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->isVirtualSection())
73 SectionOrder.push_back(&*it);
74 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
75 if (it->isVirtualSection())
76 SectionOrder.push_back(&*it);
79 bool MCAsmLayout::isFragmentValid(const MCFragment *F) const {
80 const MCSection *Sec = F->getParent();
81 const MCFragment *LastValid = LastValidFragment.lookup(Sec);
84 assert(LastValid->getParent() == Sec);
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 LastValidFragment[F->getParent()] = F->getPrevNode();
98 void MCAsmLayout::ensureValid(const MCFragment *F) const {
99 MCSection *Sec = F->getParent();
100 MCFragment *Cur = LastValidFragment[Sec];
104 Cur = Cur->getNextNode();
106 // Advance the layout position until the fragment is valid.
107 while (!isFragmentValid(F)) {
108 assert(Cur && "Layout bookkeeping error");
109 const_cast<MCAsmLayout*>(this)->layoutFragment(Cur);
110 Cur = Cur->getNextNode();
114 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
116 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
120 // Simple getSymbolOffset helper for the non-varibale case.
121 static bool getLabelOffset(const MCAsmLayout &Layout, const MCSymbol &S,
122 bool ReportError, uint64_t &Val) {
123 if (!S.getFragment()) {
125 report_fatal_error("unable to evaluate offset to undefined symbol '" +
129 Val = Layout.getFragmentOffset(S.getFragment()) + S.getOffset();
133 static bool getSymbolOffsetImpl(const MCAsmLayout &Layout, const MCSymbol &S,
134 bool ReportError, uint64_t &Val) {
136 return getLabelOffset(Layout, S, ReportError, Val);
138 // If SD is a variable, evaluate it.
140 if (!S.getVariableValue()->evaluateAsRelocatable(Target, &Layout, nullptr))
141 report_fatal_error("unable to evaluate offset for variable '" +
144 uint64_t Offset = Target.getConstant();
146 const MCSymbolRefExpr *A = Target.getSymA();
149 if (!getLabelOffset(Layout, A->getSymbol(), ReportError, ValA))
154 const MCSymbolRefExpr *B = Target.getSymB();
157 if (!getLabelOffset(Layout, B->getSymbol(), ReportError, ValB))
166 bool MCAsmLayout::getSymbolOffset(const MCSymbol &S, uint64_t &Val) const {
167 return getSymbolOffsetImpl(*this, S, false, Val);
170 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbol &S) const {
172 getSymbolOffsetImpl(*this, S, true, Val);
176 const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
177 if (!Symbol.isVariable())
180 const MCExpr *Expr = Symbol.getVariableValue();
182 if (!Expr->evaluateAsValue(Value, *this))
183 llvm_unreachable("Invalid Expression");
185 const MCSymbolRefExpr *RefB = Value.getSymB();
187 Assembler.getContext().reportFatalError(
188 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
189 "' could not be evaluated in a subtraction expression");
191 const MCSymbolRefExpr *A = Value.getSymA();
195 const MCSymbol &ASym = A->getSymbol();
196 const MCAssembler &Asm = getAssembler();
197 if (ASym.isCommon()) {
198 // FIXME: we should probably add a SMLoc to MCExpr.
199 Asm.getContext().reportFatalError(SMLoc(),
200 "Common symbol " + ASym.getName() +
201 " cannot be used in assignment expr");
207 uint64_t MCAsmLayout::getSectionAddressSize(const MCSection *Sec) const {
208 // The size is the last fragment's end offset.
209 const MCFragment &F = Sec->getFragmentList().back();
210 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
213 uint64_t MCAsmLayout::getSectionFileSize(const MCSection *Sec) const {
214 // Virtual sections have no file size.
215 if (Sec->isVirtualSection())
218 // Otherwise, the file size is the same as the address space size.
