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@section Targets

@strong{Description}@*

Each port of BFD to a different machine requries the creation

of a target back end. All the back end provides to the root

part of BFD is a structure containing pointers to functions

which perform certain low level operations on files. BFD

translates the applications's requests through a pointer into

calls to the back end routines.

When a file is opened with @code{bfd_openr}, its format and

target are unknown. BFD uses various mechanisms to determine

how to interpret the file. The operations performed are:

@itemize @bullet

@item

Create a BFD by calling the internal routine

@code{_bfd_new_bfd}, then call @code{bfd_find_target} with the

target string supplied to @code{bfd_openr} and the new BFD pointer.

@item

If a null target string was provided to @code{bfd_find_target},

look up the environment variable @code{GNUTARGET} and use

that as the target string.

@item

If the target string is still @code{NULL}, or the target string is

@code{default}, then use the first item in the target vector

as the target type, and set @code{target_defaulted} in the BFD to

cause @code{bfd_check_format} to loop through all the targets.

@xref{bfd_target}.  @xref{Formats}.

@item

Otherwise, inspect the elements in the target vector

one by one, until a match on target name is found. When found,

use it.

@item

Otherwise return the error @code{bfd_error_invalid_target} to

@code{bfd_openr}.

@item

@code{bfd_openr} attempts to open the file using

@code{bfd_open_file}, and returns the BFD.

@end itemize

Once the BFD has been opened and the target selected, the file

format may be determined. This is done by calling

@code{bfd_check_format} on the BFD with a suggested format.

If @code{target_defaulted} has been set, each possible target

type is tried to see if it recognizes the specified format.

@code{bfd_check_format} returns @code{true} when the caller guesses right.

@menu

* bfd_target::

@end menu

@node bfd_target,  , Targets, Targets

@subsection bfd_target

@strong{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 @code{xvec}

member.

The macros below are used to dispatch to functions through the

@code{bfd_target} vector. They are used in a number of macros further

down in @file{bfd.h}, and are also used when calling various

routines by hand inside the BFD implementation.  The @var{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.

@example

#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

@end example

For operations which index on the BFD format:

@example

#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

@end example

This is the structure which defines the type of BFD this is.  The

@code{xvec} member of the struct @code{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!

@example

enum bfd_flavour @{

  bfd_target_unknown_flavour,

  bfd_target_aout_flavour,

  bfd_target_coff_flavour,

  bfd_target_ecoff_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_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

@};

enum bfd_endian @{ BFD_ENDIAN_BIG, BFD_ENDIAN_LITTLE, BFD_ENDIAN_UNKNOWN @};

 /* Forward declaration.  */

typedef struct bfd_link_info _bfd_link_info;

typedef struct bfd_target

@{

@end example

Identifies the kind of target, e.g., SunOS4, Ultrix, etc.

@example

  char *name;

@end example

The "flavour" of a back end is a general indication about the contents

of a file.

@example

  enum bfd_flavour flavour;

@end example

The order of bytes within the data area of a file.

@example

  enum bfd_endian byteorder;

@end example

The order of bytes within the header parts of a file.

@example

  enum bfd_endian header_byteorder;

@end example

A mask of all the flags which an executable may have set -

from the set @code{BFD_NO_FLAGS}, @code{HAS_RELOC}, ...@code{D_PAGED}.

@example

  flagword object_flags;

@end example

A mask of all the flags which a section may have set - from

the set @code{SEC_NO_FLAGS}, @code{SEC_ALLOC}, ...@code{SET_NEVER_LOAD}.

@example

  flagword section_flags;

@end example

The character normally found at the front of a symbol

(if any), perhaps `_'.

@example

  char symbol_leading_char;

@end example

The pad character for file names within an archive header.

@example

  char ar_pad_char;

@end example

The maximum number of characters in an archive header.

@example

  unsigned short ar_max_namelen;

@end example

Entries for byte swapping for data. These are different from the other

entry points, since they don't take a BFD asthe first argument.

Certain other handlers could do the same.

@example

  bfd_vma      (*bfd_getx64) PARAMS ((const bfd_byte *));

  bfd_signed_vma (*bfd_getx_signed_64) PARAMS ((const bfd_byte *));

  void         (*bfd_putx64) PARAMS ((bfd_vma, bfd_byte *));

  bfd_vma      (*bfd_getx32) PARAMS ((const bfd_byte *));

  bfd_signed_vma (*bfd_getx_signed_32) PARAMS ((const bfd_byte *));

  void         (*bfd_putx32) PARAMS ((bfd_vma, bfd_byte *));

  bfd_vma      (*bfd_getx16) PARAMS ((const bfd_byte *));

  bfd_signed_vma (*bfd_getx_signed_16) PARAMS ((const bfd_byte *));

  void         (*bfd_putx16) PARAMS ((bfd_vma, bfd_byte *));

