netdev - Re: [PATCH net] vxlan: fix incorrect initializer in union vxlan

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Message-ID: <CAHA+R7M1DwPgLMYaSMEiU2eXZFqYYL03CJODhmuUrOthpeotzw@mail.gmail.com>
Date:	Sat, 16 Aug 2014 15:48:06 -0700
From:	Cong Wang <cwang@...pensource.com>
To:	Gerhard Stenzel <gstenzel@...ux.vnet.ibm.com>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] vxlan: fix incorrect initializer in union vxlan_addr

On Fri, Aug 15, 2014 at 2:03 AM, Gerhard Stenzel
<gstenzel@...ux.vnet.ibm.com> wrote:
>
> The first initializer in the following
>
>                 union vxlan_addr ipa = {
>                         .sin.sin_addr.s_addr = tip,
>                         .sa.sa_family = AF_INET,
>                 };
>
> is optimised away by the compiler, due to the second initializer,
> therefore initialising .sin.sin_addr.s_addr always to 0.
> This results in netlink messages indicating a L3 miss never contain the
> missed IP address. This was observed with GCC 4.8 and 4.9. I do not know
> about previous versions.
> The problem affects user space programs relying on an IP address being
> sent as part of a netlink message indicating a L3 miss.
>
> Changing
>                         .sa.sa_family = AF_INET,
> to
>                         .sin.sin_family = AF_INET,
> fixes the problem.

So GCC can't figure out we are initializing different parts of this
union through
different members... Or maybe we should not use initializer at all.

Anyway,

Acked-by: Cong Wang <cwang@...pensource.com>
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