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/ArrayRef.h"
12 #include "llvm/ADT/SmallString.h"
13 #include "llvm/ADT/SmallVector.h"
14 #include "llvm/ADT/Statistic.h"
15 #include "llvm/ADT/StringRef.h"
16 #include "llvm/ADT/Twine.h"
17 #include "llvm/MC/MCAsmBackend.h"
18 #include "llvm/MC/MCAsmInfo.h"
19 #include "llvm/MC/MCAsmLayout.h"
20 #include "llvm/MC/MCCodeEmitter.h"
21 #include "llvm/MC/MCCodeView.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCDwarf.h"
24 #include "llvm/MC/MCExpr.h"
25 #include "llvm/MC/MCFixup.h"
26 #include "llvm/MC/MCFixupKindInfo.h"
27 #include "llvm/MC/MCFragment.h"
28 #include "llvm/MC/MCInst.h"
29 #include "llvm/MC/MCObjectWriter.h"
30 #include "llvm/MC/MCSection.h"
31 #include "llvm/MC/MCSectionELF.h"
32 #include "llvm/MC/MCSymbol.h"
33 #include "llvm/MC/MCValue.h"
34 #include "llvm/Support/Casting.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/LEB128.h"
38 #include "llvm/Support/MathExtras.h"
39 #include "llvm/Support/raw_ostream.h"
48 #define DEBUG_TYPE "assembler"
53 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
54 STATISTIC(EmittedRelaxableFragments,
55 "Number of emitted assembler fragments - relaxable");
56 STATISTIC(EmittedDataFragments,
57 "Number of emitted assembler fragments - data");
58 STATISTIC(EmittedCompactEncodedInstFragments,
59 "Number of emitted assembler fragments - compact encoded inst");
60 STATISTIC(EmittedAlignFragments,
61 "Number of emitted assembler fragments - align");
62 STATISTIC(EmittedFillFragments,
63 "Number of emitted assembler fragments - fill");
64 STATISTIC(EmittedOrgFragments,
65 "Number of emitted assembler fragments - org");
66 STATISTIC(evaluateFixup, "Number of evaluated fixups");
67 STATISTIC(FragmentLayouts, "Number of fragment layouts");
68 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
69 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
70 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
71 STATISTIC(PaddingFragmentsRelaxations,
72 "Number of Padding Fragments relaxations");
73 STATISTIC(PaddingFragmentsBytes,
74 "Total size of all padding from adding Fragments");
76 } // end namespace stats
77 } // end anonymous namespace
79 // FIXME FIXME FIXME: There are number of places in this file where we convert
80 // what is a 64-bit assembler value used for computation into a value in the
81 // object file, which may truncate it. We should detect that truncation where
82 // invalid and report errors back.
86 MCAssembler::MCAssembler(MCContext &Context, MCAsmBackend &Backend,
87 MCCodeEmitter &Emitter, MCObjectWriter &Writer)
88 : Context(Context), Backend(Backend), Emitter(Emitter), Writer(Writer),
89 BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
90 IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
91 VersionInfo.Major = 0; // Major version == 0 for "none specified"
94 MCAssembler::~MCAssembler() = default;
96 void MCAssembler::reset() {
99 IndirectSymbols.clear();
101 LinkerOptions.clear();
106 SubsectionsViaSymbols = false;
107 IncrementalLinkerCompatible = false;
109 LOHContainer.reset();
110 VersionInfo.Major = 0;
112 // reset objects owned by us
113 getBackend().reset();
114 getEmitter().reset();
116 getLOHContainer().reset();
119 bool MCAssembler::registerSection(MCSection &Section) {
120 if (Section.isRegistered())
122 Sections.push_back(&Section);
123 Section.setIsRegistered(true);
127 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
128 if (ThumbFuncs.count(Symbol))
131 if (!Symbol->isVariable())
134 const MCExpr *Expr = Symbol->getVariableValue();
137 if (!Expr->evaluateAsRelocatable(V, nullptr, nullptr))
140 if (V.getSymB() || V.getRefKind() != MCSymbolRefExpr::VK_None)
143 const MCSymbolRefExpr *Ref = V.getSymA();
147 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
150 const MCSymbol &Sym = Ref->getSymbol();
151 if (!isThumbFunc(&Sym))
154 ThumbFuncs.insert(Symbol); // Cache it.
158 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
159 // Non-temporary labels should always be visible to the linker.
