Untitled Document: bfd_target

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#### 2.12.1 bfd_target

Description
This structure contains everything that BFD knows about a target. It includes things like its byte order, name, and which routines to call to do various operations.

Every BFD points to a target structure with its `xvec` member.

The macros below are used to dispatch to functions through the `bfd_target` vector. They are used in a number of macros further down in `bfd.h`, and are also used when calling various routines by hand inside the BFD implementation. The arglist argument must be parenthesized; it contains all the arguments to the called function.

They make the documentation (more) unpleasant to read, so if someone wants to fix this and not break the above, please do.

    #define BFD_SEND(bfd, message, arglist) \
      ((*((bfd)->xvec->message)) arglist)

    #ifdef DEBUG_BFD_SEND
    #undef BFD_SEND
    #define BFD_SEND(bfd, message, arglist) \
      (((bfd) && (bfd)->xvec && (bfd)->xvec->message) ? \
        ((*((bfd)->xvec->message)) arglist) : \
        (bfd_assert (__FILE__,__LINE__), NULL))
    #endif

For operations which index on the BFD format:

    #define BFD_SEND_FMT(bfd, message, arglist) \
      (((bfd)->xvec->message[(int) ((bfd)->format)]) arglist)

    #ifdef DEBUG_BFD_SEND
    #undef BFD_SEND_FMT
    #define BFD_SEND_FMT(bfd, message, arglist) \
      (((bfd) && (bfd)->xvec && (bfd)->xvec->message) ? \
       (((bfd)->xvec->message[(int) ((bfd)->format)]) arglist) : \
       (bfd_assert (__FILE__,__LINE__), NULL))
    #endif

This is the structure which defines the type of BFD this is. The `xvec` member of the struct `bfd` itself points here. Each module that implements access to a different target under BFD, defines one of these.

FIXME, these names should be rationalised with the names of the entry points which call them. Too bad we can’t have one macro to define them both!

    enum bfd_flavour
    {
      bfd_target_unknown_flavour,
      bfd_target_aout_flavour,
      bfd_target_coff_flavour,
      bfd_target_ecoff_flavour,
      bfd_target_xcoff_flavour,
      bfd_target_elf_flavour,
      bfd_target_ieee_flavour,
      bfd_target_nlm_flavour,
      bfd_target_oasys_flavour,
      bfd_target_tekhex_flavour,
      bfd_target_srec_flavour,
      bfd_target_verilog_flavour,
      bfd_target_ihex_flavour,
      bfd_target_som_flavour,
      bfd_target_os9k_flavour,
      bfd_target_versados_flavour,
      bfd_target_msdos_flavour,
      bfd_target_ovax_flavour,
      bfd_target_evax_flavour,
      bfd_target_mmo_flavour,
      bfd_target_mach_o_flavour,
      bfd_target_pef_flavour,
      bfd_target_pef_xlib_flavour,
      bfd_target_sym_flavour
    };

    enum bfd_endian { BFD_ENDIAN_BIG, BFD_ENDIAN_LITTLE, BFD_ENDIAN_UNKNOWN };

    /* Forward declaration.  */
    typedef struct bfd_link_info _bfd_link_info;

    /* Forward declaration.  */
    typedef struct flag_info flag_info;

    typedef struct bfd_target
    {
      /* Identifies the kind of target, e.g., SunOS4, Ultrix, etc.  */
      char *name;

     /* The "flavour" of a back end is a general indication about
        the contents of a file.  */
      enum bfd_flavour flavour;

      /* The order of bytes within the data area of a file.  */
      enum bfd_endian byteorder;

     /* The order of bytes within the header parts of a file.  */
      enum bfd_endian header_byteorder;

      /* A mask of all the flags which an executable may have set -
         from the set BFD_NO_FLAGS, HAS_RELOC, ...D_PAGED.  */
      flagword object_flags;

     /* A mask of all the flags which a section may have set - from
        the set SEC_NO_FLAGS, SEC_ALLOC, ...SET_NEVER_LOAD.  */
      flagword section_flags;

