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/MCAssembler.h"
19 #include "llvm/MC/MCCodeEmitter.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCELF.h"
22 #include "llvm/MC/MCELFSymbolFlags.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCInst.h"
25 #include "llvm/MC/MCObjectFileInfo.h"
26 #include "llvm/MC/MCObjectStreamer.h"
27 #include "llvm/MC/MCSection.h"
28 #include "llvm/MC/MCSectionELF.h"
29 #include "llvm/MC/MCSymbol.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/Support/Debug.h"
32 #include "llvm/Support/ELF.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/raw_ostream.h"
38 inline void MCELFStreamer::SetSectionData() {
39 SwitchSection(getContext().getObjectFileInfo()->getDataSection());
40 EmitCodeAlignment(4, 0);
43 inline void MCELFStreamer::SetSectionText() {
44 SwitchSection(getContext().getObjectFileInfo()->getTextSection());
45 EmitCodeAlignment(4, 0);
48 inline void MCELFStreamer::SetSectionBss() {
49 SwitchSection(getContext().getObjectFileInfo()->getBSSSection());
50 EmitCodeAlignment(4, 0);
53 MCELFStreamer::~MCELFStreamer() {
56 void MCELFStreamer::InitSections() {
57 // This emulates the same behavior of GNU as. This makes it easier
58 // to compare the output as the major sections are in the same order.
65 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
66 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
68 MCObjectStreamer::EmitLabel(Symbol);
70 const MCSectionELF &Section =
71 static_cast<const MCSectionELF&>(Symbol->getSection());
72 MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
73 if (Section.getFlags() & ELF::SHF_TLS)
74 MCELF::SetType(SD, ELF::STT_TLS);
77 void MCELFStreamer::EmitDebugLabel(MCSymbol *Symbol) {
81 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
82 // Let the target do whatever target specific stuff it needs to do.
83 getAssembler().getBackend().handleAssemblerFlag(Flag);
84 // Do any generic stuff we need to do.
86 case MCAF_SyntaxUnified: return; // no-op here.
87 case MCAF_Code16: return; // Change parsing mode; no-op here.
88 case MCAF_Code32: return; // Change parsing mode; no-op here.
89 case MCAF_Code64: return; // Change parsing mode; no-op here.
90 case MCAF_SubsectionsViaSymbols:
91 getAssembler().setSubsectionsViaSymbols(true);
95 llvm_unreachable("invalid assembler flag!");
98 void MCELFStreamer::ChangeSection(const MCSection *Section,
99 const MCExpr *Subsection) {
100 MCSectionData *CurSection = getCurrentSectionData();
101 if (CurSection && CurSection->isBundleLocked())
102 report_fatal_error("Unterminated .bundle_lock when changing a section");
103 const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
105 getAssembler().getOrCreateSymbolData(*Grp);
106 this->MCObjectStreamer::ChangeSection(Section, Subsection);
109 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
110 getAssembler().getOrCreateSymbolData(*Symbol);
111 MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
112 AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
113 const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, 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:
174 case MCSA_ELF_TypeGnuUniqueObject:
179 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
180 SD.setExternal(true);
181 BindingExplicitlySet.insert(Symbol);
184 case MCSA_WeakReference:
186 MCELF::SetBinding(SD, ELF::STB_WEAK);
187 SD.setExternal(true);
188 BindingExplicitlySet.insert(Symbol);
192 MCELF::SetBinding(SD, ELF::STB_LOCAL);
193 SD.setExternal(false);
194 BindingExplicitlySet.insert(Symbol);
197 case MCSA_ELF_TypeFunction:
198 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
202 case MCSA_ELF_TypeIndFunction:
203 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
204 ELF::STT_GNU_IFUNC));
207 case MCSA_ELF_TypeObject:
208 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
212 case MCSA_ELF_TypeTLS:
213 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
217 case MCSA_ELF_TypeCommon:
218 // TODO: Emit these as a common symbol.
219 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
223 case MCSA_ELF_TypeNoType:
224 MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
229 MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
233 MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
237 MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
244 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
245 unsigned ByteAlignment) {
246 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
248 if (!BindingExplicitlySet.count(Symbol)) {
249 MCELF::SetBinding(SD, ELF::STB_GLOBAL);
250 SD.setExternal(true);
253 MCELF::SetType(SD, ELF::STT_OBJECT);
255 if (MCELF::GetBinding(SD) == ELF_STB_Local) {
256 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
260 SectionKind::getBSS());
262 AssignSection(Symbol, Section);
264 struct LocalCommon L = {&SD, Size, ByteAlignment};
265 LocalCommons.push_back(L);
267 SD.setCommon(Size, ByteAlignment);
270 SD.setSize(MCConstantExpr::Create(Size, getContext()));
273 void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
274 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
278 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
279 unsigned ByteAlignment) {
280 // FIXME: Should this be caught and done earlier?
