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/MCContext.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCStreamer.h"
24 #include "llvm/MC/MCSymbol.h"
25 #include "llvm/Support/Dwarf.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/raw_ostream.h"
28 #include "llvm/Target/Mangler.h"
29 #include "llvm/Target/TargetMachine.h"
30 #include "llvm/Target/TargetOptions.h"
33 //===----------------------------------------------------------------------===//
35 //===----------------------------------------------------------------------===//
37 /// Initialize - this method must be called before any actual lowering is
38 /// done. This specifies the current context for codegen, and gives the
39 /// lowering implementations a chance to set up their default sections.
40 void TargetLoweringObjectFile::Initialize(MCContext &ctx,
41 const TargetMachine &TM) {
43 InitMCObjectFileInfo(TM.getTargetTriple(),
44 TM.getRelocationModel(), TM.getCodeModel(), *Ctx);
47 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
50 static bool isSuitableForBSS(const GlobalVariable *GV, bool NoZerosInBSS) {
51 const Constant *C = GV->getInitializer();
53 // Must have zero initializer.
54 if (!C->isNullValue())
57 // Leave constant zeros in readonly constant sections, so they can be shared.
61 // If the global has an explicit section specified, don't put it in BSS.
62 if (!GV->getSection().empty())
65 // If -nozero-initialized-in-bss is specified, don't ever use BSS.
69 // Otherwise, put it in BSS!
73 /// IsNullTerminatedString - Return true if the specified constant (which is
74 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
75 /// nul value and contains no other nuls in it. Note that this is more general
76 /// than ConstantDataSequential::isString because we allow 2 & 4 byte strings.
77 static bool IsNullTerminatedString(const Constant *C) {
78 // First check: is we have constant array terminated with zero
79 if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(C)) {
80 unsigned NumElts = CDS->getNumElements();
81 assert(NumElts != 0 && "Can't have an empty CDS");
83 if (CDS->getElementAsInteger(NumElts-1) != 0)
84 return false; // Not null terminated.
86 // Verify that the null doesn't occur anywhere else in the string.
87 for (unsigned i = 0; i != NumElts-1; ++i)
88 if (CDS->getElementAsInteger(i) == 0)
93 // Another possibility: [1 x i8] zeroinitializer
94 if (isa<ConstantAggregateZero>(C))
95 return cast<ArrayType>(C->getType())->getNumElements() == 1;
100 /// Return the MCSymbol for the specified global value. This
101 /// symbol is the main label that is the address of the global.
102 MCSymbol *TargetLoweringObjectFile::getSymbol(Mangler &M,
103 const GlobalValue *GV) const {
104 SmallString<60> NameStr;
105 M.getNameWithPrefix(NameStr, GV, false);
106 return Ctx->GetOrCreateSymbol(NameStr.str());
110 MCSymbol *TargetLoweringObjectFile::
111 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
112 MachineModuleInfo *MMI) const {
113 return getSymbol(*Mang, GV);
116 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
117 const TargetMachine &TM,
118 const MCSymbol *Sym) const {
122 /// getKindForGlobal - This is a top-level target-independent classifier for
123 /// a global variable. Given an global variable and information from TM, it
124 /// classifies the global in a variety of ways that make various target
125 /// implementations simpler. The target implementation is free to ignore this
126 /// extra info of course.
127 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
128 const TargetMachine &TM){
129 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
130 "Can only be used for global definitions");
132 Reloc::Model ReloModel = TM.getRelocationModel();
134 // Early exit - functions should be always in text sections.
135 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
137 return SectionKind::getText();
139 // Handle thread-local data first.
140 if (GVar->isThreadLocal()) {
141 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS))
142 return SectionKind::getThreadBSS();
143 return SectionKind::getThreadData();
146 // Variables with common linkage always get classified as common.
147 if (GVar->hasCommonLinkage())
148 return SectionKind::getCommon();
150 // Variable can be easily put to BSS section.
151 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
152 if (GVar->hasLocalLinkage())
153 return SectionKind::getBSSLocal();
154 else if (GVar->hasExternalLinkage())
155 return SectionKind::getBSSExtern();
156 return SectionKind::getBSS();
159 const Constant *C = GVar->getInitializer();
161 // If the global is marked constant, we can put it into a mergable section,
162 // a mergable string section, or general .data if it contains relocations.
163 if (GVar->isConstant()) {
164 // If the initializer for the global contains something that requires a
165 // relocation, then we may have to drop this into a writable data section
166 // even though it is marked const.
167 switch (C->getRelocationInfo()) {
168 case Constant::NoRelocation:
169 // If the global is required to have a unique address, it can't be put
170 // into a mergable section: just drop it into the general read-only
172 if (!GVar->hasUnnamedAddr())
173 return SectionKind::getReadOnly();
175 // If initializer is a null-terminated string, put it in a "cstring"
176 // section of the right width.
