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 #define DEBUG_TYPE "assembler"
11 #include "llvm/MC/MCAssembler.h"
12 #include "llvm/MC/MCAsmLayout.h"
13 #include "llvm/MC/MCCodeEmitter.h"
14 #include "llvm/MC/MCExpr.h"
15 #include "llvm/MC/MCObjectWriter.h"
16 #include "llvm/MC/MCSymbol.h"
17 #include "llvm/MC/MCValue.h"
18 #include "llvm/ADT/OwningPtr.h"
19 #include "llvm/ADT/Statistic.h"
20 #include "llvm/ADT/StringExtras.h"
21 #include "llvm/ADT/Twine.h"
22 #include "llvm/Support/Debug.h"
23 #include "llvm/Support/ErrorHandling.h"
24 #include "llvm/Support/raw_ostream.h"
25 #include "llvm/Target/TargetRegistry.h"
26 #include "llvm/Target/TargetAsmBackend.h"
33 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
34 STATISTIC(EvaluateFixup, "Number of evaluated fixups");
35 STATISTIC(FragmentLayouts, "Number of fragment layouts");
36 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
37 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
38 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
39 STATISTIC(SectionLayouts, "Number of section layouts");
43 // FIXME FIXME FIXME: There are number of places in this file where we convert
44 // what is a 64-bit assembler value used for computation into a value in the
45 // object file, which may truncate it. We should detect that truncation where
46 // invalid and report errors back.
50 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
51 : Assembler(Asm), LastValidFragment(0)
53 // Compute the section layout order. Virtual sections must go last.
54 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
55 if (!Asm.getBackend().isVirtualSection(it->getSection()))
56 SectionOrder.push_back(&*it);
57 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
58 if (Asm.getBackend().isVirtualSection(it->getSection()))
59 SectionOrder.push_back(&*it);
62 bool MCAsmLayout::isSectionUpToDate(const MCSectionData *SD) const {
63 // The first section is always up-to-date.
64 unsigned Index = SD->getLayoutOrder();
68 // Otherwise, sections are always implicitly computed when the preceeding
69 // fragment is layed out.
70 const MCSectionData *Prev = getSectionOrder()[Index - 1];
71 return isFragmentUpToDate(&(Prev->getFragmentList().back()));
74 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
75 return (LastValidFragment &&
76 F->getLayoutOrder() <= LastValidFragment->getLayoutOrder());
79 void MCAsmLayout::UpdateForSlide(MCFragment *F, int SlideAmount) {
80 // If this fragment wasn't already up-to-date, we don't need to do anything.
81 if (!isFragmentUpToDate(F))
84 // Otherwise, reset the last valid fragment to the predecessor of the
85 // invalidated fragment.
86 LastValidFragment = F->getPrevNode();
87 if (!LastValidFragment) {
88 unsigned Index = F->getParent()->getLayoutOrder();
90 MCSectionData *Prev = getSectionOrder()[Index - 1];
91 LastValidFragment = &(Prev->getFragmentList().back());
96 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
97 // Advance the layout position until the fragment is up-to-date.
98 while (!isFragmentUpToDate(F)) {
99 // Advance to the next fragment.
100 MCFragment *Cur = LastValidFragment;
102 Cur = Cur->getNextNode();
104 unsigned NextIndex = 0;
105 if (LastValidFragment)
106 NextIndex = LastValidFragment->getParent()->getLayoutOrder() + 1;
107 Cur = SectionOrder[NextIndex]->begin();
110 const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
114 void MCAsmLayout::FragmentReplaced(MCFragment *Src, MCFragment *Dst) {
115 if (LastValidFragment == Src)
116 LastValidFragment = Dst;
118 Dst->Offset = Src->Offset;
119 Dst->EffectiveSize = Src->EffectiveSize;
122 uint64_t MCAsmLayout::getFragmentAddress(const MCFragment *F) const {
123 assert(F->getParent() && "Missing section()!");
124 return getSectionAddress(F->getParent()) + getFragmentOffset(F);
127 uint64_t MCAsmLayout::getFragmentEffectiveSize(const MCFragment *F) const {
129 assert(F->EffectiveSize != ~UINT64_C(0) && "Address not set!");
130 return F->EffectiveSize;
133 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
135 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
139 uint64_t MCAsmLayout::getSymbolAddress(const MCSymbolData *SD) const {
140 assert(SD->getFragment() && "Invalid getAddress() on undefined symbol!");
141 return getFragmentAddress(SD->getFragment()) + SD->getOffset();
144 uint64_t MCAsmLayout::getSectionAddress(const MCSectionData *SD) const {
145 EnsureValid(SD->begin());
146 assert(SD->Address != ~UINT64_C(0) && "Address not set!");
150 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
151 // The size is the last fragment's end offset.
