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This is bfd.info, produced by makeinfo version 4.1 from bfd.texinfo.

START-INFO-DIR-ENTRY

* Bfd: (bfd).                   The Binary File Descriptor library.

END-INFO-DIR-ENTRY

   This file documents the BFD library.

   Copyright (C) 1991, 2000, 2001 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document

     under the terms of the GNU Free Documentation License, Version 1.1

     or any later version published by the Free Software Foundation;

   with no Invariant Sections, with no Front-Cover Texts, and with no

    Back-Cover Texts.  A copy of the license is included in the

section entitled "GNU Free Documentation License".

File: bfd.info,  Node: typedef asection,  Next: section prototypes,  Prev: Section Output,  Up: Sections

typedef asection

----------------

   Here is the section structure:

     /* This structure is used for a comdat section, as in PE.  A comdat

        section is associated with a particular symbol.  When the linker

        sees a comdat section, it keeps only one of the sections with a

        given name and associated with a given symbol.  */

     struct bfd_comdat_info

     {

       /* The name of the symbol associated with a comdat section.  */

       const char *name;

       /* The local symbol table index of the symbol associated with a

          comdat section.  This is only meaningful to the object file format

          specific code; it is not an index into the list returned by

          bfd_canonicalize_symtab.  */

       long symbol;

     };

     typedef struct sec

     {

       /* The name of the section; the name isn't a copy, the pointer is

          the same as that passed to bfd_make_section.  */

       const char *name;

       /* A unique sequence number.  */

       int id;

       /* Which section in the bfd; 0..n-1 as sections are created in a bfd.  */

       int index;

       /* The next section in the list belonging to the BFD, or NULL.  */

       struct sec *next;

       /* The field flags contains attributes of the section. Some

          flags are read in from the object file, and some are

          synthesized from other information.  */

       flagword flags;

     #define SEC_NO_FLAGS   0x000

       /* Tells the OS to allocate space for this section when loading.

          This is clear for a section containing debug information only.  */

     #define SEC_ALLOC      0x001

       /* Tells the OS to load the section from the file when loading.

          This is clear for a .bss section.  */

     #define SEC_LOAD       0x002

       /* The section contains data still to be relocated, so there is

          some relocation information too.  */

     #define SEC_RELOC      0x004

       /* ELF reserves 4 processor specific bits and 8 operating system

          specific bits in sh_flags; at present we can get away with just

          one in communicating between the assembler and BFD, but this

          isn't a good long-term solution.  */

     #define SEC_ARCH_BIT_0 0x008

       /* A signal to the OS that the section contains read only data.  */

     #define SEC_READONLY   0x010

       /* The section contains code only.  */

     #define SEC_CODE       0x020

       /* The section contains data only.  */

     #define SEC_DATA       0x040

       /* The section will reside in ROM.  */

     #define SEC_ROM        0x080

       /* The section contains constructor information. This section

          type is used by the linker to create lists of constructors and

          destructors used by `g++'. When a back end sees a symbol

          which should be used in a constructor list, it creates a new

          section for the type of name (e.g., `__CTOR_LIST__'), attaches

          the symbol to it, and builds a relocation. To build the lists

          of constructors, all the linker has to do is catenate all the

          sections called `__CTOR_LIST__' and relocate the data

          contained within - exactly the operations it would peform on

          standard data.  */

     #define SEC_CONSTRUCTOR 0x100

       /* The section has contents - a data section could be

          `SEC_ALLOC' | `SEC_HAS_CONTENTS'; a debug section could be

          `SEC_HAS_CONTENTS'  */

     #define SEC_HAS_CONTENTS 0x200

       /* An instruction to the linker to not output the section

          even if it has information which would normally be written.  */

     #define SEC_NEVER_LOAD 0x400

       /* The section is a COFF shared library section.  This flag is

          only for the linker.  If this type of section appears in

          the input file, the linker must copy it to the output file

          without changing the vma or size.  FIXME: Although this

          was originally intended to be general, it really is COFF

          specific (and the flag was renamed to indicate this).  It

          might be cleaner to have some more general mechanism to

          allow the back end to control what the linker does with

          sections.  */

     #define SEC_COFF_SHARED_LIBRARY 0x800

       /* The section contains thread local data.  */

     #define SEC_THREAD_LOCAL 0x1000

       /* The section has GOT references.  This flag is only for the

          linker, and is currently only used by the elf32-hppa back end.

