netdev - Re: [PATCH v2 net-next 1/3] sfc: use padding to fix alignment in loopback test

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Message-ID: <90e83021-49f3-2b0e-bb9c-01539229c50b@gmail.com>
Date: Mon, 14 Aug 2023 11:06:54 +0100
From: Edward Cree <ecree.xilinx@...il.com>
To: Arnd Bergmann <arnd@...db.de>, "edward.cree" <edward.cree@....com>,
 linux-net-drivers@....com, "David S . Miller" <davem@...emloft.net>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Netdev <netdev@...r.kernel.org>, Martin Habets
 <habetsm.xilinx@...il.com>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2 net-next 1/3] sfc: use padding to fix alignment in
 loopback test

On 12/08/2023 09:23, Arnd Bergmann wrote:
> On Fri, Jun 23, 2023, at 20:38, edward.cree@....com wrote:
> Unfortunately, the same warning now came back after commit
> 55c1528f9b97f ("sfc: fix field-spanning memcpy in selftest")
...
> I'm out of ideas for how to fix both warnings at the same time,
> with the struct group we get the iphdr at an invalid offset from
> the start of the inner structure,

But the actual address of the iphdr is properly aligned now, right?
AFAICT the concept of the offset per se being 'valid' or not is not
 even meaningful; it's the access address that must be aligned, not
 the difference from random addresses used to construct it.
In which case arguably the warning is just bogus and it's a compiler
 fix we need at this point.

-e