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/MCFixupKindInfo.h"
17 #include "llvm/MC/MCObjectWriter.h"
18 #include "llvm/MC/MCSection.h"
19 #include "llvm/MC/MCSymbol.h"
20 #include "llvm/MC/MCValue.h"
21 #include "llvm/MC/MCDwarf.h"
22 #include "llvm/MC/MCAsmBackend.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 LayoutOrder(~(0U))
162 {
163 if (Parent)
164 Parent->getFragmentList().push_back(this);
165 }
166
167 /* *** */
168
MCSectionData()169 MCSectionData::MCSectionData() : Section(0) {}
170
MCSectionData(const MCSection & _Section,MCAssembler * A)171 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
172 : Section(&_Section),
173 Ordinal(~UINT32_C(0)),
174 Alignment(1),
175 HasInstructions(false)
176 {
177 if (A)
178 A->getSectionList().push_back(this);
179 }
180
181 /* *** */
182
MCSymbolData()183 MCSymbolData::MCSymbolData() : Symbol(0) {}
184
MCSymbolData(const MCSymbol & _Symbol,MCFragment * _Fragment,uint64_t _Offset,MCAssembler * A)185 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
186 uint64_t _Offset, MCAssembler *A)
187 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
188 IsExternal(false), IsPrivateExtern(false),
189 CommonSize(0), SymbolSize(0), CommonAlign(0),
190 Flags(0), Index(0)
191 {
192 if (A)
193 A->getSymbolList().push_back(this);
194 }
195
196 /* *** */
197
MCAssembler(MCContext & Context_,MCAsmBackend & Backend_,MCCodeEmitter & Emitter_,MCObjectWriter & Writer_,raw_ostream & OS_)198 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
199 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
200 raw_ostream &OS_)
201 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(&Writer_),
202 OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
203 {
204 }
205
~MCAssembler()206 MCAssembler::~MCAssembler() {
207 }
208
setWriter(MCObjectWriter & ObjectWriter)209 void MCAssembler::setWriter(MCObjectWriter &ObjectWriter) {
210 delete Writer;
211 Writer = &ObjectWriter;
212 }
213
isSymbolLinkerVisible(const MCSymbol & Symbol) const214 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
215 // Non-temporary labels should always be visible to the linker.
216 if (!Symbol.isTemporary())
217 return true;
218
219 // Absolute temporary labels are never visible.
220 if (!Symbol.isInSection())
221 return false;
222
223 // Otherwise, check if the section requires symbols even for temporary labels.
224 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
225 }
226
getAtom(const MCSymbolData * SD) const227 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
228 // Linker visible symbols define atoms.
229 if (isSymbolLinkerVisible(SD->getSymbol()))
230 return SD;
231
232 // Absolute and undefined symbols have no defining atom.
233 if (!SD->getFragment())
234 return 0;
235
236 // Non-linker visible symbols in sections which can't be atomized have no
237 // defining atom.
238 if (!getBackend().isSectionAtomizable(
239 SD->getFragment()->getParent()->getSection()))
240 return 0;
241
242 // Otherwise, return the atom for the containing fragment.
243 return SD->getFragment()->getAtom();
244 }
245
evaluateFixup(const MCAsmLayout & Layout,const MCFixup & Fixup,const MCFragment * DF,MCValue & Target,uint64_t & Value) const246 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
247 const MCFixup &Fixup, const MCFragment *DF,
248 MCValue &Target, uint64_t &Value) const {
249 ++stats::evaluateFixup;
250
251 if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
252 getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
253
254 bool IsPCRel = Backend.getFixupKindInfo(
255 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
256
257 bool IsResolved;
258 if (IsPCRel) {
259 if (Target.getSymB()) {
260 IsResolved = false;
261 } else if (!Target.getSymA()) {
262 IsResolved = false;
263 } else {
264 const MCSymbolRefExpr *A = Target.getSymA();
265 const MCSymbol &SA = A->getSymbol();
266 if (A->getKind() != MCSymbolRefExpr::VK_None ||
267 SA.AliasedSymbol().isUndefined()) {
268 IsResolved = false;
269 } else {
270 const MCSymbolData &DataA = getSymbolData(SA);
271 IsResolved =
272 getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
273 *DF, false, true);
274 }
275 }
276 } else {
277 IsResolved = Target.isAbsolute();
278 }
279
280 Value = Target.getConstant();
281
282 if (const MCSymbolRefExpr *A = Target.getSymA()) {
283 const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
284 if (Sym.isDefined())
285 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
286 }
287 if (const MCSymbolRefExpr *B = Target.getSymB()) {
288 const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
289 if (Sym.isDefined())
290 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
291 }
292
293
294 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
295 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
296 assert((ShouldAlignPC ? IsPCRel : true) &&
297 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
298
299 if (IsPCRel) {
300 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
301
302 // A number of ARM fixups in Thumb mode require that the effective PC
303 // address be determined as the 32-bit aligned version of the actual offset.
