Date: Thu, 7 Jun 2001 18:00:41 -0400 (EDT) From: Daniel Eischen <eischen@vigrid.com> To: Stefan Hoffmeister <Stefan.Hoffmeister@Econos.de> Cc: Stefan Hoffmeister <freebsd-ml@Econos.de>, freebsd-hackers@FreeBSD.ORG Subject: Re: libc_r, signal handler ucontext modification Message-ID: <Pine.SUN.3.91.1010607175733.12795A@pcnet1.pcnet.com> In-Reply-To: <4bdvhtgru1j77uvphko0dsg8ohpj8beloh@4ax.com>
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On Thu, 7 Jun 2001, Stefan Hoffmeister wrote: > : On Thu, 7 Jun 2001 12:07:50 -0400 (EDT), Daniel Eischen wrote: > > >On Thu, 7 Jun 2001, Stefan Hoffmeister wrote: > > >> [copy context back into thread] > > >You can't do that. There is no requirement that the interrupted thread > >is the one that handles the signal. If you copy the context back to > >the current threads context storage, then you'll possibly end up with > >2 threads running (or trying to run) on the same stack! > > Ouch :-) > > >You could also easily modify the context and do a > >sigreturn(ucp) on it to achieve the same effect (being careful to make > >sure you're not trying to jump to another threads context). > > This sounds very good, indeed. I do not want to make a context switch; > essentially all I care about is that > > * the changed value of EIP is taken > > * ESP (from context) is retained > > * Changed values of EAX, EDX are taken > > AFA sigreturn is concerned: libc_r.so (!) does not export it; it only > exports _thread_sys_sigreturn. Is there some kind of "__strong_reference" > missing? > > In a slightly daring move, I am calling _thread_sys_sigreturn and, in my > trivial test scenario, this seems to work - now I wonder whether it is > supposed to work? > > IOW, is _thread_sys_sigreturn an alias for sigreturn in libc_r.so? Yeah, I don't know why sigreturn is hidden any longer. I don't think there's a need for it to be hidden. I suppose we could wrap it and check to make sure the thread performing the sigreturn isn't trying to return to a stack that isn't its own (like we do for siglongjmp/longjmp). -- Dan Eischen To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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