[parisc-linux] [RFC] using 64bit wide registers with 32bit kernel

[James Bottomley]

On Mon, 2006-05-15 at 05:10 -0400, Jes Sorensen wrote:
> James> I really don't think doubling the size of our register file on
> James> all tasks and doubling the size of the saved registers on stack
> James> for interruptions is really a sensible thing to do just so some
> James> multi-media extension can be made to work.
> 
> What about setting an ELF flag or somesuch, set a task flag based on
> this and then only do the extended register file backup for these
> apps?

It's theoretically possible (and if we do it, we'd also use it *not* to
save the upper halves of registers for ILP32 processes on LP64 kernels.
However, the task switch is only one piece of the puzzle.  The other is
the interruption path.  We have very limited resources for doing things
before saving registers in the interruption path ... I fear it may be
beyond our current capability to check the elf flag if we're
interrupting a user space process.

James