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) : Assembler(Asm) {
51 // Compute the section layout order. Virtual sections must go last.
52 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
53 if (!Asm.getBackend().isVirtualSection(it->getSection()))
54 SectionOrder.push_back(&*it);
55 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
56 if (Asm.getBackend().isVirtualSection(it->getSection()))
57 SectionOrder.push_back(&*it);
60 void MCAsmLayout::UpdateForSlide(MCFragment *F, int SlideAmount) {
61 // We shouldn't have to do anything special to support negative slides, and it
62 // is a perfectly valid thing to do as long as other parts of the system can
63 // guarantee convergence.
64 assert(SlideAmount >= 0 && "Negative slides not yet supported");
66 // Update the layout by simply recomputing the layout for the entire
67 // file. This is trivially correct, but very slow.
69 // FIXME-PERF: This is O(N^2), but will be eliminated once we get smarter.
71 // Layout the sections in order.
72 for (unsigned i = 0, e = getSectionOrder().size(); i != e; ++i)
73 getAssembler().LayoutSection(*this, i);
76 uint64_t MCAsmLayout::getFragmentAddress(const MCFragment *F) const {
77 assert(F->getParent() && "Missing section()!");
78 return getSectionAddress(F->getParent()) + getFragmentOffset(F);
81 uint64_t MCAsmLayout::getFragmentEffectiveSize(const MCFragment *F) const {
82 assert(F->EffectiveSize != ~UINT64_C(0) && "Address not set!");
83 return F->EffectiveSize;
86 void MCAsmLayout::setFragmentEffectiveSize(MCFragment *F, uint64_t Value) {
87 F->EffectiveSize = Value;
90 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
91 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
95 void MCAsmLayout::setFragmentOffset(MCFragment *F, uint64_t Value) {
99 uint64_t MCAsmLayout::getSymbolAddress(const MCSymbolData *SD) const {
100 assert(SD->getFragment() && "Invalid getAddress() on undefined symbol!");
101 return getFragmentAddress(SD->getFragment()) + SD->getOffset();
104 uint64_t MCAsmLayout::getSectionAddress(const MCSectionData *SD) const {
105 assert(SD->Address != ~UINT64_C(0) && "Address not set!");
109 void MCAsmLayout::setSectionAddress(MCSectionData *SD, uint64_t Value) {
113 uint64_t MCAsmLayout::getSectionSize(const MCSectionData *SD) const {
114 assert(SD->Size != ~UINT64_C(0) && "File size not set!");
117 void MCAsmLayout::setSectionSize(MCSectionData *SD, uint64_t Value) {
121 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
122 assert(SD->FileSize != ~UINT64_C(0) && "File size not set!");
125 void MCAsmLayout::setSectionFileSize(MCSectionData *SD, uint64_t Value) {
126 SD->FileSize = Value;
129 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
130 assert(SD->AddressSize != ~UINT64_C(0) && "Address size not set!");
131 return SD->AddressSize;
133 void MCAsmLayout::setSectionAddressSize(MCSectionData *SD, uint64_t Value) {
134 SD->AddressSize = Value;
139 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
142 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
143 : Kind(_Kind), Parent(_Parent), Atom(0), EffectiveSize(~UINT64_C(0))
146 Parent->getFragmentList().push_back(this);
149 MCFragment::~MCFragment() {
154 MCSectionData::MCSectionData() : Section(0) {}
156 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
157 : Section(&_Section),
159 Address(~UINT64_C(0)),
161 AddressSize(~UINT64_C(0)),
162 FileSize(~UINT64_C(0)),
163 HasInstructions(false)
166 A->getSectionList().push_back(this);
171 MCSymbolData::MCSymbolData() : Symbol(0) {}
173 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
174 uint64_t _Offset, MCAssembler *A)
175 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
176 IsExternal(false), IsPrivateExtern(false),
177 CommonSize(0), CommonAlign(0), Flags(0), Index(0)
180 A->getSymbolList().push_back(this);
185 MCAssembler::MCAssembler(MCContext &_Context, TargetAsmBackend &_Backend,
186 MCCodeEmitter &_Emitter, raw_ostream &_OS)
187 : Context(_Context), Backend(_Backend), Emitter(_Emitter),
188 OS(_OS), RelaxAll(false), SubsectionsViaSymbols(false)
192 MCAssembler::~MCAssembler() {
195 static bool isScatteredFixupFullyResolvedSimple(const MCAssembler &Asm,
196 const MCAsmFixup &Fixup,
197 const MCValue Target,
198 const MCSection *BaseSection) {
199 // The effective fixup address is
200 // addr(atom(A)) + offset(A)
201 // - addr(atom(B)) - offset(B)
202 // - addr(<base symbol>) + <fixup offset from base symbol>
203 // and the offsets are not relocatable, so the fixup is fully resolved when
204 // addr(atom(A)) - addr(atom(B)) - addr(<base symbol>)) == 0.
