xref: /freebsd/contrib/llvm-project/llvm/lib/MC/MCAssembler.cpp (revision acb1f1269c6f4ff89a0d28ba742f6687e9ef779d)
1 //===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #include "llvm/MC/MCAssembler.h"
10 #include "llvm/ADT/ArrayRef.h"
11 #include "llvm/ADT/SmallString.h"
12 #include "llvm/ADT/SmallVector.h"
13 #include "llvm/ADT/Statistic.h"
14 #include "llvm/ADT/StringRef.h"
15 #include "llvm/ADT/Twine.h"
16 #include "llvm/MC/MCAsmBackend.h"
17 #include "llvm/MC/MCAsmInfo.h"
18 #include "llvm/MC/MCAsmLayout.h"
19 #include "llvm/MC/MCCodeEmitter.h"
20 #include "llvm/MC/MCCodeView.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCDwarf.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCFixup.h"
25 #include "llvm/MC/MCFixupKindInfo.h"
26 #include "llvm/MC/MCFragment.h"
27 #include "llvm/MC/MCInst.h"
28 #include "llvm/MC/MCObjectWriter.h"
29 #include "llvm/MC/MCSection.h"
30 #include "llvm/MC/MCSectionELF.h"
31 #include "llvm/MC/MCSymbol.h"
32 #include "llvm/MC/MCValue.h"
33 #include "llvm/Support/Alignment.h"
34 #include "llvm/Support/Casting.h"
35 #include "llvm/Support/Debug.h"
36 #include "llvm/Support/EndianStream.h"
37 #include "llvm/Support/ErrorHandling.h"
38 #include "llvm/Support/LEB128.h"
39 #include "llvm/Support/MathExtras.h"
40 #include "llvm/Support/raw_ostream.h"
41 #include <cassert>
42 #include <cstdint>
43 #include <cstring>
44 #include <tuple>
45 #include <utility>
46 
47 using namespace llvm;
48 
49 #define DEBUG_TYPE "assembler"
50 
51 namespace {
52 namespace stats {
53 
54 STATISTIC(EmittedFragments, "Number of emitted assembler fragments - total");
55 STATISTIC(EmittedRelaxableFragments,
56           "Number of emitted assembler fragments - relaxable");
57 STATISTIC(EmittedDataFragments,
58           "Number of emitted assembler fragments - data");
59 STATISTIC(EmittedCompactEncodedInstFragments,
60           "Number of emitted assembler fragments - compact encoded inst");
61 STATISTIC(EmittedAlignFragments,
62           "Number of emitted assembler fragments - align");
63 STATISTIC(EmittedFillFragments,
64           "Number of emitted assembler fragments - fill");
65 STATISTIC(EmittedNopsFragments, "Number of emitted assembler fragments - nops");
66 STATISTIC(EmittedOrgFragments, "Number of emitted assembler fragments - org");
67 STATISTIC(evaluateFixup, "Number of evaluated fixups");
68 STATISTIC(FragmentLayouts, "Number of fragment layouts");
69 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
70 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
71 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
72 
73 } // end namespace stats
74 } // end anonymous namespace
75 
76 // FIXME FIXME FIXME: There are number of places in this file where we convert
77 // what is a 64-bit assembler value used for computation into a value in the
78 // object file, which may truncate it. We should detect that truncation where
79 // invalid and report errors back.
80 
81 /* *** */
82 
83 MCAssembler::MCAssembler(MCContext &Context,
84                          std::unique_ptr<MCAsmBackend> Backend,
85                          std::unique_ptr<MCCodeEmitter> Emitter,
86                          std::unique_ptr<MCObjectWriter> Writer)
87     : Context(Context), Backend(std::move(Backend)),
88       Emitter(std::move(Emitter)), Writer(std::move(Writer)),
89       BundleAlignSize(0), RelaxAll(false), SubsectionsViaSymbols(false),
90       IncrementalLinkerCompatible(false), ELFHeaderEFlags(0) {
91   VersionInfo.Major = 0; // Major version == 0 for "none specified"
92 }
93 
94 MCAssembler::~MCAssembler() = default;
95 
96 void MCAssembler::reset() {
97   Sections.clear();
98   Symbols.clear();
99   IndirectSymbols.clear();
100   DataRegions.clear();
101   LinkerOptions.clear();
102   FileNames.clear();
103   ThumbFuncs.clear();
104   BundleAlignSize = 0;
105   RelaxAll = false;
106   SubsectionsViaSymbols = false;
107   IncrementalLinkerCompatible = false;
108   ELFHeaderEFlags = 0;
109   LOHContainer.reset();
110   VersionInfo.Major = 0;
111   VersionInfo.SDKVersion = VersionTuple();
112 
113   // reset objects owned by us
114   if (getBackendPtr())
115     getBackendPtr()->reset();
116   if (getEmitterPtr())
117     getEmitterPtr()->reset();
118   if (getWriterPtr())
119     getWriterPtr()->reset();
120   getLOHContainer().reset();
121 }
122 
123 bool MCAssembler::registerSection(MCSection &Section) {
124   if (Section.isRegistered())
125     return false;
126   Sections.push_back(&Section);
127   Section.setIsRegistered(true);
128   return true;
129 }
130 
131 bool MCAssembler::isThumbFunc(const MCSymbol *Symbol) const {
132   if (ThumbFuncs.count(Symbol))
133     return true;
134 
135   if (!Symbol->isVariable())
136     return false;
137 
138   const MCExpr *Expr = Symbol->getVariableValue();
139 
140   MCValue V;
141   if (!Expr->evaluateAsRelocatable(V, nullptr, nullptr))
142     return false;
143 
144   if (V.getSymB() || V.getRefKind() != MCSymbolRefExpr::VK_None)
145     return false;
146 
147   const MCSymbolRefExpr *Ref = V.getSymA();
148   if (!Ref)
149     return false;
150 
151   if (Ref->getKind() != MCSymbolRefExpr::VK_None)
152     return false;
153 
154   const MCSymbol &Sym = Ref->getSymbol();
155   if (!isThumbFunc(&Sym))
156     return false;
157 
158   ThumbFuncs.insert(Symbol); // Cache it.
159   return true;
160 }
161 
162 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
163   // Non-temporary labels should always be visible to the linker.
164   if (!Symbol.isTemporary())
165     return true;
166 
167   if (Symbol.isUsedInReloc())
168     return true;
169 
170   return false;
171 }
172 
173 const MCSymbol *MCAssembler::getAtom(const MCSymbol &S) const {
174   // Linker visible symbols define atoms.
175   if (isSymbolLinkerVisible(S))
176     return &S;
177 
178   // Absolute and undefined symbols have no defining atom.