219 return getSectionAddressSize(Sec);
222 uint64_t llvm::computeBundlePadding(const MCAssembler &Assembler,
224 uint64_t FOffset, uint64_t FSize) {
225 uint64_t BundleSize = Assembler.getBundleAlignSize();
226 assert(BundleSize > 0 &&
227 "computeBundlePadding should only be called if bundling is enabled");
228 uint64_t BundleMask = BundleSize - 1;
229 uint64_t OffsetInBundle = FOffset & BundleMask;
230 uint64_t EndOfFragment = OffsetInBundle + FSize;
232 // There are two kinds of bundling restrictions:
234 // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
235 // *end* on a bundle boundary.
236 // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
237 // would, add padding until the end of the bundle so that the fragment
238 // will start in a new one.
239 if (F->alignToBundleEnd()) {
240 // Three possibilities here:
242 // A) The fragment just happens to end at a bundle boundary, so we're good.
243 // B) The fragment ends before the current bundle boundary: pad it just
244 // enough to reach the boundary.
245 // C) The fragment ends after the current bundle boundary: pad it until it
246 // reaches the end of the next bundle boundary.
248 // Note: this code could be made shorter with some modulo trickery, but it's
249 // intentionally kept in its more explicit form for simplicity.
250 if (EndOfFragment == BundleSize)
252 else if (EndOfFragment < BundleSize)
253 return BundleSize - EndOfFragment;
254 else { // EndOfFragment > BundleSize
255 return 2 * BundleSize - EndOfFragment;
257 } else if (EndOfFragment > BundleSize)
258 return BundleSize - OffsetInBundle;
265 void ilist_node_traits<MCFragment>::deleteNode(MCFragment *V) {
269 MCFragment::MCFragment() : Kind(FragmentType(~0)), HasInstructions(false),
270 AlignToBundleEnd(false), BundlePadding(0) {
273 MCFragment::~MCFragment() { }
275 MCFragment::MCFragment(FragmentType Kind, bool HasInstructions,
276 uint8_t BundlePadding, MCSection *Parent)
277 : Kind(Kind), HasInstructions(HasInstructions), AlignToBundleEnd(false),
278 BundlePadding(BundlePadding), Parent(Parent), Atom(nullptr),
279 Offset(~UINT64_C(0)) {
281 Parent->getFragmentList().push_back(this);
284 void MCFragment::destroy() {
285 // First check if we are the sentinal.
286 if (Kind == FragmentType(~0)) {
293 delete cast<MCAlignFragment>(this);
296 delete cast<MCDataFragment>(this);
298 case FT_CompactEncodedInst:
299 delete cast<MCCompactEncodedInstFragment>(this);
302 delete cast<MCFillFragment>(this);
305 delete cast<MCRelaxableFragment>(this);
308 delete cast<MCOrgFragment>(this);
311 delete cast<MCDwarfLineAddrFragment>(this);
314 delete cast<MCDwarfCallFrameFragment>(this);
317 delete cast<MCLEBFragment>(this);
320 delete cast<MCSafeSEHFragment>(this);
327 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
328 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
330 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
331 OS(OS_), BundleAlignSize(0), RelaxAll(false),
332 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
333 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
336 MCAssembler::~MCAssembler() {
339 void MCAssembler::reset() {
342 IndirectSymbols.clear();
344 LinkerOptions.clear();
349 SubsectionsViaSymbols = false;
351 LOHContainer.reset();
352 VersionMinInfo.Major = 0;
354 // reset objects owned by us
355 getBackend().reset();
356 getEmitter().reset();
358 getLOHContainer().reset();
361 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
362 if (ThumbFuncs.count(Symbol))
365 if (!Symbol->isVariable())
368 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
369 // is not clear if that is a bug or a feature.
370 const MCExpr *Expr = Symbol->getVariableValue();
371 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
375 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
378 const MCSymbol &Sym = Ref->getSymbol();
379 if (!isThumbFunc(&Sym))
382 ThumbFuncs.insert(Symbol); // Cache it.
386 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
387 // Non-temporary labels should always be visible to the linker.
