1 //===-- llvm/Target/TargetLoweringObjectFile.cpp - Object File Info -------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements classes used to handle lowerings specific to common
11 // object file formats.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Target/TargetLoweringObjectFile.h"
16 #include "llvm/Constants.h"
17 #include "llvm/DerivedTypes.h"
18 #include "llvm/GlobalVariable.h"
19 #include "llvm/Support/Mangler.h"
20 #include "llvm/Target/TargetMachine.h"
21 #include "llvm/Target/TargetData.h"
22 #include "llvm/Target/TargetOptions.h"
23 #include "llvm/ADT/StringExtras.h"
26 //===----------------------------------------------------------------------===//
28 //===----------------------------------------------------------------------===//
30 TargetLoweringObjectFile::TargetLoweringObjectFile() {
40 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
43 static bool isSuitableForBSS(const GlobalVariable *GV) {
44 Constant *C = GV->getInitializer();
46 // Must have zero initializer.
47 if (!C->isNullValue())
50 // Leave constant zeros in readonly constant sections, so they can be shared.
54 // If the global has an explicit section specified, don't put it in BSS.
55 if (!GV->getSection().empty())
58 // If -nozero-initialized-in-bss is specified, don't ever use BSS.
62 // Otherwise, put it in BSS!
66 static bool isConstantString(const Constant *C) {
67 // First check: is we have constant array of i8 terminated with zero
68 const ConstantArray *CVA = dyn_cast<ConstantArray>(C);
69 // Check, if initializer is a null-terminated string
70 if (CVA && CVA->isCString())
73 // Another possibility: [1 x i8] zeroinitializer
74 if (isa<ConstantAggregateZero>(C))
75 if (const ArrayType *Ty = dyn_cast<ArrayType>(C->getType()))
76 return (Ty->getElementType() == Type::Int8Ty &&
77 Ty->getNumElements() == 1);
82 static SectionKind::Kind SectionKindForGlobal(const GlobalValue *GV,
83 const TargetMachine &TM) {
84 Reloc::Model ReloModel = TM.getRelocationModel();
86 // Early exit - functions should be always in text sections.
87 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
89 return SectionKind::Text;
92 // Handle thread-local data first.
93 if (GVar->isThreadLocal()) {
94 if (isSuitableForBSS(GVar))
95 return SectionKind::ThreadBSS;
96 return SectionKind::ThreadData;
99 // Variable can be easily put to BSS section.
100 if (isSuitableForBSS(GVar))
101 return SectionKind::BSS;
103 Constant *C = GVar->getInitializer();
105 // If the global is marked constant, we can put it into a mergable section,
106 // a mergable string section, or general .data if it contains relocations.
107 if (GVar->isConstant()) {
108 // If the initializer for the global contains something that requires a
109 // relocation, then we may have to drop this into a wriable data section
110 // even though it is marked const.
111 switch (C->getRelocationInfo()) {
112 default: llvm_unreachable("unknown relocation info kind");
113 case Constant::NoRelocation:
114 // If initializer is a null-terminated string, put it in a "cstring"
115 // section if the target has it.
116 if (isConstantString(C))
117 return SectionKind::MergeableCString;
119 // Otherwise, just drop it into a mergable constant section. If we have
120 // a section for this size, use it, otherwise use the arbitrary sized
122 switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
123 case 4: return SectionKind::MergeableConst4;
124 case 8: return SectionKind::MergeableConst8;
125 case 16: return SectionKind::MergeableConst16;
126 default: return SectionKind::MergeableConst;
129 case Constant::LocalRelocation:
130 // In static relocation model, the linker will resolve all addresses, so
131 // the relocation entries will actually be constants by the time the app
132 // starts up. However, we can't put this into a mergable section, because
133 // the linker doesn't take relocations into consideration when it tries to
134 // merge entries in the section.
135 if (ReloModel == Reloc::Static)
136 return SectionKind::ReadOnly;
138 // Otherwise, the dynamic linker needs to fix it up, put it in the
139 // writable data.rel.local section.
140 return SectionKind::ReadOnlyWithRelLocal;
142 case Constant::GlobalRelocations:
143 // In static relocation model, the linker will resolve all addresses, so
144 // the relocation entries will actually be constants by the time the app
145 // starts up. However, we can't put this into a mergable section, because
146 // the linker doesn't take relocations into consideration when it tries to
147 // merge entries in the section.