281 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
282 MCELF::SetBinding(SD, ELF::STB_LOCAL);
283 SD.setExternal(false);
284 BindingExplicitlySet.insert(Symbol);
285 EmitCommonSymbol(Symbol, Size, ByteAlignment);
288 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size) {
289 if (getCurrentSectionData()->isBundleLocked())
290 report_fatal_error("Emitting values inside a locked bundle is forbidden");
291 fixSymbolsInTLSFixups(Value);
292 MCObjectStreamer::EmitValueImpl(Value, Size);
295 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
298 unsigned MaxBytesToEmit) {
299 if (getCurrentSectionData()->isBundleLocked())
300 report_fatal_error("Emitting values inside a locked bundle is forbidden");
301 MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
302 ValueSize, MaxBytesToEmit);
305 // Add a symbol for the file name of this module. They start after the
306 // null symbol and don't count as normal symbol, i.e. a non-STT_FILE symbol
307 // with the same name may appear.
308 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
309 getAssembler().addFileName(Filename);
312 void MCELFStreamer::EmitIdent(StringRef IdentString) {
313 const MCSection *Comment = getAssembler().getContext().getELFSection(
314 ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS,
315 SectionKind::getReadOnly(), 1, "");
317 SwitchSection(Comment);
322 EmitBytes(IdentString);
327 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
328 switch (expr->getKind()) {
330 cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
332 case MCExpr::Constant:
335 case MCExpr::Binary: {
336 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
337 fixSymbolsInTLSFixups(be->getLHS());
338 fixSymbolsInTLSFixups(be->getRHS());
342 case MCExpr::SymbolRef: {
343 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
344 switch (symRef.getKind()) {
347 case MCSymbolRefExpr::VK_GOTTPOFF:
348 case MCSymbolRefExpr::VK_INDNTPOFF:
349 case MCSymbolRefExpr::VK_NTPOFF:
350 case MCSymbolRefExpr::VK_GOTNTPOFF:
351 case MCSymbolRefExpr::VK_TLSGD:
352 case MCSymbolRefExpr::VK_TLSLD:
353 case MCSymbolRefExpr::VK_TLSLDM:
354 case MCSymbolRefExpr::VK_TPOFF:
355 case MCSymbolRefExpr::VK_DTPOFF:
356 case MCSymbolRefExpr::VK_Mips_TLSGD:
357 case MCSymbolRefExpr::VK_Mips_GOTTPREL:
358 case MCSymbolRefExpr::VK_Mips_TPREL_HI:
359 case MCSymbolRefExpr::VK_Mips_TPREL_LO:
360 case MCSymbolRefExpr::VK_PPC_DTPMOD:
361 case MCSymbolRefExpr::VK_PPC_TPREL:
362 case MCSymbolRefExpr::VK_PPC_TPREL_LO:
363 case MCSymbolRefExpr::VK_PPC_TPREL_HI:
364 case MCSymbolRefExpr::VK_PPC_TPREL_HA:
365 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
366 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
367 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
368 case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
369 case MCSymbolRefExpr::VK_PPC_DTPREL:
370 case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
371 case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
372 case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
373 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
374 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
375 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
376 case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
377 case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
378 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
379 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
380 case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
381 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
382 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
383 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
384 case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
385 case MCSymbolRefExpr::VK_PPC_TLS:
386 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
387 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
388 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
389 case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
390 case MCSymbolRefExpr::VK_PPC_TLSGD:
391 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
392 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
393 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
394 case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
395 case MCSymbolRefExpr::VK_PPC_TLSLD:
398 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
399 MCELF::SetType(SD, ELF::STT_TLS);
404 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
409 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
410 this->MCObjectStreamer::EmitInstToFragment(Inst);
411 MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
413 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
414 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
417 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
418 MCAssembler &Assembler = getAssembler();
419 SmallVector<MCFixup, 4> Fixups;
420 SmallString<256> Code;
421 raw_svector_ostream VecOS(Code);
422 Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
425 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
426 fixSymbolsInTLSFixups(Fixups[i].getValue());
428 // There are several possibilities here:
430 // If bundling is disabled, append the encoded instruction to the current data
431 // fragment (or create a new such fragment if the current fragment is not a
434 // If bundling is enabled:
435 // - If we're not in a bundle-locked group, emit the instruction into a
436 // fragment of its own. If there are no fixups registered for the
437 // instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
439 // - If we're in a bundle-locked group, append the instruction to the current
440 // data fragment because we want all the instructions in a group to get into
441 // the same fragment. Be careful not to do that for the first instruction in
442 // the group, though.
