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 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
268 MCFragment::~MCFragment() {
271 MCFragment::MCFragment(FragmentType Kind, MCSection *Parent)
272 : Kind(Kind), Parent(Parent), Atom(nullptr), Offset(~UINT64_C(0)) {
274 Parent->getFragmentList().push_back(this);
279 MCEncodedFragment::~MCEncodedFragment() {
284 MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
289 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
290 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
292 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
293 OS(OS_), BundleAlignSize(0), RelaxAll(false),
294 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
295 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
298 MCAssembler::~MCAssembler() {
301 void MCAssembler::reset() {
304 IndirectSymbols.clear();
306 LinkerOptions.clear();
311 SubsectionsViaSymbols = false;
313 LOHContainer.reset();
314 VersionMinInfo.Major = 0;
316 // reset objects owned by us
317 getBackend().reset();
318 getEmitter().reset();
320 getLOHContainer().reset();
323 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
324 if (ThumbFuncs.count(Symbol))
327 if (!Symbol->isVariable())
330 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
331 // is not clear if that is a bug or a feature.
332 const MCExpr *Expr = Symbol->getVariableValue();
333 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
337 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
340 const MCSymbol &Sym = Ref->getSymbol();
341 if (!isThumbFunc(&Sym))
344 ThumbFuncs.insert(Symbol); // Cache it.
348 void MCAssembler::addLocalUsedInReloc(const MCSymbol &Sym) {
349 assert(Sym.isTemporary());
350 LocalsUsedInReloc.insert(&Sym);
353 bool MCAssembler::isLocalUsedInReloc(const MCSymbol &Sym) const {
354 assert(Sym.isTemporary());
355 return LocalsUsedInReloc.count(&Sym);
358 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
359 // Non-temporary labels should always be visible to the linker.
360 if (!Symbol.isTemporary())
363 // Absolute temporary labels are never visible.
364 if (!Symbol.isInSection())
367 if (isLocalUsedInReloc(Symbol))
373 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
374 // Linker visible symbols define atoms.
375 if (isSymbolLinkerVisible(S))
378 // Absolute and undefined symbols have no defining atom.
379 if (!S.getFragment())
382 // Non-linker visible symbols in sections which can't be atomized have no
384 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
385 *S.getFragment()->getParent()))
388 // Otherwise, return the atom for the containing fragment.
389 return S.getFragment()->getAtom();
392 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
393 const MCFixup &Fixup, const MCFragment *DF,
394 MCValue &Target, uint64_t &Value) const {
395 ++stats::evaluateFixup;
397 // FIXME: This code has some duplication with recordRelocation. We should
398 // probably merge the two into a single callback that tries to evaluate a
399 // fixup and records a relocation if one is needed.
400 const MCExpr *Expr = Fixup.getValue();
401 if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup))
402 getContext().reportFatalError(Fixup.getLoc(), "expected relocatable expression");
404 bool IsPCRel = Backend.getFixupKindInfo(
405 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
409 if (Target.getSymB()) {
411 } else if (!Target.getSymA()) {
414 const MCSymbolRefExpr *A = Target.getSymA();
415 const MCSymbol &SA = A->getSymbol();
416 if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
419 IsResolved = getWriter().isSymbolRefDifferenceFullyResolvedImpl(
420 *this, SA, *DF, false, true);
424 IsResolved = Target.isAbsolute();
427 Value = Target.getConstant();
429 if (const MCSymbolRefExpr *A = Target.getSymA()) {
430 const MCSymbol &Sym = A->getSymbol();
432 Value += Layout.getSymbolOffset(Sym);
434 if (const MCSymbolRefExpr *B = Target.getSymB()) {
435 const MCSymbol &Sym = B->getSymbol();
437 Value -= Layout.getSymbolOffset(Sym);
441 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
442 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
443 assert((ShouldAlignPC ? IsPCRel : true) &&
444 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
447 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
449 // A number of ARM fixups in Thumb mode require that the effective PC
450 // address be determined as the 32-bit aligned version of the actual offset.
451 if (ShouldAlignPC) Offset &= ~0x3;
455 // Let the backend adjust the fixup value if necessary, including whether
456 // we need a relocation.
