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 #include "llvm/Support/LEB128.h"
31
32 using namespace llvm;
33
34 namespace {
35 namespace stats {
36 STATISTIC(EmittedFragments, "Number of emitted assembler fragments");
37 STATISTIC(evaluateFixup, "Number of evaluated fixups");
38 STATISTIC(FragmentLayouts, "Number of fragment layouts");
39 STATISTIC(ObjectBytes, "Number of emitted object file bytes");
40 STATISTIC(RelaxationSteps, "Number of assembler layout and relaxation steps");
41 STATISTIC(RelaxedInstructions, "Number of relaxed instructions");
42 }
43 }
44
45 // FIXME FIXME FIXME: There are number of places in this file where we convert
46 // what is a 64-bit assembler value used for computation into a value in the
47 // object file, which may truncate it. We should detect that truncation where
48 // invalid and report errors back.
49
50 /* *** */
51
MCAsmLayout(MCAssembler & Asm)52 MCAsmLayout::MCAsmLayout(MCAssembler &Asm)
53 : Assembler(Asm), LastValidFragment()
54 {
55 // Compute the section layout order. Virtual sections must go last.
56 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
57 if (!it->getSection().isVirtualSection())
58 SectionOrder.push_back(&*it);
59 for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it)
60 if (it->getSection().isVirtualSection())
61 SectionOrder.push_back(&*it);
62 }
63
isFragmentUpToDate(const MCFragment * F) const64 bool MCAsmLayout::isFragmentUpToDate(const MCFragment *F) const {
65 const MCSectionData &SD = *F->getParent();
66 const MCFragment *LastValid = LastValidFragment.lookup(&SD);
67 if (!LastValid)
68 return false;
69 assert(LastValid->getParent() == F->getParent());
70 return F->getLayoutOrder() <= LastValid->getLayoutOrder();
71 }
72
Invalidate(MCFragment * F)73 void MCAsmLayout::Invalidate(MCFragment *F) {
74 // If this fragment wasn't already up-to-date, we don't need to do anything.
75 if (!isFragmentUpToDate(F))
76 return;
77
78 // Otherwise, reset the last valid fragment to this fragment.
79 const MCSectionData &SD = *F->getParent();
80 LastValidFragment[&SD] = F;
81 }
82
EnsureValid(const MCFragment * F) const83 void MCAsmLayout::EnsureValid(const MCFragment *F) const {
84 MCSectionData &SD = *F->getParent();
85
86 MCFragment *Cur = LastValidFragment[&SD];
87 if (!Cur)
88 Cur = &*SD.begin();
89 else
90 Cur = Cur->getNextNode();
91
92 // Advance the layout position until the fragment is up-to-date.
93 while (!isFragmentUpToDate(F)) {
94 const_cast<MCAsmLayout*>(this)->LayoutFragment(Cur);
95 Cur = Cur->getNextNode();
96 }
97 }
98
getFragmentOffset(const MCFragment * F) const99 uint64_t MCAsmLayout::getFragmentOffset(const MCFragment *F) const {
100 EnsureValid(F);
101 assert(F->Offset != ~UINT64_C(0) && "Address not set!");
102 return F->Offset;
103 }
104
getSymbolOffset(const MCSymbolData * SD) const105 uint64_t MCAsmLayout::getSymbolOffset(const MCSymbolData *SD) const {
106 const MCSymbol &S = SD->getSymbol();
107
108 // If this is a variable, then recursively evaluate now.
109 if (S.isVariable()) {
110 MCValue Target;
111 if (!S.getVariableValue()->EvaluateAsRelocatable(Target, *this))
112 report_fatal_error("unable to evaluate offset for variable '" +
113 S.getName() + "'");
114
115 // Verify that any used symbols are defined.
116 if (Target.getSymA() && Target.getSymA()->getSymbol().isUndefined())
117 report_fatal_error("unable to evaluate offset to undefined symbol '" +
118 Target.getSymA()->getSymbol().getName() + "'");
119 if (Target.getSymB() && Target.getSymB()->getSymbol().isUndefined())
120 report_fatal_error("unable to evaluate offset to undefined symbol '" +
121 Target.getSymB()->getSymbol().getName() + "'");
122
123 uint64_t Offset = Target.getConstant();
124 if (Target.getSymA())
125 Offset += getSymbolOffset(&Assembler.getSymbolData(
126 Target.getSymA()->getSymbol()));
127 if (Target.getSymB())
128 Offset -= getSymbolOffset(&Assembler.getSymbolData(
129 Target.getSymB()->getSymbol()));
130 return Offset;
131 }
132
133 assert(SD->getFragment() && "Invalid getOffset() on undefined symbol!");
134 return getFragmentOffset(SD->getFragment()) + SD->getOffset();
135 }
136
getSectionAddressSize(const MCSectionData * SD) const137 uint64_t MCAsmLayout::getSectionAddressSize(const MCSectionData *SD) const {
138 // The size is the last fragment's end offset.
139 const MCFragment &F = SD->getFragmentList().back();
140 return getFragmentOffset(&F) + getAssembler().computeFragmentSize(*this, F);
141 }
142
getSectionFileSize(const MCSectionData * SD) const143 uint64_t MCAsmLayout::getSectionFileSize(const MCSectionData *SD) const {
144 // Virtual sections have no file size.
