[PATCH][next] wireless: ti: Replace zero-length array with flexible-array member

[PATCH][next] wireless: ti: Replace zero-length array with flexible-array member

[Gustavo A. R. Silva]

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
---
 drivers/net/wireless/ti/wl1251/cmd.h          | 4 ++--
 drivers/net/wireless/ti/wl1251/wl12xx_80211.h | 2 +-
 drivers/net/wireless/ti/wlcore/acx.h          | 2 +-
 drivers/net/wireless/ti/wlcore/boot.h         | 2 +-
 drivers/net/wireless/ti/wlcore/cmd.h          | 2 +-
 drivers/net/wireless/ti/wlcore/conf.h         | 2 +-
 drivers/net/wireless/ti/wlcore/wl12xx_80211.h | 2 +-
 7 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/net/wireless/ti/wl1251/cmd.h b/drivers/net/wireless/ti/wl1251/cmd.h
index 1c1a591c6055..e5874186f9d7 100644
--- a/drivers/net/wireless/ti/wl1251/cmd.h
+++ b/drivers/net/wireless/ti/wl1251/cmd.h
@@ -90,7 +90,7 @@ struct wl1251_cmd_header {
 	u16 id;
 	u16 status;
 	/* payload */
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct  wl1251_command {
@@ -281,7 +281,7 @@ struct wl1251_cmd_packet_template {
 	struct wl1251_cmd_header header;
 
 	__le16 size;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 #define TIM_ELE_ID    5
diff --git a/drivers/net/wireless/ti/wl1251/wl12xx_80211.h b/drivers/net/wireless/ti/wl1251/wl12xx_80211.h
index 7fabe702c4cc..7e28fe435b43 100644
--- a/drivers/net/wireless/ti/wl1251/wl12xx_80211.h
+++ b/drivers/net/wireless/ti/wl1251/wl12xx_80211.h
@@ -65,7 +65,7 @@ struct ieee80211_header {
 	u8 sa[ETH_ALEN];
 	u8 bssid[ETH_ALEN];
 	__le16 seq_ctl;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct wl12xx_ie_header {
diff --git a/drivers/net/wireless/ti/wlcore/acx.h b/drivers/net/wireless/ti/wlcore/acx.h
index a265fba0cb4c..c725f5855c13 100644
--- a/drivers/net/wireless/ti/wlcore/acx.h
+++ b/drivers/net/wireless/ti/wlcore/acx.h
@@ -938,7 +938,7 @@ struct acx_rx_filter_cfg {
 	u8 action;
 
 	u8 num_fields;
-	u8 fields[0];
+	u8 fields[];
 } __packed;
 
 struct acx_roaming_stats {
diff --git a/drivers/net/wireless/ti/wlcore/boot.h b/drivers/net/wireless/ti/wlcore/boot.h
index 14b367e98dce..24a2dfcb41ea 100644
--- a/drivers/net/wireless/ti/wlcore/boot.h
+++ b/drivers/net/wireless/ti/wlcore/boot.h
@@ -26,7 +26,7 @@ struct wl1271_static_data {
 	u8 fw_version[WL1271_FW_VERSION_MAX_LEN];
 	u32 hw_version;
 	u8 tx_power_table[WL1271_NO_SUBBANDS][WL1271_NO_POWER_LEVELS];
-	u8 priv[0];
+	u8 priv[];
 };
 
 /* number of times we try to read the INIT interrupt */
diff --git a/drivers/net/wireless/ti/wlcore/cmd.h b/drivers/net/wireless/ti/wlcore/cmd.h
index bfad7b5a1ac6..f2609d5b6bf7 100644
--- a/drivers/net/wireless/ti/wlcore/cmd.h
+++ b/drivers/net/wireless/ti/wlcore/cmd.h
@@ -209,7 +209,7 @@ struct wl1271_cmd_header {
 	__le16 id;
 	__le16 status;
 	/* payload */
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 #define WL1271_CMD_MAX_PARAMS 572
diff --git a/drivers/net/wireless/ti/wlcore/conf.h b/drivers/net/wireless/ti/wlcore/conf.h
index 6116383ee248..31be425f2332 100644
--- a/drivers/net/wireless/ti/wlcore/conf.h
+++ b/drivers/net/wireless/ti/wlcore/conf.h
@@ -1150,7 +1150,7 @@ struct wlcore_conf {
 struct wlcore_conf_file {
 	struct wlcore_conf_header header;
 	struct wlcore_conf core;
-	u8 priv[0];
+	u8 priv[];
 } __packed;
 
 #endif
diff --git a/drivers/net/wireless/ti/wlcore/wl12xx_80211.h b/drivers/net/wireless/ti/wlcore/wl12xx_80211.h
index 181be725eff8..1dd7ecc11f86 100644
--- a/drivers/net/wireless/ti/wlcore/wl12xx_80211.h
+++ b/drivers/net/wireless/ti/wlcore/wl12xx_80211.h
@@ -66,7 +66,7 @@ struct ieee80211_header {
 	u8 sa[ETH_ALEN];
 	u8 bssid[ETH_ALEN];
 	__le16 seq_ctl;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct wl12xx_ie_header {
-- 
2.25.0

Re: [PATCH][next] wireless: ti: Replace zero-length array with flexible-array member

[Kalle Valo]

"Gustavo A. R. Silva" <gustavo@embeddedor.com> wrote:

> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
> 
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> This issue was found with the help of Coccinelle.
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

Patch applied to wireless-drivers-next.git, thanks.

398978f7dfa5 wireless: ti: Replace zero-length array with flexible-array member

-- 
https://patchwork.kernel.org/patch/11402335/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches