linux-kernel - Re: [PATCH v2 2/2] r8169: Avoid pointer aliasing

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Date:   Tue, 05 Feb 2019 11:14:04 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     joe@...ches.com
Cc:     thierry.reding@...il.com, hkallweit1@...il.com, andrew@...n.ch,
        nic_swsd@...ltek.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] r8169: Avoid pointer aliasing

From: Joe Perches <joe@...ches.com>
Date: Tue, 05 Feb 2019 10:42:54 -0800

> On Mon, 2019-02-04 at 19:20 -0800, David Miller wrote:
>> From: Thierry Reding <thierry.reding@...il.com>
>> Date: Mon,  4 Feb 2019 17:42:13 +0100
>> 
>> > @@ -7316,7 +7325,7 @@ static int rtl_get_ether_clk(struct rtl8169_private *tp)
>> >  static int rtl_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
>> >  {
>> >       const struct rtl_cfg_info *cfg = rtl_cfg_infos + ent->driver_data;
>> > -     u8 mac_addr[ETH_ALEN] __aligned(4) = {};
>> > +     u8 mac_addr[ETH_ALEN] = {};
>> >       struct rtl8169_private *tp;
>> 
>> I agree with Heiner, you have to provide at least 2 byte alignment for this
>> buffer due to the reasons he stated.
> 
> It's declared after a pointer so it is already is 2 byte aligned.
> 
> A lot of drivers wouldn't work otherwise.

That's assuming a lot about what the compiler will do when it allocates
local variables to the stack.

I want it _explicit_.