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");
95 const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
97 getAssembler().getOrCreateSymbolData(*Grp);
98 this->MCObjectStreamer::ChangeSection(Section, Subsection);
101 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
102 getAssembler().getOrCreateSymbolData(*Symbol);
103 const MCExpr *Value = MCSymbolRefExpr::Create(
104 Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
105 Alias->setVariableValue(Value);
108 // When GNU as encounters more than one .type declaration for an object it seems
109 // to use a mechanism similar to the one below to decide which type is actually
110 // used in the object file. The greater of T1 and T2 is selected based on the
111 // following ordering:
112 // STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
113 // If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
115 static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
116 unsigned TypeOrdering[] = {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
117 ELF::STT_GNU_IFUNC, ELF::STT_TLS};
118 for (unsigned i = 0; i != array_lengthof(TypeOrdering); ++i) {
119 if (T1 == TypeOrdering[i])
121 if (T2 == TypeOrdering[i])
128 bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
129 MCSymbolAttr Attribute) {
130 // Indirect symbols are handled differently, to match how 'as' handles
131 // them. This makes writing matching .o files easier.
132 if (Attribute == MCSA_IndirectSymbol) {
133 // Note that we intentionally cannot use the symbol data here; this is
134 // important for matching the string table that 'as' generates.
135 IndirectSymbolData ISD;
137 ISD.SectionData = getCurrentSectionData();
138 getAssembler().getIndirectSymbols().push_back(ISD);
142 // Adding a symbol attribute always introduces the symbol, note that an
143 // important side effect of calling getOrCreateSymbolData here is to register
144 // the symbol with the assembler.
145 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
147 // The implementation of symbol attributes is designed to match 'as', but it
148 // leaves much to desired. It doesn't really make sense to arbitrarily add and
149 // remove flags, but 'as' allows this (in particular, see .desc).
151 // In the future it might be worth trying to make these operations more well
154 case MCSA_LazyReference:
156 case MCSA_SymbolResolver:
157 case MCSA_PrivateExtern:
158 case MCSA_WeakDefinition:
159 case MCSA_WeakDefAutoPrivate:
161 case MCSA_IndirectSymbol:
164 case MCSA_NoDeadStrip:
165 case MCSA_ELF_TypeGnuUniqueObject:
170 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
171 SD.setExternal(true);
172 BindingExplicitlySet.insert(Symbol);
175 case MCSA_WeakReference:
177 MCELF::SetBinding(SD, ELF::STB_WEAK);
178 SD.setExternal(true);
179 BindingExplicitlySet.insert(Symbol);
183 MCELF::SetBinding(SD, ELF::STB_LOCAL);
184 SD.setExternal(false);
185 BindingExplicitlySet.insert(Symbol);
188 case MCSA_ELF_TypeFunction:
189 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
193 case MCSA_ELF_TypeIndFunction:
194 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
195 ELF::STT_GNU_IFUNC));
198 case MCSA_ELF_TypeObject:
199 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
203 case MCSA_ELF_TypeTLS:
204 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
208 case MCSA_ELF_TypeCommon:
209 // TODO: Emit these as a common symbol.
210 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
214 case MCSA_ELF_TypeNoType:
215 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
220 MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
224 MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
228 MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
235 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
236 unsigned ByteAlignment) {
237 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
239 if (!BindingExplicitlySet.count(Symbol)) {
240 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
241 SD.setExternal(true);
244 MCELF::SetType(SD, ELF::STT_OBJECT);
246 if (MCELF::GetBinding(SD) == ELF_STB_Local) {
247 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
251 SectionKind::getBSS());
253 AssignSection(Symbol, Section);
255 struct LocalCommon L = {&SD, Size, ByteAlignment};
256 LocalCommons.push_back(L);
258 SD.setCommon(Size, ByteAlignment);
261 SD.setSize(MCConstantExpr::Create(Size, getContext()));
264 void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
265 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
269 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
270 unsigned ByteAlignment) {
271 // FIXME: Should this be caught and done earlier?