152 const MCFragment &F = SD->getFragmentList().back();
153 return getFragmentOffset(&F) + getFragmentEffectiveSize(&F);
156 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
157 // Virtual sections have no file size.
158 if (getAssembler().getBackend().isVirtualSection(SD->getSection()))
161 // Otherwise, the file size is the same as the address space size.
162 return getSectionAddressSize(SD);
165 uint64_t MCAsmLayout::getSectionSize(const MCSectionData *SD) const {
166 // The logical size is the address space size minus any tail padding.
167 uint64_t Size = getSectionAddressSize(SD);
168 const MCAlignFragment *AF =
169 dyn_cast<MCAlignFragment>(&(SD->getFragmentList().back()));
170 if (AF && AF->hasOnlyAlignAddress())
171 Size -= getFragmentEffectiveSize(AF);
178 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
181 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
182 : Kind(_Kind), Parent(_Parent), Atom(0), EffectiveSize(~UINT64_C(0))
185 Parent->getFragmentList().push_back(this);
190 MCSectionData::MCSectionData() : Section(0) {}
192 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
193 : Section(&_Section),
195 Address(~UINT64_C(0)),
196 HasInstructions(false)
199 A->getSectionList().push_back(this);
204 MCSymbolData::MCSymbolData() : Symbol(0) {}
206 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
207 uint64_t _Offset, MCAssembler *A)
208 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
209 IsExternal(false), IsPrivateExtern(false),
210 CommonSize(0), CommonAlign(0), Flags(0), Index(0)
213 A->getSymbolList().push_back(this);
218 MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
219 MCCodeEmitter &_Emitter, raw_ostream &_OS)
220 : Context(_Context), Backend(_Backend), Emitter(_Emitter),
221 OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false)
225 MCAssembler::~MCAssembler() {
228 static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
229 const MCFixup &Fixup,
230 const MCValue Target,
231 const MCSection *BaseSection) {
232 // The effective fixup address is
233 // addr(atom(A)) + offset(A)
234 // - addr(atom(B)) - offset(B)
235 // - addr(<base symbol>) + <fixup offset from base symbol>
236 // and the offsets are not relocatable, so the fixup is fully resolved when
237 // addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
239 // The simple (Darwin, except on x86_64) way of dealing with this was to
240 // assume that any reference to a temporary symbol *must* be a temporary
241 // symbol in the same atom, unless the sections differ. Therefore, any PCrel
242 // relocation to a temporary symbol (in the same section) is fully
243 // resolved. This also works in conjunction with absolutized .set, which
244 // requires the compiler to use .set to absolutize the differences between
245 // symbols which the compiler knows to be assembly time constants, so we don't
246 // need to worry about considering symbol differences fully resolved.
248 // Non-relative fixups are only resolved if constant.
250 return Target.isAbsolute();
252 // Otherwise, relative fixups are only resolved if not a difference and the
253 // target is a temporary in the same section.
254 if (Target.isAbsolute() || Target.getSymB())
257 const MCSymbol *A = &Target.getSymA()->getSymbol();
258 if (!A->isTemporary() || !A->isInSection() ||
259 &A->getSection() != BaseSection)
265 static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
266 const MCAsmLayout &Layout,
267 const MCFixup &Fixup,
268 const MCValue Target,
269 const MCSymbolData *BaseSymbol) {
270 // The effective fixup address is
271 // addr(atom(A)) + offset(A)
272 // - addr(atom(B)) - offset(B)
273 // - addr(BaseSymbol) + <fixup offset from base symbol>
274 // and the offsets are not relocatable, so the fixup is fully resolved when
275 // addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
277 // Note that "false" is almost always conservatively correct (it means we emit
278 // a relocation which is unnecessary), except when it would force us to emit a
279 // relocation which the target cannot encode.
281 const MCSymbolData *A_Base = 0, *B_Base = 0;
282 if (const MCSymbolRefExpr *A = Target.getSymA()) {
283 // Modified symbol references cannot be resolved.
