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 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()->EvaluateAsRelocatable(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))
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 const MCSymbol &ASym = A->getSymbol();
205 const MCAssembler &Asm = getAssembler();
206 const MCSymbolData &ASD = Asm.getSymbolData(ASym);
207 if (ASD.isCommon()) {
208 // FIXME: we should probably add a SMLoc to MCExpr.
209 Asm.getContext().FatalError(SMLoc(),
210 "Common symbol " + ASym.getName() +
211 " cannot be used in assignment expr");
217 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
218 // The size is the last fragment's end offset.
219 const MCFragment &F = SD->getFragmentList().back();
220 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
223 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
224 // Virtual sections have no file size.
225 if (SD->getSection().isVirtualSection())
228 // Otherwise, the file size is the same as the address space size.
229 return getSectionAddressSize(SD);
232 uint64_t llvm::computeBundlePadding(const MCAssembler &Assembler,
234 uint64_t FOffset, uint64_t FSize) {
235 uint64_t BundleSize = Assembler.getBundleAlignSize();
236 assert(BundleSize > 0 &&
237 "computeBundlePadding should only be called if bundling is enabled");
238 uint64_t BundleMask = BundleSize - 1;
239 uint64_t OffsetInBundle = FOffset & BundleMask;
240 uint64_t EndOfFragment = OffsetInBundle + FSize;
242 // There are two kinds of bundling restrictions:
244 // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
245 // *end* on a bundle boundary.
246 // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
247 // would, add padding until the end of the bundle so that the fragment
248 // will start in a new one.
249 if (F->alignToBundleEnd()) {
250 // Three possibilities here:
252 // A) The fragment just happens to end at a bundle boundary, so we're good.
253 // B) The fragment ends before the current bundle boundary: pad it just
254 // enough to reach the boundary.
255 // C) The fragment ends after the current bundle boundary: pad it until it
256 // reaches the end of the next bundle boundary.
258 // Note: this code could be made shorter with some modulo trickery, but it's
259 // intentionally kept in its more explicit form for simplicity.
260 if (EndOfFragment == BundleSize)
262 else if (EndOfFragment < BundleSize)
263 return BundleSize - EndOfFragment;
264 else { // EndOfFragment > BundleSize
265 return 2 * BundleSize - EndOfFragment;
267 } else if (EndOfFragment > BundleSize)
268 return BundleSize - OffsetInBundle;
275 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
278 MCFragment::~MCFragment() {
281 MCFragment::MCFragment(FragmentType Kind, MCSectionData *Parent)
282 : Kind(Kind), Parent(Parent), Atom(nullptr), Offset(~UINT64_C(0)) {
284 Parent->getFragmentList().push_back(this);
289 MCEncodedFragment::~MCEncodedFragment() {
294 MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
299 MCSectionData::MCSectionData() : Section(nullptr) {}
301 MCSectionData::MCSectionData(const MCSection &Section, MCAssembler *A)
302 : Section(&Section), Ordinal(~UINT32_C(0)), Alignment(1),
303 BundleLockState(NotBundleLocked), BundleLockNestingDepth(0),
304 BundleGroupBeforeFirstInst(false), HasInstructions(false) {
306 A->getSectionList().push_back(this);
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 MCSymbolData::MCSymbolData() : Symbol(nullptr) {}
363 MCSymbolData::MCSymbolData(const MCSymbol &Symbol, MCFragment *Fragment,
365 : Symbol(&Symbol), Fragment(Fragment), Offset(Offset), SymbolSize(nullptr),
366 CommonAlign(-1U), Flags(0), Index(0) {}
370 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
371 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
373 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
374 OS(OS_), BundleAlignSize(0), RelaxAll(false),
375 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
376 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
379 MCAssembler::~MCAssembler() {
382 void MCAssembler::reset() {
387 IndirectSymbols.clear();
389 LinkerOptions.clear();
394 SubsectionsViaSymbols = false;
396 LOHContainer.reset();
397 VersionMinInfo.Major = 0;
399 // reset objects owned by us
400 getBackend().reset();
401 getEmitter().reset();
403 getLOHContainer().reset();
406 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
407 if (ThumbFuncs.count(Symbol))
410 if (!Symbol->isVariable())
413 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
414 // is not clear if that is a bug or a feature.