@end example

Byte swapping for the headers

@example

  bfd_vma      (*bfd_h_getx64) PARAMS ((const bfd_byte *));

  bfd_signed_vma (*bfd_h_getx_signed_64) PARAMS ((const bfd_byte *));

  void         (*bfd_h_putx64) PARAMS ((bfd_vma, bfd_byte *));

  bfd_vma      (*bfd_h_getx32) PARAMS ((const bfd_byte *));

  bfd_signed_vma (*bfd_h_getx_signed_32) PARAMS ((const bfd_byte *));

  void         (*bfd_h_putx32) PARAMS ((bfd_vma, bfd_byte *));

  bfd_vma      (*bfd_h_getx16) PARAMS ((const bfd_byte *));

  bfd_signed_vma (*bfd_h_getx_signed_16) PARAMS ((const bfd_byte *));

  void         (*bfd_h_putx16) PARAMS ((bfd_vma, bfd_byte *));

@end example

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 @code{bfd_target *} or zero.

@example

  const struct bfd_target *(*_bfd_check_format[bfd_type_end]) PARAMS ((bfd *));

@end example

Set the format of a file being written.

@example

  boolean             (*_bfd_set_format[bfd_type_end]) PARAMS ((bfd *));

@end example

Write cached information into a file being written, at @code{bfd_close}.

@example

  boolean             (*_bfd_write_contents[bfd_type_end]) PARAMS ((bfd *));

@end example

The general target vector.  These vectors are initialized using the

BFD_JUMP_TABLE macros.

@example

   /* Generic entry points.  */

#define BFD_JUMP_TABLE_GENERIC(NAME)\

CAT(NAME,_close_and_cleanup),\

CAT(NAME,_bfd_free_cached_info),\

CAT(NAME,_new_section_hook),\

CAT(NAME,_get_section_contents),\

CAT(NAME,_get_section_contents_in_window)

   /* Called when the BFD is being closed to do any necessary cleanup.  */

  boolean       (*_close_and_cleanup) PARAMS ((bfd *));

   /* Ask the BFD to free all cached information.  */

  boolean (*_bfd_free_cached_info) PARAMS ((bfd *));

   /* Called when a new section is created.  */

  boolean       (*_new_section_hook) PARAMS ((bfd *, sec_ptr));

   /* Read the contents of a section.  */

  boolean       (*_bfd_get_section_contents) PARAMS ((bfd *, sec_ptr, PTR,

                                            file_ptr, bfd_size_type));

  boolean       (*_bfd_get_section_contents_in_window)

                          PARAMS ((bfd *, sec_ptr, bfd_window *,

                                   file_ptr, bfd_size_type));

   /* Entry points to copy private data.  */

#define BFD_JUMP_TABLE_COPY(NAME)\

CAT(NAME,_bfd_copy_private_bfd_data),\

CAT(NAME,_bfd_merge_private_bfd_data),\

CAT(NAME,_bfd_copy_private_section_data),\

CAT(NAME,_bfd_copy_private_symbol_data),\

CAT(NAME,_bfd_set_private_flags),\

CAT(NAME,_bfd_print_private_bfd_data)\

   /* Called to copy BFD general private data from one object file

     to another.  */

  boolean       (*_bfd_copy_private_bfd_data) PARAMS ((bfd *, bfd *));

   /* Called to merge BFD general private data from one object file

     to a common output file when linking.  */

  boolean       (*_bfd_merge_private_bfd_data) PARAMS ((bfd *, bfd *));

   /* Called to copy BFD private section data from one object file

     to another.  */

  boolean       (*_bfd_copy_private_section_data) PARAMS ((bfd *, sec_ptr,

                                                       bfd *, sec_ptr));

   /* Called to copy BFD private symbol data from one symbol

     to another.  */

  boolean       (*_bfd_copy_private_symbol_data) PARAMS ((bfd *, asymbol *,

                                                          bfd *, asymbol *));

   /* Called to set private backend flags */

  boolean       (*_bfd_set_private_flags) PARAMS ((bfd *, flagword));

   /* Called to print private BFD data */

  boolean       (*_bfd_print_private_bfd_data) PARAMS ((bfd *, PTR));

   /* Core file entry points.  */

#define BFD_JUMP_TABLE_CORE(NAME)\

CAT(NAME,_core_file_failing_command),\

CAT(NAME,_core_file_failing_signal),\

CAT(NAME,_core_file_matches_executable_p)

  char *   (*_core_file_failing_command) PARAMS ((bfd *));

  int      (*_core_file_failing_signal) PARAMS ((bfd *));

  boolean  (*_core_file_matches_executable_p) PARAMS ((bfd *, bfd *));