284 if (A->getKind() != MCSymbolRefExpr::VK_None)
287 A_Base = Asm.getAtom(Layout, &Asm.getSymbolData(A->getSymbol()));
292 if (const MCSymbolRefExpr *B = Target.getSymB()) {
293 // Modified symbol references cannot be resolved.
294 if (B->getKind() != MCSymbolRefExpr::VK_None)
297 B_Base = Asm.getAtom(Layout, &Asm.getSymbolData(B->getSymbol()));
302 // If there is no base, A and B have to be the same atom for this fixup to be
305 return A_Base == B_Base;
307 // Otherwise, B must be missing and A must be the base.
308 return !B_Base && BaseSymbol == A_Base;
311 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
312 // Non-temporary labels should always be visible to the linker.
313 if (!Symbol.isTemporary())
316 // Absolute temporary labels are never visible.
317 if (!Symbol.isInSection())
320 // Otherwise, check if the section requires symbols even for temporary labels.
321 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
324 const MCSymbolData *MCAssembler::getAtom(const MCAsmLayout &Layout,
325 const MCSymbolData *SD) const {
326 // Linker visible symbols define atoms.
327 if (isSymbolLinkerVisible(SD->getSymbol()))
330 // Absolute and undefined symbols have no defining atom.
331 if (!SD->getFragment())
334 // Non-linker visible symbols in sections which can't be atomized have no
336 if (!getBackend().isSectionAtomizable(
337 SD->getFragment()->getParent()->getSection()))
340 // Otherwise, return the atom for the containing fragment.
341 return SD->getFragment()->getAtom();
344 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
345 const MCFixup &Fixup, const MCFragment *DF,
346 MCValue &Target, uint64_t &Value) const {
347 ++stats::EvaluateFixup;
349 if (!Fixup.getValue()->EvaluateAsRelocatable(Target, &Layout))
350 report_fatal_error("expected relocatable expression");
352 // FIXME: How do non-scattered symbols work in ELF? I presume the linker
353 // doesn't support small relocations, but then under what criteria does the
354 // assembler allow symbol differences?
356 Value = Target.getConstant();
358 bool IsPCRel = Emitter.getFixupKindInfo(
359 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
360 bool IsResolved = true;
361 if (const MCSymbolRefExpr *A = Target.getSymA()) {
362 if (A->getSymbol().isDefined())
363 Value += Layout.getSymbolAddress(&getSymbolData(A->getSymbol()));
367 if (const MCSymbolRefExpr *B = Target.getSymB()) {
368 if (B->getSymbol().isDefined())
369 Value -= Layout.getSymbolAddress(&getSymbolData(B->getSymbol()));
374 // If we are using scattered symbols, determine whether this value is actually
375 // resolved; scattering may cause atoms to move.
376 if (IsResolved && getBackend().hasScatteredSymbols()) {
377 if (getBackend().hasReliableSymbolDifference()) {
378 // If this is a PCrel relocation, find the base atom (identified by its
379 // symbol) that the fixup value is relative to.
380 const MCSymbolData *BaseSymbol = 0;
382 BaseSymbol = DF->getAtom();
388 IsResolved = isScatteredFixupFullyResolved(*this, Layout, Fixup, Target,
391 const MCSection *BaseSection = 0;
393 BaseSection = &DF->getParent()->getSection();
395 IsResolved = isScatteredFixupFullyResolvedSimple(*this, Fixup, Target,
401 Value -= Layout.getFragmentAddress(DF) + Fixup.getOffset();
406 uint64_t MCAssembler::ComputeFragmentSize(MCAsmLayout &Layout,
408 uint64_t SectionAddress,
409 uint64_t FragmentOffset) const {
410 switch (F.getKind()) {
411 case MCFragment::FT_Data:
412 return cast<MCDataFragment>(F).getContents().size();
413 case MCFragment::FT_Fill:
414 return cast<MCFillFragment>(F).getSize();
415 case MCFragment::FT_Inst:
416 return cast<MCInstFragment>(F).getInstSize();
418 case MCFragment::FT_Align: {
419 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
421 assert((!AF.hasOnlyAlignAddress() || !AF.getNextNode()) &&
422 "Invalid OnlyAlignAddress bit, not the last fragment!");
424 uint64_t Size = OffsetToAlignment(SectionAddress + FragmentOffset,
427 // Honor MaxBytesToEmit.
