linux-kernel - Re: [PATCH v2][next] scsi: megaraid_sas: Avoid a couple -Wflex-array-member-not-at-end warnings

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Message-ID: <3a80fd1d-5a05-4db3-9dda-3ad38bedfb38@embeddedor.com>
Date: Tue, 7 Oct 2025 11:43:04 +0100
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Kashyap Desai <kashyap.desai@...adcom.com>,
 Sumit Saxena <sumit.saxena@...adcom.com>,
 Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
 Chandrakanth patil <chandrakanth.patil@...adcom.com>,
 "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2][next] scsi: megaraid_sas: Avoid a couple
 -Wflex-array-member-not-at-end warnings

Hi all,

Friendly ping: who can take this, please?

Thanks!
-Gustavo

On 9/19/25 12:56, 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.
> 
> Use the new TRAILING_OVERLAP() helper to fix the following warnings:
> 
> drivers/scsi/megaraid/megaraid_sas_fusion.h:1153:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> drivers/scsi/megaraid/megaraid_sas_fusion.h:1198:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> This helper creates a union between a flexible-array member (FAM)
> and a set of MEMBERS that would otherwise follow it --in this case
> `struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN]` and
> `struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES]` in the
> corresponding structures.
> 
> This overlays the trailing members onto the FAM (struct MR_LD_SPAN_MAP
> ldSpanMap[];) while keeping the FAM and the start of MEMBERS aligned.
> 
> The static_assert() ensures this alignment remains, and it's intentionally
> placed inmediately after the corresponding structures --no blank line in
> between.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> Changes in v2:
>   - Update changelog text --remove reference to unrelated structure.
> 
> v1:
>   - Link: https://lore.kernel.org/linux-hardening/aM1D4nPVH96DglfT@kspp/
> 
>   drivers/scsi/megaraid/megaraid_sas_fusion.h | 17 ++++++++++++-----
>   1 file changed, 12 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.h b/drivers/scsi/megaraid/megaraid_sas_fusion.h
> index b677d80e5874..ddeea0ee2834 100644
> --- a/drivers/scsi/megaraid/megaraid_sas_fusion.h
> +++ b/drivers/scsi/megaraid/megaraid_sas_fusion.h
> @@ -1150,9 +1150,13 @@ typedef struct LOG_BLOCK_SPAN_INFO {
>   } LD_SPAN_INFO, *PLD_SPAN_INFO;
>   
>   struct MR_FW_RAID_MAP_ALL {
> -	struct MR_FW_RAID_MAP raidMap;
> -	struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES];
> +	/* Must be last --ends in a flexible-array member. */
> +	TRAILING_OVERLAP(struct MR_FW_RAID_MAP, raidMap, ldSpanMap,
> +		struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES];
> +	);
>   } __attribute__ ((packed));
> +static_assert(offsetof(struct MR_FW_RAID_MAP_ALL, raidMap.ldSpanMap) ==
> +	      offsetof(struct MR_FW_RAID_MAP_ALL, ldSpanMap));
>   
>   struct MR_DRV_RAID_MAP {
>   	/* total size of this structure, including this field.
> @@ -1194,10 +1198,13 @@ struct MR_DRV_RAID_MAP {
>    * And it is mainly for code re-use purpose.
>    */
>   struct MR_DRV_RAID_MAP_ALL {
> -
> -	struct MR_DRV_RAID_MAP raidMap;
> -	struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN];
> +	/* Must be last --ends in a flexible-array member. */
> +	TRAILING_OVERLAP(struct MR_DRV_RAID_MAP, raidMap, ldSpanMap,
> +		struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN];
> +	);
>   } __packed;
> +static_assert(offsetof(struct MR_DRV_RAID_MAP_ALL, raidMap.ldSpanMap) ==
> +	      offsetof(struct MR_DRV_RAID_MAP_ALL, ldSpanMap));
>   
>   
>