---
layout: post
author: Pascal Cuoq
date: 2011-05-31 21:34 +0200
categories: csmith rant
format: xhtml
title: "The Stupidest Question I have ever heard at a Computer Science presentation"
summary:
---
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<p>Some time back, I reported a Csmith bug against the last git version.
This is in no way a rant against <a href="http://embed.cs.utah.edu/csmith/">Csmith</a> a fine piece of engineering.
Csmith does something that I would not have thought possible if you had asked
me before I saw it: it generates random C programs that are both
free of undefined behavior and varied enough to uncover a ton
of bugs in the C-accepting program you pipe it into.</p>
<blockquote><p>Unless the C-accepting program is <a href="http://compcert.inria.fr/">CompCert</a> in which case you only uncover a couple of bugs apparently.</p>
</blockquote>
<p>Bugs in random programs have a funny way to find themselves. You don't need
to try many inputs as the random program explores these for you.
Even if you think you are being quite the conservative user
they pop up uninvited from time to time (although to be fair you can see
that they are being fixed because they pop up less and less frequently).
Anyway dangling pointers were being passed as arguments to functions that didn't
use them although I was not using the option that allows this behavior
in generated programs. This was my bug. It had been good company
but I didn't feel ready for a long-term relationship. It was time to let go.</p>
<p>Fast forward a few days and there is this <a href="https://github.com/csmith-project/csmith/commit/208de0fc9b42dd74b0a7bf93527a3378d03fad79">promising commit</a> on github.
I decide I may as well upgrade although the bug was only appearing from time to
time because I had fiddled with the parameters in a way that made it more likely to appear
and I had not seen it at all since I had fiddled with the parameters again.</p>
<p>Suddenly as I re-compile with GCC this program generator that finds bugs
in GCC I am reminded of the stupidest question I ever heard at the end of
a computer science presentation.</p>
<p>Like many bad questions this question was more a remark than a question.
Adapted to the present context it would go like this:</p>
<blockquote><p>It doesn't make sense to use Csmith find bugs in C compilers since it is itself compiled with a C (technically C++) compiler.</p>
</blockquote>
<p>Apparently as a physics student much earlier the asker had been chided for using a pendulum-based chronometer to verify the constancy of a pendulum's period.</p>
<p>So if I may be so bold as to impart my own wisdom to the world in the form of random remarks there are two lessons in this post. "Be careful of circular reasoning" is one but "software is not quite as similar to the physical world as you could expect" is another.</p>
<p>Some time back, I reported a Csmith bug against the last git version.
This is in no way a rant against <a href="http://embed.cs.utah.edu/csmith/">Csmith</a> a fine piece of engineering.
Csmith does something that I would not have thought possible if you had asked
me before I saw it: it generates random C programs that are both
free of undefined behavior and varied enough to uncover a ton
of bugs in the C-accepting program you pipe it into.</p>
<blockquote><p>Unless the C-accepting program is <a href="http://compcert.inria.fr/">CompCert</a> in which case you only uncover a couple of bugs apparently.</p>
</blockquote>
<p>Bugs in random programs have a funny way to find themselves. You don't need
to try many inputs as the random program explores these for you.
Even if you think you are being quite the conservative user
they pop up uninvited from time to time (although to be fair you can see
that they are being fixed because they pop up less and less frequently).
Anyway dangling pointers were being passed as arguments to functions that didn't
use them although I was not using the option that allows this behavior
in generated programs. This was my bug. It had been good company
but I didn't feel ready for a long-term relationship. It was time to let go.</p>
<p>Fast forward a few days and there is this <a href="https://github.com/csmith-project/csmith/commit/208de0fc9b42dd74b0a7bf93527a3378d03fad79">promising commit</a> on github.
I decide I may as well upgrade although the bug was only appearing from time to
time because I had fiddled with the parameters in a way that made it more likely to appear
and I had not seen it at all since I had fiddled with the parameters again.</p>
<p>Suddenly as I re-compile with GCC this program generator that finds bugs
in GCC I am reminded of the stupidest question I ever heard at the end of
a computer science presentation.</p>
<p>Like many bad questions this question was more a remark than a question.
Adapted to the present context it would go like this:</p>
<blockquote><p>It doesn't make sense to use Csmith find bugs in C compilers since it is itself compiled with a C (technically C++) compiler.</p>
</blockquote>
<p>Apparently as a physics student much earlier the asker had been chided for using a pendulum-based chronometer to verify the constancy of a pendulum's period.</p>
<p>So if I may be so bold as to impart my own wisdom to the world in the form of random remarks there are two lessons in this post. "Be careful of circular reasoning" is one but "software is not quite as similar to the physical world as you could expect" is another.</p>
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