gold/ehframe.h

   1 // ehframe.h -- handle exception frame sections for gold  -*- C++ -*-
   2
   3 // Copyright 2006, 2007, 2008, 2010, 2011 Free Software Foundation, Inc.
   4 // Written by Ian Lance Taylor <iant@google.com>.
   5
   6 // This file is part of gold.
   7
   8 // This program is free software; you can redistribute it and/or modify
   9 // it under the terms of the GNU General Public License as published by
  10 // the Free Software Foundation; either version 3 of the License, or
  11 // (at your option) any later version.
  12
  13 // This program is distributed in the hope that it will be useful,
  14 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 // GNU General Public License for more details.
  17
  18 // You should have received a copy of the GNU General Public License
  19 // along with this program; if not, write to the Free Software
  20 // Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston,
  21 // MA 02110-1301, USA.
  22
  23 #ifndef GOLD_EHFRAME_H
  24 #define GOLD_EHFRAME_H
  25
  26 #include <map>
  27 #include <set>
  28 #include <vector>
  29
  30 #include "output.h"
  31 #include "merge.h"
  32
  33 namespace gold
  34 {
  35
  36 template<int size, bool big_endian>
  37 class Track_relocs;
  38
  39 class Eh_frame;
  40
  41 // This class manages the .eh_frame_hdr section, which holds the data
  42 // for the PT_GNU_EH_FRAME segment.  gcc's unwind support code uses
  43 // the PT_GNU_EH_FRAME segment to find the list of FDEs.  This saves
  44 // the time required to register the exception handlers at startup
  45 // time and when a shared object is loaded, and the time required to
  46 // deregister the exception handlers when a shared object is unloaded.
  47
  48 class Eh_frame_hdr : public Output_section_data
  49 {
  50  public:
  51   Eh_frame_hdr(Output_section* eh_frame_section, const Eh_frame*);
  52
  53   // Record that we found an unrecognized .eh_frame section.
  54   void
  55   found_unrecognized_eh_frame_section()
  56   { this->any_unrecognized_eh_frame_sections_ = true; }
  57
  58   // Record an FDE.
  59   void
  60   record_fde(section_offset_type fde_offset, unsigned char fde_encoding)
  61   {
  62     if (!this->any_unrecognized_eh_frame_sections_)
  63       this->fde_offsets_.push_back(std::make_pair(fde_offset, fde_encoding));
  64   }
  65
  66  protected:
  67   // Set the final data size.
  68   void
  69   set_final_data_size();
  70
  71   // Write the data to the file.
  72   void
  73   do_write(Output_file*);
  74
  75   // Write to a map file.
  76   void
  77   do_print_to_mapfile(Mapfile* mapfile) const
  78   { mapfile->print_output_data(this, _("** eh_frame_hdr")); }
  79
  80  private:
  81   // Write the data to the file with the right endianness.
  82   template<int size, bool big_endian>
  83   void
  84   do_sized_write(Output_file*);
  85
  86   // The data we record for one FDE: the offset of the FDE within the
  87   // .eh_frame section, and the FDE encoding.
  88   typedef std::pair<section_offset_type, unsigned char> Fde_offset;
  89
  90   // The list of information we record for an FDE.
  91   typedef std::vector<Fde_offset> Fde_offsets;
  92
  93   // When writing out the header, we convert the FDE offsets into FDE
  94   // addresses.  This is a list of pairs of the offset from the header
  95   // to the FDE PC and to the FDE itself.
  96   template<int size>
  97   class Fde_addresses
  98   {
  99    public:
 100     typedef typename elfcpp::Elf_types<size>::Elf_Addr Address;
 101     typedef typename std::pair<Address, Address> Fde_address;
 102     typedef typename std::vector<Fde_address> Fde_address_list;
 103     typedef typename Fde_address_list::iterator iterator;
 104
 105     Fde_addresses(unsigned int reserve)
 106       : fde_addresses_()
 107     { this->fde_addresses_.reserve(reserve); }
 108
 109     void
 110     push_back(Address pc_address, Address fde_address)
 111     {
 112       this->fde_addresses_.push_back(std::make_pair(pc_address, fde_address));
 113     }
 114
 115     iterator
 116     begin()
 117     { return this->fde_addresses_.begin(); }
 118
 119     iterator
 120     end()
 121     { return this->fde_addresses_.end(); }
 122
 123    private:
 124     Fde_address_list fde_addresses_;
 125   };
 126
 127   // Compare Fde_address objects.
 128   template<int size>
 129   struct Fde_address_compare
 130   {
 131     bool
 132     operator()(const typename Fde_addresses<size>::Fde_address& f1,
 133                const typename Fde_addresses<size>::Fde_address& f2) const
 134     { return f1.first < f2.first; }
 135   };
 136
 137   // Return the PC to which an FDE refers.
