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/MCSymbol.h"
25 #include "llvm/MC/MCValue.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/LEB128.h"
29 #include "llvm/Support/TargetRegistry.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/MC/MCSectionELF.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 MCSymbolData &SD,
124 bool ReportError, uint64_t &Val) {
125 if (!SD.getFragment()) {
127 report_fatal_error("unable to evaluate offset to undefined symbol '" +
128 SD.getSymbol().getName() + "'");
131 Val = Layout.getFragmentOffset(SD.getFragment()) + SD.getOffset();
135 static bool getSymbolOffsetImpl(const MCAsmLayout &Layout,
136 const MCSymbolData *SD, bool ReportError,
138 const MCSymbol &S = SD->getSymbol();
141 return getLabelOffset(Layout, *SD, ReportError, Val);
143 // If SD is a variable, evaluate it.
145 if (!S.getVariableValue()->EvaluateAsValue(Target, &Layout, nullptr))
146 report_fatal_error("unable to evaluate offset for variable '" +
149 uint64_t Offset = Target.getConstant();
151 const MCAssembler &Asm = Layout.getAssembler();
153 const MCSymbolRefExpr *A = Target.getSymA();
156 if (!getLabelOffset(Layout, Asm.getSymbolData(A->getSymbol()), ReportError,
162 const MCSymbolRefExpr *B = Target.getSymB();
165 if (!getLabelOffset(Layout, Asm.getSymbolData(B->getSymbol()), ReportError,
175 bool MCAsmLayout::getSymbolOffset(const MCSymbolData *SD, uint64_t &Val) const {
176 return getSymbolOffsetImpl(*this, SD, false, Val);
179 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
181 getSymbolOffsetImpl(*this, SD, true, Val);
185 const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
186 if (!Symbol.isVariable())
189 const MCExpr *Expr = Symbol.getVariableValue();
191 if (!Expr->EvaluateAsValue(Value, this, nullptr))
192 llvm_unreachable("Invalid Expression");
194 const MCSymbolRefExpr *RefB = Value.getSymB();
196 Assembler.getContext().FatalError(
197 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
198 "' could not be evaluated in a subtraction expression");
200 const MCSymbolRefExpr *A = Value.getSymA();
204 return &A->getSymbol();
207 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
208 // The size is the last fragment's end offset.
209 const MCFragment &F = SD->getFragmentList().back();
210 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
213 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
214 // Virtual sections have no file size.
215 if (SD->getSection().isVirtualSection())
218 // Otherwise, the file size is the same as the address space size.
219 return getSectionAddressSize(SD);
222 uint64_t MCAsmLayout::computeBundlePadding(const MCFragment *F,
223 uint64_t FOffset, uint64_t FSize) {
224 uint64_t BundleSize = Assembler.getBundleAlignSize();
225 assert(BundleSize > 0 &&
226 "computeBundlePadding should only be called if bundling is enabled");
227 uint64_t BundleMask = BundleSize - 1;
228 uint64_t OffsetInBundle = FOffset & BundleMask;
229 uint64_t EndOfFragment = OffsetInBundle + FSize;
231 // There are two kinds of bundling restrictions:
233 // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
234 // *end* on a bundle boundary.
235 // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
236 // would, add padding until the end of the bundle so that the fragment
237 // will start in a new one.
238 if (F->alignToBundleEnd()) {
239 // Three possibilities here:
241 // A) The fragment just happens to end at a bundle boundary, so we're good.
242 // B) The fragment ends before the current bundle boundary: pad it just
243 // enough to reach the boundary.
244 // C) The fragment ends after the current bundle boundary: pad it until it
245 // reaches the end of the next bundle boundary.
247 // Note: this code could be made shorter with some modulo trickery, but it's
248 // intentionally kept in its more explicit form for simplicity.
