1//===- lib/MC/MCELFStreamer.cpp - ELF Object Output -----------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file assembles .s files and emits ELF .o object files.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/MC/MCELFStreamer.h"
14#include "llvm/ADT/SmallString.h"
15#include "llvm/ADT/SmallVector.h"
16#include "llvm/BinaryFormat/ELF.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/MCExpr.h"
23#include "llvm/MC/MCFixup.h"
24#include "llvm/MC/MCFragment.h"
25#include "llvm/MC/MCObjectFileInfo.h"
26#include "llvm/MC/MCObjectWriter.h"
27#include "llvm/MC/MCSection.h"
28#include "llvm/MC/MCSectionELF.h"
29#include "llvm/MC/MCStreamer.h"
30#include "llvm/MC/MCSymbol.h"
31#include "llvm/MC/MCSymbolELF.h"
32#include "llvm/MC/TargetRegistry.h"
33#include "llvm/Support/Casting.h"
34#include "llvm/Support/ErrorHandling.h"
35#include "llvm/Support/LEB128.h"
36#include "llvm/Support/raw_ostream.h"
37#include <cassert>
38#include <cstdint>
39
40using namespace llvm;
41
42MCELFStreamer::MCELFStreamer(MCContext &Context,
43                             std::unique_ptr<MCAsmBackend> TAB,
44                             std::unique_ptr<MCObjectWriter> OW,
45                             std::unique_ptr<MCCodeEmitter> Emitter)
46    : MCObjectStreamer(Context, std::move(TAB), std::move(OW),
47                       std::move(Emitter)) {}
48
49bool MCELFStreamer::isBundleLocked() const {
50  return getCurrentSectionOnly()->isBundleLocked();
51}
52
53void MCELFStreamer::mergeFragment(MCDataFragment *DF,
54                                  MCDataFragment *EF) {
55  MCAssembler &Assembler = getAssembler();
56
57  if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
58    uint64_t FSize = EF->getContents().size();
59
60    if (FSize > Assembler.getBundleAlignSize())
61      report_fatal_error("Fragment can't be larger than a bundle size");
62
63    uint64_t RequiredBundlePadding = computeBundlePadding(
64        Assembler, EF, DF->getContents().size(), FSize);
65
66    if (RequiredBundlePadding > UINT8_MAX)
67      report_fatal_error("Padding cannot exceed 255 bytes");
68
69    if (RequiredBundlePadding > 0) {
70      SmallString<256> Code;
71      raw_svector_ostream VecOS(Code);
72      EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
73      Assembler.writeFragmentPadding(VecOS, *EF, FSize);
74
75      DF->getContents().append(Code.begin(), Code.end());
76    }
77  }
78
79  flushPendingLabels(DF, DF->getContents().size());
80
81  for (unsigned i = 0, e = EF->getFixups().size(); i != e; ++i) {
82    EF->getFixups()[i].setOffset(EF->getFixups()[i].getOffset() +
83                                 DF->getContents().size());
84    DF->getFixups().push_back(EF->getFixups()[i]);
85  }
86  if (DF->getSubtargetInfo() == nullptr && EF->getSubtargetInfo())
87    DF->setHasInstructions(*EF->getSubtargetInfo());
88  DF->getContents().append(EF->getContents().begin(), EF->getContents().end());
89}
90
91void MCELFStreamer::initSections(bool NoExecStack, const MCSubtargetInfo &STI) {
92  MCContext &Ctx = getContext();
93  switchSection(Ctx.getObjectFileInfo()->getTextSection());
94  emitCodeAlignment(Align(Ctx.getObjectFileInfo()->getTextSectionAlignment()),
95                    &STI);
96
97  if (NoExecStack)
98    switchSection(Ctx.getAsmInfo()->getNonexecutableStackSection(Ctx));
99}
100
101void MCELFStreamer::emitLabel(MCSymbol *S, SMLoc Loc) {
102  auto *Symbol = cast<MCSymbolELF>(S);
103  MCObjectStreamer::emitLabel(Symbol, Loc);
104
105  const MCSectionELF &Section =
106      static_cast<const MCSectionELF &>(*getCurrentSectionOnly());
107  if (Section.getFlags() & ELF::SHF_TLS)
108    Symbol->setType(ELF::STT_TLS);
109}
110
111void MCELFStreamer::emitLabelAtPos(MCSymbol *S, SMLoc Loc, MCFragment *F,
112                                   uint64_t Offset) {
113  auto *Symbol = cast<MCSymbolELF>(S);
114  MCObjectStreamer::emitLabelAtPos(Symbol, Loc, F, Offset);
115
116  const MCSectionELF &Section =
117      static_cast<const MCSectionELF &>(*getCurrentSectionOnly());
118  if (Section.getFlags() & ELF::SHF_TLS)
119    Symbol->setType(ELF::STT_TLS);
120}
121
122void MCELFStreamer::emitAssemblerFlag(MCAssemblerFlag Flag) {
123  // Let the target do whatever target specific stuff it needs to do.
