[OpenBIOS] ppc64 MMU issues

[Andreas Färber]

[snip]

Last night I finally made some small progress with ppc64: I picked up  
Alex' suggestion of using slbmte, this does work for ppc but didn't  
make a big change for ppc64. The 0x700 program exception turned out to  
be caused by a jump to the isi_exception function descriptor rather  
than the isi_exception() function. (Yet, the setup_mmu() function did  
not seem to have a function descriptor, despite both sitting in C  
code...)

I now get a 0x380 data segment exception, which seems caused by uses  
of TOC offsets in entry() with r2 being zero, leading to data accesses  
wrapping around into unmapped memory.

I thought we might be missing some ELF sections in the linker script  
but my tries based on `powerpc64-linux-gnu-ld --verbose` were  
unsuccessful. Is there a way to turn on warnings for sections dropped,  
to rule this out? Who's responsible for r2 setup - GCC-generated code  
or QEMU?

I'll flush my Forth queue now and will try to put together some more  
RFCs.

Andreas