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 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
349 // Non-temporary labels should always be visible to the linker.
350 if (!Symbol.isTemporary())
353 // Absolute temporary labels are never visible.
354 if (!Symbol.isInSection())
357 if (Symbol.isUsedInReloc())
363 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
364 // Linker visible symbols define atoms.
365 if (isSymbolLinkerVisible(S))
368 // Absolute and undefined symbols have no defining atom.
369 if (!S.getFragment())
372 // Non-linker visible symbols in sections which can't be atomized have no
374 if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
375 *S.getFragment()->getParent()))
378 // Otherwise, return the atom for the containing fragment.
379 return S.getFragment()->getAtom();
382 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
383 const MCFixup &Fixup, const MCFragment *DF,
384 MCValue &Target, uint64_t &Value) const {
385 ++stats::evaluateFixup;
387 // FIXME: This code has some duplication with recordRelocation. We should
388 // probably merge the two into a single callback that tries to evaluate a
389 // fixup and records a relocation if one is needed.
390 const MCExpr *Expr = Fixup.getValue();
391 if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup))
392 getContext().reportFatalError(Fixup.getLoc(), "expected relocatable expression");
394 bool IsPCRel = Backend.getFixupKindInfo(
395 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
399 if (Target.getSymB()) {
401 } else if (!Target.getSymA()) {
404 const MCSymbolRefExpr *A = Target.getSymA();
405 const MCSymbol &SA = A->getSymbol();
406 if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
409 IsResolved = getWriter().isSymbolRefDifferenceFullyResolvedImpl(
410 *this, SA, *DF, false, true);
414 IsResolved = Target.isAbsolute();
417 Value = Target.getConstant();
419 if (const MCSymbolRefExpr *A = Target.getSymA()) {
420 const MCSymbol &Sym = A->getSymbol();
422 Value += Layout.getSymbolOffset(Sym);
424 if (const MCSymbolRefExpr *B = Target.getSymB()) {
425 const MCSymbol &Sym = B->getSymbol();
427 Value -= Layout.getSymbolOffset(Sym);
431 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
432 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
433 assert((ShouldAlignPC ? IsPCRel : true) &&
434 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
437 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
439 // A number of ARM fixups in Thumb mode require that the effective PC
440 // address be determined as the 32-bit aligned version of the actual offset.
441 if (ShouldAlignPC) Offset &= ~0x3;
445 // Let the backend adjust the fixup value if necessary, including whether
446 // we need a relocation.
447 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
453 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
454 const MCFragment &F) const {
455 switch (F.getKind()) {
456 case MCFragment::FT_Data:
457 case MCFragment::FT_Relaxable:
458 case MCFragment::FT_CompactEncodedInst:
459 return cast<MCEncodedFragment>(F).getContents().size();
460 case MCFragment::FT_Fill:
461 return cast<MCFillFragment>(F).getSize();
463 case MCFragment::FT_LEB:
464 return cast<MCLEBFragment>(F).getContents().size();
466 case MCFragment::FT_SafeSEH:
469 case MCFragment::FT_Align: {
470 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
471 unsigned Offset = Layout.getFragmentOffset(&AF);
472 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
473 // If we are padding with nops, force the padding to be larger than the
475 if (Size > 0 && AF.hasEmitNops()) {
476 while (Size % getBackend().getMinimumNopSize())
477 Size += AF.getAlignment();
479 if (Size > AF.getMaxBytesToEmit())
484 case MCFragment::FT_Org: {
485 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
486 int64_t TargetLocation;
487 if (!OF.getOffset().evaluateAsAbsolute(TargetLocation, Layout))
488 report_fatal_error("expected assembly-time absolute expression");
490 // FIXME: We need a way to communicate this error.