249 if (EndOfFragment == BundleSize)
251 else if (EndOfFragment < BundleSize)
252 return BundleSize - EndOfFragment;
253 else { // EndOfFragment > BundleSize
254 return 2 * BundleSize - EndOfFragment;
256 } else if (EndOfFragment > BundleSize)
257 return BundleSize - OffsetInBundle;
264 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
267 MCFragment::~MCFragment() {
270 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
271 : Kind(_Kind), Parent(_Parent), Atom(nullptr), Offset(~UINT64_C(0))
274 Parent->getFragmentList().push_back(this);
279 MCEncodedFragment::~MCEncodedFragment() {
284 MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
289 MCSectionData::MCSectionData() : Section(nullptr) {}
291 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
292 : Section(&_Section),
293 Ordinal(~UINT32_C(0)),
295 BundleLockState(NotBundleLocked),
296 BundleLockNestingDepth(0),
297 BundleGroupBeforeFirstInst(false),
298 HasInstructions(false)
301 A->getSectionList().push_back(this);
304 MCSectionData::iterator
305 MCSectionData::getSubsectionInsertionPoint(unsigned Subsection) {
306 if (Subsection == 0 && SubsectionFragmentMap.empty())
309 SmallVectorImpl<std::pair<unsigned, MCFragment *> >::iterator MI =
310 std::lower_bound(SubsectionFragmentMap.begin(), SubsectionFragmentMap.end(),
311 std::make_pair(Subsection, (MCFragment *)nullptr));
312 bool ExactMatch = false;
313 if (MI != SubsectionFragmentMap.end()) {
314 ExactMatch = MI->first == Subsection;
319 if (MI == SubsectionFragmentMap.end())
323 if (!ExactMatch && Subsection != 0) {
324 // The GNU as documentation claims that subsections have an alignment of 4,
325 // although this appears not to be the case.
326 MCFragment *F = new MCDataFragment();
327 SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
328 getFragmentList().insert(IP, F);
334 void MCSectionData::setBundleLockState(BundleLockStateType NewState) {
335 if (NewState == NotBundleLocked) {
336 if (BundleLockNestingDepth == 0) {
337 report_fatal_error("Mismatched bundle_lock/unlock directives");
339 if (--BundleLockNestingDepth == 0) {
340 BundleLockState = NotBundleLocked;
345 // If any of the directives is an align_to_end directive, the whole nested
346 // group is align_to_end. So don't downgrade from align_to_end to just locked.
347 if (BundleLockState != BundleLockedAlignToEnd) {
348 BundleLockState = NewState;
350 ++BundleLockNestingDepth;
355 MCSymbolData::MCSymbolData() : Symbol(nullptr) {}
357 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
358 uint64_t _Offset, MCAssembler *A)
359 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
360 SymbolSize(nullptr), CommonAlign(-1U), Flags(0), Index(0) {
362 A->getSymbolList().push_back(this);
367 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
368 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
370 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
371 OS(OS_), BundleAlignSize(0), RelaxAll(false),
372 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
373 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
376 MCAssembler::~MCAssembler() {
379 void MCAssembler::reset() {
384 IndirectSymbols.clear();
386 LinkerOptions.clear();
391 SubsectionsViaSymbols = false;
393 LOHContainer.reset();
394 VersionMinInfo.Major = 0;
396 // reset objects owned by us
397 getBackend().reset();
398 getEmitter().reset();
400 getLOHContainer().reset();
403 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
404 if (ThumbFuncs.count(Symbol))
407 if (!Symbol->isVariable())
410 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
411 // is not clear if that is a bug or a feature.
412 const MCExpr *Expr = Symbol->getVariableValue();
413 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
417 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
420 const MCSymbol &Sym = Ref->getSymbol();
421 if (!isThumbFunc(&Sym))
424 ThumbFuncs.insert(Symbol); // Cache it.
428 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
429 // Non-temporary labels should always be visible to the linker.
430 if (!Symbol.isTemporary())
433 // Absolute temporary labels are never visible.
434 if (!Symbol.isInSection())
437 // Otherwise, check if the section requires symbols even for temporary labels.
438 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
441 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
442 // Linker visible symbols define atoms.
