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/MC/MCAsmInfo.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCStreamer.h"
25 #include "llvm/MC/MCSymbol.h"
26 #include "llvm/Support/Dwarf.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/raw_ostream.h"
29 #include "llvm/Target/Mangler.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());
114 assert(!GV->hasPrivateLinkage());
115 assert(!GV->hasLinkerPrivateLinkage());
116 assert(!GV->hasLinkerPrivateWeakLinkage());
118 SmallString<60> NameStr;
119 NameStr += DL->getPrivateGlobalPrefix();
120 M.getNameWithPrefix(NameStr, GV);
121 NameStr.append(Suffix.begin(), Suffix.end());
122 return Ctx->GetOrCreateSymbol(NameStr.str());
125 MCSymbol *TargetLoweringObjectFile::
126 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
127 MachineModuleInfo *MMI) const {
128 return getSymbol(*Mang, GV);
131 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
132 const TargetMachine &TM,
133 const MCSymbol *Sym) const {
137 /// getKindForGlobal - This is a top-level target-independent classifier for
138 /// a global variable. Given an global variable and information from TM, it
139 /// classifies the global in a variety of ways that make various target
140 /// implementations simpler. The target implementation is free to ignore this
141 /// extra info of course.
142 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
143 const TargetMachine &TM){
144 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
145 "Can only be used for global definitions");
147 Reloc::Model ReloModel = TM.getRelocationModel();
149 // Early exit - functions should be always in text sections.
150 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
152 return SectionKind::getText();
154 // Handle thread-local data first.
155 if (GVar->isThreadLocal()) {
156 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS))
157 return SectionKind::getThreadBSS();
158 return SectionKind::getThreadData();
161 // Variables with common linkage always get classified as common.
162 if (GVar->hasCommonLinkage())
163 return SectionKind::getCommon();
165 // Variable can be easily put to BSS section.
166 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
167 if (GVar->hasLocalLinkage())
168 return SectionKind::getBSSLocal();
169 else if (GVar->hasExternalLinkage())
170 return SectionKind::getBSSExtern();
171 return SectionKind::getBSS();
174 const Constant *C = GVar->getInitializer();
176 // If the global is marked constant, we can put it into a mergable section,
177 // a mergable string section, or general .data if it contains relocations.
178 if (GVar->isConstant()) {
179 // If the initializer for the global contains something that requires a
180 // relocation, then we may have to drop this into a writable data section
181 // even though it is marked const.
182 switch (C->getRelocationInfo()) {
183 case Constant::NoRelocation:
184 // If the global is required to have a unique address, it can't be put
185 // into a mergable section: just drop it into the general read-only
187 if (!GVar->hasUnnamedAddr())
188 return SectionKind::getReadOnly();
190 // If initializer is a null-terminated string, put it in a "cstring"
191 // section of the right width.
192 if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
193 if (IntegerType *ITy =
194 dyn_cast<IntegerType>(ATy->getElementType())) {
195 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
196 ITy->getBitWidth() == 32) &&
197 IsNullTerminatedString(C)) {
198 if (ITy->getBitWidth() == 8)
199 return SectionKind::getMergeable1ByteCString();
200 if (ITy->getBitWidth() == 16)
201 return SectionKind::getMergeable2ByteCString();
203 assert(ITy->getBitWidth() == 32 && "Unknown width");
204 return SectionKind::getMergeable4ByteCString();
209 // Otherwise, just drop it into a mergable constant section. If we have
210 // a section for this size, use it, otherwise use the arbitrary sized
212 switch (TM.getDataLayout()->getTypeAllocSize(C->getType())) {
213 case 4: return SectionKind::getMergeableConst4();
214 case 8: return SectionKind::getMergeableConst8();
215 case 16: return SectionKind::getMergeableConst16();
216 default: return SectionKind::getMergeableConst();
219 case Constant::LocalRelocation:
220 // In static relocation model, the linker will resolve all addresses, so
221 // the relocation entries will actually be constants by the time the app
222 // starts up. However, we can't put this into a mergable section, because
223 // the linker doesn't take relocations into consideration when it tries to
224 // merge entries in the section.
