I can tell you what the cause of the bug is, but you'll still have a lot of work to solve it.

The problem is that some piece of C level code is using a pointer that is pointing where it shouldn't. Therefore it is overwriting some other memory. When you try to use that other memory, something that should be impossible (generally a segfault) happens.

The trouble with this kind of bug is that the place where it shows up has nothing to do with where the bug really is. The bug could be in any C code, anywhere. The second problem is that anything that changes the internal memory layout of your program (eg adding print or warn statements to the file) will change what memory gets overwritten by the stray pointer and it apparently goes away. In fact the second characteristic is an indicator that this is the type of bug you are facing.

To fix it you either must track down the bug, or you must change the memory layout so that it doesn't seem to be biting you. The latter is easy - add some code until it doesn't seem to be a problem and pray. It is also unreliable. The former can be hard. Really hard. The best solution is a detailed code audit of all C code involved. I would suggest with the C libraries that you load because they are likely the least tested piece. This is sufficiently difficult that people have written tools to automate this process. Valgrind has been mentioned. More specialized tools like Coverity may be more appropriate (if more expensive).

However you tackle the problem, good luck.

In reply to Re: disappearing segfault by tilly
in thread disappearing segfault by cfreeman

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.