443 if (isSymbolLinkerVisible(SD->getSymbol()))
446 // Absolute and undefined symbols have no defining atom.
447 if (!SD->getFragment())
450 // Non-linker visible symbols in sections which can't be atomized have no
452 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
453 SD->getFragment()->getParent()->getSection()))
456 // Otherwise, return the atom for the containing fragment.
457 return SD->getFragment()->getAtom();
460 // Try to fully compute Expr to an absolute value and if that fails produce
461 // a relocatable expr.
462 // FIXME: Should this be the behavior of EvaluateAsRelocatable itself?
463 static bool evaluate(const MCExpr &Expr, const MCAsmLayout &Layout,
464 const MCFixup &Fixup, MCValue &Target) {
465 if (Expr.EvaluateAsValue(Target, &Layout, &Fixup)) {
466 if (Target.isAbsolute())
469 return Expr.EvaluateAsRelocatable(Target, &Layout, &Fixup);
472 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
473 const MCFixup &Fixup, const MCFragment *DF,
474 MCValue &Target, uint64_t &Value) const {
475 ++stats::evaluateFixup;
477 // FIXME: This code has some duplication with RecordRelocation. We should
478 // probably merge the two into a single callback that tries to evaluate a
479 // fixup and records a relocation if one is needed.
480 const MCExpr *Expr = Fixup.getValue();
481 if (!evaluate(*Expr, Layout, Fixup, Target))
482 getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
484 bool IsPCRel = Backend.getFixupKindInfo(
485 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
489 if (Target.getSymB()) {
491 } else if (!Target.getSymA()) {
494 const MCSymbolRefExpr *A = Target.getSymA();
495 const MCSymbol &SA = A->getSymbol();
496 if (A->getKind() != MCSymbolRefExpr::VK_None ||
497 SA.AliasedSymbol().isUndefined()) {
500 const MCSymbolData &DataA = getSymbolData(SA);
502 getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
507 IsResolved = Target.isAbsolute();
510 Value = Target.getConstant();
512 if (const MCSymbolRefExpr *A = Target.getSymA()) {
513 const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
515 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
517 if (const MCSymbolRefExpr *B = Target.getSymB()) {
518 const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
520 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
524 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
525 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
526 assert((ShouldAlignPC ? IsPCRel : true) &&
527 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
530 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
532 // A number of ARM fixups in Thumb mode require that the effective PC
533 // address be determined as the 32-bit aligned version of the actual offset.
534 if (ShouldAlignPC) Offset &= ~0x3;
538 // Let the backend adjust the fixup value if necessary, including whether
539 // we need a relocation.
540 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
546 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
547 const MCFragment &F) const {
548 switch (F.getKind()) {
549 case MCFragment::FT_Data:
550 case MCFragment::FT_Relaxable:
551 case MCFragment::FT_CompactEncodedInst:
552 return cast<MCEncodedFragment>(F).getContents().size();
553 case MCFragment::FT_Fill:
554 return cast<MCFillFragment>(F).getSize();
556 case MCFragment::FT_LEB:
557 return cast<MCLEBFragment>(F).getContents().size();
559 case MCFragment::FT_Align: {
560 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
561 unsigned Offset = Layout.getFragmentOffset(&AF);
562 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
563 // If we are padding with nops, force the padding to be larger than the
565 if (Size > 0 && AF.hasEmitNops()) {
566 while (Size % getBackend().getMinimumNopSize())
567 Size += AF.getAlignment();
569 if (Size > AF.getMaxBytesToEmit())
574 case MCFragment::FT_Org: {
575 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
576 int64_t TargetLocation;
577 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
578 report_fatal_error("expected assembly-time absolute expression");
580 // FIXME: We need a way to communicate this error.
