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 unsigned TypeOrdering[] = {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
126 ELF::STT_GNU_IFUNC, ELF::STT_TLS};
127 for (unsigned i = 0; i != array_lengthof(TypeOrdering); ++i) {
128 if (T1 == TypeOrdering[i])
130 if (T2 == TypeOrdering[i])
137 bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
138 MCSymbolAttr Attribute) {
139 // Indirect symbols are handled differently, to match how 'as' handles
140 // them. This makes writing matching .o files easier.
141 if (Attribute == MCSA_IndirectSymbol) {
142 // Note that we intentionally cannot use the symbol data here; this is
143 // important for matching the string table that 'as' generates.
144 IndirectSymbolData ISD;
146 ISD.SectionData = getCurrentSectionData();
147 getAssembler().getIndirectSymbols().push_back(ISD);
151 // Adding a symbol attribute always introduces the symbol, note that an
152 // important side effect of calling getOrCreateSymbolData here is to register
153 // the symbol with the assembler.
154 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
156 // The implementation of symbol attributes is designed to match 'as', but it
157 // leaves much to desired. It doesn't really make sense to arbitrarily add and
158 // remove flags, but 'as' allows this (in particular, see .desc).
160 // In the future it might be worth trying to make these operations more well
163 case MCSA_LazyReference:
165 case MCSA_SymbolResolver:
166 case MCSA_PrivateExtern:
167 case MCSA_WeakDefinition:
168 case MCSA_WeakDefAutoPrivate:
170 case MCSA_IndirectSymbol:
173 case MCSA_NoDeadStrip:
177 case MCSA_ELF_TypeGnuUniqueObject:
178 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD), ELF::STT_OBJECT));
179 MCELF::SetBinding(SD, ELF::STB_GNU_UNIQUE);
180 SD.setExternal(true);
181 BindingExplicitlySet.insert(Symbol);
185 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
186 SD.setExternal(true);
187 BindingExplicitlySet.insert(Symbol);
190 case MCSA_WeakReference:
192 MCELF::SetBinding(SD, ELF::STB_WEAK);
193 SD.setExternal(true);
194 BindingExplicitlySet.insert(Symbol);
198 MCELF::SetBinding(SD, ELF::STB_LOCAL);
199 SD.setExternal(false);
200 BindingExplicitlySet.insert(Symbol);
203 case MCSA_ELF_TypeFunction:
204 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
208 case MCSA_ELF_TypeIndFunction:
209 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
210 ELF::STT_GNU_IFUNC));
213 case MCSA_ELF_TypeObject:
214 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
218 case MCSA_ELF_TypeTLS:
219 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
223 case MCSA_ELF_TypeCommon:
224 // TODO: Emit these as a common symbol.
225 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
229 case MCSA_ELF_TypeNoType:
230 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
235 MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
239 MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
243 MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
250 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
251 unsigned ByteAlignment) {
252 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
254 if (!BindingExplicitlySet.count(Symbol)) {
255 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
256 SD.setExternal(true);
259 MCELF::SetType(SD, ELF::STT_OBJECT);
261 if (MCELF::GetBinding(SD) == ELF_STB_Local) {
262 const MCSection *Section = getAssembler().getContext().getELFSection(
263 ".bss", ELF::SHT_NOBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
265 AssignSection(Symbol, Section);
267 struct LocalCommon L = {&SD, Size, ByteAlignment};
268 LocalCommons.push_back(L);
270 SD.setCommon(Size, ByteAlignment);
273 SD.setSize(MCConstantExpr::Create(Size, getContext()));
276 void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
277 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
281 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
282 unsigned ByteAlignment) {
283 // FIXME: Should this be caught and done earlier?
284 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
285 MCELF::SetBinding(SD, ELF::STB_LOCAL);
286 SD.setExternal(false);
287 BindingExplicitlySet.insert(Symbol);
288 EmitCommonSymbol(Symbol, Size, ByteAlignment);
291 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
293 if (getCurrentSectionData()->isBundleLocked())
294 report_fatal_error("Emitting values inside a locked bundle is forbidden");
295 fixSymbolsInTLSFixups(Value);
296 MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
299 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
302 unsigned MaxBytesToEmit) {
303 if (getCurrentSectionData()->isBundleLocked())
304 report_fatal_error("Emitting values inside a locked bundle is forbidden");
305 MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
306 ValueSize, MaxBytesToEmit);
309 // Add a symbol for the file name of this module. They start after the
310 // null symbol and don't count as normal symbol, i.e. a non-STT_FILE symbol
311 // with the same name may appear.