124  getAssembler().getBackend().handleAssemblerFlag(Flag);
125  // Do any generic stuff we need to do.
126  switch (Flag) {
127  case MCAF_SyntaxUnified: return; // no-op here.
128  case MCAF_Code16: return; // Change parsing mode; no-op here.
129  case MCAF_Code32: return; // Change parsing mode; no-op here.
130  case MCAF_Code64: return; // Change parsing mode; no-op here.
131  case MCAF_SubsectionsViaSymbols:
132    getAssembler().setSubsectionsViaSymbols(true);
133    return;
134  }
135
136  llvm_unreachable("invalid assembler flag!");
137}
138
139// If bundle alignment is used and there are any instructions in the section, it
140// needs to be aligned to at least the bundle size.
141static void setSectionAlignmentForBundling(const MCAssembler &Assembler,
142                                           MCSection *Section) {
143  if (Section && Assembler.isBundlingEnabled() && Section->hasInstructions())
144    Section->ensureMinAlignment(Align(Assembler.getBundleAlignSize()));
145}
146
147void MCELFStreamer::changeSection(MCSection *Section,
148                                  const MCExpr *Subsection) {
149  MCSection *CurSection = getCurrentSectionOnly();
150  if (CurSection && isBundleLocked())
151    report_fatal_error("Unterminated .bundle_lock when changing a section");
152
153  MCAssembler &Asm = getAssembler();
154  // Ensure the previous section gets aligned if necessary.
155  setSectionAlignmentForBundling(Asm, CurSection);
156  auto *SectionELF = static_cast<const MCSectionELF *>(Section);
157  const MCSymbol *Grp = SectionELF->getGroup();
158  if (Grp)
159    Asm.registerSymbol(*Grp);
160  if (SectionELF->getFlags() & ELF::SHF_GNU_RETAIN)
161    Asm.getWriter().markGnuAbi();
162
163  changeSectionImpl(Section, Subsection);
164  Asm.registerSymbol(*Section->getBeginSymbol());
165}
166
167void MCELFStreamer::emitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
168  getAssembler().registerSymbol(*Symbol);
169  const MCExpr *Value = MCSymbolRefExpr::create(
170      Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
171  Alias->setVariableValue(Value);
172}
173
174// When GNU as encounters more than one .type declaration for an object it seems
175// to use a mechanism similar to the one below to decide which type is actually
176// used in the object file.  The greater of T1 and T2 is selected based on the
177// following ordering:
178//  STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
179// If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
180// provided type).
181static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
182  for (unsigned Type : {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
183                        ELF::STT_GNU_IFUNC, ELF::STT_TLS}) {
184    if (T1 == Type)
185      return T2;
186    if (T2 == Type)
187      return T1;
188  }
189
190  return T2;
191}
192
193bool MCELFStreamer::emitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
194  auto *Symbol = cast<MCSymbolELF>(S);
195
196  // Adding a symbol attribute always introduces the symbol, note that an
197  // important side effect of calling registerSymbol here is to register
198  // the symbol with the assembler.
199  getAssembler().registerSymbol(*Symbol);
200
201  // The implementation of symbol attributes is designed to match 'as', but it
202  // leaves much to desired. It doesn't really make sense to arbitrarily add and
203  // remove flags, but 'as' allows this (in particular, see .desc).
204  //
205  // In the future it might be worth trying to make these operations more well
206  // defined.
207  switch (Attribute) {
208  case MCSA_Cold:
209  case MCSA_Extern:
210  case MCSA_LazyReference:
211  case MCSA_Reference:
212  case MCSA_SymbolResolver:
213  case MCSA_PrivateExtern:
214  case MCSA_WeakDefinition:
215  case MCSA_WeakDefAutoPrivate:
216  case MCSA_Invalid:
217  case MCSA_IndirectSymbol:
218  case MCSA_Exported:
219  case MCSA_WeakAntiDep:
220    return false;
221
222  case MCSA_NoDeadStrip:
223    // Ignore for now.