206 // The simple (Darwin, except on x86_64) way of dealing with this was to
207 // assume that any reference to a temporary symbol *must* be a temporary
208 // symbol in the same atom, unless the sections differ. Therefore, any PCrel
209 // relocation to a temporary symbol (in the same section) is fully
210 // resolved. This also works in conjunction with absolutized .set, which
211 // requires the compiler to use .set to absolutize the differences between
212 // symbols which the compiler knows to be assembly time constants, so we don't
213 // need to worry about considering symbol differences fully resolved.
215 // Non-relative fixups are only resolved if constant.
217 return Target.isAbsolute();
219 // Otherwise, relative fixups are only resolved if not a difference and the
220 // target is a temporary in the same section.
221 if (Target.isAbsolute() || Target.getSymB())
224 const MCSymbol *A = &Target.getSymA()->getSymbol();
225 if (!A->isTemporary() || !A->isInSection() ||
226 &A->getSection() != BaseSection)
232 static bool isScatteredFixupFullyResolved(const MCAssembler &Asm,
233 const MCAsmLayout &Layout,
234 const MCAsmFixup &Fixup,
235 const MCValue Target,
236 const MCSymbolData *BaseSymbol) {
237 // The effective fixup address is
238 // addr(atom(A)) + offset(A)
239 // - addr(atom(B)) - offset(B)
240 // - addr(BaseSymbol) + <fixup offset from base symbol>
241 // and the offsets are not relocatable, so the fixup is fully resolved when
242 // addr(atom(A)) - addr(atom(B)) - addr(BaseSymbol) == 0.
244 // Note that "false" is almost always conservatively correct (it means we emit
245 // a relocation which is unnecessary), except when it would force us to emit a
246 // relocation which the target cannot encode.
248 const MCSymbolData *A_Base = 0, *B_Base = 0;
249 if (const MCSymbolRefExpr *A = Target.getSymA()) {
250 // Modified symbol references cannot be resolved.
251 if (A->getKind() != MCSymbolRefExpr::VK_None)
254 A_Base = Asm.getAtom(Layout, &Asm.getSymbolData(A->getSymbol()));
259 if (const MCSymbolRefExpr *B = Target.getSymB()) {
260 // Modified symbol references cannot be resolved.
261 if (B->getKind() != MCSymbolRefExpr::VK_None)
264 B_Base = Asm.getAtom(Layout, &Asm.getSymbolData(B->getSymbol()));
269 // If there is no base, A and B have to be the same atom for this fixup to be
272 return A_Base == B_Base;
274 // Otherwise, B must be missing and A must be the base.
275 return !B_Base && BaseSymbol == A_Base;
278 bool MCAssembler::isSymbolLinkerVisible(const MCSymbolData *SD) const {
279 // Non-temporary labels should always be visible to the linker.
280 if (!SD->getSymbol().isTemporary())
283 // Absolute temporary labels are never visible.
284 if (!SD->getFragment())
287 // Otherwise, check if the section requires symbols even for temporary labels.
288 return getBackend().doesSectionRequireSymbols(
289 SD->getFragment()->getParent()->getSection());
292 const MCSymbolData *MCAssembler::getAtom(const MCAsmLayout &Layout,
293 const MCSymbolData *SD) const {
294 // Linker visible symbols define atoms.
295 if (isSymbolLinkerVisible(SD))
298 // Absolute and undefined symbols have no defining atom.
