Before the linker calls the _bfd_final_link entry point,
it sets up some data structures for the function to use.
The input_bfds field of the bfd_link_info structure
will point to a list of all the input files included in the
link. These files are linked through the link.next field
of the bfd structure.
Each section in the output file will have a list of
link_order structures attached to the map_head.link_order
field (the link_order structure is defined in
bfdlink.h). These structures describe how to create the
contents of the output section in terms of the contents of
various input sections, fill constants, and, eventually, other
types of information. They also describe relocs that must be
created by the BFD backend, but do not correspond to any input
file; this is used to support -Ur, which builds constructors
while generating a relocatable object file.