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 (OffsetInBundle > 0 && 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 // padding directly into fragments when the instructions are emitted inside
585 // the streamer. When the fragment is larger than the bundle size, we need to
586 // ensure that it's bundle aligned. This means that if we end up with
587 // multiple fragments, we must emit bundle padding between fragments.
589 // ".align N" is an example of a directive that introduces multiple
590 // fragments. We could add a special case to handle ".align N" by emitting
591 // within-fragment padding (which would produce less padding when N is less
592 // than the bundle size), but for now we don't.
594 if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
595 assert(isa<MCEncodedFragment>(F) &&
596 "Only MCEncodedFragment implementations have instructions");
597 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
599 if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
600 report_fatal_error("Fragment can't be larger than a bundle size");
602 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
604 if (RequiredBundlePadding > UINT8_MAX)
605 report_fatal_error("Padding cannot exceed 255 bytes");
606 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
607 F->Offset += RequiredBundlePadding;
611 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
612 bool New = !Symbol.isRegistered();
616 Symbol.setIsRegistered(true);
617 Symbols.push_back(&Symbol);
621 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
622 MCObjectWriter *OW) const {
623 // Should NOP padding be written out before this fragment?
624 unsigned BundlePadding = F.getBundlePadding();
625 if (BundlePadding > 0) {
626 assert(isBundlingEnabled() &&
627 "Writing bundle padding with disabled bundling");
628 assert(F.hasInstructions() &&
629 "Writing bundle padding for a fragment without instructions");
631 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
632 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
633 // If the padding itself crosses a bundle boundary, it must be emitted
634 // in 2 pieces, since even nop instructions must not cross boundaries.
635 // v--------------v <- BundleAlignSize
636 // v---------v <- BundlePadding
637 // ----------------------------
638 // | Prev |####|####| F |
639 // ----------------------------
640 // ^-------------------^ <- TotalLength
641 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
642 if (!getBackend().writeNopData(DistanceToBoundary, OW))
643 report_fatal_error("unable to write NOP sequence of " +
644 Twine(DistanceToBoundary) + " bytes");
645 BundlePadding -= DistanceToBoundary;
647 if (!getBackend().writeNopData(BundlePadding, OW))
648 report_fatal_error("unable to write NOP sequence of " +
649 Twine(BundlePadding) + " bytes");
653 /// \brief Write the fragment \p F to the output file.
654 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
655 const MCFragment &F) {
656 MCObjectWriter *OW = &Asm.getWriter();
658 // FIXME: Embed in fragments instead?
659 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
661 Asm.writeFragmentPadding(F, FragmentSize, OW);
663 // This variable (and its dummy usage) is to participate in the assert at
664 // the end of the function.
665 uint64_t Start = OW->getStream().tell();
668 ++stats::EmittedFragments;
670 switch (F.getKind()) {
671 case MCFragment::FT_Align: {
672 ++stats::EmittedAlignFragments;
673 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
674 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
676 uint64_t Count = FragmentSize / AF.getValueSize();
678 // FIXME: This error shouldn't actually occur (the front end should emit
679 // multiple .align directives to enforce the semantics it wants), but is
680 // severe enough that we want to report it. How to handle this?
681 if (Count * AF.getValueSize() != FragmentSize)
682 report_fatal_error("undefined .align directive, value size '" +
683 Twine(AF.getValueSize()) +
684 "' is not a divisor of padding size '" +
685 Twine(FragmentSize) + "'");
687 // See if we are aligning with nops, and if so do that first to try to fill
688 // the Count bytes. Then if that did not fill any bytes or there are any
689 // bytes left to fill use the Value and ValueSize to fill the rest.
690 // If we are aligning with nops, ask that target to emit the right data.
691 if (AF.hasEmitNops()) {
692 if (!Asm.getBackend().writeNopData(Count, OW))
693 report_fatal_error("unable to write nop sequence of " +
694 Twine(Count) + " bytes");
698 // Otherwise, write out in multiples of the value size.