          It will be set if global offset table references were detected

          in this section, which indicate to the linker that the section

          contains PIC code, and must be handled specially when doing a

          static link.  */

     #define SEC_HAS_GOT_REF 0x4000

       /* The section contains common symbols (symbols may be defined

          multiple times, the value of a symbol is the amount of

          space it requires, and the largest symbol value is the one

          used).  Most targets have exactly one of these (which we

          translate to bfd_com_section_ptr), but ECOFF has two.  */

     #define SEC_IS_COMMON 0x8000

       /* The section contains only debugging information.  For

          example, this is set for ELF .debug and .stab sections.

          strip tests this flag to see if a section can be

          discarded.  */

     #define SEC_DEBUGGING 0x10000

       /* The contents of this section are held in memory pointed to

          by the contents field.  This is checked by bfd_get_section_contents,

          and the data is retrieved from memory if appropriate.  */

     #define SEC_IN_MEMORY 0x20000

       /* The contents of this section are to be excluded by the

          linker for executable and shared objects unless those

          objects are to be further relocated.  */

     #define SEC_EXCLUDE 0x40000

       /* The contents of this section are to be sorted based on the sum of

          the symbol and addend values specified by the associated relocation

          entries.  Entries without associated relocation entries will be

          appended to the end of the section in an unspecified order.  */

     #define SEC_SORT_ENTRIES 0x80000

       /* When linking, duplicate sections of the same name should be

          discarded, rather than being combined into a single section as

          is usually done.  This is similar to how common symbols are

          handled.  See SEC_LINK_DUPLICATES below.  */

     #define SEC_LINK_ONCE 0x100000

       /* If SEC_LINK_ONCE is set, this bitfield describes how the linker

          should handle duplicate sections.  */

     #define SEC_LINK_DUPLICATES 0x600000

       /* This value for SEC_LINK_DUPLICATES means that duplicate

          sections with the same name should simply be discarded.  */

     #define SEC_LINK_DUPLICATES_DISCARD 0x0

       /* This value for SEC_LINK_DUPLICATES means that the linker

          should warn if there are any duplicate sections, although

          it should still only link one copy.  */

     #define SEC_LINK_DUPLICATES_ONE_ONLY 0x200000

       /* This value for SEC_LINK_DUPLICATES means that the linker

          should warn if any duplicate sections are a different size.  */

     #define SEC_LINK_DUPLICATES_SAME_SIZE 0x400000

       /* This value for SEC_LINK_DUPLICATES means that the linker

          should warn if any duplicate sections contain different

          contents.  */

     #define SEC_LINK_DUPLICATES_SAME_CONTENTS 0x600000

       /* This section was created by the linker as part of dynamic

          relocation or other arcane processing.  It is skipped when

          going through the first-pass output, trusting that someone

          else up the line will take care of it later.  */

     #define SEC_LINKER_CREATED 0x800000

       /* This section should not be subject to garbage collection.  */

     #define SEC_KEEP 0x1000000

       /* This section contains "short" data, and should be placed

          "near" the GP.  */

     #define SEC_SMALL_DATA 0x2000000

       /* This section contains data which may be shared with other

          executables or shared objects.  */

     #define SEC_SHARED 0x4000000

       /* When a section with this flag is being linked, then if the size of

          the input section is less than a page, it should not cross a page

          boundary.  If the size of the input section is one page or more, it

          should be aligned on a page boundary.  */

     #define SEC_BLOCK 0x8000000

       /* Conditionally link this section; do not link if there are no

          references found to any symbol in the section.  */

     #define SEC_CLINK 0x10000000

       /* Attempt to merge identical entities in the section.