148 if (ReloModel == Reloc::Static)
149 return SectionKind::ReadOnly;
151 // Otherwise, the dynamic linker needs to fix it up, put it in the
152 // writable data.rel section.
153 return SectionKind::ReadOnlyWithRel;
157 // Okay, this isn't a constant. If the initializer for the global is going
158 // to require a runtime relocation by the dynamic linker, put it into a more
159 // specific section to improve startup time of the app. This coalesces these
160 // globals together onto fewer pages, improving the locality of the dynamic
162 if (ReloModel == Reloc::Static)
163 return SectionKind::DataNoRel;
165 switch (C->getRelocationInfo()) {
166 default: llvm_unreachable("unknown relocation info kind");
167 case Constant::NoRelocation:
168 return SectionKind::DataNoRel;
169 case Constant::LocalRelocation:
170 return SectionKind::DataRelLocal;
171 case Constant::GlobalRelocations:
172 return SectionKind::DataRel;
176 /// SectionForGlobal - This method computes the appropriate section to emit
177 /// the specified global variable or function definition. This should not
178 /// be passed external (or available externally) globals.
179 const Section *TargetLoweringObjectFile::
180 SectionForGlobal(const GlobalValue *GV, Mangler *Mang,
181 const TargetMachine &TM) const {
182 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
183 "Can only be used for global definitions");
185 SectionKind::Kind GVKind = SectionKindForGlobal(GV, TM);
187 SectionKind Kind = SectionKind::get(GVKind, GV->isWeakForLinker(),
191 // Select section name.
192 if (GV->hasSection()) {
193 // If the target has special section hacks for specifically named globals,
195 if (const Section *TS = getSpecialCasedSectionGlobals(GV, Mang, Kind))
198 // If the target has magic semantics for certain section names, make sure to
199 // pick up the flags. This allows the user to write things with attribute
200 // section and still get the appropriate section flags printed.
201 GVKind = getKindForNamedSection(GV->getSection().c_str(), GVKind);
203 return getOrCreateSection(GV->getSection().c_str(), false, GVKind);
207 // Use default section depending on the 'type' of global
208 return SelectSectionForGlobal(GV, Kind, Mang, TM);
211 // Lame default implementation. Calculate the section name for global.
213 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
216 const TargetMachine &TM) const{
217 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
220 return getTextSection();
222 if (Kind.isBSS() && BSSSection_ != 0)
225 if (Kind.isReadOnly() && ReadOnlySection != 0)
226 return ReadOnlySection;
228 return getDataSection();
231 /// getSectionForMergableConstant - Given a mergable constant with the
232 /// specified size and relocation information, return a section that it
233 /// should be placed in.
235 TargetLoweringObjectFile::
236 getSectionForMergeableConstant(SectionKind Kind) const {
237 if (Kind.isReadOnly() && ReadOnlySection != 0)
238 return ReadOnlySection;
244 const Section *TargetLoweringObjectFile::
245 getOrCreateSection(const char *Name, bool isDirective,
246 SectionKind::Kind Kind) const {
247 Section &S = Sections[Name];
249 // This is newly-created section, set it up properly.
250 if (S.Name.empty()) {
251 S.Kind = SectionKind::get(Kind, false /*weak*/, !isDirective);
260 //===----------------------------------------------------------------------===//
262 //===----------------------------------------------------------------------===//
264 void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
265 const TargetMachine &TM) {
267 BSSSection_ = getOrCreateSection("\t.bss", true, SectionKind::BSS);
269 // PPC/Linux doesn't support the .bss directive, it needs .section .bss.
270 // FIXME: Does .section .bss work everywhere??
