Re: Don't save registers during system calls

H. Peter Anvin (hpa@transmeta.com)
17 Apr 1998 10:29:00 GMT

Followup to: <vyz3efc7p8t.fsf@issan.informatik.uni-dortmund.de>
By author: Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
In newsgroup: linux.dev.kernel
>
> FWIW, the m68k port already essentially does this. On kernel entry it
> only saves the registers that are call-clobbered in C (plus the registers
> that contain the syscall arguments so that they can be accessed through
> the normal C argument passing), the rest are only implicitly saved in the
> normal stack frames and during context switch. Since the m68k has many
> more registers than the ix86 this is a real win.
>

That's not quite what he's proposing. You're just doing the same
thing, it's just that the saves are later. I think he was proposing
that the kernel use a smaller (clobbered) register set than user space
would, hence (hopefully) not needing to save and restore some of the
registers at all. Since the Alpha has many more registers than the
m68k, this might be a win, too.

-hpa

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