415 const MCExpr *Expr = Symbol->getVariableValue();
416 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
420 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
423 const MCSymbol &Sym = Ref->getSymbol();
424 if (!isThumbFunc(&Sym))
427 ThumbFuncs.insert(Symbol); // Cache it.
431 void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
432 assert(Sym.isTemporary());
433 LocalsUsedInReloc.insert(&Sym);
436 bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
437 assert(Sym.isTemporary());
438 return LocalsUsedInReloc.count(&Sym);
441 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
442 // Non-temporary labels should always be visible to the linker.
443 if (!Symbol.isTemporary())
446 // Absolute temporary labels are never visible.
447 if (!Symbol.isInSection())
450 if (isLocalUsedInReloc(Symbol))
456 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
457 // Linker visible symbols define atoms.
458 if (isSymbolLinkerVisible(SD->getSymbol()))
461 // Absolute and undefined symbols have no defining atom.
462 if (!SD->getFragment())
465 // Non-linker visible symbols in sections which can't be atomized have no
467 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
468 SD->getFragment()->getParent()->getSection()))
471 // Otherwise, return the atom for the containing fragment.
472 return SD->getFragment()->getAtom();
475 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
476 const MCFixup &Fixup, const MCFragment *DF,
477 MCValue &Target, uint64_t &Value) const {
478 ++stats::evaluateFixup;
480 // FIXME: This code has some duplication with RecordRelocation. We should
481 // probably merge the two into a single callback that tries to evaluate a
482 // fixup and records a relocation if one is needed.
483 const MCExpr *Expr = Fixup.getValue();
484 if (!Expr->EvaluateAsRelocatable(Target, &Layout, &Fixup))
485 getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
487 bool IsPCRel = Backend.getFixupKindInfo(
488 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
492 if (Target.getSymB()) {
494 } else if (!Target.getSymA()) {
497 const MCSymbolRefExpr *A = Target.getSymA();
498 const MCSymbol &SA = A->getSymbol();
499 if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
502 const MCSymbolData &DataA = getSymbolData(SA);
503 IsResolved = getWriter().IsSymbolRefDifferenceFullyResolvedImpl(
504 *this, DataA, *DF, false, true);
508 IsResolved = Target.isAbsolute();
511 Value = Target.getConstant();
513 if (const MCSymbolRefExpr *A = Target.getSymA()) {
514 const MCSymbol &Sym = A->getSymbol();
516 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
518 if (const MCSymbolRefExpr *B = Target.getSymB()) {
519 const MCSymbol &Sym = B->getSymbol();
521 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
525 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
526 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
527 assert((ShouldAlignPC ? IsPCRel : true) &&
528 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
531 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
533 // A number of ARM fixups in Thumb mode require that the effective PC
534 // address be determined as the 32-bit aligned version of the actual offset.
535 if (ShouldAlignPC) Offset &= ~0x3;
539 // Let the backend adjust the fixup value if necessary, including whether
540 // we need a relocation.
541 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
547 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
548 const MCFragment &F) const {
549 switch (F.getKind()) {
550 case MCFragment::FT_Data:
551 case MCFragment::FT_Relaxable:
552 case MCFragment::FT_CompactEncodedInst:
553 return cast<MCEncodedFragment>(F).getContents().size();
554 case MCFragment::FT_Fill:
555 return cast<MCFillFragment>(F).getSize();
557 case MCFragment::FT_LEB:
558 return cast<MCLEBFragment>(F).getContents().size();
560 case MCFragment::FT_Align: {
561 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
562 unsigned Offset = Layout.getFragmentOffset(&AF);
563 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
564 // If we are padding with nops, force the padding to be larger than the
566 if (Size > 0 && AF.hasEmitNops()) {
567 while (Size % getBackend().getMinimumNopSize())
568 Size += AF.getAlignment();
570 if (Size > AF.getMaxBytesToEmit())
575 case MCFragment::FT_Org: {
576 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
577 int64_t TargetLocation;
578 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
579 report_fatal_error("expected assembly-time absolute expression");
581 // FIXME: We need a way to communicate this error.
