netdev - RE: [PATCH net-next v2 1/2] libbpf: parse maps sections of varying size

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Date:   Wed, 4 Oct 2017 14:12:24 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Craig Gallek' <kraigatgoog@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
CC:     Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        Chonggang Li <chonggangli@...gle.com>,
        netdev <netdev@...r.kernel.org>, Eric Leblond <eric@...it.org>,
        "Wangnan (F)" <wangnan0@...wei.com>
Subject: RE: [PATCH net-next v2 1/2] libbpf: parse maps sections of varying
 size

From: Craig Gallek
> Sent: 04 October 2017 14:58
> >> +                     obj->maps[map_idx].def = *def;
> >
> > I'm not too happy/comfortable with this way of copying the memory of
> > "def" (the type-cased struct bpf_map_def).  I guess it works, and is
> > part of the C-standard(?).
> 
> I believe this is a C++-ism.  I'm not sure if it was pulled into the
> C99 standard or if it's just a gcc 'feature' now.  I kept it because
> it was in the initial code, but I'm happy to do an explicit copy for
> v3 if that looks better.

Structure copies have been valid C for ages.

Annoyingly gcc will call memcpy() directly (not a 'private' function).

	David