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/IR/Constants.h"
17 #include "llvm/IR/DataLayout.h"
18 #include "llvm/IR/DerivedTypes.h"
19 #include "llvm/IR/Function.h"
20 #include "llvm/IR/GlobalVariable.h"
21 #include "llvm/IR/Mangler.h"
22 #include "llvm/MC/MCAsmInfo.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCExpr.h"
25 #include "llvm/MC/MCStreamer.h"
26 #include "llvm/MC/MCSymbol.h"
27 #include "llvm/Support/Dwarf.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/Target/TargetMachine.h"
31 #include "llvm/Target/TargetOptions.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 DL = TM.getDataLayout();
45 InitMCObjectFileInfo(TM.getTargetTriple(),
46 TM.getRelocationModel(), TM.getCodeModel(), *Ctx);
49 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
52 static bool isSuitableForBSS(const GlobalVariable *GV, bool NoZerosInBSS) {
53 const Constant *C = GV->getInitializer();
55 // Must have zero initializer.
56 if (!C->isNullValue())
59 // Leave constant zeros in readonly constant sections, so they can be shared.
63 // If the global has an explicit section specified, don't put it in BSS.
64 if (!GV->getSection().empty())
67 // If -nozero-initialized-in-bss is specified, don't ever use BSS.
71 // Otherwise, put it in BSS!
75 /// IsNullTerminatedString - Return true if the specified constant (which is
76 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
77 /// nul value and contains no other nuls in it. Note that this is more general
78 /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings.
79 static bool IsNullTerminatedString(const Constant *C) {
80 // First check: is we have constant array terminated with zero
81 if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) {
82 unsigned NumElts = CDS->getNumElements();
83 assert(NumElts != 0 && "Can't have an empty CDS");
85 if (CDS->getElementAsInteger(NumElts-1) != 0)
86 return false; // Not null terminated.
88 // Verify that the null doesn't occur anywhere else in the string.
89 for (unsigned i = 0; i != NumElts-1; ++i)
90 if (CDS->getElementAsInteger(i) == 0)
95 // Another possibility: [1 x i8] zeroinitializer
96 if (isa<ConstantAggregateZero>(C))
97 return cast<ArrayType>(C->getType())->getNumElements() == 1;
102 /// Return the MCSymbol for the specified global value. This
103 /// symbol is the main label that is the address of the global.
104 MCSymbol *TargetLoweringObjectFile::getSymbol(Mangler &M,
105 const GlobalValue *GV) const {
106 SmallString<60> NameStr;
107 M.getNameWithPrefix(NameStr, GV);
108 return Ctx->GetOrCreateSymbol(NameStr.str());
111 MCSymbol *TargetLoweringObjectFile::getSymbolWithGlobalValueBase(
112 Mangler &M, const GlobalValue *GV, StringRef Suffix) const {
113 assert(!Suffix.empty());
115 SmallString<60> NameStr;
116 NameStr += DL->getPrivateGlobalPrefix();
117 M.getNameWithPrefix(NameStr, GV);
118 NameStr.append(Suffix.begin(), Suffix.end());
119 return Ctx->GetOrCreateSymbol(NameStr.str());
122 MCSymbol *TargetLoweringObjectFile::
123 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
124 MachineModuleInfo *MMI) const {
125 return getSymbol(*Mang, GV);
128 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
129 const TargetMachine &TM,
130 const MCSymbol *Sym) const {
134 /// getKindForGlobal - This is a top-level target-independent classifier for
135 /// a global variable. Given an global variable and information from TM, it
136 /// classifies the global in a variety of ways that make various target
137 /// implementations simpler. The target implementation is free to ignore this
138 /// extra info of course.
139 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
140 const TargetMachine &TM){
141 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
142 "Can only be used for global definitions");
144 Reloc::Model ReloModel = TM.getRelocationModel();
146 // Early exit - functions should be always in text sections.
147 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
149 return SectionKind::getText();
151 // Handle thread-local data first.
152 if (GVar->isThreadLocal()) {
153 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS))
154 return SectionKind::getThreadBSS();
155 return SectionKind::getThreadData();
158 // Variables with common linkage always get classified as common.
159 if (GVar->hasCommonLinkage())
160 return SectionKind::getCommon();
162 // Variable can be easily put to BSS section.
163 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
164 if (GVar->hasLocalLinkage())
165 return SectionKind::getBSSLocal();
166 else if (GVar->hasExternalLinkage())
167 return SectionKind::getBSSExtern();
168 return SectionKind::getBSS();
171 const Constant *C = GVar->getInitializer();
173 // If the global is marked constant, we can put it into a mergable section,
174 // a mergable string section, or general .data if it contains relocations.
175 if (GVar->isConstant()) {
176 // If the initializer for the global contains something that requires a
177 // relocation, then we may have to drop this into a writable data section
178 // even though it is marked const.
179 switch (C->getRelocationInfo()) {
180 case Constant::NoRelocation:
181 // If the global is required to have a unique address, it can't be put
182 // into a mergable section: just drop it into the general read-only
184 if (!GVar->hasUnnamedAddr())
185 return SectionKind::getReadOnly();
187 // If initializer is a null-terminated string, put it in a "cstring"
188 // section of the right width.