   /* Archive entry points.  */

#define BFD_JUMP_TABLE_ARCHIVE(NAME)\

CAT(NAME,_slurp_armap),\

CAT(NAME,_slurp_extended_name_table),\

CAT(NAME,_construct_extended_name_table),\

CAT(NAME,_truncate_arname),\

CAT(NAME,_write_armap),\

CAT(NAME,_read_ar_hdr),\

CAT(NAME,_openr_next_archived_file),\

CAT(NAME,_get_elt_at_index),\

CAT(NAME,_generic_stat_arch_elt),\

CAT(NAME,_update_armap_timestamp)

  boolean  (*_bfd_slurp_armap) PARAMS ((bfd *));

  boolean  (*_bfd_slurp_extended_name_table) PARAMS ((bfd *));

  boolean  (*_bfd_construct_extended_name_table)

             PARAMS ((bfd *, char **, bfd_size_type *, const char **));

  void     (*_bfd_truncate_arname) PARAMS ((bfd *, CONST char *, char *));

  boolean  (*write_armap) PARAMS ((bfd *arch,

                              unsigned int elength,

                              struct orl *map,

                              unsigned int orl_count,

                              int stridx));

  PTR (*_bfd_read_ar_hdr_fn) PARAMS ((bfd *));

  bfd *    (*openr_next_archived_file) PARAMS ((bfd *arch, bfd *prev));

#define bfd_get_elt_at_index(b,i) BFD_SEND(b, _bfd_get_elt_at_index, (b,i))

  bfd *    (*_bfd_get_elt_at_index) PARAMS ((bfd *, symindex));

  int      (*_bfd_stat_arch_elt) PARAMS ((bfd *, struct stat *));

  boolean  (*_bfd_update_armap_timestamp) PARAMS ((bfd *));

   /* Entry points used for symbols.  */

#define BFD_JUMP_TABLE_SYMBOLS(NAME)\

CAT(NAME,_get_symtab_upper_bound),\

CAT(NAME,_get_symtab),\

CAT(NAME,_make_empty_symbol),\

CAT(NAME,_print_symbol),\

CAT(NAME,_get_symbol_info),\

CAT(NAME,_bfd_is_local_label_name),\

CAT(NAME,_get_lineno),\

CAT(NAME,_find_nearest_line),\

CAT(NAME,_bfd_make_debug_symbol),\

CAT(NAME,_read_minisymbols),\

CAT(NAME,_minisymbol_to_symbol)

  long  (*_bfd_get_symtab_upper_bound) PARAMS ((bfd *));

  long  (*_bfd_canonicalize_symtab) PARAMS ((bfd *,

                                             struct symbol_cache_entry **));

  struct symbol_cache_entry  *

                (*_bfd_make_empty_symbol) PARAMS ((bfd *));

  void          (*_bfd_print_symbol) PARAMS ((bfd *, PTR,

                                      struct symbol_cache_entry *,

                                      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) PARAMS ((bfd *,

                                      struct symbol_cache_entry *,

                                      symbol_info *));

#define bfd_get_symbol_info(b,p,e) BFD_SEND(b, _bfd_get_symbol_info, (b,p,e))

  boolean       (*_bfd_is_local_label_name) PARAMS ((bfd *, const char *));

  alent *    (*_get_lineno) PARAMS ((bfd *, struct symbol_cache_entry *));

  boolean    (*_bfd_find_nearest_line) PARAMS ((bfd *abfd,

                    struct sec *section, struct symbol_cache_entry **symbols,

                    bfd_vma offset, CONST char **file, CONST char **func,

                    unsigned int *line));

  /* 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) PARAMS ((

       bfd *abfd,

       void *ptr,

       unsigned long size));

#define bfd_read_minisymbols(b, d, m, s) \

  BFD_SEND (b, _read_minisymbols, (b, d, m, s))

  long  (*_read_minisymbols) PARAMS ((bfd *, boolean, PTR *,

                                      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) PARAMS ((bfd *, boolean, const PTR,

                                             asymbol *));

   /* Routines for relocs.  */

#define BFD_JUMP_TABLE_RELOCS(NAME)\

CAT(NAME,_get_reloc_upper_bound),\

CAT(NAME,_canonicalize_reloc),\

CAT(NAME,_bfd_reloc_type_lookup)

  long  (*_get_reloc_upper_bound) PARAMS ((bfd *, sec_ptr));

  long  (*_bfd_canonicalize_reloc) PARAMS ((bfd *, sec_ptr, arelent **,

                                            struct symbol_cache_entry **));

   /* See documentation on reloc types.  */

  reloc_howto_type *

       (*reloc_type_lookup) PARAMS ((bfd *abfd,

                                     bfd_reloc_code_real_type code));