          Entity size is given in the entsize field.  */

     #define SEC_MERGE 0x20000000

       /* If given with SEC_MERGE, entities to merge are zero terminated

          strings where entsize specifies character size instead of fixed

          size entries.  */

     #define SEC_STRINGS 0x40000000

       /* This section contains data about section groups.  */

     #define SEC_GROUP 0x80000000

       /*  End of section flags.  */

       /* Some internal packed boolean fields.  */

       /* See the vma field.  */

       unsigned int user_set_vma : 1;

       /* Whether relocations have been processed.  */

       unsigned int reloc_done : 1;

       /* A mark flag used by some of the linker backends.  */

       unsigned int linker_mark : 1;

       /* Another mark flag used by some of the linker backends.  Set for

          output sections that have an input section.  */

       unsigned int linker_has_input : 1;

       /* A mark flag used by some linker backends for garbage collection.  */

       unsigned int gc_mark : 1;

       /* Used by the ELF code to mark sections which have been allocated

          to segments.  */

       unsigned int segment_mark : 1;

       /* End of internal packed boolean fields.  */

       /*  The virtual memory address of the section - where it will be

           at run time.  The symbols are relocated against this.  The

           user_set_vma flag is maintained by bfd; if it's not set, the

           backend can assign addresses (for example, in `a.out', where

           the default address for `.data' is dependent on the specific

           target and various flags).  */

       bfd_vma vma;

       /*  The load address of the section - where it would be in a

           rom image; really only used for writing section header

           information.  */

       bfd_vma lma;

       /* The size of the section in octets, as it will be output.

          Contains a value even if the section has no contents (e.g., the

          size of `.bss').  This will be filled in after relocation.  */

       bfd_size_type _cooked_size;

       /* The original size on disk of the section, in octets.  Normally this

          value is the same as the size, but if some relaxing has

          been done, then this value will be bigger.  */

       bfd_size_type _raw_size;

       /* If this section is going to be output, then this value is the

          offset in *bytes* into the output section of the first byte in the

          input section (byte ==> smallest addressable unit on the

          target).  In most cases, if this was going to start at the

          100th octet (8-bit quantity) in the output section, this value

          would be 100.  However, if the target byte size is 16 bits

          (bfd_octets_per_byte is "2"), this value would be 50.  */

       bfd_vma output_offset;

       /* The output section through which to map on output.  */

       struct sec *output_section;

       /* The alignment requirement of the section, as an exponent of 2 -

          e.g., 3 aligns to 2^3 (or 8).  */

       unsigned int alignment_power;

       /* If an input section, a pointer to a vector of relocation

          records for the data in this section.  */

       struct reloc_cache_entry *relocation;

       /* If an output section, a pointer to a vector of pointers to

          relocation records for the data in this section.  */

       struct reloc_cache_entry **orelocation;

       /* The number of relocation records in one of the above.  */

       unsigned reloc_count;

       /* Information below is back end specific - and not always used

          or updated.  */

       /* File position of section data.  */

       file_ptr filepos;

       /* File position of relocation info.  */

       file_ptr rel_filepos;

       /* File position of line data.  */

       file_ptr line_filepos;

       /* Pointer to data for applications.  */

       PTR userdata;

       /* If the SEC_IN_MEMORY flag is set, this points to the actual

          contents.  */

       unsigned char *contents;

       /* Attached line number information.  */

       alent *lineno;

       /* Number of line number records.  */

       unsigned int lineno_count;

       /* Entity size for merging purposes.  */

       unsigned int entsize;

       /* Optional information about a COMDAT entry; NULL if not COMDAT.  */

       struct bfd_comdat_info *comdat;

       /* When a section is being output, this value changes as more

          linenumbers are written out.  */

       file_ptr moving_line_filepos;

       /* What the section number is in the target world.  */

       int target_index;

       PTR used_by_bfd;

