@section @code{typedef bfd}
A BFD has type @code{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 @code{bfd}.  It
contains the major data about the file and pointers
to the rest of the data.


@example

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;

    /* To avoid dragging too many header files into every file that
       includes `@code{bfd.h}', IOSTREAM has been declared as a "char
       *", and MTIME as a "long".  Their correct types, to which they
       are cast when used, are "FILE *" and "time_t".    The iostream
       is the result of an fopen on the filename.  However, if the
       BFD_IN_MEMORY flag is set, then iostream is actually a pointer
       to a bfd_in_memory struct.  */
    PTR iostream;

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

    boolean cacheable;

    /* 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. */

    boolean target_defaulted;

    /* 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: */

    file_ptr where;              

    /* and here: (``once'' means at least once) */

    boolean opened_once;

    /* Set if we have a locally maintained mtime value, rather than
       getting it from the file each time: */

    boolean mtime_set;

    /* File modified time, if mtime_set is true: */

    long mtime;          

    /* Reserved for an unimplemented file locking extension.*/

    int ifd;

    /* The format which belongs to the BFD. (object, core, etc.) */

    bfd_format format;

    /* The direction the BFD was opened with*/

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

    /* Format_specific flags*/

    flagword flags;              

    /* 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.   */

    file_ptr origin;             

    /* Remember when output has begun, to stop strange things
       from happening. */
    boolean output_has_begun;

    /* Pointer to linked list of sections*/
    struct sec  *sections;

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

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

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

    /* Symbol table for output BFD (with symcount entries) */
    struct symbol_cache_entry  **outsymbols;             

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

    /* Stuff only useful for archives:*/
    PTR arelt_data;              
    struct _bfd *my_archive;     /* The containing archive BFD.  */
    struct _bfd *next;           /* The next BFD in the archive.  */
    struct _bfd *archive_head;   /* The first BFD in the archive.  */
    boolean has_armap;           

    /* A chain of BFD structures involved in a link.  */
    struct _bfd *link_next;

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

    /* 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 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 sun_core_struct *sun_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;
      PTR any;
      @} tdata;
  
    /* Used by the application to hold private data*/
    PTR usrdata;

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

@end example
@section Error reporting
Most BFD functions return nonzero on success (check their
individual documentation for precise semantics).  On an error,
they call @code{bfd_set_error} to set an error condition that callers
can check by calling @code{bfd_get_error}.
If that returns @code{bfd_error_system_call}, then check
@code{errno}.

The easiest way to report a BFD error to the user is to
use @code{bfd_perror}.

@subsection Type @code{bfd_error_type}
The values returned by @code{bfd_get_error} are defined by the
enumerated type @code{bfd_error_type}.


@example

typedef enum bfd_error
@{
  bfd_error_no_error = 0,
  bfd_error_system_call,
  bfd_error_invalid_target,
  bfd_error_wrong_format,
  bfd_error_invalid_operation,
  bfd_error_no_memory,
  bfd_error_no_symbols,
  bfd_error_no_armap,
  bfd_error_no_more_archived_files,
  bfd_error_malformed_archive,
  bfd_error_file_not_recognized,
  bfd_error_file_ambiguously_recognized,
  bfd_error_no_contents,
  bfd_error_nonrepresentable_section,
  bfd_error_no_debug_section,
  bfd_error_bad_value,
  bfd_error_file_truncated,
  bfd_error_file_too_big,
  bfd_error_invalid_error_code
@} bfd_error_type;

@end example
@findex bfd_get_error
@subsubsection @code{bfd_get_error}
@strong{Synopsis}
@example
bfd_error_type bfd_get_error (void);
@end example
@strong{Description}@*
Return the current BFD error condition.

@findex bfd_set_error
@subsubsection @code{bfd_set_error}
@strong{Synopsis}
@example
void bfd_set_error (bfd_error_type error_tag);
@end example
@strong{Description}@*
Set the BFD error condition to be @var{error_tag}.

@findex bfd_errmsg
@subsubsection @code{bfd_errmsg}
@strong{Synopsis}
@example
CONST char *bfd_errmsg (bfd_error_type error_tag);
@end example
@strong{Description}@*
Return a string describing the error @var{error_tag}, or
the system error if @var{error_tag} is @code{bfd_error_system_call}.

