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/MCStreamer.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/MC/MCAssembler.h"
18 #include "llvm/MC/MCContext.h"
19 #include "llvm/MC/MCCodeEmitter.h"
20 #include "llvm/MC/MCELFSymbolFlags.h"
21 #include "llvm/MC/MCExpr.h"
22 #include "llvm/MC/MCInst.h"
23 #include "llvm/MC/MCObjectStreamer.h"
24 #include "llvm/MC/MCSection.h"
25 #include "llvm/MC/MCSectionELF.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/MC/MCValue.h"
28 #include "llvm/Support/Debug.h"
29 #include "llvm/Support/ELF.h"
30 #include "llvm/Support/ErrorHandling.h"
31 #include "llvm/Support/raw_ostream.h"
32 #include "llvm/Target/TargetAsmBackend.h"
33 #include "llvm/Target/TargetAsmInfo.h"
39 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
40 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
41 Binding == ELF::STB_WEAK);
42 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
43 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
46 static unsigned GetBinding(const MCSymbolData &SD) {
47 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
48 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
49 Binding == ELF::STB_WEAK);
53 static void SetType(MCSymbolData &SD, unsigned Type) {
54 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
55 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
56 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
57 Type == ELF::STT_TLS);
59 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
60 SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
63 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
64 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
65 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
67 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
68 SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
71 class MCELFStreamer : public MCObjectStreamer {
73 MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
74 raw_ostream &OS, MCCodeEmitter *Emitter)
75 : MCObjectStreamer(Context, TAB, OS, Emitter) {}
79 /// @name MCStreamer Interface
82 virtual void InitSections();
83 virtual void EmitLabel(MCSymbol *Symbol);
84 virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
85 virtual void EmitThumbFunc(MCSymbol *Func);
86 virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
87 virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
88 virtual void SwitchSection(const MCSection *Section);
89 virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
90 virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
91 assert(0 && "ELF doesn't support this directive");
93 virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
94 unsigned ByteAlignment);
95 virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
96 assert(0 && "ELF doesn't support this directive");
99 virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
100 assert(0 && "ELF doesn't support this directive");
103 virtual void EmitCOFFSymbolType(int Type) {
104 assert(0 && "ELF doesn't support this directive");
107 virtual void EndCOFFSymbolDef() {
108 assert(0 && "ELF doesn't support this directive");
111 virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
112 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
116 virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size);
118 virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
119 unsigned Size = 0, unsigned ByteAlignment = 0) {
120 assert(0 && "ELF doesn't support this directive");
122 virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
123 uint64_t Size, unsigned ByteAlignment = 0) {
124 assert(0 && "ELF doesn't support this directive");
126 virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
127 virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
128 unsigned ValueSize = 1,
129 unsigned MaxBytesToEmit = 0);
130 virtual void EmitCodeAlignment(unsigned ByteAlignment,
131 unsigned MaxBytesToEmit = 0);
133 virtual void EmitFileDirective(StringRef Filename);
135 virtual void Finish();
138 virtual void EmitInstToFragment(const MCInst &Inst);
139 virtual void EmitInstToData(const MCInst &Inst);
141 void fixSymbolsInTLSFixups(const MCExpr *expr);
146 unsigned ByteAlignment;
148 std::vector<LocalCommon> LocalCommons;
150 SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
152 void SetSection(StringRef Section, unsigned Type, unsigned Flags,
154 SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
157 void SetSectionData() {
158 SetSection(".data", MCSectionELF::SHT_PROGBITS,
159 MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
160 SectionKind::getDataRel());
161 EmitCodeAlignment(4, 0);
163 void SetSectionText() {
164 SetSection(".text", MCSectionELF::SHT_PROGBITS,
165 MCSectionELF::SHF_EXECINSTR |
166 MCSectionELF::SHF_ALLOC, SectionKind::getText());
167 EmitCodeAlignment(4, 0);
169 void SetSectionBss() {
170 SetSection(".bss", MCSectionELF::SHT_NOBITS,
171 MCSectionELF::SHF_WRITE |
172 MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
173 EmitCodeAlignment(4, 0);
177 } // end anonymous namespace.
179 void MCELFStreamer::InitSections() {
180 // This emulates the same behavior of GNU as. This makes it easier
181 // to compare the output as the major sections are in the same order.
