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

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Date:   Tue, 1 Sep 2020 13:08:38 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     antoniprzybylik <antoni.przybylik@...pl>
Cc:     devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: gdm724x: gdm_tty: corrected macro by adding
 brackets

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 :)

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.

thanks,

greg k-h