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/MCStreamer.h"
23 #include "llvm/MC/MCSymbol.h"
24 #include "llvm/Target/Mangler.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/Target/TargetMachine.h"
27 #include "llvm/Target/TargetOptions.h"
28 #include "llvm/Support/Dwarf.h"
29 #include "llvm/Support/ErrorHandling.h"
30 #include "llvm/Support/raw_ostream.h"
31 #include "llvm/ADT/SmallString.h"
34 //===----------------------------------------------------------------------===//
36 //===----------------------------------------------------------------------===//
38 TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
43 StaticCtorSection = 0;
44 StaticDtorSection = 0;
48 DwarfAbbrevSection = 0;
51 DwarfFrameSection = 0;
52 DwarfPubNamesSection = 0;
53 DwarfPubTypesSection = 0;
54 DwarfDebugInlineSection = 0;
57 DwarfARangesSection = 0;
58 DwarfRangesSection = 0;
59 DwarfMacroInfoSection = 0;
61 IsFunctionEHSymbolGlobal = false;
62 IsFunctionEHFrameSymbolPrivate = true;
63 SupportsWeakOmittedEHFrame = true;
66 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
69 static bool isSuitableForBSS(const GlobalVariable *GV) {
70 Constant *C = GV->getInitializer();
72 // Must have zero initializer.
73 if (!C->isNullValue())
76 // Leave constant zeros in readonly constant sections, so they can be shared.
80 // If the global has an explicit section specified, don't put it in BSS.
81 if (!GV->getSection().empty())
84 // If -nozero-initialized-in-bss is specified, don't ever use BSS.
88 // Otherwise, put it in BSS!
92 /// IsNullTerminatedString - Return true if the specified constant (which is
93 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
94 /// nul value and contains no other nuls in it.
95 static bool IsNullTerminatedString(const Constant *C) {
96 const ArrayType *ATy = cast<ArrayType>(C->getType());
98 // First check: is we have constant array of i8 terminated with zero
99 if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
100 if (ATy->getNumElements() == 0) return false;
103 dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
104 if (Null == 0 || Null->getZExtValue() != 0)
105 return false; // Not null terminated.
107 // Verify that the null doesn't occur anywhere else in the string.
108 for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i)
109 // Reject constantexpr elements etc.
110 if (!isa<ConstantInt>(CVA->getOperand(i)) ||
111 CVA->getOperand(i) == Null)
116 // Another possibility: [1 x i8] zeroinitializer
117 if (isa<ConstantAggregateZero>(C))
118 return ATy->getNumElements() == 1;
123 /// getKindForGlobal - This is a top-level target-independent classifier for
124 /// a global variable. Given an global variable and information from TM, it
125 /// classifies the global in a variety of ways that make various target
126 /// implementations simpler. The target implementation is free to ignore this
127 /// extra info of course.
128 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
129 const TargetMachine &TM){
130 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
131 "Can only be used for global definitions");
133 Reloc::Model ReloModel = TM.getRelocationModel();
135 // Early exit - functions should be always in text sections.
136 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
138 return SectionKind::getText();
140 // Handle thread-local data first.
141 if (GVar->isThreadLocal()) {
142 if (isSuitableForBSS(GVar))
143 return SectionKind::getThreadBSS();
144 return SectionKind::getThreadData();
147 // Variables with common linkage always get classified as common.
148 if (GVar->hasCommonLinkage())
149 return SectionKind::getCommon();
151 // Variable can be easily put to BSS section.
152 if (isSuitableForBSS(GVar)) {
153 if (GVar->hasLocalLinkage())
154 return SectionKind::getBSSLocal();
155 else if (GVar->hasExternalLinkage())
156 return SectionKind::getBSSExtern();
157 return SectionKind::getBSS();
160 Constant *C = GVar->getInitializer();
162 // If the global is marked constant, we can put it into a mergable section,
163 // a mergable string section, or general .data if it contains relocations.
164 if (GVar->isConstant()) {
165 // If the initializer for the global contains something that requires a
166 // relocation, then we may have to drop this into a wriable data section
167 // even though it is marked const.
168 switch (C->getRelocationInfo()) {
169 default: assert(0 && "unknown relocation info kind");
170 case Constant::NoRelocation:
171 // If initializer is a null-terminated string, put it in a "cstring"
172 // section of the right width.
173 if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
174 if (const IntegerType *ITy =
175 dyn_cast<IntegerType>(ATy->getElementType())) {
176 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
177 ITy->getBitWidth() == 32) &&
178 IsNullTerminatedString(C)) {
179 if (ITy->getBitWidth() == 8)
180 return SectionKind::getMergeable1ByteCString();
181 if (ITy->getBitWidth() == 16)
182 return SectionKind::getMergeable2ByteCString();
184 assert(ITy->getBitWidth() == 32 && "Unknown width");
185 return SectionKind::getMergeable4ByteCString();
190 // Otherwise, just drop it into a mergable constant section. If we have
191 // a section for this size, use it, otherwise use the arbitrary sized
193 switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
194 case 4: return SectionKind::getMergeableConst4();
195 case 8: return SectionKind::getMergeableConst8();
196 case 16: return SectionKind::getMergeableConst16();
197 default: return SectionKind::getMergeableConst();
200 case Constant::LocalRelocation:
201 // In static relocation model, the linker will resolve all addresses, so
202 // the relocation entries will actually be constants by the time the app
203 // starts up. However, we can't put this into a mergable section, because
204 // the linker doesn't take relocations into consideration when it tries to
205 // merge entries in the section.
