1 //===- lib/MC/MCAssembler.cpp - Assembler Backend Implementation ----------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9
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/MCContext.h"
15 #include "llvm/MC/MCExpr.h"
16 #include "llvm/MC/MCObjectWriter.h"
17 #include "llvm/MC/MCSection.h"
18 #include "llvm/MC/MCSymbol.h"
19 #include "llvm/MC/MCValue.h"
20 #include "llvm/MC/MCDwarf.h"
21 #include "llvm/MC/MCAsmBackend.h"
22 #include "llvm/ADT/OwningPtr.h"
23 #include "llvm/ADT/Statistic.h"
24 #include "llvm/ADT/StringExtras.h"
25 #include "llvm/ADT/Twine.h"
26 #include "llvm/Support/Debug.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include "llvm/Support/TargetRegistry.h"
30
31 using namespace llvm;
32
33 namespace {
34 namespace stats {
35 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
36 STATISTIC(EvaluateFixup, "Number of evaluated fixups");
37 STATISTIC(FragmentLayouts, "Number of fragment layouts");
38 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
39 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
40 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
41 }
42 }
43
44 // FIXME FIXME FIXME: There are number of places in this file where we convert
45 // what is a 64-bit assembler value used for computation into a value in the
46 // object file, which may truncate it. We should detect that truncation where
47 // invalid and report errors back.
48
49 /* *** */
50
MCAsmLayout(MCAssembler & Asm)51 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
52 : Assembler(Asm), LastValidFragment()
53 {
54 // Compute the section layout order. Virtual sections must go last.
55 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
56 if (!it->getSection().isVirtualSection())
57 SectionOrder.push_back(&*it);
58 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
59 if (it->getSection().isVirtualSection())
60 SectionOrder.push_back(&*it);
61 }
62
isFragmentUpToDate(const MCFragment * F) const63 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
64 const MCSectionData &SD = *F->getParent();
65 const MCFragment *LastValid = LastValidFragment.lookup(&SD);
66 if (!LastValid)
67 return false;
68 assert(LastValid->getParent() == F->getParent());
69 return F->getLayoutOrder() <= LastValid->getLayoutOrder();
70 }
71
Invalidate(MCFragment * F)72 void MCAsmLayout::Invalidate(MCFragment *F) {
73 // If this fragment wasn't already up-to-date, we don't need to do anything.
74 if (!isFragmentUpToDate(F))
75 return;
76
77 // Otherwise, reset the last valid fragment to this fragment.
78 const MCSectionData &SD = *F->getParent();
79 LastValidFragment[&SD] = F;
80 }
81
EnsureValid(const MCFragment * F) const82 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
83 MCSectionData &SD = *F->getParent();
84
85 MCFragment *Cur = LastValidFragment[&SD];
86 if (!Cur)
87 Cur = &*SD.begin();
88 else
89 Cur = Cur->getNextNode();
90
91 // Advance the layout position until the fragment is up-to-date.
92 while (!isFragmentUpToDate(F)) {
93 const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
94 Cur = Cur->getNextNode();
95 }
96 }
97
getFragmentOffset(const MCFragment * F) const98 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
99 EnsureValid(F);
100 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
101 return F->Offset;
102 }
103
getSymbolOffset(const MCSymbolData * SD) const104 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
105 const MCSymbol &S = SD->getSymbol();
106
107 // If this is a variable, then recursively evaluate now.
108 if (S.isVariable()) {
109 MCValue Target;
110 if (!S.getVariableValue()->EvaluateAsRelocatable(Target, *this))
111 report_fatal_error("unable to evaluate offset for variable '" +
112 S.getName() + "'");
113
114 // Verify that any used symbols are defined.
115 if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
116 report_fatal_error("unable to evaluate offset to undefined symbol '" +
117 Target.getSymA()->getSymbol().getName() + "'");
118 if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
119 report_fatal_error("unable to evaluate offset to undefined symbol '" +
120 Target.getSymB()->getSymbol().getName() + "'");
121
122 uint64_t Offset = Target.getConstant();
123 if (Target.getSymA())
124 Offset += getSymbolOffset(&Assembler.getSymbolData(
125 Target.getSymA()->getSymbol()));
126 if (Target.getSymB())
127 Offset -= getSymbolOffset(&Assembler.getSymbolData(
128 Target.getSymB()->getSymbol()));
129 return Offset;
130 }
131
132 assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
133 return getFragmentOffset(SD->getFragment()) + SD->getOffset();
134 }
135
getSectionAddressSize(const MCSectionData * SD) const136 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
137 // The size is the last fragment's end offset.
