Re: [PATCH 2/3] Provide ucontext to signal handlers

[Jon TURNEY <jon dot turney at dronecode dot org dot uk>]

On 01/04/2015 18:36, Jon TURNEY wrote:
> On 01/04/2015 15:22, Corinna Vinschen wrote:
> > On Apr  1 14:19, Jon TURNEY wrote:
> > > Add ucontext.h header, defining ucontext_t and mcontext_t types.
> > >
> > > Provide sigaction sighandlers with a ucontext_t parameter, containing
> > > stack and
> > > context information.
> > >
> > >     * include/sys/ucontext.h : New header.
> > >     * include/ucontext.h : Ditto.
> > >     * exceptions.cc (call_signal_handler): Provide ucontext_t
> > >     parameter to signal handler function.
> >
> > Patch is ok with a single change:  Please add a "FIXME?" comment to:
> >
> >    else
> >      RtlCaptureContext();
> >
> > On second thought, calling RtlCaptureContext here is probably wrong.
> >
> > What we really need is the context of the thread when calling
> > call_signal_handler I think.
>
> I had the same thought, but this is going to be quite tricky to achieve.

> > It would be better to call RtlCaptureContext
> > before calling call_signal_handler.  But this requires a change in how
> > call_signal_handler is called.
> >
> > We should discuss this at one point, I think.

I noticed that we already prepare a context for continuing after the 
signal for the debugger, so perhaps this is not quite as complex as I 
thought and something like the attached is needed.

It's very hard to reason about if this is doing the right thing when the 
signal is delivered across threads, though.

Attachment: 0001-Use-the-same-continuation-context-in-a-signal-as-we-.patch
Description: Text document