeTLS:
218 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
222 case MCSA_ELF_TypeCommon:
223 // TODO: Emit these as a common symbol.
224 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
228 case MCSA_ELF_TypeNoType:
229 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
234 MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
238 MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
242 MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
249 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
250 unsigned ByteAlignment) {
251 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
253 if (!BindingExplicitlySet.count(Symbol)) {
254 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
255 SD.setExternal(true);
258 MCELF::SetType(SD, ELF::STT_OBJECT);
260 if (MCELF::GetBinding(SD) == ELF_STB_Local) {
261 const MCSection *Section = getAssembler().getContext().getELFSection(
262 ".bss", ELF::SHT_NOBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
264 AssignSection(Symbol, Section);
266 struct LocalCommon L = {&SD, Size, ByteAlignment};
267 LocalCommons.push_back(L);
269 SD.setCommon(Size, ByteAlignment);
272 SD.setSize(MCConstantExpr::Create(Size, getContext()));
275 void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
276 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
280 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
281 unsigned ByteAlignment) {
282 // FIXME: Should this be caught and done earlier?
283 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
284 MCELF::SetBinding(SD, ELF::STB_LOCAL);
285 SD.setExternal(false);
286 BindingExplicitlySet.insert(Symbol);
287 EmitCommonSymbol(Symbol, Size, ByteAlignment);
290 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
292 if (getCurrentSectionData()->isBundleLocked())
293 report_fatal_error("Emitting values inside a locked bundle is forbidden");
294 fixSymbolsInTLSFixups(Value);
295 MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
298 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
301 unsigned MaxBytesToEmit) {
302 if (getCurrentSectionData()->isBundleLocked())
303 report_fatal_error("Emitting values inside a locked bundle is forbidden");
304 MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
305 ValueSize, MaxBytesToEmit);
308 // Add a symbol for the file name of this module. They start after the
309 // null symbol and don't count as normal symbol, i.e. a non-STT_FILE symbol
310 // with the same name may appear.
311 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
312 getAssembler().addFileName(Filename);
315 void MCELFStreamer::EmitIdent(StringRef IdentString) {
316 const MCSection *Comment = getAssembler().getContext().getELFSection(
317 ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
319 SwitchSection(Comment);
324 EmitBytes(IdentString);
329 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
330 switch (expr->getKind()) {
332 cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
334 case MCExpr::Constant:
337 case MCExpr::Binary: {
338 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
339 fixSymbolsInTLSFixups(be->getLHS());
340 fixSymbolsInTLSFixups(be->getRHS());
344 case MCExpr::SymbolRef: {
345 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
346 switch (symRef.getKind()) {
349 case MCSymbolRefExpr::VK_GOTTPOFF:
350 case MCSymbolRefExpr::VK_INDNTPOFF:
351 case MCSymbolRefExpr::VK_NTPOFF:
352 case MCSymbolRefExpr::VK_GOTNTPOFF:
353 case MCSymbolRefExpr::VK_TLSGD:
354 case MCSymbolRefExpr::VK_TLSLD:
355 case MCSymbolRefExpr::VK_TLSLDM:
356 case MCSymbolRefExpr::VK_TPOFF:
357 case MCSymbolRefExpr::VK_DTPOFF:
358 case MCSymbolRefExpr::VK_Mips_TLSGD:
359 case MCSymbolRefExpr::VK_Mips_GOTTPREL:
360 case MCSymbolRefExpr::VK_Mips_TPREL_HI:
361 case MCSymbolRefExpr::VK_Mips_TPREL_LO:
362 case MCSymbolRefExpr::VK_PPC_DTPMOD:
363 case MCSymbolRefExpr::VK_PPC_TPREL:
364 case MCSymbolRefExpr::VK_PPC_TPREL_LO:
365 case MCSymbolRefExpr::VK_PPC_TPREL_HI:
366 case MCSymbolRefExpr::VK_PPC_TPREL_HA:
367 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
368 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
369 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
370 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
371 case MCSymbolRefExpr::VK_PPC_DTPREL:
372 case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
373 case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
374 case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
375 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
376 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
377 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
378 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
379 case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
380 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
381 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
382 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
383 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
384 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
385 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
386 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
387 case MCSymbolRefExpr::VK_PPC_TLS:
388 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
389 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
390 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
391 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
392 case MCSymbolRefExpr::VK_PPC_TLSGD:
393 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
394 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
395 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
396 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
397 case MCSymbolRefExpr::VK_PPC_TLSLD:
400 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
401 MCELF::SetType(SD, ELF::STT_TLS);
406 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
411 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst,
412 const MCSubtargetInfo &STI) {
413 this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
414 MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
416 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
417 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
420 void MCELFStreamer::EmitInstToData(const MCInst &Inst,
421 const MCSubtargetInfo &STI) {
422 MCAssembler &Assembler = getAssembler();
423 SmallVector<MCFixup, 4> Fixups;
424 SmallString<256> Code;
425 raw_svector_ostream VecOS(Code);
426 Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
429 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
430 fixSymbolsInTLSFixups(Fixups[i].getValue());
432 // There are several possibilities here:
434 // If bundling is disabled, append the encoded instruction to the current data
435 // fragment (or create a new such fragment if the current fragment is not a
438 // If bundling is enabled:
439 // - If we're not in a bundle-locked group, emit the instruction into a
440 // fragment of its own. If there are no fixups registered for the
441 // instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
443 // - If we're in a bundle-locked group, append the instruction to the current
444 // data fragment because we want all the instructions in a group to get into
445 // the same fragment. Be careful not to do that for the first instruction in
446 // the group, though.
