[Bug target/61044] Computed goto on AVR fails to use word-addressing

["gjl at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61044

--- Comment #9 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
(In reply to Senthil Kumar Selvaraj from comment #3)
> The primary reason I added the diff relocs was to prevent linker relaxation
> messing up DWARF line number information - as you know, relaxation can
> shorten instruction sequences, and the addresses in DWARF then go out of
> sync.
> 
> I guess I must add some user documentation about this, but ideally, this is
> supposed to be transparent to the user - just passing -mrelax to the
> compiler should work.
> 
> I turned diff reloc generation on only if -mlink-relax is passed because
> this is what other ports (xtensa) do, and I wasn't sure of the consequences
> of resolving every subtraction expression at link time.

Resolving label differences at assemble time serves a faster linking process,
but that argument does not apply to avr:  We don't have magabytes of code that
have to be fixed at load time by a dynamic linker.

And you don't know at assemble time how the linker is called.  One example is
debugging through code that comes from a library and has been linked against
the application.  It's not very common but possible and yet another plus
(besides simplicity with less options and less GCC/Binutils dependency) for
always emitting label differences as relocs.