       /* If this is a constructor section then here is a list of the

          relocations created to relocate items within it.  */

       struct relent_chain *constructor_chain;

       /* The BFD which owns the section.  */

       bfd *owner;

       /* A symbol which points at this section only.  */

       struct symbol_cache_entry *symbol;

       struct symbol_cache_entry **symbol_ptr_ptr;

       struct bfd_link_order *link_order_head;

       struct bfd_link_order *link_order_tail;

     } asection;

     /* These sections are global, and are managed by BFD.  The application

        and target back end are not permitted to change the values in

        these sections.  New code should use the section_ptr macros rather

        than referring directly to the const sections.  The const sections

        may eventually vanish.  */

     #define BFD_ABS_SECTION_NAME "*ABS*"

     #define BFD_UND_SECTION_NAME "*UND*"

     #define BFD_COM_SECTION_NAME "*COM*"

     #define BFD_IND_SECTION_NAME "*IND*"

     /* The absolute section.  */

     extern const asection bfd_abs_section;

     #define bfd_abs_section_ptr ((asection *) &bfd_abs_section)

     #define bfd_is_abs_section(sec) ((sec) == bfd_abs_section_ptr)

     /* Pointer to the undefined section.  */

     extern const asection bfd_und_section;

     #define bfd_und_section_ptr ((asection *) &bfd_und_section)

     #define bfd_is_und_section(sec) ((sec) == bfd_und_section_ptr)

     /* Pointer to the common section.  */

     extern const asection bfd_com_section;

     #define bfd_com_section_ptr ((asection *) &bfd_com_section)

     /* Pointer to the indirect section.  */

     extern const asection bfd_ind_section;

     #define bfd_ind_section_ptr ((asection *) &bfd_ind_section)

     #define bfd_is_ind_section(sec) ((sec) == bfd_ind_section_ptr)

     #define bfd_is_const_section(SEC)              \

      (   ((SEC) == bfd_abs_section_ptr)            \

       || ((SEC) == bfd_und_section_ptr)            \

       || ((SEC) == bfd_com_section_ptr)            \

       || ((SEC) == bfd_ind_section_ptr))

     extern const struct symbol_cache_entry * const bfd_abs_symbol;

     extern const struct symbol_cache_entry * const bfd_com_symbol;

     extern const struct symbol_cache_entry * const bfd_und_symbol;

     extern const struct symbol_cache_entry * const bfd_ind_symbol;

     #define bfd_get_section_size_before_reloc(section) \

          ((section)->reloc_done ? (abort (), (bfd_size_type) 1) \

                                 : (section)->_raw_size)

     #define bfd_get_section_size_after_reloc(section) \

          ((section)->reloc_done ? (section)->_cooked_size \

                                 : (abort (), (bfd_size_type) 1))

     /* Macros to handle insertion and deletion of a bfd's sections.  These

        only handle the list pointers, ie. do not adjust section_count,

        target_index etc.  */

     #define bfd_section_list_remove(ABFD, PS) \

       do                                                   \

         {                                                  \

           asection **_ps = PS;                             \

           asection *_s = *_ps;                             \

           *_ps = _s->next;                                 \

           if (_s->next == NULL)                            \

             (ABFD)->section_tail = _ps;                    \

         }                                                  \

       while (0)

     #define bfd_section_list_insert(ABFD, PS, S) \

       do                                                   \

         {                                                  \

           asection **_ps = PS;                             \

           asection *_s = S;                                \

           _s->next = *_ps;                                 \

           *_ps = _s;                                       \

           if (_s->next == NULL)                            \

             (ABFD)->section_tail = &_s->next;              \

         }                                                  \

       while (0)

File: bfd.info,  Node: section prototypes,  Prev: typedef asection,  Up: Sections

Section prototypes

------------------

   These are the functions exported by the section handling part of BFD.

`bfd_section_list_clear'

........................

   *Synopsis*

     void bfd_section_list_clear (bfd *);

   *Description*

Clears the section list, and also resets the section count and hash

table entries.