206 if (ReloModel == Reloc::Static)
207 return SectionKind::getReadOnly();
209 // Otherwise, the dynamic linker needs to fix it up, put it in the
210 // writable data.rel.local section.
211 return SectionKind::getReadOnlyWithRelLocal();
213 case Constant::GlobalRelocations:
214 // In static relocation model, the linker will resolve all addresses, so
215 // the relocation entries will actually be constants by the time the app
216 // starts up. However, we can't put this into a mergable section, because
217 // the linker doesn't take relocations into consideration when it tries to
218 // merge entries in the section.
219 if (ReloModel == Reloc::Static)
220 return SectionKind::getReadOnly();
222 // Otherwise, the dynamic linker needs to fix it up, put it in the
223 // writable data.rel section.
224 return SectionKind::getReadOnlyWithRel();
228 // Okay, this isn't a constant. If the initializer for the global is going
229 // to require a runtime relocation by the dynamic linker, put it into a more
230 // specific section to improve startup time of the app. This coalesces these
231 // globals together onto fewer pages, improving the locality of the dynamic
233 if (ReloModel == Reloc::Static)
234 return SectionKind::getDataNoRel();
236 switch (C->getRelocationInfo()) {
237 default: assert(0 && "unknown relocation info kind");
238 case Constant::NoRelocation:
239 return SectionKind::getDataNoRel();
240 case Constant::LocalRelocation:
241 return SectionKind::getDataRelLocal();
242 case Constant::GlobalRelocations:
243 return SectionKind::getDataRel();
247 /// SectionForGlobal - This method computes the appropriate section to emit
248 /// the specified global variable or function definition. This should not
249 /// be passed external (or available externally) globals.
250 const MCSection *TargetLoweringObjectFile::
251 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
252 const TargetMachine &TM) const {
253 // Select section name.
254 if (GV->hasSection())
255 return getExplicitSectionGlobal(GV, Kind, Mang, TM);
258 // Use default section depending on the 'type' of global
259 return SelectSectionForGlobal(GV, Kind, Mang, TM);
263 // Lame default implementation. Calculate the section name for global.
265 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
268 const TargetMachine &TM) const{
269 assert(!Kind.isThreadLocal() && "Doesn't support TLS");
272 return getTextSection();
274 if (Kind.isBSS() && BSSSection != 0)
277 if (Kind.isReadOnly() && ReadOnlySection != 0)
278 return ReadOnlySection;
280 return getDataSection();
283 /// getSectionForConstant - Given a mergable constant with the
284 /// specified size and relocation information, return a section that it
285 /// should be placed in.
287 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
288 if (Kind.isReadOnly() && ReadOnlySection != 0)
289 return ReadOnlySection;
294 /// getExprForDwarfGlobalReference - Return an MCExpr to use for a
295 /// reference to the specified global variable from exception
296 /// handling information.
297 const MCExpr *TargetLoweringObjectFile::
298 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
299 MachineModuleInfo *MMI, unsigned Encoding,
300 MCStreamer &Streamer) const {
301 const MCSymbol *Sym = Mang->getSymbol(GV);
302 return getExprForDwarfReference(Sym, Mang, MMI, Encoding, Streamer);
305 const MCExpr *TargetLoweringObjectFile::
306 getExprForDwarfReference(const MCSymbol *Sym, Mangler *Mang,
307 MachineModuleInfo *MMI, unsigned Encoding,
308 MCStreamer &Streamer) const {
309 const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
311 switch (Encoding & 0xF0) {
313 report_fatal_error("We do not support this DWARF encoding yet!");
314 case dwarf::DW_EH_PE_absptr:
315 // Do nothing special
317 case dwarf::DW_EH_PE_pcrel: {
318 // Emit a label to the streamer for the current position. This gives us
320 MCSymbol *PCSym = getContext().CreateTempSymbol();
321 Streamer.EmitLabel(PCSym);
322 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
323 return MCBinaryExpr::CreateSub(Res, PC, getContext());
328 unsigned TargetLoweringObjectFile::getPersonalityEncoding() const {
329 return dwarf::DW_EH_PE_absptr;
332 unsigned TargetLoweringObjectFile::getLSDAEncoding() const {
333 return dwarf::DW_EH_PE_absptr;
336 unsigned TargetLoweringObjectFile::getFDEEncoding() const {
337 return dwarf::DW_EH_PE_absptr;
340 unsigned TargetLoweringObjectFile::getTTypeEncoding() const {
341 return dwarf::DW_EH_PE_absptr;