138 const MCFragment &F = SD->getFragmentList().back();
139 return getFragmentOffset(&F) + getAssembler().ComputeFragmentSize(*this, F);
140 }
141
getSectionFileSize(const MCSectionData * SD) const142 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
143 // Virtual sections have no file size.
144 if (SD->getSection().isVirtualSection())
145 return 0;
146
147 // Otherwise, the file size is the same as the address space size.
148 return getSectionAddressSize(SD);
149 }
150
151 /* *** */
152
MCFragment()153 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
154 }
155
~MCFragment()156 MCFragment::~MCFragment() {
157 }
158
MCFragment(FragmentType _Kind,MCSectionData * _Parent)159 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
160 : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0))
161 {
162 if (Parent)
163 Parent->getFragmentList().push_back(this);
164 }
165
166 /* *** */
167
MCSectionData()168 MCSectionData::MCSectionData() : Section(0) {}
169
MCSectionData(const MCSection & _Section,MCAssembler * A)170 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
171 : Section(&_Section),
172 Ordinal(~UINT32_C(0)),
173 Alignment(1),
174 HasInstructions(false)
175 {
176 if (A)
177 A->getSectionList().push_back(this);
178 }
179
180 /* *** */
181
MCSymbolData()182 MCSymbolData::MCSymbolData() : Symbol(0) {}
183
MCSymbolData(const MCSymbol & _Symbol,MCFragment * _Fragment,uint64_t _Offset,MCAssembler * A)184 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
185 uint64_t _Offset, MCAssembler *A)
186 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
187 IsExternal(false), IsPrivateExtern(false),
188 CommonSize(0), SymbolSize(0), CommonAlign(0),
189 Flags(0), Index(0)
190 {
191 if (A)
192 A->getSymbolList().push_back(this);
193 }
194
195 /* *** */
196
MCAssembler(MCContext & Context_,MCAsmBackend & Backend_,MCCodeEmitter & Emitter_,MCObjectWriter & Writer_,raw_ostream & OS_)197 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
198 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
199 raw_ostream &OS_)
200 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(Writer_),
201 OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
202 {
203 }
204
~MCAssembler()205 MCAssembler::~MCAssembler() {
206 }
207
isSymbolLinkerVisible(const MCSymbol & Symbol) const208 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
209 // Non-temporary labels should always be visible to the linker.
210 if (!Symbol.isTemporary())
211 return true;
212
213 // Absolute temporary labels are never visible.
214 if (!Symbol.isInSection())
215 return false;
216
217 // Otherwise, check if the section requires symbols even for temporary labels.
218 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
219 }
220
getAtom(const MCSymbolData * SD) const221 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
222 // Linker visible symbols define atoms.
223 if (isSymbolLinkerVisible(SD->getSymbol()))
224 return SD;
225
226 // Absolute and undefined symbols have no defining atom.
227 if (!SD->getFragment())
228 return 0;
229
230 // Non-linker visible symbols in sections which can't be atomized have no
231 // defining atom.
232 if (!getBackend().isSectionAtomizable(
233 SD->getFragment()->getParent()->getSection()))
234 return 0;
235
236 // Otherwise, return the atom for the containing fragment.
