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Subject: Re: may I ignore "net/core/rtnetlink.c:3156:1: warning: the frame
 size of 1280 bytes ..."?
To:     =?UTF-8?Q?Toralf_F=c3=b6rster?= <toralf.foerster@gmx.de>,
        netdev@vger.kernel.org
Cc:     Linux Kernel <linux-kernel@vger.kernel.org>
References: <0cfb892c-b358-4bd6-f7c9-071a0039bc71@gmx.de>
From:   David Ahern <dsahern@gmail.com>
Message-ID: <c4a54cac-89be-157e-d158-46ba3488ccc2@gmail.com>
Date:   Mon, 5 Nov 2018 12:57:21 -0700
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On 11/4/18 9:14 AM, Toralf Förster wrote:
> compiling recent kernel (4.18.x, 4.19.1) at my server I do still get :
> 
> 
> net/core/rtnetlink.c: In function ‘rtnl_newlink’:
> net/core/rtnetlink.c:3156:1: warning: the frame size of 1280 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> 
> 
> with "gcc version 7.3.0 (Gentoo Hardened 7.3.0-r3 p1.4) " and do wonder whether it is safe to ignore it?
> 
> 

I believe the warning is coming from this part of rtnl_newlink():

        if (1) {
                struct nlattr *attr[RTNL_MAX_TYPE + 1];
                struct nlattr *slave_attr[RTNL_SLAVE_MAX_TYPE + 1];
                struct nlattr **data = NULL;
                struct nlattr **slave_data = NULL;
                struct net *dest_net, *link_net = NULL;

The heavy hitters are:
#define RTNL_MAX_TYPE           49
#define RTNL_SLAVE_MAX_TYPE     36

attr and slave_attr would amount to 696 bytes of that 1280. The earlier
defined:

struct nlattr *tb[IFLA_MAX+1];

Would be another 416, so those 3 are 1112 bytes of the warning.

I have been using CONFIG_FRAME_WARN=2048 for a while without a problem.