b2549465cd
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>
Link: https://lore.kernel.org/r/20210823172159.GA25800@embeddedor
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.