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/MCAsmLayout.h"
16 #include "llvm/MC/MCCodeEmitter.h"
17 #include "llvm/MC/MCContext.h"
18 #include "llvm/MC/MCDwarf.h"
19 #include "llvm/MC/MCExpr.h"
20 #include "llvm/MC/MCFixupKindInfo.h"
21 #include "llvm/MC/MCObjectWriter.h"
22 #include "llvm/MC/MCSection.h"
23 #include "llvm/MC/MCSymbol.h"
24 #include "llvm/MC/MCValue.h"
25 #include "llvm/Support/Debug.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/LEB128.h"
28 #include "llvm/Support/TargetRegistry.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/MC/MCSectionELF.h"
34 #define DEBUG_TYPE "assembler"
38 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
39 STATISTIC(EmittedRelaxableFragments,
40 "Number of emitted assembler fragments - relaxable");
41 STATISTIC(EmittedDataFragments,
42 "Number of emitted assembler fragments - data");
43 STATISTIC(EmittedCompactEncodedInstFragments,
44 "Number of emitted assembler fragments - compact encoded inst");
45 STATISTIC(EmittedAlignFragments,
46 "Number of emitted assembler fragments - align");
47 STATISTIC(EmittedFillFragments,
48 "Number of emitted assembler fragments - fill");
49 STATISTIC(EmittedOrgFragments,
50 "Number of emitted assembler fragments - org");
51 STATISTIC(evaluateFixup, "Number of evaluated fixups");
52 STATISTIC(FragmentLayouts, "Number of fragment layouts");
53 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
54 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
55 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
59 // FIXME FIXME FIXME: There are number of places in this file where we convert
60 // what is a 64-bit assembler value used for computation into a value in the
61 // object file, which may truncate it. We should detect that truncation where
62 // invalid and report errors back.
66 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
67 : Assembler(Asm), LastValidFragment()
69 // Compute the section layout order. Virtual sections must go last.
70 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
71 if (!it->getSection().isVirtualSection())
72 SectionOrder.push_back(&*it);
73 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
74 if (it->getSection().isVirtualSection())
75 SectionOrder.push_back(&*it);
78 bool MCAsmLayout::isFragmentValid(const MCFragment *F) const {
79 const MCSectionData &SD = *F->getParent();
80 const MCFragment *LastValid = LastValidFragment.lookup(&SD);
83 assert(LastValid->getParent() == F->getParent());
84 return F->getLayoutOrder() <= LastValid->getLayoutOrder();
87 void MCAsmLayout::invalidateFragmentsFrom(MCFragment *F) {
88 // If this fragment wasn't already valid, we don't need to do anything.
89 if (!isFragmentValid(F))
92 // Otherwise, reset the last valid fragment to the previous fragment
93 // (if this is the first fragment, it will be NULL).
94 const MCSectionData &SD = *F->getParent();
95 LastValidFragment[&SD] = F->getPrevNode();
98 void MCAsmLayout::ensureValid(const MCFragment *F) const {
99 MCSectionData &SD = *F->getParent();
101 MCFragment *Cur = LastValidFragment[&SD];
105 Cur = Cur->getNextNode();
107 // Advance the layout position until the fragment is valid.
108 while (!isFragmentValid(F)) {
109 assert(Cur && "Layout bookkeeping error");
110 const_cast<MCAsmLayout*>(this)->layoutFragment(Cur);
111 Cur = Cur->getNextNode();
115 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
117 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
121 // Simple getSymbolOffset helper for the non-varibale case.
122 static bool getLabelOffset(const MCAsmLayout &Layout, const MCSymbolData &SD,
123 bool ReportError, uint64_t &Val) {
124 if (!SD.getFragment()) {
126 report_fatal_error("unable to evaluate offset to undefined symbol '" +
127 SD.getSymbol().getName() + "'");
130 Val = Layout.getFragmentOffset(SD.getFragment()) + SD.getOffset();
134 static bool getSymbolOffsetImpl(const MCAsmLayout &Layout,
135 const MCSymbolData *SD, bool ReportError,
137 const MCSymbol &S = SD->getSymbol();
140 return getLabelOffset(Layout, *SD, ReportError, Val);
142 // If SD is a variable, evaluate it.