491 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
492 int64_t Size = TargetLocation - FragmentOffset;
493 if (Size < 0 || Size >= 0x40000000)
494 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
495 "' (at offset '" + Twine(FragmentOffset) + "')");
499 case MCFragment::FT_Dwarf:
500 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
501 case MCFragment::FT_DwarfFrame:
502 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
505 llvm_unreachable("invalid fragment kind");
508 void MCAsmLayout::layoutFragment(MCFragment *F) {
509 MCFragment *Prev = F->getPrevNode();
511 // We should never try to recompute something which is valid.
512 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
513 // We should never try to compute the fragment layout if its predecessor
515 assert((!Prev || isFragmentValid(Prev)) &&
516 "Attempt to compute fragment before its predecessor!");
518 ++stats::FragmentLayouts;
520 // Compute fragment offset and size.
522 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
525 LastValidFragment[F->getParent()] = F;
527 // If bundling is enabled and this fragment has instructions in it, it has to
528 // obey the bundling restrictions. With padding, we'll have:
533 // -------------------------------------
534 // Prev |##########| F |
535 // -------------------------------------
540 // The fragment's offset will point to after the padding, and its computed
541 // size won't include the padding.
543 // When the -mc-relax-all flag is used, we optimize bundling by writting the
544 // bundle padding directly into fragments when the instructions are emitted
545 // inside the streamer.
547 if (Assembler.isBundlingEnabled() && !Assembler.getRelaxAll() &&
548 F->hasInstructions()) {
549 assert(isa<MCEncodedFragment>(F) &&
550 "Only MCEncodedFragment implementations have instructions");
551 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
553 if (FSize > Assembler.getBundleAlignSize())
554 report_fatal_error("Fragment can't be larger than a bundle size");
556 uint64_t RequiredBundlePadding = computeBundlePadding(Assembler, F,
558 if (RequiredBundlePadding > UINT8_MAX)
559 report_fatal_error("Padding cannot exceed 255 bytes");
560 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
561 F->Offset += RequiredBundlePadding;
565 /// \brief Write the contents of a fragment to the given object writer. Expects
566 /// a MCEncodedFragment.
567 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
568 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
569 OW->writeBytes(EF.getContents());
572 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
573 bool New = !Symbol.isRegistered();
577 Symbol.setIsRegistered(true);
578 Symbols.push_back(&Symbol);
582 void MCAssembler::writeFragmentPadding(const MCFragment &F, uint64_t FSize,
583 MCObjectWriter *OW) const {
584 // Should NOP padding be written out before this fragment?
585 unsigned BundlePadding = F.getBundlePadding();
586 if (BundlePadding > 0) {
587 assert(isBundlingEnabled() &&
588 "Writing bundle padding with disabled bundling");
589 assert(F.hasInstructions() &&
590 "Writing bundle padding for a fragment without instructions");
592 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
593 if (F.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
594 // If the padding itself crosses a bundle boundary, it must be emitted
595 // in 2 pieces, since even nop instructions must not cross boundaries.
596 // v--------------v <- BundleAlignSize
597 // v---------v <- BundlePadding
598 // ----------------------------
599 // | Prev |####|####| F |
600 // ----------------------------
601 // ^-------------------^ <- TotalLength
602 unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
603 if (!getBackend().writeNopData(DistanceToBoundary, OW))
604 report_fatal_error("unable to write NOP sequence of " +
605 Twine(DistanceToBoundary) + " bytes");
606 BundlePadding -= DistanceToBoundary;
608 if (!getBackend().writeNopData(BundlePadding, OW))
609 report_fatal_error("unable to write NOP sequence of " +
610 Twine(BundlePadding) + " bytes");
614 /// \brief Write the fragment \p F to the output file.
615 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
616 const MCFragment &F) {
617 MCObjectWriter *OW = &Asm.getWriter();
619 // FIXME: Embed in fragments instead?
620 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
622 Asm.writeFragmentPadding(F, FragmentSize, OW);
624 // This variable (and its dummy usage) is to participate in the assert at
625 // the end of the function.
