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Re: emulating no-senders notifications in L4?

From: Ondrej Hurt
Subject: Re: emulating no-senders notifications in L4?
Date: Sun, 23 Dec 2001 15:30:26 +0100 (CET)

> > Is this thread running inside the task in question or in some other
> > task?

> Either inside the task or in some other task.  It's all a question of
> implementation.  One could for instance have an external entity
> handling the exception and killing the task if it that was bahaving
> incorrectly/maliciously.  One could also let some handler inside the
> task handle the exception.  This would make for faster exception
> handling in many cases (in particular on x86 and ARM) since one only
> need to do context switches inside the task.  It also enables the
> handler to directly access intra task memory, e.g., code casuing the
> exception.

The exception handler thread must be reliable i.e. in some trusted
task so we can count on it that it releases resources like port
rights and the failing task gets killed.

> If the intra task exception handler fails to handle the
> exception it should contact some external entity to take some
> appropriate measurre like killing the task.

There is a always a possibility that the internal handler won't even
be able to contact anything. (e.g. pages with its code or data were
unmapped or overwritten)

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