144 if (!S.getVariableValue()->EvaluateAsValue(Target, &Layout, nullptr))
145 report_fatal_error("unable to evaluate offset for variable '" +
148 uint64_t Offset = Target.getConstant();
150 const MCAssembler &Asm = Layout.getAssembler();
152 const MCSymbolRefExpr *A = Target.getSymA();
155 if (!getLabelOffset(Layout, Asm.getSymbolData(A->getSymbol()), ReportError,
161 const MCSymbolRefExpr *B = Target.getSymB();
164 if (!getLabelOffset(Layout, Asm.getSymbolData(B->getSymbol()), ReportError,
174 bool MCAsmLayout::getSymbolOffset(const MCSymbolData *SD, uint64_t &Val) const {
175 return getSymbolOffsetImpl(*this, SD, false, Val);
178 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
180 getSymbolOffsetImpl(*this, SD, true, Val);
184 const MCSymbol *MCAsmLayout::getBaseSymbol(const MCSymbol &Symbol) const {
185 if (!Symbol.isVariable())
188 const MCExpr *Expr = Symbol.getVariableValue();
190 if (!Expr->EvaluateAsValue(Value, this, nullptr))
191 llvm_unreachable("Invalid Expression");
193 const MCSymbolRefExpr *RefB = Value.getSymB();
195 Assembler.getContext().FatalError(
196 SMLoc(), Twine("symbol '") + RefB->getSymbol().getName() +
197 "' could not be evaluated in a subtraction expression");
199 const MCSymbolRefExpr *A = Value.getSymA();
203 return &A->getSymbol();
206 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
207 // The size is the last fragment's end offset.
208 const MCFragment &F = SD->getFragmentList().back();
209 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
212 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
213 // Virtual sections have no file size.
214 if (SD->getSection().isVirtualSection())
217 // Otherwise, the file size is the same as the address space size.
218 return getSectionAddressSize(SD);
221 uint64_t MCAsmLayout::computeBundlePadding(const MCFragment *F,
222 uint64_t FOffset, uint64_t FSize) {
223 uint64_t BundleSize = Assembler.getBundleAlignSize();
224 assert(BundleSize > 0 &&
225 "computeBundlePadding should only be called if bundling is enabled");
226 uint64_t BundleMask = BundleSize - 1;
227 uint64_t OffsetInBundle = FOffset & BundleMask;
228 uint64_t EndOfFragment = OffsetInBundle + FSize;
230 // There are two kinds of bundling restrictions:
232 // 1) For alignToBundleEnd(), add padding to ensure that the fragment will
233 // *end* on a bundle boundary.
234 // 2) Otherwise, check if the fragment would cross a bundle boundary. If it
235 // would, add padding until the end of the bundle so that the fragment
236 // will start in a new one.
237 if (F->alignToBundleEnd()) {
238 // Three possibilities here:
240 // A) The fragment just happens to end at a bundle boundary, so we're good.
241 // B) The fragment ends before the current bundle boundary: pad it just
242 // enough to reach the boundary.
243 // C) The fragment ends after the current bundle boundary: pad it until it
244 // reaches the end of the next bundle boundary.
246 // Note: this code could be made shorter with some modulo trickery, but it's
247 // intentionally kept in its more explicit form for simplicity.
248 if (EndOfFragment == BundleSize)
250 else if (EndOfFragment < BundleSize)
251 return BundleSize - EndOfFragment;
252 else { // EndOfFragment > BundleSize
253 return 2 * BundleSize - EndOfFragment;
255 } else if (EndOfFragment > BundleSize)
256 return BundleSize - OffsetInBundle;
263 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
266 MCFragment::~MCFragment() {
269 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
270 : Kind(_Kind), Parent(_Parent), Atom(nullptr), Offset(~UINT64_C(0))
273 Parent->getFragmentList().push_back(this);
278 MCEncodedFragment::~MCEncodedFragment() {
283 MCEncodedFragmentWithFixups::~MCEncodedFragmentWithFixups() {
288 MCSectionData::MCSectionData() : Section(nullptr) {}
290 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
291 : Section(&_Section),
292 Ordinal(~UINT32_C(0)),
294 BundleLockState(NotBundleLocked), BundleGroupBeforeFirstInst(false),
295 HasInstructions(false)
298 A->getSectionList().push_back(this);
301 MCSectionData::iterator
302 MCSectionData::getSubsectionInsertionPoint(unsigned Subsection) {
303 if (Subsection == 0 && SubsectionFragmentMap.empty())
306 SmallVectorImpl<std::pair<unsigned, MCFragment *> >::iterator MI =
307 std::lower_bound(SubsectionFragmentMap.begin(), SubsectionFragmentMap.end(),
308 std::make_pair(Subsection, (MCFragment *)nullptr));
309 bool ExactMatch = false;
310 if (MI != SubsectionFragmentMap.end()) {
311 ExactMatch = MI->first == Subsection;
316 if (MI == SubsectionFragmentMap.end())
320 if (!ExactMatch && Subsection != 0) {
321 // The GNU as documentation claims that subsections have an alignment of 4,
322 // although this appears not to be the case.
