netdev - Re: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

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Message-ID: <20240807165152.GD3006561@kernel.org>
Date: Wed, 7 Aug 2024 17:51:52 +0100
From: Simon Horman <horms@...nel.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Potnuri Bharat Teja <bharat@...lsio.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

On Mon, Aug 05, 2024 at 10:24:30AM -0600, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> So, in order to avoid ending up with a flexible-array member in the
> middle of multiple other structs, we use the `__struct_group()`
> helper to create a new tagged `struct tc_u32_sel_hdr`. This structure
> groups together all the members of the flexible `struct tc_u32_sel`
> except the flexible array.
> 
> As a result, the array is effectively separated from the rest of the
> members without modifying the memory layout of the flexible structure.
> We then change the type of the middle struct member currently causing
> trouble from `struct tc_u32_sel` to `struct tc_u32_sel_hdr`.
> 
> This approach avoids having to implement `struct tc_u32_sel_hdr`
> as a completely separate structure, thus preventing having to maintain
> two independent but basically identical structures, closing the door
> to potential bugs in the future.
> 
> So, with these changes, fix the following warning:
> drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h:245:27: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Reviewed-by: Simon Horman <horms@...nel.org>