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Message-ID: <20240626170605.GA66745@fedora-macbook-air-m2>
Date: Wed, 26 Jun 2024 10:06:05 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: James Smart <james.smart@...adcom.com>, Christoph Hellwig <hch@....de>,
Sagi Grimberg <sagi@...mberg.me>,
Chaitanya Kulkarni <kch@...dia.com>
Cc: Kees Cook <keescook@...omium.org>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
Bill Wendling <morbo@...gle.com>,
Justin Stitt <justinstitt@...gle.com>,
Keith Busch <kbusch@...nel.org>, linux-nvme@...ts.infradead.org,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
llvm@...ts.linux.dev, patches@...ts.linux.dev,
stable@...r.kernel.org
Subject: Re: [PATCH] nvmet-fc: Remove __counted_by from
nvmet_fc_tgt_queue.fod[]
Ping? This is still relevant and I don't think this is a compiler bug
that would justify withholding this change.
On Wed, May 29, 2024 at 02:42:40PM -0700, Nathan Chancellor wrote:
> Work for __counted_by on generic pointers in structures (not just
> flexible array members) has started landing in Clang 19 (current tip of
> tree). During the development of this feature, a restriction was added
> to __counted_by to prevent the flexible array member's element type from
> including a flexible array member itself such as:
>
> struct foo {
> int count;
> char buf[];
> };
>
> struct bar {
> int count;
> struct foo data[] __counted_by(count);
> };
>
> because the size of data cannot be calculated with the standard array
> size formula:
>
> sizeof(struct foo) * count
>
> This restriction was downgraded to a warning but due to CONFIG_WERROR,
> it can still break the build. The application of __counted_by on the fod
> member of 'struct nvmet_fc_tgt_queue' triggers this restriction,
> resulting in:
>
> drivers/nvme/target/fc.c:151:2: error: 'counted_by' should not be applied to an array with element of unknown size because 'struct nvmet_fc_fcp_iod' is a struct type with a flexible array member. This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size]
> 151 | struct nvmet_fc_fcp_iod fod[] __counted_by(sqsize);
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 1 error generated.
>
> Remove this use of __counted_by to fix the warning/error. However,
> rather than remove it altogether, leave it commented, as it may be
> possible to support this in future compiler releases.
>
> Cc: stable@...r.kernel.org
> Closes: https://github.com/ClangBuiltLinux/linux/issues/2027
> Fixes: ccd3129aca28 ("nvmet-fc: Annotate struct nvmet_fc_tgt_queue with __counted_by")
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
> drivers/nvme/target/fc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/nvme/target/fc.c b/drivers/nvme/target/fc.c
> index 337ee1cb09ae..381b4394731f 100644
> --- a/drivers/nvme/target/fc.c
> +++ b/drivers/nvme/target/fc.c
> @@ -148,7 +148,7 @@ struct nvmet_fc_tgt_queue {
> struct workqueue_struct *work_q;
> struct kref ref;
> /* array of fcp_iods */
> - struct nvmet_fc_fcp_iod fod[] __counted_by(sqsize);
> + struct nvmet_fc_fcp_iod fod[] /* __counted_by(sqsize) */;
> } __aligned(sizeof(unsigned long long));
>
> struct nvmet_fc_hostport {
>
> ---
> base-commit: c758b77d4a0a0ed3a1292b3fd7a2aeccd1a169a4
> change-id: 20240529-drop-counted-by-fod-nvmet-fc-tgt-queue-50edd2f8d60e
>
> Best regards,
> --
> Nathan Chancellor <nathan@...nel.org>
>
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