160 if (!Symbol.isTemporary())
163 // Absolute temporary labels are never visible.
164 if (!Symbol.isInSection())
167 if (Symbol.isUsedInReloc())
173 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
174 // Linker visible symbols define atoms.
175 if (isSymbolLinkerVisible(S))
178 // Absolute and undefined symbols have no defining atom.
179 if (!S.isInSection())
182 // Non-linker visible symbols in sections which can't be atomized have no
184 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
185 *S.getFragment()->getParent()))
188 // Otherwise, return the atom for the containing fragment.
189 return S.getFragment()->getAtom();
192 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
193 const MCFixup &Fixup, const MCFragment *DF,
194 MCValue &Target, uint64_t &Value) const {
195 ++stats::evaluateFixup;
197 // FIXME: This code has some duplication with recordRelocation. We should
198 // probably merge the two into a single callback that tries to evaluate a
199 // fixup and records a relocation if one is needed.
201 // On error claim to have completely evaluated the fixup, to prevent any
202 // further processing from being done.
203 const MCExpr *Expr = Fixup.getValue();
204 MCContext &Ctx = getContext();
206 if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup)) {
207 Ctx.reportError(Fixup.getLoc(), "expected relocatable expression");
210 if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
211 if (RefB->getKind() != MCSymbolRefExpr::VK_None) {
212 Ctx.reportError(Fixup.getLoc(),
213 "unsupported subtraction of qualified symbol");
218 bool IsPCRel = Backend.getFixupKindInfo(
219 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
223 if (Target.getSymB()) {
225 } else if (!Target.getSymA()) {
228 const MCSymbolRefExpr *A = Target.getSymA();
229 const MCSymbol &SA = A->getSymbol();
230 if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
233 IsResolved = getWriter().isSymbolRefDifferenceFullyResolvedImpl(
234 *this, SA, *DF, false, true);
238 IsResolved = Target.isAbsolute();
241 Value = Target.getConstant();
243 if (const MCSymbolRefExpr *A = Target.getSymA()) {
244 const MCSymbol &Sym = A->getSymbol();
246 Value += Layout.getSymbolOffset(Sym);
248 if (const MCSymbolRefExpr *B = Target.getSymB()) {
249 const MCSymbol &Sym = B->getSymbol();
251 Value -= Layout.getSymbolOffset(Sym);
254 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
255 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
256 assert((ShouldAlignPC ? IsPCRel : true) &&
257 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
260 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
262 // A number of ARM fixups in Thumb mode require that the effective PC
263 // address be determined as the 32-bit aligned version of the actual offset.
264 if (ShouldAlignPC) Offset &= ~0x3;
268 // Let the backend force a relocation if needed.
269 if (IsResolved && Backend.shouldForceRelocation(*this, Fixup, Target))
275 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
276 const MCFragment &F) const {
277 switch (F.getKind()) {
278 case MCFragment::FT_Data:
279 return cast<MCDataFragment>(F).getContents().size();
280 case MCFragment::FT_Relaxable:
281 return cast<MCRelaxableFragment>(F).getContents().size();
282 case MCFragment::FT_CompactEncodedInst:
283 return cast<MCCompactEncodedInstFragment>(F).getContents().size();
284 case MCFragment::FT_Fill:
285 return cast<MCFillFragment>(F).getSize();
287 case MCFragment::FT_LEB:
288 return cast<MCLEBFragment>(F).getContents().size();
290 case MCFragment::FT_Padding:
291 return cast<MCPaddingFragment>(F).getSize();
293 case MCFragment::FT_SymbolId:
296 case MCFragment::FT_Align: {
297 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
298 unsigned Offset = Layout.getFragmentOffset(&AF);
299 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
300 // If we are padding with nops, force the padding to be larger than the
302 if (Size > 0 && AF.hasEmitNops()) {
303 while (Size % getBackend().getMinimumNopSize())
304 Size += AF.getAlignment();
306 if (Size > AF.getMaxBytesToEmit())
311 case MCFragment::FT_Org: {
312 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
314 if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
315 getContext().reportError(OF.getLoc(),
316 "expected assembly-time absolute expression");
320 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
321 int64_t TargetLocation = Value.getConstant();
322 if (const MCSymbolRefExpr *A = Value.getSymA()) {
324 if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
325 getContext().reportError(OF.getLoc(), "expected absolute expression");
