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/MCSymbol.h"
23 #include "llvm/Target/Mangler.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Target/TargetMachine.h"
26 #include "llvm/Target/TargetOptions.h"
27 #include "llvm/Support/Dwarf.h"
28 #include "llvm/Support/ErrorHandling.h"
29 #include "llvm/Support/raw_ostream.h"
30 #include "llvm/ADT/SmallString.h"
33 //===----------------------------------------------------------------------===//
35 //===----------------------------------------------------------------------===//
37 TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
42 StaticCtorSection = 0;
43 StaticDtorSection = 0;
47 DwarfAbbrevSection = 0;
50 DwarfFrameSection = 0;
51 DwarfPubNamesSection = 0;
52 DwarfPubTypesSection = 0;
53 DwarfDebugInlineSection = 0;
56 DwarfARangesSection = 0;
57 DwarfRangesSection = 0;
58 DwarfMacroInfoSection = 0;
61 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
64 static bool isSuitableForBSS(const GlobalVariable *GV) {
65 Constant *C = GV->getInitializer();
67 // Must have zero initializer.
68 if (!C->isNullValue())
71 // Leave constant zeros in readonly constant sections, so they can be shared.
75 // If the global has an explicit section specified, don't put it in BSS.
76 if (!GV->getSection().empty())
79 // If -nozero-initialized-in-bss is specified, don't ever use BSS.
83 // Otherwise, put it in BSS!
87 /// IsNullTerminatedString - Return true if the specified constant (which is
88 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
89 /// nul value and contains no other nuls in it.
90 static bool IsNullTerminatedString(const Constant *C) {
91 const ArrayType *ATy = cast<ArrayType>(C->getType());
93 // First check: is we have constant array of i8 terminated with zero
94 if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
95 if (ATy->getNumElements() == 0) return false;
98 dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
99 if (Null == 0 || Null->getZExtValue() != 0)
100 return false; // Not null terminated.
102 // Verify that the null doesn't occur anywhere else in the string.
103 for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i)
104 // Reject constantexpr elements etc.
105 if (!isa<ConstantInt>(CVA->getOperand(i)) ||
106 CVA->getOperand(i) == Null)
111 // Another possibility: [1 x i8] zeroinitializer
112 if (isa<ConstantAggregateZero>(C))
113 return ATy->getNumElements() == 1;
118 /// getKindForGlobal - This is a top-level target-independent classifier for
119 /// a global variable. Given an global variable and information from TM, it
120 /// classifies the global in a variety of ways that make various target
121 /// implementations simpler. The target implementation is free to ignore this
122 /// extra info of course.
123 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
124 const TargetMachine &TM){
125 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
126 "Can only be used for global definitions");
128 Reloc::Model ReloModel = TM.getRelocationModel();
130 // Early exit - functions should be always in text sections.
131 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
133 return SectionKind::getText();
135 // Handle thread-local data first.
136 if (GVar->isThreadLocal()) {
137 if (isSuitableForBSS(GVar))
138 return SectionKind::getThreadBSS();
139 return SectionKind::getThreadData();
142 // Variables with common linkage always get classified as common.
143 if (GVar->hasCommonLinkage())
144 return SectionKind::getCommon();
146 // Variable can be easily put to BSS section.
147 if (isSuitableForBSS(GVar)) {
148 if (GVar->hasLocalLinkage())
149 return SectionKind::getBSSLocal();
150 else if (GVar->hasExternalLinkage())
151 return SectionKind::getBSSExtern();
152 return SectionKind::getBSS();
155 Constant *C = GVar->getInitializer();
157 // If the global is marked constant, we can put it into a mergable section,
158 // a mergable string section, or general .data if it contains relocations.
159 if (GVar->isConstant()) {
160 // If the initializer for the global contains something that requires a
161 // relocation, then we may have to drop this into a wriable data section
162 // even though it is marked const.
163 switch (C->getRelocationInfo()) {
164 default: assert(0 && "unknown relocation info kind");
165 case Constant::NoRelocation:
166 // If initializer is a null-terminated string, put it in a "cstring"
167 // section of the right width.
168 if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
169 if (const 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 default: assert(0 && "unknown relocation info kind");
233 case Constant::NoRelocation:
234 return SectionKind::getDataNoRel();
235 case Constant::LocalRelocation:
236 return SectionKind::getDataRelLocal();
237 case Constant::GlobalRelocations:
238 return SectionKind::getDataRel();
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 /// getSymbolForDwarfGlobalReference - Return an MCExpr to use for a
290 /// reference to the specified global variable from exception
291 /// handling information.
292 const MCExpr *TargetLoweringObjectFile::
293 getSymbolForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
294 MachineModuleInfo *MMI, unsigned Encoding) const {
295 // FIXME: Use GetGlobalValueSymbol.
296 SmallString<128> Name;
297 Mang->getNameWithPrefix(Name, GV, false);
298 const MCSymbol *Sym = getContext().GetOrCreateSymbol(Name.str());
300 return getSymbolForDwarfReference(Sym, MMI, Encoding);
303 const MCExpr *TargetLoweringObjectFile::
304 getSymbolForDwarfReference(const MCSymbol *Sym, MachineModuleInfo *MMI,
305 unsigned Encoding) const {
306 const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
308 switch (Encoding & 0xF0) {
310 llvm_report_error("Do not support this DWARF encoding yet!");
312 case dwarf::DW_EH_PE_absptr:
313 // Do nothing special
315 case dwarf::DW_EH_PE_pcrel:
317 const MCExpr *PC = MCSymbolRefExpr::Create(".", getContext());
318 Res = MCBinaryExpr::CreateSub(Res, PC, getContext());
325 unsigned TargetLoweringObjectFile::getPersonalityEncoding() const {
326 return dwarf::DW_EH_PE_absptr;
329 unsigned TargetLoweringObjectFile::getLSDAEncoding() const {
330 return dwarf::DW_EH_PE_absptr;
333 unsigned TargetLoweringObjectFile::getFDEEncoding() const {
334 return dwarf::DW_EH_PE_absptr;
337 unsigned TargetLoweringObjectFile::getTTypeEncoding() const {
338 return dwarf::DW_EH_PE_absptr;