     /* The character normally found at the front of a symbol.
        (if any), perhaps `_'.  */
      char symbol_leading_char;

     /* The pad character for file names within an archive header.  */
      char ar_pad_char;

      /* The maximum number of characters in an archive header.  */
      unsigned char ar_max_namelen;

      /* How well this target matches, used to select between various
         possible targets when more than one target matches.  */
      unsigned char match_priority;

      /* Entries for byte swapping for data. These are different from the
         other entry points, since they don't take a BFD as the first argument.
         Certain other handlers could do the same.  */
      bfd_uint64_t   (*bfd_getx64) (const void *);
      bfd_int64_t    (*bfd_getx_signed_64) (const void *);
      void           (*bfd_putx64) (bfd_uint64_t, void *);
      bfd_vma        (*bfd_getx32) (const void *);
      bfd_signed_vma (*bfd_getx_signed_32) (const void *);
      void           (*bfd_putx32) (bfd_vma, void *);
      bfd_vma        (*bfd_getx16) (const void *);
      bfd_signed_vma (*bfd_getx_signed_16) (const void *);
      void           (*bfd_putx16) (bfd_vma, void *);

      /* Byte swapping for the headers.  */
      bfd_uint64_t   (*bfd_h_getx64) (const void *);
      bfd_int64_t    (*bfd_h_getx_signed_64) (const void *);
      void           (*bfd_h_putx64) (bfd_uint64_t, void *);
      bfd_vma        (*bfd_h_getx32) (const void *);
      bfd_signed_vma (*bfd_h_getx_signed_32) (const void *);
      void           (*bfd_h_putx32) (bfd_vma, void *);
      bfd_vma        (*bfd_h_getx16) (const void *);
      bfd_signed_vma (*bfd_h_getx_signed_16) (const void *);
      void           (*bfd_h_putx16) (bfd_vma, void *);

      /* Format dependent routines: these are vectors of entry points
         within the target vector structure, one for each format to check.  */

      /* Check the format of a file being read.  Return a bfd_target * or zero.  */
      const struct bfd_target *(*_bfd_check_format[bfd_type_end]) (bfd *);

      /* Set the format of a file being written.  */
      bfd_boolean (*_bfd_set_format[bfd_type_end]) (bfd *);

      /* Write cached information into a file being written, at bfd_close.  */
      bfd_boolean (*_bfd_write_contents[bfd_type_end]) (bfd *);

The general target vector. These vectors are initialized using the BFD_JUMP_TABLE macros.

      /* Generic entry points.  */
    #define BFD_JUMP_TABLE_GENERIC(NAME) \
      NAME##_close_and_cleanup, \
      NAME##_bfd_free_cached_info, \
      NAME##_new_section_hook, \
      NAME##_get_section_contents, \
      NAME##_get_section_contents_in_window

      /* Called when the BFD is being closed to do any necessary cleanup.  */
      bfd_boolean (*_close_and_cleanup) (bfd *);
      /* Ask the BFD to free all cached information.  */
      bfd_boolean (*_bfd_free_cached_info) (bfd *);
      /* Called when a new section is created.  */
      bfd_boolean (*_new_section_hook) (bfd *, sec_ptr);
      /* Read the contents of a section.  */
      bfd_boolean (*_bfd_get_section_contents)
        (bfd *, sec_ptr, void *, file_ptr, bfd_size_type);
      bfd_boolean (*_bfd_get_section_contents_in_window)
        (bfd *, sec_ptr, bfd_window *, file_ptr, bfd_size_type);

      /* Entry points to copy private data.  */
    #define BFD_JUMP_TABLE_COPY(NAME) \
      NAME##_bfd_copy_private_bfd_data, \
      NAME##_bfd_merge_private_bfd_data, \
      _bfd_generic_init_private_section_data, \
      NAME##_bfd_copy_private_section_data, \
      NAME##_bfd_copy_private_symbol_data, \
      NAME##_bfd_copy_private_header_data, \
      NAME##_bfd_set_private_flags, \
      NAME##_bfd_print_private_bfd_data