@findex bfd_perror
@subsubsection @code{bfd_perror}
@strong{Synopsis}
@example
void bfd_perror (CONST char *message);
@end example
@strong{Description}@*
Print to the standard error stream a string describing the
last BFD error that occurred, or the last system error if
the last BFD error was a system call failure.  If @var{message}
is non-NULL and non-empty, the error string printed is preceded
by @var{message}, a colon, and a space.  It is followed by a newline.

@subsection BFD error handler
Some BFD functions want to print messages describing the
problem.  They call a BFD error handler function.  This
function may be overriden by the program.

The BFD error handler acts like printf.


@example

typedef void (*bfd_error_handler_type) PARAMS ((const char *, ...));

@end example
@findex bfd_set_error_handler
@subsubsection @code{bfd_set_error_handler}
@strong{Synopsis}
@example
bfd_error_handler_type bfd_set_error_handler (bfd_error_handler_type);
@end example
@strong{Description}@*
Set the BFD error handler function.  Returns the previous
function.

@findex bfd_set_error_program_name
@subsubsection @code{bfd_set_error_program_name}
@strong{Synopsis}
@example
void bfd_set_error_program_name (const char *);
@end example
@strong{Description}@*
Set the program name to use when printing a BFD error.  This
is printed before the error message followed by a colon and
space.  The string must not be changed after it is passed to
this function.

@findex bfd_get_error_handler
@subsubsection @code{bfd_get_error_handler}
@strong{Synopsis}
@example
bfd_error_handler_type bfd_get_error_handler (void);
@end example
@strong{Description}@*
Return the BFD error handler function.

@section Symbols


@findex bfd_get_reloc_upper_bound
@subsubsection @code{bfd_get_reloc_upper_bound}
@strong{Synopsis}
@example
long bfd_get_reloc_upper_bound(bfd *abfd, asection *sect);
@end example
@strong{Description}@*
Return the number of bytes required to store the
relocation information associated with section @var{sect}
attached to bfd @var{abfd}.  If an error occurs, return -1.

@findex bfd_canonicalize_reloc
@subsubsection @code{bfd_canonicalize_reloc}
@strong{Synopsis}
@example
long bfd_canonicalize_reloc
   (bfd *abfd,
    asection *sec,
    arelent **loc,
    asymbol **syms);
@end example
@strong{Description}@*
Call the back end associated with the open BFD
@var{abfd} and translate the external form of the relocation
information attached to @var{sec} into the internal canonical
form.  Place the table into memory at @var{loc}, which has
been preallocated, usually by a call to
@code{bfd_get_reloc_upper_bound}.  Returns the number of relocs, or
-1 on error.

The @var{syms} table is also needed for horrible internal magic
reasons.

@findex bfd_set_reloc
@subsubsection @code{bfd_set_reloc}
@strong{Synopsis}
@example
void bfd_set_reloc
   (bfd *abfd, asection *sec, arelent **rel, unsigned int count)
@end example
@strong{Description}@*
Set the relocation pointer and count within
section @var{sec} to the values @var{rel} and @var{count}.
The argument @var{abfd} is ignored.

@findex bfd_set_file_flags
@subsubsection @code{bfd_set_file_flags}
@strong{Synopsis}
@example
boolean bfd_set_file_flags(bfd *abfd, flagword flags);
@end example
@strong{Description}@*
Set the flag word in the BFD @var{abfd} to the value @var{flags}.

Possible errors are:
@itemize @bullet

@item
@code{bfd_error_wrong_format} - The target bfd was not of object format.
@item
@code{bfd_error_invalid_operation} - The target bfd was open for reading.
@item
@code{bfd_error_invalid_operation} -
The flag word contained a bit which was not applicable to the
type of file.  E.g., an attempt was made to set the @code{D_PAGED} bit
on a BFD format which does not support demand paging.
@end itemize

@findex bfd_set_start_address
@subsubsection @code{bfd_set_start_address}
@strong{Synopsis}
@example
boolean bfd_set_start_address(bfd *abfd, bfd_vma vma);
@end example
@strong{Description}@*
Make @var{vma} the entry point of output BFD @var{abfd}.