328 TargetLocation += Val;
330 int64_t Size = TargetLocation - FragmentOffset;
331 if (Size < 0 || Size >= 0x40000000) {
332 getContext().reportError(
333 OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
334 "' (at offset '" + Twine(FragmentOffset) + "')");
340 case MCFragment::FT_Dwarf:
341 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
342 case MCFragment::FT_DwarfFrame:
343 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
344 case MCFragment::FT_CVInlineLines:
345 return cast<MCCVInlineLineTableFragment>(F).getContents().size();
346 case MCFragment::FT_CVDefRange:
347 return cast<MCCVDefRangeFragment>(F).getContents().size();
348 case MCFragment::FT_Dummy:
349 llvm_unreachable("Should not have been added");
352 llvm_unreachable("invalid fragment kind");
355 void MCAsmLayout::layoutFragment(MCFragment *F) {
356 MCFragment *Prev = F->getPrevNode();
358 // We should never try to recompute something which is valid.
359 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
360 // We should never try to compute the fragment layout if its predecessor
362 assert((!Prev || isFragmentValid(Prev)) &&
363 "Attempt to compute fragment before its predecessor!");
365 ++stats::FragmentLayouts;
367 // Compute fragment offset and size.
369 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
372 LastValidFragment[F->getParent()] = F;
374 // If bundling is enabled and this fragment has instructions in it, it has to
375 // obey the bundling restrictions. With padding, we'll have:
380 // -------------------------------------
381 // Prev |##########| F |
382 // -------------------------------------
387 // The fragment's offset will point to after the padding, and its computed
388 // size won't include the padding.
390 // When the -mc-relax-all flag is used, we optimize bundling by writting the
391 // padding directly into fragments when the instructions are emitted inside
392 // the streamer. When the fragment is larger than the bundle size, we need to
393 // ensure that it's bundle aligned. This means that if we end up with
394 // multiple fragments, we must emit bundle padding between fragments.
396 // ".align N" is an example of a directive that introduces multiple
397 // fragments. We could add a special case to handle ".align N" by emitting
398 // within-fragment padding (which would produce less padding when N is less
399 // than the bundle size), but for now we don't.
401 if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
402 assert(isa<MCEncodedFragment>(F) &&
403 "Only MCEncodedFragment implementations have instructions");
404 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
406 if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
407 report_fatal_error("Fragment can't be larger than a bundle size");
409 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
411 if (RequiredBundlePadding > UINT8_MAX)
412 report_fatal_error("Padding cannot exceed 255 bytes");
413 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
414 F->Offset += RequiredBundlePadding;
418 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
419 bool New = !Symbol.isRegistered();
423 Symbol.setIsRegistered(true);
424 Symbols.push_back(&Symbol);
428 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
429 MCObjectWriter *OW) const {
430 // Should NOP padding be written out before this fragment?
431 unsigned BundlePadding = F.getBundlePadding();
432 if (BundlePadding > 0) {
433 assert(isBundlingEnabled() &&
434 "Writing bundle padding with disabled bundling");
435 assert(F.hasInstructions() &&
436 "Writing bundle padding for a fragment without instructions");
438 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
439 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
440 // If the padding itself crosses a bundle boundary, it must be emitted
441 // in 2 pieces, since even nop instructions must not cross boundaries.
442 // v--------------v <- BundleAlignSize
443 // v---------v <- BundlePadding
444 // ----------------------------
445 // | Prev |####|####| F |
446 // ----------------------------
447 // ^-------------------^ <- TotalLength
448 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
449 if (!getBackend().writeNopData(DistanceToBoundary, OW))
450 report_fatal_error("unable to write NOP sequence of " +
451 Twine(DistanceToBoundary) + " bytes");
452 BundlePadding -= DistanceToBoundary;
454 if (!getBackend().writeNopData(BundlePadding, OW))
455 report_fatal_error("unable to write NOP sequence of " +
456 Twine(BundlePadding) + " bytes");
460 /// \brief Write the fragment \p F to the output file.
