Re: Porting to IBM Risc 6000

[David Edelsohn <dje%watson.ibm.com@localhost>]

>>>>> Jochen Kunz writes:

Jochen> This would require a 32 bit userland, as 64 bit applications can't
Jochen> run on a 32 bit machine and 32 bit applications will run in some
Jochen> kind of emulation when a 64 bit kernel is running?
Jochen> (Sorry for this questions. I don't have The Clue (C) (R) (TM), but 
Jochen> I want to learn more about all this OS internas. This is the reason 
Jochen> for my interrest in getting the rs6k port going: Learning by doing.)

        64-bit PowerPC *is* PowerPC.  32-bit PowerPC is a subset.  There
is no emulation required.  No difference in performance.  Set the MSR to
32-bit mode and 32-bit applications run just fine.

        The only real effort for a 64-bit kernel is handling 32-bit system
calls -- translating any 64-bit offset arguments and returning 32-bit
memory addresses at the narrow system call boundary.

        Running 32-bit userland is recommended.  All 64-bit PowerPC Linux
distributions only use 32-bit userland. 

        All 64-bit issues are hidden in the kernel.  Leave it that way.

David