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());
109 MCSymbol *TargetLoweringObjectFile::getSymbolWithGlobalValueBase(
110 Mangler &M, const GlobalValue *GV, StringRef Suffix) const {
111 SmallString<60> NameStr;
112 M.getNameWithPrefix(NameStr, GV, true);
113 NameStr.append(Suffix.begin(), Suffix.end());
114 return Ctx->GetOrCreateSymbol(NameStr.str());
117 MCSymbol *TargetLoweringObjectFile::
118 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
119 MachineModuleInfo *MMI) const {
120 return getSymbol(*Mang, GV);
123 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
124 const TargetMachine &TM,
125 const MCSymbol *Sym) const {
129 /// getKindForGlobal - This is a top-level target-independent classifier for
130 /// a global variable. Given an global variable and information from TM, it
131 /// classifies the global in a variety of ways that make various target
132 /// implementations simpler. The target implementation is free to ignore this
133 /// extra info of course.
134 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
135 const TargetMachine &TM){
136 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
137 "Can only be used for global definitions");
139 Reloc::Model ReloModel = TM.getRelocationModel();
141 // Early exit - functions should be always in text sections.
142 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
144 return SectionKind::getText();
146 // Handle thread-local data first.
147 if (GVar->isThreadLocal()) {
148 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS))
149 return SectionKind::getThreadBSS();
150 return SectionKind::getThreadData();
153 // Variables with common linkage always get classified as common.
154 if (GVar->hasCommonLinkage())
155 return SectionKind::getCommon();
157 // Variable can be easily put to BSS section.
158 if (isSuitableForBSS(GVar, TM.Options.NoZerosInBSS)) {
159 if (GVar->hasLocalLinkage())
160 return SectionKind::getBSSLocal();
161 else if (GVar->hasExternalLinkage())
162 return SectionKind::getBSSExtern();
163 return SectionKind::getBSS();
166 const Constant *C = GVar->getInitializer();
168 // If the global is marked constant, we can put it into a mergable section,
169 // a mergable string section, or general .data if it contains relocations.
170 if (GVar->isConstant()) {
171 // If the initializer for the global contains something that requires a
172 // relocation, then we may have to drop this into a writable data section
173 // even though it is marked const.
174 switch (C->getRelocationInfo()) {
175 case Constant::NoRelocation:
176 // If the global is required to have a unique address, it can't be put
177 // into a mergable section: just drop it into the general read-only
179 if (!GVar->hasUnnamedAddr())
180 return SectionKind::getReadOnly();
182 // If initializer is a null-terminated string, put it in a "cstring"
183 // section of the right width.
184 if (ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
185 if (IntegerType *ITy =
186 dyn_cast<IntegerType>(ATy->getElementType())) {
187 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
188 ITy->getBitWidth() == 32) &&
189 IsNullTerminatedString(C)) {
190 if (ITy->getBitWidth() == 8)
191 return SectionKind::getMergeable1ByteCString();
192 if (ITy->getBitWidth() == 16)
193 return SectionKind::getMergeable2ByteCString();
195 assert(ITy->getBitWidth() == 32 && "Unknown width");
196 return SectionKind::getMergeable4ByteCString();
201 // Otherwise, just drop it into a mergable constant section. If we have
202 // a section for this size, use it, otherwise use the arbitrary sized
204 switch (TM.getDataLayout()->getTypeAllocSize(C->getType())) {
205 case 4: return SectionKind::getMergeableConst4();
206 case 8: return SectionKind::getMergeableConst8();
207 case 16: return SectionKind::getMergeableConst16();
208 default: return SectionKind::getMergeableConst();
211 case Constant::LocalRelocation:
212 // In static relocation model, the linker will resolve all addresses, so
213 // the relocation entries will actually be constants by the time the app
214 // starts up. However, we can't put this into a mergable section, because
215 // the linker doesn't take relocations into consideration when it tries to
216 // merge entries in the section.
217 if (ReloModel == Reloc::Static)
218 return SectionKind::getReadOnly();
220 // Otherwise, the dynamic linker needs to fix it up, put it in the
221 // writable data.rel.local section.