179   if (!S.isInSection())
180     return nullptr;
181 
182   // Non-linker visible symbols in sections which can't be atomized have no
183   // defining atom.
184   if (!getContext().getAsmInfo()->isSectionAtomizableBySymbols(
185           *S.getFragment()->getParent()))
186     return nullptr;
187 
188   // Otherwise, return the atom for the containing fragment.
189   return S.getFragment()->getAtom();
190 }
191 
192 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
193                                 const MCFixup &Fixup, const MCFragment *DF,
194                                 MCValue &Target, uint64_t &Value,
195                                 bool &WasForced) const {
196   ++stats::evaluateFixup;
197 
198   // FIXME: This code has some duplication with recordRelocation. We should
199   // probably merge the two into a single callback that tries to evaluate a
200   // fixup and records a relocation if one is needed.
201 
202   // On error claim to have completely evaluated the fixup, to prevent any
203   // further processing from being done.
204   const MCExpr *Expr = Fixup.getValue();
205   MCContext &Ctx = getContext();
206   Value = 0;
207   WasForced = false;
208   if (!Expr->evaluateAsRelocatable(Target, &Layout, &Fixup)) {
209     Ctx.reportError(Fixup.getLoc(), "expected relocatable expression");
210     return true;
211   }
212   if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
213     if (RefB->getKind() != MCSymbolRefExpr::VK_None) {
214       Ctx.reportError(Fixup.getLoc(),
215                       "unsupported subtraction of qualified symbol");
216       return true;
217     }
218   }
219 
220   assert(getBackendPtr() && "Expected assembler backend");
221   bool IsTarget = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
222                   MCFixupKindInfo::FKF_IsTarget;
223 
224   if (IsTarget)
225     return getBackend().evaluateTargetFixup(*this, Layout, Fixup, DF, Target,
226                                             Value, WasForced);
227 
228   unsigned FixupFlags = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags;
229   bool IsPCRel = getBackendPtr()->getFixupKindInfo(Fixup.getKind()).Flags &
230                  MCFixupKindInfo::FKF_IsPCRel;
231 
232   bool IsResolved = false;
233   if (IsPCRel) {
234     if (Target.getSymB()) {
235       IsResolved = false;
236     } else if (!Target.getSymA()) {
237       IsResolved = false;
238     } else {
239       const MCSymbolRefExpr *A = Target.getSymA();
240       const MCSymbol &SA = A->getSymbol();
241       if (A->getKind() != MCSymbolRefExpr::VK_None || SA.isUndefined()) {
242         IsResolved = false;
243       } else if (auto *Writer = getWriterPtr()) {
244         IsResolved = (FixupFlags & MCFixupKindInfo::FKF_Constant) ||
245                      Writer->isSymbolRefDifferenceFullyResolvedImpl(
246                          *this, SA, *DF, false, true);
247       }
248     }
249   } else {
250     IsResolved = Target.isAbsolute();
251   }
252 
253   Value = Target.getConstant();
254 
255   if (const MCSymbolRefExpr *A = Target.getSymA()) {
256     const MCSymbol &Sym = A->getSymbol();
257     if (Sym.isDefined())
258       Value += Layout.getSymbolOffset(Sym);
259   }
260   if (const MCSymbolRefExpr *B = Target.getSymB()) {
261     const MCSymbol &Sym = B->getSymbol();
262     if (Sym.isDefined())
263       Value -= Layout.getSymbolOffset(Sym);
264   }
265 
266   bool ShouldAlignPC = getBackend().getFixupKindInfo(Fixup.getKind()).Flags &
267                        MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
268   assert((ShouldAlignPC ? IsPCRel : true) &&
269     "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
270 
271   if (IsPCRel) {
272     uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
273 
274     // A number of ARM fixups in Thumb mode require that the effective PC
275     // address be determined as the 32-bit aligned version of the actual offset.
276     if (ShouldAlignPC) Offset &= ~0x3;
277     Value -= Offset;
278   }
279 
280   // Let the backend force a relocation if needed.
281   if (IsResolved && getBackend().shouldForceRelocation(*this, Fixup, Target)) {
282     IsResolved = false;
283     WasForced = true;
284   }
285 
286   return IsResolved;
287 }
288 
289 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
290                                           const MCFragment &F) const {
291   assert(getBackendPtr() && "Requires assembler backend");
292   switch (F.getKind()) {
293   case MCFragment::FT_Data:
294     return cast<MCDataFragment>(F).getContents().size();
295   case MCFragment::FT_Relaxable:
296     return cast<MCRelaxableFragment>(F).getContents().size();
297   case MCFragment::FT_CompactEncodedInst:
298     return cast<MCCompactEncodedInstFragment>(F).getContents().size();
299   case MCFragment::FT_Fill: {
300     auto &FF = cast<MCFillFragment>(F);
301     int64_t NumValues = 0;
302     if (!FF.getNumValues().evaluateAsAbsolute(NumValues, Layout)) {
303       getContext().reportError(FF.getLoc(),
304                                "expected assembly-time absolute expression");
305       return 0;
306     }
307     int64_t Size = NumValues * FF.getValueSize();
308     if (Size < 0) {
309       getContext().reportError(FF.getLoc(), "invalid number of bytes");
310       return 0;
311     }
312     return Size;
313   }
314 
315   case MCFragment::FT_Nops:
316     return cast<MCNopsFragment>(F).getNumBytes();
317 
318   case MCFragment::FT_LEB:
319     return cast<MCLEBFragment>(F).getContents().size();
320 
321   case MCFragment::FT_BoundaryAlign:
322     return cast<MCBoundaryAlignFragment>(F).getSize();
323 
324   case MCFragment::FT_SymbolId:
325     return 4;
326 
327   case MCFragment::FT_Align: {
328     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
329     unsigned Offset = Layout.getFragmentOffset(&AF);
330     unsigned Size = offsetToAlignment(Offset, Align(AF.getAlignment()));
331 
332     // Insert extra Nops for code alignment if the target define
333     // shouldInsertExtraNopBytesForCodeAlign target hook.
334     if (AF.getParent()->UseCodeAlign() && AF.hasEmitNops() &&
335         getBackend().shouldInsertExtraNopBytesForCodeAlign(AF, Size))
336       return Size;
337 
338     // If we are padding with nops, force the padding to be larger than the
339     // minimum nop size.