323 MCFragment *F = new MCDataFragment();
324 SubsectionFragmentMap.insert(MI, std::make_pair(Subsection, F));
325 getFragmentList().insert(IP, F);
333 MCSymbolData::MCSymbolData() : Symbol(nullptr) {}
335 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
336 uint64_t _Offset, MCAssembler *A)
337 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
338 IsExternal(false), IsPrivateExtern(false),
339 CommonSize(0), SymbolSize(nullptr), CommonAlign(0),
343 A->getSymbolList().push_back(this);
348 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
349 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
351 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
352 OS(OS_), BundleAlignSize(0), RelaxAll(false), NoExecStack(false),
353 SubsectionsViaSymbols(false), ELFHeaderEFlags(0) {
354 VersionMinInfo.Major = 0; // Major version == 0 for "none specified"
357 MCAssembler::~MCAssembler() {
360 void MCAssembler::reset() {
365 IndirectSymbols.clear();
370 SubsectionsViaSymbols = false;
373 // reset objects owned by us
374 getBackend().reset();
375 getEmitter().reset();
377 getLOHContainer().reset();
380 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
381 if (ThumbFuncs.count(Symbol))
384 if (!Symbol->isVariable())
387 // FIXME: It looks like gas supports some cases of the form "foo + 2". It
388 // is not clear if that is a bug or a feature.
389 const MCExpr *Expr = Symbol->getVariableValue();
390 const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr);
394 if (Ref->getKind() != MCSymbolRefExpr::VK_None)
397 const MCSymbol &Sym = Ref->getSymbol();
398 if (!isThumbFunc(&Sym))
401 ThumbFuncs.insert(Symbol); // Cache it.
405 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
406 // Non-temporary labels should always be visible to the linker.
407 if (!Symbol.isTemporary())
410 // Absolute temporary labels are never visible.
411 if (!Symbol.isInSection())
414 // Otherwise, check if the section requires symbols even for temporary labels.
415 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
418 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
419 // Linker visible symbols define atoms.
420 if (isSymbolLinkerVisible(SD->getSymbol()))
423 // Absolute and undefined symbols have no defining atom.
424 if (!SD->getFragment())
427 // Non-linker visible symbols in sections which can't be atomized have no
429 if (!getBackend().isSectionAtomizable(
430 SD->getFragment()->getParent()->getSection()))
433 // Otherwise, return the atom for the containing fragment.
434 return SD->getFragment()->getAtom();
437 // Try to fully compute Expr to an absolute value and if that fails produce
438 // a relocatable expr.
439 // FIXME: Should this be the behavior of EvaluateAsRelocatable itself?
440 static bool evaluate(const MCExpr &Expr, const MCAsmLayout &Layout,
441 const MCFixup &Fixup, MCValue &Target) {
442 if (Expr.EvaluateAsValue(Target, &Layout, &Fixup)) {
443 if (Target.isAbsolute())
446 return Expr.EvaluateAsRelocatable(Target, &Layout, &Fixup);
449 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
450 const MCFixup &Fixup, const MCFragment *DF,
451 MCValue &Target, uint64_t &Value) const {
452 ++stats::evaluateFixup;
454 // FIXME: This code has some duplication with RecordRelocation. We should
455 // probably merge the two into a single callback that tries to evaluate a
456 // fixup and records a relocation if one is needed.
457 const MCExpr *Expr = Fixup.getValue();
458 if (!evaluate(*Expr, Layout, Fixup, Target))
459 getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
461 bool IsPCRel = Backend.getFixupKindInfo(
462 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
466 if (Target.getSymB()) {
468 } else if (!Target.getSymA()) {
471 const MCSymbolRefExpr *A = Target.getSymA();
472 const MCSymbol &SA = A->getSymbol();
473 if (A->getKind() != MCSymbolRefExpr::VK_None ||
474 SA.AliasedSymbol().isUndefined()) {
477 const MCSymbolData &DataA = getSymbolData(SA);
479 getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
484 IsResolved = Target.isAbsolute();
487 Value = Target.getConstant();
489 if (const MCSymbolRefExpr *A = Target.getSymA()) {
490 const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
492 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
494 if (const MCSymbolRefExpr *B = Target.getSymB()) {
495 const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
497 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
501 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
502 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
503 assert((ShouldAlignPC ? IsPCRel : true) &&
504 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
507 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
509 // A number of ARM fixups in Thumb mode require that the effective PC
510 // address be determined as the 32-bit aligned version of the actual offset.