626 uint64_t Start = OW->getStream().tell();
629 ++stats::EmittedFragments;
631 switch (F.getKind()) {
632 case MCFragment::FT_Align: {
633 ++stats::EmittedAlignFragments;
634 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
635 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
637 uint64_t Count = FragmentSize / AF.getValueSize();
639 // FIXME: This error shouldn't actually occur (the front end should emit
640 // multiple .align directives to enforce the semantics it wants), but is
641 // severe enough that we want to report it. How to handle this?
642 if (Count * AF.getValueSize() != FragmentSize)
643 report_fatal_error("undefined .align directive, value size '" +
644 Twine(AF.getValueSize()) +
645 "' is not a divisor of padding size '" +
646 Twine(FragmentSize) + "'");
648 // See if we are aligning with nops, and if so do that first to try to fill
649 // the Count bytes. Then if that did not fill any bytes or there are any
650 // bytes left to fill use the Value and ValueSize to fill the rest.
651 // If we are aligning with nops, ask that target to emit the right data.
652 if (AF.hasEmitNops()) {
653 if (!Asm.getBackend().writeNopData(Count, OW))
654 report_fatal_error("unable to write nop sequence of " +
655 Twine(Count) + " bytes");
659 // Otherwise, write out in multiples of the value size.
660 for (uint64_t i = 0; i != Count; ++i) {
661 switch (AF.getValueSize()) {
662 default: llvm_unreachable("Invalid size!");
663 case 1: OW->write8 (uint8_t (AF.getValue())); break;
664 case 2: OW->write16(uint16_t(AF.getValue())); break;
665 case 4: OW->write32(uint32_t(AF.getValue())); break;
666 case 8: OW->write64(uint64_t(AF.getValue())); break;
672 case MCFragment::FT_Data:
673 ++stats::EmittedDataFragments;
674 writeFragmentContents(F, OW);
677 case MCFragment::FT_Relaxable:
678 ++stats::EmittedRelaxableFragments;
679 writeFragmentContents(F, OW);
682 case MCFragment::FT_CompactEncodedInst:
683 ++stats::EmittedCompactEncodedInstFragments;
684 writeFragmentContents(F, OW);
687 case MCFragment::FT_Fill: {
688 ++stats::EmittedFillFragments;
689 const MCFillFragment &FF = cast<MCFillFragment>(F);
691 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
693 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
694 switch (FF.getValueSize()) {
695 default: llvm_unreachable("Invalid size!");
696 case 1: OW->write8 (uint8_t (FF.getValue())); break;
697 case 2: OW->write16(uint16_t(FF.getValue())); break;
698 case 4: OW->write32(uint32_t(FF.getValue())); break;
699 case 8: OW->write64(uint64_t(FF.getValue())); break;
705 case MCFragment::FT_LEB: {
706 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
707 OW->writeBytes(LF.getContents());
711 case MCFragment::FT_SafeSEH: {
712 const MCSafeSEHFragment &SF = cast<MCSafeSEHFragment>(F);
713 OW->write32(SF.getSymbol()->getIndex());
717 case MCFragment::FT_Org: {
718 ++stats::EmittedOrgFragments;
719 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
721 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
722 OW->write8(uint8_t(OF.getValue()));
727 case MCFragment::FT_Dwarf: {
728 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
729 OW->writeBytes(OF.getContents());
732 case MCFragment::FT_DwarfFrame: {
733 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
734 OW->writeBytes(CF.getContents());
739 assert(OW->getStream().tell() - Start == FragmentSize &&
740 "The stream should advance by fragment size");
743 void MCAssembler::writeSectionData(const MCSection *Sec,
744 const MCAsmLayout &Layout) const {
745 // Ignore virtual sections.
746 if (Sec->isVirtualSection()) {
747 assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
749 // Check that contents are only things legal inside a virtual section.
750 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
752 switch (it->getKind()) {
753 default: llvm_unreachable("Invalid fragment in virtual section!");
754 case MCFragment::FT_Data: {
755 // Check that we aren't trying to write a non-zero contents (or fixups)
756 // into a virtual section. This is to support clients which use standard
757 // directives to fill the contents of virtual sections.