340     if (Size > 0 && AF.hasEmitNops()) {
341       while (Size % getBackend().getMinimumNopSize())
342         Size += AF.getAlignment();
343     }
344     if (Size > AF.getMaxBytesToEmit())
345       return 0;
346     return Size;
347   }
348 
349   case MCFragment::FT_Org: {
350     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
351     MCValue Value;
352     if (!OF.getOffset().evaluateAsValue(Value, Layout)) {
353       getContext().reportError(OF.getLoc(),
354                                "expected assembly-time absolute expression");
355         return 0;
356     }
357 
358     uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
359     int64_t TargetLocation = Value.getConstant();
360     if (const MCSymbolRefExpr *A = Value.getSymA()) {
361       uint64_t Val;
362       if (!Layout.getSymbolOffset(A->getSymbol(), Val)) {
363         getContext().reportError(OF.getLoc(), "expected absolute expression");
364         return 0;
365       }
366       TargetLocation += Val;
367     }
368     int64_t Size = TargetLocation - FragmentOffset;
369     if (Size < 0 || Size >= 0x40000000) {
370       getContext().reportError(
371           OF.getLoc(), "invalid .org offset '" + Twine(TargetLocation) +
372                            "' (at offset '" + Twine(FragmentOffset) + "')");
373       return 0;
374     }
375     return Size;
376   }
377 
378   case MCFragment::FT_Dwarf:
379     return cast<MCDwarfLineAddrFragment>(F).getContents().size();
380   case MCFragment::FT_DwarfFrame:
381     return cast<MCDwarfCallFrameFragment>(F).getContents().size();
382   case MCFragment::FT_CVInlineLines:
383     return cast<MCCVInlineLineTableFragment>(F).getContents().size();
384   case MCFragment::FT_CVDefRange:
385     return cast<MCCVDefRangeFragment>(F).getContents().size();
386   case MCFragment::FT_PseudoProbe:
387     return cast<MCPseudoProbeAddrFragment>(F).getContents().size();
388   case MCFragment::FT_Dummy:
389     llvm_unreachable("Should not have been added");
390   }
391 
392   llvm_unreachable("invalid fragment kind");
393 }
394 
395 void MCAsmLayout::layoutFragment(MCFragment *F) {
396   MCFragment *Prev = F->getPrevNode();
397 
398   // We should never try to recompute something which is valid.
399   assert(!isFragmentValid(F) && "Attempt to recompute a valid fragment!");
400   // We should never try to compute the fragment layout if its predecessor
401   // isn't valid.
402   assert((!Prev || isFragmentValid(Prev)) &&
403          "Attempt to compute fragment before its predecessor!");
404 
405   assert(!F->IsBeingLaidOut && "Already being laid out!");
406   F->IsBeingLaidOut = true;
407 
408   ++stats::FragmentLayouts;
409 
410   // Compute fragment offset and size.
411   if (Prev)
412     F->Offset = Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
413   else
414     F->Offset = 0;
415   F->IsBeingLaidOut = false;
416   LastValidFragment[F->getParent()] = F;
417 
418   // If bundling is enabled and this fragment has instructions in it, it has to
419   // obey the bundling restrictions. With padding, we'll have:
420   //
421   //
422   //        BundlePadding
423   //             |||
424   // -------------------------------------
425   //   Prev  |##########|       F        |
426   // -------------------------------------
427   //                    ^
428   //                    |
429   //                    F->Offset
430   //
431   // The fragment's offset will point to after the padding, and its computed
432   // size won't include the padding.
433   //
434   // When the -mc-relax-all flag is used, we optimize bundling by writting the
435   // padding directly into fragments when the instructions are emitted inside
436   // the streamer. When the fragment is larger than the bundle size, we need to
437   // ensure that it's bundle aligned. This means that if we end up with
438   // multiple fragments, we must emit bundle padding between fragments.
439   //
440   // ".align N" is an example of a directive that introduces multiple
441   // fragments. We could add a special case to handle ".align N" by emitting
442   // within-fragment padding (which would produce less padding when N is less
443   // than the bundle size), but for now we don't.
444   //
445   if (Assembler.isBundlingEnabled() && F->hasInstructions()) {
446     assert(isa<MCEncodedFragment>(F) &&
447            "Only MCEncodedFragment implementations have instructions");
448     MCEncodedFragment *EF = cast<MCEncodedFragment>(F);
449     uint64_t FSize = Assembler.computeFragmentSize(*this, *EF);
450 
451     if (!Assembler.getRelaxAll() && FSize > Assembler.getBundleAlignSize())
452       report_fatal_error("Fragment can't be larger than a bundle size");
453 
454     uint64_t RequiredBundlePadding =
455         computeBundlePadding(Assembler, EF, EF->Offset, FSize);
456     if (RequiredBundlePadding > UINT8_MAX)
457       report_fatal_error("Padding cannot exceed 255 bytes");
458     EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
459     EF->Offset += RequiredBundlePadding;
460   }
461 }
462 
463 void MCAssembler::registerSymbol(const MCSymbol &Symbol, bool *Created) {
464   bool New = !Symbol.isRegistered();
465   if (Created)
466     *Created = New;
467   if (New) {
468     Symbol.setIsRegistered(true);
469     Symbols.push_back(&Symbol);
470   }
471 }
472 
473 void MCAssembler::writeFragmentPadding(raw_ostream &OS,
474                                        const MCEncodedFragment &EF,
475                                        uint64_t FSize) const {
476   assert(getBackendPtr() && "Expected assembler backend");
477   // Should NOP padding be written out before this fragment?
478   unsigned BundlePadding = EF.getBundlePadding();
479   if (BundlePadding > 0) {
480     assert(isBundlingEnabled() &&
481            "Writing bundle padding with disabled bundling");
482     assert(EF.hasInstructions() &&
483            "Writing bundle padding for a fragment without instructions");
484 
485     unsigned TotalLength = BundlePadding + static_cast<unsigned>(FSize);
486     if (EF.alignToBundleEnd() && TotalLength > getBundleAlignSize()) {
487       // If the padding itself crosses a bundle boundary, it must be emitted
488       // in 2 pieces, since even nop instructions must not cross boundaries.
489       //             v--------------v   <- BundleAlignSize
490       //        v---------v             <- BundlePadding
491       // ----------------------------
492       // | Prev |####|####|    F    |
493       // ----------------------------
494       //        ^-------------------^   <- TotalLength
495       unsigned DistanceToBoundary = TotalLength - getBundleAlignSize();
496       if (!getBackend().writeNopData(OS, DistanceToBoundary))
497         report_fatal_error("unable to write NOP sequence of " +
498                            Twine(DistanceToBoundary) + " bytes");
499       BundlePadding -= DistanceToBoundary;
500     }
501     if (!getBackend().writeNopData(OS, BundlePadding))
502       report_fatal_error("unable to write NOP sequence of " +
503                          Twine(BundlePadding) + " bytes");
504   }
505 }
506 
507 /// Write the fragment \p F to the output file.
