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/MCAsmLayout.h"
16 #include "llvm/MC/MCCodeEmitter.h"
17 #include "llvm/MC/MCContext.h"
18 #include "llvm/MC/MCDwarf.h"
19 #include "llvm/MC/MCExpr.h"
20 #include "llvm/MC/MCFixupKindInfo.h"
21 #include "llvm/MC/MCObjectWriter.h"
22 #include "llvm/MC/MCSection.h"
23 #include "llvm/MC/MCSymbol.h"
24 #include "llvm/MC/MCValue.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/LEB128.h"
28 #include "llvm/Support/TargetRegistry.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/MC/MCSectionELF.h"
34 #define DEBUG_TYPE "assembler"
38 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
39 STATISTIC(EmittedRelaxableFragments,
40 "Number of emitted assembler fragments - relaxable");
41 STATISTIC(EmittedDataFragments,
42 "Number of emitted assembler fragments - data");
43 STATISTIC(EmittedCompactEncodedInstFragments,
44 "Number of emitted assembler fragments - compact encoded inst");
45 STATISTIC(EmittedAlignFragments,
46 "Number of emitted assembler fragments - align");
47 STATISTIC(EmittedFillFragments,
48 "Number of emitted assembler fragments - fill");
49 STATISTIC(EmittedOrgFragments,
50 "Number of emitted assembler fragments - org");
51 STATISTIC(evaluateFixup, "Number of evaluated fixups");
52 STATISTIC(FragmentLayouts, "Number of fragment layouts");
53 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
54 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
55 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
59 // FIXME FIXME FIXME: There are number of places in this file where we convert
60 // what is a 64-bit assembler value used for computation into a value in the
61 // object file, which may truncate it. We should detect that truncation where
62 // invalid and report errors back.
66 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
67 : Assembler(Asm), LastValidFragment()
69 // Compute the section layout order. Virtual sections must go last.
70 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
71 if (!it->getSection().isVirtualSection())
72 SectionOrder.push_back(&*it);
73 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
74 if (it->getSection().isVirtualSection())
75 SectionOrder.push_back(&*it);
78 bool MCAsmLayout::isFragmentValid(const MCFragment *F) const {
79 const MCSectionData &SD = *F->getParent();
80 const MCFragment *LastValid = LastValidFragment.lookup(&SD);
83 assert(LastValid->getParent() == F->getParent());
84 return F->getLayoutOrder() <= LastValid->getLayoutOrder();
87 void MCAsmLayout::invalidateFragmentsFrom(MCFragment *F) {
88 // If this fragment wasn't already valid, we don't need to do anything.
89 if (!isFragmentValid(F))
92 // Otherwise, reset the last valid fragment to the previous fragment
93 // (if this is the first fragment, it will be NULL).
94 const MCSectionData &SD = *F->getParent();
95 LastValidFragment[&SD] = F->getPrevNode();
98 void MCAsmLayout::ensureValid(const MCFragment *F) const {
99 MCSectionData &SD = *F->getParent();
101 MCFragment *Cur = LastValidFragment[&SD];
105 Cur = Cur->getNextNode();
107 // Advance the layout position until the fragment is valid.
108 while (!isFragmentValid(F)) {
109 assert(Cur && "Layout bookkeeping error");
110 const_cast<MCAsmLayout*>(this)->layoutFragment(Cur);
111 Cur = Cur->getNextNode();
115 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
117 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
121 // Simple getSymbolOffset helper for the non-varibale case.
122 static bool getLabelOffset(const MCAsmLayout &Layout, const MCSymbolData &SD,
123 bool ReportError, uint64_t &Val) {
124 if (!SD.getFragment()) {
126 report_fatal_error("unable to evaluate offset to undefined symbol '" +
127 SD.getSymbol().getName() + "'");
130 Val = Layout.getFragmentOffset(SD.getFragment()) + SD.getOffset();
134 static bool getSymbolOffsetImpl(const MCAsmLayout &Layout,
135 const MCSymbolData *SD, bool ReportError,
137 const MCSymbol &S = SD->getSymbol();
140 return getLabelOffset(Layout, *SD, ReportError, Val);
142 // If SD is a variable, evaluate it.