237 return SD->getFragment()->getAtom();
238 }
239
EvaluateFixup(const MCAsmLayout & Layout,const MCFixup & Fixup,const MCFragment * DF,MCValue & Target,uint64_t & Value) const240 bool MCAssembler::EvaluateFixup(const MCAsmLayout &Layout,
241 const MCFixup &Fixup, const MCFragment *DF,
242 MCValue &Target, uint64_t &Value) const {
243 ++stats::EvaluateFixup;
244
245 if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
246 report_fatal_error("expected relocatable expression");
247
248 bool IsPCRel = Backend.getFixupKindInfo(
249 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
250
251 bool IsResolved;
252 if (IsPCRel) {
253 if (Target.getSymB()) {
254 IsResolved = false;
255 } else if (!Target.getSymA()) {
256 IsResolved = false;
257 } else {
258 const MCSymbolRefExpr *A = Target.getSymA();
259 const MCSymbol &SA = A->getSymbol();
260 if (A->getKind() != MCSymbolRefExpr::VK_None ||
261 SA.AliasedSymbol().isUndefined()) {
262 IsResolved = false;
263 } else {
264 const MCSymbolData &DataA = getSymbolData(SA);
265 IsResolved =
266 getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
267 *DF, false, true);
268 }
269 }
270 } else {
271 IsResolved = Target.isAbsolute();
272 }
273
274 Value = Target.getConstant();
275
276 bool IsThumb = false;
277 if (const MCSymbolRefExpr *A = Target.getSymA()) {
278 const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
279 if (Sym.isDefined())
280 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
281 if (isThumbFunc(&Sym))
282 IsThumb = true;
283 }
284 if (const MCSymbolRefExpr *B = Target.getSymB()) {
285 const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
286 if (Sym.isDefined())
287 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
288 }
289
290
291 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
292 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
293 assert((ShouldAlignPC ? IsPCRel : true) &&
294 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
295
296 if (IsPCRel) {
297 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
298
299 // A number of ARM fixups in Thumb mode require that the effective PC
300 // address be determined as the 32-bit aligned version of the actual offset.
301 if (ShouldAlignPC) Offset &= ~0x3;
302 Value -= Offset;
303 }
304
305 // ARM fixups based from a thumb function address need to have the low
306 // bit set. The actual value is always at least 16-bit aligned, so the
307 // low bit is normally clear and available for use as an ISA flag for
308 // interworking.
309 if (IsThumb)
310 Value |= 1;
311
312 return IsResolved;
313 }
314
ComputeFragmentSize(const MCAsmLayout & Layout,const MCFragment & F) const315 uint64_t MCAssembler::ComputeFragmentSize(const MCAsmLayout &Layout,
316 const MCFragment &F) const {
317 switch (F.getKind()) {
318 case MCFragment::FT_Data:
319 return cast<MCDataFragment>(F).getContents().size();
320 case MCFragment::FT_Fill:
321 return cast<MCFillFragment>(F).getSize();
322 case MCFragment::FT_Inst:
323 return cast<MCInstFragment>(F).getInstSize();
324
325 case MCFragment::FT_LEB:
326 return cast<MCLEBFragment>(F).getContents().size();
327
328 case MCFragment::FT_Align: {
329 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
330 unsigned Offset = Layout.getFragmentOffset(&AF);
331 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
332 if (Size > AF.getMaxBytesToEmit())
333 return 0;
334 return Size;
335 }
336
337 case MCFragment::FT_Org: {
338 MCOrgFragment &OF = cast<MCOrgFragment>(F);
339 int64_t TargetLocation;
340 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
341 report_fatal_error("expected assembly-time absolute expression");
342
343 // FIXME: We need a way to communicate this error.
344 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
345 int64_t Size = TargetLocation - FragmentOffset;
346 if (Size < 0 || Size >= 0x40000000)
347 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
348 "' (at offset '" + Twine(FragmentOffset) + "')");
349 return Size;
350 }
351
352 case MCFragment::FT_Dwarf:
353 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
354 case MCFragment::FT_DwarfFrame:
355 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
356 }
357
358 assert(0 && "invalid fragment kind");
359 return 0;
360 }
361
LayoutFragment(MCFragment * F)362 void MCAsmLayout::LayoutFragment(MCFragment *F) {
363 MCFragment *Prev = F->getPrevNode();
364
365 // We should never try to recompute something which is up-to-date.
366 assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
367 // We should never try to compute the fragment layout if it's predecessor
368 // isn't up-to-date.
369 assert((!Prev || isFragmentUpToDate(Prev)) &&
370 "Attempt to compute fragment before it's predecessor!");
371
372 ++stats::FragmentLayouts;
373
374 // Compute fragment offset and size.
375 uint64_t Offset = 0;
376 if (Prev)
377 Offset += Prev->Offset + getAssembler().ComputeFragmentSize(*this, *Prev);
378
379 F->Offset = Offset;
380 LastValidFragment[F->getParent()] = F;
381 }
382
383 /// WriteFragmentData - Write the \arg F data to the output file.