457 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
463 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
464 const MCFragment &F) const {
465 switch (F.getKind()) {
466 case MCFragment::FT_Data:
467 case MCFragment::FT_Relaxable:
468 case MCFragment::FT_CompactEncodedInst:
469 return cast<MCEncodedFragment>(F).getContents().size();
470 case MCFragment::FT_Fill:
471 return cast<MCFillFragment>(F).getSize();
473 case MCFragment::FT_LEB:
474 return cast<MCLEBFragment>(F).getContents().size();
476 case MCFragment::FT_SafeSEH:
479 case MCFragment::FT_Align: {
480 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
481 unsigned Offset = Layout.getFragmentOffset(&AF);
482 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
483 // If we are padding with nops, force the padding to be larger than the
485 if (Size > 0 && AF.hasEmitNops()) {
486 while (Size % getBackend().getMinimumNopSize())
487 Size += AF.getAlignment();
489 if (Size > AF.getMaxBytesToEmit())
494 case MCFragment::FT_Org: {
495 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
496 int64_t TargetLocation;
497 if (!OF.getOffset().evaluateAsAbsolute(TargetLocation, Layout))
498 report_fatal_error("expected assembly-time absolute expression");
500 // FIXME: We need a way to communicate this error.
501 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
502 int64_t Size = TargetLocation - FragmentOffset;
503 if (Size < 0 || Size >= 0x40000000)
504 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
505 "' (at offset '" + Twine(FragmentOffset) + "')");
509 case MCFragment::FT_Dwarf:
510 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
511 case MCFragment::FT_DwarfFrame:
512 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
515 llvm_unreachable("invalid fragment kind");
518 void MCAsmLayout::layoutFragment(MCFragment *F) {
519 MCFragment *Prev = F->getPrevNode();
521 // We should never try to recompute something which is valid.
522 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
523 // We should never try to compute the fragment layout if its predecessor
525 assert((!Prev || isFragmentValid(Prev)) &&
526 "Attempt to compute fragment before its predecessor!");
528 ++stats::FragmentLayouts;
530 // Compute fragment offset and size.
532 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
535 LastValidFragment[F->getParent()] = F;
537 // If bundling is enabled and this fragment has instructions in it, it has to
538 // obey the bundling restrictions. With padding, we'll have:
543 // -------------------------------------
544 // Prev |##########| F |
545 // -------------------------------------
550 // The fragment's offset will point to after the padding, and its computed
551 // size won't include the padding.
553 // When the -mc-relax-all flag is used, we optimize bundling by writting the
554 // bundle padding directly into fragments when the instructions are emitted
555 // inside the streamer.
557 if (Assembler.isBundlingEnabled() && !Assembler.getRelaxAll() &&
558 F->hasInstructions()) {
559 assert(isa<MCEncodedFragment>(F) &&
560 "Only MCEncodedFragment implementations have instructions");
561 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
563 if (FSize > Assembler.getBundleAlignSize())
564 report_fatal_error("Fragment can't be larger than a bundle size");
566 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
568 if (RequiredBundlePadding > UINT8_MAX)
569 report_fatal_error("Padding cannot exceed 255 bytes");
570 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
571 F->Offset += RequiredBundlePadding;
575 /// \brief Write the contents of a fragment to the given object writer. Expects
576 /// a MCEncodedFragment.
577 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
578 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
579 OW->writeBytes(EF.getContents());
582 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
583 bool New = !Symbol.isRegistered();
587 Symbol.setIsRegistered(true);
588 Symbols.push_back(&Symbol);
592 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
593 MCObjectWriter *OW) const {
594 // Should NOP padding be written out before this fragment?
595 unsigned BundlePadding = F.getBundlePadding();
596 if (BundlePadding > 0) {
597 assert(isBundlingEnabled() &&
598 "Writing bundle padding with disabled bundling");
599 assert(F.hasInstructions() &&
600 "Writing bundle padding for a fragment without instructions");
602 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
603 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
604 // If the padding itself crosses a bundle boundary, it must be emitted
605 // in 2 pieces, since even nop instructions must not cross boundaries.
