linux-hardening - [PATCH][next] RDMA/irdma: Replace one-element array with flexible-array member

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Date:   Wed, 2 Aug 2023 08:46:26 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Mustafa Ismail <mustafa.ismail@...el.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Leon Romanovsky <leon@...nel.org>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] RDMA/irdma: Replace one-element array with
 flexible-array member

One-element and zero-length arrays are deprecated. So, replace
one-element array in struct irdma_qvlist_info with flexible-array
member.

A patch for this was sent a while ago[1]. However, it seems that, at
the time, the changes were partially folded[2][3], and the actual
flexible-array transformation was omitted. This patch fixes that.

The only binary difference seen before/after changes is shown below:

|  drivers/infiniband/hw/irdma/hw.o
| @@ -868,7 +868,7 @@
| drivers/infiniband/hw/irdma/hw.c:484 (discriminator 2)
|	size += struct_size(iw_qvlist, qv_info, rf->msix_count);
|      55b:      imul   $0x45c,%rdi,%rdi
|-     562:      add    $0x10,%rdi
|+     562:      add    $0x4,%rdi

which is, of course, expected as it reflects the mistake made
while folding the patch I've mentioned above.

Worth mentioning is the fact that with this change we save 12 bytes
of memory, as can be inferred from the diff snapshot above. Notice
that:

$ pahole -C rdma_qv_info idrivers/infiniband/hw/irdma/hw.o
struct irdma_qv_info {
	u32                        v_idx;                /*     0     4 */
	u16                        ceq_idx;              /*     4     2 */
	u16                        aeq_idx;              /*     6     2 */
	u8                         itr_idx;              /*     8     1 */

	/* size: 12, cachelines: 1, members: 4 */
	/* padding: 3 */
	/* last cacheline: 12 bytes */
};

Link: https://lore.kernel.org/linux-hardening/20210525230038.GA175516@embeddedor/ [1]
Link: https://lore.kernel.org/linux-hardening/bf46b428deef4e9e89b0ea1704b1f0e5@intel.com/ [2]
Link: https://lore.kernel.org/linux-rdma/20210520143809.819-1-shiraz.saleem@intel.com/T/#u [3]
Fixes: 44d9e52977a1 ("RDMA/irdma: Implement device initialization definitions")
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 drivers/infiniband/hw/irdma/main.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/irdma/main.h b/drivers/infiniband/hw/irdma/main.h
index 5483684a534c..82fc5f5b002c 100644
--- a/drivers/infiniband/hw/irdma/main.h
+++ b/drivers/infiniband/hw/irdma/main.h
@@ -239,7 +239,7 @@ struct irdma_qv_info {
 
 struct irdma_qvlist_info {
 	u32 num_vectors;
-	struct irdma_qv_info qv_info[1];
+	struct irdma_qv_info qv_info[];
 };
 
 struct irdma_gen_ops {
-- 
2.34.1