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/Function.h"
19 #include "llvm/GlobalVariable.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCExpr.h"
22 #include "llvm/MC/MCStreamer.h"
23 #include "llvm/MC/MCSymbol.h"
24 #include "llvm/Target/Mangler.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Target/TargetOptions.h"
28 #include "llvm/Support/Dwarf.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/ADT/SmallString.h"
34 //===----------------------------------------------------------------------===//
36 //===----------------------------------------------------------------------===//
38 /// Initialize - this method must be called before any actual lowering is
39 /// done. This specifies the current context for codegen, and gives the
40 /// lowering implementations a chance to set up their default sections.
41 void TargetLoweringObjectFile::Initialize(MCContext &ctx,
42 const TargetMachine &TM) {
44 InitMCObjectFileInfo(TM.getTargetTriple(),
45 TM.getRelocationModel(), TM.getCodeModel(), *Ctx);
48 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
51 static bool isSuitableForBSS(const GlobalVariable *GV, bool NoZerosInBSS) {
52 const Constant *C = GV->getInitializer();
54 // Must have zero initializer.
55 if (!C->isNullValue())
58 // Leave constant zeros in readonly constant sections, so they can be shared.
62 // If the global has an explicit section specified, don't put it in BSS.
63 if (!GV->getSection().empty())
66 // If -nozero-initialized-in-bss is specified, don't ever use BSS.
70 // Otherwise, put it in BSS!
74 /// IsNullTerminatedString - Return true if the specified constant (which is
75 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
76 /// nul value and contains no other nuls in it. Note that this is more general
77 /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings.
78 static bool IsNullTerminatedString(const Constant *C) {
79 // First check: is we have constant array terminated with zero
80 if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) {
81 unsigned NumElts = CDS->getNumElements();
82 assert(NumElts != 0 && "Can't have an empty CDS");
84 if (CDS->getElementAsInteger(NumElts-1) != 0)
85 return false; // Not null terminated.
87 // Verify that the null doesn't occur anywhere else in the string.
88 for (unsigned i = 0; i != NumElts-1; ++i)
89 if (CDS->getElementAsInteger(i) == 0)
94 // Another possibility: [1 x i8] zeroinitializer
95 if (isa<ConstantAggregateZero>(C))
96 return cast<ArrayType>(C->getType())->getNumElements() == 1;
101 MCSymbol *TargetLoweringObjectFile::
102 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
103 MachineModuleInfo *MMI) const {
104 return Mang->getSymbol(GV);
107 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
108 const TargetMachine &TM,
109 const MCSymbol *Sym) const {
113 /// getKindForGlobal - This is a top-level target-independent classifier for
114 /// a global variable. Given an global variable and information from TM, it
115 /// classifies the global in a variety of ways that make various target
116 /// implementations simpler. The target implementation is free to ignore this
117 /// extra info of course.
118 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
119 const TargetMachine &TM){
120 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
121 "Can only be used for global definitions");
123 Reloc::Model ReloModel = TM.getRelocationModel();
125 // Early exit - functions should be always in text sections.
126 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
128 return SectionKind::getText();
130 // Handle thread-local data first.
131 if (GVar->isThreadLocal()) {
132 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS))
133 return SectionKind::getThreadBSS();
134 return SectionKind::getThreadData();
137 // Variables with common linkage always get classified as common.
138 if (GVar->hasCommonLinkage())
139 return SectionKind::getCommon();
141 // Variable can be easily put to BSS section.
142 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
143 if (GVar->hasLocalLinkage())
144 return SectionKind::getBSSLocal();
145 else if (GVar->hasExternalLinkage())
146 return SectionKind::getBSSExtern();
147 return SectionKind::getBSS();
150 const Constant *C = GVar->getInitializer();
152 // If the global is marked constant, we can put it into a mergable section,
153 // a mergable string section, or general .data if it contains relocations.
154 if (GVar->isConstant()) {
155 // If the initializer for the global contains something that requires a
156 // relocation, then we may have to drop this into a wriable data section
157 // even though it is marked const.
158 switch (C->getRelocationInfo()) {
159 case Constant::NoRelocation:
160 // If the global is required to have a unique address, it can't be put
161 // into a mergable section: just drop it into the general read-only
163 if (!GVar->hasUnnamedAddr())
164 return SectionKind::getReadOnly();
166 // If initializer is a null-terminated string, put it in a "cstring"
167 // section of the right width.