508 static void writeFragment(raw_ostream &OS, const MCAssembler &Asm,
509                           const MCAsmLayout &Layout, const MCFragment &F) {
510   // FIXME: Embed in fragments instead?
511   uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
512 
513   support::endianness Endian = Asm.getBackend().Endian;
514 
515   if (const MCEncodedFragment *EF = dyn_cast<MCEncodedFragment>(&F))
516     Asm.writeFragmentPadding(OS, *EF, FragmentSize);
517 
518   // This variable (and its dummy usage) is to participate in the assert at
519   // the end of the function.
520   uint64_t Start = OS.tell();
521   (void) Start;
522 
523   ++stats::EmittedFragments;
524 
525   switch (F.getKind()) {
526   case MCFragment::FT_Align: {
527     ++stats::EmittedAlignFragments;
528     const MCAlignFragment &AF = cast<MCAlignFragment>(F);
529     assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
530 
531     uint64_t Count = FragmentSize / AF.getValueSize();
532 
533     // FIXME: This error shouldn't actually occur (the front end should emit
534     // multiple .align directives to enforce the semantics it wants), but is
535     // severe enough that we want to report it. How to handle this?
536     if (Count * AF.getValueSize() != FragmentSize)
537       report_fatal_error("undefined .align directive, value size '" +
538                         Twine(AF.getValueSize()) +
539                         "' is not a divisor of padding size '" +
540                         Twine(FragmentSize) + "'");
541 
542     // See if we are aligning with nops, and if so do that first to try to fill
543     // the Count bytes.  Then if that did not fill any bytes or there are any
544     // bytes left to fill use the Value and ValueSize to fill the rest.
545     // If we are aligning with nops, ask that target to emit the right data.
546     if (AF.hasEmitNops()) {
547       if (!Asm.getBackend().writeNopData(OS, Count))
548         report_fatal_error("unable to write nop sequence of " +
549                           Twine(Count) + " bytes");
550       break;
551     }
552 
553     // Otherwise, write out in multiples of the value size.
554     for (uint64_t i = 0; i != Count; ++i) {
555       switch (AF.getValueSize()) {
556       default: llvm_unreachable("Invalid size!");
557       case 1: OS << char(AF.getValue()); break;
558       case 2:
559         support::endian::write<uint16_t>(OS, AF.getValue(), Endian);
560         break;
561       case 4:
562         support::endian::write<uint32_t>(OS, AF.getValue(), Endian);
563         break;
564       case 8:
565         support::endian::write<uint64_t>(OS, AF.getValue(), Endian);
566         break;
567       }
568     }
569     break;
570   }
571 
572   case MCFragment::FT_Data:
573     ++stats::EmittedDataFragments;
574     OS << cast<MCDataFragment>(F).getContents();
575     break;
576 
577   case MCFragment::FT_Relaxable:
578     ++stats::EmittedRelaxableFragments;
579     OS << cast<MCRelaxableFragment>(F).getContents();
580     break;
581 
582   case MCFragment::FT_CompactEncodedInst:
583     ++stats::EmittedCompactEncodedInstFragments;
584     OS << cast<MCCompactEncodedInstFragment>(F).getContents();
585     break;
586 
587   case MCFragment::FT_Fill: {
588     ++stats::EmittedFillFragments;
589     const MCFillFragment &FF = cast<MCFillFragment>(F);
590     uint64_t V = FF.getValue();
591     unsigned VSize = FF.getValueSize();
592     const unsigned MaxChunkSize = 16;
593     char Data[MaxChunkSize];
594     assert(0 < VSize && VSize <= MaxChunkSize && "Illegal fragment fill size");
595     // Duplicate V into Data as byte vector to reduce number of
596     // writes done. As such, do endian conversion here.
597     for (unsigned I = 0; I != VSize; ++I) {
598       unsigned index = Endian == support::little ? I : (VSize - I - 1);
599       Data[I] = uint8_t(V >> (index * 8));
600     }
601     for (unsigned I = VSize; I < MaxChunkSize; ++I)
602       Data[I] = Data[I - VSize];
603 
604     // Set to largest multiple of VSize in Data.
605     const unsigned NumPerChunk = MaxChunkSize / VSize;
606     // Set ChunkSize to largest multiple of VSize in Data
607     const unsigned ChunkSize = VSize * NumPerChunk;
608 
609     // Do copies by chunk.
610     StringRef Ref(Data, ChunkSize);
611     for (uint64_t I = 0, E = FragmentSize / ChunkSize; I != E; ++I)
612       OS << Ref;
613 
614     // do remainder if needed.
615     unsigned TrailingCount = FragmentSize % ChunkSize;
616     if (TrailingCount)
617       OS.write(Data, TrailingCount);
618     break;
619   }
620 
621   case MCFragment::FT_Nops: {
622     ++stats::EmittedNopsFragments;
623     const MCNopsFragment &NF = cast<MCNopsFragment>(F);
624     int64_t NumBytes = NF.getNumBytes();
625     int64_t ControlledNopLength = NF.getControlledNopLength();
626     int64_t MaximumNopLength = Asm.getBackend().getMaximumNopSize();
627 
628     assert(NumBytes > 0 && "Expected positive NOPs fragment size");
629     assert(ControlledNopLength >= 0 && "Expected non-negative NOP size");
630 
631     if (ControlledNopLength > MaximumNopLength) {
632       Asm.getContext().reportError(NF.getLoc(),
633                                    "illegal NOP size " +
634                                        std::to_string(ControlledNopLength) +
635                                        ". (expected within [0, " +
636                                        std::to_string(MaximumNopLength) + "])");
637       // Clamp the NOP length as reportError does not stop the execution
638       // immediately.
