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Re: [buildd] Etch?

On Fri, 4 Aug 2006, Wouter Verhelst wrote:
> Indeed. However, I do not feel that the impact will be unbearably large.
> So far, I have found only two cases where the documentation documents
> different behaviour for a given opcode on ColdFire vs 68k:
> * Moving data from FPU registers to memory with FMOVEM will overwrite 10
>   bytes per register on classic 68k, but only 8 per register on
>   ColdFire, due to the differences in FPU register length. This is a
>   problem if you try to access the data in memory after pulling it out
>   with FMOVEM, but it is not if you use it to store the state of your
>   registers at the beginning of a function, so that you can restore the
>   state at the end of the same. I presume that that's what FMOVEM was
>   intended for anyway, so I do not consider this to be much of a
>   problem.

But I guess this is a problem if you do

    movem.l	d0-d1,-(a7)
    fmovem	fp0-fp1,-(a7)
    movem.l	d2-d3,-(a7)

and want to access the saved d0 and d1 later, relative to a7, as they will be
at different offsets.

> * Using address register indirect with predecrement or postincrement mode
>   on the stack pointer (A7) in byte context will increment resp.
>   decrement the stack pointer with 2 bytes on classic 68k, but with 1
>   byte on the ColdFire. Both still need to be aligned on two bytes,
>   however. As a result, this addressing mode should be avoided; but I do
>   not think that it is used very often.

Hmm... So what happens if you push 1 byte on the stack, and an interrupt comes



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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