linux-kernel - Re: Possible code defects: macros and precedence

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Message-ID: <alpine.DEB.2.10.1609041809260.3178@hadrien>
Date:   Sun, 4 Sep 2016 18:10:18 +0800 (SGT)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Joe Perches <joe@...ches.com>
cc:     Dan Carpenter <error27@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Possible code defects: macros and precedence



On Sat, 3 Sep 2016, Joe Perches wrote:

> There are many nominally incorrect macro definitions
> in linux-kernel source where parentheses are not used
> for various macros arguments with calculations.
>
> Does coccinelle or smatch have the ability to detect
> potential macro misuse where arguments passed to the
> macro are not correctly parenthesized by the macro?
>
> Something like:
>
> 	#define A 1
> 	#define B 2
> 	#define shift(val) (val << 1)
>
> where a use is:
>
> 	int c = shift(A | B)
>
> where the actual result is 5 but the expected result is 6?
>
> Can either tool suggest changing the macro to
>
> 	#define shift(val) ((val) << 1)

Coccinelle could do this.  It is possible to match macro parameters, and
it is possible to match binary operators generically.  I can look into it.

julia