144 if (!S.getVariableValue()->EvaluateAsValue(Target, &Layout, nullptr))
145 report_fatal_error("unable to evaluate offset for variable '" +
148 uint64_t Offset = Target.getConstant();
150 const MCAssembler &Asm = Layout.getAssembler();
152 const MCSymbolRefExpr *A = Target.getSymA();
155 if (!getLabelOffset(Layout, Asm.getSymbolData(A->getSymbol()), ReportError,
161 const MCSymbolRefExpr *B = Target.getSymB();
164 if (!getLabelOffset(Layout, Asm.getSymbolData(B->getSymbol()), ReportError,
174 bool MCAsmLayout::getSymbolOffset(const MCSymbolData *SD, uint64_t &Val) const {
175 return getSymbolOffsetImpl(*this, SD, false, Val);
178 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
180 getSymbolOffsetImpl(*this, SD, true, Val);
184 const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
185 if (!Symbol.isVariable())
188 const MCExpr *Expr = Symbol.getVariableValue();
190 if (!Expr->EvaluateAsValue(Value, this, nullptr))
191 llvm_unreachable("Invalid Expression");
193 const MCSymbolRefExpr *RefB = Value.getSymB();
195 Assembler.getContext().FatalError(
196 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
197 "' could not be evaluated in a subtraction expression");
199 const MCSymbolRefExpr *A = Value.getSymA();
203 return &A->getSymbol();
206 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
207 // The size is the last fragment's end offset.
208 const MCFragment &F = SD->getFragmentList().back();
209 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
212 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
213 // Virtual sections have no file size.
214 if (SD->getSection().isVirtualSection())
217 // Otherwise, the file size is the same as the address space size.
218 return getSectionAddressSize(SD);
221 uint64_t MCAsmLayout::computeBundlePadding(const MCFragment *F,
222 uint64_t FOffset, uint64_t FSize) {
223 uint64_t BundleSize = Assembler.getBundleAlignSize();
224 assert(BundleSize > 0 &&
225 "computeBundlePadding should only be called if bundling is enabled");
226 uint64_t BundleMask = BundleSize - 1;
227 uint64_t OffsetInBundle = FOffset & BundleMask;
228 uint64_t EndOfFragment = OffsetInBundle + FSize;
230 // There are two kinds of bundling restrictions:
232 // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
233 // *end* on a bundle boundary.
234 // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
235 // would, add padding until the end of the bundle so that the fragment
236 // will start in a new one.
237 if (F->alignToBundleEnd()) {
238 // Three possibilities here:
240 // A) The fragment just happens to end at a bundle boundary, so we're good.
241 // B) The fragment ends before the current bundle boundary: pad it just
242 // enough to reach the boundary.
243 // C) The fragment ends after the current bundle boundary: pad it until it
244 // reaches the end of the next bundle boundary.
246 // Note: this code could be made shorter with some modulo trickery, but it's
247 // intentionally kept in its more explicit form for simplicity.
248 if (EndOfFragment == BundleSize)
250 else if (EndOfFragment < BundleSize)
251 return BundleSize - EndOfFragment;
252 else { // EndOfFragment > BundleSize
253 return 2 * BundleSize - EndOfFragment;
255 } else if (EndOfFragment > BundleSize)
256 return BundleSize - OffsetInBundle;
263 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
266 MCFragment::~MCFragment() {
269 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
270 : Kind(_Kind), Parent(_Parent), Atom(nullptr), Offset(~UINT64_C(0))
273 Parent->getFragmentList().push_back(this);
278 MCEncodedFragment::~MCEncodedFragment() {
283 MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
288 MCSectionData::MCSectionData() : Section(nullptr) {}
290 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
291 : Section(&_Section),
292 Ordinal(~UINT32_C(0)),
294 BundleLockState(NotBundleLocked),
295 BundleLockNestingDepth(0),
296 BundleGroupBeforeFirstInst(false),
297 HasInstructions(false)
300 A->getSectionList().push_back(this);
303 MCSectionData::iterator
304 MCSectionData::getSubsectionInsertionPoint(unsigned Subsection) {
305 if (Subsection == 0 && SubsectionFragmentMap.empty())
308 SmallVectorImpl<std::pair<unsigned, MCFragment *> >::iterator MI =
309 std::lower_bound(SubsectionFragmentMap.begin(), SubsectionFragmentMap.end(),
310 std::make_pair(Subsection, (MCFragment *)nullptr));
311 bool ExactMatch = false;
312 if (MI != SubsectionFragmentMap.end()) {
313 ExactMatch = MI->first == Subsection;
318 if (MI == SubsectionFragmentMap.end())
322 if (!ExactMatch && Subsection != 0) {
323 // The GNU as documentation claims that subsections have an alignment of 4,
324 // although this appears not to be the case.