304 if (ShouldAlignPC) Offset &= ~0x3;
305 Value -= Offset;
306 }
307
308 // Let the backend adjust the fixup value if necessary, including whether
309 // we need a relocation.
310 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
311 IsResolved);
312
313 return IsResolved;
314 }
315
computeFragmentSize(const MCAsmLayout & Layout,const MCFragment & F) const316 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
317 const MCFragment &F) const {
318 switch (F.getKind()) {
319 case MCFragment::FT_Data:
320 return cast<MCDataFragment>(F).getContents().size();
321 case MCFragment::FT_Fill:
322 return cast<MCFillFragment>(F).getSize();
323 case MCFragment::FT_Inst:
324 return cast<MCInstFragment>(F).getInstSize();
325
326 case MCFragment::FT_LEB:
327 return cast<MCLEBFragment>(F).getContents().size();
328
329 case MCFragment::FT_Align: {
330 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
331 unsigned Offset = Layout.getFragmentOffset(&AF);
332 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
333 if (Size > AF.getMaxBytesToEmit())
334 return 0;
335 return Size;
336 }
337
338 case MCFragment::FT_Org: {
339 MCOrgFragment &OF = cast<MCOrgFragment>(F);
340 int64_t TargetLocation;
341 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
342 report_fatal_error("expected assembly-time absolute expression");
343
344 // FIXME: We need a way to communicate this error.
345 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
346 int64_t Size = TargetLocation - FragmentOffset;
347 if (Size < 0 || Size >= 0x40000000)
348 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
349 "' (at offset '" + Twine(FragmentOffset) + "')");
350 return Size;
351 }
352
353 case MCFragment::FT_Dwarf:
354 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
355 case MCFragment::FT_DwarfFrame:
356 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
357 }
358
359 llvm_unreachable("invalid fragment kind");
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: llvm_unreachable("Invalid size!");
425 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
426 case 2: OW->Write16(uint16_t(AF.getValue())); break;
427 case 4: OW->Write32(uint32_t(AF.getValue())); break;
428 case 8: OW->Write64(uint64_t(AF.getValue())); break;
429 }
430 }
431 break;
432 }
433
434 case MCFragment::FT_Data: {
435 MCDataFragment &DF = cast<MCDataFragment>(F);
436 assert(FragmentSize == DF.getContents().size() && "Invalid size!");
437 OW->WriteBytes(DF.getContents().str());
438 break;
439 }
440
441 case MCFragment::FT_Fill: {
442 MCFillFragment &FF = cast<MCFillFragment>(F);
443
444 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
445
446 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
447 switch (FF.getValueSize()) {
448 default: llvm_unreachable("Invalid size!");
449 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
450 case 2: OW->Write16(uint16_t(FF.getValue())); break;
451 case 4: OW->Write32(uint32_t(FF.getValue())); break;
452 case 8: OW->Write64(uint64_t(FF.getValue())); break;
453 }
454 }
455 break;
456 }
457
458 case MCFragment::FT_Inst: {
459 MCInstFragment &IF = cast<MCInstFragment>(F);
460 OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
461 break;
462 }
463
464 case MCFragment::FT_LEB: {
465 MCLEBFragment &LF = cast<MCLEBFragment>(F);
466 OW->WriteBytes(LF.getContents().str());
467 break;
468 }
469
470 case MCFragment::FT_Org: {
471 MCOrgFragment &OF = cast<MCOrgFragment>(F);
472
473 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
474 OW->Write8(uint8_t(OF.getValue()));
475
476 break;
477 }
478
479 case MCFragment::FT_Dwarf: {
480 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
481 OW->WriteBytes(OF.getContents().str());
482 break;
483 }
484 case MCFragment::FT_DwarfFrame: {
485 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
486 OW->WriteBytes(CF.getContents().str());
487 break;
488 }
489 }
490
491 assert(OW->getStream().tell() - Start == FragmentSize);
492 }
493
writeSectionData(const MCSectionData * SD,const MCAsmLayout & Layout) const494 void MCAssembler::writeSectionData(const MCSectionData *SD,
495 const MCAsmLayout &Layout) const {
496 // Ignore virtual sections.
