ARMLDBackend.h revision d0fbbb227051be16931a1aa9b4a7722ac039c698 
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 GNUInfo;
23class FragmentLinker;
24class SectionMap;
25
26//===----------------------------------------------------------------------===//
27/// ARMGNULDBackend - linker backend of ARM target of GNU ELF format
28///
29class ARMGNULDBackend : public GNULDBackend
30{
31public:
32  // max branch offsets for ARM, THUMB, and THUMB2
33  // @ref gold/arm.cc:99
34  static const int32_t ARM_MAX_FWD_BRANCH_OFFSET = ((((1 << 23) - 1) << 2) + 8);
35  static const int32_t ARM_MAX_BWD_BRANCH_OFFSET = ((-((1 << 23) << 2)) + 8);
36  static const int32_t THM_MAX_FWD_BRANCH_OFFSET = ((1 << 22) -2 + 4);
37  static const int32_t THM_MAX_BWD_BRANCH_OFFSET = (-(1 << 22) + 4);
38  static const int32_t THM2_MAX_FWD_BRANCH_OFFSET = (((1 << 24) - 2) + 4);
39  static const int32_t THM2_MAX_BWD_BRANCH_OFFSET = (-(1 << 24) + 4);
40
41public:
42  ARMGNULDBackend(const LinkerConfig& pConfig, GNUInfo* pInfo);
43  ~ARMGNULDBackend();
44
45public:
46  typedef std::vector<llvm::ELF::Elf32_Dyn*> ELF32DynList;
47
48  /** \enum ReservedEntryType
49   *  \brief The reserved entry type of reserved space in ResolveInfo.
50   *
51   *  This is used for sacnRelocation to record what kinds of entries are
52   *  reserved for this resolved symbol
53   *
54   *  In ARM, there are three kinds of entries, GOT, PLT, and dynamic reloction.
55   *  GOT may needs a corresponding relocation to relocate itself, so we
56   *  separate GOT to two situations: GOT and GOTRel. Besides, for the same
57   *  symbol, there might be two kinds of entries reserved for different location.
58   *  For example, reference to the same symbol, one may use GOT and the other may
59   *  use dynamic relocation.
60   *
61   *  bit:  3       2      1     0
62   *   | PLT | GOTRel | GOT | Rel |
63   *
64   *  value    Name         - Description
65   *
66   *  0000     None         - no reserved entry
67   *  0001     ReserveRel   - reserve an dynamic relocation entry
68   *  0010     ReserveGOT   - reserve an GOT entry
69   *  0011     GOTandRel    - For different relocation, we've reserved GOT and
70   *                          Rel for different location.
71   *  0100     GOTRel       - reserve an GOT entry and the corresponding Dyncamic
72   *                          relocation entry which relocate this GOT entry
73   *  0101     GOTRelandRel - For different relocation, we've reserved GOTRel
74   *                          and relocation entry for different location.
75   *  1000     ReservePLT   - reserve an PLT entry and the corresponding GOT,
76   *                          Dynamic relocation entries
77   *  1001     PLTandRel    - For different relocation, we've reserved PLT and
78   *                          Rel for different location.
79   */
80  enum ReservedEntryType {
81    None         = 0,
82    ReserveRel   = 1,
83    ReserveGOT   = 2,
84    GOTandRel    = 3,
85    GOTRel       = 4,
86    GOTRelandRel = 5,
87    ReservePLT   = 8,
88    PLTandRel    = 9
89  };
90
91public:
92  /// initTargetSections - initialize target dependent sections in output.
93  void initTargetSections(Module& pModule, ObjectBuilder& pBuilder);
94
95  /// initTargetSymbols - initialize target dependent symbols in output.
96  void initTargetSymbols(FragmentLinker& pLinker);
97
98  /// initRelocator - create and initialize Relocator.
99  bool initRelocator(const FragmentLinker& pLinker);
100
101  /// getRelocator - return relocator.
102  Relocator* getRelocator();
103
104  /// scanRelocation - determine the empty entries are needed or not and create
105  /// the empty entries if needed.
106  /// For ARM, following entries are check to create:
107  /// - GOT entry (for .got section)
108  /// - PLT entry (for .plt section)
109  /// - dynamin relocation entries (for .rel.plt and .rel.dyn sections)
110  void scanRelocation(Relocation& pReloc,
111                      FragmentLinker& pLinker,
112                      Module& pModule,
113                      const LDSection& pSection);
114
115  /// flags - the value of ElfXX_Ehdr::e_flags
116  virtual uint64_t flags() const
117  { return (llvm::ELF::EF_ARM_EABIMASK & 0x05000000); }
118
119  uint64_t defaultTextSegmentAddr() const
120  { return 0x8000; }
121
122  /// doPreLayout - Backend can do any needed modification before layout
123  void doPreLayout(FragmentLinker& pLinker);
124
125  /// doPostLayout -Backend can do any needed modification after layout
126  void doPostLayout(Module& pModule, FragmentLinker& pLinker);
127
128  /// dynamic - the dynamic section of the target machine.
129  /// Use co-variant return type to return its own dynamic section.
130  ARMELFDynamic& dynamic();
131
132  /// dynamic - the dynamic section of the target machine.
133  /// Use co-variant return type to return its own dynamic section.
134  const ARMELFDynamic& dynamic() const;
135
136
137  /// emitSectionData - write out the section data into the memory region.
138  /// When writers get a LDSection whose kind is LDFileFormat::Target, writers
139  /// call back target backend to emit the data.