325 MCFragment *F = new MCDataFragment();
326 SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
327 getFragmentList().insert(IP, F);
333 void MCSectionData::setBundleLockState(BundleLockStateType NewState) {
334 if (NewState == NotBundleLocked) {
335 if (BundleLockNestingDepth == 0) {
336 report_fatal_error("Mismatched bundle_lock/unlock directives");
338 if (--BundleLockNestingDepth == 0) {
339 BundleLockState = NotBundleLocked;
344 // If any of the directives is an align_to_end directive, the whole nested
345 // group is align_to_end. So don't downgrade from align_to_end to just locked.
346 if (BundleLockState != BundleLockedAlignToEnd) {
347 BundleLockState = NewState;
349 ++BundleLockNestingDepth;
354 MCSymbolData::MCSymbolData() : Symbol(nullptr) {}
356 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
357 uint64_t _Offset, MCAssembler *A)
358 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
359 SymbolSize(nullptr), CommonAlign(-1U), Flags(0), Index(0) {
361 A->getSymbolList().push_back(this);
366 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
367 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
369 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
370 OS(OS_), BundleAlignSize(0), RelaxAll(false),
371 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
372 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
375 MCAssembler::~MCAssembler() {
378 void MCAssembler::reset() {
383 IndirectSymbols.clear();
385 LinkerOptions.clear();
390 SubsectionsViaSymbols = false;
392 LOHContainer.reset();
393 VersionMinInfo.Major = 0;
395 // reset objects owned by us
396 getBackend().reset();
397 getEmitter().reset();
399 getLOHContainer().reset();
402 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
403 if (ThumbFuncs.count(Symbol))
406 if (!Symbol->isVariable())
409 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
410 // is not clear if that is a bug or a feature.
411 const MCExpr *Expr = Symbol->getVariableValue();
412 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
416 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
419 const MCSymbol &Sym = Ref->getSymbol();
420 if (!isThumbFunc(&Sym))
423 ThumbFuncs.insert(Symbol); // Cache it.
427 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
428 // Non-temporary labels should always be visible to the linker.
429 if (!Symbol.isTemporary())
432 // Absolute temporary labels are never visible.
433 if (!Symbol.isInSection())
436 // Otherwise, check if the section requires symbols even for temporary labels.
437 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
440 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
441 // Linker visible symbols define atoms.
442 if (isSymbolLinkerVisible(SD->getSymbol()))
445 // Absolute and undefined symbols have no defining atom.
446 if (!SD->getFragment())
449 // Non-linker visible symbols in sections which can't be atomized have no
451 if (!getBackend().isSectionAtomizable(
452 SD->getFragment()->getParent()->getSection()))
455 // Otherwise, return the atom for the containing fragment.
456 return SD->getFragment()->getAtom();
459 // Try to fully compute Expr to an absolute value and if that fails produce
460 // a relocatable expr.
461 // FIXME: Should this be the behavior of EvaluateAsRelocatable itself?
462 static bool evaluate(const MCExpr &Expr, const MCAsmLayout &Layout,
463 const MCFixup &Fixup, MCValue &Target) {
464 if (Expr.EvaluateAsValue(Target, &Layout, &Fixup)) {
465 if (Target.isAbsolute())
468 return Expr.EvaluateAsRelocatable(Target, &Layout, &Fixup);
471 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
472 const MCFixup &Fixup, const MCFragment *DF,
473 MCValue &Target, uint64_t &Value) const {
474 ++stats::evaluateFixup;
476 // FIXME: This code has some duplication with RecordRelocation. We should
477 // probably merge the two into a single callback that tries to evaluate a
478 // fixup and records a relocation if one is needed.