388 if (!Symbol.isTemporary())
391 // Absolute temporary labels are never visible.
392 if (!Symbol.isInSection())
395 if (Symbol.isUsedInReloc())
401 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
402 // Linker visible symbols define atoms.
403 if (isSymbolLinkerVisible(S))
406 // Absolute and undefined symbols have no defining atom.
407 if (!S.getFragment())
410 // Non-linker visible symbols in sections which can't be atomized have no
412 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
413 *S.getFragment()->getParent()))
416 // Otherwise, return the atom for the containing fragment.
417 return S.getFragment()->getAtom();
420 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
421 const MCFixup &Fixup, const MCFragment *DF,
422 MCValue &Target, uint64_t &Value) const {
423 ++stats::evaluateFixup;
425 // FIXME: This code has some duplication with recordRelocation. We should
426 // probably merge the two into a single callback that tries to evaluate a
427 // fixup and records a relocation if one is needed.
428 const MCExpr *Expr = Fixup.getValue();
429 if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup))
430 getContext().reportFatalError(Fixup.getLoc(), "expected relocatable expression");
432 bool IsPCRel = Backend.getFixupKindInfo(
433 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
437 if (Target.getSymB()) {
439 } else if (!Target.getSymA()) {
442 const MCSymbolRefExpr *A = Target.getSymA();
443 const MCSymbol &SA = A->getSymbol();
444 if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
447 IsResolved = getWriter().isSymbolRefDifferenceFullyResolvedImpl(
448 *this, SA, *DF, false, true);
452 IsResolved = Target.isAbsolute();
455 Value = Target.getConstant();
457 if (const MCSymbolRefExpr *A = Target.getSymA()) {
458 const MCSymbol &Sym = A->getSymbol();
460 Value += Layout.getSymbolOffset(Sym);
462 if (const MCSymbolRefExpr *B = Target.getSymB()) {
463 const MCSymbol &Sym = B->getSymbol();
465 Value -= Layout.getSymbolOffset(Sym);
469 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
470 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
471 assert((ShouldAlignPC ? IsPCRel : true) &&
472 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
475 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
477 // A number of ARM fixups in Thumb mode require that the effective PC
478 // address be determined as the 32-bit aligned version of the actual offset.
479 if (ShouldAlignPC) Offset &= ~0x3;
483 // Let the backend adjust the fixup value if necessary, including whether
484 // we need a relocation.
485 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
491 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
492 const MCFragment &F) const {
493 switch (F.getKind()) {
494 case MCFragment::FT_Data:
495 return cast<MCDataFragment>(F).getContents().size();
496 case MCFragment::FT_Relaxable:
497 return cast<MCRelaxableFragment>(F).getContents().size();
498 case MCFragment::FT_CompactEncodedInst:
499 return cast<MCCompactEncodedInstFragment>(F).getContents().size();
500 case MCFragment::FT_Fill:
501 return cast<MCFillFragment>(F).getSize();
503 case MCFragment::FT_LEB:
504 return cast<MCLEBFragment>(F).getContents().size();
506 case MCFragment::FT_SafeSEH:
509 case MCFragment::FT_Align: {
510 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
511 unsigned Offset = Layout.getFragmentOffset(&AF);
512 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
513 // If we are padding with nops, force the padding to be larger than the
515 if (Size > 0 && AF.hasEmitNops()) {
516 while (Size % getBackend().getMinimumNopSize())
517 Size += AF.getAlignment();
519 if (Size > AF.getMaxBytesToEmit())
524 case MCFragment::FT_Org: {
525 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
526 int64_t TargetLocation;
527 if (!OF.getOffset().evaluateAsAbsolute(TargetLocation, Layout))
528 report_fatal_error("expected assembly-time absolute expression");
530 // FIXME: We need a way to communicate this error.
