1 //===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
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 #include "llvm/MC/MCAssembler.h"
11 #include "llvm/ADT/Statistic.h"
12 #include "llvm/ADT/StringExtras.h"
13 #include "llvm/ADT/Twine.h"
14 #include "llvm/MC/MCAsmBackend.h"
15 #include "llvm/MC/MCAsmInfo.h"
16 #include "llvm/MC/MCAsmLayout.h"
17 #include "llvm/MC/MCCodeEmitter.h"
18 #include "llvm/MC/MCContext.h"
19 #include "llvm/MC/MCDwarf.h"
20 #include "llvm/MC/MCExpr.h"
21 #include "llvm/MC/MCFixupKindInfo.h"
22 #include "llvm/MC/MCObjectWriter.h"
23 #include "llvm/MC/MCSection.h"
24 #include "llvm/MC/MCSectionELF.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/MC/MCValue.h"
27 #include "llvm/Support/Debug.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/LEB128.h"
30 #include "llvm/Support/TargetRegistry.h"
31 #include "llvm/Support/raw_ostream.h"
35 #define DEBUG_TYPE "assembler"
39 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
40 STATISTIC(EmittedRelaxableFragments,
41 "Number of emitted assembler fragments - relaxable");
42 STATISTIC(EmittedDataFragments,
43 "Number of emitted assembler fragments - data");
44 STATISTIC(EmittedCompactEncodedInstFragments,
45 "Number of emitted assembler fragments - compact encoded inst");
46 STATISTIC(EmittedAlignFragments,
47 "Number of emitted assembler fragments - align");
48 STATISTIC(EmittedFillFragments,
49 "Number of emitted assembler fragments - fill");
50 STATISTIC(EmittedOrgFragments,
51 "Number of emitted assembler fragments - org");
52 STATISTIC(evaluateFixup, "Number of evaluated fixups");
53 STATISTIC(FragmentLayouts, "Number of fragment layouts");
54 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
55 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
56 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
60 // FIXME FIXME FIXME: There are number of places in this file where we convert
61 // what is a 64-bit assembler value used for computation into a value in the
62 // object file, which may truncate it. We should detect that truncation where
63 // invalid and report errors back.
67 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
68 : Assembler(Asm), LastValidFragment()
70 // Compute the section layout order. Virtual sections must go last.
71 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
72 if (!it->getSection().isVirtualSection())
73 SectionOrder.push_back(&*it);
74 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
75 if (it->getSection().isVirtualSection())
76 SectionOrder.push_back(&*it);
79 bool MCAsmLayout::isFragmentValid(const MCFragment *F) const {
80 const MCSectionData &SD = *F->getParent();
81 const MCFragment *LastValid = LastValidFragment.lookup(&SD);
84 assert(LastValid->getParent() == F->getParent());
85 return F->getLayoutOrder() <= LastValid->getLayoutOrder();
88 void MCAsmLayout::invalidateFragmentsFrom(MCFragment *F) {
89 // If this fragment wasn't already valid, we don't need to do anything.
90 if (!isFragmentValid(F))
93 // Otherwise, reset the last valid fragment to the previous fragment
94 // (if this is the first fragment, it will be NULL).
95 const MCSectionData &SD = *F->getParent();
96 LastValidFragment[&SD] = F->getPrevNode();
99 void MCAsmLayout::ensureValid(const MCFragment *F) const {
100 MCSectionData &SD = *F->getParent();
102 MCFragment *Cur = LastValidFragment[&SD];
106 Cur = Cur->getNextNode();
108 // Advance the layout position until the fragment is valid.
109 while (!isFragmentValid(F)) {
110 assert(Cur && "Layout bookkeeping error");
111 const_cast<MCAsmLayout*>(this)->layoutFragment(Cur);
112 Cur = Cur->getNextNode();
116 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
118 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
122 // Simple getSymbolOffset helper for the non-varibale case.
123 static bool getLabelOffset(const MCAsmLayout &Layout, const MCSymbol &S,
124 bool ReportError, uint64_t &Val) {
125 const MCSymbolData &SD = S.getData();
126 if (!SD.getFragment()) {
128 report_fatal_error("unable to evaluate offset to undefined symbol '" +
132 Val = Layout.getFragmentOffset(SD.getFragment()) + SD.getOffset();
136 static bool getSymbolOffsetImpl(const MCAsmLayout &Layout, const MCSymbol &S,
137 bool ReportError, uint64_t &Val) {
139 return getLabelOffset(Layout, S, ReportError, Val);
141 // If SD is a variable, evaluate it.