582 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
583 int64_t Size = TargetLocation - FragmentOffset;
584 if (Size < 0 || Size >= 0x40000000)
585 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
586 "' (at offset '" + Twine(FragmentOffset) + "')");
590 case MCFragment::FT_Dwarf:
591 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
592 case MCFragment::FT_DwarfFrame:
593 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
596 llvm_unreachable("invalid fragment kind");
599 void MCAsmLayout::layoutFragment(MCFragment *F) {
600 MCFragment *Prev = F->getPrevNode();
602 // We should never try to recompute something which is valid.
603 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
604 // We should never try to compute the fragment layout if its predecessor
606 assert((!Prev || isFragmentValid(Prev)) &&
607 "Attempt to compute fragment before its predecessor!");
609 ++stats::FragmentLayouts;
611 // Compute fragment offset and size.
613 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
616 LastValidFragment[F->getParent()] = F;
618 // If bundling is enabled and this fragment has instructions in it, it has to
619 // obey the bundling restrictions. With padding, we'll have:
624 // -------------------------------------
625 // Prev |##########| F |
626 // -------------------------------------
631 // The fragment's offset will point to after the padding, and its computed
632 // size won't include the padding.
634 // When the -mc-relax-all flag is used, we optimize bundling by writting the
635 // bundle padding directly into fragments when the instructions are emitted
636 // inside the streamer.
638 if (Assembler.isBundlingEnabled() && !Assembler.getRelaxAll() &&
639 F->hasInstructions()) {
640 assert(isa<MCEncodedFragment>(F) &&
641 "Only MCEncodedFragment implementations have instructions");
642 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
644 if (FSize > Assembler.getBundleAlignSize())
645 report_fatal_error("Fragment can't be larger than a bundle size");
647 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
649 if (RequiredBundlePadding > UINT8_MAX)
650 report_fatal_error("Padding cannot exceed 255 bytes");
651 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
652 F->Offset += RequiredBundlePadding;
656 /// \brief Write the contents of a fragment to the given object writer. Expects
657 /// a MCEncodedFragment.
658 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
659 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
660 OW->WriteBytes(EF.getContents());
663 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
664 MCObjectWriter *OW) const {
665 // Should NOP padding be written out before this fragment?
666 unsigned BundlePadding = F.getBundlePadding();
667 if (BundlePadding > 0) {
668 assert(isBundlingEnabled() &&
669 "Writing bundle padding with disabled bundling");
670 assert(F.hasInstructions() &&
671 "Writing bundle padding for a fragment without instructions");
673 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
674 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
675 // If the padding itself crosses a bundle boundary, it must be emitted
676 // in 2 pieces, since even nop instructions must not cross boundaries.
677 // v--------------v <- BundleAlignSize
678 // v---------v <- BundlePadding
679 // ----------------------------
680 // | Prev |####|####| F |
681 // ----------------------------
682 // ^-------------------^ <- TotalLength
683 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
684 if (!getBackend().writeNopData(DistanceToBoundary, OW))
685 report_fatal_error("unable to write NOP sequence of " +
686 Twine(DistanceToBoundary) + " bytes");
687 BundlePadding -= DistanceToBoundary;
689 if (!getBackend().writeNopData(BundlePadding, OW))
690 report_fatal_error("unable to write NOP sequence of " +
691 Twine(BundlePadding) + " bytes");
695 /// \brief Write the fragment \p F to the output file.
696 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
697 const MCFragment &F) {
698 MCObjectWriter *OW = &Asm.getWriter();
700 // FIXME: Embed in fragments instead?
701 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
703 Asm.writeFragmentPadding(F, FragmentSize, OW);
705 // This variable (and its dummy usage) is to participate in the assert at
706 // the end of the function.
