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

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Message-ID: <aM1E7Xa8qYdZ598N@kspp>
Date: Fri, 19 Sep 2025 13:56:29 +0200
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: 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,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: [PATCH v2][next] scsi: megaraid_sas: Avoid a couple
 -Wflex-array-member-not-at-end warnings

-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));
 
 
 
-- 
2.43.0