143 if (!S.getVariableValue()->EvaluateAsRelocatable(Target, &Layout, nullptr))
144 report_fatal_error("unable to evaluate offset for variable '" +
147 uint64_t Offset = Target.getConstant();
149 const MCSymbolRefExpr *A = Target.getSymA();
152 if (!getLabelOffset(Layout, A->getSymbol(), ReportError, ValA))
157 const MCSymbolRefExpr *B = Target.getSymB();
160 if (!getLabelOffset(Layout, B->getSymbol(), ReportError, ValB))
169 bool MCAsmLayout::getSymbolOffset(const MCSymbol &S, uint64_t &Val) const {
170 return getSymbolOffsetImpl(*this, S, false, Val);
173 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbol &S) const {
175 getSymbolOffsetImpl(*this, S, true, Val);
179 const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
180 if (!Symbol.isVariable())
183 const MCExpr *Expr = Symbol.getVariableValue();
185 if (!Expr->evaluateAsValue(Value, *this))
186 llvm_unreachable("Invalid Expression");
188 const MCSymbolRefExpr *RefB = Value.getSymB();
190 Assembler.getContext().reportFatalError(
191 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
192 "' could not be evaluated in a subtraction expression");
194 const MCSymbolRefExpr *A = Value.getSymA();
198 const MCSymbol &ASym = A->getSymbol();
199 const MCAssembler &Asm = getAssembler();
200 const MCSymbolData &ASD = Asm.getSymbolData(ASym);
201 if (ASD.isCommon()) {
202 // FIXME: we should probably add a SMLoc to MCExpr.
203 Asm.getContext().reportFatalError(SMLoc(),
204 "Common symbol " + ASym.getName() +
205 " cannot be used in assignment expr");
211 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
212 // The size is the last fragment's end offset.
213 const MCFragment &F = SD->getFragmentList().back();
214 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
217 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
218 // Virtual sections have no file size.
219 if (SD->getSection().isVirtualSection())
222 // Otherwise, the file size is the same as the address space size.
223 return getSectionAddressSize(SD);
226 uint64_t llvm::computeBundlePadding(const MCAssembler &Assembler,
228 uint64_t FOffset, uint64_t FSize) {
229 uint64_t BundleSize = Assembler.getBundleAlignSize();
230 assert(BundleSize > 0 &&
231 "computeBundlePadding should only be called if bundling is enabled");
232 uint64_t BundleMask = BundleSize - 1;
233 uint64_t OffsetInBundle = FOffset & BundleMask;
234 uint64_t EndOfFragment = OffsetInBundle + FSize;
236 // There are two kinds of bundling restrictions:
238 // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
239 // *end* on a bundle boundary.
240 // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
241 // would, add padding until the end of the bundle so that the fragment
242 // will start in a new one.
243 if (F->alignToBundleEnd()) {
244 // Three possibilities here:
246 // A) The fragment just happens to end at a bundle boundary, so we're good.
247 // B) The fragment ends before the current bundle boundary: pad it just
248 // enough to reach the boundary.
249 // C) The fragment ends after the current bundle boundary: pad it until it
250 // reaches the end of the next bundle boundary.
252 // Note: this code could be made shorter with some modulo trickery, but it's
253 // intentionally kept in its more explicit form for simplicity.
254 if (EndOfFragment == BundleSize)
256 else if (EndOfFragment < BundleSize)
257 return BundleSize - EndOfFragment;
258 else { // EndOfFragment > BundleSize
259 return 2 * BundleSize - EndOfFragment;
261 } else if (EndOfFragment > BundleSize)
262 return BundleSize - OffsetInBundle;
269 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
272 MCFragment::~MCFragment() {
275 MCFragment::MCFragment(FragmentType Kind, MCSectionData *Parent)
276 : Kind(Kind), Parent(Parent), Atom(nullptr), Offset(~UINT64_C(0)) {
278 Parent->getFragmentList().push_back(this);
283 MCEncodedFragment::~MCEncodedFragment() {
288 MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
293 MCSectionData::MCSectionData() : Section(nullptr) {}
295 MCSectionData::MCSectionData(MCSection &Section, MCAssembler *A)
296 : Section(&Section), Ordinal(~UINT32_C(0)),
297 BundleLockState(NotBundleLocked), BundleLockNestingDepth(0),
298 BundleGroupBeforeFirstInst(false), HasInstructions(false) {
300 A->getSectionList().push_back(this);
303 unsigned MCSectionData::getAlignment() const { return Section->getAlignment(); }
305 void MCSectionData::setAlignment(unsigned Value) {
306 Section->setAlignment(Value);
309 MCSectionData::iterator
310 MCSectionData::getSubsectionInsertionPoint(unsigned Subsection) {
311 if (Subsection == 0 && SubsectionFragmentMap.empty())
314 SmallVectorImpl<std::pair<unsigned, MCFragment *> >::iterator MI =
315 std::lower_bound(SubsectionFragmentMap.begin(), SubsectionFragmentMap.end(),
316 std::make_pair(Subsection, (MCFragment *)nullptr));
317 bool ExactMatch = false;
318 if (MI != SubsectionFragmentMap.end()) {
319 ExactMatch = MI->first == Subsection;
324 if (MI == SubsectionFragmentMap.end())
328 if (!ExactMatch && Subsection != 0) {
329 // The GNU as documentation claims that subsections have an alignment of 4,
330 // although this appears not to be the case.