188 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
189 assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
191 MCObjectStreamer::EmitLabel(Symbol);
193 const MCSectionELF &Section =
194 static_cast<const MCSectionELF&>(Symbol->getSection());
195 MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
196 if (Section.getFlags() & MCSectionELF::SHF_TLS)
197 SetType(SD, ELF::STT_TLS);
200 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
202 case MCAF_SyntaxUnified: return; // no-op here.
203 case MCAF_Code16: return; // no-op here.
204 case MCAF_Code32: return; // no-op here.
205 case MCAF_SubsectionsViaSymbols:
206 getAssembler().setSubsectionsViaSymbols(true);
210 assert(0 && "invalid assembler flag!");
213 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
214 // FIXME: Anything needed here to flag the function as thumb?
217 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
218 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
220 // FIXME: Lift context changes into super class.
221 getAssembler().getOrCreateSymbolData(*Symbol);
222 Symbol->setVariableValue(AddValueSymbols(Value));
225 void MCELFStreamer::SwitchSection(const MCSection *Section) {
226 const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
228 getAssembler().getOrCreateSymbolData(*Grp);
229 this->MCObjectStreamer::SwitchSection(Section);
232 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
233 getAssembler().getOrCreateSymbolData(*Symbol);
234 MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
235 AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
236 const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
237 Alias->setVariableValue(Value);
240 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
241 MCSymbolAttr Attribute) {
242 // Indirect symbols are handled differently, to match how 'as' handles
243 // them. This makes writing matching .o files easier.
244 if (Attribute == MCSA_IndirectSymbol) {
245 // Note that we intentionally cannot use the symbol data here; this is
246 // important for matching the string table that 'as' generates.
247 IndirectSymbolData ISD;
249 ISD.SectionData = getCurrentSectionData();
250 getAssembler().getIndirectSymbols().push_back(ISD);
254 // Adding a symbol attribute always introduces the symbol, note that an
255 // important side effect of calling getOrCreateSymbolData here is to register
256 // the symbol with the assembler.
257 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
259 // The implementation of symbol attributes is designed to match 'as', but it
260 // leaves much to desired. It doesn't really make sense to arbitrarily add and
261 // remove flags, but 'as' allows this (in particular, see .desc).
263 // In the future it might be worth trying to make these operations more well
266 case MCSA_LazyReference:
268 case MCSA_NoDeadStrip:
269 case MCSA_SymbolResolver:
270 case MCSA_PrivateExtern:
271 case MCSA_WeakDefinition:
272 case MCSA_WeakDefAutoPrivate:
274 case MCSA_ELF_TypeIndFunction:
275 case MCSA_IndirectSymbol:
276 assert(0 && "Invalid symbol attribute for ELF!");
279 case MCSA_ELF_TypeGnuUniqueObject:
284 SetBinding(SD, ELF::STB_GLOBAL);
285 SD.setExternal(true);
286 BindingExplicitlySet.insert(Symbol);
289 case MCSA_WeakReference:
291 SetBinding(SD, ELF::STB_WEAK);
292 SD.setExternal(true);
293 BindingExplicitlySet.insert(Symbol);
297 SetBinding(SD, ELF::STB_LOCAL);
298 SD.setExternal(false);
299 BindingExplicitlySet.insert(Symbol);
302 case MCSA_ELF_TypeFunction:
303 SetType(SD, ELF::STT_FUNC);
306 case MCSA_ELF_TypeObject:
307 SetType(SD, ELF::STT_OBJECT);
310 case MCSA_ELF_TypeTLS:
311 SetType(SD, ELF::STT_TLS);
314 case MCSA_ELF_TypeCommon:
315 SetType(SD, ELF::STT_COMMON);
318 case MCSA_ELF_TypeNoType:
319 SetType(SD, ELF::STT_NOTYPE);
323 SetVisibility(SD, ELF::STV_PROTECTED);
327 SetVisibility(SD, ELF::STV_HIDDEN);
331 SetVisibility(SD, ELF::STV_INTERNAL);
336 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
337 unsigned ByteAlignment) {
338 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
340 if (!BindingExplicitlySet.count(Symbol)) {
341 SetBinding(SD, ELF::STB_GLOBAL);
342 SD.setExternal(true);
345 SetType(SD, ELF::STT_OBJECT);
347 if (GetBinding(SD) == ELF_STB_Local) {
348 const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
349 MCSectionELF::SHT_NOBITS,
350 MCSectionELF::SHF_WRITE |
351 MCSectionELF::SHF_ALLOC,
352 SectionKind::getBSS());
353 Symbol->setSection(*Section);
355 struct LocalCommon L = {&SD, Size, ByteAlignment};
356 LocalCommons.push_back(L);
358 SD.setCommon(Size, ByteAlignment);
361 SD.setSize(MCConstantExpr::Create(Size, getContext()));
364 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
365 // FIXME: Should this be caught and done earlier?