497 if (SD->getSection().isVirtualSection()) {
498 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
499
500 // Check that contents are only things legal inside a virtual section.
501 for (MCSectionData::const_iterator it = SD->begin(),
502 ie = SD->end(); it != ie; ++it) {
503 switch (it->getKind()) {
504 default: llvm_unreachable("Invalid fragment in virtual section!");
505 case MCFragment::FT_Data: {
506 // Check that we aren't trying to write a non-zero contents (or fixups)
507 // into a virtual section. This is to support clients which use standard
508 // directives to fill the contents of virtual sections.
509 MCDataFragment &DF = cast<MCDataFragment>(*it);
510 assert(DF.fixup_begin() == DF.fixup_end() &&
511 "Cannot have fixups in virtual section!");
512 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
513 assert(DF.getContents()[i] == 0 &&
514 "Invalid data value for virtual section!");
515 break;
516 }
517 case MCFragment::FT_Align:
518 // Check that we aren't trying to write a non-zero value into a virtual
519 // section.
520 assert((!cast<MCAlignFragment>(it)->getValueSize() ||
521 !cast<MCAlignFragment>(it)->getValue()) &&
522 "Invalid align in virtual section!");
523 break;
524 case MCFragment::FT_Fill:
525 assert(!cast<MCFillFragment>(it)->getValueSize() &&
526 "Invalid fill in virtual section!");
527 break;
528 }
529 }
530
531 return;
532 }
533
534 uint64_t Start = getWriter().getStream().tell();
535 (void) Start;
536
537 for (MCSectionData::const_iterator it = SD->begin(),
538 ie = SD->end(); it != ie; ++it)
539 WriteFragmentData(*this, Layout, *it);
540
541 assert(getWriter().getStream().tell() - Start ==
542 Layout.getSectionAddressSize(SD));
543 }
544
545
handleFixup(const MCAsmLayout & Layout,MCFragment & F,const MCFixup & Fixup)546 uint64_t MCAssembler::handleFixup(const MCAsmLayout &Layout,
547 MCFragment &F,
548 const MCFixup &Fixup) {
549 // Evaluate the fixup.
550 MCValue Target;
551 uint64_t FixedValue;
552 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
553 // The fixup was unresolved, we need a relocation. Inform the object
554 // writer of the relocation, and give it an opportunity to adjust the
555 // fixup value if need be.
556 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
557 }
558 return FixedValue;
559 }
560
Finish()561 void MCAssembler::Finish() {
562 DEBUG_WITH_TYPE("mc-dump", {
563 llvm::errs() << "assembler backend - pre-layout\n--\n";
564 dump(); });
565
566 // Create the layout object.
567 MCAsmLayout Layout(*this);
568
569 // Create dummy fragments and assign section ordinals.
570 unsigned SectionIndex = 0;
571 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
572 // Create dummy fragments to eliminate any empty sections, this simplifies
573 // layout.
574 if (it->getFragmentList().empty())
575 new MCDataFragment(it);
576
577 it->setOrdinal(SectionIndex++);
578 }
579
580 // Assign layout order indices to sections and fragments.
581 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
582 MCSectionData *SD = Layout.getSectionOrder()[i];
583 SD->setLayoutOrder(i);
584
585 unsigned FragmentIndex = 0;
586 for (MCSectionData::iterator it2 = SD->begin(),
587 ie2 = SD->end(); it2 != ie2; ++it2)
588 it2->setLayoutOrder(FragmentIndex++);
589 }
590
591 // Layout until everything fits.
592 while (layoutOnce(Layout))
593 continue;
594
595 DEBUG_WITH_TYPE("mc-dump", {
596 llvm::errs() << "assembler backend - post-relaxation\n--\n";
597 dump(); });
598
599 // Finalize the layout, including fragment lowering.