331 MCFragment *F = new MCDataFragment();
332 SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
333 getFragmentList().insert(IP, F);
340 void MCSectionData::setBundleLockState(BundleLockStateType NewState) {
341 if (NewState == NotBundleLocked) {
342 if (BundleLockNestingDepth == 0) {
343 report_fatal_error("Mismatched bundle_lock/unlock directives");
345 if (--BundleLockNestingDepth == 0) {
346 BundleLockState = NotBundleLocked;
351 // If any of the directives is an align_to_end directive, the whole nested
352 // group is align_to_end. So don't downgrade from align_to_end to just locked.
353 if (BundleLockState != BundleLockedAlignToEnd) {
354 BundleLockState = NewState;
356 ++BundleLockNestingDepth;
361 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
362 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
364 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
365 OS(OS_), BundleAlignSize(0), RelaxAll(false),
366 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
367 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
370 MCAssembler::~MCAssembler() {
373 void MCAssembler::reset() {
377 IndirectSymbols.clear();
379 LinkerOptions.clear();
384 SubsectionsViaSymbols = false;
386 LOHContainer.reset();
387 VersionMinInfo.Major = 0;
389 // reset objects owned by us
390 getBackend().reset();
391 getEmitter().reset();
393 getLOHContainer().reset();
396 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
397 if (ThumbFuncs.count(Symbol))
400 if (!Symbol->isVariable())
403 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
404 // is not clear if that is a bug or a feature.
405 const MCExpr *Expr = Symbol->getVariableValue();
406 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
410 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
413 const MCSymbol &Sym = Ref->getSymbol();
414 if (!isThumbFunc(&Sym))
417 ThumbFuncs.insert(Symbol); // Cache it.
421 void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
422 assert(Sym.isTemporary());
423 LocalsUsedInReloc.insert(&Sym);
426 bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
427 assert(Sym.isTemporary());
428 return LocalsUsedInReloc.count(&Sym);
431 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
432 // Non-temporary labels should always be visible to the linker.
433 if (!Symbol.isTemporary())
436 // Absolute temporary labels are never visible.
437 if (!Symbol.isInSection())
440 if (isLocalUsedInReloc(Symbol))
446 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
447 // Linker visible symbols define atoms.
448 if (isSymbolLinkerVisible(S))
451 // Absolute and undefined symbols have no defining atom.
452 if (!S.getData().getFragment())
455 // Non-linker visible symbols in sections which can't be atomized have no
457 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
458 S.getData().getFragment()->getParent()->getSection()))
461 // Otherwise, return the atom for the containing fragment.
462 return S.getData().getFragment()->getAtom();
465 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
466 const MCFixup &Fixup, const MCFragment *DF,
467 MCValue &Target, uint64_t &Value) const {
468 ++stats::evaluateFixup;
470 // FIXME: This code has some duplication with RecordRelocation. We should
471 // probably merge the two into a single callback that tries to evaluate a
472 // fixup and records a relocation if one is needed.