224    break;
225
226  case MCSA_ELF_TypeGnuUniqueObject:
227    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
228    Symbol->setBinding(ELF::STB_GNU_UNIQUE);
229    getAssembler().getWriter().markGnuAbi();
230    break;
231
232  case MCSA_Global:
233    // For `.weak x; .global x`, GNU as sets the binding to STB_WEAK while we
234    // traditionally set the binding to STB_GLOBAL. This is error-prone, so we
235    // error on such cases. Note, we also disallow changed binding from .local.
236    if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_GLOBAL)
237      getContext().reportError(getStartTokLoc(),
238                               Symbol->getName() +
239                                   " changed binding to STB_GLOBAL");
240    Symbol->setBinding(ELF::STB_GLOBAL);
241    break;
242
243  case MCSA_WeakReference:
244  case MCSA_Weak:
245    // For `.global x; .weak x`, both MC and GNU as set the binding to STB_WEAK.
246    // We emit a warning for now but may switch to an error in the future.
247    if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_WEAK)
248      getContext().reportWarning(
249          getStartTokLoc(), Symbol->getName() + " changed binding to STB_WEAK");
250    Symbol->setBinding(ELF::STB_WEAK);
251    break;
252
253  case MCSA_Local:
254    if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_LOCAL)
255      getContext().reportError(getStartTokLoc(),
256                               Symbol->getName() +
257                                   " changed binding to STB_LOCAL");
258    Symbol->setBinding(ELF::STB_LOCAL);
259    break;
260
261  case MCSA_ELF_TypeFunction:
262    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_FUNC));
263    break;
264
265  case MCSA_ELF_TypeIndFunction:
266    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_GNU_IFUNC));
267    getAssembler().getWriter().markGnuAbi();
268    break;
269
270  case MCSA_ELF_TypeObject:
271    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
272    break;
273
274  case MCSA_ELF_TypeTLS:
275    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_TLS));
276    break;
277
278  case MCSA_ELF_TypeCommon:
279    // TODO: Emit these as a common symbol.
280    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
281    break;
282
283  case MCSA_ELF_TypeNoType:
284    Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_NOTYPE));
285    break;
286
287  case MCSA_Protected:
288    Symbol->setVisibility(ELF::STV_PROTECTED);
289    break;
290
291  case MCSA_Memtag:
292    Symbol->setMemtag(true);
293    break;
294
295  case MCSA_Hidden:
296    Symbol->setVisibility(ELF::STV_HIDDEN);
297    break;
298
299  case MCSA_Internal:
300    Symbol->setVisibility(ELF::STV_INTERNAL);
301    break;
302
303  case MCSA_AltEntry:
304    llvm_unreachable("ELF doesn't support the .alt_entry attribute");
305
306  case MCSA_LGlobal:
307    llvm_unreachable("ELF doesn't support the .lglobl attribute");
308  }
309
310  return true;
311}
312
313void MCELFStreamer::emitCommonSymbol(MCSymbol *S, uint64_t Size,
314                                     Align ByteAlignment) {
315  auto *Symbol = cast<MCSymbolELF>(S);
316  getAssembler().registerSymbol(*Symbol);
317
318  if (!Symbol->isBindingSet())
319    Symbol->setBinding(ELF::STB_GLOBAL);
320
321  Symbol->setType(ELF::STT_OBJECT);
322
323  if (Symbol->getBinding() == ELF::STB_LOCAL) {
324    MCSection &Section = *getAssembler().getContext().getELFSection(
325        ".bss", ELF::SHT_NOBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
326    MCSectionSubPair P = getCurrentSection();
327    switchSection(&Section);
328
329    emitValueToAlignment(ByteAlignment, 0, 1, 0);
330    emitLabel(Symbol);
331    emitZeros(Size);
332
333    switchSection(P.first, P.second);
334  } else {
335    if (Symbol->declareCommon(Size, ByteAlignment))
336      report_fatal_error(Twine("Symbol: ") + Symbol->getName() +
337                         " redeclared as different type");
338  }
339
340  cast<MCSymbolELF>(Symbol)
341      ->setSize(MCConstantExpr::create(Size, getContext()));
342}
343
344void MCELFStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
345  cast<MCSymbolELF>(Symbol)->setSize(Value);
346}
347
348void MCELFStreamer::emitELFSymverDirective(const MCSymbol *OriginalSym,
349                                           StringRef Name,
350                                           bool KeepOriginalSym) {
351  getAssembler().Symvers.push_back(MCAssembler::Symver{
352      getStartTokLoc(), OriginalSym, Name, KeepOriginalSym});
353}
354
355void MCELFStreamer::emitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
356                                          Align ByteAlignment) {
357  auto *Symbol = cast<MCSymbolELF>(S);
358  // FIXME: Should this be caught and done earlier?