699 for (uint64_t i = 0; i != Count; ++i) {
700 switch (AF.getValueSize()) {
701 default: llvm_unreachable("Invalid size!");
702 case 1: OW->write8 (uint8_t (AF.getValue())); break;
703 case 2: OW->write16(uint16_t(AF.getValue())); break;
704 case 4: OW->write32(uint32_t(AF.getValue())); break;
705 case 8: OW->write64(uint64_t(AF.getValue())); break;
711 case MCFragment::FT_Data:
712 ++stats::EmittedDataFragments;
713 OW->writeBytes(cast<MCDataFragment>(F).getContents());
716 case MCFragment::FT_Relaxable:
717 ++stats::EmittedRelaxableFragments;
718 OW->writeBytes(cast<MCRelaxableFragment>(F).getContents());
721 case MCFragment::FT_CompactEncodedInst:
722 ++stats::EmittedCompactEncodedInstFragments;
723 OW->writeBytes(cast<MCCompactEncodedInstFragment>(F).getContents());
726 case MCFragment::FT_Fill: {
727 ++stats::EmittedFillFragments;
728 const MCFillFragment &FF = cast<MCFillFragment>(F);
730 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
732 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
733 switch (FF.getValueSize()) {
734 default: llvm_unreachable("Invalid size!");
735 case 1: OW->write8 (uint8_t (FF.getValue())); break;
736 case 2: OW->write16(uint16_t(FF.getValue())); break;
737 case 4: OW->write32(uint32_t(FF.getValue())); break;
738 case 8: OW->write64(uint64_t(FF.getValue())); break;
744 case MCFragment::FT_LEB: {
745 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
746 OW->writeBytes(LF.getContents());
750 case MCFragment::FT_SafeSEH: {
751 const MCSafeSEHFragment &SF = cast<MCSafeSEHFragment>(F);
752 OW->write32(SF.getSymbol()->getIndex());
756 case MCFragment::FT_Org: {
757 ++stats::EmittedOrgFragments;
758 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
760 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
761 OW->write8(uint8_t(OF.getValue()));
766 case MCFragment::FT_Dwarf: {
767 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
768 OW->writeBytes(OF.getContents());
771 case MCFragment::FT_DwarfFrame: {
772 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
773 OW->writeBytes(CF.getContents());
778 assert(OW->getStream().tell() - Start == FragmentSize &&
779 "The stream should advance by fragment size");
782 void MCAssembler::writeSectionData(const MCSection *Sec,
783 const MCAsmLayout &Layout) const {
784 // Ignore virtual sections.
785 if (Sec->isVirtualSection()) {
786 assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
788 // Check that contents are only things legal inside a virtual section.
789 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
791 switch (it->getKind()) {
792 default: llvm_unreachable("Invalid fragment in virtual section!");
793 case MCFragment::FT_Data: {
794 // Check that we aren't trying to write a non-zero contents (or fixups)
795 // into a virtual section. This is to support clients which use standard
796 // directives to fill the contents of virtual sections.
797 const MCDataFragment &DF = cast<MCDataFragment>(*it);
798 assert(DF.fixup_begin() == DF.fixup_end() &&
799 "Cannot have fixups in virtual section!");
800 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
801 if (DF.getContents()[i]) {
802 if (auto *ELFSec = dyn_cast<const MCSectionELF>(Sec))
803 report_fatal_error("non-zero initializer found in section '" +
804 ELFSec->getSectionName() + "'");
806 report_fatal_error("non-zero initializer found in virtual section");
810 case MCFragment::FT_Align:
811 // Check that we aren't trying to write a non-zero value into a virtual
813 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
814 cast<MCAlignFragment>(it)->getValue() == 0) &&
815 "Invalid align in virtual section!");
817 case MCFragment::FT_Fill:
818 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
819 cast<MCFillFragment>(it)->getValue() == 0) &&
820 "Invalid fill in virtual section!");
828 uint64_t Start = getWriter().getStream().tell();
831 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
833 writeFragment(*this, Layout, *it);
835 assert(getWriter().getStream().tell() - Start ==
836 Layout.getSectionAddressSize(Sec));
839 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
841 const MCFixup &Fixup) {
842 // Evaluate the fixup.
845 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
846 MCFixupKindInfo::FKF_IsPCRel;
847 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
848 // The fixup was unresolved, we need a relocation. Inform the object
849 // writer of the relocation, and give it an opportunity to adjust the
850 // fixup value if need be.
851 getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
854 return std::make_pair(FixedValue, IsPCRel);
857 void MCAssembler::Finish() {
858 DEBUG_WITH_TYPE("mc-dump", {
859 llvm::errs() << "assembler backend - pre-layout\n--\n";
862 // Create the layout object.
863 MCAsmLayout Layout(*this);
865 // Create dummy fragments and assign section ordinals.
866 unsigned SectionIndex = 0;
867 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
868 // Create dummy fragments to eliminate any empty sections, this simplifies
870 if (it->getFragmentList().empty())
871 new MCDataFragment(&*it);
873 it->setOrdinal(SectionIndex++);
876 // Assign layout order indices to sections and fragments.
877 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
878 MCSection *Sec = Layout.getSectionOrder()[i];
879 Sec->setLayoutOrder(i);
881 unsigned FragmentIndex = 0;
882 for (MCSection::iterator iFrag = Sec->begin(), iFragEnd = Sec->end();
883 iFrag != iFragEnd; ++iFrag)
884 iFrag->setLayoutOrder(FragmentIndex++);
887 // Layout until everything fits.