511 if (ShouldAlignPC) Offset &= ~0x3;
515 // Let the backend adjust the fixup value if necessary, including whether
516 // we need a relocation.
517 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
523 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
524 const MCFragment &F) const {
525 switch (F.getKind()) {
526 case MCFragment::FT_Data:
527 case MCFragment::FT_Relaxable:
528 case MCFragment::FT_CompactEncodedInst:
529 return cast<MCEncodedFragment>(F).getContents().size();
530 case MCFragment::FT_Fill:
531 return cast<MCFillFragment>(F).getSize();
533 case MCFragment::FT_LEB:
534 return cast<MCLEBFragment>(F).getContents().size();
536 case MCFragment::FT_Align: {
537 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
538 unsigned Offset = Layout.getFragmentOffset(&AF);
539 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
540 // If we are padding with nops, force the padding to be larger than the
542 if (Size > 0 && AF.hasEmitNops()) {
543 while (Size % getBackend().getMinimumNopSize())
544 Size += AF.getAlignment();
546 if (Size > AF.getMaxBytesToEmit())
551 case MCFragment::FT_Org: {
552 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
553 int64_t TargetLocation;
554 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
555 report_fatal_error("expected assembly-time absolute expression");
557 // FIXME: We need a way to communicate this error.
558 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
559 int64_t Size = TargetLocation - FragmentOffset;
560 if (Size < 0 || Size >= 0x40000000)
561 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
562 "' (at offset '" + Twine(FragmentOffset) + "')");
566 case MCFragment::FT_Dwarf:
567 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
568 case MCFragment::FT_DwarfFrame:
569 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
572 llvm_unreachable("invalid fragment kind");
575 void MCAsmLayout::layoutFragment(MCFragment *F) {
576 MCFragment *Prev = F->getPrevNode();
578 // We should never try to recompute something which is valid.
579 assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
580 // We should never try to compute the fragment layout if its predecessor
582 assert((!Prev || isFragmentValid(Prev)) &&
583 "Attempt to compute fragment before its predecessor!");
585 ++stats::FragmentLayouts;
587 // Compute fragment offset and size.
589 F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
592 LastValidFragment[F->getParent()] = F;
594 // If bundling is enabled and this fragment has instructions in it, it has to
595 // obey the bundling restrictions. With padding, we'll have:
600 // -------------------------------------
601 // Prev |##########| F |
602 // -------------------------------------
607 // The fragment's offset will point to after the padding, and its computed
608 // size won't include the padding.
610 if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
611 assert(isa<MCEncodedFragment>(F) &&
612 "Only MCEncodedFragment implementations have instructions");
613 uint64_t FSize = Assembler.computeFragmentSize(*this, *F);
615 if (FSize > Assembler.getBundleAlignSize())
616 report_fatal_error("Fragment can't be larger than a bundle size");
618 uint64_t RequiredBundlePadding = computeBundlePadding(F, F->Offset, FSize);
619 if (RequiredBundlePadding > UINT8_MAX)
620 report_fatal_error("Padding cannot exceed 255 bytes");
621 F->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
622 F->Offset += RequiredBundlePadding;
626 /// \brief Write the contents of a fragment to the given object writer. Expects
627 /// a MCEncodedFragment.
628 static void writeFragmentContents(const MCFragment &F, MCObjectWriter *OW) {
629 const MCEncodedFragment &EF = cast<MCEncodedFragment>(F);
630 OW->WriteBytes(EF.getContents());
633 /// \brief Write the fragment \p F to the output file.
634 static void writeFragment(const MCAssembler &Asm, const MCAsmLayout &Layout,
635 const MCFragment &F) {
636 MCObjectWriter *OW = &Asm.getWriter();
638 // FIXME: Embed in fragments instead?
639 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
641 // Should NOP padding be written out before this fragment?
642 unsigned BundlePadding = F.getBundlePadding();
643 if (BundlePadding > 0) {
644 assert(Asm.isBundlingEnabled() &&
645 "Writing bundle padding with disabled bundling");
646 assert(F.hasInstructions() &&
647 "Writing bundle padding for a fragment without instructions");
649 unsigned TotalLength = BundlePadding + static_cast<unsigned>(FragmentSize);
650 if (F.alignToBundleEnd() && TotalLength > Asm.getBundleAlignSize()) {
651 // If the padding itself crosses a bundle boundary, it must be emitted
652 // in 2 pieces, since even nop instructions must not cross boundaries.