      /* Called to copy BFD general private data from one object file
         to another.  */
      bfd_boolean (*_bfd_copy_private_bfd_data) (bfd *, bfd *);
      /* Called to merge BFD general private data from one object file
         to a common output file when linking.  */
      bfd_boolean (*_bfd_merge_private_bfd_data) (bfd *, bfd *);
      /* Called to initialize BFD private section data from one object file
         to another.  */
    #define bfd_init_private_section_data(ibfd, isec, obfd, osec, link_info) \
      BFD_SEND (obfd, _bfd_init_private_section_data, (ibfd, isec, obfd, osec, link_info))
      bfd_boolean (*_bfd_init_private_section_data)
        (bfd *, sec_ptr, bfd *, sec_ptr, struct bfd_link_info *);
      /* Called to copy BFD private section data from one object file
         to another.  */
      bfd_boolean (*_bfd_copy_private_section_data)
        (bfd *, sec_ptr, bfd *, sec_ptr);
      /* Called to copy BFD private symbol data from one symbol
         to another.  */
      bfd_boolean (*_bfd_copy_private_symbol_data)
        (bfd *, asymbol *, bfd *, asymbol *);
      /* Called to copy BFD private header data from one object file
         to another.  */
      bfd_boolean (*_bfd_copy_private_header_data)
        (bfd *, bfd *);
      /* Called to set private backend flags.  */
      bfd_boolean (*_bfd_set_private_flags) (bfd *, flagword);

      /* Called to print private BFD data.  */
      bfd_boolean (*_bfd_print_private_bfd_data) (bfd *, void *);

      /* Core file entry points.  */
    #define BFD_JUMP_TABLE_CORE(NAME) \
      NAME##_core_file_failing_command, \
      NAME##_core_file_failing_signal, \
      NAME##_core_file_matches_executable_p, \
      NAME##_core_file_pid

      char *      (*_core_file_failing_command) (bfd *);
      int         (*_core_file_failing_signal) (bfd *);
      bfd_boolean (*_core_file_matches_executable_p) (bfd *, bfd *);
      int         (*_core_file_pid) (bfd *);

      /* Archive entry points.  */
    #define BFD_JUMP_TABLE_ARCHIVE(NAME) \
      NAME##_slurp_armap, \
      NAME##_slurp_extended_name_table, \
      NAME##_construct_extended_name_table, \
      NAME##_truncate_arname, \
      NAME##_write_armap, \
      NAME##_read_ar_hdr, \
      NAME##_write_ar_hdr, \
      NAME##_openr_next_archived_file, \
      NAME##_get_elt_at_index, \
      NAME##_generic_stat_arch_elt, \
      NAME##_update_armap_timestamp

      bfd_boolean (*_bfd_slurp_armap) (bfd *);
      bfd_boolean (*_bfd_slurp_extended_name_table) (bfd *);
      bfd_boolean (*_bfd_construct_extended_name_table)
        (bfd *, char **, bfd_size_type *, const char **);
      void        (*_bfd_truncate_arname) (bfd *, const char *, char *);
      bfd_boolean (*write_armap)
        (bfd *, unsigned int, struct orl *, unsigned int, int);
      void *      (*_bfd_read_ar_hdr_fn) (bfd *);
      bfd_boolean (*_bfd_write_ar_hdr_fn) (bfd *, bfd *);
      bfd *       (*openr_next_archived_file) (bfd *, bfd *);
    #define bfd_get_elt_at_index(b,i) BFD_SEND (b, _bfd_get_elt_at_index, (b,i))
      bfd *       (*_bfd_get_elt_at_index) (bfd *, symindex);
      int         (*_bfd_stat_arch_elt) (bfd *, struct stat *);
      bfd_boolean (*_bfd_update_armap_timestamp) (bfd *);

