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Date:      Thu, 2 Sep 1999 01:01:43 -0400 (EDT)
From:      Luoqi Chen <luoqi@watermarkgroup.com>
To:        nox@jelal.kn-bremen.de, wine-devel@winehq.com
Cc:        freebsd-emulation@FreeBSD.ORG
Subject:   Re:  wine signal handlers lose %fs on FreeBSD
Message-ID:  <199909020501.BAA17295@lor.watermarkgroup.com>

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> Here's a strange one:  Sometimes apparently wine's signal handlers receive
> %fs messed up (zeroed actually) and therefore crash/hang on FreeBSD
> (3.2-stable, wine current-cvs).  Patch this and watch for
> `warn:seh:EXC_SaveContext teb=0xsomewhere teb_sel=something, fs=0, gs=foo'
> messages, teb_sel is what fs really should have been (and what is loaded
> back there after the message, so the program actually continues too.)
> 
>  Any idea/explanation from the experts?  I have looked at the sources a bit
> but came up empty. (well i found out that fs and gs aren't set/used in
> the sigcontext struct for non-vm86 processes but wine knows that and simply
> uses the registers directly, and i couldn't find anything that looked like
> it would change them on the way into and out of the signal handler, or
> anywhere else in the kernel for that matter...)
> 
The kernel sets %fs to 0 during a context switch if it triggers a fault
(protection fault or segment not present) and signals SIGBUS. Most likely
the EXC_segv in your previous email is this signal. Unfortunately there
is no easy way to know which %fs value is causing the fault (probably you
could add a kernel printf, in file sys/i386/i386/trap.c, search for
cpu_switch_load_fs).

I took a brief look at the exception code, it probably would not work
under 4.0-current because the kernel uses %fs and signal handlers are
called with a default %fs value (the same as the default %ds). You might
need to restore %fs from the value in sigcontext at beginning of your
signal handlers (yes, fs in sigcontext is set for 4.0-current. Regarding
this, we could change the kernel, both -current and -stable, so that fs/gs
are always saved in sigcontext when the signal is delivered, and restored
during the signal trampoline, hence a consistent interface to application
authors). Alternatively, we could change the kernel to call signal handlers
with the original fs.

>  Btw could someone please subscribe this address to -emulation for me?
> freebsd-emulation-l@jelal.kn-bremen.de (which is a local mailpost alias
> in case anyone wonders, i prefer reading the lists with trn...)
> 
>  I mailed majordomo with this a while ago (and yes i did send the auth
> command back :) but alas, no messages.
> 
This is a low traffic list, chances are there were no messages...

-lq


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