Date: Sun, 1 Jun 2008 19:05:05 +0200
From: Martin Mares <mj@ucw.cz>
To: Jiri Hladky <hladky.jiri@googlemail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Bug in arch/i386/lib/delay.c file, delay_loop function
Message-ID: <mj+md-20080601.170340.5225.albireo@ucw.cz>
References: <900048340805300815u57af94b0i3971b22a9d154d1f@mail.gmail.com>
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Hi!

> when trying to understand how Bogomips are implemented I have found
> bug in arch/i386/lib/delay.c file, delay_loop function
[...]

> The function fails for loops > 2^31+1. It because SF is set when dec
> returns numbers > 2^31
> 
> The fix is to use jnz instruction instead of jns (and add one decl
> instruction to the end to have exactly the same number of loops as in
> original version):

It is a long time since I have hacked that file, but you should definitely
make sure that the function is never called with a zero argument. In such
case, the original version made just a single pass, but your version
makes 2^32 of them.

				Have a nice fortnight
-- 
Martin `MJ' Mares                          <mj@ucw.cz>   http://mj.ucw.cz/
Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
Homo homini lupus, frater fratri lupior, bohemus bohemo lupissimus.
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