479 const MCExpr *Expr = Fixup.getValue();
480 if (!evaluate(*Expr, Layout, Fixup, Target))
481 getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
483 bool IsPCRel = Backend.getFixupKindInfo(
484 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
488 if (Target.getSymB()) {
490 } else if (!Target.getSymA()) {
493 const MCSymbolRefExpr *A = Target.getSymA();
494 const MCSymbol &SA = A->getSymbol();
495 if (A->getKind() != MCSymbolRefExpr::VK_None ||
496 SA.AliasedSymbol().isUndefined()) {
499 const MCSymbolData &DataA = getSymbolData(SA);
501 getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
506 IsResolved = Target.isAbsolute();
509 Value = Target.getConstant();
511 if (const MCSymbolRefExpr *A = Target.getSymA()) {
512 const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
514 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
516 if (const MCSymbolRefExpr *B = Target.getSymB()) {
517 const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
519 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
523 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
524 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
525 assert((ShouldAlignPC ? IsPCRel : true) &&
526 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
529 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
531 // A number of ARM fixups in Thumb mode require that the effective PC
532 // address be determined as the 32-bit aligned version of the actual offset.
533 if (ShouldAlignPC) Offset &= ~0x3;
537 // Let the backend adjust the fixup value if necessary, including whether
538 // we need a relocation.
539 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
545 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
546 const MCFragment &F) const {
547 switch (F.getKind()) {
548 case MCFragment::FT_Data:
549 case MCFragment::FT_Relaxable:
550 case MCFragment::FT_CompactEncodedInst:
551 return cast<MCEncodedFragment>(F).getContents().size();
552 case MCFragment::FT_Fill:
553 return cast<MCFillFragment>(F).getSize();
555 case MCFragment::FT_LEB:
556 return cast<MCLEBFragment>(F).getContents().size();
558 case MCFragment::FT_Align: {
559 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
560 unsigned Offset = Layout.getFragmentOffset(&AF);
561 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
562 // If we are padding with nops, force the padding to be larger than the
564 if (Size > 0 && AF.hasEmitNops()) {
565 while (Size % getBackend().getMinimumNopSize())
566 Size += AF.getAlignment();
568 if (Size > AF.getMaxBytesToEmit())
573 case MCFragment::FT_Org: {
574 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
575 int64_t TargetLocation;
576 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
577 report_fatal_error("expected assembly-time absolute expression");
579 // FIXME: We need a way to communicate this error.
580 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
581 int64_t Size = TargetLocation - FragmentOffset;
582 if (Size < 0 || Size >= 0x40000000)
583 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
584 "' (at offset '" + Twine(FragmentOffset) + "')");
588 case MCFragment::FT_Dwarf:
589 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
590 case MCFragment::FT_DwarfFrame:
591 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
594 llvm_unreachable("invalid fragment kind");
597 void MCAsmLayout::layoutFragment(MCFragment *F) {
598 MCFragment *Prev = F->getPrevNode();
600 // We should never try to recompute something which is valid.
601 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
602 // We should never try to compute the fragment layout if its predecessor
604 assert((!Prev || isFragmentValid(Prev)) &&
605 "Attempt to compute fragment before its predecessor!");
607 ++stats::FragmentLayouts;
609 // Compute fragment offset and size.
611 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
614 LastValidFragment[F->getParent()] = F;
616 // If bundling is enabled and this fragment has instructions in it, it has to
617 // obey the bundling restrictions. With padding, we'll have:
622 // -------------------------------------
623 // Prev |##########| F |
624 // -------------------------------------
629 // The fragment's offset will point to after the padding, and its computed
630 // size won't include the padding.
632 if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
633 assert(isa<MCEncodedFragment>(F) &&
634 "Only MCEncodedFragment implementations have instructions");
635 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
637 if (FSize > Assembler.getBundleAlignSize())
638 report_fatal_error("Fragment can't be larger than a bundle size");
640 uint64_t RequiredBundlePadding = computeBundlePadding(F, F->Offset, FSize);
641 if (RequiredBundlePadding > UINT8_MAX)
642 report_fatal_error("Padding cannot exceed 255 bytes");
643 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
644 F->Offset += RequiredBundlePadding;
648 /// \brief Write the contents of a fragment to the given object writer. Expects
649 /// a MCEncodedFragment.
650 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
651 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
652 OW->WriteBytes(EF.getContents());
655 /// \brief Write the fragment \p F to the output file.
656 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
657 const MCFragment &F) {
658 MCObjectWriter *OW = &Asm.getWriter();
660 // FIXME: Embed in fragments instead?
661 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
663 // Should NOP padding be written out before this fragment?
664 unsigned BundlePadding = F.getBundlePadding();
665 if (BundlePadding > 0) {
666 assert(Asm.isBundlingEnabled() &&
667 "Writing bundle padding with disabled bundling");
668 assert(F.hasInstructions() &&
669 "Writing bundle padding for a fragment without instructions");
671 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FragmentSize);
672 if (F.alignToBundleEnd() && TotalLength > Asm.getBundleAlignSize()) {
673 // If the padding itself crosses a bundle boundary, it must be emitted
674 // in 2 pieces, since even nop instructions must not cross boundaries.