581 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
582 int64_t Size = TargetLocation - FragmentOffset;
583 if (Size < 0 || Size >= 0x40000000)
584 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
585 "' (at offset '" + Twine(FragmentOffset) + "')");
589 case MCFragment::FT_Dwarf:
590 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
591 case MCFragment::FT_DwarfFrame:
592 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
595 llvm_unreachable("invalid fragment kind");
598 void MCAsmLayout::layoutFragment(MCFragment *F) {
599 MCFragment *Prev = F->getPrevNode();
601 // We should never try to recompute something which is valid.
602 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
603 // We should never try to compute the fragment layout if its predecessor
605 assert((!Prev || isFragmentValid(Prev)) &&
606 "Attempt to compute fragment before its predecessor!");
608 ++stats::FragmentLayouts;
610 // Compute fragment offset and size.
612 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
615 LastValidFragment[F->getParent()] = F;
617 // If bundling is enabled and this fragment has instructions in it, it has to
618 // obey the bundling restrictions. With padding, we'll have:
623 // -------------------------------------
624 // Prev |##########| F |
625 // -------------------------------------
630 // The fragment's offset will point to after the padding, and its computed
631 // size won't include the padding.
633 if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
634 assert(isa<MCEncodedFragment>(F) &&
635 "Only MCEncodedFragment implementations have instructions");
636 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
638 if (FSize > Assembler.getBundleAlignSize())
639 report_fatal_error("Fragment can't be larger than a bundle size");
641 uint64_t RequiredBundlePadding = computeBundlePadding(F, F->Offset, FSize);
642 if (RequiredBundlePadding > UINT8_MAX)
643 report_fatal_error("Padding cannot exceed 255 bytes");
644 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
645 F->Offset += RequiredBundlePadding;
649 /// \brief Write the contents of a fragment to the given object writer. Expects
650 /// a MCEncodedFragment.
651 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
652 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
653 OW->WriteBytes(EF.getContents());
656 /// \brief Write the fragment \p F to the output file.
657 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
658 const MCFragment &F) {
659 MCObjectWriter *OW = &Asm.getWriter();
661 // FIXME: Embed in fragments instead?
662 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
664 // Should NOP padding be written out before this fragment?
665 unsigned BundlePadding = F.getBundlePadding();
666 if (BundlePadding > 0) {
667 assert(Asm.isBundlingEnabled() &&
668 "Writing bundle padding with disabled bundling");
669 assert(F.hasInstructions() &&
670 "Writing bundle padding for a fragment without instructions");
672 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FragmentSize);
673 if (F.alignToBundleEnd() && TotalLength > Asm.getBundleAlignSize()) {
674 // If the padding itself crosses a bundle boundary, it must be emitted
675 // in 2 pieces, since even nop instructions must not cross boundaries.
676 // v--------------v <- BundleAlignSize
677 // v---------v <- BundlePadding
678 // ----------------------------
679 // | Prev |####|####| F |
680 // ----------------------------
681 // ^-------------------^ <- TotalLength
682 unsigned DistanceToBoundary = TotalLength - Asm.getBundleAlignSize();
683 if (!Asm.getBackend().writeNopData(DistanceToBoundary, OW))
684 report_fatal_error("unable to write NOP sequence of " +
685 Twine(DistanceToBoundary) + " bytes");
686 BundlePadding -= DistanceToBoundary;
688 if (!Asm.getBackend().writeNopData(BundlePadding, OW))
689 report_fatal_error("unable to write NOP sequence of " +
690 Twine(BundlePadding) + " bytes");
693 // This variable (and its dummy usage) is to participate in the assert at
694 // the end of the function.
695 uint64_t Start = OW->getStream().tell();
698 ++stats::EmittedFragments;
700 switch (F.getKind()) {
701 case MCFragment::FT_Align: {
702 ++stats::EmittedAlignFragments;
703 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
704 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
706 uint64_t Count = FragmentSize / AF.getValueSize();
708 // FIXME: This error shouldn't actually occur (the front end should emit
709 // multiple .align directives to enforce the semantics it wants), but is
710 // severe enough that we want to report it. How to handle this?