312 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
313 getAssembler().addFileName(Filename);
316 void MCELFStreamer::EmitIdent(StringRef IdentString) {
317 const MCSection *Comment = getAssembler().getContext().getELFSection(
318 ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
320 SwitchSection(Comment);
325 EmitBytes(IdentString);
330 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
331 switch (expr->getKind()) {
333 cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
335 case MCExpr::Constant:
338 case MCExpr::Binary: {
339 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
340 fixSymbolsInTLSFixups(be->getLHS());
341 fixSymbolsInTLSFixups(be->getRHS());
345 case MCExpr::SymbolRef: {
346 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
347 switch (symRef.getKind()) {
350 case MCSymbolRefExpr::VK_GOTTPOFF:
351 case MCSymbolRefExpr::VK_INDNTPOFF:
352 case MCSymbolRefExpr::VK_NTPOFF:
353 case MCSymbolRefExpr::VK_GOTNTPOFF:
354 case MCSymbolRefExpr::VK_TLSGD:
355 case MCSymbolRefExpr::VK_TLSLD:
356 case MCSymbolRefExpr::VK_TLSLDM:
357 case MCSymbolRefExpr::VK_TPOFF:
358 case MCSymbolRefExpr::VK_DTPOFF:
359 case MCSymbolRefExpr::VK_Mips_TLSGD:
360 case MCSymbolRefExpr::VK_Mips_GOTTPREL:
361 case MCSymbolRefExpr::VK_Mips_TPREL_HI:
362 case MCSymbolRefExpr::VK_Mips_TPREL_LO:
363 case MCSymbolRefExpr::VK_PPC_DTPMOD:
364 case MCSymbolRefExpr::VK_PPC_TPREL:
365 case MCSymbolRefExpr::VK_PPC_TPREL_LO:
366 case MCSymbolRefExpr::VK_PPC_TPREL_HI:
367 case MCSymbolRefExpr::VK_PPC_TPREL_HA:
368 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
369 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
370 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
371 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
372 case MCSymbolRefExpr::VK_PPC_DTPREL:
373 case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
374 case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
375 case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
376 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
377 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
378 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
379 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
380 case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
381 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
382 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
383 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
384 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
385 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
386 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
387 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
388 case MCSymbolRefExpr::VK_PPC_TLS:
389 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
390 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
391 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
392 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
393 case MCSymbolRefExpr::VK_PPC_TLSGD:
394 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
395 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
396 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
397 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
398 case MCSymbolRefExpr::VK_PPC_TLSLD:
401 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
402 MCELF::SetType(SD, ELF::STT_TLS);
407 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
412 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst,
413 const MCSubtargetInfo &STI) {
414 this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
415 MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
417 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
418 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
421 void MCELFStreamer::EmitInstToData(const MCInst &Inst,
422 const MCSubtargetInfo &STI) {
423 MCAssembler &Assembler = getAssembler();
424 SmallVector<MCFixup, 4> Fixups;
425 SmallString<256> Code;
426 raw_svector_ostream VecOS(Code);
427 Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
430 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
431 fixSymbolsInTLSFixups(Fixups[i].getValue());
433 // There are several possibilities here:
435 // If bundling is disabled, append the encoded instruction to the current data
436 // fragment (or create a new such fragment if the current fragment is not a
439 // If bundling is enabled:
440 // - If we're not in a bundle-locked group, emit the instruction into a
441 // fragment of its own. If there are no fixups registered for the
442 // instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
444 // - If we're in a bundle-locked group, append the instruction to the current
445 // data fragment because we want all the instructions in a group to get into
446 // the same fragment. Be careful not to do that for the first instruction in
447 // the group, though.
450 if (Assembler.isBundlingEnabled()) {
451 MCSectionData *SD = getCurrentSectionData();
452 if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
453 // If we are bundle-locked, we re-use the current fragment.
