2020-04-30 21:39:16

by Arnd Bergmann

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 <[email protected]>
---
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

2020-05-01 07:34:57

by [email protected]

Subject: Re: [PATCH 15/15] nvme: avoid gcc-10 zero-length-bounds warning

On Thu, Apr 30, 2020 at 11:30:57PM +0200, Arnd Bergmann wrote:
> 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.

This looks like a surpression to be, but then again I find the new
code actually cleaner, so I'm fine with it :)