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

[Daniel Jacobowitz <dan@debian.org>]

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

That won't quite retain the ABI: you need to make sure everyone
locates it by using the stack pointer instead of the return pc.
Fortunately, GCC uses the return PC only for instruction matching
today.  I have a vague memory it used to use the stack pointer but
this was more reliable.

They don't necessarily have to go into the vdso; other architectures
have moved them off the stack directly to glibc.

-- 
Daniel Jacobowitz
CodeSourcery