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"
38 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
39 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
40 Binding == ELF::STB_WEAK);
41 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
42 SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
45 static unsigned GetBinding(const MCSymbolData &SD) {
46 uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
47 assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
48 Binding == ELF::STB_WEAK);
52 static void SetType(MCSymbolData &SD, unsigned Type) {
53 assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
54 Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
55 Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
56 Type == ELF::STT_TLS);
58 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
59 SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
62 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
63 assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
64 Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
66 uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
67 SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
70 class MCELFStreamer : public MCObjectStreamer {
72 MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
73 raw_ostream &OS, MCCodeEmitter *Emitter)
74 : MCObjectStreamer(Context, TAB, OS, Emitter) {}
78 /// @name MCStreamer Interface
81 virtual void InitSections();
82 virtual void EmitLabel(MCSymbol *Symbol);
83 virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
84 virtual void EmitThumbFunc(MCSymbol *Func);
85 virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
86 virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
87 virtual void SwitchSection(const MCSection *Section);
88 virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
89 virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
90 assert(0 && "ELF doesn't support this directive");
92 virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
93 unsigned ByteAlignment);
94 virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
95 assert(0 && "ELF doesn't support this directive");
98 virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
99 assert(0 && "ELF doesn't support this directive");
102 virtual void EmitCOFFSymbolType(int Type) {
103 assert(0 && "ELF doesn't support this directive");
106 virtual void EndCOFFSymbolDef() {
107 assert(0 && "ELF doesn't support this directive");
110 virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
111 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
115 virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
116 assert(0 && "ELF doesn't support this directive");
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::EmitBytes(StringRef Data, unsigned AddrSpace) {
365 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
367 getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
370 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
371 int64_t Value, unsigned ValueSize,
372 unsigned MaxBytesToEmit) {
373 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
375 if (MaxBytesToEmit == 0)
376 MaxBytesToEmit = ByteAlignment;
377 new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
378 getCurrentSectionData());
380 // Update the maximum alignment on the current section if necessary.
381 if (ByteAlignment > getCurrentSectionData()->getAlignment())
382 getCurrentSectionData()->setAlignment(ByteAlignment);
385 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
386 unsigned MaxBytesToEmit) {
387 // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
389 if (MaxBytesToEmit == 0)
390 MaxBytesToEmit = ByteAlignment;
391 MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
392 getCurrentSectionData());
393 F->setEmitNops(true);
395 // Update the maximum alignment on the current section if necessary.
396 if (ByteAlignment > getCurrentSectionData()->getAlignment())
397 getCurrentSectionData()->setAlignment(ByteAlignment);
400 // Add a symbol for the file name of this module. This is the second
401 // entry in the module's symbol table (the first being the null symbol).
402 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
403 MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
404 Symbol->setSection(*CurSection);
405 Symbol->setAbsolute();
407 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
409 SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
412 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
413 switch (expr->getKind()) {
414 case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
415 case MCExpr::Constant:
418 case MCExpr::Binary: {
419 const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
420 fixSymbolsInTLSFixups(be->getLHS());
421 fixSymbolsInTLSFixups(be->getRHS());
425 case MCExpr::SymbolRef: {
426 const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
427 switch (symRef.getKind()) {
430 case MCSymbolRefExpr::VK_NTPOFF:
431 case MCSymbolRefExpr::VK_GOTNTPOFF:
432 case MCSymbolRefExpr::VK_TLSGD:
433 case MCSymbolRefExpr::VK_TLSLDM:
434 case MCSymbolRefExpr::VK_TPOFF:
435 case MCSymbolRefExpr::VK_DTPOFF:
436 case MCSymbolRefExpr::VK_GOTTPOFF:
437 case MCSymbolRefExpr::VK_TLSLD:
438 case MCSymbolRefExpr::VK_ARM_TLSGD:
441 MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
442 SetType(SD, ELF::STT_TLS);
447 fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
452 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
453 this->MCObjectStreamer::EmitInstToFragment(Inst);
454 MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
456 for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
457 fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
460 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
461 MCDataFragment *DF = getOrCreateDataFragment();
463 SmallVector<MCFixup, 4> Fixups;
464 SmallString<256> Code;
465 raw_svector_ostream VecOS(Code);
466 getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
469 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
470 fixSymbolsInTLSFixups(Fixups[i].getValue());
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->addFixup(Fixups[i]);
477 DF->getContents().append(Code.begin(), Code.end());
480 void MCELFStreamer::Finish() {
481 // FIXME: duplicated code with the MachO streamer.
482 // Dump out the dwarf file & directory tables and line tables.
483 if (getContext().hasDwarfFiles()) {
484 const MCSection *DwarfLineSection =
485 getContext().getELFSection(".debug_line", 0, 0,
486 SectionKind::getDataRelLocal());
487 MCDwarfFileTable::Emit(this, DwarfLineSection);
490 for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
491 e = LocalCommons.end();
493 MCSymbolData *SD = i->SD;
494 uint64_t Size = i->Size;
495 unsigned ByteAlignment = i->ByteAlignment;
496 const MCSymbol &Symbol = SD->getSymbol();
497 const MCSection &Section = Symbol.getSection();
499 MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
500 new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
502 MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
505 // Update the maximum alignment of the section if necessary.
506 if (ByteAlignment > SectData.getAlignment())
507 SectData.setAlignment(ByteAlignment);
510 this->MCObjectStreamer::Finish();
513 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
514 raw_ostream &OS, MCCodeEmitter *CE,
516 MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
518 S->getAssembler().setRelaxAll(true);