758 const MCDataFragment &DF = cast<MCDataFragment>(*it);
759 assert(DF.fixup_begin() == DF.fixup_end() &&
760 "Cannot have fixups in virtual section!");
761 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
762 if (DF.getContents()[i]) {
763 if (auto *ELFSec = dyn_cast<const MCSectionELF>(Sec))
764 report_fatal_error("non-zero initializer found in section '" +
765 ELFSec->getSectionName() + "'");
767 report_fatal_error("non-zero initializer found in virtual section");
771 case MCFragment::FT_Align:
772 // Check that we aren't trying to write a non-zero value into a virtual
774 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
775 cast<MCAlignFragment>(it)->getValue() == 0) &&
776 "Invalid align in virtual section!");
778 case MCFragment::FT_Fill:
779 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
780 cast<MCFillFragment>(it)->getValue() == 0) &&
781 "Invalid fill in virtual section!");
789 uint64_t Start = getWriter().getStream().tell();
792 for (MCSection::const_iterator it = Sec->begin(), ie = Sec->end(); it != ie;
794 writeFragment(*this, Layout, *it);
796 assert(getWriter().getStream().tell() - Start ==
797 Layout.getSectionAddressSize(Sec));
800 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
802 const MCFixup &Fixup) {
803 // Evaluate the fixup.
806 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
807 MCFixupKindInfo::FKF_IsPCRel;
808 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
809 // The fixup was unresolved, we need a relocation. Inform the object
810 // writer of the relocation, and give it an opportunity to adjust the
811 // fixup value if need be.
812 getWriter().recordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
815 return std::make_pair(FixedValue, IsPCRel);
818 void MCAssembler::Finish() {
819 DEBUG_WITH_TYPE("mc-dump", {
820 llvm::errs() << "assembler backend - pre-layout\n--\n";
823 // Create the layout object.
824 MCAsmLayout Layout(*this);
826 // Create dummy fragments and assign section ordinals.
827 unsigned SectionIndex = 0;
828 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
829 // Create dummy fragments to eliminate any empty sections, this simplifies
831 if (it->getFragmentList().empty())
832 new MCDataFragment(&*it);
834 it->setOrdinal(SectionIndex++);
837 // Assign layout order indices to sections and fragments.
838 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
839 MCSection *Sec = Layout.getSectionOrder()[i];
840 Sec->setLayoutOrder(i);
842 unsigned FragmentIndex = 0;
843 for (MCSection::iterator iFrag = Sec->begin(), iFragEnd = Sec->end();
844 iFrag != iFragEnd; ++iFrag)
845 iFrag->setLayoutOrder(FragmentIndex++);
848 // Layout until everything fits.
849 while (layoutOnce(Layout))
852 DEBUG_WITH_TYPE("mc-dump", {
853 llvm::errs() << "assembler backend - post-relaxation\n--\n";
856 // Finalize the layout, including fragment lowering.
857 finishLayout(Layout);
859 DEBUG_WITH_TYPE("mc-dump", {
860 llvm::errs() << "assembler backend - final-layout\n--\n";
863 uint64_t StartOffset = OS.tell();
865 // Allow the object writer a chance to perform post-layout binding (for
866 // example, to set the index fields in the symbol data).
867 getWriter().executePostLayoutBinding(*this, Layout);
869 // Evaluate and apply the fixups, generating relocation entries as necessary.
870 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
871 for (MCSection::iterator it2 = it->begin(), ie2 = it->end(); it2 != ie2;
873 MCEncodedFragmentWithFixups *F =
874 dyn_cast<MCEncodedFragmentWithFixups>(it2);
876 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
877 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
878 MCFixup &Fixup = *it3;
881 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
882 getBackend().applyFixup(Fixup, F->getContents().data(),
883 F->getContents().size(), FixedValue, IsPCRel);
889 // Write the object file.