888 while (layoutOnce(Layout))
891 DEBUG_WITH_TYPE("mc-dump", {
892 llvm::errs() << "assembler backend - post-relaxation\n--\n";
895 // Finalize the layout, including fragment lowering.
896 finishLayout(Layout);
898 DEBUG_WITH_TYPE("mc-dump", {
899 llvm::errs() << "assembler backend - final-layout\n--\n";
902 uint64_t StartOffset = OS.tell();
904 // Allow the object writer a chance to perform post-layout binding (for
905 // example, to set the index fields in the symbol data).
906 getWriter().executePostLayoutBinding(*this, Layout);
908 // Evaluate and apply the fixups, generating relocation entries as necessary.
909 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
910 for (MCSection::iterator it2 = it->begin(), ie2 = it->end(); it2 != ie2;
912 MCEncodedFragment *F = dyn_cast<MCEncodedFragment>(it2);
913 // Data and relaxable fragments both have fixups. So only process
915 // FIXME: Is there a better way to do this? MCEncodedFragmentWithFixups
916 // being templated makes this tricky.
917 if (!F || isa<MCCompactEncodedInstFragment>(F))
919 ArrayRef<MCFixup> Fixups;
920 MutableArrayRef<char> Contents;
921 if (auto *FragWithFixups = dyn_cast<MCDataFragment>(F)) {
922 Fixups = FragWithFixups->getFixups();
923 Contents = FragWithFixups->getContents();
924 } else if (auto *FragWithFixups = dyn_cast<MCRelaxableFragment>(F)) {
925 Fixups = FragWithFixups->getFixups();
926 Contents = FragWithFixups->getContents();
928 llvm_unreachable("Unknown fragment with fixups!");
929 for (const MCFixup &Fixup : Fixups) {
932 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
933 getBackend().applyFixup(Fixup, Contents.data(),
934 Contents.size(), FixedValue, IsPCRel);
939 // Write the object file.
940 getWriter().writeObject(*this, Layout);
942 stats::ObjectBytes += OS.tell() - StartOffset;
945 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
946 const MCRelaxableFragment *DF,
947 const MCAsmLayout &Layout) const {
950 bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value);
951 return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
955 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
956 const MCAsmLayout &Layout) const {
957 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
958 // are intentionally pushing out inst fragments, or because we relaxed a
959 // previous instruction to one that doesn't need relaxation.
960 if (!getBackend().mayNeedRelaxation(F->getInst()))
963 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
964 ie = F->fixup_end(); it != ie; ++it)
965 if (fixupNeedsRelaxation(*it, F, Layout))
971 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
972 MCRelaxableFragment &F) {
973 if (!fragmentNeedsRelaxation(&F, Layout))
976 ++stats::RelaxedInstructions;
978 // FIXME-PERF: We could immediately lower out instructions if we can tell
979 // they are fully resolved, to avoid retesting on later passes.
981 // Relax the fragment.
984 getBackend().relaxInstruction(F.getInst(), Relaxed);
986 // Encode the new instruction.
988 // FIXME-PERF: If it matters, we could let the target do this. It can
989 // probably do so more efficiently in many cases.
990 SmallVector<MCFixup, 4> Fixups;
991 SmallString<256> Code;
992 raw_svector_ostream VecOS(Code);
993 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
996 // Update the fragment.
998 F.getContents() = Code;
999 F.getFixups() = Fixups;
1004 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1005 uint64_t OldSize = LF.getContents().size();
1007 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1009 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
1010 SmallString<8> &Data = LF.getContents();
1012 raw_svector_ostream OSE(Data);
1014 encodeSLEB128(Value, OSE);
1016 encodeULEB128(Value, OSE);
1018 return OldSize != LF.getContents().size();
1021 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1022 MCDwarfLineAddrFragment &DF) {
1023 MCContext &Context = Layout.getAssembler().getContext();
1024 uint64_t OldSize = DF.getContents().size();
1026 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1027 assert(Abs && "We created a line delta with an invalid expression");
1030 LineDelta = DF.getLineDelta();
1031 SmallString<8> &Data = DF.getContents();
1033 raw_svector_ostream OSE(Data);
1034 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1036 return OldSize != Data.size();
1039 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1040 MCDwarfCallFrameFragment &DF) {
1041 MCContext &Context = Layout.getAssembler().getContext();
1042 uint64_t OldSize = DF.getContents().size();
1044 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1045 assert(Abs && "We created call frame with an invalid expression");
1047 SmallString<8> &Data = DF.getContents();
1049 raw_svector_ostream OSE(Data);
1050 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1052 return OldSize != Data.size();
1055 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1056 // Holds the first fragment which needed relaxing during this layout. It will
1057 // remain NULL if none were relaxed.