WriteFragmentData(const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment & F)384 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
385 const MCFragment &F) {
386 MCObjectWriter *OW = &Asm.getWriter();
387 uint64_t Start = OW->getStream().tell();
388 (void) Start;
389
390 ++stats::EmittedFragments;
391
392 // FIXME: Embed in fragments instead?
393 uint64_t FragmentSize = Asm.ComputeFragmentSize(Layout, F);
394 switch (F.getKind()) {
395 case MCFragment::FT_Align: {
396 MCAlignFragment &AF = cast<MCAlignFragment>(F);
397 uint64_t Count = FragmentSize / AF.getValueSize();
398
399 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
400
401 // FIXME: This error shouldn't actually occur (the front end should emit
402 // multiple .align directives to enforce the semantics it wants), but is
403 // severe enough that we want to report it. How to handle this?
404 if (Count * AF.getValueSize() != FragmentSize)
405 report_fatal_error("undefined .align directive, value size '" +
406 Twine(AF.getValueSize()) +
407 "' is not a divisor of padding size '" +
408 Twine(FragmentSize) + "'");
409
410 // See if we are aligning with nops, and if so do that first to try to fill
411 // the Count bytes. Then if that did not fill any bytes or there are any
412 // bytes left to fill use the the Value and ValueSize to fill the rest.
413 // If we are aligning with nops, ask that target to emit the right data.
414 if (AF.hasEmitNops()) {
415 if (!Asm.getBackend().WriteNopData(Count, OW))
416 report_fatal_error("unable to write nop sequence of " +
417 Twine(Count) + " bytes");
418 break;
419 }
420
421 // Otherwise, write out in multiples of the value size.
422 for (uint64_t i = 0; i != Count; ++i) {
423 switch (AF.getValueSize()) {
424 default:
425 assert(0 && "Invalid size!");
426 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
427 case 2: OW->Write16(uint16_t(AF.getValue())); break;
428 case 4: OW->Write32(uint32_t(AF.getValue())); break;
429 case 8: OW->Write64(uint64_t(AF.getValue())); break;
430 }
431 }
432 break;
433 }
434
435 case MCFragment::FT_Data: {
436 MCDataFragment &DF = cast<MCDataFragment>(F);
437 assert(FragmentSize == DF.getContents().size() && "Invalid size!");
438 OW->WriteBytes(DF.getContents().str());
439 break;
440 }
441
442 case MCFragment::FT_Fill: {
443 MCFillFragment &FF = cast<MCFillFragment>(F);
444
445 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
446
447 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
448 switch (FF.getValueSize()) {
449 default:
450 assert(0 && "Invalid size!");
451 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
452 case 2: OW->Write16(uint16_t(FF.getValue())); break;
453 case 4: OW->Write32(uint32_t(FF.getValue())); break;
454 case 8: OW->Write64(uint64_t(FF.getValue())); break;
455 }
456 }
457 break;
458 }
459
460 case MCFragment::FT_Inst: {
461 MCInstFragment &IF = cast<MCInstFragment>(F);
462 OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
463 break;
464 }
465
466 case MCFragment::FT_LEB: {
467 MCLEBFragment &LF = cast<MCLEBFragment>(F);
468 OW->WriteBytes(LF.getContents().str());
469 break;
470 }
471
472 case MCFragment::FT_Org: {
473 MCOrgFragment &OF = cast<MCOrgFragment>(F);
474
475 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
476 OW->Write8(uint8_t(OF.getValue()));
477
478 break;
479 }
480
481 case MCFragment::FT_Dwarf: {
482 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
483 OW->WriteBytes(OF.getContents().str());
484 break;
485 }
486 case MCFragment::FT_DwarfFrame: {
487 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
488 OW->WriteBytes(CF.getContents().str());
489 break;
490 }
491 }
492
493 assert(OW->getStream().tell() - Start == FragmentSize);
494 }
495
WriteSectionData(const MCSectionData * SD,const MCAsmLayout & Layout) const496 void MCAssembler::WriteSectionData(const MCSectionData *SD,
497 const MCAsmLayout &Layout) const {
498 // Ignore virtual sections.