   /* Routines used when writing an object file.  */

#define BFD_JUMP_TABLE_WRITE(NAME)\

CAT(NAME,_set_arch_mach),\

CAT(NAME,_set_section_contents)

  boolean    (*_bfd_set_arch_mach) PARAMS ((bfd *, enum bfd_architecture,

                    unsigned long));

  boolean       (*_bfd_set_section_contents) PARAMS ((bfd *, sec_ptr, PTR,

                                            file_ptr, bfd_size_type));

   /* Routines used by the linker.  */

#define BFD_JUMP_TABLE_LINK(NAME)\

CAT(NAME,_sizeof_headers),\

CAT(NAME,_bfd_get_relocated_section_contents),\

CAT(NAME,_bfd_relax_section),\

CAT(NAME,_bfd_link_hash_table_create),\

CAT(NAME,_bfd_link_add_symbols),\

CAT(NAME,_bfd_final_link),\

CAT(NAME,_bfd_link_split_section),\

CAT(NAME,_bfd_gc_sections)

  int        (*_bfd_sizeof_headers) PARAMS ((bfd *, boolean));

  bfd_byte * (*_bfd_get_relocated_section_contents) PARAMS ((bfd *,

                    struct bfd_link_info *, struct bfd_link_order *,

                    bfd_byte *data, boolean relocateable,

                    struct symbol_cache_entry **));

  boolean    (*_bfd_relax_section) PARAMS ((bfd *, struct sec *,

                    struct bfd_link_info *, boolean *again));

   /* 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) PARAMS ((bfd *));

   /* Add symbols from this object file into the hash table.  */

  boolean (*_bfd_link_add_symbols) PARAMS ((bfd *, struct bfd_link_info *));

   /* Do a link based on the link_order structures attached to each

     section of the BFD.  */

  boolean (*_bfd_final_link) PARAMS ((bfd *, struct bfd_link_info *));

   /* Should this section be split up into smaller pieces during linking.  */

  boolean (*_bfd_link_split_section) PARAMS ((bfd *, struct sec *));

   /* Remove sections that are not referenced from the output.  */

  boolean (*_bfd_gc_sections) PARAMS ((bfd *, struct bfd_link_info *));

   /* Routines to handle dynamic symbols and relocs.  */

#define BFD_JUMP_TABLE_DYNAMIC(NAME)\

CAT(NAME,_get_dynamic_symtab_upper_bound),\

CAT(NAME,_canonicalize_dynamic_symtab),\

CAT(NAME,_get_dynamic_reloc_upper_bound),\

CAT(NAME,_canonicalize_dynamic_reloc)

   /* Get the amount of memory required to hold the dynamic symbols. */

  long  (*_bfd_get_dynamic_symtab_upper_bound) PARAMS ((bfd *));

   /* Read in the dynamic symbols.  */

  long  (*_bfd_canonicalize_dynamic_symtab)

    PARAMS ((bfd *, struct symbol_cache_entry **));

   /* Get the amount of memory required to hold the dynamic relocs.  */

  long  (*_bfd_get_dynamic_reloc_upper_bound) PARAMS ((bfd *));

   /* Read in the dynamic relocs.  */

  long  (*_bfd_canonicalize_dynamic_reloc)

    PARAMS ((bfd *, arelent **, struct symbol_cache_entry **));

@end example

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.

@example

  /* Opposite endian version of this target.  */

 const struct bfd_target * alternative_target;

@end example

Data for use by back-end routines, which isn't generic enough to belong

in this structure.

@example

 PTR backend_data;

@} bfd_target;

@end example

@findex bfd_set_default_target

@subsubsection @code{bfd_set_default_target}

@strong{Synopsis}

@example

boolean bfd_set_default_target (const char *name);

@end example

@strong{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.

@findex bfd_find_target

@subsubsection @code{bfd_find_target}

@strong{Synopsis}

@example

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

@end example

@strong{Description}@*

Return a pointer to the transfer vector for the object target

named @var{target_name}.  If @var{target_name} is @code{NULL}, choose the

one in the environment variable @code{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.  This causes @code{bfd_check_format} to loop over all the

targets to find the one that matches the file being read.

@findex bfd_target_list

@subsubsection @code{bfd_target_list}

@strong{Synopsis}

@example

const char **bfd_target_list(void);

@end example

@strong{Description}@*

Return a freshly malloced NULL-terminated

vector of the names of all the valid BFD targets. Do not

modify the names.

@findex bfd_seach_for_target

@subsubsection @code{bfd_seach_for_target}

@strong{Synopsis}

@example

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

@end example

@strong{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 @var{search_func}.  The

parameter @var{data} is passed, unexamined, to the search

function.