 138   template<int size, bool big_endian>
 139   typename elfcpp::Elf_types<size>::Elf_Addr
 140   get_fde_pc(typename elfcpp::Elf_types<size>::Elf_Addr eh_frame_address,
 141              const unsigned char* eh_frame_contents,
 142              section_offset_type fde_offset, unsigned char fde_encoding);
 143
 144   // Convert Fde_offsets to Fde_addresses.
 145   template<int size, bool big_endian>
 146   void
 147   get_fde_addresses(Output_file* of,
 148                     const Fde_offsets* fde_offsets,
 149                     Fde_addresses<size>* fde_addresses);
 150
 151   // The .eh_frame section.
 152   Output_section* eh_frame_section_;
 153   // The .eh_frame section data.
 154   const Eh_frame* eh_frame_data_;
 155   // Data from the FDEs in the .eh_frame sections.
 156   Fde_offsets fde_offsets_;
 157   // Whether we found any .eh_frame sections which we could not
 158   // process.
 159   bool any_unrecognized_eh_frame_sections_;
 160 };
 161
 162 // This class holds an FDE.
 163
 164 class Fde
 165 {
 166  public:
 167   Fde(Relobj* object, unsigned int shndx, section_offset_type input_offset,
 168       const unsigned char* contents, size_t length)
 169     : object_(object),
 170       contents_(reinterpret_cast<const char*>(contents), length)
 171   {
 172     this->u_.from_object.shndx = shndx;
 173     this->u_.from_object.input_offset = input_offset;
 174   }
 175
 176   // Create an FDE associated with a PLT.
 177   Fde(Output_data* plt, const unsigned char* contents, size_t length)
 178     : object_(NULL),
 179       contents_(reinterpret_cast<const char*>(contents), length)
 180   { this->u_.from_linker.plt = plt; }
 181
 182   // Return the length of this FDE.  Add 4 for the length and 4 for
 183   // the offset to the CIE.
 184   size_t
 185   length() const
 186   { return this->contents_.length() + 8; }
 187
 188   // Add a mapping for this FDE to MERGE_MAP, so that relocations
 189   // against the FDE are applied to right part of the output file.
 190   void
 191   add_mapping(section_offset_type output_offset, Merge_map* merge_map) const
 192   {
 193     if (this->object_ != NULL)
 194       merge_map->add_mapping(this->object_, this->u_.from_object.shndx,
 195                              this->u_.from_object.input_offset, this->length(),
 196                              output_offset);
 197   }
 198
 199   // Write the FDE to OVIEW starting at OFFSET.  FDE_ENCODING is the
 200   // encoding, from the CIE.  Round up the bytes to ADDRALIGN if
 201   // necessary.  ADDRESS is the virtual address of OVIEW.  Record the
 202   // FDE in EH_FRAME_HDR.  Return the new offset.
 203   template<int size, bool big_endian>
 204   section_offset_type
 205   write(unsigned char* oview, section_offset_type offset,
 206         uint64_t address, unsigned int addralign,
 207         section_offset_type cie_offset, unsigned char fde_encoding,
 208         Eh_frame_hdr* eh_frame_hdr);
 209
 210  private:
 211   // The object in which this FDE was seen.  This will be NULL for a
 212   // linker generated FDE.
 213   Relobj* object_;
 214   union
 215   {
 216     // These fields are used if the FDE is from an input object (the
 217     // object_ field is not NULL).
 218     struct
 219     {
 220       // Input section index for this FDE.
 221       unsigned int shndx;
 222       // Offset within the input section for this FDE.
 223       section_offset_type input_offset;
 224     } from_object;
 225     // This field is used if the FDE is generated by the linker (the
 226     // object_ field is NULL).
 227     struct
 228     {
 229       // The only linker generated FDEs are for PLT sections, and this
 230       // points to the PLT section.
 231       Output_data* plt;
 232     } from_linker;
 233   } u_;
 234   // FDE data.
 235   std::string contents_;
 236 };
 237
 238 // This class holds a CIE.
 239
 240 class Cie
 241 {
 242  public:
 243   Cie(Relobj* object, unsigned int shndx, section_offset_type input_offset,
 244       unsigned char fde_encoding, const char* personality_name,
 245       const unsigned char* contents, size_t length)
 246     : object_(object),
 247       shndx_(shndx),
 248       input_offset_(input_offset),
 249       fde_encoding_(fde_encoding),
 250       personality_name_(personality_name),
 251       fdes_(),
 252       contents_(reinterpret_cast<const char*>(contents), length)
 253   { }
 254
 255   ~Cie();
 256
 257   // We permit copying a CIE when there are no FDEs.  This is
 258   // convenient in the code which creates them.