454 // The bundle-locking directive ensures this is a new data fragment.
455 DF = cast<MCDataFragment>(getCurrentFragment());
456 else if (!SD->isBundleLocked() && Fixups.size() == 0) {
457 // Optimize memory usage by emitting the instruction to a
458 // MCCompactEncodedInstFragment when not in a bundle-locked group and
459 // there are no fixups registered.
460 MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
462 CEIF->getContents().append(Code.begin(), Code.end());
465 DF = new MCDataFragment();
468 if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
469 // If this fragment is for a group marked "align_to_end", set a flag
470 // in the fragment. This can happen after the fragment has already been
471 // created if there are nested bundle_align groups and an inner one
472 // is the one marked align_to_end.
473 DF->setAlignToBundleEnd(true);
476 // We're now emitting an instruction in a bundle group, so this flag has
478 SD->setBundleGroupBeforeFirstInst(false);
480 DF = getOrCreateDataFragment();
483 // Add the fixups and data.
484 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
485 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
486 DF->getFixups().push_back(Fixups[i]);
488 DF->setHasInstructions(true);
489 DF->getContents().append(Code.begin(), Code.end());
492 void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
493 assert(AlignPow2 <= 30 && "Invalid bundle alignment");
494 MCAssembler &Assembler = getAssembler();
495 if (AlignPow2 > 0 && (Assembler.getBundleAlignSize() == 0 ||
496 Assembler.getBundleAlignSize() == 1U << AlignPow2))
497 Assembler.setBundleAlignSize(1U << AlignPow2);
499 report_fatal_error(".bundle_align_mode cannot be changed once set");
502 void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
503 MCSectionData *SD = getCurrentSectionData();
507 if (!getAssembler().isBundlingEnabled())
508 report_fatal_error(".bundle_lock forbidden when bundling is disabled");
510 if (!SD->isBundleLocked())
511 SD->setBundleGroupBeforeFirstInst(true);
513 SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
514 MCSectionData::BundleLocked);
517 void MCELFStreamer::EmitBundleUnlock() {
518 MCSectionData *SD = getCurrentSectionData();
521 if (!getAssembler().isBundlingEnabled())
522 report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
523 else if (!SD->isBundleLocked())
524 report_fatal_error(".bundle_unlock without matching lock");
525 else if (SD->isBundleGroupBeforeFirstInst())
526 report_fatal_error("Empty bundle-locked group is forbidden");
528 SD->setBundleLockState(MCSectionData::NotBundleLocked);
531 void MCELFStreamer::Flush() {
532 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
533 e = LocalCommons.end();
535 MCSymbolData *SD = i->SD;
536 uint64_t Size = i->Size;
537 unsigned ByteAlignment = i->ByteAlignment;
538 const MCSymbol &Symbol = SD->getSymbol();
539 const MCSection &Section = Symbol.getSection();
541 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
542 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
544 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
547 // Update the maximum alignment of the section if necessary.
548 if (ByteAlignment > SectData.getAlignment())
549 SectData.setAlignment(ByteAlignment);
552 LocalCommons.clear();
555 void MCELFStreamer::FinishImpl() {
560 this->MCObjectStreamer::FinishImpl();
563 MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
564 raw_ostream &OS, MCCodeEmitter *CE,
566 MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
568 S->getAssembler().setRelaxAll(true);
572 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
573 llvm_unreachable("Generic ELF doesn't support this directive");
576 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
577 llvm_unreachable("ELF doesn't support this directive");
580 void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
581 llvm_unreachable("ELF doesn't support this directive");
584 void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
585 llvm_unreachable("ELF doesn't support this directive");
588 void MCELFStreamer::EmitCOFFSymbolType(int Type) {
589 llvm_unreachable("ELF doesn't support this directive");
592 void MCELFStreamer::EndCOFFSymbolDef() {
593 llvm_unreachable("ELF doesn't support this directive");
596 void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
597 uint64_t Size, unsigned ByteAlignment) {
598 llvm_unreachable("ELF doesn't support this directive");
601 void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
602 uint64_t Size, unsigned ByteAlignment) {
603 llvm_unreachable("ELF doesn't support this directive");