271 BSSSection_ = getOrCreateSection("\t.bss", false, SectionKind::BSS);
274 TextSection = getOrCreateSection("\t.text", true, SectionKind::Text);
275 DataSection = getOrCreateSection("\t.data", true, SectionKind::DataRel);
277 getOrCreateSection("\t.rodata", false, SectionKind::ReadOnly);
279 getOrCreateSection("\t.tdata", false, SectionKind::ThreadData);
280 CStringSection_ = getOrCreateSection("\t.rodata.str", true,
281 SectionKind::MergeableCString);
283 TLSBSSSection = getOrCreateSection("\t.tbss", false, SectionKind::ThreadBSS);
285 DataRelSection = getOrCreateSection("\t.data.rel", false,
286 SectionKind::DataRel);
287 DataRelLocalSection = getOrCreateSection("\t.data.rel.local", false,
288 SectionKind::DataRelLocal);
289 DataRelROSection = getOrCreateSection("\t.data.rel.ro", false,
290 SectionKind::ReadOnlyWithRel);
291 DataRelROLocalSection =
292 getOrCreateSection("\t.data.rel.ro.local", false,
293 SectionKind::ReadOnlyWithRelLocal);
295 MergeableConst4Section = getOrCreateSection(".rodata.cst4", false,
296 SectionKind::MergeableConst4);
297 MergeableConst8Section = getOrCreateSection(".rodata.cst8", false,
298 SectionKind::MergeableConst8);
299 MergeableConst16Section = getOrCreateSection(".rodata.cst16", false,
300 SectionKind::MergeableConst16);
304 SectionKind::Kind TargetLoweringObjectFileELF::
305 getKindForNamedSection(const char *Name, SectionKind::Kind K) const {
306 if (Name[0] != '.') return K;
308 // Some lame default implementation based on some magic section names.
309 if (strncmp(Name, ".gnu.linkonce.b.", 16) == 0 ||
310 strncmp(Name, ".llvm.linkonce.b.", 17) == 0 ||
311 strncmp(Name, ".gnu.linkonce.sb.", 17) == 0 ||
312 strncmp(Name, ".llvm.linkonce.sb.", 18) == 0)
313 return SectionKind::BSS;
315 if (strcmp(Name, ".tdata") == 0 ||
316 strncmp(Name, ".tdata.", 7) == 0 ||
317 strncmp(Name, ".gnu.linkonce.td.", 17) == 0 ||
318 strncmp(Name, ".llvm.linkonce.td.", 18) == 0)
319 return SectionKind::ThreadData;
321 if (strcmp(Name, ".tbss") == 0 ||
322 strncmp(Name, ".tbss.", 6) == 0 ||
323 strncmp(Name, ".gnu.linkonce.tb.", 17) == 0 ||
324 strncmp(Name, ".llvm.linkonce.tb.", 18) == 0)
325 return SectionKind::ThreadBSS;
330 void TargetLoweringObjectFileELF::
331 getSectionFlagsAsString(SectionKind Kind, SmallVectorImpl<char> &Str) const {
335 if (!Kind.isMetadata())
339 if (Kind.isWriteable())
341 if (Kind.isMergeableCString() ||
342 Kind.isMergeableConst4() ||
343 Kind.isMergeableConst8() ||
344 Kind.isMergeableConst16())
346 if (Kind.isMergeableCString())
348 if (Kind.isThreadLocal())
354 // If comment string is '@', e.g. as on ARM - use '%' instead
361 if (Kind.isBSS() || Kind.isThreadBSS())
364 KindStr = "progbits";
366 Str.append(KindStr, KindStr+strlen(KindStr));
368 if (Kind.isMergeableCString()) {
369 // TODO: Eventually handle multiple byte character strings. For now, all
370 // mergable C strings are single byte.
373 } else if (Kind.isMergeableConst4()) {
376 } else if (Kind.isMergeableConst8()) {
379 } else if (Kind.isMergeableConst16()) {
387 static const char *getSectionPrefixForUniqueGlobal(SectionKind Kind) {
388 if (Kind.isText()) return ".gnu.linkonce.t.";
389 if (Kind.isReadOnly()) return ".gnu.linkonce.r.";
391 if (Kind.isThreadData()) return ".gnu.linkonce.td.";
392 if (Kind.isThreadBSS()) return ".gnu.linkonce.tb.";
394 if (Kind.isBSS()) return ".gnu.linkonce.b.";
395 if (Kind.isDataNoRel()) return ".gnu.linkonce.d.";
396 if (Kind.isDataRelLocal()) return ".gnu.linkonce.d.rel.local.";
397 if (Kind.isDataRel()) return ".gnu.linkonce.d.rel.";
398 if (Kind.isReadOnlyWithRelLocal()) return ".gnu.linkonce.d.rel.ro.local.";
400 assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
401 return ".gnu.linkonce.d.rel.ro.";
404 const Section *TargetLoweringObjectFileELF::
405 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
406 Mangler *Mang, const TargetMachine &TM) const {
408 // If this global is linkonce/weak and the target handles this by emitting it
409 // into a 'uniqued' section name, create and return the section now.