639       ControlledNopLength = MaximumNopLength;
640     }
641 
642     // Use maximum value if the size of each NOP is not specified
643     if (!ControlledNopLength)
644       ControlledNopLength = MaximumNopLength;
645 
646     while (NumBytes) {
647       uint64_t NumBytesToEmit =
648           (uint64_t)std::min(NumBytes, ControlledNopLength);
649       assert(NumBytesToEmit && "try to emit empty NOP instruction");
650       if (!Asm.getBackend().writeNopData(OS, NumBytesToEmit)) {
651         report_fatal_error("unable to write nop sequence of the remaining " +
652                            Twine(NumBytesToEmit) + " bytes");
653         break;
654       }
655       NumBytes -= NumBytesToEmit;
656     }
657     break;
658   }
659 
660   case MCFragment::FT_LEB: {
661     const MCLEBFragment &LF = cast<MCLEBFragment>(F);
662     OS << LF.getContents();
663     break;
664   }
665 
666   case MCFragment::FT_BoundaryAlign: {
667     if (!Asm.getBackend().writeNopData(OS, FragmentSize))
668       report_fatal_error("unable to write nop sequence of " +
669                          Twine(FragmentSize) + " bytes");
670     break;
671   }
672 
673   case MCFragment::FT_SymbolId: {
674     const MCSymbolIdFragment &SF = cast<MCSymbolIdFragment>(F);
675     support::endian::write<uint32_t>(OS, SF.getSymbol()->getIndex(), Endian);
676     break;
677   }
678 
679   case MCFragment::FT_Org: {
680     ++stats::EmittedOrgFragments;
681     const MCOrgFragment &OF = cast<MCOrgFragment>(F);
682 
683     for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
684       OS << char(OF.getValue());
685 
686     break;
687   }
688 
689   case MCFragment::FT_Dwarf: {
690     const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
691     OS << OF.getContents();
692     break;
693   }
694   case MCFragment::FT_DwarfFrame: {
695     const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
696     OS << CF.getContents();
697     break;
698   }
699   case MCFragment::FT_CVInlineLines: {
700     const auto &OF = cast<MCCVInlineLineTableFragment>(F);
701     OS << OF.getContents();
702     break;
703   }
704   case MCFragment::FT_CVDefRange: {
705     const auto &DRF = cast<MCCVDefRangeFragment>(F);
706     OS << DRF.getContents();
707     break;
708   }
709   case MCFragment::FT_PseudoProbe: {
710     const MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(F);
711     OS << PF.getContents();
712     break;
713   }
714   case MCFragment::FT_Dummy:
715     llvm_unreachable("Should not have been added");
716   }
717 
718   assert(OS.tell() - Start == FragmentSize &&
719          "The stream should advance by fragment size");
720 }
721 
722 void MCAssembler::writeSectionData(raw_ostream &OS, const MCSection *Sec,
723                                    const MCAsmLayout &Layout) const {
724   assert(getBackendPtr() && "Expected assembler backend");
725 
726   // Ignore virtual sections.
727   if (Sec->isVirtualSection()) {
728     assert(Layout.getSectionFileSize(Sec) == 0 && "Invalid size for section!");
729 
730     // Check that contents are only things legal inside a virtual section.
731     for (const MCFragment &F : *Sec) {
732       switch (F.getKind()) {
733       default: llvm_unreachable("Invalid fragment in virtual section!");
734       case MCFragment::FT_Data: {
735         // Check that we aren't trying to write a non-zero contents (or fixups)
736         // into a virtual section. This is to support clients which use standard
737         // directives to fill the contents of virtual sections.
738         const MCDataFragment &DF = cast<MCDataFragment>(F);
739         if (DF.fixup_begin() != DF.fixup_end())
740           getContext().reportError(SMLoc(), Sec->getVirtualSectionKind() +
741                                                 " section '" + Sec->getName() +
742                                                 "' cannot have fixups");
743         for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
744           if (DF.getContents()[i]) {
745             getContext().reportError(SMLoc(),
746                                      Sec->getVirtualSectionKind() +
747                                          " section '" + Sec->getName() +
748                                          "' cannot have non-zero initializers");
749             break;
750           }
751         break;
752       }
753       case MCFragment::FT_Align:
754         // Check that we aren't trying to write a non-zero value into a virtual
755         // section.
756         assert((cast<MCAlignFragment>(F).getValueSize() == 0 ||
757                 cast<MCAlignFragment>(F).getValue() == 0) &&
758                "Invalid align in virtual section!");
759         break;
760       case MCFragment::FT_Fill:
761         assert((cast<MCFillFragment>(F).getValue() == 0) &&
762                "Invalid fill in virtual section!");
763         break;
764       case MCFragment::FT_Org:
765         break;
766       }
767     }
768 
769     return;
770   }
771 
772   uint64_t Start = OS.tell();
773   (void)Start;
774 
775   for (const MCFragment &F : *Sec)
776     writeFragment(OS, *this, Layout, F);
777 
778   assert(getContext().hadError() ||
779          OS.tell() - Start == Layout.getSectionAddressSize(Sec));
780 }
781 
782 std::tuple<MCValue, uint64_t, bool>
783 MCAssembler::handleFixup(const MCAsmLayout &Layout, MCFragment &F,
784                          const MCFixup &Fixup) {
785   // Evaluate the fixup.
786   MCValue Target;
787   uint64_t FixedValue;
788   bool WasForced;
789   bool IsResolved = evaluateFixup(Layout, Fixup, &F, Target, FixedValue,
790                                   WasForced);
791   if (!IsResolved) {
792     // The fixup was unresolved, we need a relocation. Inform the object
793     // writer of the relocation, and give it an opportunity to adjust the
794     // fixup value if need be.
795     if (Target.getSymA() && Target.getSymB() &&
796         getBackend().requiresDiffExpressionRelocations()) {
797       // The fixup represents the difference between two symbols, which the
798       // backend has indicated must be resolved at link time. Split up the fixup
799       // into two relocations, one for the add, and one for the sub, and emit
800       // both of these. The constant will be associated with the add half of the
801       // expression.
802       MCFixup FixupAdd = MCFixup::createAddFor(Fixup);
803       MCValue TargetAdd =
804           MCValue::get(Target.getSymA(), nullptr, Target.getConstant());
805       getWriter().recordRelocation(*this, Layout, &F, FixupAdd, TargetAdd,
806                                    FixedValue);
807       MCFixup FixupSub = MCFixup::createSubFor(Fixup);
808       MCValue TargetSub = MCValue::get(Target.getSymB());
809       getWriter().recordRelocation(*this, Layout, &F, FixupSub, TargetSub,
810                                    FixedValue);
811     } else {
812       getWriter().recordRelocation(*this, Layout, &F, Fixup, Target,
813                                    FixedValue);
814     }
815   }
816   return std::make_tuple(Target, FixedValue, IsResolved);
817 }
818 
819 void MCAssembler::layout(MCAsmLayout &Layout) {
820   assert(getBackendPtr() && "Expected assembler backend");
821   DEBUG_WITH_TYPE("mc-dump", {
822       errs() << "assembler backend - pre-layout\n--\n";
823       dump(); });
824 
825   // Create dummy fragments and assign section ordinals.
826   unsigned SectionIndex = 0;
827   for (MCSection &Sec : *this) {
828     // Create dummy fragments to eliminate any empty sections, this simplifies
829     // layout.
830     if (Sec.getFragmentList().empty())
831       new MCDataFragment(&Sec);
832 
833     Sec.setOrdinal(SectionIndex++);
834   }
835 
836   // Assign layout order indices to sections and fragments.