145 if (SD->getSection().isVirtualSection())
146 return 0;
147
148 // Otherwise, the file size is the same as the address space size.
149 return getSectionAddressSize(SD);
150 }
151
152 /* *** */
153
MCFragment()154 MCFragment::MCFragment() : Kind(FragmentType(~0)) {
155 }
156
~MCFragment()157 MCFragment::~MCFragment() {
158 }
159
MCFragment(FragmentType _Kind,MCSectionData * _Parent)160 MCFragment::MCFragment(FragmentType _Kind, MCSectionData *_Parent)
161 : Kind(_Kind), Parent(_Parent), Atom(0), Offset(~UINT64_C(0)),
162 LayoutOrder(~(0U))
163 {
164 if (Parent)
165 Parent->getFragmentList().push_back(this);
166 }
167
168 /* *** */
169
MCSectionData()170 MCSectionData::MCSectionData() : Section(0) {}
171
MCSectionData(const MCSection & _Section,MCAssembler * A)172 MCSectionData::MCSectionData(const MCSection &_Section, MCAssembler *A)
173 : Section(&_Section),
174 Ordinal(~UINT32_C(0)),
175 Alignment(1),
176 HasInstructions(false)
177 {
178 if (A)
179 A->getSectionList().push_back(this);
180 }
181
182 /* *** */
183
MCSymbolData()184 MCSymbolData::MCSymbolData() : Symbol(0) {}
185
MCSymbolData(const MCSymbol & _Symbol,MCFragment * _Fragment,uint64_t _Offset,MCAssembler * A)186 MCSymbolData::MCSymbolData(const MCSymbol &_Symbol, MCFragment *_Fragment,
187 uint64_t _Offset, MCAssembler *A)
188 : Symbol(&_Symbol), Fragment(_Fragment), Offset(_Offset),
189 IsExternal(false), IsPrivateExtern(false),
190 CommonSize(0), SymbolSize(0), CommonAlign(0),
191 Flags(0), Index(0)
192 {
193 if (A)
194 A->getSymbolList().push_back(this);
195 }
196
197 /* *** */
198
MCAssembler(MCContext & Context_,MCAsmBackend & Backend_,MCCodeEmitter & Emitter_,MCObjectWriter & Writer_,raw_ostream & OS_)199 MCAssembler::MCAssembler(MCContext &Context_, MCAsmBackend &Backend_,
200 MCCodeEmitter &Emitter_, MCObjectWriter &Writer_,
201 raw_ostream &OS_)
202 : Context(Context_), Backend(Backend_), Emitter(Emitter_), Writer(&Writer_),
203 OS(OS_), RelaxAll(false), NoExecStack(false), SubsectionsViaSymbols(false)
204 {
205 }
206
~MCAssembler()207 MCAssembler::~MCAssembler() {
208 }
209
setWriter(MCObjectWriter & ObjectWriter)210 void MCAssembler::setWriter(MCObjectWriter &ObjectWriter) {
211 delete Writer;
212 Writer = &ObjectWriter;
213 }
214
isSymbolLinkerVisible(const MCSymbol & Symbol) const215 bool MCAssembler::isSymbolLinkerVisible(const MCSymbol &Symbol) const {
216 // Non-temporary labels should always be visible to the linker.
217 if (!Symbol.isTemporary())
218 return true;
219
220 // Absolute temporary labels are never visible.
221 if (!Symbol.isInSection())
222 return false;
223
224 // Otherwise, check if the section requires symbols even for temporary labels.
225 return getBackend().doesSectionRequireSymbols(Symbol.getSection());
226 }
227
getAtom(const MCSymbolData * SD) const228 const MCSymbolData *MCAssembler::getAtom(const MCSymbolData *SD) const {
229 // Linker visible symbols define atoms.
230 if (isSymbolLinkerVisible(SD->getSymbol()))
231 return SD;
232
233 // Absolute and undefined symbols have no defining atom.
234 if (!SD->getFragment())
235 return 0;
236
237 // Non-linker visible symbols in sections which can't be atomized have no
238 // defining atom.
239 if (!getBackend().isSectionAtomizable(
240 SD->getFragment()->getParent()->getSection()))
241 return 0;
242
243 // Otherwise, return the atom for the containing fragment.