189 if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
190 if (IntegerType *ITy =
191 dyn_cast<IntegerType>(ATy->getElementType())) {
192 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
193 ITy->getBitWidth() == 32) &&
194 IsNullTerminatedString(C)) {
195 if (ITy->getBitWidth() == 8)
196 return SectionKind::getMergeable1ByteCString();
197 if (ITy->getBitWidth() == 16)
198 return SectionKind::getMergeable2ByteCString();
200 assert(ITy->getBitWidth() == 32 && "Unknown width");
201 return SectionKind::getMergeable4ByteCString();
206 // Otherwise, just drop it into a mergable constant section. If we have
207 // a section for this size, use it, otherwise use the arbitrary sized
209 switch (TM.getDataLayout()->getTypeAllocSize(C->getType())) {
210 case 4: return SectionKind::getMergeableConst4();
211 case 8: return SectionKind::getMergeableConst8();
212 case 16: return SectionKind::getMergeableConst16();
213 default: return SectionKind::getMergeableConst();
216 case Constant::LocalRelocation:
217 // In static relocation model, the linker will resolve all addresses, so
218 // the relocation entries will actually be constants by the time the app
219 // starts up. However, we can't put this into a mergable section, because
220 // the linker doesn't take relocations into consideration when it tries to
221 // merge entries in the section.
222 if (ReloModel == Reloc::Static)
223 return SectionKind::getReadOnly();
225 // Otherwise, the dynamic linker needs to fix it up, put it in the
226 // writable data.rel.local section.
227 return SectionKind::getReadOnlyWithRelLocal();
229 case Constant::GlobalRelocations:
230 // In static relocation model, the linker will resolve all addresses, so
231 // the relocation entries will actually be constants by the time the app
232 // starts up. However, we can't put this into a mergable section, because
233 // the linker doesn't take relocations into consideration when it tries to
234 // merge entries in the section.
235 if (ReloModel == Reloc::Static)
236 return SectionKind::getReadOnly();
238 // Otherwise, the dynamic linker needs to fix it up, put it in the
239 // writable data.rel section.
240 return SectionKind::getReadOnlyWithRel();
244 // Okay, this isn't a constant. If the initializer for the global is going
245 // to require a runtime relocation by the dynamic linker, put it into a more
246 // specific section to improve startup time of the app. This coalesces these
247 // globals together onto fewer pages, improving the locality of the dynamic
249 if (ReloModel == Reloc::Static)
250 return SectionKind::getDataNoRel();
252 switch (C->getRelocationInfo()) {
253 case Constant::NoRelocation:
254 return SectionKind::getDataNoRel();
255 case Constant::LocalRelocation:
256 return SectionKind::getDataRelLocal();
257 case Constant::GlobalRelocations:
258 return SectionKind::getDataRel();
260 llvm_unreachable("Invalid relocation");
263 /// SectionForGlobal - This method computes the appropriate section to emit
264 /// the specified global variable or function definition. This should not
265 /// be passed external (or available externally) globals.
266 const MCSection *TargetLoweringObjectFile::
267 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
268 const TargetMachine &TM) const {
269 // Select section name.
270 if (GV->hasSection())
271 return getExplicitSectionGlobal(GV, Kind, Mang, TM);
274 // Use default section depending on the 'type' of global
275 return SelectSectionForGlobal(GV, Kind, Mang, TM);
279 // Lame default implementation. Calculate the section name for global.
281 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
284 const TargetMachine &TM) const{
285 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
288 return getTextSection();
290 if (Kind.isBSS() && BSSSection != 0)
293 if (Kind.isReadOnly() && ReadOnlySection != 0)
294 return ReadOnlySection;
296 return getDataSection();
299 /// getSectionForConstant - Given a mergable constant with the
300 /// specified size and relocation information, return a section that it
301 /// should be placed in.
303 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
304 if (Kind.isReadOnly() && ReadOnlySection != 0)
305 return ReadOnlySection;
310 /// getTTypeGlobalReference - Return an MCExpr to use for a
311 /// reference to the specified global variable from exception
312 /// handling information.
313 const MCExpr *TargetLoweringObjectFile::
314 getTTypeGlobalReference(const GlobalValue *GV, Mangler *Mang,
315 MachineModuleInfo *MMI, unsigned Encoding,
316 MCStreamer &Streamer) const {
317 const MCSymbolRefExpr *Ref =
318 MCSymbolRefExpr::Create(getSymbol(*Mang, GV), getContext());
320 return getTTypeReference(Ref, Encoding, Streamer);
323 const MCExpr *TargetLoweringObjectFile::
324 getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
325 MCStreamer &Streamer) const {
326 switch (Encoding & 0x70) {
328 report_fatal_error("We do not support this DWARF encoding yet!");
329 case dwarf::DW_EH_PE_absptr:
330 // Do nothing special
332 case dwarf::DW_EH_PE_pcrel: {
333 // Emit a label to the streamer for the current position. This gives us
335 MCSymbol *PCSym = getContext().CreateTempSymbol();
336 Streamer.EmitLabel(PCSym);
337 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
338 return MCBinaryExpr::CreateSub(Sym, PC, getContext());
343 const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
344 // FIXME: It's not clear what, if any, default this should have - perhaps a
345 // null return could mean 'no location' & we should just do that here.
346 return MCSymbolRefExpr::Create(Sym, *Ctx);