Previous: Adding symbols from an object file, Up: Adding Symbols to the Hash Table Adding symbols from an archive

When the _bfd_link_add_symbols routine is passed an archive, it must look through the symbols defined by the archive and decide which elements of the archive should be included in the link. For each such element it must call the add_archive_element linker callback, and it must add the symbols from the object file to the linker hash table. (The callback may in fact indicate that a replacement BFD should be used, in which case the symbols from that BFD should be added to the linker hash table instead.)

In most cases the work of looking through the symbols in the archive should be done by the _bfd_generic_link_add_archive_symbols function. This function builds a hash table from the archive symbol table and looks through the list of undefined symbols to see which elements should be included. _bfd_generic_link_add_archive_symbols is passed a function to call to make the final decision about adding an archive element to the link and to do the actual work of adding the symbols to the linker hash table.

The function passed to _bfd_generic_link_add_archive_symbols must read the symbols of the archive element and decide whether the archive element should be included in the link. If the element is to be included, the add_archive_element linker callback routine must be called with the element as an argument, and the element's symbols must be added to the linker hash table just as though the element had itself been passed to the _bfd_link_add_symbols function. The add_archive_element callback has the option to indicate that it would like to replace the element archive with a substitute BFD, in which case it is the symbols of that substitute BFD that must be added to the linker hash table instead.

When the a.out _bfd_link_add_symbols function receives an archive, it calls _bfd_generic_link_add_archive_symbols passing aout_link_check_archive_element as the function argument. aout_link_check_archive_element calls aout_link_check_ar_symbols. If the latter decides to add the element (an element is only added if it provides a real, non-common, definition for a previously undefined or common symbol) it calls the add_archive_element callback and then aout_link_check_archive_element calls aout_link_add_symbols to actually add the symbols to the linker hash table - possibly those of a substitute BFD, if the add_archive_element callback avails itself of that option.

The ECOFF back end is unusual in that it does not normally call _bfd_generic_link_add_archive_symbols, because ECOFF archives already contain a hash table of symbols. The ECOFF back end searches the archive itself to avoid the overhead of creating a new hash table.