272 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
273 MCELF::SetBinding(SD, ELF::STB_LOCAL);
274 SD.setExternal(false);
275 BindingExplicitlySet.insert(Symbol);
276 EmitCommonSymbol(Symbol, Size, ByteAlignment);
279 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
281 if (getCurrentSectionData()->isBundleLocked())
282 report_fatal_error("Emitting values inside a locked bundle is forbidden");
283 fixSymbolsInTLSFixups(Value);
284 MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
287 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
290 unsigned MaxBytesToEmit) {
291 if (getCurrentSectionData()->isBundleLocked())
292 report_fatal_error("Emitting values inside a locked bundle is forbidden");
293 MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
294 ValueSize, MaxBytesToEmit);
297 // Add a symbol for the file name of this module. They start after the
298 // null symbol and don't count as normal symbol, i.e. a non-STT_FILE symbol
299 // with the same name may appear.
300 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
301 getAssembler().addFileName(Filename);
304 void MCELFStreamer::EmitIdent(StringRef IdentString) {
305 const MCSection *Comment = getAssembler().getContext().getELFSection(
306 ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS,
307 SectionKind::getReadOnly(), 1, "");
309 SwitchSection(Comment);
314 EmitBytes(IdentString);
319 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
320 switch (expr->getKind()) {
322 cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
324 case MCExpr::Constant:
327 case MCExpr::Binary: {
328 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
329 fixSymbolsInTLSFixups(be->getLHS());
330 fixSymbolsInTLSFixups(be->getRHS());
334 case MCExpr::SymbolRef: {
335 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
336 switch (symRef.getKind()) {
339 case MCSymbolRefExpr::VK_GOTTPOFF:
340 case MCSymbolRefExpr::VK_INDNTPOFF:
341 case MCSymbolRefExpr::VK_NTPOFF:
342 case MCSymbolRefExpr::VK_GOTNTPOFF:
343 case MCSymbolRefExpr::VK_TLSGD:
344 case MCSymbolRefExpr::VK_TLSLD:
345 case MCSymbolRefExpr::VK_TLSLDM:
346 case MCSymbolRefExpr::VK_TPOFF:
347 case MCSymbolRefExpr::VK_DTPOFF:
348 case MCSymbolRefExpr::VK_Mips_TLSGD:
349 case MCSymbolRefExpr::VK_Mips_GOTTPREL:
350 case MCSymbolRefExpr::VK_Mips_TPREL_HI:
351 case MCSymbolRefExpr::VK_Mips_TPREL_LO:
352 case MCSymbolRefExpr::VK_PPC_DTPMOD:
353 case MCSymbolRefExpr::VK_PPC_TPREL:
354 case MCSymbolRefExpr::VK_PPC_TPREL_LO:
355 case MCSymbolRefExpr::VK_PPC_TPREL_HI:
356 case MCSymbolRefExpr::VK_PPC_TPREL_HA:
357 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
358 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
359 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
360 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
361 case MCSymbolRefExpr::VK_PPC_DTPREL:
362 case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
363 case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
364 case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
365 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
366 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
367 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
368 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
369 case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
370 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
371 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
372 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
373 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
374 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
375 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
376 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
377 case MCSymbolRefExpr::VK_PPC_TLS:
378 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
379 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
380 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
381 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
382 case MCSymbolRefExpr::VK_PPC_TLSGD:
383 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
384 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
385 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
386 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
387 case MCSymbolRefExpr::VK_PPC_TLSLD:
390 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
391 MCELF::SetType(SD, ELF::STT_TLS);
396 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
401 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst,
402 const MCSubtargetInfo &STI) {
403 this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
404 MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
406 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
407 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
410 void MCELFStreamer::EmitInstToData(const MCInst &Inst,
411 const MCSubtargetInfo &STI) {
412 MCAssembler &Assembler = getAssembler();
413 SmallVector<MCFixup, 4> Fixups;
414 SmallString<256> Code;
415 raw_svector_ostream VecOS(Code);
416 Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
419 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
420 fixSymbolsInTLSFixups(Fixups[i].getValue());
422 // There are several possibilities here:
424 // If bundling is disabled, append the encoded instruction to the current data
425 // fragment (or create a new such fragment if the current fragment is not a
428 // If bundling is enabled:
429 // - If we're not in a bundle-locked group, emit the instruction into a
430 // fragment of its own. If there are no fixups registered for the
431 // instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
433 // - If we're in a bundle-locked group, append the instruction to the current
434 // data fragment because we want all the instructions in a group to get into
435 // the same fragment. Be careful not to do that for the first instruction in
436 // the group, though.
