linux-kernel - Re: [PATCH] Fix __ucmpdi2 in v4l2_norm_to

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Date:	Fri, 5 Jan 2007 15:20:16 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Stelian Pop <stelian@...ies.net>
Cc:	v4l-dvb-maintainer@...uxtv.org, Linus Torvalds <torvalds@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Andrew Morton <akpm@...l.org>
Subject: Re: [PATCH] Fix __ucmpdi2 in v4l2_norm_to_name()

>>> The largest value we use here is 0x02000000.  Perhaps v4l2_std_id 
>>> shouldn't
>>> be 64-bit?
>> Too late to change it to 32 bits. It is at V4L2 userspace API since
>> kernel 2.6.0. We can, however use this approach as a workaround, with
>> the proper documentation.
>
> Maybe with a BUG_ON(id > UINT_MAX) ?

If the code code is like

	u64 user_id;
	u32 kernel_id = user_id;

(or different types, just showing the difference in word
lengths here) it's easiest and safest to do

	BUG_ON(kernel_id != user_id);

i.e. cast back up to 64-bit, see if it's identical to the
original.  You won't have to worry about sign extensions or
similar that way, the BUG_ON() condition expresses the actual
requirement directly.


Segher

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