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 TargetLoweringObjectFileELF::TargetLoweringObjectFileELF(bool atIsCommentChar,
266 : AtIsCommentChar(atIsCommentChar) {
269 BSSSection_ = getOrCreateSection("\t.bss", true, SectionKind::BSS);
271 // PPC/Linux doesn't support the .bss directive, it needs .section .bss.
272 // FIXME: Does .section .bss work everywhere??
273 BSSSection_ = getOrCreateSection("\t.bss", false, SectionKind::BSS);
276 TextSection = getOrCreateSection("\t.text", true, SectionKind::Text);
277 DataSection = getOrCreateSection("\t.data", true, SectionKind::DataRel);
279 getOrCreateSection("\t.rodata", false, SectionKind::ReadOnly);
281 getOrCreateSection("\t.tdata", false, SectionKind::ThreadData);
282 CStringSection_ = getOrCreateSection("\t.rodata.str", true,
283 SectionKind::MergeableCString);
285 TLSBSSSection = getOrCreateSection("\t.tbss", false, SectionKind::ThreadBSS);
287 DataRelSection = getOrCreateSection("\t.data.rel", false,
288 SectionKind::DataRel);
289 DataRelLocalSection = getOrCreateSection("\t.data.rel.local", false,
290 SectionKind::DataRelLocal);
291 DataRelROSection = getOrCreateSection("\t.data.rel.ro", false,
292 SectionKind::ReadOnlyWithRel);
293 DataRelROLocalSection =
294 getOrCreateSection("\t.data.rel.ro.local", false,
295 SectionKind::ReadOnlyWithRelLocal);
297 MergeableConst4Section = getOrCreateSection(".rodata.cst4", false,
298 SectionKind::MergeableConst4);
299 MergeableConst8Section = getOrCreateSection(".rodata.cst8", false,
300 SectionKind::MergeableConst8);
301 MergeableConst16Section = getOrCreateSection(".rodata.cst16", false,
302 SectionKind::MergeableConst16);
306 SectionKind::Kind TargetLoweringObjectFileELF::
307 getKindForNamedSection(const char *Name, SectionKind::Kind K) const {
308 if (Name[0] != '.') return K;
310 // Some lame default implementation based on some magic section names.
311 if (strncmp(Name, ".gnu.linkonce.b.", 16) == 0 ||
312 strncmp(Name, ".llvm.linkonce.b.", 17) == 0 ||
313 strncmp(Name, ".gnu.linkonce.sb.", 17) == 0 ||
314 strncmp(Name, ".llvm.linkonce.sb.", 18) == 0)
315 return SectionKind::BSS;
317 if (strcmp(Name, ".tdata") == 0 ||
318 strncmp(Name, ".tdata.", 7) == 0 ||
319 strncmp(Name, ".gnu.linkonce.td.", 17) == 0 ||
320 strncmp(Name, ".llvm.linkonce.td.", 18) == 0)
321 return SectionKind::ThreadData;
323 if (strcmp(Name, ".tbss") == 0 ||
324 strncmp(Name, ".tbss.", 6) == 0 ||
325 strncmp(Name, ".gnu.linkonce.tb.", 17) == 0 ||
326 strncmp(Name, ".llvm.linkonce.tb.", 18) == 0)
327 return SectionKind::ThreadBSS;
332 void TargetLoweringObjectFileELF::
333 getSectionFlagsAsString(SectionKind Kind, SmallVectorImpl<char> &Str) const {
337 if (!Kind.isMetadata())
341 if (Kind.isWriteable())
343 if (Kind.isMergeableConst() || Kind.isMergeableCString())
345 if (Kind.isMergeableCString())
347 if (Kind.isThreadLocal())
353 // If comment string is '@', e.g. as on ARM - use '%' instead
360 if (Kind.isBSS() || Kind.isThreadBSS())
363 KindStr = "progbits";
365 Str.append(KindStr, KindStr+strlen(KindStr));
367 if (Kind.isMergeableCString()) {
368 // TODO: Eventually handle multiple byte character strings. For now, all
369 // mergable C strings are single byte.