461 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
462 const MCFragment &F) {
463 MCObjectWriter *OW = &Asm.getWriter();
465 // FIXME: Embed in fragments instead?
466 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
468 Asm.writeFragmentPadding(F, FragmentSize, OW);
470 // This variable (and its dummy usage) is to participate in the assert at
471 // the end of the function.
472 uint64_t Start = OW->getStream().tell();
475 ++stats::EmittedFragments;
477 switch (F.getKind()) {
478 case MCFragment::FT_Align: {
479 ++stats::EmittedAlignFragments;
480 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
481 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
483 uint64_t Count = FragmentSize / AF.getValueSize();
485 // FIXME: This error shouldn't actually occur (the front end should emit
486 // multiple .align directives to enforce the semantics it wants), but is
487 // severe enough that we want to report it. How to handle this?
488 if (Count * AF.getValueSize() != FragmentSize)
489 report_fatal_error("undefined .align directive, value size '" +
490 Twine(AF.getValueSize()) +
491 "' is not a divisor of padding size '" +
492 Twine(FragmentSize) + "'");
494 // See if we are aligning with nops, and if so do that first to try to fill
495 // the Count bytes. Then if that did not fill any bytes or there are any
496 // bytes left to fill use the Value and ValueSize to fill the rest.
497 // If we are aligning with nops, ask that target to emit the right data.
498 if (AF.hasEmitNops()) {
499 if (!Asm.getBackend().writeNopData(Count, OW))
500 report_fatal_error("unable to write nop sequence of " +
501 Twine(Count) + " bytes");
505 // Otherwise, write out in multiples of the value size.
506 for (uint64_t i = 0; i != Count; ++i) {
507 switch (AF.getValueSize()) {
508 default: llvm_unreachable("Invalid size!");
509 case 1: OW->write8 (uint8_t (AF.getValue())); break;
510 case 2: OW->write16(uint16_t(AF.getValue())); break;
511 case 4: OW->write32(uint32_t(AF.getValue())); break;
512 case 8: OW->write64(uint64_t(AF.getValue())); break;
518 case MCFragment::FT_Data:
519 ++stats::EmittedDataFragments;
520 OW->writeBytes(cast<MCDataFragment>(F).getContents());
523 case MCFragment::FT_Relaxable:
524 ++stats::EmittedRelaxableFragments;
525 OW->writeBytes(cast<MCRelaxableFragment>(F).getContents());
528 case MCFragment::FT_CompactEncodedInst:
529 ++stats::EmittedCompactEncodedInstFragments;
530 OW->writeBytes(cast<MCCompactEncodedInstFragment>(F).getContents());
533 case MCFragment::FT_Fill: {
534 ++stats::EmittedFillFragments;
535 const MCFillFragment &FF = cast<MCFillFragment>(F);
536 uint8_t V = FF.getValue();
537 const unsigned MaxChunkSize = 16;
538 char Data[MaxChunkSize];
540 for (unsigned I = 1; I < MaxChunkSize; ++I)
543 uint64_t Size = FF.getSize();
544 for (unsigned ChunkSize = MaxChunkSize; ChunkSize; ChunkSize /= 2) {
545 StringRef Ref(Data, ChunkSize);
546 for (uint64_t I = 0, E = Size / ChunkSize; I != E; ++I)
548 Size = Size % ChunkSize;
553 case MCFragment::FT_LEB: {
554 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
555 OW->writeBytes(LF.getContents());
559 case MCFragment::FT_Padding: {
560 if (!Asm.getBackend().writeNopData(FragmentSize, OW))
561 report_fatal_error("unable to write nop sequence of " +
562 Twine(FragmentSize) + " bytes");
566 case MCFragment::FT_SymbolId: {
567 const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
568 OW->write32(SF.getSymbol()->getIndex());
572 case MCFragment::FT_Org: {
573 ++stats::EmittedOrgFragments;
574 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
576 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
577 OW->write8(uint8_t(OF.getValue()));
582 case MCFragment::FT_Dwarf: {
583 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
584 OW->writeBytes(OF.getContents());
587 case MCFragment::FT_DwarfFrame: {
588 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
589 OW->writeBytes(CF.getContents());
592 case MCFragment::FT_CVInlineLines: {
593 const auto &OF = cast<MCCVInlineLineTableFragment>(F);
594 OW->writeBytes(OF.getContents());
597 case MCFragment::FT_CVDefRange: {
598 const auto &DRF = cast<MCCVDefRangeFragment>(F);
599 OW->writeBytes(DRF.getContents());
602 case MCFragment::FT_Dummy:
603 llvm_unreachable("Should not have been added");
606 assert(OW->getStream().tell() - Start == FragmentSize &&
607 "The stream should advance by fragment size");
610 void MCAssembler::writeSectionData(const MCSection *Sec,
611 const MCAsmLayout &Layout) const {
612 // Ignore virtual sections.