890 getWriter().writeObject(*this, Layout);
892 stats::ObjectBytes += OS.tell() - StartOffset;
895 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
896 const MCRelaxableFragment *DF,
897 const MCAsmLayout &Layout) const {
900 bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value);
901 return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
905 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
906 const MCAsmLayout &Layout) const {
907 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
908 // are intentionally pushing out inst fragments, or because we relaxed a
909 // previous instruction to one that doesn't need relaxation.
910 if (!getBackend().mayNeedRelaxation(F->getInst()))
913 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
914 ie = F->fixup_end(); it != ie; ++it)
915 if (fixupNeedsRelaxation(*it, F, Layout))
921 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
922 MCRelaxableFragment &F) {
923 if (!fragmentNeedsRelaxation(&F, Layout))
926 ++stats::RelaxedInstructions;
928 // FIXME-PERF: We could immediately lower out instructions if we can tell
929 // they are fully resolved, to avoid retesting on later passes.
931 // Relax the fragment.
934 getBackend().relaxInstruction(F.getInst(), Relaxed);
936 // Encode the new instruction.
938 // FIXME-PERF: If it matters, we could let the target do this. It can
939 // probably do so more efficiently in many cases.
940 SmallVector<MCFixup, 4> Fixups;
941 SmallString<256> Code;
942 raw_svector_ostream VecOS(Code);
943 getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
946 // Update the fragment.
948 F.getContents() = Code;
949 F.getFixups() = Fixups;
954 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
955 uint64_t OldSize = LF.getContents().size();
957 bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
959 report_fatal_error("sleb128 and uleb128 expressions must be absolute");
960 SmallString<8> &Data = LF.getContents();
962 raw_svector_ostream OSE(Data);
964 encodeSLEB128(Value, OSE);
966 encodeULEB128(Value, OSE);
968 return OldSize != LF.getContents().size();
971 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
972 MCDwarfLineAddrFragment &DF) {
973 MCContext &Context = Layout.getAssembler().getContext();
974 uint64_t OldSize = DF.getContents().size();
976 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
977 assert(Abs && "We created a line delta with an invalid expression");
980 LineDelta = DF.getLineDelta();
981 SmallString<8> &Data = DF.getContents();
983 raw_svector_ostream OSE(Data);
984 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
986 return OldSize != Data.size();
989 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
990 MCDwarfCallFrameFragment &DF) {
991 MCContext &Context = Layout.getAssembler().getContext();
992 uint64_t OldSize = DF.getContents().size();
994 bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
995 assert(Abs && "We created call frame with an invalid expression");
997 SmallString<8> &Data = DF.getContents();
999 raw_svector_ostream OSE(Data);
1000 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1002 return OldSize != Data.size();
1005 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1006 // Holds the first fragment which needed relaxing during this layout. It will
1007 // remain NULL if none were relaxed.
1008 // When a fragment is relaxed, all the fragments following it should get
1009 // invalidated because their offset is going to change.
1010 MCFragment *FirstRelaxedFragment = nullptr;
1012 // Attempt to relax all the fragments in the section.
1013 for (MCSection::iterator I = Sec.begin(), IE = Sec.end(); I != IE; ++I) {
1014 // Check if this is a fragment that needs relaxation.
1015 bool RelaxedFrag = false;
1016 switch(I->getKind()) {
1019 case MCFragment::FT_Relaxable:
1020 assert(!getRelaxAll() &&
1021 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1022 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1024 case MCFragment::FT_Dwarf:
1025 RelaxedFrag = relaxDwarfLineAddr(Layout,
1026 *cast<MCDwarfLineAddrFragment>(I));
1028 case MCFragment::FT_DwarfFrame:
1030 relaxDwarfCallFrameFragment(Layout,
1031 *cast<MCDwarfCallFrameFragment>(I));
1033 case MCFragment::FT_LEB:
1034 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1037 if (RelaxedFrag && !FirstRelaxedFragment)
1038 FirstRelaxedFragment = I;
1040 if (FirstRelaxedFragment) {
1041 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1047 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1048 ++stats::RelaxationSteps;
1050 bool WasRelaxed = false;
1051 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1052 MCSection &Sec = *it;
1053 while (layoutSectionOnce(Layout, Sec))
1060 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1061 // The layout is done. Mark every fragment as valid.