`bfd_get_section_by_name'

.........................

   *Synopsis*

     asection *bfd_get_section_by_name(bfd *abfd, const char *name);

   *Description*

Run through ABFD and return the one of the `asection's whose name

matches NAME, otherwise `NULL'.  *Note Sections::, for more information.

   This should only be used in special cases; the normal way to process

all sections of a given name is to use `bfd_map_over_sections' and

`strcmp' on the name (or better yet, base it on the section flags or

something else) for each section.

`bfd_get_unique_section_name'

.............................

   *Synopsis*

     char *bfd_get_unique_section_name(bfd *abfd,

         const char *templat,

         int *count);

   *Description*

Invent a section name that is unique in ABFD by tacking a dot and a

digit suffix onto the original TEMPLAT.  If COUNT is non-NULL, then it

specifies the first number tried as a suffix to generate a unique name.

The value pointed to by COUNT will be incremented in this case.

`bfd_make_section_old_way'

..........................

   *Synopsis*

     asection *bfd_make_section_old_way(bfd *abfd, const char *name);

   *Description*

Create a new empty section called NAME and attach it to the end of the

chain of sections for the BFD ABFD. An attempt to create a section with

a name which is already in use returns its pointer without changing the

section chain.

   It has the funny name since this is the way it used to be before it

was rewritten....

   Possible errors are:

   * `bfd_error_invalid_operation' - If output has already started for

     this BFD.

   * `bfd_error_no_memory' - If memory allocation fails.

`bfd_make_section_anyway'

.........................

   *Synopsis*

     asection *bfd_make_section_anyway(bfd *abfd, const char *name);

   *Description*

Create a new empty section called NAME and attach it to the end of the

chain of sections for ABFD.  Create a new section even if there is

already a section with that name.

   Return `NULL' and set `bfd_error' on error; possible errors are:

   * `bfd_error_invalid_operation' - If output has already started for

     ABFD.

   * `bfd_error_no_memory' - If memory allocation fails.

`bfd_make_section'

..................

   *Synopsis*

     asection *bfd_make_section(bfd *, const char *name);

   *Description*

Like `bfd_make_section_anyway', but return `NULL' (without calling

bfd_set_error ()) without changing the section chain if there is

already a section named NAME.  If there is an error, return `NULL' and

set `bfd_error'.

`bfd_set_section_flags'

.......................

   *Synopsis*

     boolean bfd_set_section_flags(bfd *abfd, asection *sec, flagword flags);

   *Description*

Set the attributes of the section SEC in the BFD ABFD to the value

FLAGS. Return `true' on success, `false' on error. Possible error

returns are:

   * `bfd_error_invalid_operation' - The section cannot have one or

     more of the attributes requested. For example, a .bss section in

     `a.out' may not have the `SEC_HAS_CONTENTS' field set.

`bfd_map_over_sections'

.......................

   *Synopsis*

     void bfd_map_over_sections(bfd *abfd,

         void (*func) (bfd *abfd,

         asection *sect,

         PTR obj),

         PTR obj);

   *Description*

Call the provided function FUNC for each section attached to the BFD

ABFD, passing OBJ as an argument. The function will be called as if by

            func(abfd, the_section, obj);

   This is the prefered method for iterating over sections; an

alternative would be to use a loop:

               section *p;

               for (p = abfd->sections; p != NULL; p = p->next)

                  func(abfd, p, ...)

`bfd_set_section_size'

......................

   *Synopsis*

     boolean bfd_set_section_size(bfd *abfd, asection *sec, bfd_size_type val);

   *Description*

Set SEC to the size VAL. If the operation is ok, then `true' is

returned, else `false'.

   Possible error returns:

   * `bfd_error_invalid_operation' - Writing has started to the BFD, so

     setting the size is invalid.

`bfd_set_section_contents'

..........................