675 // v--------------v <- BundleAlignSize
676 // v---------v <- BundlePadding
677 // ----------------------------
678 // | Prev |####|####| F |
679 // ----------------------------
680 // ^-------------------^ <- TotalLength
681 unsigned DistanceToBoundary = TotalLength - Asm.getBundleAlignSize();
682 if (!Asm.getBackend().writeNopData(DistanceToBoundary, OW))
683 report_fatal_error("unable to write NOP sequence of " +
684 Twine(DistanceToBoundary) + " bytes");
685 BundlePadding -= DistanceToBoundary;
687 if (!Asm.getBackend().writeNopData(BundlePadding, OW))
688 report_fatal_error("unable to write NOP sequence of " +
689 Twine(BundlePadding) + " bytes");
692 // This variable (and its dummy usage) is to participate in the assert at
693 // the end of the function.
694 uint64_t Start = OW->getStream().tell();
697 ++stats::EmittedFragments;
699 switch (F.getKind()) {
700 case MCFragment::FT_Align: {
701 ++stats::EmittedAlignFragments;
702 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
703 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
705 uint64_t Count = FragmentSize / AF.getValueSize();
707 // FIXME: This error shouldn't actually occur (the front end should emit
708 // multiple .align directives to enforce the semantics it wants), but is
709 // severe enough that we want to report it. How to handle this?
710 if (Count * AF.getValueSize() != FragmentSize)
711 report_fatal_error("undefined .align directive, value size '" +
712 Twine(AF.getValueSize()) +
713 "' is not a divisor of padding size '" +
714 Twine(FragmentSize) + "'");
716 // See if we are aligning with nops, and if so do that first to try to fill
717 // the Count bytes. Then if that did not fill any bytes or there are any
718 // bytes left to fill use the Value and ValueSize to fill the rest.
719 // If we are aligning with nops, ask that target to emit the right data.
720 if (AF.hasEmitNops()) {
721 if (!Asm.getBackend().writeNopData(Count, OW))
722 report_fatal_error("unable to write nop sequence of " +
723 Twine(Count) + " bytes");
727 // Otherwise, write out in multiples of the value size.
728 for (uint64_t i = 0; i != Count; ++i) {
729 switch (AF.getValueSize()) {
730 default: llvm_unreachable("Invalid size!");
731 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
732 case 2: OW->Write16(uint16_t(AF.getValue())); break;
733 case 4: OW->Write32(uint32_t(AF.getValue())); break;
734 case 8: OW->Write64(uint64_t(AF.getValue())); break;
740 case MCFragment::FT_Data:
741 ++stats::EmittedDataFragments;
742 writeFragmentContents(F, OW);
745 case MCFragment::FT_Relaxable:
746 ++stats::EmittedRelaxableFragments;
747 writeFragmentContents(F, OW);
750 case MCFragment::FT_CompactEncodedInst:
751 ++stats::EmittedCompactEncodedInstFragments;
752 writeFragmentContents(F, OW);
755 case MCFragment::FT_Fill: {
756 ++stats::EmittedFillFragments;
757 const MCFillFragment &FF = cast<MCFillFragment>(F);
759 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
761 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
762 switch (FF.getValueSize()) {
763 default: llvm_unreachable("Invalid size!");
764 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
765 case 2: OW->Write16(uint16_t(FF.getValue())); break;
766 case 4: OW->Write32(uint32_t(FF.getValue())); break;
767 case 8: OW->Write64(uint64_t(FF.getValue())); break;
773 case MCFragment::FT_LEB: {
774 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
775 OW->WriteBytes(LF.getContents().str());
779 case MCFragment::FT_Org: {
780 ++stats::EmittedOrgFragments;
781 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
783 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
784 OW->Write8(uint8_t(OF.getValue()));
789 case MCFragment::FT_Dwarf: {
790 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
791 OW->WriteBytes(OF.getContents().str());
794 case MCFragment::FT_DwarfFrame: {
795 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
796 OW->WriteBytes(CF.getContents().str());
801 assert(OW->getStream().tell() - Start == FragmentSize &&
802 "The stream should advance by fragment size");
805 void MCAssembler::writeSectionData(const MCSectionData *SD,
806 const MCAsmLayout &Layout) const {
807 // Ignore virtual sections.