140  ///
141  /// Backends handle the target-special tables (plt, gp,...) by themselves.
142  /// Backend can put the data of the tables in SectionData directly
143  ///  - LDSection.getSectionData can get the section data.
144  /// Or, backend can put the data into special data structure
145  ///  - backend can maintain its own map<LDSection, table> to get the table
146  /// from given LDSection.
147  ///
148  /// @param pSection - the given LDSection
149  /// @param pConfig - all options in the command line.
150  /// @param pRegion - the region to write out data
151  /// @return the size of the table in the file.
152  uint64_t emitSectionData(const LDSection& pSection,
153                           MemoryRegion& pRegion) const;
154
155  ARMGOT& getGOT();
156
157  const ARMGOT& getGOT() const;
158
159  ARMPLT& getPLT();
160
161  const ARMPLT& getPLT() const;
162
163  OutputRelocSection& getRelDyn();
164
165  const OutputRelocSection& getRelDyn() const;
166
167  OutputRelocSection& getRelPLT();
168
169  const OutputRelocSection& getRelPLT() const;
170
171  /// getTargetSectionOrder - compute the layout order of ARM target sections
172  unsigned int getTargetSectionOrder(const LDSection& pSectHdr) const;
173
174  /// finalizeTargetSymbols - finalize the symbol value
175  bool finalizeTargetSymbols(FragmentLinker& pLinker);
176
177  /// mergeSection - merge target dependent sections
178  bool mergeSection(Module& pModule, LDSection& pSection);
179
180  /// readSection - read target dependent sections
181  bool readSection(Input& pInput, SectionData& pSD);
182
183private:
184  void scanLocalReloc(Relocation& pReloc, FragmentLinker& pLinker);
185
186  void scanGlobalReloc(Relocation& pReloc, FragmentLinker& pLinker);
187
188  void checkValidReloc(Relocation& pReloc,
189                       const FragmentLinker& pLinker) const;
190
191  /// addCopyReloc - add a copy relocation into .rel.dyn for pSym
192  /// @param pSym - A resolved copy symbol that defined in BSS section
193  void addCopyReloc(ResolveInfo& pSym);
194
195  /// defineSymbolforCopyReloc - allocate a space in BSS section and
196  /// and force define the copy of pSym to BSS section
197  /// @return the output LDSymbol of the copy symbol
198  LDSymbol& defineSymbolforCopyReloc(FragmentLinker& pLinker,
199                                     const ResolveInfo& pSym);
200
201  void defineGOTSymbol(FragmentLinker& pLinker);
202
203  /// maxBranchOffset
204  /// FIXME: if we can handle arm attributes, we may refine this!
205  uint64_t maxBranchOffset() { return THM_MAX_FWD_BRANCH_OFFSET; }
206
207  /// mayRelax - Backends should override this function if they need relaxation
208  bool mayRelax() { return true; }
209
210  /// doRelax - Backend can orevride this function to add its relaxation
211  /// implementation. Return true if the output (e.g., .text) is "relaxed"
212  /// (i.e. layout is changed), and set pFinished to true if everything is fit,
213  /// otherwise set it to false.
214  bool doRelax(Module& pModule, FragmentLinker& pLinker, bool& pFinished);
215
216  /// initTargetStubs
217  bool initTargetStubs(FragmentLinker& pLinker);
218
219  /// getRelEntrySize - the size in BYTE of rel type relocation
220  size_t getRelEntrySize()
221  { return 8; }
222
223  /// getRelEntrySize - the size in BYTE of rela type relocation
224  size_t getRelaEntrySize()
225  { assert(0 && "ARM backend with Rela type relocation\n"); return 12; }
226
227  /// doCreateProgramHdrs - backend can implement this function to create the
228  /// target-dependent segments
229  virtual void doCreateProgramHdrs(Module& pModule,
230                                   const FragmentLinker& pLinker);
231
232private:
233  Relocator* m_pRelocator;
234
235  ARMGOT* m_pGOT;
236  ARMPLT* m_pPLT;
237  /// m_RelDyn - dynamic relocation table of .rel.dyn
238  OutputRelocSection* m_pRelDyn;
239  /// m_RelPLT - dynamic relocation table of .rel.plt
240  OutputRelocSection* m_pRelPLT;
241
242  ARMELFDynamic* m_pDynamic;
243  LDSymbol* m_pGOTSymbol;
244  LDSymbol* m_pEXIDXStart;
245  LDSymbol* m_pEXIDXEnd;
246
247  //     variable name           :  ELF
248  LDSection* m_pEXIDX;           // .ARM.exidx
249  LDSection* m_pEXTAB;           // .ARM.extab
250  LDSection* m_pAttributes;      // .ARM.attributes
251//  LDSection* m_pPreemptMap;      // .ARM.preemptmap
252//  LDSection* m_pDebugOverlay;    // .ARM.debug_overlay
253//  LDSection* m_pOverlayTable;    // .ARM.overlay_table
254};
255
256//===----------------------------------------------------------------------===//
257/// ARMMachOLDBackend - linker backend of ARM target of MachO format
258///
259/**
260class ARMMachOLDBackend : public DarwinARMLDBackend
261{
262public:
263  ARMMachOLDBackend();
264  ~ARMMachOLDBackend();
265
266private:
267  MCMachOTargetArchiveReader *createTargetArchiveReader() const;
268  MCMachOTargetObjectReader *createTargetObjectReader() const;
269  MCMachOTargetObjectWriter *createTargetObjectWriter() const;
270
271};
272**/
273} // namespace of mcld
274
275#endif
276
277