[gas] new port advice

[Nicholas Clifton]

Hi Peter,

> Instead the arch I am looking at
> calls to CGEN, which loses me in a twisty maze :(.

Ah yes - that would be a problem.  You may find that abandoning cgen and 
starting from (almost) scratch is an easier way to go.  Ie take an 
existing non-cgen port, eg RX or ARM, and adapt that to your 
architecture.  It may take a bit more work initially, but in the long 
run you may find it easier to mainatain.

Alternatively if you want to stick with cgen, read on...

> I can see the XXX_or1k_cgen_assemble_insn in opcodes/XXX-asm.c but
> it calls to yet more generic code, which presumably works off the
> XXX_cgen_insn_table array that I can see in opcodes/XXX-desc.c.
>
> The entries are opaque to me. The "addi" entry says
>
>    /* addi $rD,$rA,$simm16 */
>    {
>    XXX_INSN_L_ADDI, "l-addi", "l.addi", 32, { 0, { { { load_of_flags, 0 } } } }
>    },

Yeah, it is all table based and created by some Scheme scripts from data 
in the cpu/ directory.

> Any idea how I can meddle with that? I can see the code in cgen.c, but
> it's utterly opaque to me what it consults ...

Take a look at cpu/or1korbis.cpu.  It seems to me that you are going to 
have to replace the definition of ADDI as a normal instruction with some 
kind of macro instruction generating sequence.  And if you can do that 
then you are a better man than I am Gungha Din.

Cheers
   Nick