600 finishLayout(Layout);
601
602 DEBUG_WITH_TYPE("mc-dump", {
603 llvm::errs() << "assembler backend - final-layout\n--\n";
604 dump(); });
605
606 uint64_t StartOffset = OS.tell();
607
608 // Allow the object writer a chance to perform post-layout binding (for
609 // example, to set the index fields in the symbol data).
610 getWriter().ExecutePostLayoutBinding(*this, Layout);
611
612 // Evaluate and apply the fixups, generating relocation entries as necessary.
613 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
614 for (MCSectionData::iterator it2 = it->begin(),
615 ie2 = it->end(); it2 != ie2; ++it2) {
616 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
617 if (DF) {
618 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
619 ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
620 MCFixup &Fixup = *it3;
621 uint64_t FixedValue = handleFixup(Layout, *DF, Fixup);
622 getBackend().applyFixup(Fixup, DF->getContents().data(),
623 DF->getContents().size(), FixedValue);
624 }
625 }
626 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
627 if (IF) {
628 for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
629 ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
630 MCFixup &Fixup = *it3;
631 uint64_t FixedValue = handleFixup(Layout, *IF, Fixup);
632 getBackend().applyFixup(Fixup, IF->getCode().data(),
633 IF->getCode().size(), FixedValue);
634 }
635 }
636 }
637 }
638
639 // Write the object file.
640 getWriter().WriteObject(*this, Layout);
641
642 stats::ObjectBytes += OS.tell() - StartOffset;
643 }
644
fixupNeedsRelaxation(const MCFixup & Fixup,const MCInstFragment * DF,const MCAsmLayout & Layout) const645 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
646 const MCInstFragment *DF,
647 const MCAsmLayout &Layout) const {
648 if (getRelaxAll())
649 return true;
650
651 // If we cannot resolve the fixup value, it requires relaxation.
652 MCValue Target;
653 uint64_t Value;
654 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
655 return true;
656
657 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
658 }
659
fragmentNeedsRelaxation(const MCInstFragment * IF,const MCAsmLayout & Layout) const660 bool MCAssembler::fragmentNeedsRelaxation(const MCInstFragment *IF,
661 const MCAsmLayout &Layout) const {
662 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
663 // are intentionally pushing out inst fragments, or because we relaxed a
664 // previous instruction to one that doesn't need relaxation.
665 if (!getBackend().mayNeedRelaxation(IF->getInst()))
666 return false;
667
668 for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
669 ie = IF->fixup_end(); it != ie; ++it)
670 if (fixupNeedsRelaxation(*it, IF, Layout))
671 return true;
672
673 return false;
674 }
675
relaxInstruction(MCAsmLayout & Layout,MCInstFragment & IF)676 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
677 MCInstFragment &IF) {
678 if (!fragmentNeedsRelaxation(&IF, Layout))
679 return false;
680
681 ++stats::RelaxedInstructions;
682
683 // FIXME-PERF: We could immediately lower out instructions if we can tell
684 // they are fully resolved, to avoid retesting on later passes.
685
686 // Relax the fragment.
687
688 MCInst Relaxed;
689 getBackend().relaxInstruction(IF.getInst(), Relaxed);
690
691 // Encode the new instruction.
692 //
693 // FIXME-PERF: If it matters, we could let the target do this. It can
694 // probably do so more efficiently in many cases.
695 SmallVector<MCFixup, 4> Fixups;
696 SmallString<256> Code;
697 raw_svector_ostream VecOS(Code);
698 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
699 VecOS.flush();
700
701 // Update the instruction fragment.
702 IF.setInst(Relaxed);
703 IF.getCode() = Code;
704 IF.getFixups().clear();
705 // FIXME: Eliminate copy.