499 if (SD->getSection().isVirtualSection()) {
500 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
501
502 // Check that contents are only things legal inside a virtual section.
503 for (MCSectionData::const_iterator it = SD->begin(),
504 ie = SD->end(); it != ie; ++it) {
505 switch (it->getKind()) {
506 default:
507 assert(0 && "Invalid fragment in virtual section!");
508 case MCFragment::FT_Data: {
509 // Check that we aren't trying to write a non-zero contents (or fixups)
510 // into a virtual section. This is to support clients which use standard
511 // directives to fill the contents of virtual sections.
512 MCDataFragment &DF = cast<MCDataFragment>(*it);
513 assert(DF.fixup_begin() == DF.fixup_end() &&
514 "Cannot have fixups in virtual section!");
515 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
516 assert(DF.getContents()[i] == 0 &&
517 "Invalid data value for virtual section!");
518 break;
519 }
520 case MCFragment::FT_Align:
521 // Check that we aren't trying to write a non-zero value into a virtual
522 // section.
523 assert((!cast<MCAlignFragment>(it)->getValueSize() ||
524 !cast<MCAlignFragment>(it)->getValue()) &&
525 "Invalid align in virtual section!");
526 break;
527 case MCFragment::FT_Fill:
528 assert(!cast<MCFillFragment>(it)->getValueSize() &&
529 "Invalid fill in virtual section!");
530 break;
531 }
532 }
533
534 return;
535 }
536
537 uint64_t Start = getWriter().getStream().tell();
538 (void) Start;
539
540 for (MCSectionData::const_iterator it = SD->begin(),
541 ie = SD->end(); it != ie; ++it)
542 WriteFragmentData(*this, Layout, *it);
543
544 assert(getWriter().getStream().tell() - Start ==
545 Layout.getSectionAddressSize(SD));
546 }
547
548
HandleFixup(const MCAsmLayout & Layout,MCFragment & F,const MCFixup & Fixup)549 uint64_t MCAssembler::HandleFixup(const MCAsmLayout &Layout,
550 MCFragment &F,
551 const MCFixup &Fixup) {
552 // Evaluate the fixup.
553 MCValue Target;
554 uint64_t FixedValue;
555 if (!EvaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
556 // The fixup was unresolved, we need a relocation. Inform the object
557 // writer of the relocation, and give it an opportunity to adjust the
558 // fixup value if need be.
559 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
560 }
561 return FixedValue;
562 }
563
Finish()564 void MCAssembler::Finish() {
565 DEBUG_WITH_TYPE("mc-dump", {
566 llvm::errs() << "assembler backend - pre-layout\n--\n";
567 dump(); });
568
569 // Create the layout object.
570 MCAsmLayout Layout(*this);
571
572 // Create dummy fragments and assign section ordinals.
573 unsigned SectionIndex = 0;
574 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
575 // Create dummy fragments to eliminate any empty sections, this simplifies
576 // layout.
577 if (it->getFragmentList().empty())
578 new MCDataFragment(it);
579
580 it->setOrdinal(SectionIndex++);
581 }
582
583 // Assign layout order indices to sections and fragments.
584 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
585 MCSectionData *SD = Layout.getSectionOrder()[i];
586 SD->setLayoutOrder(i);
587
588 unsigned FragmentIndex = 0;
589 for (MCSectionData::iterator it2 = SD->begin(),
590 ie2 = SD->end(); it2 != ie2; ++it2)
591 it2->setLayoutOrder(FragmentIndex++);
592 }
593
594 // Layout until everything fits.
595 while (LayoutOnce(Layout))
596 continue;
597
598 DEBUG_WITH_TYPE("mc-dump", {
599 llvm::errs() << "assembler backend - post-relaxation\n--\n";
600 dump(); });
601
602 // Finalize the layout, including fragment lowering.
603 FinishLayout(Layout);
604
605 DEBUG_WITH_TYPE("mc-dump", {
606 llvm::errs() << "assembler backend - final-layout\n--\n";
607 dump(); });
608
609 uint64_t StartOffset = OS.tell();
610
611 // Allow the object writer a chance to perform post-layout binding (for
612 // example, to set the index fields in the symbol data).