711 if (Count * AF.getValueSize() != FragmentSize)
712 report_fatal_error("undefined .align directive, value size '" +
713 Twine(AF.getValueSize()) +
714 "' is not a divisor of padding size '" +
715 Twine(FragmentSize) + "'");
717 // See if we are aligning with nops, and if so do that first to try to fill
718 // the Count bytes. Then if that did not fill any bytes or there are any
719 // bytes left to fill use the Value and ValueSize to fill the rest.
720 // If we are aligning with nops, ask that target to emit the right data.
721 if (AF.hasEmitNops()) {
722 if (!Asm.getBackend().writeNopData(Count, OW))
723 report_fatal_error("unable to write nop sequence of " +
724 Twine(Count) + " bytes");
728 // Otherwise, write out in multiples of the value size.
729 for (uint64_t i = 0; i != Count; ++i) {
730 switch (AF.getValueSize()) {
731 default: llvm_unreachable("Invalid size!");
732 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
733 case 2: OW->Write16(uint16_t(AF.getValue())); break;
734 case 4: OW->Write32(uint32_t(AF.getValue())); break;
735 case 8: OW->Write64(uint64_t(AF.getValue())); break;
741 case MCFragment::FT_Data:
742 ++stats::EmittedDataFragments;
743 writeFragmentContents(F, OW);
746 case MCFragment::FT_Relaxable:
747 ++stats::EmittedRelaxableFragments;
748 writeFragmentContents(F, OW);
751 case MCFragment::FT_CompactEncodedInst:
752 ++stats::EmittedCompactEncodedInstFragments;
753 writeFragmentContents(F, OW);
756 case MCFragment::FT_Fill: {
757 ++stats::EmittedFillFragments;
758 const MCFillFragment &FF = cast<MCFillFragment>(F);
760 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
762 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
763 switch (FF.getValueSize()) {
764 default: llvm_unreachable("Invalid size!");
765 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
766 case 2: OW->Write16(uint16_t(FF.getValue())); break;
767 case 4: OW->Write32(uint32_t(FF.getValue())); break;
768 case 8: OW->Write64(uint64_t(FF.getValue())); break;
774 case MCFragment::FT_LEB: {
775 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
776 OW->WriteBytes(LF.getContents().str());
780 case MCFragment::FT_Org: {
781 ++stats::EmittedOrgFragments;
782 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
784 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
785 OW->Write8(uint8_t(OF.getValue()));
790 case MCFragment::FT_Dwarf: {
791 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
792 OW->WriteBytes(OF.getContents().str());
795 case MCFragment::FT_DwarfFrame: {
796 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
797 OW->WriteBytes(CF.getContents().str());
802 assert(OW->getStream().tell() - Start == FragmentSize &&
803 "The stream should advance by fragment size");
806 void MCAssembler::writeSectionData(const MCSectionData *SD,
807 const MCAsmLayout &Layout) const {
808 // Ignore virtual sections.
809 if (SD->getSection().isVirtualSection()) {
810 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
812 // Check that contents are only things legal inside a virtual section.
813 for (MCSectionData::const_iterator it = SD->begin(),
814 ie = SD->end(); it != ie; ++it) {
815 switch (it->getKind()) {
816 default: llvm_unreachable("Invalid fragment in virtual section!");
817 case MCFragment::FT_Data: {
818 // Check that we aren't trying to write a non-zero contents (or fixups)
819 // into a virtual section. This is to support clients which use standard
820 // directives to fill the contents of virtual sections.