168 if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
169 if (IntegerType *ITy =
170 dyn_cast<IntegerType>(ATy->getElementType())) {
171 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
172 ITy->getBitWidth() == 32) &&
173 IsNullTerminatedString(C)) {
174 if (ITy->getBitWidth() == 8)
175 return SectionKind::getMergeable1ByteCString();
176 if (ITy->getBitWidth() == 16)
177 return SectionKind::getMergeable2ByteCString();
179 assert(ITy->getBitWidth() == 32 && "Unknown width");
180 return SectionKind::getMergeable4ByteCString();
185 // Otherwise, just drop it into a mergable constant section. If we have
186 // a section for this size, use it, otherwise use the arbitrary sized
188 switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
189 case 4: return SectionKind::getMergeableConst4();
190 case 8: return SectionKind::getMergeableConst8();
191 case 16: return SectionKind::getMergeableConst16();
192 default: return SectionKind::getMergeableConst();
195 case Constant::LocalRelocation:
196 // In static relocation model, the linker will resolve all addresses, so
197 // the relocation entries will actually be constants by the time the app
198 // starts up. However, we can't put this into a mergable section, because
199 // the linker doesn't take relocations into consideration when it tries to
200 // merge entries in the section.
201 if (ReloModel == Reloc::Static)
202 return SectionKind::getReadOnly();
204 // Otherwise, the dynamic linker needs to fix it up, put it in the
205 // writable data.rel.local section.
206 return SectionKind::getReadOnlyWithRelLocal();
208 case Constant::GlobalRelocations:
209 // In static relocation model, the linker will resolve all addresses, so
210 // the relocation entries will actually be constants by the time the app
211 // starts up. However, we can't put this into a mergable section, because
212 // the linker doesn't take relocations into consideration when it tries to
213 // merge entries in the section.
214 if (ReloModel == Reloc::Static)
215 return SectionKind::getReadOnly();
217 // Otherwise, the dynamic linker needs to fix it up, put it in the
218 // writable data.rel section.
219 return SectionKind::getReadOnlyWithRel();
223 // Okay, this isn't a constant. If the initializer for the global is going
224 // to require a runtime relocation by the dynamic linker, put it into a more
225 // specific section to improve startup time of the app. This coalesces these
226 // globals together onto fewer pages, improving the locality of the dynamic
228 if (ReloModel == Reloc::Static)
229 return SectionKind::getDataNoRel();
231 switch (C->getRelocationInfo()) {
232 case Constant::NoRelocation:
233 return SectionKind::getDataNoRel();
234 case Constant::LocalRelocation:
235 return SectionKind::getDataRelLocal();
236 case Constant::GlobalRelocations:
237 return SectionKind::getDataRel();
239 llvm_unreachable("Invalid relocation");
242 /// SectionForGlobal - This method computes the appropriate section to emit
243 /// the specified global variable or function definition. This should not
244 /// be passed external (or available externally) globals.
245 const MCSection *TargetLoweringObjectFile::
246 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
247 const TargetMachine &TM) const {
248 // Select section name.
249 if (GV->hasSection())
250 return getExplicitSectionGlobal(GV, Kind, Mang, TM);
253 // Use default section depending on the 'type' of global
254 return SelectSectionForGlobal(GV, Kind, Mang, TM);
258 // Lame default implementation. Calculate the section name for global.
260 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
263 const TargetMachine &TM) const{
264 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
267 return getTextSection();
269 if (Kind.isBSS() && BSSSection != 0)
272 if (Kind.isReadOnly() && ReadOnlySection != 0)
273 return ReadOnlySection;
275 return getDataSection();
278 /// getSectionForConstant - Given a mergable constant with the
279 /// specified size and relocation information, return a section that it
280 /// should be placed in.
282 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
283 if (Kind.isReadOnly() && ReadOnlySection != 0)
284 return ReadOnlySection;
289 /// getExprForDwarfGlobalReference - Return an MCExpr to use for a
290 /// reference to the specified global variable from exception
291 /// handling information.
292 const MCExpr *TargetLoweringObjectFile::
293 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
294 MachineModuleInfo *MMI, unsigned Encoding,
295 MCStreamer &Streamer) const {
296 const MCSymbol *Sym = Mang->getSymbol(GV);
297 return getExprForDwarfReference(Sym, Encoding, Streamer);
300 const MCExpr *TargetLoweringObjectFile::
301 getExprForDwarfReference(const MCSymbol *Sym, unsigned Encoding,
302 MCStreamer &Streamer) const {
303 const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
305 switch (Encoding & 0x70) {
307 report_fatal_error("We do not support this DWARF encoding yet!");
308 case dwarf::DW_EH_PE_absptr:
309 // Do nothing special
311 case dwarf::DW_EH_PE_pcrel: {
312 // Emit a label to the streamer for the current position. This gives us
314 MCSymbol *PCSym = getContext().CreateTempSymbol();
315 Streamer.EmitLabel(PCSym);
316 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
317 return MCBinaryExpr::CreateSub(Res, PC, getContext());