TargetLoweringObjectFile.cpp revision 4788c3e839203dc75ba9fe2026f315095677715c 
1//===-- llvm/Target/TargetLoweringObjectFile.cpp - Object File Info -------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements classes used to handle lowerings specific to common
11// object file formats.
12//
13//===----------------------------------------------------------------------===//
14
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"
32using namespace llvm;
33
34//===----------------------------------------------------------------------===//
35//                              Generic Code
36//===----------------------------------------------------------------------===//
37
38TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
39  TextSection = 0;
40  DataSection = 0;
41  BSSSection = 0;
42  ReadOnlySection = 0;
43  StaticCtorSection = 0;
44  StaticDtorSection = 0;
45  LSDASection = 0;
46
47  CommDirectiveSupportsAlignment = true;
48  DwarfAbbrevSection = 0;
49  DwarfInfoSection = 0;
50  DwarfLineSection = 0;
51  DwarfFrameSection = 0;
52  DwarfPubNamesSection = 0;
53  DwarfPubTypesSection = 0;
54  DwarfDebugInlineSection = 0;
55  DwarfStrSection = 0;
56  DwarfLocSection = 0;
57  DwarfARangesSection = 0;
58  DwarfRangesSection = 0;
59  DwarfMacroInfoSection = 0;
60
61  IsFunctionEHSymbolGlobal = false;
62  IsFunctionEHFrameSymbolPrivate = true;
63  SupportsWeakOmittedEHFrame = true;
64}
65
66TargetLoweringObjectFile::~TargetLoweringObjectFile() {
67}
68
69static bool isSuitableForBSS(const GlobalVariable *GV) {
70  Constant *C = GV->getInitializer();
71
72  // Must have zero initializer.
73  if (!C->isNullValue())
74    return false;
75
76  // Leave constant zeros in readonly constant sections, so they can be shared.
77  if (GV->isConstant())
78    return false;
79
80  // If the global has an explicit section specified, don't put it in BSS.
81  if (!GV->getSection().empty())
82    return false;
83
84  // If -nozero-initialized-in-bss is specified, don't ever use BSS.
85  if (NoZerosInBSS)
86    return false;
87
88  // Otherwise, put it in BSS!
89  return true;
90}
91
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.
95static bool IsNullTerminatedString(const Constant *C) {
96  const ArrayType *ATy = cast<ArrayType>(C->getType());
97
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;
101
102    ConstantInt *Null =
103      dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
104    if (Null == 0 || !Null->isZero())
105      return false; // Not null terminated.
106
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)
112        return false;
113    return true;
114  }
115
116  // Another possibility: [1 x i8] zeroinitializer
117  if (isa<ConstantAggregateZero>(C))
118    return ATy->getNumElements() == 1;
119
120  return false;
121}
122
123MCSymbol *
124TargetLoweringObjectFile::getPersonalityPICSymbol(StringRef Name) const {
125  assert(0 && "Not Available in this format.");
126  return 0;
127}
128
129void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
130                                                    const TargetMachine &TM,
131                                                    const MCSymbol *Sym) const {
132  assert(0 && "Not Available in this format.");
133}
134
135
136/// getKindForGlobal - This is a top-level target-independent classifier for
137/// a global variable.  Given an global variable and information from TM, it
138/// classifies the global in a variety of ways that make various target
139/// implementations simpler.  The target implementation is free to ignore this
140/// extra info of course.
141SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
142                                                       const TargetMachine &TM){
143  assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
144         "Can only be used for global definitions");
145
146  Reloc::Model ReloModel = TM.getRelocationModel();
147
148  // Early exit - functions should be always in text sections.
149  const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
150  if (GVar == 0)
151    return SectionKind::getText();
152
153  // Handle thread-local data first.
154  if (GVar->isThreadLocal()) {
155    if (isSuitableForBSS(GVar))
156      return SectionKind::getThreadBSS();
157    return SectionKind::getThreadData();
158  }
159
160  // Variables with common linkage always get classified as common.
161  if (GVar->hasCommonLinkage())
162    return SectionKind::getCommon();
163
164  // Variable can be easily put to BSS section.
165  if (isSuitableForBSS(GVar)) {
166    if (GVar->hasLocalLinkage())
167      return SectionKind::getBSSLocal();
168    else if (GVar->hasExternalLinkage())
169      return SectionKind::getBSSExtern();
170    return SectionKind::getBSS();
171  }
172
173  Constant *C = GVar->getInitializer();
174
175  // If the global is marked constant, we can put it into a mergable section,
176  // a mergable string section, or general .data if it contains relocations.
