Daniel Jacobowitz wrote:
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.
That is correct. Due to various errata the trampoline cannot always be
at a fixed offset to the signal context bits. So we had to use the
return PC as you indicate.
David Daney