653 // v--------------v <- BundleAlignSize
654 // v---------v <- BundlePadding
655 // ----------------------------
656 // | Prev |####|####| F |
657 // ----------------------------
658 // ^-------------------^ <- TotalLength
659 unsigned DistanceToBoundary = TotalLength - Asm.getBundleAlignSize();
660 if (!Asm.getBackend().writeNopData(DistanceToBoundary, OW))
661 report_fatal_error("unable to write NOP sequence of " +
662 Twine(DistanceToBoundary) + " bytes");
663 BundlePadding -= DistanceToBoundary;
665 if (!Asm.getBackend().writeNopData(BundlePadding, OW))
666 report_fatal_error("unable to write NOP sequence of " +
667 Twine(BundlePadding) + " bytes");
670 // This variable (and its dummy usage) is to participate in the assert at
671 // the end of the function.
672 uint64_t Start = OW->getStream().tell();
675 ++stats::EmittedFragments;
677 switch (F.getKind()) {
678 case MCFragment::FT_Align: {
679 ++stats::EmittedAlignFragments;
680 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
681 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
683 uint64_t Count = FragmentSize / AF.getValueSize();
685 // FIXME: This error shouldn't actually occur (the front end should emit
686 // multiple .align directives to enforce the semantics it wants), but is
687 // severe enough that we want to report it. How to handle this?
688 if (Count * AF.getValueSize() != FragmentSize)
689 report_fatal_error("undefined .align directive, value size '" +
690 Twine(AF.getValueSize()) +
691 "' is not a divisor of padding size '" +
692 Twine(FragmentSize) + "'");
694 // See if we are aligning with nops, and if so do that first to try to fill
695 // the Count bytes. Then if that did not fill any bytes or there are any
696 // bytes left to fill use the Value and ValueSize to fill the rest.
697 // If we are aligning with nops, ask that target to emit the right data.
698 if (AF.hasEmitNops()) {
699 if (!Asm.getBackend().writeNopData(Count, OW))
700 report_fatal_error("unable to write nop sequence of " +
701 Twine(Count) + " bytes");
705 // Otherwise, write out in multiples of the value size.
706 for (uint64_t i = 0; i != Count; ++i) {
707 switch (AF.getValueSize()) {
708 default: llvm_unreachable("Invalid size!");
709 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
710 case 2: OW->Write16(uint16_t(AF.getValue())); break;
711 case 4: OW->Write32(uint32_t(AF.getValue())); break;
712 case 8: OW->Write64(uint64_t(AF.getValue())); break;
718 case MCFragment::FT_Data:
719 ++stats::EmittedDataFragments;
720 writeFragmentContents(F, OW);
723 case MCFragment::FT_Relaxable:
724 ++stats::EmittedRelaxableFragments;
725 writeFragmentContents(F, OW);
728 case MCFragment::FT_CompactEncodedInst:
729 ++stats::EmittedCompactEncodedInstFragments;
730 writeFragmentContents(F, OW);
733 case MCFragment::FT_Fill: {
734 ++stats::EmittedFillFragments;
735 const MCFillFragment &FF = cast<MCFillFragment>(F);
737 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
739 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
740 switch (FF.getValueSize()) {
741 default: llvm_unreachable("Invalid size!");
742 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
743 case 2: OW->Write16(uint16_t(FF.getValue())); break;
744 case 4: OW->Write32(uint32_t(FF.getValue())); break;
745 case 8: OW->Write64(uint64_t(FF.getValue())); break;
751 case MCFragment::FT_LEB: {
752 const MCLEBFragment &LF = cast<MCLEBFragment>(F);
753 OW->WriteBytes(LF.getContents().str());
757 case MCFragment::FT_Org: {
758 ++stats::EmittedOrgFragments;
759 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
761 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
762 OW->Write8(uint8_t(OF.getValue()));
767 case MCFragment::FT_Dwarf: {
768 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
769 OW->WriteBytes(OF.getContents().str());
772 case MCFragment::FT_DwarfFrame: {
773 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
774 OW->WriteBytes(CF.getContents().str());
779 assert(OW->getStream().tell() - Start == FragmentSize &&
780 "The stream should advance by fragment size");
783 void MCAssembler::writeSectionData(const MCSectionData *SD,
784 const MCAsmLayout &Layout) const {
785 // Ignore virtual sections.
786 if (SD->getSection().isVirtualSection()) {
787 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
789 // Check that contents are only things legal inside a virtual section.
790 for (MCSectionData::const_iterator it = SD->begin(),
791 ie = SD->end(); it != ie; ++it) {
792 switch (it->getKind()) {
793 default: llvm_unreachable("Invalid fragment in virtual section!");
794 case MCFragment::FT_Data: {
795 // Check that we aren't trying to write a non-zero contents (or fixups)
796 // into a virtual section. This is to support clients which use standard
797 // directives to fill the contents of virtual sections.