707 uint64_t Start = OW->getStream().tell();
710 ++stats::EmittedFragments;
712 switch (F.getKind()) {
713 case MCFragment::FT_Align: {
714 ++stats::EmittedAlignFragments;
715 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
716 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
718 uint64_t Count = FragmentSize / AF.getValueSize();
720 // FIXME: This error shouldn't actually occur (the front end should emit
721 // multiple .align directives to enforce the semantics it wants), but is
722 // severe enough that we want to report it. How to handle this?
723 if (Count * AF.getValueSize() != FragmentSize)
724 report_fatal_error("undefined .align directive, value size '" +
725 Twine(AF.getValueSize()) +
726 "' is not a divisor of padding size '" +
727 Twine(FragmentSize) + "'");
729 // See if we are aligning with nops, and if so do that first to try to fill
730 // the Count bytes. Then if that did not fill any bytes or there are any
731 // bytes left to fill use the Value and ValueSize to fill the rest.
732 // If we are aligning with nops, ask that target to emit the right data.
733 if (AF.hasEmitNops()) {
734 if (!Asm.getBackend().writeNopData(Count, OW))
735 report_fatal_error("unable to write nop sequence of " +
736 Twine(Count) + " bytes");
740 // Otherwise, write out in multiples of the value size.
741 for (uint64_t i = 0; i != Count; ++i) {
742 switch (AF.getValueSize()) {
743 default: llvm_unreachable("Invalid size!");
744 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
745 case 2: OW->Write16(uint16_t(AF.getValue())); break;
746 case 4: OW->Write32(uint32_t(AF.getValue())); break;
747 case 8: OW->Write64(uint64_t(AF.getValue())); break;
753 case MCFragment::FT_Data:
754 ++stats::EmittedDataFragments;
755 writeFragmentContents(F, OW);
758 case MCFragment::FT_Relaxable:
759 ++stats::EmittedRelaxableFragments;
760 writeFragmentContents(F, OW);
763 case MCFragment::FT_CompactEncodedInst:
764 ++stats::EmittedCompactEncodedInstFragments;
765 writeFragmentContents(F, OW);
768 case MCFragment::FT_Fill: {
769 ++stats::EmittedFillFragments;
770 const MCFillFragment &FF = cast<MCFillFragment>(F);
772 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
774 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
775 switch (FF.getValueSize()) {
776 default: llvm_unreachable("Invalid size!");
777 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
778 case 2: OW->Write16(uint16_t(FF.getValue())); break;
779 case 4: OW->Write32(uint32_t(FF.getValue())); break;
780 case 8: OW->Write64(uint64_t(FF.getValue())); break;
786 case MCFragment::FT_LEB: {
787 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
788 OW->WriteBytes(LF.getContents());
792 case MCFragment::FT_Org: {
793 ++stats::EmittedOrgFragments;
794 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
796 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
797 OW->Write8(uint8_t(OF.getValue()));
802 case MCFragment::FT_Dwarf: {
803 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
804 OW->WriteBytes(OF.getContents());
807 case MCFragment::FT_DwarfFrame: {
808 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
809 OW->WriteBytes(CF.getContents());
814 assert(OW->getStream().tell() - Start == FragmentSize &&
815 "The stream should advance by fragment size");
818 void MCAssembler::writeSectionData(const MCSectionData *SD,
819 const MCAsmLayout &Layout) const {
820 // Ignore virtual sections.
821 if (SD->getSection().isVirtualSection()) {
822 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
824 // Check that contents are only things legal inside a virtual section.
825 for (MCSectionData::const_iterator it = SD->begin(),
826 ie = SD->end(); it != ie; ++it) {
827 switch (it->getKind()) {
828 default: llvm_unreachable("Invalid fragment in virtual section!");
829 case MCFragment::FT_Data: {
830 // Check that we aren't trying to write a non-zero contents (or fixups)
831 // into a virtual section. This is to support clients which use standard
832 // directives to fill the contents of virtual sections.