222 return SectionKind::getReadOnlyWithRelLocal();
224 case Constant::GlobalRelocations:
225 // In static relocation model, the linker will resolve all addresses, so
226 // the relocation entries will actually be constants by the time the app
227 // starts up. However, we can't put this into a mergable section, because
228 // the linker doesn't take relocations into consideration when it tries to
229 // merge entries in the section.
230 if (ReloModel == Reloc::Static)
231 return SectionKind::getReadOnly();
233 // Otherwise, the dynamic linker needs to fix it up, put it in the
234 // writable data.rel section.
235 return SectionKind::getReadOnlyWithRel();
239 // Okay, this isn't a constant. If the initializer for the global is going
240 // to require a runtime relocation by the dynamic linker, put it into a more
241 // specific section to improve startup time of the app. This coalesces these
242 // globals together onto fewer pages, improving the locality of the dynamic
244 if (ReloModel == Reloc::Static)
245 return SectionKind::getDataNoRel();
247 switch (C->getRelocationInfo()) {
248 case Constant::NoRelocation:
249 return SectionKind::getDataNoRel();
250 case Constant::LocalRelocation:
251 return SectionKind::getDataRelLocal();
252 case Constant::GlobalRelocations:
253 return SectionKind::getDataRel();
255 llvm_unreachable("Invalid relocation");
258 /// SectionForGlobal - This method computes the appropriate section to emit
259 /// the specified global variable or function definition. This should not
260 /// be passed external (or available externally) globals.
261 const MCSection *TargetLoweringObjectFile::
262 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
263 const TargetMachine &TM) const {
264 // Select section name.
265 if (GV->hasSection())
266 return getExplicitSectionGlobal(GV, Kind, Mang, TM);
269 // Use default section depending on the 'type' of global
270 return SelectSectionForGlobal(GV, Kind, Mang, TM);
274 // Lame default implementation. Calculate the section name for global.
276 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
279 const TargetMachine &TM) const{
280 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
283 return getTextSection();
285 if (Kind.isBSS() && BSSSection != 0)
288 if (Kind.isReadOnly() && ReadOnlySection != 0)
289 return ReadOnlySection;
291 return getDataSection();
294 /// getSectionForConstant - Given a mergable constant with the
295 /// specified size and relocation information, return a section that it
296 /// should be placed in.
298 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
299 if (Kind.isReadOnly() && ReadOnlySection != 0)
300 return ReadOnlySection;
305 /// getTTypeGlobalReference - Return an MCExpr to use for a
306 /// reference to the specified global variable from exception
307 /// handling information.
308 const MCExpr *TargetLoweringObjectFile::
309 getTTypeGlobalReference(const GlobalValue *GV, Mangler *Mang,
310 MachineModuleInfo *MMI, unsigned Encoding,
311 MCStreamer &Streamer) const {
312 const MCSymbolRefExpr *Ref =
313 MCSymbolRefExpr::Create(getSymbol(*Mang, GV), getContext());
315 return getTTypeReference(Ref, Encoding, Streamer);
318 const MCExpr *TargetLoweringObjectFile::
319 getTTypeReference(const MCSymbolRefExpr *Sym, unsigned Encoding,
320 MCStreamer &Streamer) const {
321 switch (Encoding & 0x70) {
323 report_fatal_error("We do not support this DWARF encoding yet!");
324 case dwarf::DW_EH_PE_absptr:
325 // Do nothing special
327 case dwarf::DW_EH_PE_pcrel: {
328 // Emit a label to the streamer for the current position. This gives us
330 MCSymbol *PCSym = getContext().CreateTempSymbol();
331 Streamer.EmitLabel(PCSym);
332 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
333 return MCBinaryExpr::CreateSub(Sym, PC, getContext());
338 const MCExpr *TargetLoweringObjectFile::getDebugThreadLocalSymbol(const MCSymbol *Sym) const {
339 // FIXME: It's not clear what, if any, default this should have - perhaps a
340 // null return could mean 'no location' & we should just do that here.
341 return MCSymbolRefExpr::Create(Sym, *Ctx);