linux-kernel - Re: [PATCH][next] wifi: mt76: Replace zero-length array with flexible-array member

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Message-ID: <ZC/FA/t1mzrRydD7@corigine.com>
Date:   Fri, 7 Apr 2023 09:23:47 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc:     Felix Fietkau <nbd@....name>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Shayne Chen <shayne.chen@...iatek.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Kalle Valo <kvalo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] wifi: mt76: Replace zero-length array with
 flexible-array member

On Thu, Apr 06, 2023 at 08:32:12AM -0600, Gustavo A. R. Silva wrote:
> Zero-length arrays are deprecated [1] and have to be replaced by C99
> flexible-array members.
> 
> This helps with the ongoing efforts to tighten the FORTIFY_SOURCE routines
> on memcpy() and help to make progress towards globally enabling
> -fstrict-flex-arrays=3 [2]
> 
> Link: https://github.com/KSPP/linux/issues/78 [1]
> Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [2]
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Reviewed-by: Simon Horman <simon.horman@...igine.com>

> ---
>  drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h b/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h
> index a5e6ee4daf92..9bf4b4199ee3 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h
> +++ b/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.h
> @@ -127,7 +127,7 @@ struct mt76_connac2_mcu_rxd {
>  	u8 rsv1[2];
>  	u8 s2d_index;
>  
> -	u8 tlv[0];
> +	u8 tlv[];
>  };
>  
>  struct mt76_connac2_patch_hdr {

Curiously -fstrict-flex-arrays=3 didn't flag this one in my environment,
Ubuntu Lunar.

 gcc-13 --version
 gcc-13 (Ubuntu 13-20230320-1ubuntu1) 13.0.1 20230320 (experimental) [master r13-6759-g5194ad1958c]
 Copyright (C) 2023 Free Software Foundation, Inc.
 This is free software; see the source for copying conditions.  There is NO
 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I did, however, notice some other problems reported by gcc-13 with
-fstrict-flex-arrays=3 in drivers/net/wireless/mediatek/mt76
when run against net-next wireless. I've listed them in diff format below.

Are these on your radar too?

diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/acpi_sar.h b/drivers/net/wireless/mediatek/mt76/mt7921/acpi_sar.h
index 35268b0890ad..d09bb4eed1ec 100644
--- a/drivers/net/wireless/mediatek/mt76/mt7921/acpi_sar.h
+++ b/drivers/net/wireless/mediatek/mt76/mt7921/acpi_sar.h
@@ -24,7 +24,7 @@ struct mt7921_asar_dyn {
 	u8 names[4];
 	u8 enable;
 	u8 nr_tbl;
-	struct mt7921_asar_dyn_limit tbl[0];
+	struct mt7921_asar_dyn_limit tbl[];
 } __packed;
 
 struct mt7921_asar_dyn_limit_v2 {
@@ -37,7 +37,7 @@ struct mt7921_asar_dyn_v2 {
 	u8 enable;
 	u8 rsvd;
 	u8 nr_tbl;
-	struct mt7921_asar_dyn_limit_v2 tbl[0];
+	struct mt7921_asar_dyn_limit_v2 tbl[];
 } __packed;
 
 struct mt7921_asar_geo_band {
@@ -55,7 +55,7 @@ struct mt7921_asar_geo {
 	u8 names[4];
 	u8 version;
 	u8 nr_tbl;
-	struct mt7921_asar_geo_limit tbl[0];
+	struct mt7921_asar_geo_limit tbl[];
 } __packed;
 
 struct mt7921_asar_geo_limit_v2 {
@@ -69,7 +69,7 @@ struct mt7921_asar_geo_v2 {
 	u8 version;
 	u8 rsvd;
 	u8 nr_tbl;
-	struct mt7921_asar_geo_limit_v2 tbl[0];
+	struct mt7921_asar_geo_limit_v2 tbl[];
 } __packed;
 
 struct mt7921_asar_cl {
@@ -85,7 +85,7 @@ struct mt7921_asar_fg {
 	u8 rsvd;
 	u8 nr_flag;
 	u8 rsvd1;
-	u8 flag[0];
+	u8 flag[];
 } __packed;
 
 struct mt7921_acpi_sar {