366 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
367 SetBinding(SD, ELF::STB_LOCAL);
368 SD.setExternal(false);
369 BindingExplicitlySet.insert(Symbol);
370 // FIXME: ByteAlignment is not needed here, but is required.
371 EmitCommonSymbol(Symbol, Size, 1);
374 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
375 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
377 getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
380 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
381 int64_t Value, unsigned ValueSize,
382 unsigned MaxBytesToEmit) {
383 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
385 if (MaxBytesToEmit == 0)
386 MaxBytesToEmit = ByteAlignment;
387 new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
388 getCurrentSectionData());
390 // Update the maximum alignment on the current section if necessary.
391 if (ByteAlignment > getCurrentSectionData()->getAlignment())
392 getCurrentSectionData()->setAlignment(ByteAlignment);
395 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
396 unsigned MaxBytesToEmit) {
397 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
399 if (MaxBytesToEmit == 0)
400 MaxBytesToEmit = ByteAlignment;
401 MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
402 getCurrentSectionData());
403 F->setEmitNops(true);
405 // Update the maximum alignment on the current section if necessary.
406 if (ByteAlignment > getCurrentSectionData()->getAlignment())
407 getCurrentSectionData()->setAlignment(ByteAlignment);
410 // Add a symbol for the file name of this module. This is the second
411 // entry in the module's symbol table (the first being the null symbol).
412 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
413 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
414 Symbol->setSection(*CurSection);
415 Symbol->setAbsolute();
417 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
419 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
422 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
423 switch (expr->getKind()) {
424 case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
425 case MCExpr::Constant:
428 case MCExpr::Binary: {
429 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
430 fixSymbolsInTLSFixups(be->getLHS());
431 fixSymbolsInTLSFixups(be->getRHS());
435 case MCExpr::SymbolRef: {
436 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
437 switch (symRef.getKind()) {
440 case MCSymbolRefExpr::VK_NTPOFF:
441 case MCSymbolRefExpr::VK_GOTNTPOFF:
442 case MCSymbolRefExpr::VK_TLSGD:
443 case MCSymbolRefExpr::VK_TLSLDM:
444 case MCSymbolRefExpr::VK_TPOFF:
445 case MCSymbolRefExpr::VK_DTPOFF:
446 case MCSymbolRefExpr::VK_GOTTPOFF:
447 case MCSymbolRefExpr::VK_TLSLD:
448 case MCSymbolRefExpr::VK_ARM_TLSGD:
451 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
452 SetType(SD, ELF::STT_TLS);
457 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
462 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
463 this->MCObjectStreamer::EmitInstToFragment(Inst);
464 MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
466 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
467 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
470 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
471 MCDataFragment *DF = getOrCreateDataFragment();
473 SmallVector<MCFixup, 4> Fixups;
474 SmallString<256> Code;
475 raw_svector_ostream VecOS(Code);
476 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
479 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
480 fixSymbolsInTLSFixups(Fixups[i].getValue());
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->addFixup(Fixups[i]);
487 DF->getContents().append(Code.begin(), Code.end());
490 void MCELFStreamer::Finish() {
491 if (!FrameInfos.empty())
492 MCDwarfFrameEmitter::Emit(*this);
494 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
495 e = LocalCommons.end();
497 MCSymbolData *SD = i->SD;
498 uint64_t Size = i->Size;
499 unsigned ByteAlignment = i->ByteAlignment;
500 const MCSymbol &Symbol = SD->getSymbol();
501 const MCSection &Section = Symbol.getSection();
503 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
504 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
506 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
509 // Update the maximum alignment of the section if necessary.
510 if (ByteAlignment > SectData.getAlignment())
511 SectData.setAlignment(ByteAlignment);
514 this->MCObjectStreamer::Finish();
517 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
518 raw_ostream &OS, MCCodeEmitter *CE,
520 MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
522 S->getAssembler().setRelaxAll(true);