359  getAssembler().registerSymbol(*Symbol);
360  Symbol->setBinding(ELF::STB_LOCAL);
361  emitCommonSymbol(Symbol, Size, ByteAlignment);
362}
363
364void MCELFStreamer::emitValueImpl(const MCExpr *Value, unsigned Size,
365                                  SMLoc Loc) {
366  if (isBundleLocked())
367    report_fatal_error("Emitting values inside a locked bundle is forbidden");
368  fixSymbolsInTLSFixups(Value);
369  MCObjectStreamer::emitValueImpl(Value, Size, Loc);
370}
371
372void MCELFStreamer::emitValueToAlignment(Align Alignment, int64_t Value,
373                                         unsigned ValueSize,
374                                         unsigned MaxBytesToEmit) {
375  if (isBundleLocked())
376    report_fatal_error("Emitting values inside a locked bundle is forbidden");
377  MCObjectStreamer::emitValueToAlignment(Alignment, Value, ValueSize,
378                                         MaxBytesToEmit);
379}
380
381void MCELFStreamer::emitCGProfileEntry(const MCSymbolRefExpr *From,
382                                       const MCSymbolRefExpr *To,
383                                       uint64_t Count) {
384  getAssembler().CGProfile.push_back({From, To, Count});
385}
386
387void MCELFStreamer::emitIdent(StringRef IdentString) {
388  MCSection *Comment = getAssembler().getContext().getELFSection(
389      ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS, 1);
390  pushSection();
391  switchSection(Comment);
392  if (!SeenIdent) {
393    emitInt8(0);
394    SeenIdent = true;
395  }
396  emitBytes(IdentString);
397  emitInt8(0);
398  popSection();
399}
400
401void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
402  switch (expr->getKind()) {
403  case MCExpr::Target:
404    cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
405    break;
406  case MCExpr::Constant:
407    break;
408
409  case MCExpr::Binary: {
410    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
411    fixSymbolsInTLSFixups(be->getLHS());
412    fixSymbolsInTLSFixups(be->getRHS());
413    break;
414  }
415
416  case MCExpr::SymbolRef: {
417    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
418    switch (symRef.getKind()) {
419    default:
420      return;
421    case MCSymbolRefExpr::VK_GOTTPOFF:
422    case MCSymbolRefExpr::VK_INDNTPOFF:
423    case MCSymbolRefExpr::VK_NTPOFF:
424    case MCSymbolRefExpr::VK_GOTNTPOFF:
425    case MCSymbolRefExpr::VK_TLSCALL:
426    case MCSymbolRefExpr::VK_TLSDESC:
427    case MCSymbolRefExpr::VK_TLSGD:
428    case MCSymbolRefExpr::VK_TLSLD:
429    case MCSymbolRefExpr::VK_TLSLDM:
430    case MCSymbolRefExpr::VK_TPOFF:
431    case MCSymbolRefExpr::VK_TPREL:
432    case MCSymbolRefExpr::VK_DTPOFF:
433    case MCSymbolRefExpr::VK_DTPREL:
434    case MCSymbolRefExpr::VK_PPC_DTPMOD:
435    case MCSymbolRefExpr::VK_PPC_TPREL_LO:
436    case MCSymbolRefExpr::VK_PPC_TPREL_HI:
437    case MCSymbolRefExpr::VK_PPC_TPREL_HA:
438    case MCSymbolRefExpr::VK_PPC_TPREL_HIGH:
439    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHA:
440    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
441    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
442    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
443    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
444    case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
445    case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
446    case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
447    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGH:
448    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHA:
449    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
450    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
451    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
452    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
453    case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
454    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
455    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
456    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
457    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_PCREL:
458    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
459    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
460    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
461    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
462    case MCSymbolRefExpr::VK_PPC_TLS:
463    case MCSymbolRefExpr::VK_PPC_TLS_PCREL:
464    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
465    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
