Adding symbols from an object file - Untitled
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##### 2.17.2.2 Adding symbols from an object file

When the `_bfd_link_add_symbols` routine is passed an object file, it must add all externally visible symbols in that object file to the hash table. The actual work of adding the symbol to the hash table is normally handled by the function `_bfd_generic_link_add_one_symbol`. The `_bfd_link_add_symbols` routine is responsible for reading all the symbols from the object file and passing the correct information to `_bfd_generic_link_add_one_symbol`.

The `_bfd_link_add_symbols` routine should not use `bfd_canonicalize_symtab` to read the symbols. The point of providing this routine is to avoid the overhead of converting the symbols into generic `asymbol` structures.

`_bfd_generic_link_add_one_symbol` handles the details of combining common symbols, warning about multiple definitions, and so forth. It takes arguments which describe the symbol to add, notably symbol flags, a section, and an offset. The symbol flags include such things as `BSF_WEAK` or `BSF_INDIRECT`. The section is a section in the object file, or something like `bfd_und_section_ptr` for an undefined symbol or `bfd_com_section_ptr` for a common symbol.

If the `_bfd_final_link` routine is also going to need to read the symbol information, the `_bfd_link_add_symbols` routine should save it somewhere attached to the object file BFD. However, the information should only be saved if the `keep_memory` field of the `info` argument is TRUE, so that the `-no-keep-memory` linker switch is effective.

The a.out function which adds symbols from an object file is `aout_link_add_object_symbols`, and most of the interesting work is in `aout_link_add_symbols`. The latter saves pointers to the hash tables entries created by `_bfd_generic_link_add_one_symbol` indexed by symbol number, so that the `_bfd_final_link` routine does not have to call the hash table lookup routine to locate the entry.