netdev - RE: [PATCH net-next] drivers: net: sky2: Fix -Wstringop-truncation with W=1

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Date:   Tue, 3 Nov 2020 10:19:55 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jakub Kicinski' <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>
CC:     netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH net-next] drivers: net: sky2: Fix -Wstringop-truncation
 with W=1

From: Jakub Kicinski
> Sent: 03 November 2020 00:01
> 
> On Sat, 31 Oct 2020 18:40:28 +0100 Andrew Lunn wrote:
> > In function ‘strncpy’,
> >     inlined from ‘sky2_name’ at drivers/net/ethernet/marvell/sky2.c:4903:3,
> >     inlined from ‘sky2_probe’ at drivers/net/ethernet/marvell/sky2.c:5049:2:
> > ./include/linux/string.h:297:30: warning: ‘__builtin_strncpy’ specified bound 16 equals destination
> size [-Wstringop-truncation]
> >
> > None of the device names are 16 characters long, so it was never an
> > issue, but reduce the length of the buffer size by one to avoid the
> > warning.
> >
> > Signed-off-by: Andrew Lunn <andrew@...n.ch>
> > ---
> >  drivers/net/ethernet/marvell/sky2.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/marvell/sky2.c b/drivers/net/ethernet/marvell/sky2.c
> > index 25981a7a43b5..35b0ec5afe13 100644
> > --- a/drivers/net/ethernet/marvell/sky2.c
> > +++ b/drivers/net/ethernet/marvell/sky2.c
> > @@ -4900,7 +4900,7 @@ static const char *sky2_name(u8 chipid, char *buf, int sz)
> >  	};
> >
> >  	if (chipid >= CHIP_ID_YUKON_XL && chipid <= CHIP_ID_YUKON_OP_2)
> > -		strncpy(buf, name[chipid - CHIP_ID_YUKON_XL], sz);
> > +		strncpy(buf, name[chipid - CHIP_ID_YUKON_XL], sz - 1);
> 
> Hm. This irks the eye a little. AFAIK the idiomatic code would be:
> 
> 	strncpy(buf, name..., sz - 1);
> 	buf[sz - 1] = '\0';
> 
> Perhaps it's easier to convert to strscpy()/strscpy_pad()?
> 
> >  	else
> >  		snprintf(buf, sz, "(chip %#x)", chipid);
> >  	return buf;

Is the pad needed?
It isn't present in the 'else' branch.

	David

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