ARMLDBackend.h revision 22add6ff3426df1a85089fe6a6e1597ee3b6f300 
1//===- ARMLDBackend.h -----------------------------------------------------===//
2//
3//                     The MCLinker Project
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9#ifndef MCLD_ARM_LDBACKEND_H
10#define MCLD_ARM_LDBACKEND_H
11
12#include "ARMELFDynamic.h"
13#include "ARMGOT.h"
14#include "ARMPLT.h"
15#include <mcld/LD/LDSection.h>
16#include <mcld/Target/GNULDBackend.h>
17#include <mcld/Target/OutputRelocSection.h>
18
19namespace mcld {
20
21class LinkerConfig;
22class FragmentLinker;
23class SectionMap;
24
25//===----------------------------------------------------------------------===//
26/// ARMGNULDBackend - linker backend of ARM target of GNU ELF format
27///
28class ARMGNULDBackend : public GNULDBackend
29{
30public:
31  // max branch offsets for ARM, THUMB, and THUMB2
32  // @ref gold/arm.cc:99
33  static const int32_t ARM_MAX_FWD_BRANCH_OFFSET = ((((1 << 23) - 1) << 2) + 8);
34  static const int32_t ARM_MAX_BWD_BRANCH_OFFSET = ((-((1 << 23) << 2)) + 8);
35  static const int32_t THM_MAX_FWD_BRANCH_OFFSET = ((1 << 22) -2 + 4);
36  static const int32_t THM_MAX_BWD_BRANCH_OFFSET = (-(1 << 22) + 4);
37  static const int32_t THM2_MAX_FWD_BRANCH_OFFSET = (((1 << 24) - 2) + 4);
38  static const int32_t THM2_MAX_BWD_BRANCH_OFFSET = (-(1 << 24) + 4);
39
40public:
41  ARMGNULDBackend(const LinkerConfig& pConfig);
42  ~ARMGNULDBackend();
43
44public:
45  typedef std::vector<llvm::ELF::Elf32_Dyn*> ELF32DynList;
46
47  /** \enum ReservedEntryType
48   *  \brief The reserved entry type of reserved space in ResolveInfo.
49   *
50   *  This is used for sacnRelocation to record what kinds of entries are
51   *  reserved for this resolved symbol
52   *
53   *  In ARM, there are three kinds of entries, GOT, PLT, and dynamic reloction.
54   *  GOT may needs a corresponding relocation to relocate itself, so we
55   *  separate GOT to two situations: GOT and GOTRel. Besides, for the same
56   *  symbol, there might be two kinds of entries reserved for different location.
57   *  For example, reference to the same symbol, one may use GOT and the other may
58   *  use dynamic relocation.
59   *
60   *  bit:  3       2      1     0
61   *   | PLT | GOTRel | GOT | Rel |
62   *
63   *  value    Name         - Description
64   *
65   *  0000     None         - no reserved entry
66   *  0001     ReserveRel   - reserve an dynamic relocation entry
67   *  0010     ReserveGOT   - reserve an GOT entry
68   *  0011     GOTandRel    - For different relocation, we've reserved GOT and
69   *                          Rel for different location.
70   *  0100     GOTRel       - reserve an GOT entry and the corresponding Dyncamic
71   *                          relocation entry which relocate this GOT entry
72   *  0101     GOTRelandRel - For different relocation, we've reserved GOTRel
73   *                          and relocation entry for different location.
74   *  1000     ReservePLT   - reserve an PLT entry and the corresponding GOT,
75   *                          Dynamic relocation entries
76   *  1001     PLTandRel    - For different relocation, we've reserved PLT and
77   *                          Rel for different location.
78   */
79  enum ReservedEntryType {
80    None         = 0,
81    ReserveRel   = 1,
82    ReserveGOT   = 2,
83    GOTandRel    = 3,
84    GOTRel       = 4,
85    GOTRelandRel = 5,
86    ReservePLT   = 8,
87    PLTandRel    = 9
88  };
89
90public:
91  /// initTargetSections - initialize target dependent sections in output.