531 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
532 int64_t Size = TargetLocation - FragmentOffset;
533 if (Size < 0 || Size >= 0x40000000)
534 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
535 "' (at offset '" + Twine(FragmentOffset) + "')");
539 case MCFragment::FT_Dwarf:
540 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
541 case MCFragment::FT_DwarfFrame:
542 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
545 llvm_unreachable("invalid fragment kind");
548 void MCAsmLayout::layoutFragment(MCFragment *F) {
549 MCFragment *Prev = F->getPrevNode();
551 // We should never try to recompute something which is valid.
552 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
553 // We should never try to compute the fragment layout if its predecessor
555 assert((!Prev || isFragmentValid(Prev)) &&
556 "Attempt to compute fragment before its predecessor!");
558 ++stats::FragmentLayouts;
560 // Compute fragment offset and size.
562 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
565 LastValidFragment[F->getParent()] = F;
567 // If bundling is enabled and this fragment has instructions in it, it has to
568 // obey the bundling restrictions. With padding, we'll have:
573 // -------------------------------------
574 // Prev |##########| F |
575 // -------------------------------------
580 // The fragment's offset will point to after the padding, and its computed
581 // size won't include the padding.
583 // When the -mc-relax-all flag is used, we optimize bundling by writting the
584 // bundle padding directly into fragments when the instructions are emitted
585 // inside the streamer.
587 if (Assembler.isBundlingEnabled() && !Assembler.getRelaxAll() &&
588 F->hasInstructions()) {
589 assert(isa<MCEncodedFragment>(F) &&
590 "Only MCEncodedFragment implementations have instructions");
591 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
593 if (FSize > Assembler.getBundleAlignSize())
594 report_fatal_error("Fragment can't be larger than a bundle size");
596 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
598 if (RequiredBundlePadding > UINT8_MAX)
599 report_fatal_error("Padding cannot exceed 255 bytes");
600 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
601 F->Offset += RequiredBundlePadding;
605 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
606 bool New = !Symbol.isRegistered();
610 Symbol.setIsRegistered(true);
611 Symbols.push_back(&Symbol);
615 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
616 MCObjectWriter *OW) const {
617 // Should NOP padding be written out before this fragment?
618 unsigned BundlePadding = F.getBundlePadding();
619 if (BundlePadding > 0) {
620 assert(isBundlingEnabled() &&
621 "Writing bundle padding with disabled bundling");
622 assert(F.hasInstructions() &&
623 "Writing bundle padding for a fragment without instructions");
625 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
626 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
627 // If the padding itself crosses a bundle boundary, it must be emitted
628 // in 2 pieces, since even nop instructions must not cross boundaries.
629 // v--------------v <- BundleAlignSize
630 // v---------v <- BundlePadding
631 // ----------------------------
632 // | Prev |####|####| F |
633 // ----------------------------
634 // ^-------------------^ <- TotalLength
635 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
636 if (!getBackend().writeNopData(DistanceToBoundary, OW))
637 report_fatal_error("unable to write NOP sequence of " +
638 Twine(DistanceToBoundary) + " bytes");
639 BundlePadding -= DistanceToBoundary;
641 if (!getBackend().writeNopData(BundlePadding, OW))
642 report_fatal_error("unable to write NOP sequence of " +
643 Twine(BundlePadding) + " bytes");
647 /// \brief Write the fragment \p F to the output file.
648 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
649 const MCFragment &F) {
650 MCObjectWriter *OW = &Asm.getWriter();
652 // FIXME: Embed in fragments instead?
653 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
655 Asm.writeFragmentPadding(F, FragmentSize, OW);
657 // This variable (and its dummy usage) is to participate in the assert at
658 // the end of the function.
659 uint64_t Start = OW->getStream().tell();
662 ++stats::EmittedFragments;
664 switch (F.getKind()) {
665 case MCFragment::FT_Align: {
666 ++stats::EmittedAlignFragments;
667 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
668 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
670 uint64_t Count = FragmentSize / AF.getValueSize();
672 // FIXME: This error shouldn't actually occur (the front end should emit
673 // multiple .align directives to enforce the semantics it wants), but is
674 // severe enough that we want to report it. How to handle this?
