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From:   Ping-Ke Shih <pkshih@realtek.com>
To:     kernel test robot <lkp@intel.com>
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        Kalle Valo <kvalo@kernel.org>
Subject: RE: drivers/net/wireless/realtek/rtw89/coex.c:1448:17: warning: writing 8 bytes into a region of size 0
Thread-Topic: drivers/net/wireless/realtek/rtw89/coex.c:1448:17: warning:
 writing 8 bytes into a region of size 0
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Date:   Thu, 2 Nov 2023 00:46:44 +0000
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> -----Original Message-----
> From: kernel test robot <lkp@intel.com>
> Sent: Monday, October 30, 2023 7:48 PM
> To: Ping-Ke Shih <pkshih@realtek.com>
> Cc: oe-kbuild-all@lists.linux.dev; linux-kernel@vger.kernel.org; Kalle Valo <kvalo@kernel.org>
> Subject: drivers/net/wireless/realtek/rtw89/coex.c:1448:17: warning: writing 8 bytes into a region of size
> 0

   drivers/net/wireless/realtek/rtw89/coex.c: In function '_append_tdma':
>> drivers/net/wireless/realtek/rtw89/coex.c:1448:17: warning: writing 8 bytes into a region of size 0 [-Wstringop-overflow=]
    1448 |                 memcpy(v, &dm->tdma, sizeof(*v));
         |                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

> e3ec7017f6a20d Ping-Ke Shih 2021-10-11  1442
> e3ec7017f6a20d Ping-Ke Shih 2021-10-11  1443    tlv = (struct rtw89_btc_btf_tlv *)&btc->policy[len];
> e3ec7017f6a20d Ping-Ke Shih 2021-10-11  1444    tlv->type = CXPOLICY_TDMA;
> ce986f3dc4fc69 Ching-Te Ku  2022-07-25  1445    if (chip->chip_id == RTL8852A) {
> ce986f3dc4fc69 Ching-Te Ku  2022-07-25  1446            v = (struct rtw89_btc_fbtc_tdma *)&tlv->val[0];
> e3ec7017f6a20d Ping-Ke Shih 2021-10-11  1447            tlv->len = sizeof(*v);
> e3ec7017f6a20d Ping-Ke Shih 2021-10-11 @1448            memcpy(v, &dm->tdma, sizeof(*v));

This statement is to append a struct named rtw89_btc_fbtc_tdma to value field of
a TLV struct, but compiler warns dst of memcpy() because of tlv->val[]. Maybe,
this is a false alarm?

Anyway, for this case, a simple assignment "*v = dm->tdma;" would be easier to
understand what it wants and also avoid compiler warnings. Then, I sent a
patch [1] for this.

[1] https://lore.kernel.org/linux-wireless/20231102003716.25815-1-pkshih@realtek.com/T/#u