808 if (SD->getSection().isVirtualSection()) {
809 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
811 // Check that contents are only things legal inside a virtual section.
812 for (MCSectionData::const_iterator it = SD->begin(),
813 ie = SD->end(); it != ie; ++it) {
814 switch (it->getKind()) {
815 default: llvm_unreachable("Invalid fragment in virtual section!");
816 case MCFragment::FT_Data: {
817 // Check that we aren't trying to write a non-zero contents (or fixups)
818 // into a virtual section. This is to support clients which use standard
819 // directives to fill the contents of virtual sections.
820 const MCDataFragment &DF = cast<MCDataFragment>(*it);
821 assert(DF.fixup_begin() == DF.fixup_end() &&
822 "Cannot have fixups in virtual section!");
823 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
824 if (DF.getContents()[i]) {
825 if (auto *ELFSec = dyn_cast<const MCSectionELF>(&SD->getSection()))
826 report_fatal_error("non-zero initializer found in section '" +
827 ELFSec->getSectionName() + "'");
829 report_fatal_error("non-zero initializer found in virtual section");
833 case MCFragment::FT_Align:
834 // Check that we aren't trying to write a non-zero value into a virtual
836 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
837 cast<MCAlignFragment>(it)->getValue() == 0) &&
838 "Invalid align in virtual section!");
840 case MCFragment::FT_Fill:
841 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
842 cast<MCFillFragment>(it)->getValue() == 0) &&
843 "Invalid fill in virtual section!");
851 uint64_t Start = getWriter().getStream().tell();
854 for (MCSectionData::const_iterator it = SD->begin(), ie = SD->end();
856 writeFragment(*this, Layout, *it);
858 assert(getWriter().getStream().tell() - Start ==
859 Layout.getSectionAddressSize(SD));
862 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
864 const MCFixup &Fixup) {
865 // Evaluate the fixup.
868 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
869 MCFixupKindInfo::FKF_IsPCRel;
870 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
871 // The fixup was unresolved, we need a relocation. Inform the object
872 // writer of the relocation, and give it an opportunity to adjust the
873 // fixup value if need be.
874 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
877 return std::make_pair(FixedValue, IsPCRel);
880 void MCAssembler::Finish() {
881 DEBUG_WITH_TYPE("mc-dump", {
882 llvm::errs() << "assembler backend - pre-layout\n--\n";
885 // Create the layout object.
886 MCAsmLayout Layout(*this);
888 // Create dummy fragments and assign section ordinals.
889 unsigned SectionIndex = 0;
890 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
891 // Create dummy fragments to eliminate any empty sections, this simplifies
893 if (it->getFragmentList().empty())
894 new MCDataFragment(it);
896 it->setOrdinal(SectionIndex++);
899 // Assign layout order indices to sections and fragments.
900 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
901 MCSectionData *SD = Layout.getSectionOrder()[i];
902 SD->setLayoutOrder(i);
904 unsigned FragmentIndex = 0;
905 for (MCSectionData::iterator iFrag = SD->begin(), iFragEnd = SD->end();
906 iFrag != iFragEnd; ++iFrag)
907 iFrag->setLayoutOrder(FragmentIndex++);
910 // Layout until everything fits.
911 while (layoutOnce(Layout))
914 DEBUG_WITH_TYPE("mc-dump", {
915 llvm::errs() << "assembler backend - post-relaxation\n--\n";
918 // Finalize the layout, including fragment lowering.
919 finishLayout(Layout);
921 DEBUG_WITH_TYPE("mc-dump", {
922 llvm::errs() << "assembler backend - final-layout\n--\n";
925 uint64_t StartOffset = OS.tell();
927 // Allow the object writer a chance to perform post-layout binding (for
928 // example, to set the index fields in the symbol data).
929 getWriter().ExecutePostLayoutBinding(*this, Layout);
931 // Evaluate and apply the fixups, generating relocation entries as necessary.
932 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
933 for (MCSectionData::iterator it2 = it->begin(),
934 ie2 = it->end(); it2 != ie2; ++it2) {
935 MCEncodedFragmentWithFixups *F =
936 dyn_cast<MCEncodedFragmentWithFixups>(it2);
938 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
939 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
940 MCFixup &Fixup = *it3;
943 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
944 getBackend().applyFixup(Fixup, F->getContents().data(),
945 F->getContents().size(), FixedValue, IsPCRel);
951 // Write the object file.