821 const MCDataFragment &DF = cast<MCDataFragment>(*it);
822 assert(DF.fixup_begin() == DF.fixup_end() &&
823 "Cannot have fixups in virtual section!");
824 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
825 if (DF.getContents()[i]) {
826 if (auto *ELFSec = dyn_cast<const MCSectionELF>(&SD->getSection()))
827 report_fatal_error("non-zero initializer found in section '" +
828 ELFSec->getSectionName() + "'");
830 report_fatal_error("non-zero initializer found in virtual section");
834 case MCFragment::FT_Align:
835 // Check that we aren't trying to write a non-zero value into a virtual
837 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
838 cast<MCAlignFragment>(it)->getValue() == 0) &&
839 "Invalid align in virtual section!");
841 case MCFragment::FT_Fill:
842 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
843 cast<MCFillFragment>(it)->getValue() == 0) &&
844 "Invalid fill in virtual section!");
852 uint64_t Start = getWriter().getStream().tell();
855 for (MCSectionData::const_iterator it = SD->begin(), ie = SD->end();
857 writeFragment(*this, Layout, *it);
859 assert(getWriter().getStream().tell() - Start ==
860 Layout.getSectionAddressSize(SD));
863 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
865 const MCFixup &Fixup) {
866 // Evaluate the fixup.
869 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
870 MCFixupKindInfo::FKF_IsPCRel;
871 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
872 // The fixup was unresolved, we need a relocation. Inform the object
873 // writer of the relocation, and give it an opportunity to adjust the
874 // fixup value if need be.
875 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
878 return std::make_pair(FixedValue, IsPCRel);
881 void MCAssembler::Finish() {
882 DEBUG_WITH_TYPE("mc-dump", {
883 llvm::errs() << "assembler backend - pre-layout\n--\n";
886 // Create the layout object.
887 MCAsmLayout Layout(*this);
889 // Create dummy fragments and assign section ordinals.
890 unsigned SectionIndex = 0;
891 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
892 // Create dummy fragments to eliminate any empty sections, this simplifies
894 if (it->getFragmentList().empty())
895 new MCDataFragment(it);
897 it->setOrdinal(SectionIndex++);
900 // Assign layout order indices to sections and fragments.
901 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
902 MCSectionData *SD = Layout.getSectionOrder()[i];
903 SD->setLayoutOrder(i);
905 unsigned FragmentIndex = 0;
906 for (MCSectionData::iterator iFrag = SD->begin(), iFragEnd = SD->end();
907 iFrag != iFragEnd; ++iFrag)
908 iFrag->setLayoutOrder(FragmentIndex++);
911 // Layout until everything fits.
912 while (layoutOnce(Layout))
915 DEBUG_WITH_TYPE("mc-dump", {
916 llvm::errs() << "assembler backend - post-relaxation\n--\n";
919 // Finalize the layout, including fragment lowering.
920 finishLayout(Layout);
922 DEBUG_WITH_TYPE("mc-dump", {
923 llvm::errs() << "assembler backend - final-layout\n--\n";
926 uint64_t StartOffset = OS.tell();
928 // Allow the object writer a chance to perform post-layout binding (for
929 // example, to set the index fields in the symbol data).
930 getWriter().ExecutePostLayoutBinding(*this, Layout);
932 // Evaluate and apply the fixups, generating relocation entries as necessary.
933 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
934 for (MCSectionData::iterator it2 = it->begin(),
935 ie2 = it->end(); it2 != ie2; ++it2) {
936 MCEncodedFragmentWithFixups *F =
937 dyn_cast<MCEncodedFragmentWithFixups>(it2);
939 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
940 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
941 MCFixup &Fixup = *it3;
944 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
945 getBackend().applyFixup(Fixup, F->getContents().data(),
946 F->getContents().size(), FixedValue, IsPCRel);
952 // Write the object file.
953 getWriter().WriteObject(*this, Layout);
955 stats::ObjectBytes += OS.tell() - StartOffset;
958 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
959 const MCRelaxableFragment *DF,
960 const MCAsmLayout &Layout) const {
961 // If we cannot resolve the fixup value, it requires relaxation.
964 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
967 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
970 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
971 const MCAsmLayout &Layout) const {
972 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
973 // are intentionally pushing out inst fragments, or because we relaxed a
974 // previous instruction to one that doesn't need relaxation.
