BFD front end

Go forward to BFD back ends
Go backward to Overview
Go up to Top
Go to the top op bfd

BFD Front End

`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.
     struct bfd
       /* A unique identifier of the BFD  */
       unsigned int id;
       /* 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;
       /* Is the file descriptor being cached?  That is, can it be closed as
          needed, and re-opened when accessed later?  */
       bfd_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.  */
       bfd_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...  */
       ufile_ptr where;
       /* ... and here: (``once'' means at least once).  */
       bfd_boolean opened_once;
       /* Set if we have a locally maintained mtime value, rather than
          getting it from the file each time.  */
       bfd_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 with which the BFD was opened.  */
       enum bfd_direction
           no_direction = 0,
           read_direction = 1,
           write_direction = 2,
           both_direction = 3
       /* 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.  */
       ufile_ptr origin;
       /* Remember when output has begun, to stop strange things
          from happening.  */
       bfd_boolean output_has_begun;
       /* A hash table for section names.  */
       struct bfd_hash_table section_htab;
       /* Pointer to linked list of sections.  */
       struct bfd_section *sections;
       /* The place where we add to the section list.  */
       struct bfd_section **section_tail;
       /* 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 bfd_symbol  **outsymbols;
       /* 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 *next;            /* The next BFD in the archive.  */
       struct bfd *archive_head;    /* The first BFD in the archive.  */
       bfd_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.  */
           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 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 bfd_pef_data_struct *pef_data;
           struct bfd_pef_xlib_data_struct *pef_xlib_data;
           struct bfd_sym_data_struct *sym_data;
           void *any;
       /* 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;

Error reporting

Most BFD functions return nonzero on success (check their individual
documentation for precise semantics).  On an error, they call
`bfd_set_error' to set an error condition that callers can check by
calling `bfd_get_error'.  If that returns `bfd_error_system_call', then
check `errno'.
   The easiest way to report a BFD error to the user is to use

Type `bfd_error_type'

The values returned by `bfd_get_error' are defined by the enumerated
type `bfd_error_type'.
     typedef enum bfd_error
       bfd_error_no_error = 0,


     bfd_error_type bfd_get_error (void);
Return the current BFD error condition.


     void bfd_set_error (bfd_error_type error_tag);
Set the BFD error condition to be ERROR_TAG.


     const char *bfd_errmsg (bfd_error_type error_tag);
Return a string describing the error ERROR_TAG, or the system error if
ERROR_TAG is `bfd_error_system_call'.


     void bfd_perror (const char *message);
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 MESSAGE is non-NULL and non-empty, the error
string printed is preceded by MESSAGE, a colon, and a space.  It is
followed by a newline.

BFD error handler

Some BFD functions want to print messages describing the problem.  They
call a BFD error handler function.  This function may be overridden by
the program.
   The BFD error handler acts like printf.
     typedef void (*bfd_error_handler_type) (const char *, ...);


     bfd_error_handler_type bfd_set_error_handler (bfd_error_handler_type);
Set the BFD error handler function.  Returns the previous function.


     void bfd_set_error_program_name (const char *);
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.


     bfd_error_handler_type bfd_get_error_handler (void);
Return the BFD error handler function.


     const char *bfd_archive_filename (bfd *);
For a BFD that is a component of an archive, returns a string with both
the archive name and file name.  For other BFDs, just returns the file



     long bfd_get_reloc_upper_bound (bfd *abfd, asection *sect);
Return the number of bytes required to store the relocation information
associated with section SECT attached to bfd ABFD.  If an error occurs,
return -1.


     long bfd_canonicalize_reloc
        (bfd *abfd, asection *sec, arelent **loc, asymbol **syms);
Call the back end associated with the open BFD ABFD and translate the
external form of the relocation information attached to SEC into the
internal canonical form.  Place the table into memory at LOC, which has
been preallocated, usually by a call to `bfd_get_reloc_upper_bound'.
Returns the number of relocs, or -1 on error.
   The SYMS table is also needed for horrible internal magic reasons.


     void bfd_set_reloc
        (bfd *abfd, asection *sec, arelent **rel, unsigned int count);
Set the relocation pointer and count within section SEC to the values
REL and COUNT.  The argument ABFD is ignored.


