linux-kernel - Fwd: Re: [PATCH] staging: gdm724x: gdm_tty: corrected macro by adding brackets

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Message-ID: <15764d01-0602-18c6-e2b1-089b71a2061d@wp.pl>
Date:   Tue, 1 Sep 2020 14:06:23 +0200
From:   "antoni.przybylik@...pl" <antoni.przybylik@...pl>
To:     Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org
Subject: Fwd: Re: [PATCH] staging: gdm724x: gdm_tty: corrected macro by adding
 brackets

On 01.09.2020 13:08, Greg KH wrote:
> On Tue, Sep 01, 2020 at 12:43:11PM +0200, antoniprzybylik wrote:
>> Such macros are dangerous. Consider following example:
>> 	#define GDM_TTY_READY(gdm) (gdm && gdm->tty_dev && gdm->port.count)
>> 	GDM_TTY_READY(a + b)
>> This macro will be expanded in such a way:
>> 	(a + b && a + b->tty_dev && a + b->port.count)
>> And it will lead to errors.
> This is for a pointer, no one would ever do that :)

Nobody adds a pointer to a pointer, but it's common to add to it some 
value like that:

GDM_TTY_READY(myptr + 0x1000)

> But, if you really worry about this, turn it into an inline function,
> that way you get the proper typedef safety, which is what something like
> this should really be, not a macro.

How to do it? Do I need to send another patch?

Antoni Przybylik