244 return SD->getFragment()->getAtom();
245 }
246
evaluateFixup(const MCAsmLayout & Layout,const MCFixup & Fixup,const MCFragment * DF,MCValue & Target,uint64_t & Value) const247 bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
248 const MCFixup &Fixup, const MCFragment *DF,
249 MCValue &Target, uint64_t &Value) const {
250 ++stats::evaluateFixup;
251
252 if (!Fixup.getValue()->EvaluateAsRelocatable(Target, Layout))
253 getContext().FatalError(Fixup.getLoc(), "expected relocatable expression");
254
255 bool IsPCRel = Backend.getFixupKindInfo(
256 Fixup.getKind()).Flags & MCFixupKindInfo::FKF_IsPCRel;
257
258 bool IsResolved;
259 if (IsPCRel) {
260 if (Target.getSymB()) {
261 IsResolved = false;
262 } else if (!Target.getSymA()) {
263 IsResolved = false;
264 } else {
265 const MCSymbolRefExpr *A = Target.getSymA();
266 const MCSymbol &SA = A->getSymbol();
267 if (A->getKind() != MCSymbolRefExpr::VK_None ||
268 SA.AliasedSymbol().isUndefined()) {
269 IsResolved = false;
270 } else {
271 const MCSymbolData &DataA = getSymbolData(SA);
272 IsResolved =
273 getWriter().IsSymbolRefDifferenceFullyResolvedImpl(*this, DataA,
274 *DF, false, true);
275 }
276 }
277 } else {
278 IsResolved = Target.isAbsolute();
279 }
280
281 Value = Target.getConstant();
282
283 if (const MCSymbolRefExpr *A = Target.getSymA()) {
284 const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
285 if (Sym.isDefined())
286 Value += Layout.getSymbolOffset(&getSymbolData(Sym));
287 }
288 if (const MCSymbolRefExpr *B = Target.getSymB()) {
289 const MCSymbol &Sym = B->getSymbol().AliasedSymbol();
290 if (Sym.isDefined())
291 Value -= Layout.getSymbolOffset(&getSymbolData(Sym));
292 }
293
294
295 bool ShouldAlignPC = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
296 MCFixupKindInfo::FKF_IsAlignedDownTo32Bits;
297 assert((ShouldAlignPC ? IsPCRel : true) &&
298 "FKF_IsAlignedDownTo32Bits is only allowed on PC-relative fixups!");
299
300 if (IsPCRel) {
301 uint32_t Offset = Layout.getFragmentOffset(DF) + Fixup.getOffset();
302
303 // A number of ARM fixups in Thumb mode require that the effective PC
304 // address be determined as the 32-bit aligned version of the actual offset.
305 if (ShouldAlignPC) Offset &= ~0x3;
306 Value -= Offset;
307 }
308
309 // Let the backend adjust the fixup value if necessary, including whether
310 // we need a relocation.
311 Backend.processFixupValue(*this, Layout, Fixup, DF, Target, Value,
312 IsResolved);
313
314 return IsResolved;
315 }
316
computeFragmentSize(const MCAsmLayout & Layout,const MCFragment & F) const317 uint64_t MCAssembler::computeFragmentSize(const MCAsmLayout &Layout,
318 const MCFragment &F) const {
319 switch (F.getKind()) {
320 case MCFragment::FT_Data:
321 return cast<MCDataFragment>(F).getContents().size();
322 case MCFragment::FT_Fill:
323 return cast<MCFillFragment>(F).getSize();
324 case MCFragment::FT_Inst:
325 return cast<MCInstFragment>(F).getInstSize();
326
327 case MCFragment::FT_LEB:
328 return cast<MCLEBFragment>(F).getContents().size();
329
330 case MCFragment::FT_Align: {
331 const MCAlignFragment &AF = cast<MCAlignFragment>(F);
332 unsigned Offset = Layout.getFragmentOffset(&AF);
333 unsigned Size = OffsetToAlignment(Offset, AF.getAlignment());
334 // If we are padding with nops, force the padding to be larger than the
335 // minimum nop size.
336 if (Size > 0 && AF.hasEmitNops()) {
337 while (Size % getBackend().getMinimumNopSize())
338 Size += AF.getAlignment();
339 }
340 if (Size > AF.getMaxBytesToEmit())
341 return 0;
342 return Size;
343 }
344
345 case MCFragment::FT_Org: {
346 MCOrgFragment &OF = cast<MCOrgFragment>(F);
347 int64_t TargetLocation;
348 if (!OF.getOffset().EvaluateAsAbsolute(TargetLocation, Layout))
349 report_fatal_error("expected assembly-time absolute expression");
350
351 // FIXME: We need a way to communicate this error.
352 uint64_t FragmentOffset = Layout.getFragmentOffset(&OF);
353 int64_t Size = TargetLocation - FragmentOffset;
354 if (Size < 0 || Size >= 0x40000000)
355 report_fatal_error("invalid .org offset '" + Twine(TargetLocation) +
356 "' (at offset '" + Twine(FragmentOffset) + "')");
357 return Size;
358 }
359
360 case MCFragment::FT_Dwarf:
361 return cast<MCDwarfLineAddrFragment>(F).getContents().size();
362 case MCFragment::FT_DwarfFrame:
363 return cast<MCDwarfCallFrameFragment>(F).getContents().size();
364 }
365
366 llvm_unreachable("invalid fragment kind");
367 }
368
LayoutFragment(MCFragment * F)369 void MCAsmLayout::LayoutFragment(MCFragment *F) {
370 MCFragment *Prev = F->getPrevNode();
371
372 // We should never try to recompute something which is up-to-date.
373 assert(!isFragmentUpToDate(F) && "Attempt to recompute up-to-date fragment!");
374 // We should never try to compute the fragment layout if it's predecessor
375 // isn't up-to-date.
376 assert((!Prev || isFragmentUpToDate(Prev)) &&
377 "Attempt to compute fragment before it's predecessor!");
378
379 ++stats::FragmentLayouts;
380
381 // Compute fragment offset and size.
