Re: [PATCH] net: ethernet: mscc: fix missing brace warning for old compilers

From: Jakub Kicinski
Date: Mon Nov 02 2020 - 17:08:12 EST


On Mon, 2 Nov 2020 13:56:55 +0000 Vladimir Oltean wrote:
> On Mon, Nov 02, 2020 at 09:41:36PM +0800, Pujin Shi wrote:
> > For older versions of gcc, the array = {0}; will cause warnings:
> >
> > drivers/net/ethernet/mscc/ocelot_vcap.c: In function 'is1_entry_set':
> > drivers/net/ethernet/mscc/ocelot_vcap.c:755:11: warning: missing braces around initializer [-Wmissing-braces]
> > struct ocelot_vcap_u16 etype = {0};
> > ^
> > drivers/net/ethernet/mscc/ocelot_vcap.c:755:11: warning: (near initialization for 'etype.value') [-Wmissing-braces]
> >
> > 1 warnings generated
> >
> > Fixes: 75944fda1dfe ("net: mscc: ocelot: offload ingress skbedit and vlan actions to VCAP IS1")
> > Signed-off-by: Pujin Shi <shipujin.t@xxxxxxxxx>
> > ---
> > drivers/net/ethernet/mscc/ocelot_vcap.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ethernet/mscc/ocelot_vcap.c b/drivers/net/ethernet/mscc/ocelot_vcap.c
> > index d8c778ee6f1b..b96eab4583e7 100644
> > --- a/drivers/net/ethernet/mscc/ocelot_vcap.c
> > +++ b/drivers/net/ethernet/mscc/ocelot_vcap.c
> > @@ -752,7 +752,7 @@ static void is1_entry_set(struct ocelot *ocelot, int ix,
> > dport);
> > } else {
> > /* IPv4 "other" frame */
> > - struct ocelot_vcap_u16 etype = {0};
> > + struct ocelot_vcap_u16 etype = {};
> >
>
> Sorry, I don't understand what the problem is, or why your patch fixes
> it. What version of gcc are you testing with?

Old GCC does not like the 0, if the members of struct are not scalars.

struct ocelot_vcap_u16 {
u8 value[2];
u8 mask[2];
};

In this case the first member is an array.

It wants us to add another curly brace:

struct ocelot_vcap_u16 etype = {{0}};

... or we can just skip the 0.

That's just FWIW. I don't remember which versions of GCC behave like
that, I just know we get a constant stream of this sort of fixes.
I think clang may generate a similar warning.

Pujin, please specify the version of GCC you're using and repost.