299 if (!SD->getFragment())
302 // Non-linker visible symbols in sections which can't be atomized have no
304 if (!getBackend().isSectionAtomizable(
305 SD->getFragment()->getParent()->getSection()))
308 // Otherwise, return the atom for the containing fragment.
309 return SD->getFragment()->getAtom();
312 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
313 const MCAsmFixup &Fixup, const MCFragment *DF,
314 MCValue &Target, uint64_t &Value) const {
315 ++stats::EvaluateFixup;
317 if (!Fixup.Value->EvaluateAsRelocatable(Target, &Layout))
318 report_fatal_error("expected relocatable expression");
320 // FIXME: How do non-scattered symbols work in ELF? I presume the linker
321 // doesn't support small relocations, but then under what criteria does the
322 // assembler allow symbol differences?
324 Value = Target.getConstant();
327 Emitter.getFixupKindInfo(Fixup.Kind).Flags & MCFixupKindInfo::FKF_IsPCRel;
328 bool IsResolved = true;
329 if (const MCSymbolRefExpr *A = Target.getSymA()) {
330 if (A->getSymbol().isDefined())
331 Value += Layout.getSymbolAddress(&getSymbolData(A->getSymbol()));
335 if (const MCSymbolRefExpr *B = Target.getSymB()) {
336 if (B->getSymbol().isDefined())
337 Value -= Layout.getSymbolAddress(&getSymbolData(B->getSymbol()));
342 // If we are using scattered symbols, determine whether this value is actually
343 // resolved; scattering may cause atoms to move.
344 if (IsResolved && getBackend().hasScatteredSymbols()) {
345 if (getBackend().hasReliableSymbolDifference()) {
346 // If this is a PCrel relocation, find the base atom (identified by its
347 // symbol) that the fixup value is relative to.
348 const MCSymbolData *BaseSymbol = 0;
350 BaseSymbol = DF->getAtom();
356 IsResolved = isScatteredFixupFullyResolved(*this, Layout, Fixup, Target,
359 const MCSection *BaseSection = 0;
361 BaseSection = &DF->getParent()->getSection();
363 IsResolved = isScatteredFixupFullyResolvedSimple(*this, Fixup, Target,
369 Value -= Layout.getFragmentAddress(DF) + Fixup.Offset;
374 void MCAssembler::LayoutFragment(MCAsmLayout &Layout, MCFragment &F) {
375 uint64_t StartAddress = Layout.getSectionAddress(F.getParent());
377 // Get the fragment start address.
378 uint64_t Address = StartAddress;
379 MCSectionData::iterator it = &F;
380 if (MCFragment *Prev = F.getPrevNode())
381 Address = (StartAddress + Layout.getFragmentOffset(Prev) +
382 Layout.getFragmentEffectiveSize(Prev));
384 ++stats::FragmentLayouts;
386 uint64_t FragmentOffset = Address - StartAddress;
387 Layout.setFragmentOffset(&F, FragmentOffset);
389 // Evaluate fragment size.
390 uint64_t EffectiveSize = 0;
391 switch (F.getKind()) {
392 case MCFragment::FT_Align: {
393 MCAlignFragment &AF = cast<MCAlignFragment>(F);
395 EffectiveSize = OffsetToAlignment(Address, AF.getAlignment());
396 if (EffectiveSize > AF.getMaxBytesToEmit())
401 case MCFragment::FT_Data:
402 EffectiveSize = cast<MCDataFragment>(F).getContents().size();
405 case MCFragment::FT_Fill: {
406 EffectiveSize = cast<MCFillFragment>(F).getSize();
410 case MCFragment::FT_Inst:
411 EffectiveSize = cast<MCInstFragment>(F).getInstSize();
414 case MCFragment::FT_Org: {
415 MCOrgFragment &OF = cast<MCOrgFragment>(F);
417 int64_t TargetLocation;
418 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, &Layout))
419 report_fatal_error("expected assembly-time absolute expression");
421 // FIXME: We need a way to communicate this error.