798 const MCDataFragment &DF = cast<MCDataFragment>(*it);
799 assert(DF.fixup_begin() == DF.fixup_end() &&
800 "Cannot have fixups in virtual section!");
801 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
802 if (DF.getContents()[i]) {
803 if (auto *ELFSec = dyn_cast<const MCSectionELF>(&SD->getSection()))
804 report_fatal_error("non-zero initializer found in section '" +
805 ELFSec->getSectionName() + "'");
807 report_fatal_error("non-zero initializer found in virtual section");
811 case MCFragment::FT_Align:
812 // Check that we aren't trying to write a non-zero value into a virtual
814 assert((cast<MCAlignFragment>(it)->getValueSize() == 0 ||
815 cast<MCAlignFragment>(it)->getValue() == 0) &&
816 "Invalid align in virtual section!");
818 case MCFragment::FT_Fill:
819 assert((cast<MCFillFragment>(it)->getValueSize() == 0 ||
820 cast<MCFillFragment>(it)->getValue() == 0) &&
821 "Invalid fill in virtual section!");
829 uint64_t Start = getWriter().getStream().tell();
832 for (MCSectionData::const_iterator it = SD->begin(), ie = SD->end();
834 writeFragment(*this, Layout, *it);
836 assert(getWriter().getStream().tell() - Start ==
837 Layout.getSectionAddressSize(SD));
840 std::pair<uint64_t, bool> MCAssembler::handleFixup(const MCAsmLayout &Layout,
842 const MCFixup &Fixup) {
843 // Evaluate the fixup.
846 bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
847 MCFixupKindInfo::FKF_IsPCRel;
848 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
849 // The fixup was unresolved, we need a relocation. Inform the object
850 // writer of the relocation, and give it an opportunity to adjust the
851 // fixup value if need be.
852 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, IsPCRel,
855 return std::make_pair(FixedValue, IsPCRel);
858 void MCAssembler::Finish() {
859 DEBUG_WITH_TYPE("mc-dump", {
860 llvm::errs() << "assembler backend - pre-layout\n--\n";
863 // Create the layout object.
864 MCAsmLayout Layout(*this);
866 // Create dummy fragments and assign section ordinals.
867 unsigned SectionIndex = 0;
868 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
869 // Create dummy fragments to eliminate any empty sections, this simplifies
871 if (it->getFragmentList().empty())
872 new MCDataFragment(it);
874 it->setOrdinal(SectionIndex++);
877 // Assign layout order indices to sections and fragments.
878 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
879 MCSectionData *SD = Layout.getSectionOrder()[i];
880 SD->setLayoutOrder(i);
882 unsigned FragmentIndex = 0;
883 for (MCSectionData::iterator iFrag = SD->begin(), iFragEnd = SD->end();
884 iFrag != iFragEnd; ++iFrag)
885 iFrag->setLayoutOrder(FragmentIndex++);
888 // Layout until everything fits.
889 while (layoutOnce(Layout))
892 DEBUG_WITH_TYPE("mc-dump", {
893 llvm::errs() << "assembler backend - post-relaxation\n--\n";
896 // Finalize the layout, including fragment lowering.
897 finishLayout(Layout);
899 DEBUG_WITH_TYPE("mc-dump", {
900 llvm::errs() << "assembler backend - final-layout\n--\n";
903 uint64_t StartOffset = OS.tell();
905 // Allow the object writer a chance to perform post-layout binding (for
906 // example, to set the index fields in the symbol data).
907 getWriter().ExecutePostLayoutBinding(*this, Layout);
909 // Evaluate and apply the fixups, generating relocation entries as necessary.
910 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
911 for (MCSectionData::iterator it2 = it->begin(),
912 ie2 = it->end(); it2 != ie2; ++it2) {
913 MCEncodedFragmentWithFixups *F =
914 dyn_cast<MCEncodedFragmentWithFixups>(it2);
916 for (MCEncodedFragmentWithFixups::fixup_iterator it3 = F->fixup_begin(),
917 ie3 = F->fixup_end(); it3 != ie3; ++it3) {
918 MCFixup &Fixup = *it3;
921 std::tie(FixedValue, IsPCRel) = handleFixup(Layout, *F, Fixup);
922 getBackend().applyFixup(Fixup, F->getContents().data(),
923 F->getContents().size(), FixedValue, IsPCRel);
929 // Write the object file.
930 getWriter().WriteObject(*this, Layout);
932 stats::ObjectBytes += OS.tell() - StartOffset;
935 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
936 const MCRelaxableFragment *DF,
937 const MCAsmLayout &Layout) const {
938 // If we cannot resolve the fixup value, it requires relaxation.
