linux-kernel - Re: [net] a6211caa63: dmesg.UBSAN:signed-integer-overflow_in

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Date:   Fri, 5 Jun 2020 16:05:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     kernel test robot <rong.a.chen@...el.com>,
        Yuqi Jin <jinyuqi@...wei.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Jiong Wang <jiongwang@...wei.com>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org
Subject: Re: [net] a6211caa63:
 dmesg.UBSAN:signed-integer-overflow_in_arch/x86/include/asm/atomic.h

On Fri, Jun 05, 2020 at 06:17:51AM -0700, Eric Dumazet wrote:
> On Fri, Jun 5, 2020 at 1:10 AM kernel test robot <rong.a.chen@...el.com> wrote:

> There you go.
> 
> We decided this was a bogus report, and that UBSAN requires sane compilers.
> 
> Please read the fine comment that was added in this commit and update
> your compiler or do not mess with compiler flags.
> 
> +       /* If UBSAN reports an error there, please make sure your compiler
> +        * supports -fno-strict-overflow before reporting it that was a bug
> +        * in UBSAN, and it has been fixed in GCC-8.
> +        */
> +       return atomic_add_return(segs + delta, p_id) - segs;

> >         make HOSTCC=gcc-4.9 CC=gcc-4.9 ARCH=i386 olddefconfig prepare modules_prepare bzImage

Rong, can you make sure to exclude gcc<8 for UBSAN reports ?