      /* Entry points used for symbols.  */
    #define BFD_JUMP_TABLE_SYMBOLS(NAME) \
      NAME##_get_symtab_upper_bound, \
      NAME##_canonicalize_symtab, \
      NAME##_make_empty_symbol, \
      NAME##_print_symbol, \
      NAME##_get_symbol_info, \
      NAME##_bfd_is_local_label_name, \
      NAME##_bfd_is_target_special_symbol, \
      NAME##_get_lineno, \
      NAME##_find_nearest_line, \
      NAME##_find_line, \
      NAME##_find_inliner_info, \
      NAME##_bfd_make_debug_symbol, \
      NAME##_read_minisymbols, \
      NAME##_minisymbol_to_symbol

      long        (*_bfd_get_symtab_upper_bound) (bfd *);
      long        (*_bfd_canonicalize_symtab)
        (bfd *, struct bfd_symbol **);
      struct bfd_symbol *
                  (*_bfd_make_empty_symbol) (bfd *);
      void        (*_bfd_print_symbol)
        (bfd *, void *, struct bfd_symbol *, bfd_print_symbol_type);
    #define bfd_print_symbol(b,p,s,e) BFD_SEND (b, _bfd_print_symbol, (b,p,s,e))
      void        (*_bfd_get_symbol_info)
        (bfd *, struct bfd_symbol *, symbol_info *);
    #define bfd_get_symbol_info(b,p,e) BFD_SEND (b, _bfd_get_symbol_info, (b,p,e))
      bfd_boolean (*_bfd_is_local_label_name) (bfd *, const char *);
      bfd_boolean (*_bfd_is_target_special_symbol) (bfd *, asymbol *);
      alent *     (*_get_lineno) (bfd *, struct bfd_symbol *);
      bfd_boolean (*_bfd_find_nearest_line)
        (bfd *, struct bfd_symbol **, struct bfd_section *, bfd_vma,
         const char **, const char **, unsigned int *, unsigned int *);
      bfd_boolean (*_bfd_find_line)
        (bfd *, struct bfd_symbol **, struct bfd_symbol *,
         const char **, unsigned int *);
      bfd_boolean (*_bfd_find_inliner_info)
        (bfd *, const char **, const char **, unsigned int *);
     /* Back-door to allow format-aware applications to create debug symbols
        while using BFD for everything else.  Currently used by the assembler
        when creating COFF files.  */
      asymbol *   (*_bfd_make_debug_symbol)
        (bfd *, void *, unsigned long size);
    #define bfd_read_minisymbols(b, d, m, s) \
      BFD_SEND (b, _read_minisymbols, (b, d, m, s))
      long        (*_read_minisymbols)
        (bfd *, bfd_boolean, void **, unsigned int *);
    #define bfd_minisymbol_to_symbol(b, d, m, f) \
      BFD_SEND (b, _minisymbol_to_symbol, (b, d, m, f))
      asymbol *   (*_minisymbol_to_symbol)
        (bfd *, bfd_boolean, const void *, asymbol *);

      /* Routines for relocs.  */
    #define BFD_JUMP_TABLE_RELOCS(NAME) \
      NAME##_get_reloc_upper_bound, \
      NAME##_canonicalize_reloc, \
      NAME##_bfd_reloc_type_lookup, \
      NAME##_bfd_reloc_name_lookup

      long        (*_get_reloc_upper_bound) (bfd *, sec_ptr);
      long        (*_bfd_canonicalize_reloc)
        (bfd *, sec_ptr, arelent **, struct bfd_symbol **);
      /* See documentation on reloc types.  */
      reloc_howto_type *
                  (*reloc_type_lookup) (bfd *, bfd_reloc_code_real_type);
      reloc_howto_type *
                  (*reloc_name_lookup) (bfd *, const char *);

      /* Routines used when writing an object file.  */
    #define BFD_JUMP_TABLE_WRITE(NAME) \
      NAME##_set_arch_mach, \
      NAME##_set_section_contents

      bfd_boolean (*_bfd_set_arch_mach)
        (bfd *, enum bfd_architecture, unsigned long);
      bfd_boolean (*_bfd_set_section_contents)
        (bfd *, sec_ptr, const void *, file_ptr, bfd_size_type);