 259   Cie(const Cie& cie)
 260     : object_(cie.object_),
 261       shndx_(cie.shndx_),
 262       input_offset_(cie.input_offset_),
 263       fde_encoding_(cie.fde_encoding_),
 264       personality_name_(cie.personality_name_),
 265       fdes_(),
 266       contents_(cie.contents_)
 267   { gold_assert(cie.fdes_.empty()); }
 268
 269   // Add an FDE associated with this CIE.
 270   void
 271   add_fde(Fde* fde)
 272   { this->fdes_.push_back(fde); }
 273
 274   // Return the number of FDEs.
 275   unsigned int
 276   fde_count() const
 277   { return this->fdes_.size(); }
 278
 279   // Set the output offset of this CIE to OUTPUT_OFFSET.  It will be
 280   // followed by all its FDEs.  ADDRALIGN is the required address
 281   // alignment, typically 4 or 8.  This updates MERGE_MAP with the
 282   // mapping.  It returns the new output offset.
 283   section_offset_type
 284   set_output_offset(section_offset_type output_offset, unsigned int addralign,
 285                     Merge_map*);
 286
 287   // Write the CIE to OVIEW starting at OFFSET.  EH_FRAME_HDR is the
 288   // exception frame header for FDE recording.  Round up the bytes to
 289   // ADDRALIGN.  ADDRESS is the virtual address of OVIEW.  Return the
 290   // new offset.
 291   template<int size, bool big_endian>
 292   section_offset_type
 293   write(unsigned char* oview, section_offset_type offset, uint64_t address,
 294         unsigned int addralign, Eh_frame_hdr* eh_frame_hdr);
 295
 296   friend bool operator<(const Cie&, const Cie&);
 297   friend bool operator==(const Cie&, const Cie&);
 298
 299  private:
 300   // The class is not assignable.
 301   Cie& operator=(const Cie&);
 302
 303   // The object in which this CIE was first seen.  This will be NULL
 304   // for a linker generated CIE.
 305   Relobj* object_;
 306   // Input section index for this CIE.  This will be 0 for a linker
 307   // generated CIE.
 308   unsigned int shndx_;
 309   // Offset within the input section for this CIE.  This will be 0 for
 310   // a linker generated CIE.
 311   section_offset_type input_offset_;
 312   // The encoding of the FDE.  This is a DW_EH_PE code.
 313   unsigned char fde_encoding_;
 314   // The name of the personality routine.  This will be the name of a
 315   // global symbol, or will be the empty string.
 316   std::string personality_name_;
 317   // List of FDEs.
 318   std::vector<Fde*> fdes_;
 319   // CIE data.
 320   std::string contents_;
 321 };
 322
 323 extern bool operator<(const Cie&, const Cie&);
 324 extern bool operator==(const Cie&, const Cie&);
 325
 326 // This class manages .eh_frame sections.  It discards duplicate
 327 // exception information.
 328
 329 class Eh_frame : public Output_section_data
 330 {
 331  public:
 332   Eh_frame();
 333
 334   // Record the associated Eh_frame_hdr, if any.
 335   void
 336   set_eh_frame_hdr(Eh_frame_hdr* hdr)
 337   { this->eh_frame_hdr_ = hdr; }
 338
 339   // Add the input section SHNDX in OBJECT.  SYMBOLS is the contents
 340   // of the symbol table section (size SYMBOLS_SIZE), SYMBOL_NAMES is
 341   // the symbol names section (size SYMBOL_NAMES_SIZE).  RELOC_SHNDX
 342   // is the relocation section if any (0 for none, -1U for multiple).
 343   // RELOC_TYPE is the type of the relocation section if any.  This
 344   // returns whether the section was incorporated into the .eh_frame
 345   // data.
 346   template<int size, bool big_endian>
 347   bool
 348   add_ehframe_input_section(Sized_relobj_file<size, big_endian>* object,
 349                             const unsigned char* symbols,
 350                             section_size_type symbols_size,
 351                             const unsigned char* symbol_names,
 352                             section_size_type symbol_names_size,
 353                             unsigned int shndx, unsigned int reloc_shndx,
 354                             unsigned int reloc_type);
 355
 356   // Add a CIE and an FDE for a PLT section, to permit unwinding
 357   // through a PLT.  The FDE data should start with 8 bytes of zero,
 358   // which will be replaced by a 4 byte PC relative reference to the
 359   // address of PLT and a 4 byte size of PLT.