     bfd_boolean bfd_set_file_flags (bfd *abfd, flagword flags);
Set the flag word in the BFD ABFD to the value FLAGS.
   Possible errors are:
   * `bfd_error_wrong_format' - The target bfd was not of object format.
   * `bfd_error_invalid_operation' - The target bfd was open for
   * `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 `D_PAGED' bit on a BFD format which does not
     support demand paging.


     int bfd_get_arch_size (bfd *abfd);
Returns the architecture address size, in bits, as determined by the
object file's format.  For ELF, this information is included in the
Returns the arch size in bits if known, `-1' otherwise.


     int bfd_get_sign_extend_vma (bfd *abfd);
Indicates if the target architecture "naturally" sign extends an
address.  Some architectures implicitly sign extend address values when
they are converted to types larger than the size of an address.  For
instance, bfd_get_start_address() will return an address sign extended
to fill a bfd_vma when this is the case.
Returns `1' if the target architecture is known to sign extend
addresses, `0' if the target architecture is known to not sign extend
addresses, and `-1' otherwise.


     bfd_boolean bfd_set_start_address (bfd *abfd, bfd_vma vma);
Make VMA the entry point of output BFD ABFD.
Returns `TRUE' on success, `FALSE' otherwise.


     unsigned int bfd_get_gp_size (bfd *abfd);
Return the maximum size of objects to be optimized using the GP
register under MIPS ECOFF.  This is typically set by the `-G' argument
to the compiler, assembler or linker.


     void bfd_set_gp_size (bfd *abfd, unsigned int i);
Set the maximum size of objects to be optimized using the GP register
under ECOFF or MIPS ELF.  This is typically set by the `-G' argument to
the compiler, assembler or linker.


     bfd_vma bfd_scan_vma (const char *string, const char **end, int base);
Convert, like `strtoul', a numerical expression STRING into a `bfd_vma'
integer, and return that integer.  (Though without as many bells and
whistles as `strtoul'.)  The expression is assumed to be unsigned
(i.e., positive).  If given a 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.
   If the value would overflow, the maximum `bfd_vma' value is returned.


     bfd_boolean bfd_copy_private_header_data (bfd *ibfd, bfd *obfd);
Copy private BFD header information from the BFD IBFD to the the BFD
OBFD.  This copies information that may require sections to exist, but
does not require symbol tables.  Return `true' on success, `false' on
error.  Possible error returns are:
   * `bfd_error_no_memory' - Not enough memory exists to create private
     data for OBFD.
     #define bfd_copy_private_header_data(ibfd, obfd) \
          BFD_SEND (obfd, _bfd_copy_private_header_data, \
                    (ibfd, obfd))


     bfd_boolean bfd_copy_private_bfd_data (bfd *ibfd, bfd *obfd);
Copy private BFD information from the BFD IBFD to the the BFD OBFD.
Return `TRUE' on success, `FALSE' on error.  Possible error returns are:
   * `bfd_error_no_memory' - Not enough memory exists to create private
     data for OBFD.
     #define bfd_copy_private_bfd_data(ibfd, obfd) \
          BFD_SEND (obfd, _bfd_copy_private_bfd_data, \
                    (ibfd, obfd))


     bfd_boolean bfd_merge_private_bfd_data (bfd *ibfd, bfd *obfd);
Merge private BFD information from the BFD IBFD to the the output file
BFD OBFD when linking.  Return `TRUE' on success, `FALSE' on error.
Possible error returns are:
   * `bfd_error_no_memory' - Not enough memory exists to create private
     data for OBFD.
     #define bfd_merge_private_bfd_data(ibfd, obfd) \
          BFD_SEND (obfd, _bfd_merge_private_bfd_data, \
                    (ibfd, obfd))


     bfd_boolean bfd_set_private_flags (bfd *abfd, flagword flags);
Set private BFD flag information in the BFD ABFD.  Return `TRUE' on
success, `FALSE' on error.  Possible error returns are:
   * `bfd_error_no_memory' - Not enough memory exists to create private
     data for OBFD.
     #define bfd_set_private_flags(abfd, flags) \
          BFD_SEND (abfd, _bfd_set_private_flags, (abfd, flags))

`Other functions'