837   for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
838     MCSection *Sec = Layout.getSectionOrder()[i];
839     Sec->setLayoutOrder(i);
840 
841     unsigned FragmentIndex = 0;
842     for (MCFragment &Frag : *Sec)
843       Frag.setLayoutOrder(FragmentIndex++);
844   }
845 
846   // Layout until everything fits.
847   while (layoutOnce(Layout)) {
848     if (getContext().hadError())
849       return;
850     // Size of fragments in one section can depend on the size of fragments in
851     // another. If any fragment has changed size, we have to re-layout (and
852     // as a result possibly further relax) all.
853     for (MCSection &Sec : *this)
854       Layout.invalidateFragmentsFrom(&*Sec.begin());
855   }
856 
857   DEBUG_WITH_TYPE("mc-dump", {
858       errs() << "assembler backend - post-relaxation\n--\n";
859       dump(); });
860 
861   // Finalize the layout, including fragment lowering.
862   finishLayout(Layout);
863 
864   DEBUG_WITH_TYPE("mc-dump", {
865       errs() << "assembler backend - final-layout\n--\n";
866       dump(); });
867 
868   // Allow the object writer a chance to perform post-layout binding (for
869   // example, to set the index fields in the symbol data).
870   getWriter().executePostLayoutBinding(*this, Layout);
871 
872   // Evaluate and apply the fixups, generating relocation entries as necessary.
873   for (MCSection &Sec : *this) {
874     for (MCFragment &Frag : Sec) {
875       ArrayRef<MCFixup> Fixups;
876       MutableArrayRef<char> Contents;
877       const MCSubtargetInfo *STI = nullptr;
878 
879       // Process MCAlignFragment and MCEncodedFragmentWithFixups here.
880       switch (Frag.getKind()) {
881       default:
882         continue;
883       case MCFragment::FT_Align: {
884         MCAlignFragment &AF = cast<MCAlignFragment>(Frag);
885         // Insert fixup type for code alignment if the target define
886         // shouldInsertFixupForCodeAlign target hook.
887         if (Sec.UseCodeAlign() && AF.hasEmitNops())
888           getBackend().shouldInsertFixupForCodeAlign(*this, Layout, AF);
889         continue;
890       }
891       case MCFragment::FT_Data: {
892         MCDataFragment &DF = cast<MCDataFragment>(Frag);
893         Fixups = DF.getFixups();
894         Contents = DF.getContents();
895         STI = DF.getSubtargetInfo();
896         assert(!DF.hasInstructions() || STI != nullptr);
897         break;
898       }
899       case MCFragment::FT_Relaxable: {
900         MCRelaxableFragment &RF = cast<MCRelaxableFragment>(Frag);
901         Fixups = RF.getFixups();
902         Contents = RF.getContents();
903         STI = RF.getSubtargetInfo();
904         assert(!RF.hasInstructions() || STI != nullptr);
905         break;
906       }
907       case MCFragment::FT_CVDefRange: {
908         MCCVDefRangeFragment &CF = cast<MCCVDefRangeFragment>(Frag);
909         Fixups = CF.getFixups();
910         Contents = CF.getContents();
911         break;
912       }
913       case MCFragment::FT_Dwarf: {
914         MCDwarfLineAddrFragment &DF = cast<MCDwarfLineAddrFragment>(Frag);
915         Fixups = DF.getFixups();
916         Contents = DF.getContents();
917         break;
918       }
919       case MCFragment::FT_DwarfFrame: {
920         MCDwarfCallFrameFragment &DF = cast<MCDwarfCallFrameFragment>(Frag);
921         Fixups = DF.getFixups();
922         Contents = DF.getContents();
923         break;
924       }
925       case MCFragment::FT_PseudoProbe: {
926         MCPseudoProbeAddrFragment &PF = cast<MCPseudoProbeAddrFragment>(Frag);
927         Fixups = PF.getFixups();
928         Contents = PF.getContents();
929         break;
930       }
931       }
932       for (const MCFixup &Fixup : Fixups) {
933         uint64_t FixedValue;
934         bool IsResolved;
935         MCValue Target;
936         std::tie(Target, FixedValue, IsResolved) =
937             handleFixup(Layout, Frag, Fixup);
938         getBackend().applyFixup(*this, Fixup, Target, Contents, FixedValue,
939                                 IsResolved, STI);
940       }
941     }
942   }
943 }
944 
945 void MCAssembler::Finish() {
946   // Create the layout object.
947   MCAsmLayout Layout(*this);
948   layout(Layout);
949 
950   // Write the object file.
951   stats::ObjectBytes += getWriter().writeObject(*this, Layout);
952 }
953 
954 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
955                                        const MCRelaxableFragment *DF,
956                                        const MCAsmLayout &Layout) const {
957   assert(getBackendPtr() && "Expected assembler backend");
958   MCValue Target;
959   uint64_t Value;
960   bool WasForced;
961   bool Resolved = evaluateFixup(Layout, Fixup, DF, Target, Value, WasForced);
962   if (Target.getSymA() &&
963       Target.getSymA()->getKind() == MCSymbolRefExpr::VK_X86_ABS8 &&
964       Fixup.getKind() == FK_Data_1)
965     return false;
966   return getBackend().fixupNeedsRelaxationAdvanced(Fixup, Resolved, Value, DF,
967                                                    Layout, WasForced);
968 }
969 
970 bool MCAssembler::fragmentNeedsRelaxation(const MCRelaxableFragment *F,
971                                           const MCAsmLayout &Layout) const {
972   assert(getBackendPtr() && "Expected assembler backend");
973   // If this inst doesn't ever need relaxation, ignore it. This occurs when we
974   // are intentionally pushing out inst fragments, or because we relaxed a
975   // previous instruction to one that doesn't need relaxation.
976   if (!getBackend().mayNeedRelaxation(F->getInst(), *F->getSubtargetInfo()))
977     return false;
978 
979   for (const MCFixup &Fixup : F->getFixups())
980     if (fixupNeedsRelaxation(Fixup, F, Layout))
981       return true;
982 
983   return false;
984 }
985 
986 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
987                                    MCRelaxableFragment &F) {
988   assert(getEmitterPtr() &&
989          "Expected CodeEmitter defined for relaxInstruction");
990   if (!fragmentNeedsRelaxation(&F, Layout))
991     return false;
992 
993   ++stats::RelaxedInstructions;
994 
995   // FIXME-PERF: We could immediately lower out instructions if we can tell
996   // they are fully resolved, to avoid retesting on later passes.
997 
998   // Relax the fragment.
