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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Joe Perches <joe@perches.com>
Cc: William Hubbs <w.d.hubbs@gmail.com>,
        Chris Brannon <chris@the-brannons.com>, Kirk Reiser <kirk@reisers.ca>,
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Subject: Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x
Organization: D03
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Date: Sun, 06 Dec 2015 01:21:30 +0100
In-Reply-To: <1449360735.20344.6.camel@perches.com> (Joe Perches's message of
	"Sat, 05 Dec 2015 16:12:15 -0800")
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On Sun, Dec 06 2015, Joe Perches <joe@perches.com> wrote:

> On Sun, 2015-12-06 at 01:05 +0100, Rasmus Villemoes wrote:
>> If char is signed and ch happens to be negative, printing ch with
>> "%02x" will not do as intended (when ch is -19, one will get
>> "ffffffed"). Fix that by masking with 0xff.
>
> I presume there are a lot of these in the kernel.
> Did you use a tool to find this or just inspection?

Initially I just used coccinelle, for the most obvious candidates (with
--include-headers-for-types):

@r depends on !patch@
char c;
@@
* \( sprintf \| snprintf \| scnprintf \) (..., c, ...)

That gives lots of false positives (arguments to %c), but it's not too
bad piping to less, searching for "%[0.]2[xX]", and then checking
manually.

I'm now doing a much wider range of printf functions, but it's really
past my bedtime, so feel free to pick up the ball :-)

Rasmus