411 const char *Prefix = getSectionPrefixForUniqueGlobal(Kind);
412 std::string Name = Mang->makeNameProper(GV->getNameStr());
413 return getOrCreateSection((Prefix+Name).c_str(), false, Kind.getKind());
416 if (Kind.isText()) return TextSection;
418 if (Kind.isMergeableCString()) {
419 assert(CStringSection_ && "Should have string section prefix");
421 // We also need alignment here.
422 // FIXME: this is getting the alignment of the character, not the
423 // alignment of the global!
425 TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));
427 std::string Name = CStringSection_->getName() + "1." + utostr(Align);
428 return getOrCreateSection(Name.c_str(), false,
429 SectionKind::MergeableCString);
432 if (Kind.isMergeableConst()) {
433 if (Kind.isMergeableConst4())
434 return MergeableConst4Section;
435 if (Kind.isMergeableConst8())
436 return MergeableConst8Section;
437 if (Kind.isMergeableConst16())
438 return MergeableConst16Section;
439 return ReadOnlySection; // .const
442 if (Kind.isReadOnly()) return ReadOnlySection;
444 if (Kind.isThreadData()) return TLSDataSection;
445 if (Kind.isThreadBSS()) return TLSBSSSection;
447 if (Kind.isBSS()) return BSSSection_;
449 if (Kind.isDataNoRel()) return DataSection;
450 if (Kind.isDataRelLocal()) return DataRelLocalSection;
451 if (Kind.isDataRel()) return DataRelSection;
452 if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
454 assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
455 return DataRelROSection;
458 /// getSectionForMergeableConstant - Given a mergeable constant with the
459 /// specified size and relocation information, return a section that it
460 /// should be placed in.
461 const Section *TargetLoweringObjectFileELF::
462 getSectionForMergeableConstant(SectionKind Kind) const {
463 if (Kind.isMergeableConst4())
464 return MergeableConst4Section;
465 if (Kind.isMergeableConst8())
466 return MergeableConst8Section;
467 if (Kind.isMergeableConst16())
468 return MergeableConst16Section;
469 if (Kind.isReadOnly())
470 return ReadOnlySection;
472 if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
473 assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
474 return DataRelROSection;
477 //===----------------------------------------------------------------------===//
479 //===----------------------------------------------------------------------===//
481 void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
482 const TargetMachine &TM) {
483 TextSection = getOrCreateSection("\t.text", true, SectionKind::Text);
484 DataSection = getOrCreateSection("\t.data", true, SectionKind::DataRel);
486 CStringSection_ = getOrCreateSection("\t.cstring", true,
487 SectionKind::MergeableCString);
488 FourByteConstantSection = getOrCreateSection("\t.literal4\n", true,
489 SectionKind::MergeableConst4);
490 EightByteConstantSection = getOrCreateSection("\t.literal8\n", true,
491 SectionKind::MergeableConst8);
493 // ld_classic doesn't support .literal16 in 32-bit mode, and ld64 falls back
494 // to using it in -static mode.
495 if (TM.getRelocationModel() != Reloc::Static &&
496 TM.getTargetData()->getPointerSize() == 32)
497 SixteenByteConstantSection =
498 getOrCreateSection("\t.literal16\n", true, SectionKind::MergeableConst16);
500 SixteenByteConstantSection = 0;
502 ReadOnlySection = getOrCreateSection("\t.const", true, SectionKind::ReadOnly);
505 getOrCreateSection("\t__TEXT,__textcoal_nt,coalesced,pure_instructions",
506 false, SectionKind::Text);
507 ConstTextCoalSection = getOrCreateSection("\t__TEXT,__const_coal,coalesced",
508 false, SectionKind::Text);
509 ConstDataCoalSection = getOrCreateSection("\t__DATA,__const_coal,coalesced",
510 false, SectionKind::Text);
511 ConstDataSection = getOrCreateSection("\t.const_data", true,
512 SectionKind::ReadOnlyWithRel);
513 DataCoalSection = getOrCreateSection("\t__DATA,__datacoal_nt,coalesced",
514 false, SectionKind::DataRel);
517 const Section *TargetLoweringObjectFileMachO::
518 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
519 Mangler *Mang, const TargetMachine &TM) const {
520 assert(!Kind.isThreadLocal() && "Darwin doesn't support TLS");
523 return Kind.isWeak() ? TextCoalSection : TextSection;
525 // If this is weak/linkonce, put this in a coalescable section, either in text
526 // or data depending on if it is writable.
