linux-kernel - Re: [PATCH v2] drm/pl111: Use 64-bit arithmetic instead of 32-bit

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Date:   Tue, 17 Jul 2018 14:52:01 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Eric Anholt <eric@...olt.net>, David Airlie <airlied@...ux.ie>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/pl111: Use 64-bit arithmetic instead of 32-bit

Hi Eric,

On 07/17/2018 01:40 PM, Eric Anholt wrote:
> "Gustavo A. R. Silva" <gustavo@...eddedor.com> writes:
> 
>> Add suffix ULL to constant 1000 in order to give the compiler complete
>> information about the proper arithmetic to use.
>>
>> Notice that such constant is used in a context that expects an
>> expression of type u64 (64 bits, unsigned) and the following
>> expression is currently being evaluated using 32-bit arithmetic:
>>
>> mode->clock * 1000
>>
>> Addresses-Coverity-ID: 1466139 ("Unintentional integer overflow")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> 
> This is silly.  The clock won't be over 4ghz -- we haven't seen anything
> over 1024x768 on this hardware as far as I know.  The u64 is for the
> multiplication by width/height below.
> 

Yep. I understand. That's why I didn't use the word *fix* anywhere in
the changelog.

> I've still applied the patch to shut up the tool.
> 

Thanks
--
Gustavo