833 const MCDataFragment &DF = cast<MCDataFragment>(*it);
834 assert(DF.fixup_begin() == DF.fixup_end() &&
835 "Cannot have fixups in virtual section!");
836 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
837 if (DF.getContents()[i]) {
838 if (auto *ELFSec = dyn_cast<const MCSectionELF>(&SD->getSection()))
839 report_fatal_error("non-zero initializer found in section '" +
840 ELFSec->getSectionName() + "'");
842 report_fatal_error("non-zero initializer found in virtual section");
846 case MCFragment::FT_Align:
847 // Check that we aren't trying to write a non-zero value into a virtual
849 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
850 cast<MCAlignFragment>(it)->getValue() == 0) &&
851 "Invalid align in virtual section!");
853 case MCFragment::FT_Fill:
854 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
855 cast<MCFillFragment>(it)->getValue() == 0) &&
856 "Invalid fill in virtual section!");
864 uint64_t Start = getWriter().getStream().tell();
867 for (MCSectionData::const_iterator it = SD->begin(), ie = SD->end();
869 writeFragment(*this, Layout, *it);
871 assert(getWriter().getStream().tell() - Start ==
872 Layout.getSectionAddressSize(SD));
875 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
877 const MCFixup &Fixup) {
878 // Evaluate the fixup.
881 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
882 MCFixupKindInfo::FKF_IsPCRel;
883 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
884 // The fixup was unresolved, we need a relocation. Inform the object
885 // writer of the relocation, and give it an opportunity to adjust the
886 // fixup value if need be.
887 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
890 return std::make_pair(FixedValue, IsPCRel);
893 void MCAssembler::Finish() {
894 DEBUG_WITH_TYPE("mc-dump", {
895 llvm::errs() << "assembler backend - pre-layout\n--\n";
898 // Create the layout object.
899 MCAsmLayout Layout(*this);
901 // Create dummy fragments and assign section ordinals.
902 unsigned SectionIndex = 0;
903 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
904 // Create dummy fragments to eliminate any empty sections, this simplifies
906 if (it->getFragmentList().empty())
907 new MCDataFragment(it);
909 it->setOrdinal(SectionIndex++);
912 // Assign layout order indices to sections and fragments.
913 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
914 MCSectionData *SD = Layout.getSectionOrder()[i];
915 SD->setLayoutOrder(i);
917 unsigned FragmentIndex = 0;
918 for (MCSectionData::iterator iFrag = SD->begin(), iFragEnd = SD->end();
919 iFrag != iFragEnd; ++iFrag)
920 iFrag->setLayoutOrder(FragmentIndex++);
923 // Layout until everything fits.
924 while (layoutOnce(Layout))
927 DEBUG_WITH_TYPE("mc-dump", {
928 llvm::errs() << "assembler backend - post-relaxation\n--\n";
931 // Finalize the layout, including fragment lowering.
932 finishLayout(Layout);
934 DEBUG_WITH_TYPE("mc-dump", {
935 llvm::errs() << "assembler backend - final-layout\n--\n";
938 uint64_t StartOffset = OS.tell();
940 // Allow the object writer a chance to perform post-layout binding (for
941 // example, to set the index fields in the symbol data).
942 getWriter().ExecutePostLayoutBinding(*this, Layout);
944 // Evaluate and apply the fixups, generating relocation entries as necessary.
945 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
946 for (MCSectionData::iterator it2 = it->begin(),
947 ie2 = it->end(); it2 != ie2; ++it2) {
948 MCEncodedFragmentWithFixups *F =
949 dyn_cast<MCEncodedFragmentWithFixups>(it2);
951 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
952 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
953 MCFixup &Fixup = *it3;
956 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
957 getBackend().applyFixup(Fixup, F->getContents().data(),
958 F->getContents().size(), FixedValue, IsPCRel);
964 // Write the object file.
965 getWriter().WriteObject(*this, Layout);
967 stats::ObjectBytes += OS.tell() - StartOffset;
970 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
971 const MCRelaxableFragment *DF,
972 const MCAsmLayout &Layout) const {
973 // If we cannot resolve the fixup value, it requires relaxation.
976 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
979 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
982 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
983 const MCAsmLayout &Layout) const {
984 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
985 // are intentionally pushing out inst fragments, or because we relaxed a
986 // previous instruction to one that doesn't need relaxation.
