Re: [PATCH, RFC] MIPS: Implement the getcontext API

[Ralf Baechle <ralf@linux-mips.org>]

On Wed, Mar 04, 2009 at 09:19:28AM +0100, Brian Foster wrote:

> On Tuesday 03 March 2009 17:56:25 David Daney wrote:
> >[ ... ]
> > When (and if) we move the sigreturn trampoline to a vdso we should be
> > able to maintain the ABI.
> 
>  it's more a matter of “when” rather than “if”.
>  there is still an intention here to use XI (we
>  have SmartMIPS), which requires not using the
>  signal (or FP) trampoline on the stack.
> 
>  moving the signal trampoline to a vdso (which
>  is(? was?) called, maybe misleadingly, ‘vsyscall’,
>  on other architectures) is the obvious solution to
>  that part of the puzzle.  and yes, it is possible
>  to maintain the ABI; the signal trampoline is still
>  also put on the stack, and modulo XI, would work if
>  used — the trampoline-on-stack is simply not used
>  if there is a vdso with the signal trampoline.

We generally want to get rid of stack trampolines.  Trampolines require
cacheflushing which especially on SMP systems can be a rather expensive
operation.

  Ralf