ARMLDBackend.h revision 6f75755c9204b1d8817ae5a65a2f7e5af0ec3f70 
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 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, GNUInfo* pInfo);
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(IRBuilder& pBuilder, Module& pModule);
96
97  /// initRelocator - create and initialize Relocator.
98  bool initRelocator();
99
100  /// getRelocator - return relocator.
101  Relocator* getRelocator();
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                      IRBuilder& pBuilder,
111                      Module& pModule,
112                      LDSection& pSection);
113
114  /// doPreLayout - Backend can do any needed modification before layout
115  void doPreLayout(IRBuilder& pBuilder);
116
117  /// doPostLayout -Backend can do any needed modification after layout
118  void doPostLayout(Module& pModule, IRBuilder& pBuilder);
119
120  /// dynamic - the dynamic section of the target machine.
121  /// Use co-variant return type to return its own dynamic section.
122  ARMELFDynamic& dynamic();
123
124  /// dynamic - the dynamic section of the target machine.
125  /// Use co-variant return type to return its own dynamic section.
126  const ARMELFDynamic& dynamic() const;
127
128
129  /// emitSectionData - write out the section data into the memory region.
130  /// When writers get a LDSection whose kind is LDFileFormat::Target, writers
131  /// call back target backend to emit the data.
132  ///
133  /// Backends handle the target-special tables (plt, gp,...) by themselves.
134  /// Backend can put the data of the tables in SectionData directly
135  ///  - LDSection.getSectionData can get the section data.
136  /// Or, backend can put the data into special data structure
137  ///  - backend can maintain its own map<LDSection, table> to get the table
138  /// from given LDSection.
139  ///
140  /// @param pSection - the given LDSection
141  /// @param pConfig - all options in the command line.
142  /// @param pRegion - the region to write out data
143  /// @return the size of the table in the file.
144  uint64_t emitSectionData(const LDSection& pSection,
145                           MemoryRegion& pRegion) const;
146
147  ARMGOT& getGOT();
148
149  const ARMGOT& getGOT() const;
150
151  ARMPLT& getPLT();
152
153  const ARMPLT& getPLT() const;
154
155  OutputRelocSection& getRelDyn();
156
157  const OutputRelocSection& getRelDyn() const;
158
159  OutputRelocSection& getRelPLT();
160
161  const OutputRelocSection& getRelPLT() const;
162
163  /// getTargetSectionOrder - compute the layout order of ARM target sections
164  unsigned int getTargetSectionOrder(const LDSection& pSectHdr) const;
165
166  /// finalizeTargetSymbols - finalize the symbol value
167  bool finalizeTargetSymbols();
168
169  /// mergeSection - merge target dependent sections
170  bool mergeSection(Module& pModule, LDSection& pSection);
171
172  /// readSection - read target dependent sections
173  bool readSection(Input& pInput, SectionData& pSD);
174
175private:
176  void scanLocalReloc(Relocation& pReloc, const LDSection& pSection);
177
178  void scanGlobalReloc(Relocation& pReloc,
179                       IRBuilder& pBuilder,
180                       const LDSection& pSection);
181
182  void checkValidReloc(Relocation& pReloc) const;
183
184  /// addCopyReloc - add a copy relocation into .rel.dyn for pSym
185  /// @param pSym - A resolved copy symbol that defined in BSS section
186  void addCopyReloc(ResolveInfo& pSym);
187
188  /// defineSymbolforCopyReloc - allocate a space in BSS section and
189  /// and force define the copy of pSym to BSS section
190  /// @return the output LDSymbol of the copy symbol
191  LDSymbol& defineSymbolforCopyReloc(IRBuilder& pLinker,
192                                     const ResolveInfo& pSym);
193
194  void defineGOTSymbol(IRBuilder& pBuilder);
195
196  /// maxBranchOffset
197  /// FIXME: if we can handle arm attributes, we may refine this!
198  uint64_t maxBranchOffset() { return THM_MAX_FWD_BRANCH_OFFSET; }
199
200  /// mayRelax - Backends should override this function if they need relaxation
201  bool mayRelax() { return true; }
202
203  /// doRelax - Backend can orevride this function to add its relaxation
204  /// implementation. Return true if the output (e.g., .text) is "relaxed"
205  /// (i.e. layout is changed), and set pFinished to true if everything is fit,
206  /// otherwise set it to false.
207  bool doRelax(Module& pModule, IRBuilder& pBuilder, bool& pFinished);
208
209  /// initTargetStubs
210  bool initTargetStubs();
211
212  /// getRelEntrySize - the size in BYTE of rel type relocation
213  size_t getRelEntrySize()
214  { return 8; }
215
216  /// getRelEntrySize - the size in BYTE of rela type relocation
217  size_t getRelaEntrySize()
218  { assert(0 && "ARM backend with Rela type relocation\n"); return 12; }
219
220  /// doCreateProgramHdrs - backend can implement this function to create the
221  /// target-dependent segments
222  virtual void doCreateProgramHdrs(Module& pModule);
223
224private:
225  Relocator* m_pRelocator;
226
227  ARMGOT* m_pGOT;
228  ARMPLT* m_pPLT;
229  /// m_RelDyn - dynamic relocation table of .rel.dyn
230  OutputRelocSection* m_pRelDyn;
231  /// m_RelPLT - dynamic relocation table of .rel.plt
232  OutputRelocSection* m_pRelPLT;
233
234  ARMELFDynamic* m_pDynamic;
235  LDSymbol* m_pGOTSymbol;
236  LDSymbol* m_pEXIDXStart;
237  LDSymbol* m_pEXIDXEnd;
238
239  //     variable name           :  ELF
240  LDSection* m_pEXIDX;           // .ARM.exidx
241  LDSection* m_pEXTAB;           // .ARM.extab
242  LDSection* m_pAttributes;      // .ARM.attributes
243//  LDSection* m_pPreemptMap;      // .ARM.preemptmap
244//  LDSection* m_pDebugOverlay;    // .ARM.debug_overlay
245//  LDSection* m_pOverlayTable;    // .ARM.overlay_table
246};
247} // namespace of mcld
248
249#endif
250
251