706 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
707 IF.getFixups().push_back(Fixups[i]);
708
709 return true;
710 }
711
relaxLEB(MCAsmLayout & Layout,MCLEBFragment & LF)712 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
713 int64_t Value = 0;
714 uint64_t OldSize = LF.getContents().size();
715 bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
716 (void)IsAbs;
717 assert(IsAbs);
718 SmallString<8> &Data = LF.getContents();
719 Data.clear();
720 raw_svector_ostream OSE(Data);
721 if (LF.isSigned())
722 MCObjectWriter::EncodeSLEB128(Value, OSE);
723 else
724 MCObjectWriter::EncodeULEB128(Value, OSE);
725 OSE.flush();
726 return OldSize != LF.getContents().size();
727 }
728
relaxDwarfLineAddr(MCAsmLayout & Layout,MCDwarfLineAddrFragment & DF)729 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
730 MCDwarfLineAddrFragment &DF) {
731 int64_t AddrDelta = 0;
732 uint64_t OldSize = DF.getContents().size();
733 bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
734 (void)IsAbs;
735 assert(IsAbs);
736 int64_t LineDelta;
737 LineDelta = DF.getLineDelta();
738 SmallString<8> &Data = DF.getContents();
739 Data.clear();
740 raw_svector_ostream OSE(Data);
741 MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
742 OSE.flush();
743 return OldSize != Data.size();
744 }
745
relaxDwarfCallFrameFragment(MCAsmLayout & Layout,MCDwarfCallFrameFragment & DF)746 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
747 MCDwarfCallFrameFragment &DF) {
748 int64_t AddrDelta = 0;
749 uint64_t OldSize = DF.getContents().size();
750 bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
751 (void)IsAbs;
752 assert(IsAbs);
753 SmallString<8> &Data = DF.getContents();
754 Data.clear();
755 raw_svector_ostream OSE(Data);
756 MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
757 OSE.flush();
758 return OldSize != Data.size();
759 }
760
layoutSectionOnce(MCAsmLayout & Layout,MCSectionData & SD)761 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout,
762 MCSectionData &SD) {
763 MCFragment *FirstInvalidFragment = NULL;
764 // Scan for fragments that need relaxation.
765 for (MCSectionData::iterator it2 = SD.begin(),
766 ie2 = SD.end(); it2 != ie2; ++it2) {
767 // Check if this is an fragment that needs relaxation.
768 bool relaxedFrag = false;
769 switch(it2->getKind()) {
770 default:
771 break;
772 case MCFragment::FT_Inst:
773 relaxedFrag = relaxInstruction(Layout, *cast<MCInstFragment>(it2));
774 break;
775 case MCFragment::FT_Dwarf:
776 relaxedFrag = relaxDwarfLineAddr(Layout,
777 *cast<MCDwarfLineAddrFragment>(it2));
778 break;
779 case MCFragment::FT_DwarfFrame:
780 relaxedFrag =
781 relaxDwarfCallFrameFragment(Layout,
782 *cast<MCDwarfCallFrameFragment>(it2));
783 break;
784 case MCFragment::FT_LEB:
785 relaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(it2));
786 break;
787 }
788 // Update the layout, and remember that we relaxed.
789 if (relaxedFrag && !FirstInvalidFragment)
790 FirstInvalidFragment = it2;
791 }
792 if (FirstInvalidFragment) {
793 Layout.Invalidate(FirstInvalidFragment);
794 return true;
795 }
796 return false;
797 }
798
layoutOnce(MCAsmLayout & Layout)799 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
800 ++stats::RelaxationSteps;
801
802 bool WasRelaxed = false;
803 for (iterator it = begin(), ie = end(); it != ie; ++it) {
804 MCSectionData &SD = *it;
805 while(layoutSectionOnce(Layout, SD))
806 WasRelaxed = true;
807 }
808
809 return WasRelaxed;
810 }
811
finishLayout(MCAsmLayout & Layout)812 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
813 // The layout is done. Mark every fragment as valid.