   *Synopsis*

     boolean bfd_set_section_contents (bfd *abfd, asection *section,

         PTR data, file_ptr offset,

         bfd_size_type count);

   *Description*

Sets the contents of the section SECTION in BFD ABFD to the data

starting in memory at DATA. The data is written to the output section

starting at offset OFFSET for COUNT octets.

   Normally `true' is returned, else `false'. Possible error returns

are:

   * `bfd_error_no_contents' - The output section does not have the

     `SEC_HAS_CONTENTS' attribute, so nothing can be written to it.

   * and some more too

   This routine is front end to the back end function

`_bfd_set_section_contents'.

`bfd_get_section_contents'

..........................

   *Synopsis*

     boolean bfd_get_section_contents (bfd *abfd, asection *section,

         PTR location, file_ptr offset,

         bfd_size_type count);

   *Description*

Read data from SECTION in BFD ABFD into memory starting at LOCATION.

The data is read at an offset of OFFSET from the start of the input

section, and is read for COUNT bytes.

   If the contents of a constructor with the `SEC_CONSTRUCTOR' flag set

are requested or if the section does not have the `SEC_HAS_CONTENTS'

flag set, then the LOCATION is filled with zeroes. If no errors occur,

`true' is returned, else `false'.

`bfd_copy_private_section_data'

...............................

   *Synopsis*

     boolean bfd_copy_private_section_data (bfd *ibfd, asection *isec,

         bfd *obfd, asection *osec);

   *Description*

Copy private section information from ISEC in the BFD IBFD to the

section OSEC in 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 OSEC.

     #define bfd_copy_private_section_data(ibfd, isection, obfd, osection) \

          BFD_SEND (obfd, _bfd_copy_private_section_data, \

                    (ibfd, isection, obfd, osection))

`_bfd_strip_section_from_output'

................................

   *Synopsis*

     void _bfd_strip_section_from_output

        (struct bfd_link_info *info, asection *section);

   *Description*

Remove SECTION from the output.  If the output section becomes empty,

remove it from the output bfd.

   This function won't actually do anything except twiddle flags if

called too late in the linking process, when it's not safe to remove

sections.

`bfd_generic_discard_group'

...........................

   *Synopsis*

     boolean bfd_generic_discard_group (bfd *abfd, asection *group);

   *Description*

Remove all members of GROUP from the output.

File: bfd.info,  Node: Symbols,  Next: Archives,  Prev: Sections,  Up: BFD front end

Symbols

=======

   BFD tries to maintain as much symbol information as it can when it

moves information from file to file. BFD passes information to

applications though the `asymbol' structure. When the application

requests the symbol table, BFD reads the table in the native form and

translates parts of it into the internal format. To maintain more than

the information passed to applications, some targets keep some

information "behind the scenes" in a structure only the particular back

end knows about. For example, the coff back end keeps the original

symbol table structure as well as the canonical structure when a BFD is

read in. On output, the coff back end can reconstruct the output symbol

table so that no information is lost, even information unique to coff

which BFD doesn't know or understand. If a coff symbol table were read,

but were written through an a.out back end, all the coff specific

information would be lost. The symbol table of a BFD is not necessarily

read in until a canonicalize request is made. Then the BFD back end

fills in a table provided by the application with pointers to the

canonical information.  To output symbols, the application provides BFD

with a table of pointers to pointers to `asymbol's. This allows

applications like the linker to output a symbol as it was read, since

the "behind the scenes" information will be still available.

* Menu:

* Reading Symbols::

* Writing Symbols::

* Mini Symbols::

* typedef asymbol::

* symbol handling functions::

File: bfd.info,  Node: Reading Symbols,  Next: Writing Symbols,  Prev: Symbols,  Up: Symbols

Reading symbols

---------------

   There are two stages to reading a symbol table from a BFD:

allocating storage, and the actual reading process. This is an excerpt

from an application which reads the symbol table:

              long storage_needed;

              asymbol **symbol_table;

              long number_of_symbols;

              long i;

              storage_needed = bfd_get_symtab_upper_bound (abfd);

              if (storage_needed < 0)

                FAIL

              if (storage_needed == 0) {

                 return ;

              }

              symbol_table = (asymbol **) xmalloc (storage_needed);

                ...

              number_of_symbols =

                 bfd_canonicalize_symtab (abfd, symbol_table);

              if (number_of_symbols < 0)

                FAIL

              for (i = 0; i < number_of_symbols; i++) {

                 process_symbol (symbol_table[i]);

              }

   All storage for the symbols themselves is in an objalloc connected

to the BFD; it is freed when the BFD is closed.