422 int64_t Offset = TargetLocation - FragmentOffset;
424 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
425 "' (at offset '" + Twine(FragmentOffset) + "'");
427 EffectiveSize = Offset;
432 Layout.setFragmentEffectiveSize(&F, EffectiveSize);
435 void MCAssembler::LayoutSection(MCAsmLayout &Layout,
436 unsigned SectionOrderIndex) {
437 MCSectionData &SD = *Layout.getSectionOrder()[SectionOrderIndex];
438 bool IsVirtual = getBackend().isVirtualSection(SD.getSection());
440 ++stats::SectionLayouts;
442 // Get the section start address.
443 uint64_t StartAddress = 0;
444 if (SectionOrderIndex) {
445 MCSectionData *Prev = Layout.getSectionOrder()[SectionOrderIndex - 1];
446 StartAddress = (Layout.getSectionAddress(Prev) +
447 Layout.getSectionAddressSize(Prev));
450 // Align this section if necessary by adding padding bytes to the previous
451 // section. It is safe to adjust this out-of-band, because no symbol or
452 // fragment is allowed to point past the end of the section at any time.
453 if (uint64_t Pad = OffsetToAlignment(StartAddress, SD.getAlignment())) {
454 // Unless this section is virtual (where we are allowed to adjust the offset
455 // freely), the padding goes in the previous section.
457 assert(SectionOrderIndex && "Invalid initial section address!");
458 MCSectionData *Prev = Layout.getSectionOrder()[SectionOrderIndex - 1];
459 Layout.setSectionFileSize(Prev, Layout.getSectionFileSize(Prev) + Pad);
465 // Set the aligned section address.
466 Layout.setSectionAddress(&SD, StartAddress);
468 for (MCSectionData::iterator it = SD.begin(), ie = SD.end(); it != ie; ++it)
469 LayoutFragment(Layout, *it);
471 // Set the section sizes.
473 if (!SD.getFragmentList().empty()) {
474 MCFragment *F = &SD.getFragmentList().back();
475 Size = Layout.getFragmentOffset(F) + Layout.getFragmentEffectiveSize(F);
477 Layout.setSectionSize(&SD, Size);
478 Layout.setSectionAddressSize(&SD, Size);
479 Layout.setSectionFileSize(&SD, IsVirtual ? 0 : Size);
482 /// WriteFragmentData - Write the \arg F data to the output file.
483 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
484 const MCFragment &F, MCObjectWriter *OW) {
485 uint64_t Start = OW->getStream().tell();
488 ++stats::EmittedFragments;
490 // FIXME: Embed in fragments instead?
491 uint64_t FragmentSize = Layout.getFragmentEffectiveSize(&F);
492 switch (F.getKind()) {
493 case MCFragment::FT_Align: {
494 MCAlignFragment &AF = cast<MCAlignFragment>(F);
495 uint64_t Count = FragmentSize / AF.getValueSize();
497 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
499 // FIXME: This error shouldn't actually occur (the front end should emit
500 // multiple .align directives to enforce the semantics it wants), but is
501 // severe enough that we want to report it. How to handle this?
502 if (Count * AF.getValueSize() != FragmentSize)
503 report_fatal_error("undefined .align directive, value size '" +
504 Twine(AF.getValueSize()) +
505 "' is not a divisor of padding size '" +
506 Twine(FragmentSize) + "'");
508 // See if we are aligning with nops, and if so do that first to try to fill
509 // the Count bytes. Then if that did not fill any bytes or there are any
510 // bytes left to fill use the the Value and ValueSize to fill the rest.
511 // If we are aligning with nops, ask that target to emit the right data.
512 if (AF.hasEmitNops()) {
513 if (!Asm.getBackend().WriteNopData(Count, OW))
514 report_fatal_error("unable to write nop sequence of " +
515 Twine(Count) + " bytes");
519 // Otherwise, write out in multiples of the value size.
