netdev - RE: [PATCH net-next 2/2] net: rose: Escape trigraph to fix warning with W=1

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Date:   Thu, 29 Oct 2020 14:52:52 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Andrew Lunn' <andrew@...n.ch>
CC:     Jakub Kicinski <kuba@...nel.org>, netdev <netdev@...r.kernel.org>,
        "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: RE: [PATCH net-next 2/2] net: rose: Escape trigraph to fix warning
 with W=1

From: Andrew Lunn
> Sent: 29 October 2020 14:31
> On Thu, Oct 29, 2020 at 02:19:27PM +0000, David Laight wrote:
> > From: Andrew Lunn
> > > Sent: 28 October 2020 00:23
> > >
> > > net/rose/af_rose.c: In function ‘rose_info_show’:
> > > net/rose/af_rose.c:1413:20: warning: trigraph ??- ignored, use -trigraphs to enable [-Wtrigraphs]
> > >  1413 |    callsign = "??????-?";
> > >
> > > ??- is a trigraph, and should be replaced by a ˜ by the
> > > compiler. However, trigraphs are being ignored in the build. Fix the
> > > warning by escaping the ?? prefix of a trigraph.
> > >
> > > Signed-off-by: Andrew Lunn <andrew@...n.ch>
> > > ---
> > >  net/rose/af_rose.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
> > > index cf7d974e0f61..2c297834d268 100644
> > > --- a/net/rose/af_rose.c
> > > +++ b/net/rose/af_rose.c
> > > @@ -1410,7 +1410,7 @@ static int rose_info_show(struct seq_file *seq, void *v)
> > >  			   ax2asc(buf, &rose->dest_call));
> > >
> > >  		if (ax25cmp(&rose->source_call, &null_ax25_address) == 0)
> > > -			callsign = "??????-?";
> > > +			callsign = "????\?\?-?";
> >
> > I think I'd just split the string, eg: "?????" "-?".
> 
> Humm. I think we need a language lawyer.
> 
> Does it concatenate the strings and then evaluate for trigraphs? Or
> does it evaluate for trigraphs, and then concatenate the strings?

I'm 99.9999% sure trigraphs are evaluated before string concatenation.

Although trigraphs are such a stupid idea I'd be tempted to just
turn the warning off.
There is good reason why they are ignored by default.

	David

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