606 // v--------------v <- BundleAlignSize
607 // v---------v <- BundlePadding
608 // ----------------------------
609 // | Prev |####|####| F |
610 // ----------------------------
611 // ^-------------------^ <- TotalLength
612 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
613 if (!getBackend().writeNopData(DistanceToBoundary, OW))
614 report_fatal_error("unable to write NOP sequence of " +
615 Twine(DistanceToBoundary) + " bytes");
616 BundlePadding -= DistanceToBoundary;
618 if (!getBackend().writeNopData(BundlePadding, OW))
619 report_fatal_error("unable to write NOP sequence of " +
620 Twine(BundlePadding) + " bytes");
624 /// \brief Write the fragment \p F to the output file.
625 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
626 const MCFragment &F) {
627 MCObjectWriter *OW = &Asm.getWriter();
629 // FIXME: Embed in fragments instead?
630 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
632 Asm.writeFragmentPadding(F, FragmentSize, OW);
634 // This variable (and its dummy usage) is to participate in the assert at
635 // the end of the function.
636 uint64_t Start = OW->getStream().tell();
639 ++stats::EmittedFragments;
641 switch (F.getKind()) {
642 case MCFragment::FT_Align: {
643 ++stats::EmittedAlignFragments;
644 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
645 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
647 uint64_t Count = FragmentSize / AF.getValueSize();
649 // FIXME: This error shouldn't actually occur (the front end should emit
650 // multiple .align directives to enforce the semantics it wants), but is
651 // severe enough that we want to report it. How to handle this?
652 if (Count * AF.getValueSize() != FragmentSize)
653 report_fatal_error("undefined .align directive, value size '" +
654 Twine(AF.getValueSize()) +
655 "' is not a divisor of padding size '" +
656 Twine(FragmentSize) + "'");
658 // See if we are aligning with nops, and if so do that first to try to fill
659 // the Count bytes. Then if that did not fill any bytes or there are any
660 // bytes left to fill use the Value and ValueSize to fill the rest.
661 // If we are aligning with nops, ask that target to emit the right data.
662 if (AF.hasEmitNops()) {
663 if (!Asm.getBackend().writeNopData(Count, OW))
664 report_fatal_error("unable to write nop sequence of " +
665 Twine(Count) + " bytes");
669 // Otherwise, write out in multiples of the value size.
670 for (uint64_t i = 0; i != Count; ++i) {
671 switch (AF.getValueSize()) {
672 default: llvm_unreachable("Invalid size!");
673 case 1: OW->write8 (uint8_t (AF.getValue())); break;
674 case 2: OW->write16(uint16_t(AF.getValue())); break;
675 case 4: OW->write32(uint32_t(AF.getValue())); break;
676 case 8: OW->write64(uint64_t(AF.getValue())); break;
682 case MCFragment::FT_Data:
683 ++stats::EmittedDataFragments;
684 writeFragmentContents(F, OW);
687 case MCFragment::FT_Relaxable:
688 ++stats::EmittedRelaxableFragments;
689 writeFragmentContents(F, OW);
692 case MCFragment::FT_CompactEncodedInst:
693 ++stats::EmittedCompactEncodedInstFragments;
694 writeFragmentContents(F, OW);
697 case MCFragment::FT_Fill: {
698 ++stats::EmittedFillFragments;
699 const MCFillFragment &FF = cast<MCFillFragment>(F);
701 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
703 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
704 switch (FF.getValueSize()) {
705 default: llvm_unreachable("Invalid size!");
706 case 1: OW->write8 (uint8_t (FF.getValue())); break;
707 case 2: OW->write16(uint16_t(FF.getValue())); break;
708 case 4: OW->write32(uint32_t(FF.getValue())); break;
709 case 8: OW->write64(uint64_t(FF.getValue())); break;
715 case MCFragment::FT_LEB: {
716 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
717 OW->writeBytes(LF.getContents());
721 case MCFragment::FT_SafeSEH: {
722 const MCSafeSEHFragment &SF = cast<MCSafeSEHFragment>(F);
723 OW->write32(SF.getSymbol()->getIndex());
727 case MCFragment::FT_Org: {
728 ++stats::EmittedOrgFragments;
729 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
731 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
732 OW->write8(uint8_t(OF.getValue()));
737 case MCFragment::FT_Dwarf: {
738 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
739 OW->writeBytes(OF.getContents());
742 case MCFragment::FT_DwarfFrame: {
743 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
744 OW->writeBytes(CF.getContents());
749 assert(OW->getStream().tell() - Start == FragmentSize &&
750 "The stream should advance by fragment size");
753 void MCAssembler::writeSectionData(const MCSection *Sec,
754 const MCAsmLayout &Layout) const {
755 // Ignore virtual sections.
756 if (Sec->isVirtualSection()) {
757 assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
759 // Check that contents are only things legal inside a virtual section.
760 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
762 switch (it->getKind()) {
763 default: llvm_unreachable("Invalid fragment in virtual section!");
764 case MCFragment::FT_Data: {
765 // Check that we aren't trying to write a non-zero contents (or fixups)
766 // into a virtual section. This is to support clients which use standard
767 // directives to fill the contents of virtual sections.
768 const MCDataFragment &DF = cast<MCDataFragment>(*it);
769 assert(DF.fixup_begin() == DF.fixup_end() &&
770 "Cannot have fixups in virtual section!");
771 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
772 if (DF.getContents()[i]) {
773 if (auto *ELFSec = dyn_cast<const MCSectionELF>(Sec))
774 report_fatal_error("non-zero initializer found in section '" +
775 ELFSec->getSectionName() + "'");
777 report_fatal_error("non-zero initializer found in virtual section");
781 case MCFragment::FT_Align:
782 // Check that we aren't trying to write a non-zero value into a virtual
784 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
785 cast<MCAlignFragment>(it)->getValue() == 0) &&
786 "Invalid align in virtual section!");
788 case MCFragment::FT_Fill:
789 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
790 cast<MCFillFragment>(it)->getValue() == 0) &&
791 "Invalid fill in virtual section!");
799 uint64_t Start = getWriter().getStream().tell();
802 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
804 writeFragment(*this, Layout, *it);
806 assert(getWriter().getStream().tell() - Start ==
807 Layout.getSectionAddressSize(Sec));
810 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
812 const MCFixup &Fixup) {
813 // Evaluate the fixup.
816 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
817 MCFixupKindInfo::FKF_IsPCRel;
818 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
819 // The fixup was unresolved, we need a relocation. Inform the object
820 // writer of the relocation, and give it an opportunity to adjust the
821 // fixup value if need be.
822 getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
825 return std::make_pair(FixedValue, IsPCRel);
828 void MCAssembler::Finish() {
829 DEBUG_WITH_TYPE("mc-dump", {
830 llvm::errs() << "assembler backend - pre-layout\n--\n";
833 // Create the layout object.
834 MCAsmLayout Layout(*this);
836 // Create dummy fragments and assign section ordinals.
837 unsigned SectionIndex = 0;
838 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
839 // Create dummy fragments to eliminate any empty sections, this simplifies
841 if (it->getFragmentList().empty())
842 new MCDataFragment(&*it);
844 it->setOrdinal(SectionIndex++);
847 // Assign layout order indices to sections and fragments.
848 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
849 MCSection *Sec = Layout.getSectionOrder()[i];
850 Sec->setLayoutOrder(i);
852 unsigned FragmentIndex = 0;
853 for (MCSection::iterator iFrag = Sec->begin(), iFragEnd = Sec->end();
854 iFrag != iFragEnd; ++iFrag)
855 iFrag->setLayoutOrder(FragmentIndex++);
858 // Layout until everything fits.
859 while (layoutOnce(Layout))
862 DEBUG_WITH_TYPE("mc-dump", {
863 llvm::errs() << "assembler backend - post-relaxation\n--\n";
866 // Finalize the layout, including fragment lowering.
867 finishLayout(Layout);
869 DEBUG_WITH_TYPE("mc-dump", {
870 llvm::errs() << "assembler backend - final-layout\n--\n";
873 uint64_t StartOffset = OS.tell();
875 // Allow the object writer a chance to perform post-layout binding (for
876 // example, to set the index fields in the symbol data).
877 getWriter().executePostLayoutBinding(*this, Layout);
879 // Evaluate and apply the fixups, generating relocation entries as necessary.