      /* Routines used by the linker.  */
    #define BFD_JUMP_TABLE_LINK(NAME) \
      NAME##_sizeof_headers, \
      NAME##_bfd_get_relocated_section_contents, \
      NAME##_bfd_relax_section, \
      NAME##_bfd_link_hash_table_create, \
      NAME##_bfd_link_add_symbols, \
      NAME##_bfd_link_just_syms, \
      NAME##_bfd_copy_link_hash_symbol_type, \
      NAME##_bfd_final_link, \
      NAME##_bfd_link_split_section, \
      NAME##_bfd_gc_sections, \
      NAME##_bfd_lookup_section_flags, \
      NAME##_bfd_merge_sections, \
      NAME##_bfd_is_group_section, \
      NAME##_bfd_discard_group, \
      NAME##_section_already_linked, \
      NAME##_bfd_define_common_symbol

      int         (*_bfd_sizeof_headers) (bfd *, struct bfd_link_info *);
      bfd_byte *  (*_bfd_get_relocated_section_contents)
        (bfd *, struct bfd_link_info *, struct bfd_link_order *,
         bfd_byte *, bfd_boolean, struct bfd_symbol **);

      bfd_boolean (*_bfd_relax_section)
        (bfd *, struct bfd_section *, struct bfd_link_info *, bfd_boolean *);

      /* Create a hash table for the linker.  Different backends store
         different information in this table.  */
      struct bfd_link_hash_table *
                  (*_bfd_link_hash_table_create) (bfd *);

      /* Add symbols from this object file into the hash table.  */
      bfd_boolean (*_bfd_link_add_symbols) (bfd *, struct bfd_link_info *);

      /* Indicate that we are only retrieving symbol values from this section.  */
      void        (*_bfd_link_just_syms) (asection *, struct bfd_link_info *);

      /* Copy the symbol type and other attributes for a linker script
         assignment of one symbol to another.  */
    #define bfd_copy_link_hash_symbol_type(b, t, f) \
      BFD_SEND (b, _bfd_copy_link_hash_symbol_type, (b, t, f))
      void (*_bfd_copy_link_hash_symbol_type)
        (bfd *, struct bfd_link_hash_entry *, struct bfd_link_hash_entry *);

      /* Do a link based on the link_order structures attached to each
         section of the BFD.  */
      bfd_boolean (*_bfd_final_link) (bfd *, struct bfd_link_info *);

      /* Should this section be split up into smaller pieces during linking.  */
      bfd_boolean (*_bfd_link_split_section) (bfd *, struct bfd_section *);

      /* Remove sections that are not referenced from the output.  */
      bfd_boolean (*_bfd_gc_sections) (bfd *, struct bfd_link_info *);

      /* Sets the bitmask of allowed and disallowed section flags.  */
      bfd_boolean (*_bfd_lookup_section_flags) (struct bfd_link_info *,
                                                struct flag_info *,
                                                asection *);

      /* Attempt to merge SEC_MERGE sections.  */
      bfd_boolean (*_bfd_merge_sections) (bfd *, struct bfd_link_info *);

      /* Is this section a member of a group?  */
      bfd_boolean (*_bfd_is_group_section) (bfd *, const struct bfd_section *);

      /* Discard members of a group.  */
      bfd_boolean (*_bfd_discard_group) (bfd *, struct bfd_section *);

      /* Check if SEC has been already linked during a reloceatable or
         final link.  */
      bfd_boolean (*_section_already_linked) (bfd *, asection *,
                                              struct bfd_link_info *);

      /* Define a common symbol.  */
      bfd_boolean (*_bfd_define_common_symbol) (bfd *, struct bfd_link_info *,
                                                struct bfd_link_hash_entry *);

      /* Routines to handle dynamic symbols and relocs.  */
    #define BFD_JUMP_TABLE_DYNAMIC(NAME) \
      NAME##_get_dynamic_symtab_upper_bound, \
      NAME##_canonicalize_dynamic_symtab, \
      NAME##_get_synthetic_symtab, \
      NAME##_get_dynamic_reloc_upper_bound, \
      NAME##_canonicalize_dynamic_reloc