613 if (Sec->isVirtualSection()) {
614 assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
616 // Check that contents are only things legal inside a virtual section.
617 for (const MCFragment &F : *Sec) {
618 switch (F.getKind()) {
619 default: llvm_unreachable("Invalid fragment in virtual section!");
620 case MCFragment::FT_Data: {
621 // Check that we aren't trying to write a non-zero contents (or fixups)
622 // into a virtual section. This is to support clients which use standard
623 // directives to fill the contents of virtual sections.
624 const MCDataFragment &DF = cast<MCDataFragment>(F);
625 if (DF.fixup_begin() != DF.fixup_end())
626 report_fatal_error("cannot have fixups in virtual section!");
627 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
628 if (DF.getContents()[i]) {
629 if (auto *ELFSec = dyn_cast<const MCSectionELF>(Sec))
630 report_fatal_error("non-zero initializer found in section '" +
631 ELFSec->getSectionName() + "'");
633 report_fatal_error("non-zero initializer found in virtual section");
637 case MCFragment::FT_Align:
638 // Check that we aren't trying to write a non-zero value into a virtual
640 assert((cast<MCAlignFragment>(F).getValueSize() == 0 ||
641 cast<MCAlignFragment>(F).getValue() == 0) &&
642 "Invalid align in virtual section!");
644 case MCFragment::FT_Fill:
645 assert((cast<MCFillFragment>(F).getValue() == 0) &&
646 "Invalid fill in virtual section!");
654 uint64_t Start = getWriter().getStream().tell();
657 for (const MCFragment &F : *Sec)
658 writeFragment(*this, Layout, F);
660 assert(getWriter().getStream().tell() - Start ==
661 Layout.getSectionAddressSize(Sec));
664 std::tuple<MCValue, uint64_t, bool>
665 MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
666 const MCFixup &Fixup) {
667 // Evaluate the fixup.
670 bool IsResolved = evaluateFixup(Layout, Fixup, &F, Target, FixedValue);
672 // The fixup was unresolved, we need a relocation. Inform the object
673 // writer of the relocation, and give it an opportunity to adjust the
674 // fixup value if need be.
675 getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
677 return std::make_tuple(Target, FixedValue, IsResolved);
680 void MCAssembler::layout(MCAsmLayout &Layout) {
681 DEBUG_WITH_TYPE("mc-dump", {
682 errs() << "assembler backend - pre-layout\n--\n";
685 // Create dummy fragments and assign section ordinals.
686 unsigned SectionIndex = 0;
687 for (MCSection &Sec : *this) {
688 // Create dummy fragments to eliminate any empty sections, this simplifies
690 if (Sec.getFragmentList().empty())
691 new MCDataFragment(&Sec);
693 Sec.setOrdinal(SectionIndex++);
696 // Assign layout order indices to sections and fragments.
697 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
698 MCSection *Sec = Layout.getSectionOrder()[i];
699 Sec->setLayoutOrder(i);
701 unsigned FragmentIndex = 0;
702 for (MCFragment &Frag : *Sec)
703 Frag.setLayoutOrder(FragmentIndex++);
706 // Layout until everything fits.