428 if (Size > AF.getMaxBytesToEmit())
434 case MCFragment::FT_Org: {
435 const MCOrgFragment &OF = cast<MCOrgFragment>(F);
437 // FIXME: We should compute this sooner, we don't want to recurse here, and
438 // we would like to be more functional.
439 int64_t TargetLocation;
440 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, &Layout))
441 report_fatal_error("expected assembly-time absolute expression");
443 // FIXME: We need a way to communicate this error.
444 int64_t Offset = TargetLocation - FragmentOffset;
446 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
447 "' (at offset '" + Twine(FragmentOffset) + "'");
453 assert(0 && "invalid fragment kind");
457 void MCAsmLayout::LayoutFile() {
458 // Initialize the first section and set the valid fragment layout point. All
459 // actual layout computations are done lazily.
460 LastValidFragment = 0;
461 if (!getSectionOrder().empty())
462 getSectionOrder().front()->Address = 0;
465 void MCAsmLayout::LayoutFragment(MCFragment *F) {
466 MCFragment *Prev = F->getPrevNode();
468 // We should never try to recompute something which is up-to-date.
469 assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
470 // We should never try to compute the fragment layout if the section isn't
472 assert(isSectionUpToDate(F->getParent()) &&
473 "Attempt to compute fragment before it's section!");
474 // We should never try to compute the fragment layout if it's predecessor
476 assert((!Prev || isFragmentUpToDate(Prev)) &&
477 "Attempt to compute fragment before it's predecessor!");
479 ++stats::FragmentLayouts;
481 // Compute the fragment start address.
482 uint64_t StartAddress = F->getParent()->Address;
483 uint64_t Address = StartAddress;
485 Address += Prev->Offset + Prev->EffectiveSize;
487 // Compute fragment offset and size.
488 F->Offset = Address - StartAddress;
489 F->EffectiveSize = getAssembler().ComputeFragmentSize(*this, *F, StartAddress,
491 LastValidFragment = F;
493 // If this is the last fragment in a section, update the next section address.
494 if (!F->getNextNode()) {
495 unsigned NextIndex = F->getParent()->getLayoutOrder() + 1;
496 if (NextIndex != getSectionOrder().size())
497 LayoutSection(getSectionOrder()[NextIndex]);
501 void MCAsmLayout::LayoutSection(MCSectionData *SD) {
502 unsigned SectionOrderIndex = SD->getLayoutOrder();
504 ++stats::SectionLayouts;
506 // Compute the section start address.
507 uint64_t StartAddress = 0;
508 if (SectionOrderIndex) {
509 MCSectionData *Prev = getSectionOrder()[SectionOrderIndex - 1];
510 StartAddress = getSectionAddress(Prev) + getSectionAddressSize(Prev);
513 // Honor the section alignment requirements.
514 StartAddress = RoundUpToAlignment(StartAddress, SD->getAlignment());
516 // Set the section address.
517 SD->Address = StartAddress;
520 /// WriteFragmentData - Write the \arg F data to the output file.
521 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
522 const MCFragment &F, MCObjectWriter *OW) {
523 uint64_t Start = OW->getStream().tell();
526 ++stats::EmittedFragments;
528 // FIXME: Embed in fragments instead?
529 uint64_t FragmentSize = Layout.getFragmentEffectiveSize(&F);
530 switch (F.getKind()) {
531 case MCFragment::FT_Align: {
532 MCAlignFragment &AF = cast<MCAlignFragment>(F);
533 uint64_t Count = FragmentSize / AF.getValueSize();
535 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
537 // FIXME: This error shouldn't actually occur (the front end should emit
538 // multiple .align directives to enforce the semantics it wants), but is
539 // severe enough that we want to report it. How to handle this?
540 if (Count * AF.getValueSize() != FragmentSize)
541 report_fatal_error("undefined .align directive, value size '" +
542 Twine(AF.getValueSize()) +
543 "' is not a divisor of padding size '" +
544 Twine(FragmentSize) + "'");
546 // See if we are aligning with nops, and if so do that first to try to fill
547 // the Count bytes. Then if that did not fill any bytes or there are any
548 // bytes left to fill use the the Value and ValueSize to fill the rest.
549 // If we are aligning with nops, ask that target to emit the right data.