      /* Get the amount of memory required to hold the dynamic symbols.  */
      long        (*_bfd_get_dynamic_symtab_upper_bound) (bfd *);
      /* Read in the dynamic symbols.  */
      long        (*_bfd_canonicalize_dynamic_symtab)
        (bfd *, struct bfd_symbol **);
      /* Create synthetized symbols.  */
      long        (*_bfd_get_synthetic_symtab)
        (bfd *, long, struct bfd_symbol **, long, struct bfd_symbol **,
         struct bfd_symbol **);
      /* Get the amount of memory required to hold the dynamic relocs.  */
      long        (*_bfd_get_dynamic_reloc_upper_bound) (bfd *);
      /* Read in the dynamic relocs.  */
      long        (*_bfd_canonicalize_dynamic_reloc)
        (bfd *, arelent **, struct bfd_symbol **);

A pointer to an alternative bfd_target in case the current one is not satisfactory. This can happen when the target cpu supports both big and little endian code, and target chosen by the linker has the wrong endianness. The function open_output() in ld/ldlang.c uses this field to find an alternative output format that is suitable.

      /* Opposite endian version of this target.  */
      const struct bfd_target * alternative_target;

      /* Data for use by back-end routines, which isn't
         generic enough to belong in this structure.  */
      const void *backend_data;

    } bfd_target;

#### 2.12.1.1 `bfd_set_default_target`

Synopsis

    bfd_boolean bfd_set_default_target (const char *name);

Description
Set the default target vector to use when recognizing a BFD. This takes the name of the target, which may be a BFD target name or a configuration triplet.

#### 2.12.1.2 `bfd_find_target`

Synopsis

    const bfd_target *bfd_find_target (const char *target_name, bfd *abfd);

Description
Return a pointer to the transfer vector for the object target named target_name. If target_name is `NULL`, choose the one in the environment variable `GNUTARGET`; if that is null or not defined, then choose the first entry in the target list. Passing in the string "default" or setting the environment variable to "default" will cause the first entry in the target list to be returned, and "target_defaulted" will be set in the BFD if abfd isn’t `NULL`. This causes `bfd_check_format` to loop over all the targets to find the one that matches the file being read.

#### 2.12.1.3 `bfd_get_target_info`

Synopsis

    const bfd_target *bfd_get_target_info (const char *target_name,
        bfd *abfd,
        bfd_boolean *is_bigendian,
        int *underscoring,
        const char **def_target_arch);

Description
Return a pointer to the transfer vector for the object target named target_name. If target_name is `NULL`, choose the one in the environment variable `GNUTARGET`; if that is null or not defined, then choose the first entry in the target list. Passing in the string "default" or setting the environment variable to "default" will cause the first entry in the target list to be returned, and "target_defaulted" will be set in the BFD if abfd isn’t `NULL`. This causes `bfd_check_format` to loop over all the targets to find the one that matches the file being read. If is_bigendian is not `NULL`, then set this value to target’s endian mode. True for big-endian, FALSE for little-endian or for invalid target. If underscoring is not `NULL`, then set this value to target’s underscoring mode. Zero for none-underscoring, -1 for invalid target, else the value of target vector’s symbol underscoring. If def_target_arch is not `NULL`, then set it to the architecture string specified by the target_name.

#### 2.12.1.4 `bfd_target_list`

Synopsis

    const char ** bfd_target_list (void);

Description
Return a freshly malloced NULL-terminated vector of the names of all the valid BFD targets. Do not modify the names.

#### 2.12.1.5 `bfd_seach_for_target`

Synopsis

    const bfd_target *bfd_search_for_target
       (int (*search_func) (const bfd_target *, void *),
        void *);

Description
Return a pointer to the first transfer vector in the list of transfer vectors maintained by BFD that produces a non-zero result when passed to the function search_func. The parameter data is passed, unexamined, to the search function.

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