177 if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
178 if (IntegerType *ITy =
179 dyn_cast<IntegerType>(ATy->getElementType())) {
180 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
181 ITy->getBitWidth() == 32) &&
182 IsNullTerminatedString(C)) {
183 if (ITy->getBitWidth() == 8)
184 return SectionKind::getMergeable1ByteCString();
185 if (ITy->getBitWidth() == 16)
186 return SectionKind::getMergeable2ByteCString();
188 assert(ITy->getBitWidth() == 32 && "Unknown width");
189 return SectionKind::getMergeable4ByteCString();
194 // Otherwise, just drop it into a mergable constant section. If we have
195 // a section for this size, use it, otherwise use the arbitrary sized
197 switch (TM.getDataLayout()->getTypeAllocSize(C->getType())) {
198 case 4: return SectionKind::getMergeableConst4();
199 case 8: return SectionKind::getMergeableConst8();
200 case 16: return SectionKind::getMergeableConst16();
201 default: return SectionKind::getMergeableConst();
204 case Constant::LocalRelocation:
205 // In static relocation model, the linker will resolve all addresses, so
206 // the relocation entries will actually be constants by the time the app
207 // starts up. However, we can't put this into a mergable section, because
208 // the linker doesn't take relocations into consideration when it tries to
209 // merge entries in the section.
210 if (ReloModel == Reloc::Static)
211 return SectionKind::getReadOnly();
213 // Otherwise, the dynamic linker needs to fix it up, put it in the
214 // writable data.rel.local section.
215 return SectionKind::getReadOnlyWithRelLocal();
217 case Constant::GlobalRelocations:
218 // In static relocation model, the linker will resolve all addresses, so
219 // the relocation entries will actually be constants by the time the app
220 // starts up. However, we can't put this into a mergable section, because
221 // the linker doesn't take relocations into consideration when it tries to
222 // merge entries in the section.
223 if (ReloModel == Reloc::Static)
224 return SectionKind::getReadOnly();
226 // Otherwise, the dynamic linker needs to fix it up, put it in the
227 // writable data.rel section.
228 return SectionKind::getReadOnlyWithRel();
232 // Okay, this isn't a constant. If the initializer for the global is going
233 // to require a runtime relocation by the dynamic linker, put it into a more
234 // specific section to improve startup time of the app. This coalesces these
235 // globals together onto fewer pages, improving the locality of the dynamic
237 if (ReloModel == Reloc::Static)
238 return SectionKind::getDataNoRel();
240 switch (C->getRelocationInfo()) {
241 case Constant::NoRelocation:
242 return SectionKind::getDataNoRel();
243 case Constant::LocalRelocation:
244 return SectionKind::getDataRelLocal();
245 case Constant::GlobalRelocations:
246 return SectionKind::getDataRel();
248 llvm_unreachable("Invalid relocation");
251 /// SectionForGlobal - This method computes the appropriate section to emit
252 /// the specified global variable or function definition. This should not
253 /// be passed external (or available externally) globals.
254 const MCSection *TargetLoweringObjectFile::
255 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
256 const TargetMachine &TM) const {
257 // Select section name.
258 if (GV->hasSection())
259 return getExplicitSectionGlobal(GV, Kind, Mang, TM);
262 // Use default section depending on the 'type' of global
263 return SelectSectionForGlobal(GV, Kind, Mang, TM);
267 // Lame default implementation. Calculate the section name for global.
269 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
272 const TargetMachine &TM) const{
273 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
276 return getTextSection();
278 if (Kind.isBSS() && BSSSection != 0)
281 if (Kind.isReadOnly() && ReadOnlySection != 0)
282 return ReadOnlySection;
284 return getDataSection();
287 /// getSectionForConstant - Given a mergable constant with the
288 /// specified size and relocation information, return a section that it
289 /// should be placed in.
291 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
292 if (Kind.isReadOnly() && ReadOnlySection != 0)
293 return ReadOnlySection;
298 /// getTTypeGlobalReference - Return an MCExpr to use for a
299 /// reference to the specified global variable from exception
300 /// handling information.
301 const MCExpr *TargetLoweringObjectFile::
302 getTTypeGlobalReference(const GlobalValue *GV, Mangler *Mang,
303 MachineModuleInfo *MMI, unsigned Encoding,
304 MCStreamer &Streamer) const {
305 const MCSymbolRefExpr *Ref =
306 MCSymbolRefExpr::Create(getSymbol(*Mang, GV), getContext());
308 return getTTypeReference(Ref, Encoding, Streamer);
311 const MCExpr *TargetLoweringObjectFile::
312 getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
313 MCStreamer &Streamer) const {
314 switch (Encoding & 0x70) {
316 report_fatal_error("We do not support this DWARF encoding yet!");
317 case dwarf::DW_EH_PE_absptr:
318 // Do nothing special
320 case dwarf::DW_EH_PE_pcrel: {
321 // Emit a label to the streamer for the current position. This gives us
323 MCSymbol *PCSym = getContext().CreateTempSymbol();
324 Streamer.EmitLabel(PCSym);
325 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
326 return MCBinaryExpr::CreateSub(Sym, PC, getContext());
331 const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
332 // FIXME: It's not clear what, if any, default this should have - perhaps a
333 // null return could mean 'no location' & we should just do that here.
334 return MCSymbolRefExpr::Create(Sym, *Ctx);