987 if (!getBackend().mayNeedRelaxation(F->getInst()))
990 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
991 ie = F->fixup_end(); it != ie; ++it)
992 if (fixupNeedsRelaxation(*it, F, Layout))
998 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
999 MCRelaxableFragment &F) {
1000 if (!fragmentNeedsRelaxation(&F, Layout))
1003 ++stats::RelaxedInstructions;
1005 // FIXME-PERF: We could immediately lower out instructions if we can tell
1006 // they are fully resolved, to avoid retesting on later passes.
1008 // Relax the fragment.
1011 getBackend().relaxInstruction(F.getInst(), Relaxed);
1013 // Encode the new instruction.
1015 // FIXME-PERF: If it matters, we could let the target do this. It can
1016 // probably do so more efficiently in many cases.
1017 SmallVector<MCFixup, 4> Fixups;
1018 SmallString<256> Code;
1019 raw_svector_ostream VecOS(Code);
1020 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
1023 // Update the fragment.
1025 F.getContents() = Code;
1026 F.getFixups() = Fixups;
1031 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1032 uint64_t OldSize = LF.getContents().size();
1034 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1036 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
1037 SmallString<8> &Data = LF.getContents();
1039 raw_svector_ostream OSE(Data);
1041 encodeSLEB128(Value, OSE);
1043 encodeULEB128(Value, OSE);
1045 return OldSize != LF.getContents().size();
1048 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1049 MCDwarfLineAddrFragment &DF) {
1050 MCContext &Context = Layout.getAssembler().getContext();
1051 uint64_t OldSize = DF.getContents().size();
1053 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1054 assert(Abs && "We created a line delta with an invalid expression");
1057 LineDelta = DF.getLineDelta();
1058 SmallString<8> &Data = DF.getContents();
1060 raw_svector_ostream OSE(Data);
1061 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1063 return OldSize != Data.size();
1066 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1067 MCDwarfCallFrameFragment &DF) {
1068 MCContext &Context = Layout.getAssembler().getContext();
1069 uint64_t OldSize = DF.getContents().size();
1071 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1072 assert(Abs && "We created call frame with an invalid expression");
1074 SmallString<8> &Data = DF.getContents();
1076 raw_svector_ostream OSE(Data);
1077 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1079 return OldSize != Data.size();
1082 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSectionData &SD) {
1083 // Holds the first fragment which needed relaxing during this layout. It will
1084 // remain NULL if none were relaxed.
1085 // When a fragment is relaxed, all the fragments following it should get
1086 // invalidated because their offset is going to change.
1087 MCFragment *FirstRelaxedFragment = nullptr;
1089 // Attempt to relax all the fragments in the section.
1090 for (MCSectionData::iterator I = SD.begin(), IE = SD.end(); I != IE; ++I) {
1091 // Check if this is a fragment that needs relaxation.
1092 bool RelaxedFrag = false;
1093 switch(I->getKind()) {
1096 case MCFragment::FT_Relaxable:
1097 assert(!getRelaxAll() &&
1098 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1099 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1101 case MCFragment::FT_Dwarf:
1102 RelaxedFrag = relaxDwarfLineAddr(Layout,
1103 *cast<MCDwarfLineAddrFragment>(I));
1105 case MCFragment::FT_DwarfFrame:
1107 relaxDwarfCallFrameFragment(Layout,
1108 *cast<MCDwarfCallFrameFragment>(I));
1110 case MCFragment::FT_LEB:
1111 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1114 if (RelaxedFrag && !FirstRelaxedFragment)
1115 FirstRelaxedFragment = I;
1117 if (FirstRelaxedFragment) {
1118 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1124 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1125 ++stats::RelaxationSteps;
1127 bool WasRelaxed = false;
1128 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1129 MCSectionData &SD = *it;
1130 while (layoutSectionOnce(Layout, SD))
1137 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1138 // The layout is done. Mark every fragment as valid.