975 if (!getBackend().mayNeedRelaxation(F->getInst()))
978 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
979 ie = F->fixup_end(); it != ie; ++it)
980 if (fixupNeedsRelaxation(*it, F, Layout))
986 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
987 MCRelaxableFragment &F) {
988 if (!fragmentNeedsRelaxation(&F, Layout))
991 ++stats::RelaxedInstructions;
993 // FIXME-PERF: We could immediately lower out instructions if we can tell
994 // they are fully resolved, to avoid retesting on later passes.
996 // Relax the fragment.
999 getBackend().relaxInstruction(F.getInst(), Relaxed);
1001 // Encode the new instruction.
1003 // FIXME-PERF: If it matters, we could let the target do this. It can
1004 // probably do so more efficiently in many cases.
1005 SmallVector<MCFixup, 4> Fixups;
1006 SmallString<256> Code;
1007 raw_svector_ostream VecOS(Code);
1008 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
1011 // Update the fragment.
1013 F.getContents() = Code;
1014 F.getFixups() = Fixups;
1019 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1020 uint64_t OldSize = LF.getContents().size();
1021 int64_t Value = LF.getValue().evaluateKnownAbsolute(Layout);
1022 SmallString<8> &Data = LF.getContents();
1024 raw_svector_ostream OSE(Data);
1026 encodeSLEB128(Value, OSE);
1028 encodeULEB128(Value, OSE);
1030 return OldSize != LF.getContents().size();
1033 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1034 MCDwarfLineAddrFragment &DF) {
1035 MCContext &Context = Layout.getAssembler().getContext();
1036 uint64_t OldSize = DF.getContents().size();
1037 int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
1039 LineDelta = DF.getLineDelta();
1040 SmallString<8> &Data = DF.getContents();
1042 raw_svector_ostream OSE(Data);
1043 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1045 return OldSize != Data.size();
1048 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1049 MCDwarfCallFrameFragment &DF) {
1050 MCContext &Context = Layout.getAssembler().getContext();
1051 uint64_t OldSize = DF.getContents().size();
1052 int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
1053 SmallString<8> &Data = DF.getContents();
1055 raw_svector_ostream OSE(Data);
1056 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1058 return OldSize != Data.size();
1061 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSectionData &SD) {
1062 // Holds the first fragment which needed relaxing during this layout. It will
1063 // remain NULL if none were relaxed.
1064 // When a fragment is relaxed, all the fragments following it should get
1065 // invalidated because their offset is going to change.
1066 MCFragment *FirstRelaxedFragment = nullptr;
1068 // Attempt to relax all the fragments in the section.
1069 for (MCSectionData::iterator I = SD.begin(), IE = SD.end(); I != IE; ++I) {
1070 // Check if this is a fragment that needs relaxation.
1071 bool RelaxedFrag = false;
1072 switch(I->getKind()) {
1075 case MCFragment::FT_Relaxable:
1076 assert(!getRelaxAll() &&
1077 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1078 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1080 case MCFragment::FT_Dwarf:
1081 RelaxedFrag = relaxDwarfLineAddr(Layout,
1082 *cast<MCDwarfLineAddrFragment>(I));
1084 case MCFragment::FT_DwarfFrame:
1086 relaxDwarfCallFrameFragment(Layout,
1087 *cast<MCDwarfCallFrameFragment>(I));
1089 case MCFragment::FT_LEB:
1090 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1093 if (RelaxedFrag && !FirstRelaxedFragment)
1094 FirstRelaxedFragment = I;
1096 if (FirstRelaxedFragment) {
1097 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1103 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1104 ++stats::RelaxationSteps;
1106 bool WasRelaxed = false;
1107 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1108 MCSectionData &SD = *it;
1109 while (layoutSectionOnce(Layout, SD))
1116 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1117 // The layout is done. Mark every fragment as valid.
