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/SmallPtrSet.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/MC/MCAssembler.h"
18 #include "llvm/MC/MCCodeEmitter.h"
19 #include "llvm/MC/MCContext.h"
20 #include "llvm/MC/MCELF.h"
21 #include "llvm/MC/MCELFSymbolFlags.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCInst.h"
24 #include "llvm/MC/MCObjectStreamer.h"
25 #include "llvm/MC/MCSection.h"
26 #include "llvm/MC/MCSectionELF.h"
27 #include "llvm/MC/MCSymbol.h"
28 #include "llvm/MC/MCValue.h"
29 #include "llvm/Support/Debug.h"
30 #include "llvm/Support/ELF.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/raw_ostream.h"
37 inline void MCELFStreamer::SetSection(StringRef Section, unsigned Type,
38 unsigned Flags, SectionKind Kind) {
39 SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
42 inline void MCELFStreamer::SetSectionData() {
45 ELF::SHF_WRITE | ELF::SHF_ALLOC,
46 SectionKind::getDataRel());
47 EmitCodeAlignment(4, 0);
50 inline void MCELFStreamer::SetSectionText() {
53 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
54 SectionKind::getText());
55 EmitCodeAlignment(4, 0);
58 inline void MCELFStreamer::SetSectionBss() {
61 ELF::SHF_WRITE | ELF::SHF_ALLOC,
62 SectionKind::getBSS());
63 EmitCodeAlignment(4, 0);
66 MCELFStreamer::~MCELFStreamer() {
69 void MCELFStreamer::InitToTextSection() {
73 void MCELFStreamer::InitSections() {
74 // This emulates the same behavior of GNU as. This makes it easier
75 // to compare the output as the major sections are in the same order.
82 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
83 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
85 MCObjectStreamer::EmitLabel(Symbol);
87 const MCSectionELF &Section =
88 static_cast<const MCSectionELF&>(Symbol->getSection());
89 MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
90 if (Section.getFlags() & ELF::SHF_TLS)
91 MCELF::SetType(SD, ELF::STT_TLS);
94 void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
98 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
100 case MCAF_SyntaxUnified: return; // no-op here.
101 case MCAF_Code16: return; // Change parsing mode; no-op here.
102 case MCAF_Code32: return; // Change parsing mode; no-op here.
103 case MCAF_Code64: return; // Change parsing mode; no-op here.
104 case MCAF_SubsectionsViaSymbols:
105 getAssembler().setSubsectionsViaSymbols(true);
109 llvm_unreachable("invalid assembler flag!");
112 void MCELFStreamer::ChangeSection(const MCSection *Section,
113 const MCExpr *Subsection) {
114 MCSectionData *CurSection = getCurrentSectionData();
115 if (CurSection && CurSection->isBundleLocked())
116 report_fatal_error("Unterminated .bundle_lock when changing a section");
117 const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
119 getAssembler().getOrCreateSymbolData(*Grp);
120 this->MCObjectStreamer::ChangeSection(Section, Subsection);
123 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
124 getAssembler().getOrCreateSymbolData(*Symbol);
125 MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
126 AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
127 const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
128 Alias->setVariableValue(Value);
131 // When GNU as encounters more than one .type declaration for an object it seems
132 // to use a mechanism similar to the one below to decide which type is actually
133 // used in the object file. The greater of T1 and T2 is selected based on the
134 // following ordering:
135 // STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
136 // If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
138 static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
139 unsigned TypeOrdering[] = {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
140 ELF::STT_GNU_IFUNC, ELF::STT_TLS};
141 for (unsigned i = 0; i != array_lengthof(TypeOrdering); ++i) {
142 if (T1 == TypeOrdering[i])
144 if (T2 == TypeOrdering[i])
151 bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
152 MCSymbolAttr Attribute) {
153 // Indirect symbols are handled differently, to match how 'as' handles
154 // them. This makes writing matching .o files easier.
155 if (Attribute == MCSA_IndirectSymbol) {
156 // Note that we intentionally cannot use the symbol data here; this is
157 // important for matching the string table that 'as' generates.
158 IndirectSymbolData ISD;
160 ISD.SectionData = getCurrentSectionData();
161 getAssembler().getIndirectSymbols().push_back(ISD);
165 // Adding a symbol attribute always introduces the symbol, note that an
166 // important side effect of calling getOrCreateSymbolData here is to register
167 // the symbol with the assembler.
168 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
170 // The implementation of symbol attributes is designed to match 'as', but it
171 // leaves much to desired. It doesn't really make sense to arbitrarily add and
172 // remove flags, but 'as' allows this (in particular, see .desc).
