linux-kernel - Re: [PATCH] tracehook: add some self tests

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Date:	Mon, 15 Feb 2010 16:11:01 -0500
From:	Mike Frysinger <vapier.adi@...il.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracehook: add some self tests

On Mon, Feb 15, 2010 at 15:28, Roland McGrath wrote:
> This is something of a misnomer, since asm/syscall.h is the only thing you
> are testing.

it's meant as a starting point, not the end point.  so overtime people
can easily extend it.

> I'd make the more general point that this sort of "synthetic" test does not
> seem very useful.  At best, it can test the asm/syscall.h code for being
> internally consistent--but that doesn't test whether it's really correct.

i wrote it because i needed it when trying to make sure the various
i/n values worked correctly.  writing a bit of static code based on
just "n" is trivial, but avoiding a nest of code with i/n is a lot
harder.  and as i noted earlier, there is on code in the kernel that
ever calls with i being non-zero.

> IMHO this is not worth having unless it's an "empirical" test.  What I mean
> by that is one that really uses the asm/syscall.h calls as specified, and
> in the context specified.  So, you'd have to fork a user process and use
> ptrace on it to get it stopped at a syscall entry.  Then you can fetch the
> arguments, modify them, and look at the arguments it actually passes in to
> the syscall.

that would indeed be useful as a next point
-mike
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