382 uint64_t Offset = 0;
383 if (Prev)
384 Offset += Prev->Offset + getAssembler().computeFragmentSize(*this, *Prev);
385
386 F->Offset = Offset;
387 LastValidFragment[F->getParent()] = F;
388 }
389
390 /// WriteFragmentData - Write the \arg F data to the output file.
WriteFragmentData(const MCAssembler & Asm,const MCAsmLayout & Layout,const MCFragment & F)391 static void WriteFragmentData(const MCAssembler &Asm, const MCAsmLayout &Layout,
392 const MCFragment &F) {
393 MCObjectWriter *OW = &Asm.getWriter();
394 uint64_t Start = OW->getStream().tell();
395 (void) Start;
396
397 ++stats::EmittedFragments;
398
399 // FIXME: Embed in fragments instead?
400 uint64_t FragmentSize = Asm.computeFragmentSize(Layout, F);
401 switch (F.getKind()) {
402 case MCFragment::FT_Align: {
403 MCAlignFragment &AF = cast<MCAlignFragment>(F);
404 uint64_t Count = FragmentSize / AF.getValueSize();
405
406 assert(AF.getValueSize() && "Invalid virtual align in concrete fragment!");
407
408 // FIXME: This error shouldn't actually occur (the front end should emit
409 // multiple .align directives to enforce the semantics it wants), but is
410 // severe enough that we want to report it. How to handle this?
411 if (Count * AF.getValueSize() != FragmentSize)
412 report_fatal_error("undefined .align directive, value size '" +
413 Twine(AF.getValueSize()) +
414 "' is not a divisor of padding size '" +
415 Twine(FragmentSize) + "'");
416
417 // See if we are aligning with nops, and if so do that first to try to fill
418 // the Count bytes. Then if that did not fill any bytes or there are any
419 // bytes left to fill use the Value and ValueSize to fill the rest.
420 // If we are aligning with nops, ask that target to emit the right data.
421 if (AF.hasEmitNops()) {
422 if (!Asm.getBackend().writeNopData(Count, OW))
423 report_fatal_error("unable to write nop sequence of " +
424 Twine(Count) + " bytes");
425 break;
426 }
427
428 // Otherwise, write out in multiples of the value size.
429 for (uint64_t i = 0; i != Count; ++i) {
430 switch (AF.getValueSize()) {
431 default: llvm_unreachable("Invalid size!");
432 case 1: OW->Write8 (uint8_t (AF.getValue())); break;
433 case 2: OW->Write16(uint16_t(AF.getValue())); break;
434 case 4: OW->Write32(uint32_t(AF.getValue())); break;
435 case 8: OW->Write64(uint64_t(AF.getValue())); break;
436 }
437 }
438 break;
439 }
440
441 case MCFragment::FT_Data: {
442 MCDataFragment &DF = cast<MCDataFragment>(F);
443 assert(FragmentSize == DF.getContents().size() && "Invalid size!");
444 OW->WriteBytes(DF.getContents().str());
445 break;
446 }
447
448 case MCFragment::FT_Fill: {
449 MCFillFragment &FF = cast<MCFillFragment>(F);
450
451 assert(FF.getValueSize() && "Invalid virtual align in concrete fragment!");
452
453 for (uint64_t i = 0, e = FF.getSize() / FF.getValueSize(); i != e; ++i) {
454 switch (FF.getValueSize()) {
455 default: llvm_unreachable("Invalid size!");
456 case 1: OW->Write8 (uint8_t (FF.getValue())); break;
457 case 2: OW->Write16(uint16_t(FF.getValue())); break;
458 case 4: OW->Write32(uint32_t(FF.getValue())); break;
459 case 8: OW->Write64(uint64_t(FF.getValue())); break;
460 }
461 }
462 break;
463 }
464
465 case MCFragment::FT_Inst: {
466 MCInstFragment &IF = cast<MCInstFragment>(F);
467 OW->WriteBytes(StringRef(IF.getCode().begin(), IF.getCode().size()));
468 break;
469 }
470
471 case MCFragment::FT_LEB: {
472 MCLEBFragment &LF = cast<MCLEBFragment>(F);
473 OW->WriteBytes(LF.getContents().str());
474 break;
475 }
476
477 case MCFragment::FT_Org: {
478 MCOrgFragment &OF = cast<MCOrgFragment>(F);
479
480 for (uint64_t i = 0, e = FragmentSize; i != e; ++i)
481 OW->Write8(uint8_t(OF.getValue()));
482
483 break;
484 }
485
486 case MCFragment::FT_Dwarf: {
487 const MCDwarfLineAddrFragment &OF = cast<MCDwarfLineAddrFragment>(F);
488 OW->WriteBytes(OF.getContents().str());
489 break;
490 }
491 case MCFragment::FT_DwarfFrame: {
492 const MCDwarfCallFrameFragment &CF = cast<MCDwarfCallFrameFragment>(F);
493 OW->WriteBytes(CF.getContents().str());
494 break;
495 }
496 }
497
498 assert(OW->getStream().tell() - Start == FragmentSize);
499 }
500
writeSectionData(const MCSectionData * SD,const MCAsmLayout & Layout) const501 void MCAssembler::writeSectionData(const MCSectionData *SD,
502 const MCAsmLayout &Layout) const {
503 // Ignore virtual sections.
