linux-kernel - Re: [PATCH 1/2] net/mlx5e: shut up maybe-uninitialized warning

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Message-ID: <CAJ3xEMgoPh0teRZYvp42CkbU62K=1sZvdbY1zeRbHYz-AzPm3g@mail.gmail.com>
Date:   Sat, 1 Oct 2016 18:08:02 +0300
From:   Or Gerlitz <gerlitz.or@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        Matan Barak <matanb@...lanox.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Amir Vadai <amirva@...lanox.com>,
        Maor Gottlieb <maorg@...lanox.com>,
        Linux Netdev List <netdev@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] net/mlx5e: shut up maybe-uninitialized warning

On Fri, Sep 30, 2016 at 7:17 PM, Arnd Bergmann <arnd@...db.de> wrote:
> Build-testing this driver with -Wmaybe-uninitialized gives a new false-positive
> warning that I can't really explain:
>
> drivers/net/ethernet/mellanox/mlx5/core/en_tc.c: In function 'mlx5e_configure_flower':
> drivers/net/ethernet/mellanox/mlx5/core/en_tc.c:509:3: error: 'old_attr' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> It's obvious from the code that 'old_attr' is initialized whenever 'old'
> is non-NULL here. The warning appears with all versions I tested from gcc-4.7
> through gcc-6.1, and I could not come up with a way to rewrite the function
> in a more readable way that avoids the warning, so I'm adding another
> initialization to shut it up.
>
> Fixes: 8b32580df1cb ("net/mlx5e: Add TC vlan action for SRIOV offloads")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Yeah, this is clearly false positive and I was sure that newish GCCs
don't show that, but you are the master here.. so FWIW

Acked-by: Or Gerlitz <ogerlitz@...lanox.com>