linux-kernel - Re: [PATCH] clk: vt8500: don't return possibly uninitialized data

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Message-ID: <1624352.DBIo65mLZO@wuerfel>
Date:	Wed, 03 Feb 2016 10:15:34 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Roman Volkov <v1ron@...l.ru>,
	Michael Turquette <mturquette@...libre.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, Tony Prisk <linux@...sktech.co.nz>,
	Andrzej Hajda <a.hajda@...sung.com>, linux-clk@...r.kernel.org
Subject: Re: [PATCH] clk: vt8500: don't return possibly uninitialized data

On Wednesday 03 February 2016 11:36:26 Roman Volkov wrote:
> 
> Hi Arnd,
> 
> Thanks for fixing this code! Did someone reproduce this bug, or this
> is something theoretical, based on the code analysis? I just never
> heard about the issue. I can look into the code on the weekends too, I
> have WM8505\WM8650 machines to test.

I only fixed it after analysing the gcc warnings I got after Andrzej Hajda's
patch, and he also did it to fix the initial problem he found using
coccinelle, so I don't think anyone has run into the problem on live
hardware.

As long as all drivers ask for clock rates that are valid, you won't
see either problem.

> Is it enough to run the regular kernel build for WM8650 to see the
> warnings, or there are special options in the kernel to run the compiler
> test?

The warning is hidden if you build with -Os (CONFIG_CC_OPTIMIZE_FOR_SIZE),
and it may not happen with all gcc versions. I was using gcc-5.2.

	Arnd