linux-kernel - RE: [PATCH] staging: gdm724x: Fix Duplication of Side Effects

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Message-ID: <acde5b1e8495431dac05403c593d4679@AcuMS.aculab.com>
Date:   Thu, 31 Mar 2022 10:49:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Dan Carpenter' <dan.carpenter@...cle.com>
CC:     'Alaa Mohamed' <eng.alaamohamedsoliman.am@...il.com>,
        "outreachy@...ts.linux.dev" <outreachy@...ts.linux.dev>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] staging: gdm724x: Fix Duplication of Side Effects

From: Dan Carpenter
> Sent: 31 March 2022 11:40
> 
> On Thu, Mar 31, 2022 at 10:29:04AM +0000, David Laight wrote:
> > From: Alaa Mohamed
> > > Sent: 31 March 2022 11:19
> > >
> > > Fix Duplication of Side Effects for GDM_TTY_READY(gdm) macro
> > > reported by checkpatch
> > > "CHECK: Macro argument reuse 'gdm' - possible side-effects?"
> > >
> > > Signed-off-by: Alaa Mohamed <eng.alaamohamedsoliman.am@...il.com>
> > > ---
> > >  drivers/staging/gdm724x/gdm_tty.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/gdm724x/gdm_tty.c b/drivers/staging/gdm724x/gdm_tty.c
> > > index 04df6f9f5403..6f0274470e69 100644
> > > --- a/drivers/staging/gdm724x/gdm_tty.c
> > > +++ b/drivers/staging/gdm724x/gdm_tty.c
> > > @@ -27,7 +27,9 @@
> > >
> > >  #define MUX_TX_MAX_SIZE 2048
> > >
> > > -#define GDM_TTY_READY(gdm) (gdm && gdm->tty_dev && gdm->port.count)
> > > +#define GDM_TTY_READY(_gdm) \
> > > +	({ typeof(_gdm) (gdm) = (_gdm); \
> > > +	(gdm && gdm->tty_dev && gdm->port.count); })
> >
> > Did you test this?
> >
> > see https://godbolt.org/z/cazPrrzPv
> >
> 
> I don't understand the link.  The patch should work as far as I can see.

If you call GDM_TTY_READY(gdm) the first line ends up as:
	struct xxx *gdm = gdm;
which shadows the parameter.
There's probably a warning about an uninitialised variable as well.

The 'gdm' and '_gdm' would need swapping over.
But, as you said, just:
#define GDM_TTY_READY(gdm) ((gdm) && (gdm)->tty_dev && (gdm)->port.count)
is fine - I'd add the () but not worry about multiple evaluation.

	David

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