1062 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1063 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1067 // Debugging methods
1071 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1072 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1073 << " Value:" << *AF.getValue()
1074 << " Kind:" << AF.getKind() << ">";
1080 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1081 void MCFragment::dump() {
1082 raw_ostream &OS = llvm::errs();
1085 switch (getKind()) {
1086 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1087 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1088 case MCFragment::FT_CompactEncodedInst:
1089 OS << "MCCompactEncodedInstFragment"; break;
1090 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1091 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1092 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1093 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1094 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1095 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1096 case MCFragment::FT_SafeSEH: OS << "MCSafeSEHFragment"; break;
1099 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1100 << " Offset:" << Offset
1101 << " HasInstructions:" << hasInstructions()
1102 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1104 switch (getKind()) {
1105 case MCFragment::FT_Align: {
1106 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1107 if (AF->hasEmitNops())
1108 OS << " (emit nops)";
1110 OS << " Alignment:" << AF->getAlignment()
1111 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1112 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1115 case MCFragment::FT_Data: {
1116 const MCDataFragment *DF = cast<MCDataFragment>(this);
1118 OS << " Contents:[";
1119 const SmallVectorImpl<char> &Contents = DF->getContents();
1120 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1122 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1124 OS << "] (" << Contents.size() << " bytes)";
1126 if (DF->fixup_begin() != DF->fixup_end()) {
1129 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1130 ie = DF->fixup_end(); it != ie; ++it) {
1131 if (it != DF->fixup_begin()) OS << ",\n ";
1138 case MCFragment::FT_CompactEncodedInst: {
1139 const MCCompactEncodedInstFragment *CEIF =
1140 cast<MCCompactEncodedInstFragment>(this);
1142 OS << " Contents:[";
1143 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1144 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1146 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1148 OS << "] (" << Contents.size() << " bytes)";
1151 case MCFragment::FT_Fill: {
1152 const MCFillFragment *FF = cast<MCFillFragment>(this);
1153 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1154 << " Size:" << FF->getSize();
1157 case MCFragment::FT_Relaxable: {
1158 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1161 F->getInst().dump_pretty(OS);
1164 case MCFragment::FT_Org: {
1165 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1167 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1170 case MCFragment::FT_Dwarf: {
1171 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1173 OS << " AddrDelta:" << OF->getAddrDelta()
1174 << " LineDelta:" << OF->getLineDelta();
1177 case MCFragment::FT_DwarfFrame: {
1178 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1180 OS << " AddrDelta:" << CF->getAddrDelta();
1183 case MCFragment::FT_LEB: {
1184 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1186 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1189 case MCFragment::FT_SafeSEH: {
1190 const MCSafeSEHFragment *F = cast<MCSafeSEHFragment>(this);
1192 OS << " Sym:" << F->getSymbol();
1199 void MCAssembler::dump() {
1200 raw_ostream &OS = llvm::errs();
1202 OS << "<MCAssembler\n";
1203 OS << " Sections:[\n ";
1204 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1205 if (it != begin()) OS << ",\n ";
1211 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1212 if (it != symbol_begin()) OS << ",\n ";
1215 OS << ", Index:" << it->getIndex() << ", ";
1222 // anchors for MC*Fragment vtables
1223 void MCEncodedFragment::anchor() { }
1224 void MCEncodedFragmentWithFixups::anchor() { }
1225 void MCDataFragment::anchor() { }
1226 void MCCompactEncodedInstFragment::anchor() { }
1227 void MCRelaxableFragment::anchor() { }
1228 void MCAlignFragment::anchor() { }
1229 void MCFillFragment::anchor() { }
1230 void MCOrgFragment::anchor() { }
1231 void MCLEBFragment::anchor() { }
1232 void MCSafeSEHFragment::anchor() { }
1233 void MCDwarfLineAddrFragment::anchor() { }
1234 void MCDwarfCallFrameFragment::anchor() { }