504 if (SD->getSection().isVirtualSection()) {
505 assert(Layout.getSectionFileSize(SD) == 0 && "Invalid size for section!");
506
507 // Check that contents are only things legal inside a virtual section.
508 for (MCSectionData::const_iterator it = SD->begin(),
509 ie = SD->end(); it != ie; ++it) {
510 switch (it->getKind()) {
511 default: llvm_unreachable("Invalid fragment in virtual section!");
512 case MCFragment::FT_Data: {
513 // Check that we aren't trying to write a non-zero contents (or fixups)
514 // into a virtual section. This is to support clients which use standard
515 // directives to fill the contents of virtual sections.
516 MCDataFragment &DF = cast<MCDataFragment>(*it);
517 assert(DF.fixup_begin() == DF.fixup_end() &&
518 "Cannot have fixups in virtual section!");
519 for (unsigned i = 0, e = DF.getContents().size(); i != e; ++i)
520 assert(DF.getContents()[i] == 0 &&
521 "Invalid data value for virtual section!");
522 break;
523 }
524 case MCFragment::FT_Align:
525 // Check that we aren't trying to write a non-zero value into a virtual
526 // section.
527 assert((!cast<MCAlignFragment>(it)->getValueSize() ||
528 !cast<MCAlignFragment>(it)->getValue()) &&
529 "Invalid align in virtual section!");
530 break;
531 case MCFragment::FT_Fill:
532 assert(!cast<MCFillFragment>(it)->getValueSize() &&
533 "Invalid fill in virtual section!");
534 break;
535 }
536 }
537
538 return;
539 }
540
541 uint64_t Start = getWriter().getStream().tell();
542 (void) Start;
543
544 for (MCSectionData::const_iterator it = SD->begin(),
545 ie = SD->end(); it != ie; ++it)
546 WriteFragmentData(*this, Layout, *it);
547
548 assert(getWriter().getStream().tell() - Start ==
549 Layout.getSectionAddressSize(SD));
550 }
551
552
handleFixup(const MCAsmLayout & Layout,MCFragment & F,const MCFixup & Fixup)553 uint64_t MCAssembler::handleFixup(const MCAsmLayout &Layout,
554 MCFragment &F,
555 const MCFixup &Fixup) {
556 // Evaluate the fixup.
557 MCValue Target;
558 uint64_t FixedValue;
559 if (!evaluateFixup(Layout, Fixup, &F, Target, FixedValue)) {
560 // The fixup was unresolved, we need a relocation. Inform the object
561 // writer of the relocation, and give it an opportunity to adjust the
562 // fixup value if need be.
563 getWriter().RecordRelocation(*this, Layout, &F, Fixup, Target, FixedValue);
564 }
565 return FixedValue;
566 }
567
Finish()568 void MCAssembler::Finish() {
569 DEBUG_WITH_TYPE("mc-dump", {
570 llvm::errs() << "assembler backend - pre-layout\n--\n";
571 dump(); });
572
573 // Create the layout object.
574 MCAsmLayout Layout(*this);
575
576 // Create dummy fragments and assign section ordinals.
577 unsigned SectionIndex = 0;
578 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
579 // Create dummy fragments to eliminate any empty sections, this simplifies
580 // layout.
581 if (it->getFragmentList().empty())
582 new MCDataFragment(it);
583
584 it->setOrdinal(SectionIndex++);
585 }
586
587 // Assign layout order indices to sections and fragments.
588 for (unsigned i = 0, e = Layout.getSectionOrder().size(); i != e; ++i) {
589 MCSectionData *SD = Layout.getSectionOrder()[i];
590 SD->setLayoutOrder(i);
591
592 unsigned FragmentIndex = 0;
593 for (MCSectionData::iterator it2 = SD->begin(),
594 ie2 = SD->end(); it2 != ie2; ++it2)
595 it2->setLayoutOrder(FragmentIndex++);
596 }
597
598 // Layout until everything fits.
599 while (layoutOnce(Layout))
600 continue;
601
602 DEBUG_WITH_TYPE("mc-dump", {
603 llvm::errs() << "assembler backend - post-relaxation\n--\n";
604 dump(); });
605
606 // Finalize the layout, including fragment lowering.
607 finishLayout(Layout);
608
609 DEBUG_WITH_TYPE("mc-dump", {
610 llvm::errs() << "assembler backend - final-layout\n--\n";
611 dump(); });
612
613 uint64_t StartOffset = OS.tell();
614
615 // Allow the object writer a chance to perform post-layout binding (for
616 // example, to set the index fields in the symbol data).
617 getWriter().ExecutePostLayoutBinding(*this, Layout);
618
619 // Evaluate and apply the fixups, generating relocation entries as necessary.