520 for (uint64_t i = 0; i != Count; ++i) {
521 switch (AF.getValueSize()) {
523 assert(0 && "Invalid size!");
524 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
525 case 2: OW->Write16(uint16_t(AF.getValue())); break;
526 case 4: OW->Write32(uint32_t(AF.getValue())); break;
527 case 8: OW->Write64(uint64_t(AF.getValue())); break;
533 case MCFragment::FT_Data: {
534 MCDataFragment &DF = cast<MCDataFragment>(F);
535 assert(FragmentSize == DF.getContents().size() && "Invalid size!");
536 OW->WriteBytes(DF.getContents().str());
540 case MCFragment::FT_Fill: {
541 MCFillFragment &FF = cast<MCFillFragment>(F);
543 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
545 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
546 switch (FF.getValueSize()) {
548 assert(0 && "Invalid size!");
549 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
550 case 2: OW->Write16(uint16_t(FF.getValue())); break;
551 case 4: OW->Write32(uint32_t(FF.getValue())); break;
552 case 8: OW->Write64(uint64_t(FF.getValue())); break;
558 case MCFragment::FT_Inst:
559 llvm_unreachable("unexpected inst fragment after lowering");
562 case MCFragment::FT_Org: {
563 MCOrgFragment &OF = cast<MCOrgFragment>(F);
565 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
566 OW->Write8(uint8_t(OF.getValue()));
572 assert(OW->getStream().tell() - Start == FragmentSize);
575 void MCAssembler::WriteSectionData(const MCSectionData *SD,
576 const MCAsmLayout &Layout,
577 MCObjectWriter *OW) const {
578 uint64_t SectionSize = Layout.getSectionSize(SD);
579 uint64_t SectionFileSize = Layout.getSectionFileSize(SD);
581 // Ignore virtual sections.
582 if (getBackend().isVirtualSection(SD->getSection())) {
583 assert(SectionFileSize == 0 && "Invalid size for section!");
585 // Check that contents are only things legal inside a virtual section.
586 for (MCSectionData::const_iterator it = SD->begin(),
587 ie = SD->end(); it != ie; ++it) {
588 switch (it->getKind()) {
590 assert(0 && "Invalid fragment in virtual section!");
591 case MCFragment::FT_Align:
592 assert(!cast<MCAlignFragment>(it)->getValueSize() &&
593 "Invalid align in virtual section!");
595 case MCFragment::FT_Fill:
596 assert(!cast<MCFillFragment>(it)->getValueSize() &&
597 "Invalid fill in virtual section!");
605 uint64_t Start = OW->getStream().tell();
608 for (MCSectionData::const_iterator it = SD->begin(),
609 ie = SD->end(); it != ie; ++it)
610 WriteFragmentData(*this, Layout, *it, OW);
612 // Add section padding.
613 assert(SectionFileSize >= SectionSize && "Invalid section sizes!");
614 OW->WriteZeros(SectionFileSize - SectionSize);
616 assert(OW->getStream().tell() - Start == SectionFileSize);
619 void MCAssembler::Finish() {
620 DEBUG_WITH_TYPE("mc-dump", {
621 llvm::errs() << "assembler backend - pre-layout\n--\n";
624 // Assign section and fragment ordinals, all subsequent backend code is
625 // responsible for updating these in place.
626 unsigned SectionIndex = 0;
627 unsigned FragmentIndex = 0;
628 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
629 it->setOrdinal(SectionIndex++);
631 for (MCSectionData::iterator it2 = it->begin(),
632 ie2 = it->end(); it2 != ie2; ++it2)
633 it2->setOrdinal(FragmentIndex++);
636 // Layout until everything fits.
637 MCAsmLayout Layout(*this);
638 while (LayoutOnce(Layout))
641 DEBUG_WITH_TYPE("mc-dump", {
642 llvm::errs() << "assembler backend - post-relaxation\n--\n";
645 // Finalize the layout, including fragment lowering.
646 FinishLayout(Layout);
648 DEBUG_WITH_TYPE("mc-dump", {
649 llvm::errs() << "assembler backend - final-layout\n--\n";
652 uint64_t StartOffset = OS.tell();
653 llvm::OwningPtr<MCObjectWriter> Writer(getBackend().createObjectWriter(OS));
655 report_fatal_error("unable to create object writer!");
657 // Allow the object writer a chance to perform post-layout binding (for
658 // example, to set the index fields in the symbol data).
659 Writer->ExecutePostLayoutBinding(*this);
661 // Evaluate and apply the fixups, generating relocation entries as necessary.
662 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
663 for (MCSectionData::iterator it2 = it->begin(),
664 ie2 = it->end(); it2 != ie2; ++it2) {
665 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
669 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
670 ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
671 MCAsmFixup &Fixup = *it3;
673 // Evaluate the fixup.