814 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
815 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
816 }
817 }
818
819 // Debugging methods
820
821 namespace llvm {
822
operator <<(raw_ostream & OS,const MCFixup & AF)823 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
824 OS << "<MCFixup" << " Offset:" << AF.getOffset()
825 << " Value:" << *AF.getValue()
826 << " Kind:" << AF.getKind() << ">";
827 return OS;
828 }
829
830 }
831
dump()832 void MCFragment::dump() {
833 raw_ostream &OS = llvm::errs();
834
835 OS << "<";
836 switch (getKind()) {
837 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
838 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
839 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
840 case MCFragment::FT_Inst: OS << "MCInstFragment"; break;
841 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
842 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
843 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
844 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
845 }
846
847 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
848 << " Offset:" << Offset << ">";
849
850 switch (getKind()) {
851 case MCFragment::FT_Align: {
852 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
853 if (AF->hasEmitNops())
854 OS << " (emit nops)";
855 OS << "\n ";
856 OS << " Alignment:" << AF->getAlignment()
857 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
858 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
859 break;
860 }
861 case MCFragment::FT_Data: {
862 const MCDataFragment *DF = cast<MCDataFragment>(this);
863 OS << "\n ";
864 OS << " Contents:[";
865 const SmallVectorImpl<char> &Contents = DF->getContents();
866 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
867 if (i) OS << ",";
868 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
869 }
870 OS << "] (" << Contents.size() << " bytes)";
871
872 if (!DF->getFixups().empty()) {
873 OS << ",\n ";
874 OS << " Fixups:[";
875 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
876 ie = DF->fixup_end(); it != ie; ++it) {
877 if (it != DF->fixup_begin()) OS << ",\n ";
878 OS << *it;
879 }
880 OS << "]";
881 }
882 break;
883 }
884 case MCFragment::FT_Fill: {
885 const MCFillFragment *FF = cast<MCFillFragment>(this);
886 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
887 << " Size:" << FF->getSize();
888 break;
889 }
890 case MCFragment::FT_Inst: {
891 const MCInstFragment *IF = cast<MCInstFragment>(this);
892 OS << "\n ";
893 OS << " Inst:";
894 IF->getInst().dump_pretty(OS);
895 break;
896 }
897 case MCFragment::FT_Org: {
898 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
899 OS << "\n ";
900 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
901 break;
902 }
903 case MCFragment::FT_Dwarf: {
904 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
905 OS << "\n ";
906 OS << " AddrDelta:" << OF->getAddrDelta()
907 << " LineDelta:" << OF->getLineDelta();
908 break;
909 }
910 case MCFragment::FT_DwarfFrame: {
911 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
912 OS << "\n ";
913 OS << " AddrDelta:" << CF->getAddrDelta();
914 break;
915 }
916 case MCFragment::FT_LEB: {
917 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
918 OS << "\n ";
919 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
920 break;
921 }
922 }
923 OS << ">";
924 }
925
dump()926 void MCSectionData::dump() {
927 raw_ostream &OS = llvm::errs();
928
929 OS << "<MCSectionData";
930 OS << " Alignment:" << getAlignment() << " Fragments:[\n ";
931 for (iterator it = begin(), ie = end(); it != ie; ++it) {
932 if (it != begin()) OS << ",\n ";
933 it->dump();
934 }
935 OS << "]>";
936 }
937
dump()938 void MCSymbolData::dump() {
939 raw_ostream &OS = llvm::errs();
940
941 OS << "<MCSymbolData Symbol:" << getSymbol()
942 << " Fragment:" << getFragment() << " Offset:" << getOffset()
943 << " Flags:" << getFlags() << " Index:" << getIndex();
944 if (isCommon())
945 OS << " (common, size:" << getCommonSize()
946 << " align: " << getCommonAlignment() << ")";
947 if (isExternal())
948 OS << " (external)";
949 if (isPrivateExtern())
950 OS << " (private extern)";
951 OS << ">";
952 }
953
dump()954 void MCAssembler::dump() {
955 raw_ostream &OS = llvm::errs();
956
957 OS << "<MCAssembler\n";
958 OS << " Sections:[\n ";
959 for (iterator it = begin(), ie = end(); it != ie; ++it) {
960 if (it != begin()) OS << ",\n ";
961 it->dump();
962 }
963 OS << "],\n";
964 OS << " Symbols:[";
965
966 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
967 if (it != symbol_begin()) OS << ",\n ";
968 it->dump();
969 }
970 OS << "]>\n";
971 }
972
973 // anchors for MC*Fragment vtables
anchor()974 void MCDataFragment::anchor() { }
anchor()975 void MCInstFragment::anchor() { }
anchor()976 void MCAlignFragment::anchor() { }
anchor()977 void MCFillFragment::anchor() { }
anchor()978 void MCOrgFragment::anchor() { }
anchor()979 void MCLEBFragment::anchor() { }
anchor()980 void MCDwarfLineAddrFragment::anchor() { }
anchor()981 void MCDwarfCallFrameFragment::anchor() { }
982