999 
1000   MCInst Relaxed = F.getInst();
1001   getBackend().relaxInstruction(Relaxed, *F.getSubtargetInfo());
1002 
1003   // Encode the new instruction.
1004   //
1005   // FIXME-PERF: If it matters, we could let the target do this. It can
1006   // probably do so more efficiently in many cases.
1007   SmallVector<MCFixup, 4> Fixups;
1008   SmallString<256> Code;
1009   raw_svector_ostream VecOS(Code);
1010   getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, *F.getSubtargetInfo());
1011 
1012   // Update the fragment.
1013   F.setInst(Relaxed);
1014   F.getContents() = Code;
1015   F.getFixups() = Fixups;
1016 
1017   return true;
1018 }
1019 
1020 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
1021   uint64_t OldSize = LF.getContents().size();
1022   int64_t Value;
1023   bool Abs = LF.getValue().evaluateKnownAbsolute(Value, Layout);
1024   if (!Abs)
1025     report_fatal_error("sleb128 and uleb128 expressions must be absolute");
1026   SmallString<8> &Data = LF.getContents();
1027   Data.clear();
1028   raw_svector_ostream OSE(Data);
1029   // The compiler can generate EH table assembly that is impossible to assemble
1030   // without either adding padding to an LEB fragment or adding extra padding
1031   // to a later alignment fragment. To accommodate such tables, relaxation can
1032   // only increase an LEB fragment size here, not decrease it. See PR35809.
1033   if (LF.isSigned())
1034     encodeSLEB128(Value, OSE, OldSize);
1035   else
1036     encodeULEB128(Value, OSE, OldSize);
1037   return OldSize != LF.getContents().size();
1038 }
1039 
1040 /// Check if the branch crosses the boundary.
1041 ///
1042 /// \param StartAddr start address of the fused/unfused branch.
1043 /// \param Size size of the fused/unfused branch.
1044 /// \param BoundaryAlignment alignment requirement of the branch.
1045 /// \returns true if the branch cross the boundary.
1046 static bool mayCrossBoundary(uint64_t StartAddr, uint64_t Size,
1047                              Align BoundaryAlignment) {
1048   uint64_t EndAddr = StartAddr + Size;
1049   return (StartAddr >> Log2(BoundaryAlignment)) !=
1050          ((EndAddr - 1) >> Log2(BoundaryAlignment));
1051 }
1052 
1053 /// Check if the branch is against the boundary.
1054 ///
1055 /// \param StartAddr start address of the fused/unfused branch.
1056 /// \param Size size of the fused/unfused branch.
1057 /// \param BoundaryAlignment alignment requirement of the branch.
1058 /// \returns true if the branch is against the boundary.
1059 static bool isAgainstBoundary(uint64_t StartAddr, uint64_t Size,
1060                               Align BoundaryAlignment) {
1061   uint64_t EndAddr = StartAddr + Size;
1062   return (EndAddr & (BoundaryAlignment.value() - 1)) == 0;
1063 }
1064 
1065 /// Check if the branch needs padding.
1066 ///
1067 /// \param StartAddr start address of the fused/unfused branch.
1068 /// \param Size size of the fused/unfused branch.
1069 /// \param BoundaryAlignment alignment requirement of the branch.
1070 /// \returns true if the branch needs padding.
1071 static bool needPadding(uint64_t StartAddr, uint64_t Size,
1072                         Align BoundaryAlignment) {
1073   return mayCrossBoundary(StartAddr, Size, BoundaryAlignment) ||
1074          isAgainstBoundary(StartAddr, Size, BoundaryAlignment);
1075 }
1076 
1077 bool MCAssembler::relaxBoundaryAlign(MCAsmLayout &Layout,
1078                                      MCBoundaryAlignFragment &BF) {
1079   // BoundaryAlignFragment that doesn't need to align any fragment should not be
1080   // relaxed.
1081   if (!BF.getLastFragment())
1082     return false;
1083 
1084   uint64_t AlignedOffset = Layout.getFragmentOffset(&BF);
1085   uint64_t AlignedSize = 0;
1086   for (const MCFragment *F = BF.getLastFragment(); F != &BF;
1087        F = F->getPrevNode())
1088     AlignedSize += computeFragmentSize(Layout, *F);
1089 
1090   Align BoundaryAlignment = BF.getAlignment();
1091   uint64_t NewSize = needPadding(AlignedOffset, AlignedSize, BoundaryAlignment)
1092                          ? offsetToAlignment(AlignedOffset, BoundaryAlignment)
1093                          : 0U;
1094   if (NewSize == BF.getSize())
1095     return false;
1096   BF.setSize(NewSize);
1097   Layout.invalidateFragmentsFrom(&BF);
1098   return true;
1099 }
1100 
1101 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
1102                                      MCDwarfLineAddrFragment &DF) {
1103   MCContext &Context = Layout.getAssembler().getContext();
1104   uint64_t OldSize = DF.getContents().size();
1105   int64_t AddrDelta;
1106   bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1107   assert(Abs && "We created a line delta with an invalid expression");
1108   (void)Abs;
1109   int64_t LineDelta;
1110   LineDelta = DF.getLineDelta();
1111   SmallVectorImpl<char> &Data = DF.getContents();
1112   Data.clear();
1113   raw_svector_ostream OSE(Data);
1114   DF.getFixups().clear();
1115 
1116   if (!getBackend().requiresDiffExpressionRelocations()) {
1117     MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
1118                             AddrDelta, OSE);
1119   } else {
1120     uint32_t Offset;
1121     uint32_t Size;
1122     bool SetDelta;
1123     std::tie(Offset, Size, SetDelta) =
1124         MCDwarfLineAddr::fixedEncode(Context, LineDelta, AddrDelta, OSE);
1125     // Add Fixups for address delta or new address.
