Subject: Re: [PATCH] libiptc.c: pragma disable a gcc compiler warning

From: Pablo Neira Ayuso <[email-masked]>
Date: Thu, 14 May 2020 19:58:51 +0200

On Mon, May 11, 2020 at 02:34:04PM -0700, Maciej Żenczykowski wrote:
> From: Maciej Żenczykowski <[email-masked]>
> 
> Fixes:
>   In file included from libip4tc.c:113:
>   In function ‘iptcc_compile_chain’,
>       inlined from ‘iptcc_compile_table’ at libiptc.c:1246:13,
>       inlined from ‘iptc_commit’ at libiptc.c:2575:8,
>       inlined from ‘iptc_commit’ at libiptc.c:2513:1:
>   libiptc.c:1172:2: warning: writing 16 bytes into a region of size 0 [-Wstringop-overflow=]
>    1172 |  memcpy(&foot->e.counters, &c->counters, sizeof(STRUCT_COUNTERS));
>         |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   In file included from ../include/libiptc/libiptc.h:12,
>                    from libip4tc.c:29:
>   libiptc.c: In function ‘iptc_commit’:
>   ../include/linux/netfilter_ipv4/ip_tables.h:202:19: note: at offset 0 to object ‘entries’ with size 0 declared here
>     202 |  struct ipt_entry entries[0];
>         |                   ^~~~~~~
> 
> Which was found via compilation on Fedora 32.
> 
> Test: builds without warnings
> Signed-off-by: Maciej Żenczykowski <[email-masked]>
> ---
>  libiptc/libiptc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/libiptc/libiptc.c b/libiptc/libiptc.c
> index 58882015..1a92b267 100644
> --- a/libiptc/libiptc.c
> +++ b/libiptc/libiptc.c
> @@ -1169,7 +1169,10 @@ static int iptcc_compile_chain(struct xtc_handle *h, STRUCT_REPLACE *repl, struc
>  	else
>  		foot->target.verdict = RETURN;
>  	/* set policy-counters */
> +#pragma GCC diagnostic push
> +#pragma GCC diagnostic ignored "-Wstringop-overflow"
>  	memcpy(&foot->e.counters, &c->counters, sizeof(STRUCT_COUNTERS));
> +#pragma GCC diagnostic pop

Probably make a casting from foot->e.counters to the counters object
to make gcc happy?