675 if (Count * AF.getValueSize() != FragmentSize)
676 report_fatal_error("undefined .align directive, value size '" +
677 Twine(AF.getValueSize()) +
678 "' is not a divisor of padding size '" +
679 Twine(FragmentSize) + "'");
681 // See if we are aligning with nops, and if so do that first to try to fill
682 // the Count bytes. Then if that did not fill any bytes or there are any
683 // bytes left to fill use the Value and ValueSize to fill the rest.
684 // If we are aligning with nops, ask that target to emit the right data.
685 if (AF.hasEmitNops()) {
686 if (!Asm.getBackend().writeNopData(Count, OW))
687 report_fatal_error("unable to write nop sequence of " +
688 Twine(Count) + " bytes");
692 // Otherwise, write out in multiples of the value size.
693 for (uint64_t i = 0; i != Count; ++i) {
694 switch (AF.getValueSize()) {
695 default: llvm_unreachable("Invalid size!");
696 case 1: OW->write8 (uint8_t (AF.getValue())); break;
697 case 2: OW->write16(uint16_t(AF.getValue())); break;
698 case 4: OW->write32(uint32_t(AF.getValue())); break;
699 case 8: OW->write64(uint64_t(AF.getValue())); break;
705 case MCFragment::FT_Data:
706 ++stats::EmittedDataFragments;
707 OW->writeBytes(cast<MCDataFragment>(F).getContents());
710 case MCFragment::FT_Relaxable:
711 ++stats::EmittedRelaxableFragments;
712 OW->writeBytes(cast<MCRelaxableFragment>(F).getContents());
715 case MCFragment::FT_CompactEncodedInst:
716 ++stats::EmittedCompactEncodedInstFragments;
717 OW->writeBytes(cast<MCCompactEncodedInstFragment>(F).getContents());
720 case MCFragment::FT_Fill: {
721 ++stats::EmittedFillFragments;
722 const MCFillFragment &FF = cast<MCFillFragment>(F);
724 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
726 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
727 switch (FF.getValueSize()) {
728 default: llvm_unreachable("Invalid size!");
729 case 1: OW->write8 (uint8_t (FF.getValue())); break;
730 case 2: OW->write16(uint16_t(FF.getValue())); break;
731 case 4: OW->write32(uint32_t(FF.getValue())); break;
732 case 8: OW->write64(uint64_t(FF.getValue())); break;
738 case MCFragment::FT_LEB: {
739 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
740 OW->writeBytes(LF.getContents());
744 case MCFragment::FT_SafeSEH: {
745 const MCSafeSEHFragment &SF = cast<MCSafeSEHFragment>(F);
746 OW->write32(SF.getSymbol()->getIndex());
750 case MCFragment::FT_Org: {
751 ++stats::EmittedOrgFragments;
752 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
754 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
755 OW->write8(uint8_t(OF.getValue()));
760 case MCFragment::FT_Dwarf: {
761 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
762 OW->writeBytes(OF.getContents());
765 case MCFragment::FT_DwarfFrame: {
766 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
767 OW->writeBytes(CF.getContents());
772 assert(OW->getStream().tell() - Start == FragmentSize &&
773 "The stream should advance by fragment size");
776 void MCAssembler::writeSectionData(const MCSection *Sec,
777 const MCAsmLayout &Layout) const {
778 // Ignore virtual sections.
779 if (Sec->isVirtualSection()) {
780 assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
782 // Check that contents are only things legal inside a virtual section.
783 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
785 switch (it->getKind()) {
786 default: llvm_unreachable("Invalid fragment in virtual section!");
787 case MCFragment::FT_Data: {
788 // Check that we aren't trying to write a non-zero contents (or fixups)
789 // into a virtual section. This is to support clients which use standard
790 // directives to fill the contents of virtual sections.