174 // In the future it might be worth trying to make these operations more well
177 case MCSA_LazyReference:
179 case MCSA_SymbolResolver:
180 case MCSA_PrivateExtern:
181 case MCSA_WeakDefinition:
182 case MCSA_WeakDefAutoPrivate:
184 case MCSA_IndirectSymbol:
187 case MCSA_NoDeadStrip:
188 case MCSA_ELF_TypeGnuUniqueObject:
193 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
194 SD.setExternal(true);
195 BindingExplicitlySet.insert(Symbol);
198 case MCSA_WeakReference:
200 MCELF::SetBinding(SD, ELF::STB_WEAK);
201 SD.setExternal(true);
202 BindingExplicitlySet.insert(Symbol);
206 MCELF::SetBinding(SD, ELF::STB_LOCAL);
207 SD.setExternal(false);
208 BindingExplicitlySet.insert(Symbol);
211 case MCSA_ELF_TypeFunction:
212 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
216 case MCSA_ELF_TypeIndFunction:
217 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
218 ELF::STT_GNU_IFUNC));
221 case MCSA_ELF_TypeObject:
222 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
226 case MCSA_ELF_TypeTLS:
227 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
231 case MCSA_ELF_TypeCommon:
232 // TODO: Emit these as a common symbol.
233 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
237 case MCSA_ELF_TypeNoType:
238 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
243 MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
247 MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
251 MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
258 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
259 unsigned ByteAlignment) {
260 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
262 if (!BindingExplicitlySet.count(Symbol)) {
263 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
264 SD.setExternal(true);
267 MCELF::SetType(SD, ELF::STT_OBJECT);
269 if (MCELF::GetBinding(SD) == ELF_STB_Local) {
270 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
274 SectionKind::getBSS());
275 Symbol->setSection(*Section);
277 struct LocalCommon L = {&SD, Size, ByteAlignment};
278 LocalCommons.push_back(L);
280 SD.setCommon(Size, ByteAlignment);
283 SD.setSize(MCConstantExpr::Create(Size, getContext()));
286 void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
287 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
291 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
292 unsigned ByteAlignment) {
293 // FIXME: Should this be caught and done earlier?
294 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
295 MCELF::SetBinding(SD, ELF::STB_LOCAL);
296 SD.setExternal(false);
297 BindingExplicitlySet.insert(Symbol);
298 EmitCommonSymbol(Symbol, Size, ByteAlignment);
301 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size) {
302 if (getCurrentSectionData()->isBundleLocked())
303 report_fatal_error("Emitting values inside a locked bundle is forbidden");
304 fixSymbolsInTLSFixups(Value);
305 MCObjectStreamer::EmitValueImpl(Value, Size);
308 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
311 unsigned MaxBytesToEmit) {
312 if (getCurrentSectionData()->isBundleLocked())
313 report_fatal_error("Emitting values inside a locked bundle is forbidden");
314 MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
315 ValueSize, MaxBytesToEmit);
319 // Add a symbol for the file name of this module. This is the second
320 // entry in the module's symbol table (the first being the null symbol).
321 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
322 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
323 Symbol->setSection(*getCurrentSection().first);
324 Symbol->setAbsolute();
326 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
328 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
331 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
332 switch (expr->getKind()) {
334 cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
336 case MCExpr::Constant:
339 case MCExpr::Binary: {
340 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
341 fixSymbolsInTLSFixups(be->getLHS());
342 fixSymbolsInTLSFixups(be->getRHS());
346 case MCExpr::SymbolRef: {
347 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
348 switch (symRef.getKind()) {
351 case MCSymbolRefExpr::VK_GOTTPOFF:
352 case MCSymbolRefExpr::VK_INDNTPOFF:
353 case MCSymbolRefExpr::VK_NTPOFF:
354 case MCSymbolRefExpr::VK_GOTNTPOFF:
355 case MCSymbolRefExpr::VK_TLSGD:
356 case MCSymbolRefExpr::VK_TLSLD:
357 case MCSymbolRefExpr::VK_TLSLDM:
358 case MCSymbolRefExpr::VK_TPOFF:
359 case MCSymbolRefExpr::VK_DTPOFF:
360 case MCSymbolRefExpr::VK_ARM_TLSGD:
361 case MCSymbolRefExpr::VK_ARM_TPOFF:
362 case MCSymbolRefExpr::VK_ARM_GOTTPOFF:
363 case MCSymbolRefExpr::VK_Mips_TLSGD:
364 case MCSymbolRefExpr::VK_Mips_GOTTPREL:
365 case MCSymbolRefExpr::VK_Mips_TPREL_HI:
366 case MCSymbolRefExpr::VK_Mips_TPREL_LO:
367 case MCSymbolRefExpr::VK_PPC_DTPMOD:
368 case MCSymbolRefExpr::VK_PPC_TPREL:
369 case MCSymbolRefExpr::VK_PPC_TPREL_LO:
370 case MCSymbolRefExpr::VK_PPC_TPREL_HI:
371 case MCSymbolRefExpr::VK_PPC_TPREL_HA:
372 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
373 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
374 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
375 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
376 case MCSymbolRefExpr::VK_PPC_DTPREL:
377 case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
378 case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
379 case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
380 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
381 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
382 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
383 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
384 case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
385 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
386 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
387 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
388 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
389 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