1058 // When a fragment is relaxed, all the fragments following it should get
1059 // invalidated because their offset is going to change.
1060 MCFragment *FirstRelaxedFragment = nullptr;
1062 // Attempt to relax all the fragments in the section.
1063 for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
1064 // Check if this is a fragment that needs relaxation.
1065 bool RelaxedFrag = false;
1066 switch(I->getKind()) {
1069 case MCFragment::FT_Relaxable:
1070 assert(!getRelaxAll() &&
1071 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1072 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1074 case MCFragment::FT_Dwarf:
1075 RelaxedFrag = relaxDwarfLineAddr(Layout,
1076 *cast<MCDwarfLineAddrFragment>(I));
1078 case MCFragment::FT_DwarfFrame:
1080 relaxDwarfCallFrameFragment(Layout,
1081 *cast<MCDwarfCallFrameFragment>(I));
1083 case MCFragment::FT_LEB:
1084 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1087 if (RelaxedFrag && !FirstRelaxedFragment)
1088 FirstRelaxedFragment = I;
1090 if (FirstRelaxedFragment) {
1091 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1097 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1098 ++stats::RelaxationSteps;
1100 bool WasRelaxed = false;
1101 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1102 MCSection &Sec = *it;
1103 while (layoutSectionOnce(Layout, Sec))
1110 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1111 // The layout is done. Mark every fragment as valid.
1112 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1113 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1117 // Debugging methods
1121 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1122 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1123 << " Value:" << *AF.getValue()
1124 << " Kind:" << AF.getKind() << ">";
1130 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1131 void MCFragment::dump() {
1132 raw_ostream &OS = llvm::errs();
1135 switch (getKind()) {
1136 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1137 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1138 case MCFragment::FT_CompactEncodedInst:
1139 OS << "MCCompactEncodedInstFragment"; break;
1140 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1141 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1142 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1143 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1144 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1145 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1146 case MCFragment::FT_SafeSEH: OS << "MCSafeSEHFragment"; break;
1149 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1150 << " Offset:" << Offset
1151 << " HasInstructions:" << hasInstructions()
1152 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1154 switch (getKind()) {
1155 case MCFragment::FT_Align: {
1156 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1157 if (AF->hasEmitNops())
1158 OS << " (emit nops)";
1160 OS << " Alignment:" << AF->getAlignment()
1161 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1162 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1165 case MCFragment::FT_Data: {
1166 const MCDataFragment *DF = cast<MCDataFragment>(this);
1168 OS << " Contents:[";
1169 const SmallVectorImpl<char> &Contents = DF->getContents();
1170 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1172 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1174 OS << "] (" << Contents.size() << " bytes)";
1176 if (DF->fixup_begin() != DF->fixup_end()) {
1179 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1180 ie = DF->fixup_end(); it != ie; ++it) {
1181 if (it != DF->fixup_begin()) OS << ",\n ";
1188 case MCFragment::FT_CompactEncodedInst: {
1189 const MCCompactEncodedInstFragment *CEIF =
1190 cast<MCCompactEncodedInstFragment>(this);
1192 OS << " Contents:[";
1193 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1194 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1196 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1198 OS << "] (" << Contents.size() << " bytes)";
1201 case MCFragment::FT_Fill: {
1202 const MCFillFragment *FF = cast<MCFillFragment>(this);
1203 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1204 << " Size:" << FF->getSize();
1207 case MCFragment::FT_Relaxable: {
1208 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1211 F->getInst().dump_pretty(OS);
1214 case MCFragment::FT_Org: {
1215 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1217 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1220 case MCFragment::FT_Dwarf: {
1221 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1223 OS << " AddrDelta:" << OF->getAddrDelta()
1224 << " LineDelta:" << OF->getLineDelta();
1227 case MCFragment::FT_DwarfFrame: {
1228 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1230 OS << " AddrDelta:" << CF->getAddrDelta();
1233 case MCFragment::FT_LEB: {
1234 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1236 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1239 case MCFragment::FT_SafeSEH: {
1240 const MCSafeSEHFragment *F = cast<MCSafeSEHFragment>(this);
1242 OS << " Sym:" << F->getSymbol();
1249 void MCAssembler::dump() {
1250 raw_ostream &OS = llvm::errs();
1252 OS << "<MCAssembler\n";
1253 OS << " Sections:[\n ";
1254 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1255 if (it != begin()) OS << ",\n ";
1261 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1262 if (it != symbol_begin()) OS << ",\n ";
1265 OS << ", Index:" << it->getIndex() << ", ";