791 const MCDataFragment &DF = cast<MCDataFragment>(*it);
792 assert(DF.fixup_begin() == DF.fixup_end() &&
793 "Cannot have fixups in virtual section!");
794 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
795 if (DF.getContents()[i]) {
796 if (auto *ELFSec = dyn_cast<const MCSectionELF>(Sec))
797 report_fatal_error("non-zero initializer found in section '" +
798 ELFSec->getSectionName() + "'");
800 report_fatal_error("non-zero initializer found in virtual section");
804 case MCFragment::FT_Align:
805 // Check that we aren't trying to write a non-zero value into a virtual
807 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
808 cast<MCAlignFragment>(it)->getValue() == 0) &&
809 "Invalid align in virtual section!");
811 case MCFragment::FT_Fill:
812 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
813 cast<MCFillFragment>(it)->getValue() == 0) &&
814 "Invalid fill in virtual section!");
822 uint64_t Start = getWriter().getStream().tell();
825 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
827 writeFragment(*this, Layout, *it);
829 assert(getWriter().getStream().tell() - Start ==
830 Layout.getSectionAddressSize(Sec));
833 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
835 const MCFixup &Fixup) {
836 // Evaluate the fixup.
839 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
840 MCFixupKindInfo::FKF_IsPCRel;
841 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
842 // The fixup was unresolved, we need a relocation. Inform the object
843 // writer of the relocation, and give it an opportunity to adjust the
844 // fixup value if need be.
845 getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
848 return std::make_pair(FixedValue, IsPCRel);
851 void MCAssembler::Finish() {
852 DEBUG_WITH_TYPE("mc-dump", {
853 llvm::errs() << "assembler backend - pre-layout\n--\n";
856 // Create the layout object.
857 MCAsmLayout Layout(*this);
859 // Create dummy fragments and assign section ordinals.
860 unsigned SectionIndex = 0;
861 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
862 // Create dummy fragments to eliminate any empty sections, this simplifies
864 if (it->getFragmentList().empty())
865 new MCDataFragment(&*it);
867 it->setOrdinal(SectionIndex++);
870 // Assign layout order indices to sections and fragments.
871 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
872 MCSection *Sec = Layout.getSectionOrder()[i];
873 Sec->setLayoutOrder(i);
875 unsigned FragmentIndex = 0;
876 for (MCSection::iterator iFrag = Sec->begin(), iFragEnd = Sec->end();
877 iFrag != iFragEnd; ++iFrag)
878 iFrag->setLayoutOrder(FragmentIndex++);
881 // Layout until everything fits.
882 while (layoutOnce(Layout))
885 DEBUG_WITH_TYPE("mc-dump", {
886 llvm::errs() << "assembler backend - post-relaxation\n--\n";
889 // Finalize the layout, including fragment lowering.
890 finishLayout(Layout);
892 DEBUG_WITH_TYPE("mc-dump", {
893 llvm::errs() << "assembler backend - final-layout\n--\n";
896 uint64_t StartOffset = OS.tell();
898 // Allow the object writer a chance to perform post-layout binding (for
899 // example, to set the index fields in the symbol data).
900 getWriter().executePostLayoutBinding(*this, Layout);
902 // Evaluate and apply the fixups, generating relocation entries as necessary.
903 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
904 for (MCSection::iterator it2 = it->begin(), ie2 = it->end(); it2 != ie2;
906 MCEncodedFragment *F = dyn_cast<MCEncodedFragment>(it2);
907 // Data and relaxable fragments both have fixups. So only process
909 // FIXME: Is there a better way to do this? MCEncodedFragmentWithFixups
910 // being templated makes this tricky.