473 const MCExpr *Expr = Fixup.getValue();
474 if (!Expr->EvaluateAsRelocatable(Target, &Layout, &Fixup))
475 getContext().reportFatalError(Fixup.getLoc(), "expected relocatable expression");
477 bool IsPCRel = Backend.getFixupKindInfo(
478 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
482 if (Target.getSymB()) {
484 } else if (!Target.getSymA()) {
487 const MCSymbolRefExpr *A = Target.getSymA();
488 const MCSymbol &SA = A->getSymbol();
489 if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
492 IsResolved = getWriter().IsSymbolRefDifferenceFullyResolvedImpl(
493 *this, SA, *DF, false, true);
497 IsResolved = Target.isAbsolute();
500 Value = Target.getConstant();
502 if (const MCSymbolRefExpr *A = Target.getSymA()) {
503 const MCSymbol &Sym = A->getSymbol();
505 Value += Layout.getSymbolOffset(Sym);
507 if (const MCSymbolRefExpr *B = Target.getSymB()) {
508 const MCSymbol &Sym = B->getSymbol();
510 Value -= Layout.getSymbolOffset(Sym);
514 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
515 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
516 assert((ShouldAlignPC ? IsPCRel : true) &&
517 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
520 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
522 // A number of ARM fixups in Thumb mode require that the effective PC
523 // address be determined as the 32-bit aligned version of the actual offset.
524 if (ShouldAlignPC) Offset &= ~0x3;
528 // Let the backend adjust the fixup value if necessary, including whether
529 // we need a relocation.
530 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
536 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
537 const MCFragment &F) const {
538 switch (F.getKind()) {
539 case MCFragment::FT_Data:
540 case MCFragment::FT_Relaxable:
541 case MCFragment::FT_CompactEncodedInst:
542 return cast<MCEncodedFragment>(F).getContents().size();
543 case MCFragment::FT_Fill:
544 return cast<MCFillFragment>(F).getSize();
546 case MCFragment::FT_LEB:
547 return cast<MCLEBFragment>(F).getContents().size();
549 case MCFragment::FT_Align: {
550 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
551 unsigned Offset = Layout.getFragmentOffset(&AF);
552 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
553 // If we are padding with nops, force the padding to be larger than the
555 if (Size > 0 && AF.hasEmitNops()) {
556 while (Size % getBackend().getMinimumNopSize())
557 Size += AF.getAlignment();
559 if (Size > AF.getMaxBytesToEmit())
564 case MCFragment::FT_Org: {
565 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
566 int64_t TargetLocation;
567 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
568 report_fatal_error("expected assembly-time absolute expression");
570 // FIXME: We need a way to communicate this error.
571 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
572 int64_t Size = TargetLocation - FragmentOffset;
573 if (Size < 0 || Size >= 0x40000000)
574 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
575 "' (at offset '" + Twine(FragmentOffset) + "')");
579 case MCFragment::FT_Dwarf:
580 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
581 case MCFragment::FT_DwarfFrame:
582 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
585 llvm_unreachable("invalid fragment kind");
588 void MCAsmLayout::layoutFragment(MCFragment *F) {
589 MCFragment *Prev = F->getPrevNode();
591 // We should never try to recompute something which is valid.
592 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
593 // We should never try to compute the fragment layout if its predecessor
595 assert((!Prev || isFragmentValid(Prev)) &&
596 "Attempt to compute fragment before its predecessor!");
598 ++stats::FragmentLayouts;
600 // Compute fragment offset and size.
602 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
605 LastValidFragment[F->getParent()] = F;
607 // If bundling is enabled and this fragment has instructions in it, it has to
608 // obey the bundling restrictions. With padding, we'll have:
613 // -------------------------------------
614 // Prev |##########| F |
615 // -------------------------------------
620 // The fragment's offset will point to after the padding, and its computed
621 // size won't include the padding.
623 // When the -mc-relax-all flag is used, we optimize bundling by writting the
624 // bundle padding directly into fragments when the instructions are emitted
625 // inside the streamer.
627 if (Assembler.isBundlingEnabled() && !Assembler.getRelaxAll() &&
628 F->hasInstructions()) {
629 assert(isa<MCEncodedFragment>(F) &&
630 "Only MCEncodedFragment implementations have instructions");
631 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
633 if (FSize > Assembler.getBundleAlignSize())
634 report_fatal_error("Fragment can't be larger than a bundle size");
636 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
638 if (RequiredBundlePadding > UINT8_MAX)
639 report_fatal_error("Padding cannot exceed 255 bytes");
640 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
641 F->Offset += RequiredBundlePadding;
645 /// \brief Write the contents of a fragment to the given object writer. Expects
646 /// a MCEncodedFragment.
647 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
648 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
649 OW->WriteBytes(EF.getContents());
652 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
653 MCObjectWriter *OW) const {
654 // Should NOP padding be written out before this fragment?
