linux-kernel - [PATCH 15/15] nvme: avoid gcc-10 zero-length-bounds warning

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Date:   Thu, 30 Apr 2020 23:30:57 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-kernel@...r.kernel.org,
        James Smart <james.smart@...adcom.com>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Israel Rukshin <israelr@...lanox.com>,
        Max Gurtovoy <maxg@...lanox.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Ming Lei <ming.lei@...hat.com>,
        Hannes Reinecke <hare@...e.de>, linux-nvme@...ts.infradead.org
Subject: [PATCH 15/15] nvme: avoid gcc-10 zero-length-bounds warning

When CONFIG_ARCH_NO_SG_CHAIN is set, op->sgl[0] cannot be dereferenced,
as gcc-10 now points out:

drivers/nvme/host/fc.c: In function 'nvme_fc_init_request':
drivers/nvme/host/fc.c:1774:29: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct scatterlist[0]' [-Wzero-length-bounds]
 1774 |  op->op.fcp_req.first_sgl = &op->sgl[0];
      |                             ^~~~~~~~~~~
drivers/nvme/host/fc.c:98:21: note: while referencing 'sgl'
   98 |  struct scatterlist sgl[NVME_INLINE_SG_CNT];
      |                     ^~~

I don't know if this is a legitimate warning or a false-positive.
If this is just a false alarm, the warning is easily suppressed
by interpreting the array as a pointer.

Fixes: b1ae1a238900 ("nvme-fc: Avoid preallocating big SGL for data")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/nvme/host/fc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index 887537d1243f..b7ecda48d597 100644
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -1771,7 +1771,7 @@ nvme_fc_init_request(struct blk_mq_tag_set *set, struct request *rq,
 	res = __nvme_fc_init_request(ctrl, queue, &op->op, rq, queue->rqcnt++);
 	if (res)
 		return res;
-	op->op.fcp_req.first_sgl = &op->sgl[0];
+	op->op.fcp_req.first_sgl = op->sgl;
 	op->op.fcp_req.private = &op->priv[0];
 	nvme_req(rq)->ctrl = &ctrl->ctrl;
 	return res;
-- 
2.26.0