941 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
944 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
947 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
948 const MCAsmLayout &Layout) const {
949 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
950 // are intentionally pushing out inst fragments, or because we relaxed a
951 // previous instruction to one that doesn't need relaxation.
952 if (!getBackend().mayNeedRelaxation(F->getInst()))
955 for (MCRelaxableFragment::const_fixup_iterator it = F->fixup_begin(),
956 ie = F->fixup_end(); it != ie; ++it)
957 if (fixupNeedsRelaxation(*it, F, Layout))
963 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
964 MCRelaxableFragment &F) {
965 if (!fragmentNeedsRelaxation(&F, Layout))
968 ++stats::RelaxedInstructions;
970 // FIXME-PERF: We could immediately lower out instructions if we can tell
971 // they are fully resolved, to avoid retesting on later passes.
973 // Relax the fragment.
976 getBackend().relaxInstruction(F.getInst(), Relaxed);
978 // Encode the new instruction.
980 // FIXME-PERF: If it matters, we could let the target do this. It can
981 // probably do so more efficiently in many cases.
982 SmallVector<MCFixup, 4> Fixups;
983 SmallString<256> Code;
984 raw_svector_ostream VecOS(Code);
985 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
988 // Update the fragment.
990 F.getContents() = Code;
991 F.getFixups() = Fixups;
996 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
997 uint64_t OldSize = LF.getContents().size();
998 int64_t Value = LF.getValue().evaluateKnownAbsolute(Layout);
999 SmallString<8> &Data = LF.getContents();
1001 raw_svector_ostream OSE(Data);
1003 encodeSLEB128(Value, OSE);
1005 encodeULEB128(Value, OSE);
1007 return OldSize != LF.getContents().size();
1010 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1011 MCDwarfLineAddrFragment &DF) {
1012 MCContext &Context = Layout.getAssembler().getContext();
1013 uint64_t OldSize = DF.getContents().size();
1014 int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
1016 LineDelta = DF.getLineDelta();
1017 SmallString<8> &Data = DF.getContents();
1019 raw_svector_ostream OSE(Data);
1020 MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OSE);
1022 return OldSize != Data.size();
1025 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1026 MCDwarfCallFrameFragment &DF) {
1027 MCContext &Context = Layout.getAssembler().getContext();
1028 uint64_t OldSize = DF.getContents().size();
1029 int64_t AddrDelta = DF.getAddrDelta().evaluateKnownAbsolute(Layout);
1030 SmallString<8> &Data = DF.getContents();
1032 raw_svector_ostream OSE(Data);
1033 MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1035 return OldSize != Data.size();
1038 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSectionData &SD) {
1039 // Holds the first fragment which needed relaxing during this layout. It will
1040 // remain NULL if none were relaxed.
1041 // When a fragment is relaxed, all the fragments following it should get
1042 // invalidated because their offset is going to change.
1043 MCFragment *FirstRelaxedFragment = nullptr;
1045 // Attempt to relax all the fragments in the section.
1046 for (MCSectionData::iterator I = SD.begin(), IE = SD.end(); I != IE; ++I) {
1047 // Check if this is a fragment that needs relaxation.
1048 bool RelaxedFrag = false;
1049 switch(I->getKind()) {
1052 case MCFragment::FT_Relaxable:
1053 assert(!getRelaxAll() &&
1054 "Did not expect a MCRelaxableFragment in RelaxAll mode");
1055 RelaxedFrag = relaxInstruction(Layout, *cast<MCRelaxableFragment>(I));
1057 case MCFragment::FT_Dwarf:
1058 RelaxedFrag = relaxDwarfLineAddr(Layout,
1059 *cast<MCDwarfLineAddrFragment>(I));
1061 case MCFragment::FT_DwarfFrame:
1063 relaxDwarfCallFrameFragment(Layout,
1064 *cast<MCDwarfCallFrameFragment>(I));
1066 case MCFragment::FT_LEB:
1067 RelaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(I));
1070 if (RelaxedFrag && !FirstRelaxedFragment)
1071 FirstRelaxedFragment = I;
1073 if (FirstRelaxedFragment) {
1074 Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1080 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1081 ++stats::RelaxationSteps;
1083 bool WasRelaxed = false;
1084 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1085 MCSectionData &SD = *it;
1086 while (layoutSectionOnce(Layout, SD))
1093 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1094 // The layout is done. Mark every fragment as valid.