620 for (MCAssembler::iterator it = begin(), ie = end(); it != ie; ++it) {
621 for (MCSectionData::iterator it2 = it->begin(),
622 ie2 = it->end(); it2 != ie2; ++it2) {
623 MCDataFragment *DF = dyn_cast<MCDataFragment>(it2);
624 if (DF) {
625 for (MCDataFragment::fixup_iterator it3 = DF->fixup_begin(),
626 ie3 = DF->fixup_end(); it3 != ie3; ++it3) {
627 MCFixup &Fixup = *it3;
628 uint64_t FixedValue = handleFixup(Layout, *DF, Fixup);
629 getBackend().applyFixup(Fixup, DF->getContents().data(),
630 DF->getContents().size(), FixedValue);
631 }
632 }
633 MCInstFragment *IF = dyn_cast<MCInstFragment>(it2);
634 if (IF) {
635 for (MCInstFragment::fixup_iterator it3 = IF->fixup_begin(),
636 ie3 = IF->fixup_end(); it3 != ie3; ++it3) {
637 MCFixup &Fixup = *it3;
638 uint64_t FixedValue = handleFixup(Layout, *IF, Fixup);
639 getBackend().applyFixup(Fixup, IF->getCode().data(),
640 IF->getCode().size(), FixedValue);
641 }
642 }
643 }
644 }
645
646 // Write the object file.
647 getWriter().WriteObject(*this, Layout);
648
649 stats::ObjectBytes += OS.tell() - StartOffset;
650 }
651
fixupNeedsRelaxation(const MCFixup & Fixup,const MCInstFragment * DF,const MCAsmLayout & Layout) const652 bool MCAssembler::fixupNeedsRelaxation(const MCFixup &Fixup,
653 const MCInstFragment *DF,
654 const MCAsmLayout &Layout) const {
655 if (getRelaxAll())
656 return true;
657
658 // If we cannot resolve the fixup value, it requires relaxation.
659 MCValue Target;
660 uint64_t Value;
661 if (!evaluateFixup(Layout, Fixup, DF, Target, Value))
662 return true;
663
664 return getBackend().fixupNeedsRelaxation(Fixup, Value, DF, Layout);
665 }
666
fragmentNeedsRelaxation(const MCInstFragment * IF,const MCAsmLayout & Layout) const667 bool MCAssembler::fragmentNeedsRelaxation(const MCInstFragment *IF,
668 const MCAsmLayout &Layout) const {
669 // If this inst doesn't ever need relaxation, ignore it. This occurs when we
670 // are intentionally pushing out inst fragments, or because we relaxed a
671 // previous instruction to one that doesn't need relaxation.
672 if (!getBackend().mayNeedRelaxation(IF->getInst()))
673 return false;
674
675 for (MCInstFragment::const_fixup_iterator it = IF->fixup_begin(),
676 ie = IF->fixup_end(); it != ie; ++it)
677 if (fixupNeedsRelaxation(*it, IF, Layout))
678 return true;
679
680 return false;
681 }
682
relaxInstruction(MCAsmLayout & Layout,MCInstFragment & IF)683 bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
684 MCInstFragment &IF) {
685 if (!fragmentNeedsRelaxation(&IF, Layout))
686 return false;
687
688 ++stats::RelaxedInstructions;
689
690 // FIXME-PERF: We could immediately lower out instructions if we can tell
691 // they are fully resolved, to avoid retesting on later passes.
692
693 // Relax the fragment.
694
695 MCInst Relaxed;
696 getBackend().relaxInstruction(IF.getInst(), Relaxed);
697
698 // Encode the new instruction.
699 //
700 // FIXME-PERF: If it matters, we could let the target do this. It can
701 // probably do so more efficiently in many cases.
702 SmallVector<MCFixup, 4> Fixups;
703 SmallString<256> Code;
704 raw_svector_ostream VecOS(Code);
705 getEmitter().EncodeInstruction(Relaxed, VecOS, Fixups);
706 VecOS.flush();
707
708 // Update the instruction fragment.
709 IF.setInst(Relaxed);
710 IF.getCode() = Code;
711 IF.getFixups().clear();
712 // FIXME: Eliminate copy.
713 for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
714 IF.getFixups().push_back(Fixups[i]);
715
716 return true;
717 }
718
relaxLEB(MCAsmLayout & Layout,MCLEBFragment & LF)719 bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
720 int64_t Value = 0;
721 uint64_t OldSize = LF.getContents().size();
722 bool IsAbs = LF.getValue().EvaluateAsAbsolute(Value, Layout);
723 (void)IsAbs;
724 assert(IsAbs);
725 SmallString<8> &Data = LF.getContents();
726 Data.clear();
727 raw_svector_ostream OSE(Data);
728 if (LF.isSigned())
729 encodeSLEB128(Value, OSE);
730 else
731 encodeULEB128(Value, OSE);
732 OSE.flush();
733 return OldSize != LF.getContents().size();
734 }
735
relaxDwarfLineAddr(MCAsmLayout & Layout,MCDwarfLineAddrFragment & DF)736 bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
737 MCDwarfLineAddrFragment &DF) {
738 int64_t AddrDelta = 0;
739 uint64_t OldSize = DF.getContents().size();
740 bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
741 (void)IsAbs;
742 assert(IsAbs);
743 int64_t LineDelta;
744 LineDelta = DF.getLineDelta();
745 SmallString<8> &Data = DF.getContents();
746 Data.clear();
747 raw_svector_ostream OSE(Data);
748 MCDwarfLineAddr::Encode(LineDelta, AddrDelta, OSE);
749 OSE.flush();
750 return OldSize != Data.size();
751 }
752
relaxDwarfCallFrameFragment(MCAsmLayout & Layout,MCDwarfCallFrameFragment & DF)753 bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
754 MCDwarfCallFrameFragment &DF) {
755 int64_t AddrDelta = 0;
756 uint64_t OldSize = DF.getContents().size();
757 bool IsAbs = DF.getAddrDelta().EvaluateAsAbsolute(AddrDelta, Layout);
758 (void)IsAbs;
759 assert(IsAbs);
760 SmallString<8> &Data = DF.getContents();
761 Data.clear();
762 raw_svector_ostream OSE(Data);
763 MCDwarfFrameEmitter::EncodeAdvanceLoc(AddrDelta, OSE);
764 OSE.flush();
765 return OldSize != Data.size();
766 }
767
layoutSectionOnce(MCAsmLayout & Layout,MCSectionData & SD)768 bool MCAssembler::layoutSectionOnce(MCAsmLayout &Layout,
769 MCSectionData &SD) {
770 MCFragment *FirstInvalidFragment = NULL;
771 // Scan for fragments that need relaxation.