613 getWriter().ExecutePostLayoutBinding(*this, Layout);
614
615 // Evaluate and apply the fixups, generating relocation entries as necessary.
616 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
617 for (MCSectionData::iterator it2 = it->begin(),
618 ie2 = it->end(); it2 != ie2; ++it2) {
619 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
620 if (DF) {
621 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
622 ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
623 MCFixup &Fixup = *it3;
624 uint64_t FixedValue = HandleFixup(Layout, *DF, Fixup);
625 getBackend().ApplyFixup(Fixup, DF->getContents().data(),
626 DF->getContents().size(), FixedValue);
627 }
628 }
629 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
630 if (IF) {
631 for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
632 ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
633 MCFixup &Fixup = *it3;
634 uint64_t FixedValue = HandleFixup(Layout, *IF, Fixup);
635 getBackend().ApplyFixup(Fixup, IF->getCode().data(),
636 IF->getCode().size(), FixedValue);
637 }
638 }
639 }
640 }
641
642 // Write the object file.
643 getWriter().WriteObject(*this, Layout);
644
645 stats::ObjectBytes += OS.tell() - StartOffset;
646 }
647
FixupNeedsRelaxation(const MCFixup & Fixup,const MCFragment * DF,const MCAsmLayout & Layout) const648 bool MCAssembler::FixupNeedsRelaxation(const MCFixup &Fixup,
649 const MCFragment *DF,
650 const MCAsmLayout &Layout) const {
651 if (getRelaxAll())
652 return true;
653
654 // If we cannot resolve the fixup value, it requires relaxation.
655 MCValue Target;
656 uint64_t Value;
657 if (!EvaluateFixup(Layout, Fixup, DF, Target, Value))
658 return true;
659
660 // Otherwise, relax if the value is too big for a (signed) i8.
661 //
662 // FIXME: This is target dependent!
663 return int64_t(Value) != int64_t(int8_t(Value));
664 }
665
FragmentNeedsRelaxation(const MCInstFragment * IF,const MCAsmLayout & Layout) const666 bool MCAssembler::FragmentNeedsRelaxation(const MCInstFragment *IF,
667 const MCAsmLayout &Layout) const {
668 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
669 // are intentionally pushing out inst fragments, or because we relaxed a
670 // previous instruction to one that doesn't need relaxation.
671 if (!getBackend().MayNeedRelaxation(IF->getInst()))
672 return false;
673
674 for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
675 ie = IF->fixup_end(); it != ie; ++it)
676 if (FixupNeedsRelaxation(*it, IF, Layout))
677 return true;
678
679 return false;
680 }
681
RelaxInstruction(MCAsmLayout & Layout,MCInstFragment & IF)682 bool MCAssembler::RelaxInstruction(MCAsmLayout &Layout,
683 MCInstFragment &IF) {
684 if (!FragmentNeedsRelaxation(&IF, Layout))
685 return false;
686
687 ++stats::RelaxedInstructions;
688
689 // FIXME-PERF: We could immediately lower out instructions if we can tell
690 // they are fully resolved, to avoid retesting on later passes.
691
692 // Relax the fragment.
693
694 MCInst Relaxed;
695 getBackend().RelaxInstruction(IF.getInst(), Relaxed);
696
697 // Encode the new instruction.
698 //
699 // FIXME-PERF: If it matters, we could let the target do this. It can
700 // probably do so more efficiently in many cases.
701 SmallVector<MCFixup, 4> Fixups;
702 SmallString<256> Code;
703 raw_svector_ostream VecOS(Code);
704 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
705 VecOS.flush();
706
707 // Update the instruction fragment.
708 IF.setInst(Relaxed);
709 IF.getCode() = Code;
710 IF.getFixups().clear();
711 // FIXME: Eliminate copy.