1095 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1096 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
1100 // Debugging methods
1104 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
1105 OS << "<MCFixup" << " Offset:" << AF.getOffset()
1106 << " Value:" << *AF.getValue()
1107 << " Kind:" << AF.getKind() << ">";
1113 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1114 void MCFragment::dump() {
1115 raw_ostream &OS = llvm::errs();
1118 switch (getKind()) {
1119 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
1120 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
1121 case MCFragment::FT_CompactEncodedInst:
1122 OS << "MCCompactEncodedInstFragment"; break;
1123 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
1124 case MCFragment::FT_Relaxable: OS << "MCRelaxableFragment"; break;
1125 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
1126 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
1127 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
1128 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
1131 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
1132 << " Offset:" << Offset
1133 << " HasInstructions:" << hasInstructions()
1134 << " BundlePadding:" << static_cast<unsigned>(getBundlePadding()) << ">";
1136 switch (getKind()) {
1137 case MCFragment::FT_Align: {
1138 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
1139 if (AF->hasEmitNops())
1140 OS << " (emit nops)";
1142 OS << " Alignment:" << AF->getAlignment()
1143 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
1144 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
1147 case MCFragment::FT_Data: {
1148 const MCDataFragment *DF = cast<MCDataFragment>(this);
1150 OS << " Contents:[";
1151 const SmallVectorImpl<char> &Contents = DF->getContents();
1152 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1154 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1156 OS << "] (" << Contents.size() << " bytes)";
1158 if (DF->fixup_begin() != DF->fixup_end()) {
1161 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
1162 ie = DF->fixup_end(); it != ie; ++it) {
1163 if (it != DF->fixup_begin()) OS << ",\n ";
1170 case MCFragment::FT_CompactEncodedInst: {
1171 const MCCompactEncodedInstFragment *CEIF =
1172 cast<MCCompactEncodedInstFragment>(this);
1174 OS << " Contents:[";
1175 const SmallVectorImpl<char> &Contents = CEIF->getContents();
1176 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
1178 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
1180 OS << "] (" << Contents.size() << " bytes)";
1183 case MCFragment::FT_Fill: {
1184 const MCFillFragment *FF = cast<MCFillFragment>(this);
1185 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
1186 << " Size:" << FF->getSize();
1189 case MCFragment::FT_Relaxable: {
1190 const MCRelaxableFragment *F = cast<MCRelaxableFragment>(this);
1193 F->getInst().dump_pretty(OS);
1196 case MCFragment::FT_Org: {
1197 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
1199 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
1202 case MCFragment::FT_Dwarf: {
1203 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
1205 OS << " AddrDelta:" << OF->getAddrDelta()
1206 << " LineDelta:" << OF->getLineDelta();
1209 case MCFragment::FT_DwarfFrame: {
1210 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
1212 OS << " AddrDelta:" << CF->getAddrDelta();
1215 case MCFragment::FT_LEB: {
1216 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
1218 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
1225 void MCSectionData::dump() {
1226 raw_ostream &OS = llvm::errs();
1228 OS << "<MCSectionData";
1229 OS << " Alignment:" << getAlignment()
1230 << " Fragments:[\n ";
1231 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1232 if (it != begin()) OS << ",\n ";
1238 void MCSymbolData::dump() const {
1239 raw_ostream &OS = llvm::errs();
1241 OS << "<MCSymbolData Symbol:" << getSymbol()
1242 << " Fragment:" << getFragment() << " Offset:" << getOffset()
1243 << " Flags:" << getFlags() << " Index:" << getIndex();
1245 OS << " (common, size:" << getCommonSize()
1246 << " align: " << getCommonAlignment() << ")";
1248 OS << " (external)";
1249 if (isPrivateExtern())
1250 OS << " (private extern)";
1254 void MCAssembler::dump() {
1255 raw_ostream &OS = llvm::errs();
1257 OS << "<MCAssembler\n";
1258 OS << " Sections:[\n ";
1259 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1260 if (it != begin()) OS << ",\n ";
1266 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1267 if (it != symbol_begin()) OS << ",\n ";
1274 // anchors for MC*Fragment vtables
1275 void MCEncodedFragment::anchor() { }
1276 void MCEncodedFragmentWithFixups::anchor() { }
1277 void MCDataFragment::anchor() { }
1278 void MCCompactEncodedInstFragment::anchor() { }
1279 void MCRelaxableFragment::anchor() { }
1280 void MCAlignFragment::anchor() { }
1281 void MCFillFragment::anchor() { }
1282 void MCOrgFragment::anchor() { }
1283 void MCLEBFragment::anchor() { }
1284 void MCDwarfLineAddrFragment::anchor() { }
1285 void MCDwarfCallFrameFragment::anchor() { }