466    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
467    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
468    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_PCREL:
469    case MCSymbolRefExpr::VK_PPC_TLSGD:
470    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
471    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
472    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
473    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
474    case MCSymbolRefExpr::VK_PPC_TLSLD:
475      break;
476    }
477    getAssembler().registerSymbol(symRef.getSymbol());
478    cast<MCSymbolELF>(symRef.getSymbol()).setType(ELF::STT_TLS);
479    break;
480  }
481
482  case MCExpr::Unary:
483    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
484    break;
485  }
486}
487
488void MCELFStreamer::finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE,
489                                           uint64_t Offset) {
490  const MCSymbol *S = &SRE->getSymbol();
491  if (S->isTemporary()) {
492    if (!S->isInSection()) {
493      getContext().reportError(
494          SRE->getLoc(), Twine("Reference to undefined temporary symbol ") +
495                             "`" + S->getName() + "`");
496      return;
497    }
498    S = S->getSection().getBeginSymbol();
499    S->setUsedInReloc();
500    SRE = MCSymbolRefExpr::create(S, MCSymbolRefExpr::VK_None, getContext(),
501                                  SRE->getLoc());
502  }
503  const MCConstantExpr *MCOffset = MCConstantExpr::create(Offset, getContext());
504  if (std::optional<std::pair<bool, std::string>> Err =
505          MCObjectStreamer::emitRelocDirective(
506              *MCOffset, "BFD_RELOC_NONE", SRE, SRE->getLoc(),
507              *getContext().getSubtargetInfo()))
508    report_fatal_error("Relocation for CG Profile could not be created: " +
509                       Twine(Err->second));
510}
511
512void MCELFStreamer::finalizeCGProfile() {
513  MCAssembler &Asm = getAssembler();
514  if (Asm.CGProfile.empty())
515    return;
516  MCSection *CGProfile = getAssembler().getContext().getELFSection(
517      ".llvm.call-graph-profile", ELF::SHT_LLVM_CALL_GRAPH_PROFILE,
518      ELF::SHF_EXCLUDE, /*sizeof(Elf_CGProfile_Impl<>)=*/8);
519  pushSection();
520  switchSection(CGProfile);
521  uint64_t Offset = 0;
522  for (MCAssembler::CGProfileEntry &E : Asm.CGProfile) {
523    finalizeCGProfileEntry(E.From, Offset);
524    finalizeCGProfileEntry(E.To, Offset);
525    emitIntValue(E.Count, sizeof(uint64_t));
526    Offset += sizeof(uint64_t);
527  }
528  popSection();
529}
530
531void MCELFStreamer::emitInstToFragment(const MCInst &Inst,
532                                       const MCSubtargetInfo &STI) {
533  this->MCObjectStreamer::emitInstToFragment(Inst, STI);
534  MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
535
536  for (auto &Fixup : F.getFixups())
537    fixSymbolsInTLSFixups(Fixup.getValue());
538}
539
540// A fragment can only have one Subtarget, and when bundling is enabled we
541// sometimes need to use the same fragment. We give an error if there
542// are conflicting Subtargets.
543static void CheckBundleSubtargets(const MCSubtargetInfo *OldSTI,
544                                  const MCSubtargetInfo *NewSTI) {
545  if (OldSTI && NewSTI && OldSTI != NewSTI)
546    report_fatal_error("A Bundle can only have one Subtarget.");
547}
548
549void MCELFStreamer::emitInstToData(const MCInst &Inst,
550                                   const MCSubtargetInfo &STI) {
551  MCAssembler &Assembler = getAssembler();
552  SmallVector<MCFixup, 4> Fixups;
553  SmallString<256> Code;
554  Assembler.getEmitter().encodeInstruction(Inst, Code, Fixups, STI);
555
556  for (auto &Fixup : Fixups)
557    fixSymbolsInTLSFixups(Fixup.getValue());
558
559  // There are several possibilities here:
560  //
561  // If bundling is disabled, append the encoded instruction to the current data
562  // fragment (or create a new such fragment if the current fragment is not a
563  // data fragment, or the Subtarget has changed).
564  //
565  // If bundling is enabled:
566  // - If we're not in a bundle-locked group, emit the instruction into a
567  //   fragment of its own. If there are no fixups registered for the
568  //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
569  //   MCDataFragment.
570  // - If we're in a bundle-locked group, append the instruction to the current
571  //   data fragment because we want all the instructions in a group to get into
572  //   the same fragment. Be careful not to do that for the first instruction in
573  //   the group, though.