952 getWriter().WriteObject(*this, Layout);
954 stats::ObjectBytes += OS.tell() - StartOffset;
957 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
958 const MCRelaxableFragment *DF,
959 const MCAsmLayout &Layout) const {
960 // If we cannot resolve the fixup value, it requires relaxation.
963 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
966 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
969 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
970 const MCAsmLayout &Layout) const {
971 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
972 // are intentionally pushing out inst fragments, or because we relaxed a
973 // previous instruction to one that doesn't need relaxation.
974 if (!getBackend().mayNeedRelaxation(F->getInst()))
977 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
978 ie = F->fixup_end(); it != ie; ++it)
979 if (fixupNeedsRelaxation(*it, F, Layout))
985 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
986 MCRelaxableFragment &F) {
987 if (!fragmentNeedsRelaxation(&F, Layout))
990 ++stats::RelaxedInstructions;
992 // FIXME-PERF: We could immediately lower out instructions if we can tell
993 // they are fully resolved, to avoid retesting on later passes.
995 // Relax the fragment.
998 getBackend().relaxInstruction(F.getInst(), Relaxed);
1000 // Encode the new instruction.
1002 // FIXME-PERF: If it matters, we could let the target do this. It can
1003 // probably do so more efficiently in many cases.
1004 SmallVector<MCFixup, 4> Fixups;
1005 SmallString<256> Code;
1006 raw_svector_ostream VecOS(Code);
1007 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
1010 // Update the fragment.
1012 F.getContents() = Code;
1013 F.getFixups() = Fixups;
1018 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1019 uint64_t OldSize = LF.getContents().size();
1020 int64_t Value = LF.getValue().evaluateKnownAbsolute(Layout);
1021 SmallString<8> &Data = LF.getContents();
1023 raw_svector_ostream OSE(Data);
1025 encodeSLEB128(Value, OSE);
1027 encodeULEB128(Value, OSE);
1029 return OldSize != LF.getContents().size();
1032 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1033 MCDwarfLineAddrFragment &DF) {
1034 MCContext &Context = Layout.getAssembler().getContext();
1035 uint64_t OldSize = DF.getContents().size();
1036 int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
1038 LineDelta = DF.getLineDelta();
1039 SmallString<8> &Data = DF.getContents();
1041 raw_svector_ostream OSE(Data);
1042 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1044 return OldSize != Data.size();
1047 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1048 MCDwarfCallFrameFragment &DF) {
1049 MCContext &Context = Layout.getAssembler().getContext();
1050 uint64_t OldSize = DF.getContents().size();
1051 int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
1052 SmallString<8> &Data = DF.getContents();
1054 raw_svector_ostream OSE(Data);
1055 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1057 return OldSize != Data.size();
1060 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSectionData &SD) {
1061 // Holds the first fragment which needed relaxing during this layout. It will
1062 // remain NULL if none were relaxed.
1063 // When a fragment is relaxed, all the fragments following it should get
1064 // invalidated because their offset is going to change.
1065 MCFragment *FirstRelaxedFragment = nullptr;
1067 // Attempt to relax all the fragments in the section.
1068 for (MCSectionData::iterator I = SD.begin(), IE = SD.end(); I != IE; ++I) {
1069 // Check if this is a fragment that needs relaxation.
1070 bool RelaxedFrag = false;
1071 switch(I->getKind()) {
1074 case MCFragment::FT_Relaxable:
1075 assert(!getRelaxAll() &&
1076 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1077 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1079 case MCFragment::FT_Dwarf:
1080 RelaxedFrag = relaxDwarfLineAddr(Layout,
1081 *cast<MCDwarfLineAddrFragment>(I));
1083 case MCFragment::FT_DwarfFrame:
1085 relaxDwarfCallFrameFragment(Layout,
1086 *cast<MCDwarfCallFrameFragment>(I));
1088 case MCFragment::FT_LEB:
1089 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1092 if (RelaxedFrag && !FirstRelaxedFragment)
1093 FirstRelaxedFragment = I;
1095 if (FirstRelaxedFragment) {
1096 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1102 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1103 ++stats::RelaxationSteps;
1105 bool WasRelaxed = false;
1106 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1107 MCSectionData &SD = *it;
1108 while (layoutSectionOnce(Layout, SD))
1115 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1116 // The layout is done. Mark every fragment as valid.