655 unsigned BundlePadding = F.getBundlePadding();
656 if (BundlePadding > 0) {
657 assert(isBundlingEnabled() &&
658 "Writing bundle padding with disabled bundling");
659 assert(F.hasInstructions() &&
660 "Writing bundle padding for a fragment without instructions");
662 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
663 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
664 // If the padding itself crosses a bundle boundary, it must be emitted
665 // in 2 pieces, since even nop instructions must not cross boundaries.
666 // v--------------v <- BundleAlignSize
667 // v---------v <- BundlePadding
668 // ----------------------------
669 // | Prev |####|####| F |
670 // ----------------------------
671 // ^-------------------^ <- TotalLength
672 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
673 if (!getBackend().writeNopData(DistanceToBoundary, OW))
674 report_fatal_error("unable to write NOP sequence of " +
675 Twine(DistanceToBoundary) + " bytes");
676 BundlePadding -= DistanceToBoundary;
678 if (!getBackend().writeNopData(BundlePadding, OW))
679 report_fatal_error("unable to write NOP sequence of " +
680 Twine(BundlePadding) + " bytes");
684 /// \brief Write the fragment \p F to the output file.
685 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
686 const MCFragment &F) {
687 MCObjectWriter *OW = &Asm.getWriter();
689 // FIXME: Embed in fragments instead?
690 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
692 Asm.writeFragmentPadding(F, FragmentSize, OW);
694 // This variable (and its dummy usage) is to participate in the assert at
695 // the end of the function.
696 uint64_t Start = OW->getStream().tell();
699 ++stats::EmittedFragments;
701 switch (F.getKind()) {
702 case MCFragment::FT_Align: {
703 ++stats::EmittedAlignFragments;
704 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
705 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
707 uint64_t Count = FragmentSize / AF.getValueSize();
709 // FIXME: This error shouldn't actually occur (the front end should emit
710 // multiple .align directives to enforce the semantics it wants), but is
711 // severe enough that we want to report it. How to handle this?
712 if (Count * AF.getValueSize() != FragmentSize)
713 report_fatal_error("undefined .align directive, value size '" +
714 Twine(AF.getValueSize()) +
715 "' is not a divisor of padding size '" +
716 Twine(FragmentSize) + "'");
718 // See if we are aligning with nops, and if so do that first to try to fill
719 // the Count bytes. Then if that did not fill any bytes or there are any
720 // bytes left to fill use the Value and ValueSize to fill the rest.
721 // If we are aligning with nops, ask that target to emit the right data.
722 if (AF.hasEmitNops()) {
723 if (!Asm.getBackend().writeNopData(Count, OW))
724 report_fatal_error("unable to write nop sequence of " +
725 Twine(Count) + " bytes");
729 // Otherwise, write out in multiples of the value size.
730 for (uint64_t i = 0; i != Count; ++i) {
731 switch (AF.getValueSize()) {
732 default: llvm_unreachable("Invalid size!");
733 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
734 case 2: OW->Write16(uint16_t(AF.getValue())); break;
735 case 4: OW->Write32(uint32_t(AF.getValue())); break;
736 case 8: OW->Write64(uint64_t(AF.getValue())); break;
742 case MCFragment::FT_Data:
743 ++stats::EmittedDataFragments;
744 writeFragmentContents(F, OW);
747 case MCFragment::FT_Relaxable:
748 ++stats::EmittedRelaxableFragments;
749 writeFragmentContents(F, OW);
752 case MCFragment::FT_CompactEncodedInst:
753 ++stats::EmittedCompactEncodedInstFragments;
754 writeFragmentContents(F, OW);
757 case MCFragment::FT_Fill: {
758 ++stats::EmittedFillFragments;
759 const MCFillFragment &FF = cast<MCFillFragment>(F);
761 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
763 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
764 switch (FF.getValueSize()) {
765 default: llvm_unreachable("Invalid size!");
766 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
767 case 2: OW->Write16(uint16_t(FF.getValue())); break;
768 case 4: OW->Write32(uint32_t(FF.getValue())); break;
769 case 8: OW->Write64(uint64_t(FF.getValue())); break;
775 case MCFragment::FT_LEB: {
776 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
777 OW->WriteBytes(LF.getContents());
781 case MCFragment::FT_Org: {
782 ++stats::EmittedOrgFragments;
783 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
785 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
786 OW->Write8(uint8_t(OF.getValue()));
791 case MCFragment::FT_Dwarf: {
792 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
793 OW->WriteBytes(OF.getContents());
796 case MCFragment::FT_DwarfFrame: {
797 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
798 OW->WriteBytes(CF.getContents());
803 assert(OW->getStream().tell() - Start == FragmentSize &&
804 "The stream should advance by fragment size");
807 void MCAssembler::writeSectionData(const MCSectionData *SD,
808 const MCAsmLayout &Layout) const {
809 // Ignore virtual sections.