372 } else if (Kind.isMergeableConst4()) {
375 } else if (Kind.isMergeableConst8()) {
378 } else if (Kind.isMergeableConst16()) {
386 static const char *getSectionPrefixForUniqueGlobal(SectionKind Kind) {
387 if (Kind.isText()) return ".gnu.linkonce.t.";
388 if (Kind.isReadOnly()) return ".gnu.linkonce.r.";
390 if (Kind.isThreadData()) return ".gnu.linkonce.td.";
391 if (Kind.isThreadBSS()) return ".gnu.linkonce.tb.";
393 if (Kind.isBSS()) return ".gnu.linkonce.b.";
394 if (Kind.isDataNoRel()) return ".gnu.linkonce.d.";
395 if (Kind.isDataRelLocal()) return ".gnu.linkonce.d.rel.local.";
396 if (Kind.isDataRel()) return ".gnu.linkonce.d.rel.";
397 if (Kind.isReadOnlyWithRelLocal()) return ".gnu.linkonce.d.rel.ro.local.";
399 assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
400 return ".gnu.linkonce.d.rel.ro.";
403 const Section *TargetLoweringObjectFileELF::
404 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
405 Mangler *Mang, const TargetMachine &TM) const {
407 // If this global is linkonce/weak and the target handles this by emitting it
408 // into a 'uniqued' section name, create and return the section now.
410 const char *Prefix = getSectionPrefixForUniqueGlobal(Kind);
411 std::string Name = Mang->makeNameProper(GV->getNameStr());
412 return getOrCreateSection((Prefix+Name).c_str(), false, Kind.getKind());
415 if (Kind.isText()) return TextSection;
417 if (Kind.isMergeableCString()) {
418 assert(CStringSection_ && "Should have string section prefix");
420 // We also need alignment here.
421 // FIXME: this is getting the alignment of the character, not the
422 // alignment of the global!
424 TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));
426 std::string Name = CStringSection_->getName() + "1." + utostr(Align);
427 return getOrCreateSection(Name.c_str(), false,
428 SectionKind::MergeableCString);
431 if (Kind.isMergeableConst()) {
432 if (Kind.isMergeableConst4())
433 return MergeableConst4Section;
434 if (Kind.isMergeableConst8())
435 return MergeableConst8Section;
436 if (Kind.isMergeableConst16())
437 return MergeableConst16Section;
438 return ReadOnlySection; // .const
441 if (Kind.isReadOnly()) return ReadOnlySection;
443 if (Kind.isThreadData()) return TLSDataSection;
444 if (Kind.isThreadBSS()) return TLSBSSSection;
446 if (Kind.isBSS()) return BSSSection_;
448 if (Kind.isDataNoRel()) return DataSection;
449 if (Kind.isDataRelLocal()) return DataRelLocalSection;
450 if (Kind.isDataRel()) return DataRelSection;
451 if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
453 assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
454 return DataRelROSection;
457 /// getSectionForMergeableConstant - Given a mergeable constant with the
458 /// specified size and relocation information, return a section that it
459 /// should be placed in.
460 const Section *TargetLoweringObjectFileELF::
461 getSectionForMergeableConstant(SectionKind Kind) const {
462 if (Kind.isMergeableConst4())
463 return MergeableConst4Section;
464 if (Kind.isMergeableConst8())
465 return MergeableConst8Section;
466 if (Kind.isMergeableConst16())
467 return MergeableConst16Section;
468 if (Kind.isReadOnly())
469 return ReadOnlySection;
471 if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
472 assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
473 return DataRelROSection;
476 //===----------------------------------------------------------------------===//
478 //===----------------------------------------------------------------------===//
480 TargetLoweringObjectFileMachO::
481 TargetLoweringObjectFileMachO(const TargetMachine &TM) {
482 TextSection = getOrCreateSection("\t.text", true, SectionKind::Text);
483 DataSection = getOrCreateSection("\t.data", true, SectionKind::DataRel);
485 CStringSection_ = getOrCreateSection("\t.cstring", true,
486 SectionKind::MergeableCString);
487 FourByteConstantSection = getOrCreateSection("\t.literal4\n", true,
488 SectionKind::MergeableConst4);
489 EightByteConstantSection = getOrCreateSection("\t.literal8\n", true,
490 SectionKind::MergeableConst8);
492 // ld_classic doesn't support .literal16 in 32-bit mode, and ld64 falls back
493 // to using it in -static mode.
