### 2.1 `typedef bfd`

A BFD has type `bfd`; objects of this type are the cornerstone of any application using BFD. Using BFD consists of making references though the BFD and to data in the BFD.

Here is the structure that defines the type `bfd`. It contains the major data about the file and pointers to the rest of the data.

         enum bfd_direction
           {
             no_direction = 0,
             read_direction = 1,
             write_direction = 2,
             both_direction = 3
           };

         enum bfd_plugin_format
           {
             bfd_plugin_uknown = 0,
             bfd_plugin_yes = 1,
             bfd_plugin_no = 2
           };

         struct bfd_build_id
           {
             bfd_size_type size;
             bfd_byte data[1];
           };

         struct bfd
         {
           /* The filename the application opened the BFD with.  */
           const char *filename;

           /* A pointer to the target jump table.  */
           const struct bfd_target *xvec;

           /* The IOSTREAM, and corresponding IO vector that provide access
              to the file backing the BFD.  */
           void *iostream;
           const struct bfd_iovec *iovec;

           /* The caching routines use these to maintain a
              least-recently-used list of BFDs.  */
           struct bfd *lru_prev, *lru_next;

           /* When a file is closed by the caching routines, BFD retains
              state information on the file here...  */
           ufile_ptr where;

           /* File modified time, if mtime_set is TRUE.  */
           long mtime;

           /* A unique identifier of the BFD  */
           unsigned int id;

           /* The format which belongs to the BFD. (object, core, etc.)  */
           ENUM_BITFIELD (bfd_format) format : 3;

           /* The direction with which the BFD was opened.  */
           ENUM_BITFIELD (bfd_direction) direction : 2;

           /* Format_specific flags.  */
           flagword flags : 18;

           /* Values that may appear in the flags field of a BFD.  These also
              appear in the object_flags field of the bfd_target structure, where
              they indicate the set of flags used by that backend (not all flags
              are meaningful for all object file formats) (FIXME: at the moment,
              the object_flags values have mostly just been copied from backend
              to another, and are not necessarily correct).  */

         #define BFD_NO_FLAGS   0x00

           /* BFD contains relocation entries.  */
         #define HAS_RELOC      0x01

           /* BFD is directly executable.  */
         #define EXEC_P         0x02

           /* BFD has line number information (basically used for F_LNNO in a
              COFF header).  */
         #define HAS_LINENO     0x04

           /* BFD has debugging information.  */
         #define HAS_DEBUG      0x08

           /* BFD has symbols.  */
         #define HAS_SYMS       0x10

           /* BFD has local symbols (basically used for F_LSYMS in a COFF
              header).  */
         #define HAS_LOCALS     0x20

           /* BFD is a dynamic object.  */
         #define DYNAMIC        0x40

           /* Text section is write protected (if D_PAGED is not set, this is
              like an a.out NMAGIC file) (the linker sets this by default, but
              clears it for -r or -N).  */
         #define WP_TEXT        0x80

           /* BFD is dynamically paged (this is like an a.out ZMAGIC file) (the
              linker sets this by default, but clears it for -r or -n or -N).  */
         #define D_PAGED        0x100

           /* BFD is relaxable (this means that bfd_relax_section may be able to
              do something) (sometimes bfd_relax_section can do something even if
              this is not set).  */
         #define BFD_IS_RELAXABLE 0x200

           /* This may be set before writing out a BFD to request using a
              traditional format.  For example, this is used to request that when
              writing out an a.out object the symbols not be hashed to eliminate
              duplicates.  */
         #define BFD_TRADITIONAL_FORMAT 0x400

           /* This flag indicates that the BFD contents are actually cached
              in memory.  If this is set, iostream points to a bfd_in_memory
              struct.  */
         #define BFD_IN_MEMORY 0x800

           /* This BFD has been created by the linker and doesn't correspond
              to any input file.  */
         #define BFD_LINKER_CREATED 0x1000

           /* This may be set before writing out a BFD to request that it
              be written using values for UIDs, GIDs, timestamps, etc. that
              will be consistent from run to run.  */
         #define BFD_DETERMINISTIC_OUTPUT 0x2000

           /* Compress sections in this BFD.  */
         #define BFD_COMPRESS 0x4000

           /* Decompress sections in this BFD.  */
         #define BFD_DECOMPRESS 0x8000

           /* BFD is a dummy, for plugins.  */
         #define BFD_PLUGIN 0x10000

           /* Compress sections in this BFD with SHF_COMPRESSED from gABI.  */
         #define BFD_COMPRESS_GABI 0x20000

           /* Flags bits to be saved in bfd_preserve_save.  */
         #define BFD_FLAGS_SAVED \
           (BFD_IN_MEMORY | BFD_COMPRESS | BFD_DECOMPRESS | BFD_PLUGIN \
            | BFD_COMPRESS_GABI)

           /* Flags bits which are for BFD use only.  */
         #define BFD_FLAGS_FOR_BFD_USE_MASK \
           (BFD_IN_MEMORY | BFD_COMPRESS | BFD_DECOMPRESS | BFD_LINKER_CREATED \
            | BFD_PLUGIN | BFD_TRADITIONAL_FORMAT | BFD_DETERMINISTIC_OUTPUT \
            | BFD_COMPRESS_GABI)

           /* Is the file descriptor being cached?  That is, can it be closed as
              needed, and re-opened when accessed later?  */
           unsigned int cacheable : 1;

           /* Marks whether there was a default target specified when the
              BFD was opened. This is used to select which matching algorithm
              to use to choose the back end.  */
           unsigned int target_defaulted : 1;

           /* ... and here: (``once'' means at least once).  */
           unsigned int opened_once : 1;

