patch for %gs saving
Daniel Eischen
eischen at pcnet1.pcnet.com
Thu Apr 10 22:55:34 PDT 2003
On Fri, 11 Apr 2003, David Xu wrote:
> Here is the patch for kernel to save %gs,
> it works well on my machine.
> http://people.freebsd.org/~davidxu/i386_gs.diff
Thanks, I'll give it a go.
> Daniel, is this the reason in your libpthread
> patch that doesn't use getcontext syscall ?
No, we already had userland versions of getcontext()
so I simply reused them to avoid the system call.
That's why THR_GETCONTEXT is a macro; it can be
defined to be getcontext() for those archs that
don't have userland versions and want to use the
system call instead.
Note that we still need userland versions of
_thread_switch() and _thread_enter_uts() anyways,
so writing a userland [gs]etcontext() is probably
pretty simple once you have those.
Plus, when you get a context in order to make a
context for a new thread, you still can't rely on
%gs because it may be scheduled on another KSE or
the thread could be a scope system thread in which
case it be scheduled in another KSEG. So the current
%gs isn't necessarily correct for a new thread.
Hmm, this raises a good point. Once you set up a
thread to run a signal handler, the %gs register has
already been set. We have to be sure that the
interrupted context and the thread's new (signal)
context both have the same %gs and that it runs on
the correct KSE. Either that, or we have to be able
to change the contexts to be the correct %gs before
running the thread and invoking the handler.
--
Dan Eischen
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