From: Kalle Valo <kvalo@codeaurora.org>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
ath11k@lists.infradead.org, linux-wireless@vger.kernel.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] ath11k: Replace one-element array with flexible-array member
Date: Tue, 28 Sep 2021 10:54:52 +0000 (UTC) [thread overview]
Message-ID: <20210928105452.AADC9C4360C@smtp.codeaurora.org> (raw)
In-Reply-To: <20210823172159.GA25800@embeddedor>
"Gustavo A. R. Silva" <gustavoars@kernel.org> wrote:
> There is a regular need in the kernel to provide a way to declare having a
> dynamically sized set of trailing elements in a structure. Kernel code
> should always use "flexible array members"[1] for these cases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Refactor the code a bit according to the use of a flexible-array member in
> struct scan_chan_list_params instead of a one-element array, and use the
> struct_size() helper.
>
> Also, save 25 (too many) bytes that were being allocated:
>
> $ pahole -C channel_param drivers/net/wireless/ath/ath11k/reg.o
> struct channel_param {
> u8 chan_id; /* 0 1 */
> u8 pwr; /* 1 1 */
> u32 mhz; /* 2 4 */
>
> /* Bitfield combined with next fields */
>
> u32 half_rate:1; /* 4:16 4 */
> u32 quarter_rate:1; /* 4:17 4 */
> u32 dfs_set:1; /* 4:18 4 */
> u32 dfs_set_cfreq2:1; /* 4:19 4 */
> u32 is_chan_passive:1; /* 4:20 4 */
> u32 allow_ht:1; /* 4:21 4 */
> u32 allow_vht:1; /* 4:22 4 */
> u32 allow_he:1; /* 4:23 4 */
> u32 set_agile:1; /* 4:24 4 */
> u32 psc_channel:1; /* 4:25 4 */
>
> /* XXX 6 bits hole, try to pack */
>
> u32 phy_mode; /* 8 4 */
> u32 cfreq1; /* 12 4 */
> u32 cfreq2; /* 16 4 */
> char maxpower; /* 20 1 */
> char minpower; /* 21 1 */
> char maxregpower; /* 22 1 */
> u8 antennamax; /* 23 1 */
> u8 reg_class_id; /* 24 1 */
>
> /* size: 25, cachelines: 1, members: 21 */
> /* sum members: 23 */
> /* sum bitfield members: 10 bits, bit holes: 1, sum bit holes: 6 bits */
> /* last cacheline: 25 bytes */
> } __attribute__((__packed__));
>
> as previously, sizeof(struct scan_chan_list_params) was 32 bytes:
>
> $ pahole -C scan_chan_list_params drivers/net/wireless/ath/ath11k/reg.o
> struct scan_chan_list_params {
> u32 pdev_id; /* 0 4 */
> u16 nallchans; /* 4 2 */
> struct channel_param ch_param[1]; /* 6 25 */
>
> /* size: 32, cachelines: 1, members: 3 */
> /* padding: 1 */
> /* last cacheline: 32 bytes */
> };
>
> and now with the flexible array transformation it is just 8 bytes:
>
> $ pahole -C scan_chan_list_params drivers/net/wireless/ath/ath11k/reg.o
> struct scan_chan_list_params {
> u32 pdev_id; /* 0 4 */
> u16 nallchans; /* 4 2 */
> struct channel_param ch_param[]; /* 6 0 */
>
> /* size: 8, cachelines: 1, members: 3 */
> /* padding: 2 */
> /* last cacheline: 8 bytes */
> };
>
> This helps with the ongoing efforts to globally enable -Warray-bounds and
> get us closer to being able to tighten the FORTIFY_SOURCE routines on
> memcpy().
>
> This issue was found with the help of Coccinelle and audited and fixed,
> manually.
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.10/process/deprecated.html#zero-length-and-one-element-arrays
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Patch applied to ath-next branch of ath.git, thanks.
b2549465cdea ath11k: Replace one-element array with flexible-array member
--
https://patchwork.kernel.org/project/linux-wireless/patch/20210823172159.GA25800@embeddedor/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
--
ath11k mailing list
ath11k@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/ath11k
next prev parent reply other threads:[~2021-09-28 10:55 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-23 17:21 [PATCH][next] ath11k: Replace one-element array with flexible-array member Gustavo A. R. Silva
2021-08-23 17:21 ` Gustavo A. R. Silva
2021-09-12 19:44 ` Gustavo A. R. Silva
2021-09-12 19:44 ` Gustavo A. R. Silva
2021-09-14 7:07 ` Kalle Valo
2021-09-14 7:07 ` Kalle Valo
2021-09-14 17:36 ` Gustavo A. R. Silva
2021-09-14 17:36 ` Gustavo A. R. Silva
2021-09-28 10:54 ` Kalle Valo [this message]
2021-09-28 10:54 ` Kalle Valo
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210928105452.AADC9C4360C@smtp.codeaurora.org \
--to=kvalo@codeaurora.org \
--cc=ath11k@lists.infradead.org \
--cc=davem@davemloft.net \
--cc=gustavoars@kernel.org \
--cc=kuba@kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-wireless@vger.kernel.org \
--cc=netdev@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.