92  void initTargetSections(Module& pModule, ObjectBuilder& pBuilder);
93
94  /// initTargetSymbols - initialize target dependent symbols in output.
95  void initTargetSymbols(FragmentLinker& pLinker);
96
97  /// initRelocFactory - create and initialize RelocationFactory
98  bool initRelocFactory(const FragmentLinker& pLinker);
99
100  /// getRelocFactory
101  RelocationFactory* getRelocFactory();
102
103  /// scanRelocation - determine the empty entries are needed or not and create
104  /// the empty entries if needed.
105  /// For ARM, following entries are check to create:
106  /// - GOT entry (for .got section)
107  /// - PLT entry (for .plt section)
108  /// - dynamin relocation entries (for .rel.plt and .rel.dyn sections)
109  void scanRelocation(Relocation& pReloc,
110                      FragmentLinker& pLinker,
111                      Module& pModule,
112                      const LDSection& pSection);
113
114  uint32_t machine() const
115  { return llvm::ELF::EM_ARM; }
116
117  /// OSABI - the value of e_ident[EI_OSABI]
118  virtual uint8_t OSABI() const
119  { return llvm::ELF::ELFOSABI_NONE; }
120
121  /// ABIVersion - the value of e_ident[EI_ABIVRESION]
122  virtual uint8_t ABIVersion() const
123  { return 0x0; }
124
125  /// flags - the value of ElfXX_Ehdr::e_flags
126  virtual uint64_t flags() const
127  { return (llvm::ELF::EF_ARM_EABIMASK & 0x05000000); }
128
129  bool isLittleEndian() const
130  { return true; }
131
132  unsigned int bitclass() const
133  { return 32; }
134
135  uint64_t defaultTextSegmentAddr() const
136  { return 0x8000; }
137
138  /// doPreLayout - Backend can do any needed modification before layout
139  void doPreLayout(FragmentLinker& pLinker);
140
141  /// doPostLayout -Backend can do any needed modification after layout
142  void doPostLayout(Module& pModule, FragmentLinker& pLinker);
143
144  /// dynamic - the dynamic section of the target machine.
145  /// Use co-variant return type to return its own dynamic section.
146  ARMELFDynamic& dynamic();
147
148  /// dynamic - the dynamic section of the target machine.
149  /// Use co-variant return type to return its own dynamic section.
150  const ARMELFDynamic& dynamic() const;
151
152
153  /// emitSectionData - write out the section data into the memory region.
154  /// When writers get a LDSection whose kind is LDFileFormat::Target, writers
155  /// call back target backend to emit the data.
156  ///
157  /// Backends handle the target-special tables (plt, gp,...) by themselves.
158  /// Backend can put the data of the tables in SectionData directly
159  ///  - LDSection.getSectionData can get the section data.
160  /// Or, backend can put the data into special data structure
161  ///  - backend can maintain its own map<LDSection, table> to get the table
162  /// from given LDSection.
163  ///
164  /// @param pSection - the given LDSection
165  /// @param pConfig - all options in the command line.
166  /// @param pRegion - the region to write out data
167  /// @return the size of the table in the file.