 360   void
 361   add_ehframe_for_plt(Output_data* plt, const unsigned char* cie_data,
 362                       size_t cie_length, const unsigned char* fde_data,
 363                       size_t fde_length);
 364
 365   // Return the number of FDEs.
 366   unsigned int
 367   fde_count() const;
 368
 369  protected:
 370   // Set the final data size.
 371   void
 372   set_final_data_size();
 373
 374   // Return the output address for an input address.
 375   bool
 376   do_output_offset(const Relobj*, unsigned int shndx,
 377                    section_offset_type offset,
 378                    section_offset_type* poutput) const;
 379
 380   // Return whether this is the merge section for an input section.
 381   bool
 382   do_is_merge_section_for(const Relobj*, unsigned int shndx) const;
 383
 384   // Write the data to the file.
 385   void
 386   do_write(Output_file*);
 387
 388   // Write to a map file.
 389   void
 390   do_print_to_mapfile(Mapfile* mapfile) const
 391   { mapfile->print_output_data(this, _("** eh_frame")); }
 392
 393  private:
 394   // The comparison routine for the CIE map.
 395   struct Cie_less
 396   {
 397     bool
 398     operator()(const Cie* cie1, const Cie* cie2) const
 399     { return *cie1 < *cie2; }
 400   };
 401
 402   // A set of unique CIEs.
 403   typedef std::set<Cie*, Cie_less> Cie_offsets;
 404
 405   // A list of unmergeable CIEs.
 406   typedef std::vector<Cie*> Unmergeable_cie_offsets;
 407
 408   // A mapping from offsets to CIEs.  This is used while reading an
 409   // input section.
 410   typedef std::map<uint64_t, Cie*> Offsets_to_cie;
 411
 412   // A list of CIEs, and a bool indicating whether the CIE is
 413   // mergeable.
 414   typedef std::vector<std::pair<Cie*, bool> > New_cies;
 415
 416   // Skip an LEB128.
 417   static bool
 418   skip_leb128(const unsigned char**, const unsigned char*);
 419
 420   // The implementation of add_ehframe_input_section.
 421   template<int size, bool big_endian>
 422   bool
 423   do_add_ehframe_input_section(Sized_relobj_file<size, big_endian>* object,
 424                                const unsigned char* symbols,
 425                                section_size_type symbols_size,
 426                                const unsigned char* symbol_names,
 427                                section_size_type symbol_names_size,
 428                                unsigned int shndx,
 429                                unsigned int reloc_shndx,
 430                                unsigned int reloc_type,
 431                                const unsigned char* pcontents,
 432                                section_size_type contents_len,
 433                                New_cies*);
 434
 435   // Read a CIE.
 436   template<int size, bool big_endian>
 437   bool
 438   read_cie(Sized_relobj_file<size, big_endian>* object,
 439            unsigned int shndx,
 440            const unsigned char* symbols,
 441            section_size_type symbols_size,
 442            const unsigned char* symbol_names,
 443            section_size_type symbol_names_size,
 444            const unsigned char* pcontents,
 445            const unsigned char* pcie,
 446            const unsigned char* pcieend,
 447            Track_relocs<size, big_endian>* relocs,
 448            Offsets_to_cie* cies,
 449            New_cies* new_cies);
 450
 451   // Read an FDE.
 452   template<int size, bool big_endian>
 453   bool
 454   read_fde(Sized_relobj_file<size, big_endian>* object,
 455            unsigned int shndx,
 456            const unsigned char* symbols,
 457            section_size_type symbols_size,
 458            const unsigned char* pcontents,
 459            unsigned int offset,
 460            const unsigned char* pfde,
 461            const unsigned char* pfdeend,
 462            Track_relocs<size, big_endian>* relocs,
 463            Offsets_to_cie* cies);
 464
 465   // Template version of write function.
 466   template<int size, bool big_endian>
 467   void
 468   do_sized_write(unsigned char* oview);
 469
 470   // The exception frame header, if any.
 471   Eh_frame_hdr* eh_frame_hdr_;
 472   // A mapping from all unique CIEs to their offset in the output
 473   // file.
 474   Cie_offsets cie_offsets_;
 475   // A mapping from unmergeable CIEs to their offset in the output
 476   // file.
 477   Unmergeable_cie_offsets unmergeable_cie_offsets_;
 478   // A mapping from input sections to the output section.
 479   Merge_map merge_map_;
 480   // Whether we have created the mappings to the output section.
 481   bool mappings_are_done_;
 482   // The final data size.  This is only set if mappings_are_done_ is
 483   // true.
 484   section_size_type final_data_size_;
 485 };
 486
 487 } // End namespace gold.
 488
 489 #endif // !defined(GOLD_EHFRAME_H)