1139 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1140 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1144 // Debugging methods
1148 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1149 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1150 << " Value:" << *AF.getValue()
1151 << " Kind:" << AF.getKind() << ">";
1157 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1158 void MCFragment::dump() {
1159 raw_ostream &OS = llvm::errs();
1162 switch (getKind()) {
1163 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1164 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1165 case MCFragment::FT_CompactEncodedInst:
1166 OS << "MCCompactEncodedInstFragment"; break;
1167 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1168 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1169 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1170 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1171 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1172 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1175 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1176 << " Offset:" << Offset
1177 << " HasInstructions:" << hasInstructions()
1178 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1180 switch (getKind()) {
1181 case MCFragment::FT_Align: {
1182 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1183 if (AF->hasEmitNops())
1184 OS << " (emit nops)";
1186 OS << " Alignment:" << AF->getAlignment()
1187 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1188 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1191 case MCFragment::FT_Data: {
1192 const MCDataFragment *DF = cast<MCDataFragment>(this);
1194 OS << " Contents:[";
1195 const SmallVectorImpl<char> &Contents = DF->getContents();
1196 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1198 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1200 OS << "] (" << Contents.size() << " bytes)";
1202 if (DF->fixup_begin() != DF->fixup_end()) {
1205 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1206 ie = DF->fixup_end(); it != ie; ++it) {
1207 if (it != DF->fixup_begin()) OS << ",\n ";
1214 case MCFragment::FT_CompactEncodedInst: {
1215 const MCCompactEncodedInstFragment *CEIF =
1216 cast<MCCompactEncodedInstFragment>(this);
1218 OS << " Contents:[";
1219 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1220 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1222 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1224 OS << "] (" << Contents.size() << " bytes)";
1227 case MCFragment::FT_Fill: {
1228 const MCFillFragment *FF = cast<MCFillFragment>(this);
1229 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1230 << " Size:" << FF->getSize();
1233 case MCFragment::FT_Relaxable: {
1234 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1237 F->getInst().dump_pretty(OS);
1240 case MCFragment::FT_Org: {
1241 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1243 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1246 case MCFragment::FT_Dwarf: {
1247 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1249 OS << " AddrDelta:" << OF->getAddrDelta()
1250 << " LineDelta:" << OF->getLineDelta();
1253 case MCFragment::FT_DwarfFrame: {
1254 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1256 OS << " AddrDelta:" << CF->getAddrDelta();
1259 case MCFragment::FT_LEB: {
1260 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1262 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1269 void MCSectionData::dump() {
1270 raw_ostream &OS = llvm::errs();
1272 OS << "<MCSectionData";
1273 OS << " Alignment:" << getAlignment()
1274 << " Fragments:[\n ";
1275 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1276 if (it != begin()) OS << ",\n ";
1282 void MCSymbolData::dump() const {
1283 raw_ostream &OS = llvm::errs();
1285 OS << "<MCSymbolData Symbol:" << getSymbol()
1286 << " Fragment:" << getFragment();
1288 OS << " Offset:" << getOffset();
1289 OS << " Flags:" << getFlags() << " Index:" << getIndex();
1291 OS << " (common, size:" << getCommonSize()
1292 << " align: " << getCommonAlignment() << ")";
1294 OS << " (external)";
1295 if (isPrivateExtern())
1296 OS << " (private extern)";
1300 void MCAssembler::dump() {
1301 raw_ostream &OS = llvm::errs();
1303 OS << "<MCAssembler\n";
1304 OS << " Sections:[\n ";
1305 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1306 if (it != begin()) OS << ",\n ";
1312 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1313 if (it != symbol_begin()) OS << ",\n ";
1320 // anchors for MC*Fragment vtables
1321 void MCEncodedFragment::anchor() { }
1322 void MCEncodedFragmentWithFixups::anchor() { }
1323 void MCDataFragment::anchor() { }
1324 void MCCompactEncodedInstFragment::anchor() { }
1325 void MCRelaxableFragment::anchor() { }
1326 void MCAlignFragment::anchor() { }
1327 void MCFillFragment::anchor() { }
1328 void MCOrgFragment::anchor() { }
1329 void MCLEBFragment::anchor() { }
1330 void MCDwarfLineAddrFragment::anchor() { }
1331 void MCDwarfCallFrameFragment::anchor() { }