@strong{Returns}@*
Returns @code{true} on success, @code{false} otherwise.

@findex bfd_get_mtime
@subsubsection @code{bfd_get_mtime}
@strong{Synopsis}
@example
long bfd_get_mtime(bfd *abfd);
@end example
@strong{Description}@*
Return the file modification time (as read from the file system, or
from the archive header for archive members).

@findex bfd_get_size
@subsubsection @code{bfd_get_size}
@strong{Synopsis}
@example
long bfd_get_size(bfd *abfd);
@end example
@strong{Description}@*
Return the file size (as read from file system) for the file
associated with BFD @var{abfd}.

The initial motivation for, and use of, this routine is not
so we can get the exact size of the object the BFD applies to, since
that might not be generally possible (archive members for example).
It would be ideal if someone could eventually modify
it so that such results were guaranteed.

Instead, we want to ask questions like "is this NNN byte sized
object I'm about to try read from file offset YYY reasonable?"
As as example of where we might do this, some object formats
use string tables for which the first @code{sizeof(long)} bytes of the
table contain the size of the table itself, including the size bytes.
If an application tries to read what it thinks is one of these
string tables, without some way to validate the size, and for
some reason the size is wrong (byte swapping error, wrong location
for the string table, etc.), the only clue is likely to be a read
error when it tries to read the table, or a "virtual memory
exhausted" error when it tries to allocate 15 bazillon bytes
of space for the 15 bazillon byte table it is about to read.
This function at least allows us to answer the quesion, "is the
size reasonable?".

@findex bfd_get_gp_size
@subsubsection @code{bfd_get_gp_size}
@strong{Synopsis}
@example
int bfd_get_gp_size(bfd *abfd);
@end example
@strong{Description}@*
Return the maximum size of objects to be optimized using the GP
register under MIPS ECOFF.  This is typically set by the @code{-G}
argument to the compiler, assembler or linker.

@findex bfd_set_gp_size
@subsubsection @code{bfd_set_gp_size}
@strong{Synopsis}
@example
void bfd_set_gp_size(bfd *abfd, int i);
@end example
@strong{Description}@*
Set the maximum size of objects to be optimized using the GP
register under ECOFF or MIPS ELF.  This is typically set by
the @code{-G} argument to the compiler, assembler or linker.

@findex bfd_scan_vma
@subsubsection @code{bfd_scan_vma}
@strong{Synopsis}
@example
bfd_vma bfd_scan_vma(CONST char *string, CONST char **end, int base);
@end example
@strong{Description}@*
Convert, like @code{strtoul}, a numerical expression
@var{string} into a @code{bfd_vma} integer, and return that integer.
(Though without as many bells and whistles as @code{strtoul}.)
The expression is assumed to be unsigned (i.e., positive).
If given a @var{base}, it is used as the base for conversion.
A base of 0 causes the function to interpret the string
in hex if a leading "0x" or "0X" is found, otherwise
in octal if a leading zero is found, otherwise in decimal.

Overflow is not detected.

@findex bfd_copy_private_bfd_data
@subsubsection @code{bfd_copy_private_bfd_data}
@strong{Synopsis}
@example
boolean bfd_copy_private_bfd_data(bfd *ibfd, bfd *obfd);
@end example
@strong{Description}@*
Copy private BFD information from the BFD @var{ibfd} to the 
the BFD @var{obfd}.  Return @code{true} on success, @code{false} on error.
Possible error returns are:

@itemize @bullet

@item
@code{bfd_error_no_memory} -
Not enough memory exists to create private data for @var{obfd}.
@end itemize
@example
#define bfd_copy_private_bfd_data(ibfd, obfd) \
     BFD_SEND (obfd, _bfd_copy_private_bfd_data, \
               (ibfd, obfd))
@end example

@findex bfd_merge_private_bfd_data
@subsubsection @code{bfd_merge_private_bfd_data}
@strong{Synopsis}
@example
boolean bfd_merge_private_bfd_data(bfd *ibfd, bfd *obfd);
@end example
@strong{Description}@*
Merge private BFD information from the BFD @var{ibfd} to the 
the output file BFD @var{obfd} when linking.  Return @code{true}
on success, @code{false} on error.  Possible error returns are:

@itemize @bullet

@item
@code{bfd_error_no_memory} -
Not enough memory exists to create private data for @var{obfd}.
@end itemize
@example
#define bfd_merge_private_bfd_data(ibfd, obfd) \
     BFD_SEND (obfd, _bfd_merge_private_bfd_data, \
               (ibfd, obfd))
@end example

@findex bfd_set_private_flags
@subsubsection @code{bfd_set_private_flags}
@strong{Synopsis}
@example
boolean bfd_set_private_flags(bfd *abfd, flagword flags);
@end example
@strong{Description}@*
Set private BFD flag information in the BFD @var{abfd}.
Return @code{true} on success, @code{false} on error.  Possible error
returns are:

@itemize @bullet

@item
@code{bfd_error_no_memory} -
Not enough memory exists to create private data for @var{obfd}.
@end itemize
@example
#define bfd_set_private_flags(abfd, flags) \
     BFD_SEND (abfd, _bfd_set_private_flags, \
               (abfd, flags))
@end example

@findex stuff
@subsubsection @code{stuff}
@strong{Description}@*
Stuff which should be documented:
@example
#define bfd_sizeof_headers(abfd, reloc) \
     BFD_SEND (abfd, _bfd_sizeof_headers, (abfd, reloc))

#define bfd_find_nearest_line(abfd, sec, syms, off, file, func, line) \
     BFD_SEND (abfd, _bfd_find_nearest_line,  (abfd, sec, syms, off, file, func, line))

        /* Do these three do anything useful at all, for any back end?  */
#define bfd_debug_info_start(abfd) \
        BFD_SEND (abfd, _bfd_debug_info_start, (abfd))

#define bfd_debug_info_end(abfd) \
        BFD_SEND (abfd, _bfd_debug_info_end, (abfd))

#define bfd_debug_info_accumulate(abfd, section) \
        BFD_SEND (abfd, _bfd_debug_info_accumulate, (abfd, section))


#define bfd_stat_arch_elt(abfd, stat) \
        BFD_SEND (abfd, _bfd_stat_arch_elt,(abfd, stat))

#define bfd_update_armap_timestamp(abfd) \
        BFD_SEND (abfd, _bfd_update_armap_timestamp, (abfd))

#define bfd_set_arch_mach(abfd, arch, mach)\
        BFD_SEND ( abfd, _bfd_set_arch_mach, (abfd, arch, mach))

#define bfd_relax_section(abfd, section, link_info, again) \
       BFD_SEND (abfd, _bfd_relax_section, (abfd, section, link_info, again))

#define bfd_link_hash_table_create(abfd) \
       BFD_SEND (abfd, _bfd_link_hash_table_create, (abfd))

#define bfd_link_add_symbols(abfd, info) \
       BFD_SEND (abfd, _bfd_link_add_symbols, (abfd, info))

#define bfd_final_link(abfd, info) \
       BFD_SEND (abfd, _bfd_final_link, (abfd, info))

#define bfd_free_cached_info(abfd) \
       BFD_SEND (abfd, _bfd_free_cached_info, (abfd))

#define bfd_get_dynamic_symtab_upper_bound(abfd) \
       BFD_SEND (abfd, _bfd_get_dynamic_symtab_upper_bound, (abfd))

#define bfd_print_private_bfd_data(abfd, file)\
       BFD_SEND (abfd, _bfd_print_private_bfd_data, (abfd, file))

#define bfd_canonicalize_dynamic_symtab(abfd, asymbols) \
       BFD_SEND (abfd, _bfd_canonicalize_dynamic_symtab, (abfd, asymbols))

#define bfd_get_dynamic_reloc_upper_bound(abfd) \
       BFD_SEND (abfd, _bfd_get_dynamic_reloc_upper_bound, (abfd))

#define bfd_canonicalize_dynamic_reloc(abfd, arels, asyms) \
       BFD_SEND (abfd, _bfd_canonicalize_dynamic_reloc, (abfd, arels, asyms))

extern bfd_byte *bfd_get_relocated_section_contents
       PARAMS ((bfd *, struct bfd_link_info *,
                 struct bfd_link_order *, bfd_byte *,
                 boolean, asymbol **));

@end example

