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[174.17.117.135]) by smtp.gmail.com with ESMTPSA id m67sm7046416pfb.25.2019.02.05.18.27.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 05 Feb 2019 18:27:49 -0800 (PST) Date: Tue, 5 Feb 2019 19:27:33 -0700 From: Paul Zimmerman To: Joe Perches Cc: Eric Dumazet , Heiner Kallweit , David Miller , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/2] r8169: Avoid pointer aliasing Message-Id: <20190205192733.b4bd98988d1e4695f740d445@gmail.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.30; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2019-02-05, Joe Perches wrote: > On Tue, 2019-02-05 at 12:04 -0800, Eric Dumazet wrote: >> >> On 02/05/2019 10:42 AM, Joe Perches wrote: >> > It's declared after a pointer so it is already is 2 byte aligned. >> > >> > A lot of drivers wouldn't work otherwise. >> >> Maybe these drivers are only used on arches where this does not matter. > > Possible. > > I had only grepped through the sources looking for > declarations using: > > $ git grep -B1 '\[ETH_ALEN\];' -- '*.c' | grep -A1 '\*' > > It's quite a few files in net/ too btw. > > I still think adding __align() is unnecessary here unless > it follows something like a bool or a u8. Um, guys, this is practically C-101. From C99, 6.7.2.1: > 13/ Within a structure object, the non-bit-field members and the units in > which bit-fields reside have addresses that increase in the order in which > they are declared. A pointer to a structure object, suitably converted, > points to its initial member (or if that member is a bit-field, then to the > unit in which it resides), and vice versa. There may be unnamed padding > within a structure object, but not at its beginning. AFAIK there is no such language in the spec regarding variable layout on the stack. So Joe, you are totally off-base here. -- Paul