kern_threads.c.. upcall question..

[David Xu]

----- Original Message ----- 
From: "Daniel Eischen" <eischen at pcnet1.pcnet.com>
To: "Julian Elischer" <julian at elischer.org>
Cc: <threads at freebsd.org>
Sent: Tuesday, May 06, 2003 8:49 AM
Subject: Re: kern_threads.c.. upcall question..


> On Mon, 5 May 2003, Julian Elischer wrote:
> > On Mon, 5 May 2003, Daniel Eischen wrote:
> > 
> > > On Mon, 5 May 2003, Julian Elischer wrote:
> > > 
> > > > 
> > > > In kern_threads.c, in function thread_export_context()
> > > > it first does a copyin() of the
> > > > context storage area. I think this is un-needed (and a complete waste of
> > > > cycles) but I am not sure if there is some strange condition
> > > > regarding floating point registers or something that may want this..
> > > > 
> > > > Dan, Jon, David?
> > > > do any of you have a good reason why I shouldn't remove the copyin().??
> > > 
> > > Yeah, the threads library keeps the thread's active signal
> > > mask in the context area.  The stack and flags may also
> > > be used in the context.
> > > 
> > > You should be able to safely copy out the mcontext without
> > > a copyin().  Is that what you're currently doing?  Or is
> > > the entire context (ucontext) being exported?
> > 
> > it does:
> > 
> > *) copyin the ucontext_t
> > 
> > *) load context into it using thread_getcontext() which uses
> >   get_mcontext() and adds the kernel thread sigmask (this must have
> >   been added by jeff in some way) (note it doesn't OR, just writes)
> 
> Eek.  That could cause problems for libpthread.  We
> don't want the kernel thread signal mask being copied
> to the exported context.
> 
> > *) copyout of the ucontext_t
> > 
> > The ucontext is:
> > 
> >         sigset_t        uc_sigmask;   <-- gets over-written (!)
> >         mcontext_t      uc_mcontext;  <-- gets over-written
> >         struct __ucontext *uc_link;   <-- one in userland MAY be
> > valuable
> >         stack_t         uc_stack;     <-- probably worth saving..
> >         int             uc_flags;     <-- probably worth saving
> >         int             __spare__[4];
> > 
> > 
> > 
> > 
> > It seems to me that just copying out the sigset_t and mcontext_t
> > may be all that is needed. (and I'm not so sure about the sigset_t
> > at that..
> 
> Yes, please don't copyout the sigset.
> 
> -- 
> Dan Eischen

Yes, I think only copying out mcontext is enough, we needn't copying in.

David Xu