449 if (Assembler.isBundlingEnabled()) {
450 MCSectionData *SD = getCurrentSectionData();
451 if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
452 // If we are bundle-locked, we re-use the current fragment.
453 // The bundle-locking directive ensures this is a new data fragment.
454 DF = cast<MCDataFragment>(getCurrentFragment());
455 else if (!SD->isBundleLocked() && Fixups.size() == 0) {
456 // Optimize memory usage by emitting the instruction to a
457 // MCCompactEncodedInstFragment when not in a bundle-locked group and
458 // there are no fixups registered.
459 MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
461 CEIF->getContents().append(Code.begin(), Code.end());
464 DF = new MCDataFragment();
467 if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
468 // If this fragment is for a group marked "align_to_end", set a flag
469 // in the fragment. This can happen after the fragment has already been
470 // created if there are nested bundle_align groups and an inner one
471 // is the one marked align_to_end.
472 DF->setAlignToBundleEnd(true);
475 // We're now emitting an instruction in a bundle group, so this flag has
477 SD->setBundleGroupBeforeFirstInst(false);
479 DF = getOrCreateDataFragment();
482 // Add the fixups and data.
483 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
484 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
485 DF->getFixups().push_back(Fixups[i]);
487 DF->setHasInstructions(true);
488 DF->getContents().append(Code.begin(), Code.end());
491 void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
492 assert(AlignPow2 <= 30 && "Invalid bundle alignment");
493 MCAssembler &Assembler = getAssembler();
494 if (AlignPow2 > 0 && (Assembler.getBundleAlignSize() == 0 ||
495 Assembler.getBundleAlignSize() == 1U << AlignPow2))
496 Assembler.setBundleAlignSize(1U << AlignPow2);
498 report_fatal_error(".bundle_align_mode cannot be changed once set");
501 void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
502 MCSectionData *SD = getCurrentSectionData();
506 if (!getAssembler().isBundlingEnabled())
507 report_fatal_error(".bundle_lock forbidden when bundling is disabled");
509 if (!SD->isBundleLocked())
510 SD->setBundleGroupBeforeFirstInst(true);
512 SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
513 MCSectionData::BundleLocked);
516 void MCELFStreamer::EmitBundleUnlock() {
517 MCSectionData *SD = getCurrentSectionData();
520 if (!getAssembler().isBundlingEnabled())
521 report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
522 else if (!SD->isBundleLocked())
523 report_fatal_error(".bundle_unlock without matching lock");
524 else if (SD->isBundleGroupBeforeFirstInst())
525 report_fatal_error("Empty bundle-locked group is forbidden");
527 SD->setBundleLockState(MCSectionData::NotBundleLocked);
530 void MCELFStreamer::Flush() {
531 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
532 e = LocalCommons.end();
534 MCSymbolData *SD = i->SD;
535 uint64_t Size = i->Size;
536 unsigned ByteAlignment = i->ByteAlignment;
537 const MCSymbol &Symbol = SD->getSymbol();
538 const MCSection &Section = Symbol.getSection();
540 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
541 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
543 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
546 // Update the maximum alignment of the section if necessary.
547 if (ByteAlignment > SectData.getAlignment())
548 SectData.setAlignment(ByteAlignment);
551 LocalCommons.clear();
554 void MCELFStreamer::FinishImpl() {
559 this->MCObjectStreamer::FinishImpl();
562 MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
563 raw_ostream &OS, MCCodeEmitter *CE,
565 MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
567 S->getAssembler().setRelaxAll(true);
571 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
572 llvm_unreachable("Generic ELF doesn't support this directive");
575 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
576 llvm_unreachable("ELF doesn't support this directive");
579 void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
580 llvm_unreachable("ELF doesn't support this directive");
583 void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
584 llvm_unreachable("ELF doesn't support this directive");
587 void MCELFStreamer::EmitCOFFSymbolType(int Type) {
588 llvm_unreachable("ELF doesn't support this directive");
591 void MCELFStreamer::EndCOFFSymbolDef() {
592 llvm_unreachable("ELF doesn't support this directive");
595 void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
596 uint64_t Size, unsigned ByteAlignment) {
597 llvm_unreachable("ELF doesn't support this directive");
600 void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
601 uint64_t Size, unsigned ByteAlignment) {
602 llvm_unreachable("ELF doesn't support this directive");