528 if (Kind.isReadOnly())
529 return ConstTextCoalSection;
530 return DataCoalSection;
533 // FIXME: Alignment check should be handled by section classifier.
534 if (Kind.isMergeableCString()) {
535 Constant *C = cast<GlobalVariable>(GV)->getInitializer();
536 const Type *Ty = cast<ArrayType>(C->getType())->getElementType();
537 const TargetData &TD = *TM.getTargetData();
538 unsigned Size = TD.getTypeAllocSize(Ty);
540 unsigned Align = TD.getPreferredAlignment(cast<GlobalVariable>(GV));
542 return CStringSection_;
545 return ReadOnlySection;
548 if (Kind.isMergeableConst()) {
549 if (Kind.isMergeableConst4())
550 return FourByteConstantSection;
551 if (Kind.isMergeableConst8())
552 return EightByteConstantSection;
553 if (Kind.isMergeableConst16() && SixteenByteConstantSection)
554 return SixteenByteConstantSection;
555 return ReadOnlySection; // .const
558 // FIXME: ROData -> const in -static mode that is relocatable but they happen
559 // by the static linker. Why not mergeable?
560 if (Kind.isReadOnly())
561 return ReadOnlySection;
563 // If this is marked const, put it into a const section. But if the dynamic
564 // linker needs to write to it, put it in the data segment.
565 if (Kind.isReadOnlyWithRel())
566 return ConstDataSection;
568 // Otherwise, just drop the variable in the normal data section.
573 TargetLoweringObjectFileMachO::
574 getSectionForMergeableConstant(SectionKind Kind) const {
575 // If this constant requires a relocation, we have to put it in the data
576 // segment, not in the text segment.
577 if (Kind.isDataRel())
578 return ConstDataSection;
580 if (Kind.isMergeableConst4())
581 return FourByteConstantSection;
582 if (Kind.isMergeableConst8())
583 return EightByteConstantSection;
584 if (Kind.isMergeableConst16() && SixteenByteConstantSection)
585 return SixteenByteConstantSection;
586 return ReadOnlySection; // .const
589 //===----------------------------------------------------------------------===//
591 //===----------------------------------------------------------------------===//
593 void TargetLoweringObjectFileCOFF::Initialize(MCContext &Ctx,
594 const TargetMachine &TM) {
595 TextSection = getOrCreateSection("\t.text", true, SectionKind::Text);
596 DataSection = getOrCreateSection("\t.data", true, SectionKind::DataRel);
599 void TargetLoweringObjectFileCOFF::
600 getSectionFlagsAsString(SectionKind Kind, SmallVectorImpl<char> &Str) const {
601 // FIXME: Inefficient.
602 std::string Res = ",\"";
605 if (Kind.isWriteable())
609 Str.append(Res.begin(), Res.end());
612 static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
614 return ".text$linkonce";
615 if (Kind.isWriteable())
616 return ".data$linkonce";
617 return ".rdata$linkonce";
621 const Section *TargetLoweringObjectFileCOFF::
622 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
623 Mangler *Mang, const TargetMachine &TM) const {
624 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
626 // If this global is linkonce/weak and the target handles this by emitting it
627 // into a 'uniqued' section name, create and return the section now.
629 const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
630 // FIXME: Use mangler interface (PR4584).
631 std::string Name = Prefix+GV->getNameStr();
632 return getOrCreateSection(Name.c_str(), false, Kind.getKind());
636 return getTextSection();
639 if (const Section *S = BSSSection_)
642 if (Kind.isReadOnly() && ReadOnlySection != 0)
643 return ReadOnlySection;
645 return getDataSection();