168  uint64_t emitSectionData(const LDSection& pSection,
169                           MemoryRegion& pRegion) const;
170
171  ARMGOT& getGOT();
172
173  const ARMGOT& getGOT() const;
174
175  ARMPLT& getPLT();
176
177  const ARMPLT& getPLT() const;
178
179  OutputRelocSection& getRelDyn();
180
181  const OutputRelocSection& getRelDyn() const;
182
183  OutputRelocSection& getRelPLT();
184
185  const OutputRelocSection& getRelPLT() const;
186
187  /// getTargetSectionOrder - compute the layout order of ARM target sections
188  unsigned int getTargetSectionOrder(const LDSection& pSectHdr) const;
189
190  /// finalizeTargetSymbols - finalize the symbol value
191  bool finalizeTargetSymbols(FragmentLinker& pLinker);
192
193  /// mergeSection - merge target dependent sections
194  bool mergeSection(Module& pModule, LDSection& pSection);
195
196  /// readSection - read target dependent sections
197  bool readSection(Input& pInput, SectionData& pSD);
198
199private:
200  void scanLocalReloc(Relocation& pReloc, FragmentLinker& pLinker);
201
202  void scanGlobalReloc(Relocation& pReloc, FragmentLinker& pLinker);
203
204  void checkValidReloc(Relocation& pReloc,
205                       const FragmentLinker& pLinker) const;
206
207  /// addCopyReloc - add a copy relocation into .rel.dyn for pSym
208  /// @param pSym - A resolved copy symbol that defined in BSS section
209  void addCopyReloc(ResolveInfo& pSym);
210
211  /// defineSymbolforCopyReloc - allocate a space in BSS section and
212  /// and force define the copy of pSym to BSS section
213  /// @return the output LDSymbol of the copy symbol
214  LDSymbol& defineSymbolforCopyReloc(FragmentLinker& pLinker,
215                                     const ResolveInfo& pSym);
216
217  void defineGOTSymbol(FragmentLinker& pLinker);
218
219  /// maxBranchOffset
220  /// FIXME: if we can handle arm attributes, we may refine this!
221  uint64_t maxBranchOffset() { return THM_MAX_FWD_BRANCH_OFFSET; }
222
223  /// mayRelax - Backends should override this function if they need relaxation
224  bool mayRelax() { return true; }
225
226  /// doRelax - Backend can orevride this function to add its relaxation
227  /// implementation. Return true if the output (e.g., .text) is "relaxed"
228  /// (i.e. layout is changed), and set pFinished to true if everything is fit,
229  /// otherwise set it to false.
230  bool doRelax(Module& pModule, FragmentLinker& pLinker, bool& pFinished);
231
232  /// initTargetStubs
233  bool initTargetStubs(FragmentLinker& pLinker);
234
235  /// getRelEntrySize - the size in BYTE of rel type relocation
236  size_t getRelEntrySize()
237  { return 8; }
238
239  /// getRelEntrySize - the size in BYTE of rela type relocation
240  size_t getRelaEntrySize()
241  { assert(0 && "ARM backend with Rela type relocation\n"); return 12; }
242
243  /// doCreateProgramHdrs - backend can implement this function to create the
244  /// target-dependent segments
245  virtual void doCreateProgramHdrs(Module& pModule,
246                                   const FragmentLinker& pLinker);
247
248private:
249  RelocationFactory* m_pRelocFactory;
250  ARMGOT* m_pGOT;
251  ARMPLT* m_pPLT;
252  /// m_RelDyn - dynamic relocation table of .rel.dyn
253  OutputRelocSection* m_pRelDyn;
254  /// m_RelPLT - dynamic relocation table of .rel.plt
255  OutputRelocSection* m_pRelPLT;
256
257  ARMELFDynamic* m_pDynamic;
258  LDSymbol* m_pGOTSymbol;
259  LDSymbol* m_pEXIDXStart;
260  LDSymbol* m_pEXIDXEnd;
261
262  //     variable name           :  ELF
263  LDSection* m_pEXIDX;           // .ARM.exidx
264  LDSection* m_pEXTAB;           // .ARM.extab
265  LDSection* m_pAttributes;      // .ARM.attributes
266//  LDSection* m_pPreemptMap;      // .ARM.preemptmap
267//  LDSection* m_pDebugOverlay;    // .ARM.debug_overlay
268//  LDSection* m_pOverlayTable;    // .ARM.overlay_table
269};
270
271//===----------------------------------------------------------------------===//
272/// ARMMachOLDBackend - linker backend of ARM target of MachO format
273///
274/**
275class ARMMachOLDBackend : public DarwinARMLDBackend
276{
277public:
278  ARMMachOLDBackend();
279  ~ARMMachOLDBackend();
280
281private:
282  MCMachOTargetArchiveReader *createTargetArchiveReader() const;
283  MCMachOTargetObjectReader *createTargetObjectReader() const;
284  MCMachOTargetObjectWriter *createTargetObjectWriter() const;
285
286};
287**/
288} // namespace of mcld
289
290#endif
291
292