550 if (AF.hasEmitNops()) {
551 if (!Asm.getBackend().WriteNopData(Count, OW))
552 report_fatal_error("unable to write nop sequence of " +
553 Twine(Count) + " bytes");
557 // Otherwise, write out in multiples of the value size.
558 for (uint64_t i = 0; i != Count; ++i) {
559 switch (AF.getValueSize()) {
561 assert(0 && "Invalid size!");
562 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
563 case 2: OW->Write16(uint16_t(AF.getValue())); break;
564 case 4: OW->Write32(uint32_t(AF.getValue())); break;
565 case 8: OW->Write64(uint64_t(AF.getValue())); break;
571 case MCFragment::FT_Data: {
572 MCDataFragment &DF = cast<MCDataFragment>(F);
573 assert(FragmentSize == DF.getContents().size() && "Invalid size!");
574 OW->WriteBytes(DF.getContents().str());
578 case MCFragment::FT_Fill: {
579 MCFillFragment &FF = cast<MCFillFragment>(F);
581 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
583 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
584 switch (FF.getValueSize()) {
586 assert(0 && "Invalid size!");
587 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
588 case 2: OW->Write16(uint16_t(FF.getValue())); break;
589 case 4: OW->Write32(uint32_t(FF.getValue())); break;
590 case 8: OW->Write64(uint64_t(FF.getValue())); break;
596 case MCFragment::FT_Inst:
597 llvm_unreachable("unexpected inst fragment after lowering");
600 case MCFragment::FT_Org: {
601 MCOrgFragment &OF = cast<MCOrgFragment>(F);
603 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
604 OW->Write8(uint8_t(OF.getValue()));
610 assert(OW->getStream().tell() - Start == FragmentSize);
613 void MCAssembler::WriteSectionData(const MCSectionData *SD,
614 const MCAsmLayout &Layout,
615 MCObjectWriter *OW) const {
616 // Ignore virtual sections.
617 if (getBackend().isVirtualSection(SD->getSection())) {
618 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
620 // Check that contents are only things legal inside a virtual section.
621 for (MCSectionData::const_iterator it = SD->begin(),
622 ie = SD->end(); it != ie; ++it) {
623 switch (it->getKind()) {
625 assert(0 && "Invalid fragment in virtual section!");
626 case MCFragment::FT_Align:
627 assert(!cast<MCAlignFragment>(it)->getValueSize() &&
628 "Invalid align in virtual section!");
630 case MCFragment::FT_Fill:
631 assert(!cast<MCFillFragment>(it)->getValueSize() &&
632 "Invalid fill in virtual section!");
640 uint64_t Start = OW->getStream().tell();
643 for (MCSectionData::const_iterator it = SD->begin(),
644 ie = SD->end(); it != ie; ++it)
645 WriteFragmentData(*this, Layout, *it, OW);
647 assert(OW->getStream().tell() - Start == Layout.getSectionFileSize(SD));
650 void MCAssembler::Finish() {
651 DEBUG_WITH_TYPE("mc-dump", {
652 llvm::errs() << "assembler backend - pre-layout\n--\n";
655 // Create the layout object.
656 MCAsmLayout Layout(*this);
658 // Insert additional align fragments for concrete sections to explicitly pad
659 // the previous section to match their alignment requirements. This is for
660 // 'gas' compatibility, it shouldn't strictly be necessary.
662 // FIXME: This may be Mach-O specific.
663 for (unsigned i = 1, e = Layout.getSectionOrder().size(); i < e; ++i) {
664 MCSectionData *SD = Layout.getSectionOrder()[i];
666 // Ignore sections without alignment requirements.
667 unsigned Align = SD->getAlignment();
671 // Ignore virtual sections, they don't cause file size modifications.
672 if (getBackend().isVirtualSection(SD->getSection()))
675 // Otherwise, create a new align fragment at the end of the previous
677 MCAlignFragment *AF = new MCAlignFragment(Align, 0, 1, Align,
678 Layout.getSectionOrder()[i - 1]);
679 AF->setOnlyAlignAddress(true);
682 // Create dummy fragments and assign section ordinals.
683 unsigned SectionIndex = 0;
684 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
685 // Create dummy fragments to eliminate any empty sections, this simplifies
687 if (it->getFragmentList().empty())
688 new MCFillFragment(0, 1, 0, it);
690 it->setOrdinal(SectionIndex++);
693 // Assign layout order indices to sections and fragments.