177  if (GVar->isConstant()) {
178    // If the initializer for the global contains something that requires a
179    // relocation, then we may have to drop this into a wriable data section
180    // even though it is marked const.
181    switch (C->getRelocationInfo()) {
182    default: assert(0 && "unknown relocation info kind");
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
186      // section instead.
187      if (!GVar->hasUnnamedAddr())
188        return SectionKind::getReadOnly();
189
190      // If initializer is a null-terminated string, put it in a "cstring"
191      // section of the right width.
192      if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
193        if (const 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();
202
203            assert(ITy->getBitWidth() == 32 && "Unknown width");
204            return SectionKind::getMergeable4ByteCString();
205          }
206        }
207      }
208
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
211      // mergable section.
212      switch (TM.getTargetData()->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();
217      }
218
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();
227
228      // Otherwise, the dynamic linker needs to fix it up, put it in the
229      // writable data.rel.local section.
230      return SectionKind::getReadOnlyWithRelLocal();
231
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();
240
241      // Otherwise, the dynamic linker needs to fix it up, put it in the
242      // writable data.rel section.
243      return SectionKind::getReadOnlyWithRel();
244    }
245  }
246
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
251  // linker.
252  if (ReloModel == Reloc::Static)
253    return SectionKind::getDataNoRel();
254
255  switch (C->getRelocationInfo()) {
256  default: assert(0 && "unknown relocation info kind");
257  case Constant::NoRelocation:
258    return SectionKind::getDataNoRel();
259  case Constant::LocalRelocation:
260    return SectionKind::getDataRelLocal();
261  case Constant::GlobalRelocations:
262    return SectionKind::getDataRel();
263  }
264}
265
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.
269const MCSection *TargetLoweringObjectFile::
270SectionForGlobal(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);
275
276
277  // Use default section depending on the 'type' of global
278  return SelectSectionForGlobal(GV, Kind, Mang, TM);
279}
280
281
282// Lame default implementation. Calculate the section name for global.
283const MCSection *
284TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
285                                                 SectionKind Kind,
286                                                 Mangler *Mang,
287                                                 const TargetMachine &TM) const{
288  assert(!Kind.isThreadLocal() && "Doesn't support TLS");
289
290  if (Kind.isText())
291    return getTextSection();
292
293  if (Kind.isBSS() && BSSSection != 0)
294    return BSSSection;
295
296  if (Kind.isReadOnly() && ReadOnlySection != 0)
297    return ReadOnlySection;
298
299  return getDataSection();
300}
301
302/// getSectionForConstant - Given a mergable constant with the
303/// specified size and relocation information, return a section that it
304/// should be placed in.
305const MCSection *
306TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
307  if (Kind.isReadOnly() && ReadOnlySection != 0)
308    return ReadOnlySection;
309
310  return DataSection;
311}
312
313/// getExprForDwarfGlobalReference - Return an MCExpr to use for a
314/// reference to the specified global variable from exception
315/// handling information.
316const MCExpr *TargetLoweringObjectFile::
317getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
318                               MachineModuleInfo *MMI, unsigned Encoding,
319                               MCStreamer &Streamer) const {
320  const MCSymbol *Sym = Mang->getSymbol(GV);
321  return getExprForDwarfReference(Sym, Encoding, Streamer);
322}
323
324const MCExpr *TargetLoweringObjectFile::
325getExprForDwarfReference(const MCSymbol *Sym, unsigned Encoding,
326                         MCStreamer &Streamer) const {
327  const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
328
329  switch (Encoding & 0x70) {
330  default:
331    report_fatal_error("We do not support this DWARF encoding yet!");
332  case dwarf::DW_EH_PE_absptr:
333    // Do nothing special
334    return Res;
335  case dwarf::DW_EH_PE_pcrel: {
336    // Emit a label to the streamer for the current position.  This gives us
337    // .-foo addressing.
338    MCSymbol *PCSym = getContext().CreateTempSymbol();
339    Streamer.EmitLabel(PCSym);
340    const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
341    return MCBinaryExpr::CreateSub(Res, PC, getContext());
342  }
343  }
344}
345
346unsigned TargetLoweringObjectFile::getPersonalityEncoding() const {
347  return dwarf::DW_EH_PE_absptr;
348}
349
350unsigned TargetLoweringObjectFile::getLSDAEncoding() const {
351  return dwarf::DW_EH_PE_absptr;
352}
353
354unsigned TargetLoweringObjectFile::getFDEEncoding() const {
355  return dwarf::DW_EH_PE_absptr;
356}
357
358unsigned TargetLoweringObjectFile::getTTypeEncoding() const {
359  return dwarf::DW_EH_PE_absptr;
360}
361
362