810 if (SD->getSection().isVirtualSection()) {
811 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
813 // Check that contents are only things legal inside a virtual section.
814 for (MCSectionData::const_iterator it = SD->begin(),
815 ie = SD->end(); it != ie; ++it) {
816 switch (it->getKind()) {
817 default: llvm_unreachable("Invalid fragment in virtual section!");
818 case MCFragment::FT_Data: {
819 // Check that we aren't trying to write a non-zero contents (or fixups)
820 // into a virtual section. This is to support clients which use standard
821 // directives to fill the contents of virtual sections.
822 const MCDataFragment &DF = cast<MCDataFragment>(*it);
823 assert(DF.fixup_begin() == DF.fixup_end() &&
824 "Cannot have fixups in virtual section!");
825 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
826 if (DF.getContents()[i]) {
827 if (auto *ELFSec = dyn_cast<const MCSectionELF>(&SD->getSection()))
828 report_fatal_error("non-zero initializer found in section '" +
829 ELFSec->getSectionName() + "'");
831 report_fatal_error("non-zero initializer found in virtual section");
835 case MCFragment::FT_Align:
836 // Check that we aren't trying to write a non-zero value into a virtual
838 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
839 cast<MCAlignFragment>(it)->getValue() == 0) &&
840 "Invalid align in virtual section!");
842 case MCFragment::FT_Fill:
843 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
844 cast<MCFillFragment>(it)->getValue() == 0) &&
845 "Invalid fill in virtual section!");
853 uint64_t Start = getWriter().getStream().tell();
856 for (MCSectionData::const_iterator it = SD->begin(), ie = SD->end();
858 writeFragment(*this, Layout, *it);
860 assert(getWriter().getStream().tell() - Start ==
861 Layout.getSectionAddressSize(SD));
864 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
866 const MCFixup &Fixup) {
867 // Evaluate the fixup.
870 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
871 MCFixupKindInfo::FKF_IsPCRel;
872 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
873 // The fixup was unresolved, we need a relocation. Inform the object
874 // writer of the relocation, and give it an opportunity to adjust the
875 // fixup value if need be.
876 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
879 return std::make_pair(FixedValue, IsPCRel);
882 void MCAssembler::Finish() {
883 DEBUG_WITH_TYPE("mc-dump", {
884 llvm::errs() << "assembler backend - pre-layout\n--\n";
887 // Create the layout object.
888 MCAsmLayout Layout(*this);
890 // Create dummy fragments and assign section ordinals.
891 unsigned SectionIndex = 0;
892 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
893 // Create dummy fragments to eliminate any empty sections, this simplifies
895 if (it->getFragmentList().empty())
896 new MCDataFragment(it);
898 it->setOrdinal(SectionIndex++);
901 // Assign layout order indices to sections and fragments.
902 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
903 MCSectionData *SD = Layout.getSectionOrder()[i];
904 SD->setLayoutOrder(i);
906 unsigned FragmentIndex = 0;
907 for (MCSectionData::iterator iFrag = SD->begin(), iFragEnd = SD->end();
908 iFrag != iFragEnd; ++iFrag)
909 iFrag->setLayoutOrder(FragmentIndex++);
912 // Layout until everything fits.
913 while (layoutOnce(Layout))
916 DEBUG_WITH_TYPE("mc-dump", {
917 llvm::errs() << "assembler backend - post-relaxation\n--\n";
920 // Finalize the layout, including fragment lowering.
921 finishLayout(Layout);
923 DEBUG_WITH_TYPE("mc-dump", {
924 llvm::errs() << "assembler backend - final-layout\n--\n";
927 uint64_t StartOffset = OS.tell();
929 // Allow the object writer a chance to perform post-layout binding (for
930 // example, to set the index fields in the symbol data).
931 getWriter().ExecutePostLayoutBinding(*this, Layout);
933 // Evaluate and apply the fixups, generating relocation entries as necessary.