911 if (!F || isa<MCCompactEncodedInstFragment>(F))
913 ArrayRef<MCFixup> Fixups;
914 MutableArrayRef<char> Contents;
915 if (auto *FragWithFixups = dyn_cast<MCDataFragment>(F)) {
916 Fixups = FragWithFixups->getFixups();
917 Contents = FragWithFixups->getContents();
918 } else if (auto *FragWithFixups = dyn_cast<MCRelaxableFragment>(F)) {
919 Fixups = FragWithFixups->getFixups();
920 Contents = FragWithFixups->getContents();
922 llvm_unreachable("Unknow fragment with fixups!");
923 for (const MCFixup &Fixup : Fixups) {
926 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
927 getBackend().applyFixup(Fixup, Contents.data(),
928 Contents.size(), FixedValue, IsPCRel);
933 // Write the object file.
934 getWriter().writeObject(*this, Layout);
936 stats::ObjectBytes += OS.tell() - StartOffset;
939 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
940 const MCRelaxableFragment *DF,
941 const MCAsmLayout &Layout) const {
944 bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value);
945 return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
949 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
950 const MCAsmLayout &Layout) const {
951 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
952 // are intentionally pushing out inst fragments, or because we relaxed a
953 // previous instruction to one that doesn't need relaxation.
954 if (!getBackend().mayNeedRelaxation(F->getInst()))
957 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
958 ie = F->fixup_end(); it != ie; ++it)
959 if (fixupNeedsRelaxation(*it, F, Layout))
965 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
966 MCRelaxableFragment &F) {
967 if (!fragmentNeedsRelaxation(&F, Layout))
970 ++stats::RelaxedInstructions;
972 // FIXME-PERF: We could immediately lower out instructions if we can tell
973 // they are fully resolved, to avoid retesting on later passes.
975 // Relax the fragment.
978 getBackend().relaxInstruction(F.getInst(), Relaxed);
980 // Encode the new instruction.
982 // FIXME-PERF: If it matters, we could let the target do this. It can
983 // probably do so more efficiently in many cases.
984 SmallVector<MCFixup, 4> Fixups;
985 SmallString<256> Code;
986 raw_svector_ostream VecOS(Code);
987 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
990 // Update the fragment.
992 F.getContents() = Code;
993 F.getFixups() = Fixups;
998 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
999 uint64_t OldSize = LF.getContents().size();
1001 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1003 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
1004 SmallString<8> &Data = LF.getContents();
1006 raw_svector_ostream OSE(Data);
1008 encodeSLEB128(Value, OSE);
1010 encodeULEB128(Value, OSE);
1012 return OldSize != LF.getContents().size();
1015 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1016 MCDwarfLineAddrFragment &DF) {
1017 MCContext &Context = Layout.getAssembler().getContext();
1018 uint64_t OldSize = DF.getContents().size();
1020 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1021 assert(Abs && "We created a line delta with an invalid expression");
1024 LineDelta = DF.getLineDelta();
1025 SmallString<8> &Data = DF.getContents();
1027 raw_svector_ostream OSE(Data);
1028 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1030 return OldSize != Data.size();
1033 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1034 MCDwarfCallFrameFragment &DF) {
1035 MCContext &Context = Layout.getAssembler().getContext();
1036 uint64_t OldSize = DF.getContents().size();
1038 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1039 assert(Abs && "We created call frame with an invalid expression");
1041 SmallString<8> &Data = DF.getContents();
1043 raw_svector_ostream OSE(Data);
1044 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1046 return OldSize != Data.size();
1049 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1050 // Holds the first fragment which needed relaxing during this layout. It will
1051 // remain NULL if none were relaxed.
1052 // When a fragment is relaxed, all the fragments following it should get
1053 // invalidated because their offset is going to change.
1054 MCFragment *FirstRelaxedFragment = nullptr;
1056 // Attempt to relax all the fragments in the section.
1057 for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
1058 // Check if this is a fragment that needs relaxation.