574  MCDataFragment *DF;
575
576  if (Assembler.isBundlingEnabled()) {
577    MCSection &Sec = *getCurrentSectionOnly();
578    if (Assembler.getRelaxAll() && isBundleLocked()) {
579      // If the -mc-relax-all flag is used and we are bundle-locked, we re-use
580      // the current bundle group.
581      DF = BundleGroups.back();
582      CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
583    }
584    else if (Assembler.getRelaxAll() && !isBundleLocked())
585      // When not in a bundle-locked group and the -mc-relax-all flag is used,
586      // we create a new temporary fragment which will be later merged into
587      // the current fragment.
588      DF = new MCDataFragment();
589    else if (isBundleLocked() && !Sec.isBundleGroupBeforeFirstInst()) {
590      // If we are bundle-locked, we re-use the current fragment.
591      // The bundle-locking directive ensures this is a new data fragment.
592      DF = cast<MCDataFragment>(getCurrentFragment());
593      CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
594    }
595    else if (!isBundleLocked() && Fixups.size() == 0) {
596      // Optimize memory usage by emitting the instruction to a
597      // MCCompactEncodedInstFragment when not in a bundle-locked group and
598      // there are no fixups registered.
599      MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
600      insert(CEIF);
601      CEIF->getContents().append(Code.begin(), Code.end());
602      CEIF->setHasInstructions(STI);
603      return;
604    } else {
605      DF = new MCDataFragment();
606      insert(DF);
607    }
608    if (Sec.getBundleLockState() == MCSection::BundleLockedAlignToEnd) {
609      // If this fragment is for a group marked "align_to_end", set a flag
610      // in the fragment. This can happen after the fragment has already been
611      // created if there are nested bundle_align groups and an inner one
612      // is the one marked align_to_end.
613      DF->setAlignToBundleEnd(true);
614    }
615
616    // We're now emitting an instruction in a bundle group, so this flag has
617    // to be turned off.
618    Sec.setBundleGroupBeforeFirstInst(false);
619  } else {
620    DF = getOrCreateDataFragment(&STI);
621  }
622
623  // Add the fixups and data.
624  for (auto &Fixup : Fixups) {
625    Fixup.setOffset(Fixup.getOffset() + DF->getContents().size());
626    DF->getFixups().push_back(Fixup);
627  }
628
629  DF->setHasInstructions(STI);
630  if (!Fixups.empty() && Fixups.back().getTargetKind() ==
631                             getAssembler().getBackend().RelaxFixupKind)
632    DF->setLinkerRelaxable();
633  DF->getContents().append(Code.begin(), Code.end());
634
635  if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
636    if (!isBundleLocked()) {
637      mergeFragment(getOrCreateDataFragment(&STI), DF);
638      delete DF;
639    }
640  }
641}
642
643void MCELFStreamer::emitBundleAlignMode(Align Alignment) {
644  assert(Log2(Alignment) <= 30 && "Invalid bundle alignment");
645  MCAssembler &Assembler = getAssembler();
646  if (Alignment > 1 && (Assembler.getBundleAlignSize() == 0 ||
647                        Assembler.getBundleAlignSize() == Alignment.value()))
648    Assembler.setBundleAlignSize(Alignment.value());
649  else
650    report_fatal_error(".bundle_align_mode cannot be changed once set");
651}
652
653void MCELFStreamer::emitBundleLock(bool AlignToEnd) {
654  MCSection &Sec = *getCurrentSectionOnly();
655
656  if (!getAssembler().isBundlingEnabled())
657    report_fatal_error(".bundle_lock forbidden when bundling is disabled");
658
659  if (!isBundleLocked())
660    Sec.setBundleGroupBeforeFirstInst(true);
661
662  if (getAssembler().getRelaxAll() && !isBundleLocked()) {
663    // TODO: drop the lock state and set directly in the fragment
664    MCDataFragment *DF = new MCDataFragment();
665    BundleGroups.push_back(DF);
666  }
667
668  Sec.setBundleLockState(AlignToEnd ? MCSection::BundleLockedAlignToEnd
669                                    : MCSection::BundleLocked);
670}
671
672void MCELFStreamer::emitBundleUnlock() {
673  MCSection &Sec = *getCurrentSectionOnly();
674
675  if (!getAssembler().isBundlingEnabled())
676    report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
677  else if (!isBundleLocked())
678    report_fatal_error(".bundle_unlock without matching lock");
679  else if (Sec.isBundleGroupBeforeFirstInst())
680    report_fatal_error("Empty bundle-locked group is forbidden");
681
682  // When the -mc-relax-all flag is used, we emit instructions to fragments
683  // stored on a stack. When the bundle unlock is emitted, we pop a fragment
684  // from the stack a merge it to the one below.