File: bfd.info,  Node: Writing Symbols,  Next: Mini Symbols,  Prev: Reading Symbols,  Up: Symbols

Writing symbols

---------------

   Writing of a symbol table is automatic when a BFD open for writing

is closed. The application attaches a vector of pointers to pointers to

symbols to the BFD being written, and fills in the symbol count. The

close and cleanup code reads through the table provided and performs

all the necessary operations. The BFD output code must always be

provided with an "owned" symbol: one which has come from another BFD,

or one which has been created using `bfd_make_empty_symbol'.  Here is an

example showing the creation of a symbol table with only one element:

            #include "bfd.h"

            main()

            {

              bfd *abfd;

              asymbol *ptrs[2];

              asymbol *new;

              abfd = bfd_openw("foo","a.out-sunos-big");

              bfd_set_format(abfd, bfd_object);

              new = bfd_make_empty_symbol(abfd);

              new->name = "dummy_symbol";

              new->section = bfd_make_section_old_way(abfd, ".text");

              new->flags = BSF_GLOBAL;

              new->value = 0x12345;

              ptrs[0] = new;

              ptrs[1] = (asymbol *)0;

              bfd_set_symtab(abfd, ptrs, 1);

              bfd_close(abfd);

            }

            ./makesym

            nm foo

            00012345 A dummy_symbol

   Many formats cannot represent arbitary symbol information; for

instance, the `a.out' object format does not allow an arbitary number

of sections. A symbol pointing to a section which is not one  of

`.text', `.data' or `.bss' cannot be described.

File: bfd.info,  Node: Mini Symbols,  Next: typedef asymbol,  Prev: Writing Symbols,  Up: Symbols

Mini Symbols

------------

   Mini symbols provide read-only access to the symbol table.  They use

less memory space, but require more time to access.  They can be useful

for tools like nm or objdump, which may have to handle symbol tables of

extremely large executables.

   The `bfd_read_minisymbols' function will read the symbols into

memory in an internal form.  It will return a `void *' pointer to a

block of memory, a symbol count, and the size of each symbol.  The

pointer is allocated using `malloc', and should be freed by the caller

when it is no longer needed.

   The function `bfd_minisymbol_to_symbol' will take a pointer to a

minisymbol, and a pointer to a structure returned by

`bfd_make_empty_symbol', and return a `asymbol' structure.  The return

value may or may not be the same as the value from

`bfd_make_empty_symbol' which was passed in.

File: bfd.info,  Node: typedef asymbol,  Next: symbol handling functions,  Prev: Mini Symbols,  Up: Symbols

typedef asymbol

---------------

   An `asymbol' has the form:

     typedef struct symbol_cache_entry

     {

       /* A pointer to the BFD which owns the symbol. This information

          is necessary so that a back end can work out what additional

          information (invisible to the application writer) is carried

          with the symbol.

          This field is *almost* redundant, since you can use section->owner

          instead, except that some symbols point to the global sections

          bfd_{abs,com,und}_section.  This could be fixed by making

          these globals be per-bfd (or per-target-flavor).  FIXME.  */

       struct _bfd *the_bfd; /* Use bfd_asymbol_bfd(sym) to access this field.  */

       /* The text of the symbol. The name is left alone, and not copied; the

          application may not alter it.  */

       const char *name;

       /* The value of the symbol.  This really should be a union of a

          numeric value with a pointer, since some flags indicate that

          a pointer to another symbol is stored here.  */

       symvalue value;

