Date: Sun, 17 Aug 2003 23:12:34 -0400 (EDT)
From: Daniel Eischen <eischen@vigrid.com>
To: David Xu <davidxu@freebsd.org>
Cc: Marcel Moolenaar <marcel@xcllnt.net>
Subject: Re: First draft: rewrite of {get|set|swap}context(3)
Message-ID: <Pine.GSO.4.10.10308172306080.29967-100000@pcnet5.pcnet.com>
In-Reply-To: <200308180647.52744.davidxu@FreeBSD.org>
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yOn Mon, 18 Aug 2003, David Xu wrote: > 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 I think so too. > 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. That works for M:N, but not when THR_GETCONTEXT() (and perhaps someday THR_SETCONTEXT()) is used for a scope system thread. Hmm, this wouldn't seem to result in a context that needs to be restored by the syscall though. -- Dan Eischen
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