1118 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1119 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1123 // Debugging methods
1127 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1128 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1129 << " Value:" << *AF.getValue()
1130 << " Kind:" << AF.getKind() << ">";
1136 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1137 void MCFragment::dump() {
1138 raw_ostream &OS = llvm::errs();
1141 switch (getKind()) {
1142 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1143 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1144 case MCFragment::FT_CompactEncodedInst:
1145 OS << "MCCompactEncodedInstFragment"; break;
1146 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1147 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1148 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1149 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1150 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1151 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1154 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1155 << " Offset:" << Offset
1156 << " HasInstructions:" << hasInstructions()
1157 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1159 switch (getKind()) {
1160 case MCFragment::FT_Align: {
1161 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1162 if (AF->hasEmitNops())
1163 OS << " (emit nops)";
1165 OS << " Alignment:" << AF->getAlignment()
1166 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1167 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1170 case MCFragment::FT_Data: {
1171 const MCDataFragment *DF = cast<MCDataFragment>(this);
1173 OS << " Contents:[";
1174 const SmallVectorImpl<char> &Contents = DF->getContents();
1175 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1177 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1179 OS << "] (" << Contents.size() << " bytes)";
1181 if (DF->fixup_begin() != DF->fixup_end()) {
1184 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1185 ie = DF->fixup_end(); it != ie; ++it) {
1186 if (it != DF->fixup_begin()) OS << ",\n ";
1193 case MCFragment::FT_CompactEncodedInst: {
1194 const MCCompactEncodedInstFragment *CEIF =
1195 cast<MCCompactEncodedInstFragment>(this);
1197 OS << " Contents:[";
1198 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1199 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1201 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1203 OS << "] (" << Contents.size() << " bytes)";
1206 case MCFragment::FT_Fill: {
1207 const MCFillFragment *FF = cast<MCFillFragment>(this);
1208 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1209 << " Size:" << FF->getSize();
1212 case MCFragment::FT_Relaxable: {
1213 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1216 F->getInst().dump_pretty(OS);
1219 case MCFragment::FT_Org: {
1220 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1222 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1225 case MCFragment::FT_Dwarf: {
1226 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1228 OS << " AddrDelta:" << OF->getAddrDelta()
1229 << " LineDelta:" << OF->getLineDelta();
1232 case MCFragment::FT_DwarfFrame: {
1233 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1235 OS << " AddrDelta:" << CF->getAddrDelta();
1238 case MCFragment::FT_LEB: {
1239 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1241 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1248 void MCSectionData::dump() {
1249 raw_ostream &OS = llvm::errs();
1251 OS << "<MCSectionData";
1252 OS << " Alignment:" << getAlignment()
1253 << " Fragments:[\n ";
1254 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1255 if (it != begin()) OS << ",\n ";
1261 void MCSymbolData::dump() const {
1262 raw_ostream &OS = llvm::errs();
1264 OS << "<MCSymbolData Symbol:" << getSymbol()
1265 << " Fragment:" << getFragment();
1267 OS << " Offset:" << getOffset();
1268 OS << " Flags:" << getFlags() << " Index:" << getIndex();
1270 OS << " (common, size:" << getCommonSize()
1271 << " align: " << getCommonAlignment() << ")";
1273 OS << " (external)";
1274 if (isPrivateExtern())
1275 OS << " (private extern)";
1279 void MCAssembler::dump() {
1280 raw_ostream &OS = llvm::errs();
1282 OS << "<MCAssembler\n";
1283 OS << " Sections:[\n ";
1284 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1285 if (it != begin()) OS << ",\n ";
1291 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1292 if (it != symbol_begin()) OS << ",\n ";
1299 // anchors for MC*Fragment vtables
1300 void MCEncodedFragment::anchor() { }
1301 void MCEncodedFragmentWithFixups::anchor() { }
1302 void MCDataFragment::anchor() { }
1303 void MCCompactEncodedInstFragment::anchor() { }
1304 void MCRelaxableFragment::anchor() { }
1305 void MCAlignFragment::anchor() { }
1306 void MCFillFragment::anchor() { }
1307 void MCOrgFragment::anchor() { }
1308 void MCLEBFragment::anchor() { }
1309 void MCDwarfLineAddrFragment::anchor() { }
1310 void MCDwarfCallFrameFragment::anchor() { }