694 unsigned FragmentIndex = 0;
695 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
696 MCSectionData *SD = Layout.getSectionOrder()[i];
697 SD->setLayoutOrder(i);
699 for (MCSectionData::iterator it2 = SD->begin(),
700 ie2 = SD->end(); it2 != ie2; ++it2)
701 it2->setLayoutOrder(FragmentIndex++);
704 // Layout until everything fits.
705 while (LayoutOnce(Layout))
708 DEBUG_WITH_TYPE("mc-dump", {
709 llvm::errs() << "assembler backend - post-relaxation\n--\n";
712 // Finalize the layout, including fragment lowering.
713 FinishLayout(Layout);
715 DEBUG_WITH_TYPE("mc-dump", {
716 llvm::errs() << "assembler backend - final-layout\n--\n";
719 uint64_t StartOffset = OS.tell();
720 llvm::OwningPtr<MCObjectWriter> Writer(getBackend().createObjectWriter(OS));
722 report_fatal_error("unable to create object writer!");
724 // Allow the object writer a chance to perform post-layout binding (for
725 // example, to set the index fields in the symbol data).
726 Writer->ExecutePostLayoutBinding(*this);
728 // Evaluate and apply the fixups, generating relocation entries as necessary.
729 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
730 for (MCSectionData::iterator it2 = it->begin(),
731 ie2 = it->end(); it2 != ie2; ++it2) {
732 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
736 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
737 ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
738 MCFixup &Fixup = *it3;
740 // Evaluate the fixup.
743 if (!EvaluateFixup(Layout, Fixup, DF, Target, FixedValue)) {
744 // The fixup was unresolved, we need a relocation. Inform the object
745 // writer of the relocation, and give it an opportunity to adjust the
746 // fixup value if need be.
747 Writer->RecordRelocation(*this, Layout, DF, Fixup, Target,FixedValue);
750 getBackend().ApplyFixup(Fixup, *DF, FixedValue);
755 // Write the object file.
756 Writer->WriteObject(*this, Layout);
758 stats::ObjectBytes += OS.tell() - StartOffset;
761 bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
762 const MCFragment *DF,
763 const MCAsmLayout &Layout) const {
767 // If we cannot resolve the fixup value, it requires relaxation.
770 if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
773 // Otherwise, relax if the value is too big for a (signed) i8.
775 // FIXME: This is target dependent!
776 return int64_t(Value) != int64_t(int8_t(Value));
779 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
780 const MCAsmLayout &Layout) const {
781 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
782 // are intentionally pushing out inst fragments, or because we relaxed a
783 // previous instruction to one that doesn't need relaxation.
784 if (!getBackend().MayNeedRelaxation(IF->getInst()))
787 for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
788 ie = IF->fixup_end(); it != ie; ++it)
789 if (FixupNeedsRelaxation(*it, IF, Layout))
795 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
796 ++stats::RelaxationSteps;
798 // Layout the sections in order.
801 // Scan for fragments that need relaxation.
802 bool WasRelaxed = false;
803 for (iterator it = begin(), ie = end(); it != ie; ++it) {
804 MCSectionData &SD = *it;
806 for (MCSectionData::iterator it2 = SD.begin(),
807 ie2 = SD.end(); it2 != ie2; ++it2) {
808 // Check if this is an instruction fragment that needs relaxation.
809 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
810 if (!IF || !FragmentNeedsRelaxation(IF, Layout))
813 ++stats::RelaxedInstructions;
815 // FIXME-PERF: We could immediately lower out instructions if we can tell
816 // they are fully resolved, to avoid retesting on later passes.
818 // Relax the fragment.
821 getBackend().RelaxInstruction(IF->getInst(), Relaxed);
823 // Encode the new instruction.
825 // FIXME-PERF: If it matters, we could let the target do this. It can
826 // probably do so more efficiently in many cases.
827 SmallVector<MCFixup, 4> Fixups;
828 SmallString<256> Code;
829 raw_svector_ostream VecOS(Code);
830 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
833 // Update the instruction fragment.
834 int SlideAmount = Code.size() - IF->getInstSize();
835 IF->setInst(Relaxed);
836 IF->getCode() = Code;
837 IF->getFixups().clear();
838 // FIXME: Eliminate copy.
839 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
840 IF->getFixups().push_back(Fixups[i]);
842 // Update the layout, and remember that we relaxed.
