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Message-ID: <3AF6E0E8.4E9B14E6@yahoo.com>
Date: Mon, 07 May 2001 13:52:40 -0400
From: Earnie Boyd <earnie_boyd AT yahoo DOT com>
Reply-To: Cygwin Developers <cygwin-developers AT cygwin DOT com>
MIME-Version: 1.0
To: cygwin-developers AT cygwin DOT com
Subject: Re: Signal fixes [WAS: Re: Fix for ssh problems]
References: <20010504224503 DOT A20310 AT redhat DOT com> <20010505104012 DOT A29822 AT cygbert DOT vinschen DOT de> <20010505124737 DOT B4038 AT redhat DOT com>
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Christopher Faylor wrote:
> 
> It only took two days or so for me to realize that my stack walking code
> was screwed up.  The way signals work is that cygwin routines register
> their frame pointers on entry.  If a signal occurs, then the location on
> the stack which has the return address is replaced with a call to a
> signal handler prefix which resets a "signal_arrived" event and calls
> any appropriate signal handler.
> 
> I'd changed things so that the call to the signal handler prefix was
> being put on the caller of the function's return rather than the
> functions return.  So, the signal_arrived event was never being reset.
> This caused a WaitForMultipleObjects in select() to be continually
> triggered.
> 
> I have had this problem so many times that I'm embarrassed that it took
> two days for me to figure out what the problem was.  This was due to my
> changes to the stack dump stuff in cygwin.  It uses the same code to
> walk the stack as the signal handler.  So, when I made the stack dumper
> work better for exceptions, I broke the signal handler.
> 
> Exceptions are strange because, while they set up something that looks
> like a frame pointer on the stack, it isn't a true frame pointer, so you
> have to make allowances.  You don't have to make those allowances for
> the signal handler.
> 
> After seeing this problem, I have another idea on how to handle signals.
> It could be a cleaner implementation but now that the current version
> isn't broke, I'm a little reluctant to fix it.  Maybe in 1.3.4...
> 

Just a note that this also fixed a problem of rxvt not ending when bash
logged out.

Earnie.

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