1059 bool RelaxedFrag = false;
1060 switch(I->getKind()) {
1063 case MCFragment::FT_Relaxable:
1064 assert(!getRelaxAll() &&
1065 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1066 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1068 case MCFragment::FT_Dwarf:
1069 RelaxedFrag = relaxDwarfLineAddr(Layout,
1070 *cast<MCDwarfLineAddrFragment>(I));
1072 case MCFragment::FT_DwarfFrame:
1074 relaxDwarfCallFrameFragment(Layout,
1075 *cast<MCDwarfCallFrameFragment>(I));
1077 case MCFragment::FT_LEB:
1078 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1081 if (RelaxedFrag && !FirstRelaxedFragment)
1082 FirstRelaxedFragment = I;
1084 if (FirstRelaxedFragment) {
1085 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1091 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1092 ++stats::RelaxationSteps;
1094 bool WasRelaxed = false;
1095 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1096 MCSection &Sec = *it;
1097 while (layoutSectionOnce(Layout, Sec))
1104 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1105 // The layout is done. Mark every fragment as valid.
1106 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1107 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1111 // Debugging methods
1115 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1116 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1117 << " Value:" << *AF.getValue()
1118 << " Kind:" << AF.getKind() << ">";
1124 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1125 void MCFragment::dump() {
1126 raw_ostream &OS = llvm::errs();
1129 switch (getKind()) {
1130 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1131 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1132 case MCFragment::FT_CompactEncodedInst:
1133 OS << "MCCompactEncodedInstFragment"; break;
1134 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1135 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1136 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1137 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1138 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1139 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1140 case MCFragment::FT_SafeSEH: OS << "MCSafeSEHFragment"; break;
1143 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1144 << " Offset:" << Offset
1145 << " HasInstructions:" << hasInstructions()
1146 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1148 switch (getKind()) {
1149 case MCFragment::FT_Align: {
1150 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1151 if (AF->hasEmitNops())
1152 OS << " (emit nops)";
1154 OS << " Alignment:" << AF->getAlignment()
1155 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1156 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1159 case MCFragment::FT_Data: {
1160 const MCDataFragment *DF = cast<MCDataFragment>(this);
1162 OS << " Contents:[";
1163 const SmallVectorImpl<char> &Contents = DF->getContents();
1164 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1166 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1168 OS << "] (" << Contents.size() << " bytes)";
1170 if (DF->fixup_begin() != DF->fixup_end()) {
1173 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1174 ie = DF->fixup_end(); it != ie; ++it) {
1175 if (it != DF->fixup_begin()) OS << ",\n ";
1182 case MCFragment::FT_CompactEncodedInst: {
1183 const MCCompactEncodedInstFragment *CEIF =
1184 cast<MCCompactEncodedInstFragment>(this);
1186 OS << " Contents:[";
1187 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1188 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1190 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1192 OS << "] (" << Contents.size() << " bytes)";
1195 case MCFragment::FT_Fill: {
1196 const MCFillFragment *FF = cast<MCFillFragment>(this);
1197 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1198 << " Size:" << FF->getSize();
1201 case MCFragment::FT_Relaxable: {
1202 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1205 F->getInst().dump_pretty(OS);
1208 case MCFragment::FT_Org: {
1209 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1211 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1214 case MCFragment::FT_Dwarf: {
1215 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1217 OS << " AddrDelta:" << OF->getAddrDelta()
1218 << " LineDelta:" << OF->getLineDelta();
1221 case MCFragment::FT_DwarfFrame: {
1222 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1224 OS << " AddrDelta:" << CF->getAddrDelta();
1227 case MCFragment::FT_LEB: {
1228 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1230 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1233 case MCFragment::FT_SafeSEH: {
1234 const MCSafeSEHFragment *F = cast<MCSafeSEHFragment>(this);
1236 OS << " Sym:" << F->getSymbol();
1243 void MCAssembler::dump() {
1244 raw_ostream &OS = llvm::errs();
1246 OS << "<MCAssembler\n";
1247 OS << " Sections:[\n ";
1248 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1249 if (it != begin()) OS << ",\n ";
1255 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1256 if (it != symbol_begin()) OS << ",\n ";
1259 OS << ", Index:" << it->getIndex() << ", ";