The following functions exist but have not yet been documented.
     #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))
     #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_gc_sections(abfd, link_info) \
            BFD_SEND (abfd, _bfd_gc_sections, (abfd, link_info))
     #define bfd_merge_sections(abfd, link_info) \
            BFD_SEND (abfd, _bfd_merge_sections, (abfd, link_info))
     #define bfd_is_group_section(abfd, sec) \
            BFD_SEND (abfd, _bfd_is_group_section, (abfd, sec))
     #define bfd_discard_group(abfd, sec) \
            BFD_SEND (abfd, _bfd_discard_group, (abfd, sec))
     #define bfd_link_hash_table_create(abfd) \
            BFD_SEND (abfd, _bfd_link_hash_table_create, (abfd))
     #define bfd_link_hash_table_free(abfd, hash) \
            BFD_SEND (abfd, _bfd_link_hash_table_free, (hash))
     #define bfd_link_add_symbols(abfd, info) \
            BFD_SEND (abfd, _bfd_link_add_symbols, (abfd, info))
     #define bfd_link_just_syms(sec, info) \
            BFD_SEND (abfd, _bfd_link_just_syms, (sec, 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_synthetic_symtab(abfd, dynsyms, ret) \
            BFD_SEND (abfd, _bfd_get_synthetic_symtab, (abfd, dynsyms, ret))
     #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
       (bfd *, struct bfd_link_info *, struct bfd_link_order *, bfd_byte *,
        bfd_boolean, asymbol **);


     bfd_boolean bfd_alt_mach_code (bfd *abfd, int alternative);
When more than one machine code number is available for the same
machine type, this function can be used to switch between the preferred
one (alternative == 0) and any others.  Currently, only ELF supports
this feature, with up to two alternate machine codes.
     struct bfd_preserve
       void *marker;
       void *tdata;
       flagword flags;
       const struct bfd_arch_info *arch_info;
       struct bfd_section *sections;
       struct bfd_section **section_tail;
       unsigned int section_count;
       struct bfd_hash_table section_htab;


     bfd_boolean bfd_preserve_save (bfd *, struct bfd_preserve *);
When testing an object for compatibility with a particular target
back-end, the back-end object_p function needs to set up certain fields
in the bfd on successfully recognizing the object.  This typically
happens in a piecemeal fashion, with failures possible at many points.
On failure, the bfd is supposed to be restored to its initial state,
which is virtually impossible.  However, restoring a subset of the bfd
state works in practice.  This function stores the subset and
reinitializes the bfd.


     void bfd_preserve_restore (bfd *, struct bfd_preserve *);
This function restores bfd state saved by bfd_preserve_save.  If MARKER
is non-NULL in struct bfd_preserve then that block and all subsequently
bfd_alloc'd memory is freed.


     void bfd_preserve_finish (bfd *, struct bfd_preserve *);
This function should be called when the bfd state saved by
bfd_preserve_save is no longer needed.  ie. when the back-end object_p
function returns with success.


     char *bfd_get_section_ident (asection *sec);
This function returns "section name[group name]" in a malloced buffer
if SEC is a member of an ELF section group and returns NULL otherwise.
The caller should free the non-NULL return after use.

`struct bfd_iovec'

The `struct bfd_iovec' contains the internal file I/O class.  Each
`BFD' has an instance of this class and all file I/O is routed through
it (it is assumed that the instance implements all methods listed
     struct bfd_iovec
       /* To avoid problems with macros, a "b" rather than "f"
          prefix is prepended to each method name.  */
       /* Attempt to read/write NBYTES on ABFD's IOSTREAM storing/fetching
          bytes starting at PTR.  Return the number of bytes actually
          transfered (a read past end-of-file returns less than NBYTES),
          or -1 (setting `bfd_error') if an error occurs.  */
       file_ptr (*bread) (struct bfd *abfd, void *ptr, file_ptr nbytes);
       file_ptr (*bwrite) (struct bfd *abfd, const void *ptr,
                           file_ptr nbytes);
       /* Return the current IOSTREAM file offset, or -1 (setting `bfd_error'
          if an error occurs.  */
       file_ptr (*btell) (struct bfd *abfd);
       /* For the following, on successful completion a value of 0 is returned.
          Otherwise, a value of -1 is returned (and  `bfd_error' is set).  */
       int (*bseek) (struct bfd *abfd, file_ptr offset, int whence);
       int (*bclose) (struct bfd *abfd);
       int (*bflush) (struct bfd *abfd);
       int (*bstat) (struct bfd *abfd, struct stat *sb);


     long bfd_get_mtime (bfd *abfd);
Return the file modification time (as read from the file system, or
from the archive header for archive members).


     long bfd_get_size (bfd *abfd);
Return the file size (as read from file system) for the file associated
with BFD 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 `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 question, "is
the size reasonable?".