1117 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1118 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1122 // Debugging methods
1126 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1127 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1128 << " Value:" << *AF.getValue()
1129 << " Kind:" << AF.getKind() << ">";
1135 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1136 void MCFragment::dump() {
1137 raw_ostream &OS = llvm::errs();
1140 switch (getKind()) {
1141 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1142 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1143 case MCFragment::FT_CompactEncodedInst:
1144 OS << "MCCompactEncodedInstFragment"; break;
1145 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1146 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1147 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1148 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1149 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1150 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1153 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1154 << " Offset:" << Offset
1155 << " HasInstructions:" << hasInstructions()
1156 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1158 switch (getKind()) {
1159 case MCFragment::FT_Align: {
1160 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1161 if (AF->hasEmitNops())
1162 OS << " (emit nops)";
1164 OS << " Alignment:" << AF->getAlignment()
1165 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1166 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1169 case MCFragment::FT_Data: {
1170 const MCDataFragment *DF = cast<MCDataFragment>(this);
1172 OS << " Contents:[";
1173 const SmallVectorImpl<char> &Contents = DF->getContents();
1174 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1176 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1178 OS << "] (" << Contents.size() << " bytes)";
1180 if (DF->fixup_begin() != DF->fixup_end()) {
1183 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1184 ie = DF->fixup_end(); it != ie; ++it) {
1185 if (it != DF->fixup_begin()) OS << ",\n ";
1192 case MCFragment::FT_CompactEncodedInst: {
1193 const MCCompactEncodedInstFragment *CEIF =
1194 cast<MCCompactEncodedInstFragment>(this);
1196 OS << " Contents:[";
1197 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1198 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1200 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1202 OS << "] (" << Contents.size() << " bytes)";
1205 case MCFragment::FT_Fill: {
1206 const MCFillFragment *FF = cast<MCFillFragment>(this);
1207 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1208 << " Size:" << FF->getSize();
1211 case MCFragment::FT_Relaxable: {
1212 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1215 F->getInst().dump_pretty(OS);
1218 case MCFragment::FT_Org: {
1219 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1221 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1224 case MCFragment::FT_Dwarf: {
1225 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1227 OS << " AddrDelta:" << OF->getAddrDelta()
1228 << " LineDelta:" << OF->getLineDelta();
1231 case MCFragment::FT_DwarfFrame: {
1232 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1234 OS << " AddrDelta:" << CF->getAddrDelta();
1237 case MCFragment::FT_LEB: {
1238 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1240 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1247 void MCSectionData::dump() {
1248 raw_ostream &OS = llvm::errs();
1250 OS << "<MCSectionData";
1251 OS << " Alignment:" << getAlignment()
1252 << " Fragments:[\n ";
1253 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1254 if (it != begin()) OS << ",\n ";
1260 void MCSymbolData::dump() const {
1261 raw_ostream &OS = llvm::errs();
1263 OS << "<MCSymbolData Symbol:" << getSymbol()
1264 << " Fragment:" << getFragment();
1266 OS << " Offset:" << getOffset();
1267 OS << " Flags:" << getFlags() << " Index:" << getIndex();
1269 OS << " (common, size:" << getCommonSize()
1270 << " align: " << getCommonAlignment() << ")";
1272 OS << " (external)";
1273 if (isPrivateExtern())
1274 OS << " (private extern)";
1278 void MCAssembler::dump() {
1279 raw_ostream &OS = llvm::errs();
1281 OS << "<MCAssembler\n";
1282 OS << " Sections:[\n ";
1283 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1284 if (it != begin()) OS << ",\n ";
1290 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1291 if (it != symbol_begin()) OS << ",\n ";
1298 // anchors for MC*Fragment vtables
1299 void MCEncodedFragment::anchor() { }
1300 void MCEncodedFragmentWithFixups::anchor() { }
1301 void MCDataFragment::anchor() { }
1302 void MCCompactEncodedInstFragment::anchor() { }
1303 void MCRelaxableFragment::anchor() { }
1304 void MCAlignFragment::anchor() { }
1305 void MCFillFragment::anchor() { }
1306 void MCOrgFragment::anchor() { }
1307 void MCLEBFragment::anchor() { }
1308 void MCDwarfLineAddrFragment::anchor() { }
1309 void MCDwarfCallFrameFragment::anchor() { }