Hi Raúl,

>   I'm currently have a patchset working on 2.17 that I'm trying to port to
> 2.18.50. The main author of the patch is unknown, but I'm trying to find
> out who could be. So far I'm treating that information as public domain so
> I hope it can be relicensed to GPL after my modifications.

This may be a problem if the original author did not put their work into the 
public domain.  Please do make your best efforts to contact them and ascertain 
if they agree to the donation.

>   As I've been told on the #gcc development channel, I need to fill in some
> forms before I'm able to add any contribution upstream. Hence I'm asking
> here to know what the requirements are.

The requirements are:

   1. You have an FSF copyright assignment on file with the FSF for
      contributions to the binutils project.  I have attached a form to start
      the application process if you do not already have one.

   2. The original author should ideally also have an FSF copyright assignment
      in place.  If not you must be able to show that they have released the
      copyright on their work into the public domain and that however it was
      licensed when it was released, that license is compatible with the code
      being relicensed under the GPLv3.

   3. As you suggested:

>   · Applying cleanly.
>   · Don't break anything.
>   · Don't fix if it's not broken.
>   · Unified diff format.

     Plus:

     * Contains ChangeLog entries for the patches.
     * Documents any new command line options or targets in the appropriate
       places (gas/doc, ld/ld.texinfo, binutils/doc/binutils.texi, gas/NEWS,
       ld/NEWS).
     * Contains new assembler and linker testsuite directories to check the
       particulars of the new port.
     * Follows the GNU Coding Standards: http://www.gnu.org/prep/standards

Cheers
   Nick