712 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
713 IF.getFixups().push_back(Fixups[i]);
714
715 return true;
716 }
717
RelaxLEB(MCAsmLayout & Layout,MCLEBFragment & LF)718 bool MCAssembler::RelaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
719 int64_t Value = 0;
720 uint64_t OldSize = LF.getContents().size();
721 bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
722 (void)IsAbs;
723 assert(IsAbs);
724 SmallString<8> &Data = LF.getContents();
725 Data.clear();
726 raw_svector_ostream OSE(Data);
727 if (LF.isSigned())
728 MCObjectWriter::EncodeSLEB128(Value, OSE);
729 else
730 MCObjectWriter::EncodeULEB128(Value, OSE);
731 OSE.flush();
732 return OldSize != LF.getContents().size();
733 }
734
RelaxDwarfLineAddr(MCAsmLayout & Layout,MCDwarfLineAddrFragment & DF)735 bool MCAssembler::RelaxDwarfLineAddr(MCAsmLayout &Layout,
736 MCDwarfLineAddrFragment &DF) {
737 int64_t AddrDelta = 0;
738 uint64_t OldSize = DF.getContents().size();
739 bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
740 (void)IsAbs;
741 assert(IsAbs);
742 int64_t LineDelta;
743 LineDelta = DF.getLineDelta();
744 SmallString<8> &Data = DF.getContents();
745 Data.clear();
746 raw_svector_ostream OSE(Data);
747 MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
748 OSE.flush();
749 return OldSize != Data.size();
750 }
751
RelaxDwarfCallFrameFragment(MCAsmLayout & Layout,MCDwarfCallFrameFragment & DF)752 bool MCAssembler::RelaxDwarfCallFrameFragment(MCAsmLayout &Layout,
753 MCDwarfCallFrameFragment &DF) {
754 int64_t AddrDelta = 0;
755 uint64_t OldSize = DF.getContents().size();
756 bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
757 (void)IsAbs;
758 assert(IsAbs);
759 SmallString<8> &Data = DF.getContents();
760 Data.clear();
761 raw_svector_ostream OSE(Data);
762 MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
763 OSE.flush();
764 return OldSize != Data.size();
765 }
766
LayoutSectionOnce(MCAsmLayout & Layout,MCSectionData & SD)767 bool MCAssembler::LayoutSectionOnce(MCAsmLayout &Layout,
768 MCSectionData &SD) {
769 MCFragment *FirstInvalidFragment = NULL;
770 // Scan for fragments that need relaxation.
771 for (MCSectionData::iterator it2 = SD.begin(),
772 ie2 = SD.end(); it2 != ie2; ++it2) {
773 // Check if this is an fragment that needs relaxation.
774 bool relaxedFrag = false;
775 switch(it2->getKind()) {
776 default:
777 break;
778 case MCFragment::FT_Inst:
779 relaxedFrag = RelaxInstruction(Layout, *cast<MCInstFragment>(it2));
780 break;
781 case MCFragment::FT_Dwarf:
782 relaxedFrag = RelaxDwarfLineAddr(Layout,
783 *cast<MCDwarfLineAddrFragment>(it2));
784 break;
785 case MCFragment::FT_DwarfFrame:
786 relaxedFrag =
787 RelaxDwarfCallFrameFragment(Layout,
788 *cast<MCDwarfCallFrameFragment>(it2));
789 break;
790 case MCFragment::FT_LEB:
791 relaxedFrag = RelaxLEB(Layout, *cast<MCLEBFragment>(it2));
792 break;
793 }
794 // Update the layout, and remember that we relaxed.
795 if (relaxedFrag && !FirstInvalidFragment)
796 FirstInvalidFragment = it2;
797 }
798 if (FirstInvalidFragment) {
799 Layout.Invalidate(FirstInvalidFragment);
800 return true;
801 }
802 return false;
803 }
804
LayoutOnce(MCAsmLayout & Layout)805 bool MCAssembler::LayoutOnce(MCAsmLayout &Layout) {
806 ++stats::RelaxationSteps;
807
808 bool WasRelaxed = false;
809 for (iterator it = begin(), ie = end(); it != ie; ++it) {
810 MCSectionData &SD = *it;
811 while(LayoutSectionOnce(Layout, SD))
812 WasRelaxed = true;
813 }
814
815 return WasRelaxed;
816 }
817
FinishLayout(MCAsmLayout & Layout)818 void MCAssembler::FinishLayout(MCAsmLayout &Layout) {
819 // The layout is done. Mark every fragment as valid.
