netdev - Re: [PATCH] net: usb: initialize tmp in dm9601.c to avoid warning

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Message-Id: <20130118.030341.2246222347501217868.davem@davemloft.net>
Date:	Fri, 18 Jan 2013 03:03:41 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	jacmet@...site.dk
Cc:	sque@...omium.org, netdev@...r.kernel.org, msb@...omium.org
Subject: Re: [PATCH] net: usb: initialize tmp in dm9601.c to avoid warning

From: Peter Korsgaard <jacmet@...site.dk>
Date: Fri, 18 Jan 2013 08:37:41 +0100

>>>>>> "David" == David Miller <davem@...emloft.net> writes:
> 
>  >> What warning and what compiler version are you using?
> 
>  David> I wouldn't bother asking this, unless it's so that you personally
>  David> can reproduce this in the future.
> 
>  David> The compiler cannot determine with %100 certainty that tmp is
>  David> initialized in all paths.  Any time there are conditional
>  David> statements guarding setting and the use, the compiler is going
>  David> to err on the side of caution and say that if any of those
>  David> paths lead to a use without a set it's going to warn.
> 
> Sure, I just wondered as the code hasn't changed in 5+ years, and the
> function that gets called is defined just above, so the compiler should
> be able to figure it out.

Nothing guarentees that a piece of memory passed into an external
function has it's contents initialized completely by that function.

The compiler can't see what usbnet_read_cmd() does with the memory
behind the 'data' pointer argument.  So it makes the only assumption
it can make, which is that 'tmp' might be uninitialized.
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