880 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
881 for (MCSection::iterator it2 = it->begin(), ie2 = it->end(); it2 != ie2;
883 MCEncodedFragmentWithFixups *F =
884 dyn_cast<MCEncodedFragmentWithFixups>(it2);
886 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
887 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
888 MCFixup &Fixup = *it3;
891 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
892 getBackend().applyFixup(Fixup, F->getContents().data(),
893 F->getContents().size(), FixedValue, IsPCRel);
899 // Write the object file.
900 getWriter().writeObject(*this, Layout);
902 stats::ObjectBytes += OS.tell() - StartOffset;
905 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
906 const MCRelaxableFragment *DF,
907 const MCAsmLayout &Layout) const {
910 bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value);
911 return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
915 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
916 const MCAsmLayout &Layout) const {
917 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
918 // are intentionally pushing out inst fragments, or because we relaxed a
919 // previous instruction to one that doesn't need relaxation.
920 if (!getBackend().mayNeedRelaxation(F->getInst()))
923 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
924 ie = F->fixup_end(); it != ie; ++it)
925 if (fixupNeedsRelaxation(*it, F, Layout))
931 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
932 MCRelaxableFragment &F) {
933 if (!fragmentNeedsRelaxation(&F, Layout))
936 ++stats::RelaxedInstructions;
938 // FIXME-PERF: We could immediately lower out instructions if we can tell
939 // they are fully resolved, to avoid retesting on later passes.
941 // Relax the fragment.
944 getBackend().relaxInstruction(F.getInst(), Relaxed);
946 // Encode the new instruction.
948 // FIXME-PERF: If it matters, we could let the target do this. It can
949 // probably do so more efficiently in many cases.
950 SmallVector<MCFixup, 4> Fixups;
951 SmallString<256> Code;
952 raw_svector_ostream VecOS(Code);
953 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
956 // Update the fragment.
958 F.getContents() = Code;
959 F.getFixups() = Fixups;
964 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
965 uint64_t OldSize = LF.getContents().size();
967 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
969 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
970 SmallString<8> &Data = LF.getContents();
972 raw_svector_ostream OSE(Data);
974 encodeSLEB128(Value, OSE);
976 encodeULEB128(Value, OSE);
978 return OldSize != LF.getContents().size();
981 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
982 MCDwarfLineAddrFragment &DF) {
983 MCContext &Context = Layout.getAssembler().getContext();
984 uint64_t OldSize = DF.getContents().size();
986 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
987 assert(Abs && "We created a line delta with an invalid expression");
990 LineDelta = DF.getLineDelta();
991 SmallString<8> &Data = DF.getContents();
993 raw_svector_ostream OSE(Data);
994 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
996 return OldSize != Data.size();
999 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1000 MCDwarfCallFrameFragment &DF) {
1001 MCContext &Context = Layout.getAssembler().getContext();
1002 uint64_t OldSize = DF.getContents().size();
1004 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1005 assert(Abs && "We created call frame with an invalid expression");
1007 SmallString<8> &Data = DF.getContents();
1009 raw_svector_ostream OSE(Data);
1010 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1012 return OldSize != Data.size();
1015 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1016 // Holds the first fragment which needed relaxing during this layout. It will
1017 // remain NULL if none were relaxed.
1018 // When a fragment is relaxed, all the fragments following it should get
1019 // invalidated because their offset is going to change.
1020 MCFragment *FirstRelaxedFragment = nullptr;
1022 // Attempt to relax all the fragments in the section.
1023 for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
1024 // Check if this is a fragment that needs relaxation.
1025 bool RelaxedFrag = false;
1026 switch(I->getKind()) {
1029 case MCFragment::FT_Relaxable:
1030 assert(!getRelaxAll() &&
1031 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1032 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1034 case MCFragment::FT_Dwarf:
1035 RelaxedFrag = relaxDwarfLineAddr(Layout,
1036 *cast<MCDwarfLineAddrFragment>(I));
1038 case MCFragment::FT_DwarfFrame:
1040 relaxDwarfCallFrameFragment(Layout,
1041 *cast<MCDwarfCallFrameFragment>(I));
1043 case MCFragment::FT_LEB:
1044 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1047 if (RelaxedFrag && !FirstRelaxedFragment)
1048 FirstRelaxedFragment = I;
1050 if (FirstRelaxedFragment) {
1051 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1057 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1058 ++stats::RelaxationSteps;
1060 bool WasRelaxed = false;
1061 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1062 MCSection &Sec = *it;
1063 while (layoutSectionOnce(Layout, Sec))
1070 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1071 // The layout is done. Mark every fragment as valid.