707 while (layoutOnce(Layout))
708 if (getContext().hadError())
711 DEBUG_WITH_TYPE("mc-dump", {
712 errs() << "assembler backend - post-relaxation\n--\n";
715 // Finalize the layout, including fragment lowering.
716 finishLayout(Layout);
718 DEBUG_WITH_TYPE("mc-dump", {
719 errs() << "assembler backend - final-layout\n--\n";
722 // Allow the object writer a chance to perform post-layout binding (for
723 // example, to set the index fields in the symbol data).
724 getWriter().executePostLayoutBinding(*this, Layout);
726 // Evaluate and apply the fixups, generating relocation entries as necessary.
727 for (MCSection &Sec : *this) {
728 for (MCFragment &Frag : Sec) {
729 // Data and relaxable fragments both have fixups. So only process
731 // FIXME: Is there a better way to do this? MCEncodedFragmentWithFixups
732 // being templated makes this tricky.
733 if (isa<MCEncodedFragment>(&Frag) &&
734 isa<MCCompactEncodedInstFragment>(&Frag))
736 if (!isa<MCEncodedFragment>(&Frag) && !isa<MCCVDefRangeFragment>(&Frag))
738 ArrayRef<MCFixup> Fixups;
739 MutableArrayRef<char> Contents;
740 if (auto *FragWithFixups = dyn_cast<MCDataFragment>(&Frag)) {
741 Fixups = FragWithFixups->getFixups();
742 Contents = FragWithFixups->getContents();
743 } else if (auto *FragWithFixups = dyn_cast<MCRelaxableFragment>(&Frag)) {
744 Fixups = FragWithFixups->getFixups();
745 Contents = FragWithFixups->getContents();
746 } else if (auto *FragWithFixups = dyn_cast<MCCVDefRangeFragment>(&Frag)) {
747 Fixups = FragWithFixups->getFixups();
748 Contents = FragWithFixups->getContents();
750 llvm_unreachable("Unknown fragment with fixups!");
751 for (const MCFixup &Fixup : Fixups) {
755 std::tie(Target, FixedValue, IsResolved) =
756 handleFixup(Layout, Frag, Fixup);
757 getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
764 void MCAssembler::Finish() {
765 // Create the layout object.
766 MCAsmLayout Layout(*this);
769 raw_ostream &OS = getWriter().getStream();
770 uint64_t StartOffset = OS.tell();
772 // Write the object file.
773 getWriter().writeObject(*this, Layout);
775 stats::ObjectBytes += OS.tell() - StartOffset;
778 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
779 const MCRelaxableFragment *DF,
780 const MCAsmLayout &Layout) const {
783 bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value);
784 if (Target.getSymA() &&
785 Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
786 Fixup.getKind() == FK_Data_1)
788 return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
792 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
793 const MCAsmLayout &Layout) const {
794 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
795 // are intentionally pushing out inst fragments, or because we relaxed a
796 // previous instruction to one that doesn't need relaxation.
797 if (!getBackend().mayNeedRelaxation(F->getInst()))
800 for (const MCFixup &Fixup : F->getFixups())
801 if (fixupNeedsRelaxation(Fixup, F, Layout))
807 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
808 MCRelaxableFragment &F) {
809 if (!fragmentNeedsRelaxation(&F, Layout))
812 ++stats::RelaxedInstructions;
814 // FIXME-PERF: We could immediately lower out instructions if we can tell
815 // they are fully resolved, to avoid retesting on later passes.
817 // Relax the fragment.
820 getBackend().relaxInstruction(F.getInst(), F.getSubtargetInfo(), Relaxed);
822 // Encode the new instruction.
824 // FIXME-PERF: If it matters, we could let the target do this. It can
825 // probably do so more efficiently in many cases.
826 SmallVector<MCFixup, 4> Fixups;
827 SmallString<256> Code;
828 raw_svector_ostream VecOS(Code);
829 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
831 // Update the fragment.