       /* Attributes of a symbol.  */

     #define BSF_NO_FLAGS    0x00

       /* The symbol has local scope; `static' in `C'. The value

          is the offset into the section of the data.  */

     #define BSF_LOCAL      0x01

       /* The symbol has global scope; initialized data in `C'. The

          value is the offset into the section of the data.  */

     #define BSF_GLOBAL     0x02

       /* The symbol has global scope and is exported. The value is

          the offset into the section of the data.  */

     #define BSF_EXPORT     BSF_GLOBAL /* No real difference.  */

       /* A normal C symbol would be one of:

          `BSF_LOCAL', `BSF_FORT_COMM',  `BSF_UNDEFINED' or

          `BSF_GLOBAL'.  */

       /* The symbol is a debugging record. The value has an arbitary

          meaning, unless BSF_DEBUGGING_RELOC is also set.  */

     #define BSF_DEBUGGING  0x08

       /* The symbol denotes a function entry point.  Used in ELF,

          perhaps others someday.  */

     #define BSF_FUNCTION    0x10

       /* Used by the linker.  */

     #define BSF_KEEP        0x20

     #define BSF_KEEP_G      0x40

       /* A weak global symbol, overridable without warnings by

          a regular global symbol of the same name.  */

     #define BSF_WEAK        0x80

       /* This symbol was created to point to a section, e.g. ELF's

          STT_SECTION symbols.  */

     #define BSF_SECTION_SYM 0x100

       /* The symbol used to be a common symbol, but now it is

          allocated.  */

     #define BSF_OLD_COMMON  0x200

       /* The default value for common data.  */

     #define BFD_FORT_COMM_DEFAULT_VALUE 0

       /* In some files the type of a symbol sometimes alters its

          location in an output file - ie in coff a `ISFCN' symbol

          which is also `C_EXT' symbol appears where it was

          declared and not at the end of a section.  This bit is set

          by the target BFD part to convey this information.  */

     #define BSF_NOT_AT_END    0x400

       /* Signal that the symbol is the label of constructor section.  */

     #define BSF_CONSTRUCTOR   0x800

       /* Signal that the symbol is a warning symbol.  The name is a

          warning.  The name of the next symbol is the one to warn about;

          if a reference is made to a symbol with the same name as the next

          symbol, a warning is issued by the linker.  */

     #define BSF_WARNING       0x1000

       /* Signal that the symbol is indirect.  This symbol is an indirect

          pointer to the symbol with the same name as the next symbol.  */

     #define BSF_INDIRECT      0x2000

       /* BSF_FILE marks symbols that contain a file name.  This is used

          for ELF STT_FILE symbols.  */

     #define BSF_FILE          0x4000

       /* Symbol is from dynamic linking information.  */

     #define BSF_DYNAMIC       0x8000

       /* The symbol denotes a data object.  Used in ELF, and perhaps

          others someday.  */

     #define BSF_OBJECT        0x10000

       /* This symbol is a debugging symbol.  The value is the offset

          into the section of the data.  BSF_DEBUGGING should be set

          as well.  */

     #define BSF_DEBUGGING_RELOC 0x20000

       /* This symbol is thread local.  Used in ELF.  */

     #define BSF_THREAD_LOCAL  0x40000

       flagword flags;

       /* A pointer to the section to which this symbol is

          relative.  This will always be non NULL, there are special

          sections for undefined and absolute symbols.  */

       struct sec *section;

       /* Back end special data.  */

       union

         {

           PTR p;

           bfd_vma i;

         }

       udata;

     }

     asymbol;

File: bfd.info,  Node: symbol handling functions,  Prev: typedef asymbol,  Up: Symbols

Symbol handling functions

-------------------------

`bfd_get_symtab_upper_bound'

............................

   *Description*

Return the number of bytes required to store a vector of pointers to

`asymbols' for all the symbols in the BFD ABFD, including a terminal

NULL pointer. If there are no symbols in the BFD, then return 0.  If an

error occurs, return -1.