KSE/ia64: NULL thread pointer in _thr_sig_add()

[Marcel Moolenaar]

On Sun, Aug 17, 2003 at 08:54:56AM -0400, Daniel Eischen wrote:
> > > 
> > > One question.  When you call (the syscall) setcontext() from
> > > _ia64_break_setcontext(), do you ignore the signal mask (uc.uc_sigmask)?
> > 
> > Good point. I don't think so.
> 
> OK, this will cause signal handling problems.  You can
> use another flag, but that would dirty up MI setcontext().
> Perhaps a separate ia64-specific system call?

I actually have been thinking about using a flag. One that simply
indicates that the sigmask field is valid or not. The advantage
of such flag is that it makes the general interaction with user
land versions of getcontext() much more predictable and increases
the overall applicability of the *context syscalls.

For example: libthr uses getcontext(2) but is not interested in
the sigmask. It simply uses the syscall as an initialization for
new threads. The context is passed to thr_create where we only
use the mcontext part to setup the registers. libkse tries to
avoid the syscalls. The userland versions don't save or restore
signal masks. There too we use contexts without actually being
interested in sigmasks. Also in libkse we see that the contexts
created in the kernel and given to userland are not contexts that
contains sigmasks. We simply copyout the mcontext part of the
ucontext. So, it appears that most of our uses of contexts are
such that we don't need to save and/or restore sigmasks.

I think an UCF_SIGMASK flag to indicate that the context has a
valid sigmask is a logical or natural way to have setcontext(2)
operate well with getcontext(2), which always defines contexts
with sigmasks and userland versions of getcontext() or other
more specific uses of contexts that may or may not have a need
to save the sigmask.

Reasoning differently: if we were to introduce a new syscall,
then the syscall would in effect be a clone of setcontext(2)
with the difference that we don't restore a part of the context.
This is duplication to avoid variation. Also, with a new syscall
we introduce the notion of having 2 seperate contexts. This not
only begs for a getcontext() clone that does not save the sigmask,
but also begs for a flag to differentiate between those 2 contexts.

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel at xcllnt.net