820 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
821 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
822 }
823 }
824
825 // Debugging methods
826
827 namespace llvm {
828
operator <<(raw_ostream & OS,const MCFixup & AF)829 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
830 OS << "<MCFixup" << " Offset:" << AF.getOffset()
831 << " Value:" << *AF.getValue()
832 << " Kind:" << AF.getKind() << ">";
833 return OS;
834 }
835
836 }
837
dump()838 void MCFragment::dump() {
839 raw_ostream &OS = llvm::errs();
840
841 OS << "<";
842 switch (getKind()) {
843 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
844 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
845 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
846 case MCFragment::FT_Inst: OS << "MCInstFragment"; break;
847 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
848 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
849 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
850 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
851 }
852
853 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
854 << " Offset:" << Offset << ">";
855
856 switch (getKind()) {
857 case MCFragment::FT_Align: {
858 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
859 if (AF->hasEmitNops())
860 OS << " (emit nops)";
861 OS << "\n ";
862 OS << " Alignment:" << AF->getAlignment()
863 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
864 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
865 break;
866 }
867 case MCFragment::FT_Data: {
868 const MCDataFragment *DF = cast<MCDataFragment>(this);
869 OS << "\n ";
870 OS << " Contents:[";
871 const SmallVectorImpl<char> &Contents = DF->getContents();
872 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
873 if (i) OS << ",";
874 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
875 }
876 OS << "] (" << Contents.size() << " bytes)";
877
878 if (!DF->getFixups().empty()) {
879 OS << ",\n ";
880 OS << " Fixups:[";
881 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
882 ie = DF->fixup_end(); it != ie; ++it) {
883 if (it != DF->fixup_begin()) OS << ",\n ";
884 OS << *it;
885 }
886 OS << "]";
887 }
888 break;
889 }
890 case MCFragment::FT_Fill: {
891 const MCFillFragment *FF = cast<MCFillFragment>(this);
892 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
893 << " Size:" << FF->getSize();
894 break;
895 }
896 case MCFragment::FT_Inst: {
897 const MCInstFragment *IF = cast<MCInstFragment>(this);
898 OS << "\n ";
899 OS << " Inst:";
900 IF->getInst().dump_pretty(OS);
901 break;
902 }
903 case MCFragment::FT_Org: {
904 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
905 OS << "\n ";
906 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
907 break;
908 }
909 case MCFragment::FT_Dwarf: {
910 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
911 OS << "\n ";
912 OS << " AddrDelta:" << OF->getAddrDelta()
913 << " LineDelta:" << OF->getLineDelta();
914 break;
915 }
916 case MCFragment::FT_DwarfFrame: {
917 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
918 OS << "\n ";
919 OS << " AddrDelta:" << CF->getAddrDelta();
920 break;
921 }
922 case MCFragment::FT_LEB: {
923 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
924 OS << "\n ";
925 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
926 break;
927 }
928 }
929 OS << ">";
930 }
931
dump()932 void MCSectionData::dump() {
933 raw_ostream &OS = llvm::errs();
934
935 OS << "<MCSectionData";
936 OS << " Alignment:" << getAlignment() << " Fragments:[\n ";
937 for (iterator it = begin(), ie = end(); it != ie; ++it) {
938 if (it != begin()) OS << ",\n ";
939 it->dump();
940 }
941 OS << "]>";
942 }
943
dump()944 void MCSymbolData::dump() {
945 raw_ostream &OS = llvm::errs();
946
947 OS << "<MCSymbolData Symbol:" << getSymbol()
948 << " Fragment:" << getFragment() << " Offset:" << getOffset()
949 << " Flags:" << getFlags() << " Index:" << getIndex();
950 if (isCommon())
951 OS << " (common, size:" << getCommonSize()
952 << " align: " << getCommonAlignment() << ")";
953 if (isExternal())
954 OS << " (external)";
955 if (isPrivateExtern())
956 OS << " (private extern)";
957 OS << ">";
958 }
959
dump()960 void MCAssembler::dump() {
961 raw_ostream &OS = llvm::errs();
962
963 OS << "<MCAssembler\n";
964 OS << " Sections:[\n ";
965 for (iterator it = begin(), ie = end(); it != ie; ++it) {
966 if (it != begin()) OS << ",\n ";
967 it->dump();
968 }
969 OS << "],\n";
970 OS << " Symbols:[";
971
972 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
973 if (it != symbol_begin()) OS << ",\n ";
974 it->dump();
975 }
976 OS << "]>\n";
977 }
978