225 if (ReloModel == Reloc::Static)
226 return SectionKind::getReadOnly();
228 // Otherwise, the dynamic linker needs to fix it up, put it in the
229 // writable data.rel.local section.
230 return SectionKind::getReadOnlyWithRelLocal();
232 case Constant::GlobalRelocations:
233 // In static relocation model, the linker will resolve all addresses, so
234 // the relocation entries will actually be constants by the time the app
235 // starts up. However, we can't put this into a mergable section, because
236 // the linker doesn't take relocations into consideration when it tries to
237 // merge entries in the section.
238 if (ReloModel == Reloc::Static)
239 return SectionKind::getReadOnly();
241 // Otherwise, the dynamic linker needs to fix it up, put it in the
242 // writable data.rel section.
243 return SectionKind::getReadOnlyWithRel();
247 // Okay, this isn't a constant. If the initializer for the global is going
248 // to require a runtime relocation by the dynamic linker, put it into a more
249 // specific section to improve startup time of the app. This coalesces these
250 // globals together onto fewer pages, improving the locality of the dynamic
252 if (ReloModel == Reloc::Static)
253 return SectionKind::getDataNoRel();
255 switch (C->getRelocationInfo()) {
256 case Constant::NoRelocation:
257 return SectionKind::getDataNoRel();
258 case Constant::LocalRelocation:
259 return SectionKind::getDataRelLocal();
260 case Constant::GlobalRelocations:
261 return SectionKind::getDataRel();
263 llvm_unreachable("Invalid relocation");
266 /// SectionForGlobal - This method computes the appropriate section to emit
267 /// the specified global variable or function definition. This should not
268 /// be passed external (or available externally) globals.
269 const MCSection *TargetLoweringObjectFile::
270 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
271 const TargetMachine &TM) const {
272 // Select section name.
273 if (GV->hasSection())
274 return getExplicitSectionGlobal(GV, Kind, Mang, TM);
277 // Use default section depending on the 'type' of global
278 return SelectSectionForGlobal(GV, Kind, Mang, TM);
282 // Lame default implementation. Calculate the section name for global.
284 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
287 const TargetMachine &TM) const{
288 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
291 return getTextSection();
293 if (Kind.isBSS() && BSSSection != 0)
296 if (Kind.isReadOnly() && ReadOnlySection != 0)
297 return ReadOnlySection;
299 return getDataSection();
302 /// getSectionForConstant - Given a mergable constant with the
303 /// specified size and relocation information, return a section that it
304 /// should be placed in.
306 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
307 if (Kind.isReadOnly() && ReadOnlySection != 0)
308 return ReadOnlySection;
313 /// getTTypeGlobalReference - Return an MCExpr to use for a
314 /// reference to the specified global variable from exception
315 /// handling information.
316 const MCExpr *TargetLoweringObjectFile::
317 getTTypeGlobalReference(const GlobalValue *GV, Mangler *Mang,
318 MachineModuleInfo *MMI, unsigned Encoding,
319 MCStreamer &Streamer) const {
320 const MCSymbolRefExpr *Ref =
321 MCSymbolRefExpr::Create(getSymbol(*Mang, GV), getContext());
323 return getTTypeReference(Ref, Encoding, Streamer);
326 const MCExpr *TargetLoweringObjectFile::
327 getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
328 MCStreamer &Streamer) const {
329 switch (Encoding & 0x70) {
331 report_fatal_error("We do not support this DWARF encoding yet!");
332 case dwarf::DW_EH_PE_absptr:
333 // Do nothing special
335 case dwarf::DW_EH_PE_pcrel: {
336 // Emit a label to the streamer for the current position. This gives us
338 MCSymbol *PCSym = getContext().CreateTempSymbol();
339 Streamer.EmitLabel(PCSym);
340 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
341 return MCBinaryExpr::CreateSub(Sym, PC, getContext());
346 const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
347 // FIXME: It's not clear what, if any, default this should have - perhaps a
348 // null return could mean 'no location' & we should just do that here.
349 return MCSymbolRefExpr::Create(Sym, *Ctx);