Untitled Document: Writing the symbol table

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#### 2.17.3.3 Writing the symbol table

The `_bfd_final_link` function must gather all the symbols in the input files and write them out. It must also write out all the symbols in the global hash table. This must be controlled by the `strip` and `discard` fields of the `bfd_link_info` structure.

The local symbols of the input files will not have been entered into the linker hash table. The `_bfd_final_link` routine must consider each input file and include the symbols in the output file. It may be convenient to do this when looking through the `link_order` structures, or it may be done by stepping through the `input_bfds` list.

The `_bfd_final_link` routine must also traverse the global hash table to gather all the externally visible symbols. It is possible that most of the externally visible symbols may be written out when considering the symbols of each input file, but it is still necessary to traverse the hash table since the linker script may have defined some symbols that are not in any of the input files.

The `strip` field of the `bfd_link_info` structure controls which symbols are written out. The possible values are listed in `bfdlink.h`. If the value is `strip_some`, then the `keep_hash` field of the `bfd_link_info` structure is a hash table of symbols to keep; each symbol should be looked up in this hash table, and only symbols which are present should be included in the output file.

If the `strip` field of the `bfd_link_info` structure permits local symbols to be written out, the `discard` field is used to further controls which local symbols are included in the output file. If the value is `discard_l`, then all local symbols which begin with a certain prefix are discarded; this is controlled by the `bfd_is_local_label_name` entry point.

The a.out backend handles symbols by calling `aout_link_write_symbols` on each input BFD and then traversing the global hash table with the function `aout_link_write_other_symbol`. It builds a string table while writing out the symbols, which is written to the output file at the end of `NAME(aout,final_link)`.

#### 2.17.3.4 `bfd_link_split_section`

Synopsis

    bfd_boolean bfd_link_split_section (bfd *abfd, asection *sec);

Description
Return nonzero if sec should be split during a reloceatable or final link.

    #define bfd_link_split_section(abfd, sec) \
           BFD_SEND (abfd, _bfd_link_split_section, (abfd, sec))

#### 2.17.3.5 `bfd_section_already_linked`

Synopsis

    bfd_boolean bfd_section_already_linked (bfd *abfd,
        asection *sec,
        struct bfd_link_info *info);

Description
Check if data has been already linked during a reloceatable or final link. Return TRUE if it has.

    #define bfd_section_already_linked(abfd, sec, info) \
           BFD_SEND (abfd, _section_already_linked, (abfd, sec, info))

#### 2.17.3.6 `bfd_generic_define_common_symbol`

Synopsis

    bfd_boolean bfd_generic_define_common_symbol
       (bfd *output_bfd, struct bfd_link_info *info,
        struct bfd_link_hash_entry *h);

Description
Convert common symbol h into a defined symbol. Return TRUE on success and FALSE on failure.

    #define bfd_define_common_symbol(output_bfd, info, h) \
           BFD_SEND (output_bfd, _bfd_define_common_symbol, (output_bfd, info, h))

#### 2.17.3.7 `bfd_find_version_for_sym`

Synopsis

    struct bfd_elf_version_tree * bfd_find_version_for_sym
       (struct bfd_elf_version_tree *verdefs,
        const char *sym_name, bfd_boolean *hide);

Description
Search an elf version script tree for symbol versioning info and export / don’t-export status for a given symbol. Return non-NULL on success and NULL on failure; also sets the output ‘`hide`’ boolean parameter.

#### 2.17.3.8 `bfd_hide_sym_by_version`

Synopsis

    bfd_boolean bfd_hide_sym_by_version
       (struct bfd_elf_version_tree *verdefs, const char *sym_name);

Description
Search an elf version script tree for symbol versioning info for a given symbol. Return TRUE if the symbol is hidden.

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