bfd/doc/bfdt.texi

@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
@{
  /* 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;

  /* 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;

  /* 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
    @}
  direction;

  /* Format_specific flags.  */
  flagword flags;

  /* 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

  /* The sections in this BFD specify a memory page.  */
#define HAS_LOAD_PAGE 0x1000

  /* This BFD has been created by the linker and doesn't correspond
     to any input file.  */
#define BFD_LINKER_CREATED 0x2000

  /* 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;

  /* 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).
     Also used by the linker to cache input BFD symbols.  */
  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 *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.  */

  /* 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 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;
    @}
  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;

  /* 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;
@};

@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_wrong_object_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_on_input,
  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}.
If @var{error_tag} is bfd_error_on_input, then this function
takes two more parameters, the input bfd where the error
occurred, and the bfd_error_type error.

@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 overridden by the program.

The BFD error handler acts like printf.


@example

typedef void (*bfd_error_handler_type) (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 Miscellaneous


@subsection Miscellaneous functions


@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
bfd_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_get_arch_size
@subsubsection @code{bfd_get_arch_size}
@strong{Synopsis}
@example
int bfd_get_arch_size (bfd *abfd);
@end example
@strong{Description}@*
Returns the architecture address size, in bits, as determined
by the object file's format.  For ELF, this information is
included in the header.

@strong{Returns}@*
Returns the arch size in bits if known, @code{-1} otherwise.

@findex bfd_get_sign_extend_vma
@subsubsection @code{bfd_get_sign_extend_vma}
@strong{Synopsis}
@example
int bfd_get_sign_extend_vma (bfd *abfd);
@end example
@strong{Description}@*
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.

@strong{Returns}@*
Returns @code{1} if the target architecture is known to sign
extend addresses, @code{0} if the target architecture is known to
not sign extend addresses, and @code{-1} otherwise.

@findex bfd_set_start_address
@subsubsection @code{bfd_set_start_address}
@strong{Synopsis}
@example
bfd_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_gp_size
@subsubsection @code{bfd_get_gp_size}
@strong{Synopsis}
@example
unsigned 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, unsigned 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.

If the value would overflow, the maximum @code{bfd_vma} value is
returned.

@findex bfd_copy_private_header_data
@subsubsection @code{bfd_copy_private_header_data}
@strong{Synopsis}
@example
bfd_boolean bfd_copy_private_header_data (bfd *ibfd, bfd *obfd);
@end example
@strong{Description}@*
Copy private BFD header information from the BFD @var{ibfd} to the
the BFD @var{obfd}.  This copies information that may require
sections to exist, but does not require symbol tables.  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_header_data(ibfd, obfd) \
     BFD_SEND (obfd, _bfd_copy_private_header_data, \
               (ibfd, obfd))
@end example

@findex bfd_copy_private_bfd_data
@subsubsection @code{bfd_copy_private_bfd_data}
@strong{Synopsis}
@example
bfd_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
bfd_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
bfd_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 Other functions
@subsubsection @code{Other functions}
@strong{Description}@*
The following functions exist but have not yet been documented.
@example
#define bfd_sizeof_headers(abfd, info) \
       BFD_SEND (abfd, _bfd_sizeof_headers, (abfd, info))

#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_find_line(abfd, syms, sym, file, line) \
       BFD_SEND (abfd, _bfd_find_line, \
                 (abfd, syms, sym, file, line))

#define bfd_find_inliner_info(abfd, file, func, line) \
       BFD_SEND (abfd, _bfd_find_inliner_info, \
                 (abfd, 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(abfd, 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, count, syms, dyncount, dynsyms, ret) \
       BFD_SEND (abfd, _bfd_get_synthetic_symtab, (abfd, count, syms, \
                                                   dyncount, 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 **);

@end example

@findex bfd_alt_mach_code
@subsubsection @code{bfd_alt_mach_code}
@strong{Synopsis}
@example
bfd_boolean bfd_alt_mach_code (bfd *abfd, int alternative);
@end example
@strong{Description}@*
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.


@example
struct bfd_preserve
@{
  void *marker;
  void *tdata;
  flagword flags;
  const struct bfd_arch_info *arch_info;
  struct bfd_section *sections;
  struct bfd_section *section_last;
  unsigned int section_count;
  struct bfd_hash_table section_htab;
@};

@end example
@findex bfd_preserve_save
@subsubsection @code{bfd_preserve_save}
@strong{Synopsis}
@example
bfd_boolean bfd_preserve_save (bfd *, struct bfd_preserve *);
@end example
@strong{Description}@*
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.

@findex bfd_preserve_restore
@subsubsection @code{bfd_preserve_restore}
@strong{Synopsis}
@example
void bfd_preserve_restore (bfd *, struct bfd_preserve *);
@end example
@strong{Description}@*
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.

@findex bfd_preserve_finish
@subsubsection @code{bfd_preserve_finish}
@strong{Synopsis}
@example
void bfd_preserve_finish (bfd *, struct bfd_preserve *);
@end example
@strong{Description}@*
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.

@findex bfd_emul_get_maxpagesize
@subsubsection @code{bfd_emul_get_maxpagesize}
@strong{Synopsis}
@example
bfd_vma bfd_emul_get_maxpagesize (const char *);
@end example
@strong{Description}@*
Returns the maximum page size, in bytes, as determined by
emulation.

@strong{Returns}@*
Returns the maximum page size in bytes for ELF, abort
otherwise.

@findex bfd_emul_set_maxpagesize
@subsubsection @code{bfd_emul_set_maxpagesize}
@strong{Synopsis}
@example
void bfd_emul_set_maxpagesize (const char *, bfd_vma);
@end example
@strong{Description}@*
For ELF, set the maximum page size for the emulation.  It is
a no-op for other formats.

@findex bfd_emul_get_commonpagesize
@subsubsection @code{bfd_emul_get_commonpagesize}
@strong{Synopsis}
@example
bfd_vma bfd_emul_get_commonpagesize (const char *);
@end example
@strong{Description}@*
Returns the common page size, in bytes, as determined by
emulation.

@strong{Returns}@*
Returns the common page size in bytes for ELF, abort otherwise.

@findex bfd_emul_set_commonpagesize
@subsubsection @code{bfd_emul_set_commonpagesize}
@strong{Synopsis}
@example
void bfd_emul_set_commonpagesize (const char *, bfd_vma);
@end example
@strong{Description}@*
For ELF, set the common page size for the emulation.  It is
a no-op for other formats.

@findex bfd_demangle
@subsubsection @code{bfd_demangle}
@strong{Synopsis}
@example
char *bfd_demangle (bfd *, const char *, int);
@end example
@strong{Description}@*
Wrapper around cplus_demangle.  Strips leading underscores and
other such chars that would otherwise confuse the demangler.
If passed a g++ v3 ABI mangled name, returns a buffer allocated
with malloc holding the demangled name.  Returns NULL otherwise
and on memory alloc failure.