From owner-freebsd-stable  Tue Jan  9  0:19:24 2001
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Date: Tue, 9 Jan 2001 09:00:32 +0100
From: Thomas Zenker <thz@lennartz-electronic.de>
To: freebsd-stable@freebsd.org
Subject: Re: SIGSEGV can be blocked!?
Message-ID: <20010109090032.A795@mezcal.tue.le>
References: <20010108161854.A3547@mezcal.tue.le> <200101082132.f08LWhL18526@saturn.home.ben.com>
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In-Reply-To: <200101082132.f08LWhL18526@saturn.home.ben.com>; from ben@ben.com on Mon, Jan 08, 2001 at 01:32:43PM -0800
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On Mon, Jan 08, 2001 at 01:32:43PM -0800, Ben Jackson wrote:
> > Blocking SIGSEGV with sigprocmask does really BLOCK it. 
> > I think, this is a bug. I discovered this because I wanted to
> > provoke a core dump by a write to (int *)0, but the process got hung,
> 
> The instruction that caused the SEGV is going to restart after any handler
> runs because the handler may have mapped the page that caused the fault.
> 
> On other operating systems you can block SEGV for purposes of asynchronous
> signals (ie `kill -SEGV') but not for synchronous signals.  To quote from
> the Solaris sigprocmask manpage:
> 
>      Signals that  are  generated  synchronously  should  not  be
>      masked.  If  such  a  signal  is  blocked and delivered, the
>      receiving process is killed.
> 
> and indeed a test program shows that you still get SEGV in that case.
> You can still shoot yourself in the foot with a SEGV handler that doesn't
> eliminate the fault.

there is no handler for SEGV - it is simply blocked, if QUIT have been
blocked the machine would lockup.

-- Thomas Zenker
   c/o Lennartz electronic GmbH
   Bismarckstrasse 136, D-72072 Tuebingen, Germany
   Phone:  +49-(0)7071-93550
   Email:  thz@lennartz-electronic.de


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