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

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Date:   Fri, 1 May 2020 09:32:56 +0200
From:   Christoph Hellwig <hch@....de>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     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>,
        Ming Lei <ming.lei@...hat.com>, Hannes Reinecke <hare@...e.de>,
        linux-nvme@...ts.infradead.org
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 :)