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Subject: Re: [PATCH v5] net: ip, diag -- Add diag interface for raw sockets
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>,
        David Ahern <dsa@cumulusnetworks.com>, netdev@vger.kernel.org,
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Date: Wed, 28 Sep 2016 06:29:08 -0700
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On Wed, 2016-09-28 at 16:03 +0300, Cyrill Gorcunov wrote:
> On Wed, Sep 28, 2016 at 05:57:12AM -0700, Eric Dumazet wrote:
> ...
> > Note that some programs could fail to compile with the added union
> > anyway.
> > 
> > Some gcc versions are unable to compile a static init with an union
> > 
> > struct inet_diag_req_v2 foo = { .pad = 0, sdiag_family = AF_INET, };
> > 
> > When I cooked my recent fq commit I simply removed a pad and replaced
> > it :
> > 
> > git show fefa569a9d4bc4 -- include
> 
> Oh, crap :( I've been looking into uapi headers, found that we
> use anonymous unions (for example include/uapi/linux/bcache.h)
> and thought it will be safe (and my test builds didn't fail).
> Are you happen to know which gcc versions cant do that?

The most recent example I have in mind is a kbuild bot report on the
recent TCP BBR patches. We had to rework the patch to avoid the problem.

If I remember well, this was a gcc-4.7, but not on x86.