439 if (Assembler.isBundlingEnabled()) {
440 MCSectionData *SD = getCurrentSectionData();
441 if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
442 // If we are bundle-locked, we re-use the current fragment.
443 // The bundle-locking directive ensures this is a new data fragment.
444 DF = cast<MCDataFragment>(getCurrentFragment());
445 else if (!SD->isBundleLocked() && Fixups.size() == 0) {
446 // Optimize memory usage by emitting the instruction to a
447 // MCCompactEncodedInstFragment when not in a bundle-locked group and
448 // there are no fixups registered.
449 MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
451 CEIF->getContents().append(Code.begin(), Code.end());
454 DF = new MCDataFragment();
457 if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
458 // If this fragment is for a group marked "align_to_end", set a flag
459 // in the fragment. This can happen after the fragment has already been
460 // created if there are nested bundle_align groups and an inner one
461 // is the one marked align_to_end.
462 DF->setAlignToBundleEnd(true);
465 // We're now emitting an instruction in a bundle group, so this flag has
467 SD->setBundleGroupBeforeFirstInst(false);
469 DF = getOrCreateDataFragment();
472 // Add the fixups and data.
473 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
474 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
475 DF->getFixups().push_back(Fixups[i]);
477 DF->setHasInstructions(true);
478 DF->getContents().append(Code.begin(), Code.end());
481 void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
482 assert(AlignPow2 <= 30 && "Invalid bundle alignment");
483 MCAssembler &Assembler = getAssembler();
484 if (AlignPow2 > 0 && (Assembler.getBundleAlignSize() == 0 ||
485 Assembler.getBundleAlignSize() == 1U << AlignPow2))
486 Assembler.setBundleAlignSize(1U << AlignPow2);
488 report_fatal_error(".bundle_align_mode cannot be changed once set");
491 void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
492 MCSectionData *SD = getCurrentSectionData();
496 if (!getAssembler().isBundlingEnabled())
497 report_fatal_error(".bundle_lock forbidden when bundling is disabled");
499 if (!SD->isBundleLocked())
500 SD->setBundleGroupBeforeFirstInst(true);
502 SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
503 MCSectionData::BundleLocked);
506 void MCELFStreamer::EmitBundleUnlock() {
507 MCSectionData *SD = getCurrentSectionData();
510 if (!getAssembler().isBundlingEnabled())
511 report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
512 else if (!SD->isBundleLocked())
513 report_fatal_error(".bundle_unlock without matching lock");
514 else if (SD->isBundleGroupBeforeFirstInst())
515 report_fatal_error("Empty bundle-locked group is forbidden");
517 SD->setBundleLockState(MCSectionData::NotBundleLocked);
520 void MCELFStreamer::Flush() {
521 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
522 e = LocalCommons.end();
524 MCSymbolData *SD = i->SD;
525 uint64_t Size = i->Size;
526 unsigned ByteAlignment = i->ByteAlignment;
527 const MCSymbol &Symbol = SD->getSymbol();
528 const MCSection &Section = Symbol.getSection();
530 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
531 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
533 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
536 // Update the maximum alignment of the section if necessary.
537 if (ByteAlignment > SectData.getAlignment())
538 SectData.setAlignment(ByteAlignment);
541 LocalCommons.clear();
544 void MCELFStreamer::FinishImpl() {
549 this->MCObjectStreamer::FinishImpl();
552 MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
553 raw_ostream &OS, MCCodeEmitter *CE,
555 MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
557 S->getAssembler().setRelaxAll(true);
561 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
562 llvm_unreachable("Generic ELF doesn't support this directive");
565 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
566 llvm_unreachable("ELF doesn't support this directive");
569 void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
570 llvm_unreachable("ELF doesn't support this directive");
573 void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
574 llvm_unreachable("ELF doesn't support this directive");
577 void MCELFStreamer::EmitCOFFSymbolType(int Type) {
578 llvm_unreachable("ELF doesn't support this directive");
581 void MCELFStreamer::EndCOFFSymbolDef() {
582 llvm_unreachable("ELF doesn't support this directive");
585 void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
586 uint64_t Size, unsigned ByteAlignment) {
587 llvm_unreachable("ELF doesn't support this directive");
590 void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
591 uint64_t Size, unsigned ByteAlignment) {
592 llvm_unreachable("ELF doesn't support this directive");