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From: David Xu <davidxu@FreeBSD.org>
To: Marcel Moolenaar <marcel@xcllnt.net>, threads@FreeBSD.org
Date: Mon, 18 Aug 2003 06:47:52 +0800
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Subject: Re: First draft: rewrite of {get|set|swap}context(3)
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On Monday 18 August 2003 02:50, Marcel Moolenaar wrote:
> Gang,
>
> Please review the attached patch and let me know to what extend it
> introduces breakages. It is the result of "aggressive engineering"
> to provoke comments and further fuel discussion. The reason for this
> approach is that we currently do not initialize any fields other than
> the mcontext and sigmask and only partially copyin() and copyout()
> the contexts (typically only the mcontext and sigmask fields). This
> generally is very sensitive to breakages, especially when we intro-
> duce flags or need to use any of the spare fields.
>
> getcontext(3): the whole ucontext is zeroed before (partially) filled
> 	and we copyout() all of it. This means that uc_link can only
> 	be set/defined after calling setcontext().
> setcontext(3): we copyin() the whole ucontext but partially restore
> 	its fields. The sigmask is restored conditionally based upon
> 	the UCF_SIGMASK flag.
> swapcontext(3): we preserve uc_link by doing a partial copyin(). The
> 	context is otherwise zeroed and partially filled. we copyout()
> 	the whole context.
>
> The patch has only been compile-tested.
>
> Shoot...

Then doesn't signal context in signal handler have a UCF_SIGMASK ?

void    (*__sa_sigaction)(int, struct __siginfo *, ucontext_t *ucp);
the context *ucp should have UCF_SIGMASK now.
I think it should be UCF_NOSIGMASK. But for libkse, we really needn't
this kind of hack, because M:N thread in kernel always masks all signals,
you can always SIGFILLSET(&uc.uc_sigmask) before call set_context.

--
David Xu