676 if (!EvaluateFixup(Layout, Fixup, DF, Target, FixedValue)) {
677 // The fixup was unresolved, we need a relocation. Inform the object
678 // writer of the relocation, and give it an opportunity to adjust the
679 // fixup value if need be.
680 Writer->RecordRelocation(*this, Layout, DF, Fixup, Target,FixedValue);
683 getBackend().ApplyFixup(Fixup, *DF, FixedValue);
688 // Write the object file.
689 Writer->WriteObject(*this, Layout);
692 stats::ObjectBytes += OS.tell() - StartOffset;
695 bool MCAssembler::FixupNeedsRelaxation(const MCAsmFixup &Fixup,
696 const MCFragment *DF,
697 const MCAsmLayout &Layout) const {
701 // If we cannot resolve the fixup value, it requires relaxation.
704 if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
707 // Otherwise, relax if the value is too big for a (signed) i8.
709 // FIXME: This is target dependent!
710 return int64_t(Value) != int64_t(int8_t(Value));
713 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
714 const MCAsmLayout &Layout) const {
715 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
716 // are intentionally pushing out inst fragments, or because we relaxed a
717 // previous instruction to one that doesn't need relaxation.
718 if (!getBackend().MayNeedRelaxation(IF->getInst(), IF->getFixups()))
721 for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
722 ie = IF->fixup_end(); it != ie; ++it)
723 if (FixupNeedsRelaxation(*it, IF, Layout))
729 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
730 ++stats::RelaxationSteps;
732 // Layout the sections in order.
733 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i)
734 LayoutSection(Layout, i);
736 // Scan for fragments that need relaxation.
737 bool WasRelaxed = false;
738 for (iterator it = begin(), ie = end(); it != ie; ++it) {
739 MCSectionData &SD = *it;
741 for (MCSectionData::iterator it2 = SD.begin(),
742 ie2 = SD.end(); it2 != ie2; ++it2) {
743 // Check if this is an instruction fragment that needs relaxation.
744 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
745 if (!IF || !FragmentNeedsRelaxation(IF, Layout))
748 ++stats::RelaxedInstructions;
750 // FIXME-PERF: We could immediately lower out instructions if we can tell
751 // they are fully resolved, to avoid retesting on later passes.
753 // Relax the fragment.
756 getBackend().RelaxInstruction(IF, Relaxed);
758 // Encode the new instruction.
760 // FIXME-PERF: If it matters, we could let the target do this. It can
761 // probably do so more efficiently in many cases.
762 SmallVector<MCFixup, 4> Fixups;
763 SmallString<256> Code;
764 raw_svector_ostream VecOS(Code);
765 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
768 // Update the instruction fragment.
769 int SlideAmount = Code.size() - IF->getInstSize();
770 IF->setInst(Relaxed);
771 IF->getCode() = Code;
772 IF->getFixups().clear();
773 for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
774 MCFixup &F = Fixups[i];
775 IF->getFixups().push_back(MCAsmFixup(F.getOffset(), *F.getValue(),
779 // Update the layout, and remember that we relaxed. If we are relaxing
780 // everything, we can skip this step since nothing will depend on updating
783 Layout.UpdateForSlide(IF, SlideAmount);
791 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
792 // Lower out any instruction fragments, to simplify the fixup application and
795 // FIXME-PERF: We don't have to do this, but the assumption is that it is
796 // cheap (we will mostly end up eliminating fragments and appending on to data
797 // fragments), so the extra complexity downstream isn't worth it. Evaluate
799 for (iterator it = begin(), ie = end(); it != ie; ++it) {
800 MCSectionData &SD = *it;
802 for (MCSectionData::iterator it2 = SD.begin(),
803 ie2 = SD.end(); it2 != ie2; ++it2) {
804 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
808 // Create a new data fragment for the instruction.
810 // FIXME-PERF: Reuse previous data fragment if possible.
811 MCDataFragment *DF = new MCDataFragment();
812 SD.getFragmentList().insert(it2, DF);
814 // Update the data fragments layout data.
816 // FIXME: Add MCAsmLayout utility for this.