           /* Set if we have a locally maintained mtime value, rather than
              getting it from the file each time.  */
           unsigned int mtime_set : 1;

           /* Flag set if symbols from this BFD should not be exported.  */
           unsigned int no_export : 1;

           /* Remember when output has begun, to stop strange things
              from happening.  */
           unsigned int output_has_begun : 1;

           /* Have archive map.  */
           unsigned int has_armap : 1;

           /* Set if this is a thin archive.  */
           unsigned int is_thin_archive : 1;

           /* Set if only required symbols should be added in the link hash table for
              this object.  Used by VMS linkers.  */
           unsigned int selective_search : 1;

           /* Set if this is the linker output BFD.  */
           unsigned int is_linker_output : 1;

           /* Set if this is the linker input BFD.  */
           unsigned int is_linker_input : 1;

           /* If this is an input for a compiler plug-in library.  */
           ENUM_BITFIELD (bfd_plugin_format) plugin_format : 2;

           /* Set if this is a plugin output file.  */
           unsigned int lto_output : 1;

           /* Set to dummy BFD created when claimed by a compiler plug-in
              library.  */
           bfd *plugin_dummy_bfd;

           /* Currently my_archive is tested before adding origin to
              anything. I believe that this can become always an add of
              origin, with origin set to 0 for non archive files.  */
           ufile_ptr origin;

           /* The origin in the archive of the proxy entry.  This will
              normally be the same as origin, except for thin archives,
              when it will contain the current offset of the proxy in the
              thin archive rather than the offset of the bfd in its actual
              container.  */
           ufile_ptr proxy_origin;

           /* A hash table for section names.  */
           struct bfd_hash_table section_htab;

           /* Pointer to linked list of sections.  */
           struct bfd_section *sections;

           /* The last section on the section list.  */
           struct bfd_section *section_last;

           /* The number of sections.  */
           unsigned int section_count;

           /* A field used by _bfd_generic_link_add_archive_symbols.  This will
              be used only for archive elements.  */
           int archive_pass;

           /* Stuff only useful for object files:
              The start address.  */
           bfd_vma start_address;

           /* Symbol table for output BFD (with symcount entries).
              Also used by the linker to cache input BFD symbols.  */
           struct bfd_symbol  **outsymbols;

           /* Used for input and output.  */
           unsigned int symcount;

           /* Used for slurped dynamic symbol tables.  */
           unsigned int dynsymcount;

           /* Pointer to structure which contains architecture information.  */
           const struct bfd_arch_info *arch_info;

           /* Stuff only useful for archives.  */
           void *arelt_data;
           struct bfd *my_archive;      /* The containing archive BFD.  */
           struct bfd *archive_next;    /* The next BFD in the archive.  */
           struct bfd *archive_head;    /* The first BFD in the archive.  */
           struct bfd *nested_archives; /* List of nested archive in a flattened
                                           thin archive.  */

           union {
             /* For input BFDs, a chain of BFDs involved in a link.  */
             struct bfd *next;
             /* For output BFD, the linker hash table.  */
             struct bfd_link_hash_table *hash;
           } link;

           /* Used by the back end to hold private data.  */
           union
             {
               struct aout_data_struct *aout_data;
               struct artdata *aout_ar_data;
               struct _oasys_data *oasys_obj_data;
               struct _oasys_ar_data *oasys_ar_data;
               struct coff_tdata *coff_obj_data;
               struct pe_tdata *pe_obj_data;
               struct xcoff_tdata *xcoff_obj_data;
               struct ecoff_tdata *ecoff_obj_data;
               struct ieee_data_struct *ieee_data;
               struct ieee_ar_data_struct *ieee_ar_data;
               struct srec_data_struct *srec_data;
               struct verilog_data_struct *verilog_data;
               struct ihex_data_struct *ihex_data;
               struct tekhex_data_struct *tekhex_data;
               struct elf_obj_tdata *elf_obj_data;
               struct nlm_obj_tdata *nlm_obj_data;
               struct bout_data_struct *bout_data;
               struct mmo_data_struct *mmo_data;
               struct sun_core_struct *sun_core_data;
               struct sco5_core_struct *sco5_core_data;
               struct trad_core_struct *trad_core_data;
               struct som_data_struct *som_data;
               struct hpux_core_struct *hpux_core_data;
               struct hppabsd_core_struct *hppabsd_core_data;
               struct sgi_core_struct *sgi_core_data;
               struct lynx_core_struct *lynx_core_data;
               struct osf_core_struct *osf_core_data;
               struct cisco_core_struct *cisco_core_data;
               struct versados_data_struct *versados_data;
               struct netbsd_core_struct *netbsd_core_data;
               struct mach_o_data_struct *mach_o_data;
               struct mach_o_fat_data_struct *mach_o_fat_data;
               struct plugin_data_struct *plugin_data;
               struct bfd_pef_data_struct *pef_data;
               struct bfd_pef_xlib_data_struct *pef_xlib_data;
               struct bfd_sym_data_struct *sym_data;
               void *any;
             }
           tdata;

           /* Used by the application to hold private data.  */
           void *usrdata;

           /* Where all the allocated stuff under this BFD goes.  This is a
              struct objalloc *, but we use void * to avoid requiring the inclusion
              of objalloc.h.  */
           void *memory;

           /* For input BFDs, the build ID, if the object has one. */
           const struct bfd_build_id *build_id;
         };

         /* See note beside bfd_set_section_userdata.  */
         static inline bfd_boolean
         bfd_set_cacheable (bfd * abfd, bfd_boolean val)
         {
           abfd->cacheable = val;
           return TRUE;
         }