843 Layout.UpdateForSlide(IF, SlideAmount);
851 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
852 // Lower out any instruction fragments, to simplify the fixup application and
855 // FIXME-PERF: We don't have to do this, but the assumption is that it is
856 // cheap (we will mostly end up eliminating fragments and appending on to data
857 // fragments), so the extra complexity downstream isn't worth it. Evaluate
859 for (iterator it = begin(), ie = end(); it != ie; ++it) {
860 MCSectionData &SD = *it;
862 for (MCSectionData::iterator it2 = SD.begin(),
863 ie2 = SD.end(); it2 != ie2; ++it2) {
864 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
868 // Create a new data fragment for the instruction.
870 // FIXME-PERF: Reuse previous data fragment if possible.
871 MCDataFragment *DF = new MCDataFragment();
872 SD.getFragmentList().insert(it2, DF);
874 // Update the data fragments layout data.
875 DF->setParent(IF->getParent());
876 DF->setAtom(IF->getAtom());
877 DF->setLayoutOrder(IF->getLayoutOrder());
878 Layout.FragmentReplaced(IF, DF);
880 // Copy in the data and the fixups.
881 DF->getContents().append(IF->getCode().begin(), IF->getCode().end());
882 for (unsigned i = 0, e = IF->getFixups().size(); i != e; ++i)
883 DF->getFixups().push_back(IF->getFixups()[i]);
885 // Delete the instruction fragment and update the iterator.
886 SD.getFragmentList().erase(IF);
896 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
897 OS << "<MCFixup" << " Offset:" << AF.getOffset()
898 << " Value:" << *AF.getValue()
899 << " Kind:" << AF.getKind() << ">";
905 void MCFragment::dump() {
906 raw_ostream &OS = llvm::errs();
910 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
911 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
912 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
913 case MCFragment::FT_Inst: OS << "MCInstFragment"; break;
914 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
917 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
918 << " Offset:" << Offset << " EffectiveSize:" << EffectiveSize << ">";
921 case MCFragment::FT_Align: {
922 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
923 if (AF->hasEmitNops())
924 OS << " (emit nops)";
925 if (AF->hasOnlyAlignAddress())
926 OS << " (only align section)";
928 OS << " Alignment:" << AF->getAlignment()
929 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
930 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
933 case MCFragment::FT_Data: {
934 const MCDataFragment *DF = cast<MCDataFragment>(this);
937 const SmallVectorImpl<char> &Contents = DF->getContents();
938 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
940 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
942 OS << "] (" << Contents.size() << " bytes)";
944 if (!DF->getFixups().empty()) {
947 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
948 ie = DF->fixup_end(); it != ie; ++it) {
949 if (it != DF->fixup_begin()) OS << ",\n ";
956 case MCFragment::FT_Fill: {
957 const MCFillFragment *FF = cast<MCFillFragment>(this);
958 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
959 << " Size:" << FF->getSize();
962 case MCFragment::FT_Inst: {
963 const MCInstFragment *IF = cast<MCInstFragment>(this);
966 IF->getInst().dump_pretty(OS);
969 case MCFragment::FT_Org: {
970 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
972 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
979 void MCSectionData::dump() {
980 raw_ostream &OS = llvm::errs();
982 OS << "<MCSectionData";
983 OS << " Alignment:" << getAlignment() << " Address:" << Address
984 << " Fragments:[\n ";
985 for (iterator it = begin(), ie = end(); it != ie; ++it) {
986 if (it != begin()) OS << ",\n ";
992 void MCSymbolData::dump() {
993 raw_ostream &OS = llvm::errs();
995 OS << "<MCSymbolData Symbol:" << getSymbol()
996 << " Fragment:" << getFragment() << " Offset:" << getOffset()
997 << " Flags:" << getFlags() << " Index:" << getIndex();
999 OS << " (common, size:" << getCommonSize()
1000 << " align: " << getCommonAlignment() << ")";
1002 OS << " (external)";
1003 if (isPrivateExtern())
1004 OS << " (private extern)";
1008 void MCAssembler::dump() {
1009 raw_ostream &OS = llvm::errs();
1011 OS << "<MCAssembler\n";
1012 OS << " Sections:[\n ";
1013 for (iterator it = begin(), ie = end(); it != ie; ++it) {
1014 if (it != begin()) OS << ",\n ";
1020 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1021 if (it != symbol_begin()) OS << ",\n ";