linux-kernel - Re: idio{,ma}tic typos (was Re: + fix-vm_can_nonlinear-check-in-sys_remap_file

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Date:	Wed, 10 Oct 2007 11:08:53 -0700
From:	Josh Triplett <josh@...edesktop.org>
To:	Morten Welinder <mwelinder@...il.com>
CC:	Alexey Dobriyan <adobriyan@...ru>, Al Viro <viro@....linux.org.uk>,
	linux-kernel@...r.kernel.org, davej@...emonkey.org.uk,
	Pierre Ossman <drzeus@...eus.cx>, akpm@...l.org,
	linux-sparse@...r.kernel.org
Subject: Re: idio{,ma}tic typos (was Re: + fix-vm_can_nonlinear-check-in-sys_remap_file_pages.patch
 added to -mm tree)

Morten Welinder wrote:
>> While we're at it, below is somewhat ugly sparse patch for detecting
>> "&& 0x" typos.
> 
> Excellent idea, and there is something to be said about a low-footprint patch
> like that.  However, if you really want to capture this kind of bugs, you would
> need to have some kind "not a boolean" or "bitfield" attribute that
> can propagate.
> For example, you would want
> 
>     if (foo && (BAR | BAZ)) ...;
> 
> with BAR and BAZ being hex constants to produce the same warning.
> 
> Incidentally, it is probably not just hex constants that deserve this treatment:
> octal constants and variations of (1 << cst) are of the same nature.  As well
> as enums defined in such manners.

Sparse has a notion of "integer constant expression" already, which it
uses to validate expressions used for things like bitfield widths or
array sizes.  I could easily have Sparse warn on any use of an integer
constant expression as an operand of || or &&.  However, I can imagine
that that might lead to some false positives when intentionally using
an integer constant expression in a condition and expecting the
compiler to optimize it out at compile time.

- Josh Triplett
-
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