Hello,

>> No, the box runs multiuser and the Xserver as root. Only one single
>> mmap() fails - the others which map the linear framebuffer, voodoo3
>> specific registers and so on work - but succeeds when using a 
>> different
>> file descriptor on /dev/mem. The file descriptor XFree uses isn't
>> corrupted or anything, it's just picky about this single memory range
>> for some weird reason.
>
> a mem protect somewhere ?

That should affect other platforms than macppc too, but at least i386 
obviously doesn't have this problem.

have fun
Michael