817 DF->setParent(IF->getParent());
818 DF->setAtom(IF->getAtom());
819 DF->setOrdinal(IF->getOrdinal());
820 Layout.setFragmentOffset(DF, Layout.getFragmentOffset(IF));
821 Layout.setFragmentEffectiveSize(DF, Layout.getFragmentEffectiveSize(IF));
823 // Copy in the data and the fixups.
824 DF->getContents().append(IF->getCode().begin(), IF->getCode().end());
825 for (unsigned i = 0, e = IF->getFixups().size(); i != e; ++i)
826 DF->getFixups().push_back(IF->getFixups()[i]);
828 // Delete the instruction fragment and update the iterator.
829 SD.getFragmentList().erase(IF);
839 raw_ostream &operator<<(raw_ostream &OS, const MCAsmFixup &AF) {
840 OS << "<MCAsmFixup" << " Offset:" << AF.Offset << " Value:" << *AF.Value
841 << " Kind:" << AF.Kind << ">";
847 void MCFragment::dump() {
848 raw_ostream &OS = llvm::errs();
850 OS << "<MCFragment " << (void*) this << " Offset:" << Offset
851 << " EffectiveSize:" << EffectiveSize << ">";
854 void MCAlignFragment::dump() {
855 raw_ostream &OS = llvm::errs();
857 OS << "<MCAlignFragment ";
858 this->MCFragment::dump();
860 OS << " Alignment:" << getAlignment()
861 << " Value:" << getValue() << " ValueSize:" << getValueSize()
862 << " MaxBytesToEmit:" << getMaxBytesToEmit() << ">";
865 void MCDataFragment::dump() {
866 raw_ostream &OS = llvm::errs();
868 OS << "<MCDataFragment ";
869 this->MCFragment::dump();
872 for (unsigned i = 0, e = getContents().size(); i != e; ++i) {
874 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
876 OS << "] (" << getContents().size() << " bytes)";
878 if (!getFixups().empty()) {
881 for (fixup_iterator it = fixup_begin(), ie = fixup_end(); it != ie; ++it) {
882 if (it != fixup_begin()) OS << ",\n ";
891 void MCFillFragment::dump() {
892 raw_ostream &OS = llvm::errs();
894 OS << "<MCFillFragment ";
895 this->MCFragment::dump();
897 OS << " Value:" << getValue() << " ValueSize:" << getValueSize()
898 << " Size:" << getSize() << ">";
901 void MCInstFragment::dump() {
902 raw_ostream &OS = llvm::errs();
904 OS << "<MCInstFragment ";
905 this->MCFragment::dump();
908 getInst().dump_pretty(OS);
912 void MCOrgFragment::dump() {
913 raw_ostream &OS = llvm::errs();
915 OS << "<MCOrgFragment ";
916 this->MCFragment::dump();
918 OS << " Offset:" << getOffset() << " Value:" << getValue() << ">";
921 void MCSectionData::dump() {
922 raw_ostream &OS = llvm::errs();
924 OS << "<MCSectionData";
925 OS << " Alignment:" << getAlignment() << " Address:" << Address
926 << " Size:" << Size << " AddressSize:" << AddressSize
927 << " FileSize:" << FileSize << " Fragments:[\n ";
928 for (iterator it = begin(), ie = end(); it != ie; ++it) {
929 if (it != begin()) OS << ",\n ";
935 void MCSymbolData::dump() {
936 raw_ostream &OS = llvm::errs();
938 OS << "<MCSymbolData Symbol:" << getSymbol()
939 << " Fragment:" << getFragment() << " Offset:" << getOffset()
940 << " Flags:" << getFlags() << " Index:" << getIndex();
942 OS << " (common, size:" << getCommonSize()
943 << " align: " << getCommonAlignment() << ")";
946 if (isPrivateExtern())
947 OS << " (private extern)";
951 void MCAssembler::dump() {
952 raw_ostream &OS = llvm::errs();
954 OS << "<MCAssembler\n";
955 OS << " Sections:[\n ";
956 for (iterator it = begin(), ie = end(); it != ie; ++it) {
957 if (it != begin()) OS << ",\n ";
963 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
964 if (it != symbol_begin()) OS << ",\n ";