772 for (MCSectionData::iterator it2 = SD.begin(),
773 ie2 = SD.end(); it2 != ie2; ++it2) {
774 // Check if this is an fragment that needs relaxation.
775 bool relaxedFrag = false;
776 switch(it2->getKind()) {
777 default:
778 break;
779 case MCFragment::FT_Inst:
780 relaxedFrag = relaxInstruction(Layout, *cast<MCInstFragment>(it2));
781 break;
782 case MCFragment::FT_Dwarf:
783 relaxedFrag = relaxDwarfLineAddr(Layout,
784 *cast<MCDwarfLineAddrFragment>(it2));
785 break;
786 case MCFragment::FT_DwarfFrame:
787 relaxedFrag =
788 relaxDwarfCallFrameFragment(Layout,
789 *cast<MCDwarfCallFrameFragment>(it2));
790 break;
791 case MCFragment::FT_LEB:
792 relaxedFrag = relaxLEB(Layout, *cast<MCLEBFragment>(it2));
793 break;
794 }
795 // Update the layout, and remember that we relaxed.
796 if (relaxedFrag && !FirstInvalidFragment)
797 FirstInvalidFragment = it2;
798 }
799 if (FirstInvalidFragment) {
800 Layout.Invalidate(FirstInvalidFragment);
801 return true;
802 }
803 return false;
804 }
805
layoutOnce(MCAsmLayout & Layout)806 bool MCAssembler::layoutOnce(MCAsmLayout &Layout) {
807 ++stats::RelaxationSteps;
808
809 bool WasRelaxed = false;
810 for (iterator it = begin(), ie = end(); it != ie; ++it) {
811 MCSectionData &SD = *it;
812 while(layoutSectionOnce(Layout, SD))
813 WasRelaxed = true;
814 }
815
816 return WasRelaxed;
817 }
818
finishLayout(MCAsmLayout & Layout)819 void MCAssembler::finishLayout(MCAsmLayout &Layout) {
820 // The layout is done. Mark every fragment as valid.
821 for (unsigned int i = 0, n = Layout.getSectionOrder().size(); i != n; ++i) {
822 Layout.getFragmentOffset(&*Layout.getSectionOrder()[i]->rbegin());
823 }
824 }
825
826 // Debugging methods
827
828 namespace llvm {
829
operator <<(raw_ostream & OS,const MCFixup & AF)830 raw_ostream &operator<<(raw_ostream &OS, const MCFixup &AF) {
831 OS << "<MCFixup" << " Offset:" << AF.getOffset()
832 << " Value:" << *AF.getValue()
833 << " Kind:" << AF.getKind() << ">";
834 return OS;
835 }
836
837 }
838
839 #ifndef NDEBUG
dump()840 void MCFragment::dump() {
841 raw_ostream &OS = llvm::errs();
842
843 OS << "<";
844 switch (getKind()) {
845 case MCFragment::FT_Align: OS << "MCAlignFragment"; break;
846 case MCFragment::FT_Data: OS << "MCDataFragment"; break;
847 case MCFragment::FT_Fill: OS << "MCFillFragment"; break;
848 case MCFragment::FT_Inst: OS << "MCInstFragment"; break;
849 case MCFragment::FT_Org: OS << "MCOrgFragment"; break;
850 case MCFragment::FT_Dwarf: OS << "MCDwarfFragment"; break;
851 case MCFragment::FT_DwarfFrame: OS << "MCDwarfCallFrameFragment"; break;
852 case MCFragment::FT_LEB: OS << "MCLEBFragment"; break;
853 }
854
855 OS << "<MCFragment " << (void*) this << " LayoutOrder:" << LayoutOrder
856 << " Offset:" << Offset << ">";
857
858 switch (getKind()) {
859 case MCFragment::FT_Align: {
860 const MCAlignFragment *AF = cast<MCAlignFragment>(this);
861 if (AF->hasEmitNops())
862 OS << " (emit nops)";
863 OS << "\n ";
864 OS << " Alignment:" << AF->getAlignment()
865 << " Value:" << AF->getValue() << " ValueSize:" << AF->getValueSize()
866 << " MaxBytesToEmit:" << AF->getMaxBytesToEmit() << ">";
867 break;
868 }
869 case MCFragment::FT_Data: {
870 const MCDataFragment *DF = cast<MCDataFragment>(this);
871 OS << "\n ";
872 OS << " Contents:[";
873 const SmallVectorImpl<char> &Contents = DF->getContents();
874 for (unsigned i = 0, e = Contents.size(); i != e; ++i) {
875 if (i) OS << ",";