934 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
935 for (MCSectionData::iterator it2 = it->begin(),
936 ie2 = it->end(); it2 != ie2; ++it2) {
937 MCEncodedFragmentWithFixups *F =
938 dyn_cast<MCEncodedFragmentWithFixups>(it2);
940 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
941 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
942 MCFixup &Fixup = *it3;
945 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
946 getBackend().applyFixup(Fixup, F->getContents().data(),
947 F->getContents().size(), FixedValue, IsPCRel);
953 // Write the object file.
954 getWriter().WriteObject(*this, Layout);
956 stats::ObjectBytes += OS.tell() - StartOffset;
959 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
960 const MCRelaxableFragment *DF,
961 const MCAsmLayout &Layout) const {
962 // If we cannot resolve the fixup value, it requires relaxation.
965 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
968 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
971 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
972 const MCAsmLayout &Layout) const {
973 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
974 // are intentionally pushing out inst fragments, or because we relaxed a
975 // previous instruction to one that doesn't need relaxation.
976 if (!getBackend().mayNeedRelaxation(F->getInst()))
979 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
980 ie = F->fixup_end(); it != ie; ++it)
981 if (fixupNeedsRelaxation(*it, F, Layout))
987 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
988 MCRelaxableFragment &F) {
989 if (!fragmentNeedsRelaxation(&F, Layout))
992 ++stats::RelaxedInstructions;
994 // FIXME-PERF: We could immediately lower out instructions if we can tell
995 // they are fully resolved, to avoid retesting on later passes.
997 // Relax the fragment.
1000 getBackend().relaxInstruction(F.getInst(), Relaxed);
1002 // Encode the new instruction.
1004 // FIXME-PERF: If it matters, we could let the target do this. It can
1005 // probably do so more efficiently in many cases.
1006 SmallVector<MCFixup, 4> Fixups;
1007 SmallString<256> Code;
1008 raw_svector_ostream VecOS(Code);
1009 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
1012 // Update the fragment.
1014 F.getContents() = Code;
1015 F.getFixups() = Fixups;
1020 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1021 uint64_t OldSize = LF.getContents().size();
1023 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1025 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
1026 SmallString<8> &Data = LF.getContents();
1028 raw_svector_ostream OSE(Data);
1030 encodeSLEB128(Value, OSE);
1032 encodeULEB128(Value, OSE);
1034 return OldSize != LF.getContents().size();
1037 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1038 MCDwarfLineAddrFragment &DF) {
1039 MCContext &Context = Layout.getAssembler().getContext();
1040 uint64_t OldSize = DF.getContents().size();
1042 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1043 assert(Abs && "We created a line delta with an invalid expression");
1046 LineDelta = DF.getLineDelta();
1047 SmallString<8> &Data = DF.getContents();
1049 raw_svector_ostream OSE(Data);
1050 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1052 return OldSize != Data.size();
1055 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1056 MCDwarfCallFrameFragment &DF) {
1057 MCContext &Context = Layout.getAssembler().getContext();
1058 uint64_t OldSize = DF.getContents().size();
1060 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1061 assert(Abs && "We created call frame with an invalid expression");
1063 SmallString<8> &Data = DF.getContents();
1065 raw_svector_ostream OSE(Data);
1066 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1068 return OldSize != Data.size();
1071 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSectionData &SD) {
1072 // Holds the first fragment which needed relaxing during this layout. It will
1073 // remain NULL if none were relaxed.
1074 // When a fragment is relaxed, all the fragments following it should get
1075 // invalidated because their offset is going to change.
1076 MCFragment *FirstRelaxedFragment = nullptr;
1078 // Attempt to relax all the fragments in the section.
1079 for (MCSectionData::iterator I = SD.begin(), IE = SD.end(); I != IE; ++I) {
1080 // Check if this is a fragment that needs relaxation.
1081 bool RelaxedFrag = false;
1082 switch(I->getKind()) {
1085 case MCFragment::FT_Relaxable:
1086 assert(!getRelaxAll() &&
1087 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1088 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1090 case MCFragment::FT_Dwarf:
1091 RelaxedFrag = relaxDwarfLineAddr(Layout,
1092 *cast<MCDwarfLineAddrFragment>(I));
1094 case MCFragment::FT_DwarfFrame:
1096 relaxDwarfCallFrameFragment(Layout,
1097 *cast<MCDwarfCallFrameFragment>(I));
1099 case MCFragment::FT_LEB:
1100 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1103 if (RelaxedFrag && !FirstRelaxedFragment)
1104 FirstRelaxedFragment = I;
1106 if (FirstRelaxedFragment) {
1107 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1113 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1114 ++stats::RelaxationSteps;
1116 bool WasRelaxed = false;
1117 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1118 MCSectionData &SD = *it;
1119 while (layoutSectionOnce(Layout, SD))
1126 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1127 // The layout is done. Mark every fragment as valid.
