### 2.17 Linker Functions

The linker uses three special entry points in the BFD target vector. It is not necessary to write special routines for these entry points when creating a new BFD back end, since generic versions are provided. However, writing them can speed up linking and make it use significantly less runtime memory.

The first routine creates a hash table used by the other routines. The second routine adds the symbols from an object file to the hash table. The third routine takes all the object files and links them together to create the output file. These routines are designed so that the linker proper does not need to know anything about the symbols in the object files that it is linking. The linker merely arranges the sections as directed by the linker script and lets BFD handle the details of symbols and relocs.

The second routine and third routines are passed a pointer to a `struct bfd_link_info` structure (defined in `bfdlink.h`) which holds information relevant to the link, including the linker hash table (which was created by the first routine) and a set of callback functions to the linker proper.

The generic linker routines are in `linker.c`, and use the header file `genlink.h`. As of this writing, the only back ends which have implemented versions of these routines are a.out (in `aoutx.h`) and ECOFF (in `ecoff.c`). The a.out routines are used as examples throughout this section.