876 OS << hexdigit((Contents[i] >> 4) & 0xF) << hexdigit(Contents[i] & 0xF);
877 }
878 OS << "] (" << Contents.size() << " bytes)";
879
880 if (!DF->getFixups().empty()) {
881 OS << ",\n ";
882 OS << " Fixups:[";
883 for (MCDataFragment::const_fixup_iterator it = DF->fixup_begin(),
884 ie = DF->fixup_end(); it != ie; ++it) {
885 if (it != DF->fixup_begin()) OS << ",\n ";
886 OS << *it;
887 }
888 OS << "]";
889 }
890 break;
891 }
892 case MCFragment::FT_Fill: {
893 const MCFillFragment *FF = cast<MCFillFragment>(this);
894 OS << " Value:" << FF->getValue() << " ValueSize:" << FF->getValueSize()
895 << " Size:" << FF->getSize();
896 break;
897 }
898 case MCFragment::FT_Inst: {
899 const MCInstFragment *IF = cast<MCInstFragment>(this);
900 OS << "\n ";
901 OS << " Inst:";
902 IF->getInst().dump_pretty(OS);
903 break;
904 }
905 case MCFragment::FT_Org: {
906 const MCOrgFragment *OF = cast<MCOrgFragment>(this);
907 OS << "\n ";
908 OS << " Offset:" << OF->getOffset() << " Value:" << OF->getValue();
909 break;
910 }
911 case MCFragment::FT_Dwarf: {
912 const MCDwarfLineAddrFragment *OF = cast<MCDwarfLineAddrFragment>(this);
913 OS << "\n ";
914 OS << " AddrDelta:" << OF->getAddrDelta()
915 << " LineDelta:" << OF->getLineDelta();
916 break;
917 }
918 case MCFragment::FT_DwarfFrame: {
919 const MCDwarfCallFrameFragment *CF = cast<MCDwarfCallFrameFragment>(this);
920 OS << "\n ";
921 OS << " AddrDelta:" << CF->getAddrDelta();
922 break;
923 }
924 case MCFragment::FT_LEB: {
925 const MCLEBFragment *LF = cast<MCLEBFragment>(this);
926 OS << "\n ";
927 OS << " Value:" << LF->getValue() << " Signed:" << LF->isSigned();
928 break;
929 }
930 }
931 OS << ">";
932 }
933
dump()934 void MCSectionData::dump() {
935 raw_ostream &OS = llvm::errs();
936
937 OS << "<MCSectionData";
938 OS << " Alignment:" << getAlignment() << " Fragments:[\n ";
939 for (iterator it = begin(), ie = end(); it != ie; ++it) {
940 if (it != begin()) OS << ",\n ";
941 it->dump();
942 }
943 OS << "]>";
944 }
945
dump()946 void MCSymbolData::dump() {
947 raw_ostream &OS = llvm::errs();
948
949 OS << "<MCSymbolData Symbol:" << getSymbol()
950 << " Fragment:" << getFragment() << " Offset:" << getOffset()
951 << " Flags:" << getFlags() << " Index:" << getIndex();
952 if (isCommon())
953 OS << " (common, size:" << getCommonSize()
954 << " align: " << getCommonAlignment() << ")";
955 if (isExternal())
956 OS << " (external)";
957 if (isPrivateExtern())
958 OS << " (private extern)";
959 OS << ">";
960 }
961
dump()962 void MCAssembler::dump() {
963 raw_ostream &OS = llvm::errs();
964
965 OS << "<MCAssembler\n";
966 OS << " Sections:[\n ";
967 for (iterator it = begin(), ie = end(); it != ie; ++it) {
968 if (it != begin()) OS << ",\n ";
969 it->dump();
970 }
971 OS << "],\n";
972 OS << " Symbols:[";
973
974 for (symbol_iterator it = symbol_begin(), ie = symbol_end(); it != ie; ++it) {
975 if (it != symbol_begin()) OS << ",\n ";
976 it->dump();
977 }
978 OS << "]>\n";
979 }
980 #endif
981
982 // anchors for MC*Fragment vtables
anchor()983 void MCDataFragment::anchor() { }
anchor()984 void MCInstFragment::anchor() { }
anchor()985 void MCAlignFragment::anchor() { }
anchor()986 void MCFillFragment::anchor() { }
anchor()987 void MCOrgFragment::anchor() { }
anchor()988 void MCLEBFragment::anchor() { }
anchor()989 void MCDwarfLineAddrFragment::anchor() { }
anchor()990 void MCDwarfCallFrameFragment::anchor() { }
991