1126     const MCExpr *FixupExpr;
1127     if (SetDelta) {
1128       FixupExpr = &DF.getAddrDelta();
1129     } else {
1130       const MCBinaryExpr *ABE = cast<MCBinaryExpr>(&DF.getAddrDelta());
1131       FixupExpr = ABE->getLHS();
1132     }
1133     DF.getFixups().push_back(
1134         MCFixup::create(Offset, FixupExpr,
1135                         MCFixup::getKindForSize(Size, false /*isPCRel*/)));
1136   }
1137 
1138   return OldSize != Data.size();
1139 }
1140 
1141 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
1142                                               MCDwarfCallFrameFragment &DF) {
1143   MCContext &Context = Layout.getAssembler().getContext();
1144   uint64_t OldSize = DF.getContents().size();
1145   int64_t AddrDelta;
1146   bool Abs = DF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1147   assert(Abs && "We created call frame with an invalid expression");
1148   (void) Abs;
1149   SmallVectorImpl<char> &Data = DF.getContents();
1150   Data.clear();
1151   raw_svector_ostream OSE(Data);
1152   DF.getFixups().clear();
1153 
1154   if (getBackend().requiresDiffExpressionRelocations()) {
1155     uint32_t Offset;
1156     uint32_t Size;
1157     MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE, &Offset,
1158                                           &Size);
1159     if (Size) {
1160       DF.getFixups().push_back(MCFixup::create(
1161           Offset, &DF.getAddrDelta(),
1162           MCFixup::getKindForSizeInBits(Size /*In bits.*/, false /*isPCRel*/)));
1163     }
1164   } else {
1165     MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
1166   }
1167 
1168   return OldSize != Data.size();
1169 }
1170 
1171 bool MCAssembler::relaxCVInlineLineTable(MCAsmLayout &Layout,
1172                                          MCCVInlineLineTableFragment &F) {
1173   unsigned OldSize = F.getContents().size();
1174   getContext().getCVContext().encodeInlineLineTable(Layout, F);
1175   return OldSize != F.getContents().size();
1176 }
1177 
1178 bool MCAssembler::relaxCVDefRange(MCAsmLayout &Layout,
1179                                   MCCVDefRangeFragment &F) {
1180   unsigned OldSize = F.getContents().size();
1181   getContext().getCVContext().encodeDefRange(Layout, F);
1182   return OldSize != F.getContents().size();
1183 }
1184 
1185 bool MCAssembler::relaxPseudoProbeAddr(MCAsmLayout &Layout,
1186                                        MCPseudoProbeAddrFragment &PF) {
1187   uint64_t OldSize = PF.getContents().size();
1188   int64_t AddrDelta;
1189   bool Abs = PF.getAddrDelta().evaluateKnownAbsolute(AddrDelta, Layout);
1190   assert(Abs && "We created a pseudo probe with an invalid expression");
1191   (void)Abs;
1192   SmallVectorImpl<char> &Data = PF.getContents();
1193   Data.clear();
1194   raw_svector_ostream OSE(Data);
1195   PF.getFixups().clear();
1196 
1197   // Relocations should not be needed in general except on RISC-V which we are
1198   // not targeted for now.
1199   assert(!getBackend().requiresDiffExpressionRelocations() &&
1200          "cannot relax relocations");
1201   // AddrDelta is a signed integer
1202   encodeSLEB128(AddrDelta, OSE, OldSize);
1203   return OldSize != Data.size();
1204 }
1205 
1206 bool MCAssembler::relaxFragment(MCAsmLayout &Layout, MCFragment &F) {
1207   switch(F.getKind()) {
1208   default:
1209     return false;
1210   case MCFragment::FT_Relaxable:
1211     assert(!getRelaxAll() &&
1212            "Did not expect a MCRelaxableFragment in RelaxAll mode");
1213     return relaxInstruction(Layout, cast<MCRelaxableFragment>(F));
1214   case MCFragment::FT_Dwarf:
1215     return relaxDwarfLineAddr(Layout, cast<MCDwarfLineAddrFragment>(F));
1216   case MCFragment::FT_DwarfFrame:
1217     return relaxDwarfCallFrameFragment(Layout,
1218                                        cast<MCDwarfCallFrameFragment>(F));
1219   case MCFragment::FT_LEB:
1220     return relaxLEB(Layout, cast<MCLEBFragment>(F));
1221   case MCFragment::FT_BoundaryAlign:
1222     return relaxBoundaryAlign(Layout, cast<MCBoundaryAlignFragment>(F));
1223   case MCFragment::FT_CVInlineLines:
1224     return relaxCVInlineLineTable(Layout, cast<MCCVInlineLineTableFragment>(F));
1225   case MCFragment::FT_CVDefRange:
1226     return relaxCVDefRange(Layout, cast<MCCVDefRangeFragment>(F));
1227   case MCFragment::FT_PseudoProbe:
1228     return relaxPseudoProbeAddr(Layout, cast<MCPseudoProbeAddrFragment>(F));
1229   }
1230 }
1231 
1232 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout, MCSection &Sec) {
1233   // Holds the first fragment which needed relaxing during this layout. It will
1234   // remain NULL if none were relaxed.
1235   // When a fragment is relaxed, all the fragments following it should get
1236   // invalidated because their offset is going to change.
1237   MCFragment *FirstRelaxedFragment = nullptr;
1238 
1239   // Attempt to relax all the fragments in the section.
1240   for (MCFragment &Frag : Sec) {
1241     // Check if this is a fragment that needs relaxation.
1242     bool RelaxedFrag = relaxFragment(Layout, Frag);
1243     if (RelaxedFrag && !FirstRelaxedFragment)
1244       FirstRelaxedFragment = &Frag;
1245   }
1246   if (FirstRelaxedFragment) {
1247     Layout.invalidateFragmentsFrom(FirstRelaxedFragment);
1248     return true;
1249   }
1250   return false;
1251 }
1252 
1253 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
1254   ++stats::RelaxationSteps;
1255 
1256   bool WasRelaxed = false;
1257   for (MCSection &Sec : *this) {
1258     while (layoutSectionOnce(Layout, Sec))
1259       WasRelaxed = true;
1260   }
1261 
1262   return WasRelaxed;
1263 }
1264 
1265 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
1266   assert(getBackendPtr() && "Expected assembler backend");
1267   // The layout is done. Mark every fragment as valid.
1268   for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
1269     MCSection &Section = *Layout.getSectionOrder()[i];
1270     Layout.getFragmentOffset(&*Section.getFragmentList().rbegin());
1271     computeFragmentSize(Layout, *Section.getFragmentList().rbegin());
1272   }
1273   getBackend().finishLayout(*this, Layout);
1274 }
1275 
1276 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1277 LLVM_DUMP_METHOD void MCAssembler::dump() const{
1278   raw_ostream &OS = errs();
1279 
1280   OS << "<MCAssembler\n";
1281   OS << "  Sections:[\n    ";
1282   for (const_iterator it = begin(), ie = end(); it != ie; ++it) {
1283     if (it != begin()) OS << ",\n    ";
1284     it->dump();
1285   }
1286   OS << "],\n";
1287   OS << "  Symbols:[";
1288 
1289   for (const_symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
1290     if (it != symbol_begin()) OS << ",\n           ";
1291     OS << "(";
1292     it->dump();
1293     OS << ", Index:" << it->getIndex() << ", ";
1294     OS << ")";
1295   }
1296   OS << "]>\n";
1297 }
1298 #endif
1299