445 if (Assembler.isBundlingEnabled()) {
446 MCSectionData *SD = getCurrentSectionData();
447 if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
448 // If we are bundle-locked, we re-use the current fragment.
449 // The bundle-locking directive ensures this is a new data fragment.
450 DF = cast<MCDataFragment>(getCurrentFragment());
451 else if (!SD->isBundleLocked() && Fixups.size() == 0) {
452 // Optimize memory usage by emitting the instruction to a
453 // MCCompactEncodedInstFragment when not in a bundle-locked group and
454 // there are no fixups registered.
455 MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
457 CEIF->getContents().append(Code.begin(), Code.end());
460 DF = new MCDataFragment();
462 if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
463 // If this is a new fragment created for a bundle-locked group, and the
464 // group was marked as "align_to_end", set a flag in the fragment.
465 DF->setAlignToBundleEnd(true);
469 // We're now emitting an instruction in a bundle group, so this flag has
471 SD->setBundleGroupBeforeFirstInst(false);
473 DF = getOrCreateDataFragment();
476 // Add the fixups and data.
477 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
478 Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
479 DF->getFixups().push_back(Fixups[i]);
481 DF->setHasInstructions(true);
482 DF->getContents().append(Code.begin(), Code.end());
485 void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
486 assert(AlignPow2 <= 30 && "Invalid bundle alignment");
487 MCAssembler &Assembler = getAssembler();
488 if (Assembler.getBundleAlignSize() == 0 && AlignPow2 > 0)
489 Assembler.setBundleAlignSize(1 << AlignPow2);
491 report_fatal_error(".bundle_align_mode should be only set once per file");
494 void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
495 MCSectionData *SD = getCurrentSectionData();
499 if (!getAssembler().isBundlingEnabled())
500 report_fatal_error(".bundle_lock forbidden when bundling is disabled");
501 else if (SD->isBundleLocked())
502 report_fatal_error("Nesting of .bundle_lock is forbidden");
504 SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
505 MCSectionData::BundleLocked);
506 SD->setBundleGroupBeforeFirstInst(true);
509 void MCELFStreamer::EmitBundleUnlock() {
510 MCSectionData *SD = getCurrentSectionData();
513 if (!getAssembler().isBundlingEnabled())
514 report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
515 else if (!SD->isBundleLocked())
516 report_fatal_error(".bundle_unlock without matching lock");
517 else if (SD->isBundleGroupBeforeFirstInst())
518 report_fatal_error("Empty bundle-locked group is forbidden");
520 SD->setBundleLockState(MCSectionData::NotBundleLocked);
523 void MCELFStreamer::Flush() {
524 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
525 e = LocalCommons.end();
527 MCSymbolData *SD = i->SD;
528 uint64_t Size = i->Size;
529 unsigned ByteAlignment = i->ByteAlignment;
530 const MCSymbol &Symbol = SD->getSymbol();
531 const MCSection &Section = Symbol.getSection();
533 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
534 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
536 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
539 // Update the maximum alignment of the section if necessary.
540 if (ByteAlignment > SectData.getAlignment())
541 SectData.setAlignment(ByteAlignment);
544 LocalCommons.clear();
547 void MCELFStreamer::FinishImpl() {
548 EmitFrames(NULL, true);
552 this->MCObjectStreamer::FinishImpl();
555 MCStreamer *llvm::createELFStreamer(MCContext &Context,
556 MCTargetStreamer *Streamer,
557 MCAsmBackend &MAB, raw_ostream &OS,
558 MCCodeEmitter *CE, bool RelaxAll,
560 MCELFStreamer *S = new MCELFStreamer(Context, Streamer, MAB, OS, CE);
562 S->getAssembler().setRelaxAll(true);
564 S->getAssembler().setNoExecStack(true);
568 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
569 llvm_unreachable("Generic ELF doesn't support this directive");
572 MCSymbolData &MCELFStreamer::getOrCreateSymbolData(MCSymbol *Symbol) {
573 return getAssembler().getOrCreateSymbolData(*Symbol);
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");