linux-kernel - Re: [linux-next20250912] Build warnings at drivers/net/ethernet/intel/idpf/xdp.c:6

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Message-ID: <75df59a5-56d1-4938-919d-b9e9e2f81251@intel.com>
Date: Mon, 13 Oct 2025 17:32:31 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Venkat <venkat88@...ux.ibm.com>
CC: Madhavan Srinivasan <maddy@...ux.ibm.com>, Stephen Rothwell
	<sfr@...b.auug.org.au>, <michal.kubiak@...el.com>, <ramu.r@...el.com>,
	<anthony.l.nguyen@...el.com>, LKML <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>, Linux Next Mailing List
	<linux-next@...r.kernel.org>
Subject: Re: [linux-next20250912] Build warnings at
 drivers/net/ethernet/intel/idpf/xdp.c:6

From: Venkat <venkat88@...ux.ibm.com>
Date: Mon, 13 Oct 2025 09:27:14 +0530

> 
> 
>> On 12 Sep 2025, at 7:00 PM, Alexander Lobakin <aleksander.lobakin@...el.com> wrote:
>>
>> From: Venkat Rao Bagalkote <venkat88@...ux.ibm.com>
>> Date: Fri, 12 Sep 2025 18:39:33 +0530
>>
>>> Greetings!!!
>>>
>>>
>>> IBM CI has reported a build warning on IBM Power Server, on linux-
>>> next20250912 kernel.
>>>
>>>
>>> gcc version 11.5.0 20240719 (Red Hat 11.5.0-2) (GCC)
>>>
>>> GNU ld version 2.35.2-54.el9
>>>
>>>
>>> Attached is the .config file.
>>>
>>>
>>> Warnings:
>>>
>>> In file included from drivers/net/ethernet/intel/idpf/xdp.c:6:
>>> drivers/net/ethernet/intel/idpf/xdp.h: In function ‘idpf_xdp_tx_xmit’:
>>> drivers/net/ethernet/intel/idpf/xdp.h:28:20: note: the ABI of passing
>>> aggregates with 16-byte alignment has changed in GCC 5

BTW wait, "note"? It's not even a warning?

>>>   28 | static inline void idpf_xdp_tx_xmit(struct libeth_xdp_tx_desc
>>> desc, u32 i,
>>>      |                    ^~~~~~~~~~~~~~~~
>>
>> Yes, I do pass 16-byte variables/structures directly.
>>
>> I would say this warning makes no sense, due to the following reasons:
>>
>> 1. IIRC the minimum required GCC version for building the latest kernel
>>   is way above 5.
>> 2. This warning should appear only with `-Wabi`, which the upstream
>>   kernel never sets.
> 
> Now, this warning is seen on upstream kernel also. 

Then how to reproduce it? I've never seen a single report from the
upstream CI bots which would point out to such warning.

Could RH enable some additional output by default in their GCC?

> 
> Not sure if this is something we need to fix it or suppress the warning?

There's nothing to fix nor suppress.

> 
> Regards,
> Venkat.
> 
>> 3. Kernel is a self-contained project, this function is not uAPI, so we
>>   shouldn't care in general about backward ABI compatibility for purely
>>   in-kernel stuff.
>>
>> We have plenty of functions, mostly generic, which either passes or
>> returns >= 16-byte objects, but I see this warning for the first time.
>> Despite that my repo is attached to the open Intel CI bots infra which
>> does daily builds on a good bunch of different architectures and
>> toolchains (inc. GCC 8+).
Thanks,
Olek