Re: Question on BIGGEST_ALIGNMENT in GCC on NetBSD/m68k

[Greg Ungerer <gerg@kernel.org>]

Hi Geert,

On 18/6/25 22:54, Geert Uytterhoeven wrote:
> Hi Adrian,
>
> On Wed, 18 Jun 2025 at 14:27, John Paul Adrian Glaubitz
> <glaubitz@physik.fu-berlin.de> wrote:
> > On Wed, 2025-06-18 at 22:21 +1000, Greg Ungerer wrote:
> > > > Could you please elaborate this a bit more, please?
> > > >
> > > > Coldfire is handled as a separate target via TARGET_COLDFIRE in GCC, so we
> > > > would certainly be able to toggle the alignment settings independent of
> > > > what's done on classic m68k.
> > >
> > > The net out is that it is the same gcc compiler, m68k-linux-gcc.
> > > ColdFire just needs specific code generation via command line switches,
> > > like -m5200 (or -m5206e or -m5307 or -mcfv4e, etc). This is the same way
> > > you would specify 680x0 level - m68020, -m68030, etc.
> >
> > Yes, but there is a TARGET_COLDFIRE macro as I mentioned above which could
> > be used to trigger which alignment to use by default. I don't see how that
> > would complicate things.
> >
> > > The bulk of the instruction set is the same. Asm code will look totally
> > > familiar to anyone who knows m68k :-)   One notable difference is that
> > > there is a more limited set addressing modes for some instructions.
> >
> > True, but you won't be able to run any classic m68k binaries on ColdFire
> > and the other way around, are you?
>
> IIIRC if you use a proper subset of the user mode instructions, you
> can create binaries that run on both.

You might be right on that. If you chose the lowest common denominator
of ColdFire code generation, -m5200, then I seem to recall for user
space that would just be a subset of traditional 68k.

Regards
Greg