Re: Unit testing kexts

Subject: Re: Unit testing kexts
From: Thomas Tempelmann <email@hidden>
Date: Thu, 25 Aug 2016 16:49:07 +0200

Just thinking out loud - can dtrace be used here? In order to invoke the kext functions when it's loaded normlly? But then, you could probably as well extend your kext with some extra calls that you call from an application.

But either way - it won't be proper unit testing with getting a list of pass/fail msgs so much as testing if anything crashes :) Which, if you usually have no failed tests in your code, may be sufficient to tell that the new build is not fine.

Thomas

On Thu, Aug 25, 2016 at 4:29 PM, Andrew Keller <email@hidden> wrote:

Hi all,

For a while now, we’ve been unit testing individual pieces of our kernel extension by cross-compiling them as a standard user-space application and performing our tests there. Over time, as we have increased our code coverage of the unit tests, we’re noticing a pretty strong upward trend of the number of compiler conditionals required to support cross-compiling between a kext and a user-space app. For example:

#ifdef UNIT_TEST
#include <stdio.h> // for snprintf
#else
#include <libkern/libkern.h> // for snprintf
#endif

and

#ifdef UNIT_TEST
str = (char*) malloc(sz);
#else
str = (char*) OSMalloc(sz, gOSMallocTag);
#endif

(There are some more ugly examples, but I’m betting you can imagine how bad it can get at times)

Suffice it to say, we’re wondering if there’s a better way. Ideally, we would like to unit test the code that’s actually running in production. These compiler-level conditionals force us to essentially maintain two versions of our code. Worse than that, the unit tested version is not the production version.

Off the top of my head, I wonder if it would be sane to build the unit tests as a kext and run them as such, which would allow us to have only one version of our code. However, that sounds a bit like a sledgehammer. Before I go down that road myself, I figured I’d ask around.

How do various people here unit test their kexts?

Thanks,
- Andrew Keller

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References:
	>Unit testing kexts (From: Andrew Keller <email@hidden>)

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