685  if (getAssembler().getRelaxAll()) {
686    assert(!BundleGroups.empty() && "There are no bundle groups");
687    MCDataFragment *DF = BundleGroups.back();
688
689    // FIXME: Use BundleGroups to track the lock state instead.
690    Sec.setBundleLockState(MCSection::NotBundleLocked);
691
692    // FIXME: Use more separate fragments for nested groups.
693    if (!isBundleLocked()) {
694      mergeFragment(getOrCreateDataFragment(DF->getSubtargetInfo()), DF);
695      BundleGroups.pop_back();
696      delete DF;
697    }
698
699    if (Sec.getBundleLockState() != MCSection::BundleLockedAlignToEnd)
700      getOrCreateDataFragment()->setAlignToBundleEnd(false);
701  } else
702    Sec.setBundleLockState(MCSection::NotBundleLocked);
703}
704
705void MCELFStreamer::finishImpl() {
706  // Emit the .gnu attributes section if any attributes have been added.
707  if (!GNUAttributes.empty()) {
708    MCSection *DummyAttributeSection = nullptr;
709    createAttributesSection("gnu", ".gnu.attributes", ELF::SHT_GNU_ATTRIBUTES,
710                            DummyAttributeSection, GNUAttributes);
711  }
712
713  // Ensure the last section gets aligned if necessary.
714  MCSection *CurSection = getCurrentSectionOnly();
715  setSectionAlignmentForBundling(getAssembler(), CurSection);
716
717  finalizeCGProfile();
718  emitFrames(nullptr);
719
720  this->MCObjectStreamer::finishImpl();
721}
722
723void MCELFStreamer::emitThumbFunc(MCSymbol *Func) {
724  llvm_unreachable("Generic ELF doesn't support this directive");
725}
726
727void MCELFStreamer::emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
728  llvm_unreachable("ELF doesn't support this directive");
729}
730
731void MCELFStreamer::emitZerofill(MCSection *Section, MCSymbol *Symbol,
732                                 uint64_t Size, Align ByteAlignment,
733                                 SMLoc Loc) {
734  llvm_unreachable("ELF doesn't support this directive");
735}
736
737void MCELFStreamer::emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
738                                   uint64_t Size, Align ByteAlignment) {
739  llvm_unreachable("ELF doesn't support this directive");
740}
741
742void MCELFStreamer::setAttributeItem(unsigned Attribute, unsigned Value,
743                                     bool OverwriteExisting) {
744  // Look for existing attribute item
745  if (AttributeItem *Item = getAttributeItem(Attribute)) {
746    if (!OverwriteExisting)
747      return;
748    Item->Type = AttributeItem::NumericAttribute;
749    Item->IntValue = Value;
750    return;
751  }
752
753  // Create new attribute item
754  AttributeItem Item = {AttributeItem::NumericAttribute, Attribute, Value,
755                        std::string(StringRef(""))};
756  Contents.push_back(Item);
757}
758
759void MCELFStreamer::setAttributeItem(unsigned Attribute, StringRef Value,
760                                     bool OverwriteExisting) {
761  // Look for existing attribute item
762  if (AttributeItem *Item = getAttributeItem(Attribute)) {
763    if (!OverwriteExisting)
764      return;
765    Item->Type = AttributeItem::TextAttribute;
766    Item->StringValue = std::string(Value);
767    return;
768  }
769
770  // Create new attribute item
771  AttributeItem Item = {AttributeItem::TextAttribute, Attribute, 0,
772                        std::string(Value)};
773  Contents.push_back(Item);
774}
775
776void MCELFStreamer::setAttributeItems(unsigned Attribute, unsigned IntValue,
777                                      StringRef StringValue,
778                                      bool OverwriteExisting) {
779  // Look for existing attribute item
780  if (AttributeItem *Item = getAttributeItem(Attribute)) {
781    if (!OverwriteExisting)
782      return;
783    Item->Type = AttributeItem::NumericAndTextAttributes;
784    Item->IntValue = IntValue;
785    Item->StringValue = std::string(StringValue);
786    return;