1072 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1073 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1077 // Debugging methods
1081 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1082 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1083 << " Value:" << *AF.getValue()
1084 << " Kind:" << AF.getKind() << ">";
1090 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1091 void MCFragment::dump() {
1092 raw_ostream &OS = llvm::errs();
1095 switch (getKind()) {
1096 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1097 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1098 case MCFragment::FT_CompactEncodedInst:
1099 OS << "MCCompactEncodedInstFragment"; break;
1100 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1101 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1102 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1103 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1104 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1105 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1106 case MCFragment::FT_SafeSEH: OS << "MCSafeSEHFragment"; break;
1109 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1110 << " Offset:" << Offset
1111 << " HasInstructions:" << hasInstructions()
1112 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1114 switch (getKind()) {
1115 case MCFragment::FT_Align: {
1116 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1117 if (AF->hasEmitNops())
1118 OS << " (emit nops)";
1120 OS << " Alignment:" << AF->getAlignment()
1121 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1122 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1125 case MCFragment::FT_Data: {
1126 const MCDataFragment *DF = cast<MCDataFragment>(this);
1128 OS << " Contents:[";
1129 const SmallVectorImpl<char> &Contents = DF->getContents();
1130 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1132 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1134 OS << "] (" << Contents.size() << " bytes)";
1136 if (DF->fixup_begin() != DF->fixup_end()) {
1139 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1140 ie = DF->fixup_end(); it != ie; ++it) {
1141 if (it != DF->fixup_begin()) OS << ",\n ";
1148 case MCFragment::FT_CompactEncodedInst: {
1149 const MCCompactEncodedInstFragment *CEIF =
1150 cast<MCCompactEncodedInstFragment>(this);
1152 OS << " Contents:[";
1153 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1154 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1156 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1158 OS << "] (" << Contents.size() << " bytes)";
1161 case MCFragment::FT_Fill: {
1162 const MCFillFragment *FF = cast<MCFillFragment>(this);
1163 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1164 << " Size:" << FF->getSize();
1167 case MCFragment::FT_Relaxable: {
1168 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1171 F->getInst().dump_pretty(OS);
1174 case MCFragment::FT_Org: {
1175 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1177 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1180 case MCFragment::FT_Dwarf: {
1181 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1183 OS << " AddrDelta:" << OF->getAddrDelta()
1184 << " LineDelta:" << OF->getLineDelta();
1187 case MCFragment::FT_DwarfFrame: {
1188 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1190 OS << " AddrDelta:" << CF->getAddrDelta();
1193 case MCFragment::FT_LEB: {
1194 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1196 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1199 case MCFragment::FT_SafeSEH: {
1200 const MCSafeSEHFragment *F = cast<MCSafeSEHFragment>(this);
1202 OS << " Sym:" << F->getSymbol();
1209 void MCAssembler::dump() {
1210 raw_ostream &OS = llvm::errs();
1212 OS << "<MCAssembler\n";
1213 OS << " Sections:[\n ";
1214 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1215 if (it != begin()) OS << ",\n ";
1221 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1222 if (it != symbol_begin()) OS << ",\n ";
1225 OS << ", Index:" << it->getIndex() << ", ";
1232 // anchors for MC*Fragment vtables
1233 void MCEncodedFragment::anchor() { }
1234 void MCEncodedFragmentWithFixups::anchor() { }
1235 void MCDataFragment::anchor() { }
1236 void MCCompactEncodedInstFragment::anchor() { }
1237 void MCRelaxableFragment::anchor() { }
1238 void MCAlignFragment::anchor() { }
1239 void MCFillFragment::anchor() { }
1240 void MCOrgFragment::anchor() { }
1241 void MCLEBFragment::anchor() { }
1242 void MCSafeSEHFragment::anchor() { }
1243 void MCDwarfLineAddrFragment::anchor() { }
1244 void MCDwarfCallFrameFragment::anchor() { }