390 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
391 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
392 case MCSymbolRefExpr::VK_PPC_TLS:
393 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
394 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
395 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
396 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
397 case MCSymbolRefExpr::VK_PPC_TLSGD:
398 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
399 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
400 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
401 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
402 case MCSymbolRefExpr::VK_PPC_TLSLD:
405 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
406 MCELF::SetType(SD, ELF::STT_TLS);
411 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
416 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
417 this->MCObjectStreamer::EmitInstToFragment(Inst);
418 MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
420 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
421 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
424 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
425 MCAssembler &Assembler = getAssembler();
426 SmallVector<MCFixup, 4> Fixups;
427 SmallString<256> Code;
428 raw_svector_ostream VecOS(Code);
429 Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
432 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
433 fixSymbolsInTLSFixups(Fixups[i].getValue());
435 // There are several possibilities here:
437 // If bundling is disabled, append the encoded instruction to the current data
438 // fragment (or create a new such fragment if the current fragment is not a
441 // If bundling is enabled:
442 // - If we're not in a bundle-locked group, emit the instruction into a
443 // fragment of its own. If there are no fixups registered for the
444 // instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
446 // - If we're in a bundle-locked group, append the instruction to the current
447 // data fragment because we want all the instructions in a group to get into
448 // the same fragment. Be careful not to do that for the first instruction in
449 // the group, though.
452 if (Assembler.isBundlingEnabled()) {
453 MCSectionData *SD = getCurrentSectionData();
454 if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
455 // If we are bundle-locked, we re-use the current fragment.
456 // The bundle-locking directive ensures this is a new data fragment.
457 DF = cast<MCDataFragment>(getCurrentFragment());
458 else if (!SD->isBundleLocked() && Fixups.size() == 0) {
459 // Optimize memory usage by emitting the instruction to a
460 // MCCompactEncodedInstFragment when not in a bundle-locked group and
461 // there are no fixups registered.
462 MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
464 CEIF->getContents().append(Code.begin(), Code.end());
467 DF = new MCDataFragment();
469 if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
470 // If this is a new fragment created for a bundle-locked group, and the
471 // group was marked as "align_to_end", set a flag in the fragment.
472 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 (Assembler.getBundleAlignSize() == 0 && AlignPow2 > 0)
496 Assembler.setBundleAlignSize(1 << AlignPow2);
498 report_fatal_error(".bundle_align_mode should be only set once per file");
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");
508 else if (SD->isBundleLocked())
509 report_fatal_error("Nesting of .bundle_lock is forbidden");
511 SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
512 MCSectionData::BundleLocked);
513 SD->setBundleGroupBeforeFirstInst(true);
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::FinishImpl() {
533 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
534 e = LocalCommons.end();
536 MCSymbolData *SD = i->SD;
537 uint64_t Size = i->Size;
538 unsigned ByteAlignment = i->ByteAlignment;
539 const MCSymbol &Symbol = SD->getSymbol();
540 const MCSection &Section = Symbol.getSection();
542 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
543 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
545 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
548 // Update the maximum alignment of the section if necessary.
549 if (ByteAlignment > SectData.getAlignment())
550 SectData.setAlignment(ByteAlignment);
553 this->MCObjectStreamer::FinishImpl();
555 void MCELFStreamer::EmitTCEntry(const MCSymbol &S) {
556 // Creates a R_PPC64_TOC relocation
557 MCObjectStreamer::EmitSymbolValue(&S, 8);
560 MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
561 raw_ostream &OS, MCCodeEmitter *CE,
562 bool RelaxAll, bool NoExecStack) {
563 MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
565 S->getAssembler().setRelaxAll(true);
567 S->getAssembler().setNoExecStack(true);
571 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
572 llvm_unreachable("Generic ELF doesn't support this directive");
575 MCSymbolData &MCELFStreamer::getOrCreateSymbolData(MCSymbol *Symbol) {
576 return getAssembler().getOrCreateSymbolData(*Symbol);
579 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
580 llvm_unreachable("ELF doesn't support this directive");
583 void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
584 llvm_unreachable("ELF doesn't support this directive");
587 void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
588 llvm_unreachable("ELF doesn't support this directive");
591 void MCELFStreamer::EmitCOFFSymbolType(int Type) {
592 llvm_unreachable("ELF doesn't support this directive");
595 void MCELFStreamer::EndCOFFSymbolDef() {
596 llvm_unreachable("ELF doesn't support this directive");
599 void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
600 uint64_t Size, unsigned ByteAlignment) {
601 llvm_unreachable("ELF doesn't support this directive");
604 void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
605 uint64_t Size, unsigned ByteAlignment) {
606 llvm_unreachable("ELF doesn't support this directive");