787  }
788
789  // Create new attribute item
790  AttributeItem Item = {AttributeItem::NumericAndTextAttributes, Attribute,
791                        IntValue, std::string(StringValue)};
792  Contents.push_back(Item);
793}
794
795MCELFStreamer::AttributeItem *
796MCELFStreamer::getAttributeItem(unsigned Attribute) {
797  for (size_t I = 0; I < Contents.size(); ++I)
798    if (Contents[I].Tag == Attribute)
799      return &Contents[I];
800  return nullptr;
801}
802
803size_t
804MCELFStreamer::calculateContentSize(SmallVector<AttributeItem, 64> &AttrsVec) {
805  size_t Result = 0;
806  for (size_t I = 0; I < AttrsVec.size(); ++I) {
807    AttributeItem Item = AttrsVec[I];
808    switch (Item.Type) {
809    case AttributeItem::HiddenAttribute:
810      break;
811    case AttributeItem::NumericAttribute:
812      Result += getULEB128Size(Item.Tag);
813      Result += getULEB128Size(Item.IntValue);
814      break;
815    case AttributeItem::TextAttribute:
816      Result += getULEB128Size(Item.Tag);
817      Result += Item.StringValue.size() + 1; // string + '\0'
818      break;
819    case AttributeItem::NumericAndTextAttributes:
820      Result += getULEB128Size(Item.Tag);
821      Result += getULEB128Size(Item.IntValue);
822      Result += Item.StringValue.size() + 1; // string + '\0';
823      break;
824    }
825  }
826  return Result;
827}
828
829void MCELFStreamer::createAttributesSection(
830    StringRef Vendor, const Twine &Section, unsigned Type,
831    MCSection *&AttributeSection, SmallVector<AttributeItem, 64> &AttrsVec) {
832  // <format-version>
833  // [ <section-length> "vendor-name"
834  // [ <file-tag> <size> <attribute>*
835  //   | <section-tag> <size> <section-number>* 0 <attribute>*
836  //   | <symbol-tag> <size> <symbol-number>* 0 <attribute>*
837  //   ]+
838  // ]*
839
840  // Switch section to AttributeSection or get/create the section.
841  if (AttributeSection) {
842    switchSection(AttributeSection);
843  } else {
844    AttributeSection = getContext().getELFSection(Section, Type, 0);
845    switchSection(AttributeSection);
846
847    // Format version
848    emitInt8(0x41);
849  }
850
851  // Vendor size + Vendor name + '\0'
852  const size_t VendorHeaderSize = 4 + Vendor.size() + 1;
853
854  // Tag + Tag Size
855  const size_t TagHeaderSize = 1 + 4;
856
857  const size_t ContentsSize = calculateContentSize(AttrsVec);
858
859  emitInt32(VendorHeaderSize + TagHeaderSize + ContentsSize);
860  emitBytes(Vendor);
861  emitInt8(0); // '\0'
862
863  emitInt8(ARMBuildAttrs::File);
864  emitInt32(TagHeaderSize + ContentsSize);
865
866  // Size should have been accounted for already, now
867  // emit each field as its type (ULEB or String)
868  for (size_t I = 0; I < AttrsVec.size(); ++I) {
869    AttributeItem Item = AttrsVec[I];
870    emitULEB128IntValue(Item.Tag);
871    switch (Item.Type) {
872    default:
873      llvm_unreachable("Invalid attribute type");
874    case AttributeItem::NumericAttribute:
875      emitULEB128IntValue(Item.IntValue);
876      break;
877    case AttributeItem::TextAttribute:
878      emitBytes(Item.StringValue);
879      emitInt8(0); // '\0'
880      break;
881    case AttributeItem::NumericAndTextAttributes:
882      emitULEB128IntValue(Item.IntValue);
883      emitBytes(Item.StringValue);
884      emitInt8(0); // '\0'
885      break;
886    }
887  }
888
889  AttrsVec.clear();
890}
891
892MCStreamer *llvm::createELFStreamer(MCContext &Context,
893                                    std::unique_ptr<MCAsmBackend> &&MAB,
894                                    std::unique_ptr<MCObjectWriter> &&OW,
895                                    std::unique_ptr<MCCodeEmitter> &&CE,
896                                    bool RelaxAll) {
897  MCELFStreamer *S =
898      new MCELFStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
899  if (RelaxAll)
900    S->getAssembler().setRelaxAll(true);
901  return S;
902}
903