833 F.getContents() = Code;
834 F.getFixups() = Fixups;
839 bool MCAssembler::relaxPaddingFragment(MCAsmLayout &Layout,
840 MCPaddingFragment &PF) {
841 uint64_t OldSize = PF.getSize();
842 if (!getBackend().relaxFragment(&PF, Layout))
844 uint64_t NewSize = PF.getSize();
846 ++stats::PaddingFragmentsRelaxations;
847 stats::PaddingFragmentsBytes += NewSize;
848 stats::PaddingFragmentsBytes -= OldSize;
852 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
853 uint64_t OldSize = LF.getContents().size();
855 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
857 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
858 SmallString<8> &Data = LF.getContents();
860 raw_svector_ostream OSE(Data);
862 encodeSLEB128(Value, OSE);
864 encodeULEB128(Value, OSE);
865 return OldSize != LF.getContents().size();
868 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
869 MCDwarfLineAddrFragment &DF) {
870 MCContext &Context = Layout.getAssembler().getContext();
871 uint64_t OldSize = DF.getContents().size();
873 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
874 assert(Abs && "We created a line delta with an invalid expression");
877 LineDelta = DF.getLineDelta();
878 SmallString<8> &Data = DF.getContents();
880 raw_svector_ostream OSE(Data);
881 MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
883 return OldSize != Data.size();
886 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
887 MCDwarfCallFrameFragment &DF) {
888 MCContext &Context = Layout.getAssembler().getContext();
889 uint64_t OldSize = DF.getContents().size();
891 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
892 assert(Abs && "We created call frame with an invalid expression");
894 SmallString<8> &Data = DF.getContents();
896 raw_svector_ostream OSE(Data);
897 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
898 return OldSize != Data.size();
901 bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
902 MCCVInlineLineTableFragment &F) {
903 unsigned OldSize = F.getContents().size();
904 getContext().getCVContext().encodeInlineLineTable(Layout, F);
905 return OldSize != F.getContents().size();
908 bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
909 MCCVDefRangeFragment &F) {
910 unsigned OldSize = F.getContents().size();
911 getContext().getCVContext().encodeDefRange(Layout, F);
912 return OldSize != F.getContents().size();
915 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
916 // Holds the first fragment which needed relaxing during this layout. It will
917 // remain NULL if none were relaxed.
918 // When a fragment is relaxed, all the fragments following it should get
919 // invalidated because their offset is going to change.
920 MCFragment *FirstRelaxedFragment = nullptr;
922 // Attempt to relax all the fragments in the section.
923 for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
924 // Check if this is a fragment that needs relaxation.
925 bool RelaxedFrag = false;
926 switch(I->getKind()) {
929 case MCFragment::FT_Relaxable:
930 assert(!getRelaxAll() &&
931 "Did not expect a MCRelaxableFragment in RelaxAll mode");
932 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
934 case MCFragment::FT_Dwarf:
935 RelaxedFrag = relaxDwarfLineAddr(Layout,
936 *cast<MCDwarfLineAddrFragment>(I));
938 case MCFragment::FT_DwarfFrame:
940 relaxDwarfCallFrameFragment(Layout,
941 *cast<MCDwarfCallFrameFragment>(I));
943 case MCFragment::FT_LEB:
944 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
946 case MCFragment::FT_Padding:
947 RelaxedFrag = relaxPaddingFragment(Layout, *cast<MCPaddingFragment>(I));
949 case MCFragment::FT_CVInlineLines:
951 relaxCVInlineLineTable(Layout, *cast<MCCVInlineLineTableFragment>(I));
953 case MCFragment::FT_CVDefRange:
954 RelaxedFrag = relaxCVDefRange(Layout, *cast<MCCVDefRangeFragment>(I));
957 if (RelaxedFrag && !FirstRelaxedFragment)
958 FirstRelaxedFragment = &*I;
960 if (FirstRelaxedFragment) {
961 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
967 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
968 ++stats::RelaxationSteps;
970 bool WasRelaxed = false;
971 for (iterator it = begin(), ie = end(); it != ie; ++it) {
972 MCSection &Sec = *it;
973 while (layoutSectionOnce(Layout, Sec))
980 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
981 // The layout is done. Mark every fragment as valid.
982 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
983 MCSection &Section = *Layout.getSectionOrder()[i];
984 Layout.getFragmentOffset(&*Section.rbegin());
985 computeFragmentSize(Layout, *Section.rbegin());
987 getBackend().finishLayout(*this, Layout);