1128 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1129 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1133 // Debugging methods
1137 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1138 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1139 << " Value:" << *AF.getValue()
1140 << " Kind:" << AF.getKind() << ">";
1146 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1147 void MCFragment::dump() {
1148 raw_ostream &OS = llvm::errs();
1151 switch (getKind()) {
1152 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1153 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1154 case MCFragment::FT_CompactEncodedInst:
1155 OS << "MCCompactEncodedInstFragment"; break;
1156 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1157 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1158 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1159 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1160 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1161 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1164 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1165 << " Offset:" << Offset
1166 << " HasInstructions:" << hasInstructions()
1167 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1169 switch (getKind()) {
1170 case MCFragment::FT_Align: {
1171 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1172 if (AF->hasEmitNops())
1173 OS << " (emit nops)";
1175 OS << " Alignment:" << AF->getAlignment()
1176 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1177 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1180 case MCFragment::FT_Data: {
1181 const MCDataFragment *DF = cast<MCDataFragment>(this);
1183 OS << " Contents:[";
1184 const SmallVectorImpl<char> &Contents = DF->getContents();
1185 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1187 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1189 OS << "] (" << Contents.size() << " bytes)";
1191 if (DF->fixup_begin() != DF->fixup_end()) {
1194 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1195 ie = DF->fixup_end(); it != ie; ++it) {
1196 if (it != DF->fixup_begin()) OS << ",\n ";
1203 case MCFragment::FT_CompactEncodedInst: {
1204 const MCCompactEncodedInstFragment *CEIF =
1205 cast<MCCompactEncodedInstFragment>(this);
1207 OS << " Contents:[";
1208 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1209 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1211 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1213 OS << "] (" << Contents.size() << " bytes)";
1216 case MCFragment::FT_Fill: {
1217 const MCFillFragment *FF = cast<MCFillFragment>(this);
1218 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1219 << " Size:" << FF->getSize();
1222 case MCFragment::FT_Relaxable: {
1223 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1226 F->getInst().dump_pretty(OS);
1229 case MCFragment::FT_Org: {
1230 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1232 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1235 case MCFragment::FT_Dwarf: {
1236 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1238 OS << " AddrDelta:" << OF->getAddrDelta()
1239 << " LineDelta:" << OF->getLineDelta();
1242 case MCFragment::FT_DwarfFrame: {
1243 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1245 OS << " AddrDelta:" << CF->getAddrDelta();
1248 case MCFragment::FT_LEB: {
1249 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1251 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1258 void MCSectionData::dump() {
1259 raw_ostream &OS = llvm::errs();
1261 OS << "<MCSectionData";
1262 OS << " Alignment:" << getAlignment()
1263 << " Fragments:[\n ";
1264 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1265 if (it != begin()) OS << ",\n ";
1271 void MCSymbolData::dump() const {
1272 raw_ostream &OS = llvm::errs();
1274 OS << "<MCSymbolData"
1275 << " Fragment:" << getFragment();
1277 OS << " Offset:" << getOffset();
1278 OS << " Flags:" << getFlags() << " Index:" << getIndex();
1280 OS << " (common, size:" << getCommonSize()
1281 << " align: " << getCommonAlignment() << ")";
1283 OS << " (external)";
1284 if (isPrivateExtern())
1285 OS << " (private extern)";
1289 void MCAssembler::dump() {
1290 raw_ostream &OS = llvm::errs();
1292 OS << "<MCAssembler\n";
1293 OS << " Sections:[\n ";
1294 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1295 if (it != begin()) OS << ",\n ";
1301 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1302 if (it != symbol_begin()) OS << ",\n ";
1306 it->getData().dump();
1313 // anchors for MC*Fragment vtables
1314 void MCEncodedFragment::anchor() { }
1315 void MCEncodedFragmentWithFixups::anchor() { }
1316 void MCDataFragment::anchor() { }
1317 void MCCompactEncodedInstFragment::anchor() { }
1318 void MCRelaxableFragment::anchor() { }
1319 void MCAlignFragment::anchor() { }
1320 void MCFillFragment::anchor() { }
1321 void MCOrgFragment::anchor() { }
1322 void MCLEBFragment::anchor() { }
1323 void MCDwarfLineAddrFragment::anchor() { }
1324 void MCDwarfCallFrameFragment::anchor() { }