Mailing-List: contact modperl-help@perl.apache.org; run by ezmlm
Precedence: bulk
Subject: Re: Random segmentation fault
To: Steve Hay <steve.m.hay@googlemail.com>, John Dunlap <john@lariat.co>
References: 
 <CAC5eUSu85CoiT0MkQvwvxjfrhJcn13DqJfV=EgFuXvwsWYrXLg@mail.gmail.com>
 <55EBFDC0.90903@sanger.ac.uk>
 <CAC5eUSuKHh4ZCaohK8GFvHsoRMAn+H1Tf7prJL_cmHq7REO1YA@mail.gmail.com>
 <55F6D959.60606@gkg.net>
 <CAC5eUSsbiTHpBh1yG_7RB8oHzf4gB4Lq45=O2StQxSNCYwWWmw@mail.gmail.com>
 <CADED=K7oK0Of_V5DUPff4QbXWe0++DGbNkUnUrqchnm7JzjfOQ@mail.gmail.com>
Cc: mod_perl list <modperl@perl.apache.org>
From: Michael Schout <mschout@gkg.net>
Message-ID: <55F88687.6040306@gkg.net>
Date: Tue, 15 Sep 2015 15:58:47 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0)
 Gecko/20100101 Thunderbird/38.2.0
MIME-Version: 1.0
In-Reply-To: 
 <CADED=K7oK0Of_V5DUPff4QbXWe0++DGbNkUnUrqchnm7JzjfOQ@mail.gmail.com>
Content-Type: multipart/mixed;
 boundary="------------020207090609040702080900"

This is a multi-part message in MIME format.
--------------020207090609040702080900
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit

Steve, John:

I did a bisect today against perl git, using mod_perl 2.0.9 and apache
2.2.29 to find out where my two issues were caused.  It turns out that
both of my problems, which were:

- panic: attempt to copy freed scalar xxxx to yyyy

and also

- segmentation fault caused by a specific "return" statement

Are *BOTH* caused by the following commit made to perl between 5.19.6
and 5.19.7:

> commit 437e3a7dac994ebace1195549170c81f474d9c20
> Author: Matthew Horsfall <WolfSage@gmail.com>
> Date:   Wed Dec 11 18:28:21 2013 -0500
> 
>     Optimise out PUSHMARK/RETURN if return is the last statement in a sub.
>     
>     This makes:
>     
>       sub baz { return $cat; }
>     
>     Behave like:
>     
>       sub baz { $cat; }
>     
>     Which is notably faster.
...

I created a patch that reverses this (at least the change to op.c.. the
other parts of the patch are just new macros, and a test case), then
both of my problems are fixed.

John:  I'd be interested to know if your problem is related.  If
possible, can you build perl with the attached patch applied and see  if
that fixes your segfault also?

This seems to be mod_perl specific.  I have a very
straightforward/minimal test case that causes the "panic" error under
mod_perl, but the same code runs fine under the command line outside of
mod_perl.

Regards,
Michael Schout

--------------020207090609040702080900
Content-Type: text/plain; charset=UTF-8; x-mac-type="0"; x-mac-creator="0";
 name="perl-return.patch"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
 filename="perl-return.patch"
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--------------020207090609040702080900--