494 if (TM.getRelocationModel() != Reloc::Static &&
495 TM.getTargetData()->getPointerSize() == 32)
496 SixteenByteConstantSection =
497 getOrCreateSection("\t.literal16\n", true, SectionKind::MergeableConst16);
499 SixteenByteConstantSection = 0;
501 ReadOnlySection = getOrCreateSection("\t.const", true, SectionKind::ReadOnly);
504 getOrCreateSection("\t__TEXT,__textcoal_nt,coalesced,pure_instructions",
505 false, SectionKind::Text);
506 ConstTextCoalSection = getOrCreateSection("\t__TEXT,__const_coal,coalesced",
507 false, SectionKind::Text);
508 ConstDataCoalSection = getOrCreateSection("\t__DATA,__const_coal,coalesced",
509 false, SectionKind::Text);
510 ConstDataSection = getOrCreateSection("\t.const_data", true,
511 SectionKind::ReadOnlyWithRel);
512 DataCoalSection = getOrCreateSection("\t__DATA,__datacoal_nt,coalesced",
513 false, SectionKind::DataRel);
516 const Section *TargetLoweringObjectFileMachO::
517 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
518 Mangler *Mang, const TargetMachine &TM) const {
519 assert(!Kind.isThreadLocal() && "Darwin doesn't support TLS");
522 return Kind.isWeak() ? TextCoalSection : TextSection;
524 // If this is weak/linkonce, put this in a coalescable section, either in text
525 // or data depending on if it is writable.
527 if (Kind.isReadOnly())
528 return ConstTextCoalSection;
529 return DataCoalSection;
532 // FIXME: Alignment check should be handled by section classifier.
533 if (Kind.isMergeableCString()) {
534 Constant *C = cast<GlobalVariable>(GV)->getInitializer();
535 const Type *Ty = cast<ArrayType>(C->getType())->getElementType();
536 const TargetData &TD = *TM.getTargetData();
537 unsigned Size = TD.getTypeAllocSize(Ty);
539 unsigned Align = TD.getPreferredAlignment(cast<GlobalVariable>(GV));
541 return CStringSection_;
544 return ReadOnlySection;
547 if (Kind.isMergeableConst()) {
548 if (Kind.isMergeableConst4())
549 return FourByteConstantSection;
550 if (Kind.isMergeableConst8())
551 return EightByteConstantSection;
552 if (Kind.isMergeableConst16() && SixteenByteConstantSection)
553 return SixteenByteConstantSection;
554 return ReadOnlySection; // .const
557 // FIXME: ROData -> const in -static mode that is relocatable but they happen
558 // by the static linker. Why not mergeable?
559 if (Kind.isReadOnly())
560 return ReadOnlySection;
562 // If this is marked const, put it into a const section. But if the dynamic
563 // linker needs to write to it, put it in the data segment.
564 if (Kind.isReadOnlyWithRel())
565 return ConstDataSection;
567 // Otherwise, just drop the variable in the normal data section.
572 TargetLoweringObjectFileMachO::
573 getSectionForMergeableConstant(SectionKind Kind) const {
574 // If this constant requires a relocation, we have to put it in the data
575 // segment, not in the text segment.
576 if (Kind.isDataRel())
577 return ConstDataSection;
579 if (Kind.isMergeableConst4())
580 return FourByteConstantSection;
581 if (Kind.isMergeableConst8())
582 return EightByteConstantSection;
583 if (Kind.isMergeableConst16() && SixteenByteConstantSection)
584 return SixteenByteConstantSection;
585 return ReadOnlySection; // .const
588 //===----------------------------------------------------------------------===//
590 //===----------------------------------------------------------------------===//
592 TargetLoweringObjectFileCOFF::TargetLoweringObjectFileCOFF() {
593 TextSection = getOrCreateSection("\t.text", true, SectionKind::Text);
594 DataSection = getOrCreateSection("\t.data", true, SectionKind::DataRel);
597 void TargetLoweringObjectFileCOFF::
598 getSectionFlagsAsString(SectionKind Kind, SmallVectorImpl<char> &Str) const {
599 // FIXME: Inefficient.
600 std::string Res = ",\"";
603 if (Kind.isWriteable())
607 Str.append(Res.begin(), Res.end());
610 static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
612 return ".text$linkonce";
613 if (Kind.isWriteable())
614 return ".data$linkonce";
615 return ".rdata$linkonce";
619 const Section *TargetLoweringObjectFileCOFF::
620 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
621 Mangler *Mang, const TargetMachine &TM) const {
622 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
624 // If this global is linkonce/weak and the target handles this by emitting it
625 // into a 'uniqued' section name, create and return the section now.
627 const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
628 // FIXME: Use mangler interface (PR4584).
629 std::string Name = Prefix+GV->getNameStr();
630 return getOrCreateSection(Name.c_str(), false, Kind.getKind());
634 return getTextSection();
637 if (const Section *S = BSSSection_)
640 if (Kind.isReadOnly() && ReadOnlySection != 0)
641 return ReadOnlySection;
643 return getDataSection();