[v2] Bluetooth: Avoid a couple dozen -Wflex-array-member-not-at-end warnings

[PATCH v2][next] Bluetooth: Avoid a couple dozen -Wflex-array-member-not-at-end warnings

Posted by Gustavo A. R. Silva 3 weeks, 2 days ago

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the __struct_group() helper to fix 31 instances of the following
type of warnings:

30 net/bluetooth/mgmt_config.c:16:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
1 net/bluetooth/mgmt_config.c:22:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
 - Use __struct_group() instead of TRAILING_OVERLAP().

v1:
 - Link: https://lore.kernel.org/linux-hardening/aLSCu8U62Hve7Dau@kspp/

 include/net/bluetooth/mgmt.h | 9 +++++++--
 net/bluetooth/mgmt_config.c  | 4 ++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/include/net/bluetooth/mgmt.h b/include/net/bluetooth/mgmt.h
index 3575cd16049a..74edea06985b 100644
--- a/include/net/bluetooth/mgmt.h
+++ b/include/net/bluetooth/mgmt.h
@@ -53,10 +53,15 @@ struct mgmt_hdr {
 } __packed;
 
 struct mgmt_tlv {
-	__le16 type;
-	__u8   length;
+	/* New members MUST be added within the __struct_group() macro below. */
+	__struct_group(mgmt_tlv_hdr, __hdr, __packed,
+		__le16 type;
+		__u8   length;
+	);
 	__u8   value[];
 } __packed;
+static_assert(offsetof(struct mgmt_tlv, value) == sizeof(struct mgmt_tlv_hdr),
+	      "struct member likely outside of __struct_group()");
 
 struct mgmt_addr_info {
 	bdaddr_t	bdaddr;
diff --git a/net/bluetooth/mgmt_config.c b/net/bluetooth/mgmt_config.c
index 6ef701c27da4..c4063d200c0a 100644
--- a/net/bluetooth/mgmt_config.c
+++ b/net/bluetooth/mgmt_config.c
@@ -13,13 +13,13 @@
 
 #define HDEV_PARAM_U16(_param_name_) \
 	struct {\
-		struct mgmt_tlv entry; \
+		struct mgmt_tlv_hdr entry; \
 		__le16 value; \
 	} __packed _param_name_
 
 #define HDEV_PARAM_U8(_param_name_) \
 	struct {\
-		struct mgmt_tlv entry; \
+		struct mgmt_tlv_hdr entry; \
 		__u8 value; \
 	} __packed _param_name_
 
-- 
2.43.0

Re: [PATCH v2][next] Bluetooth: Avoid a couple dozen -Wflex-array-member-not-at-end warnings

Posted by Gustavo A. R. Silva 1 week ago

Hi all,

Friendly ping: who can take this, please? :)

Thanks!
-Gustavo

On 9/9/25 14:13, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the __struct_group() helper to fix 31 instances of the following
> type of warnings:
> 
> 30 net/bluetooth/mgmt_config.c:16:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 1 net/bluetooth/mgmt_config.c:22:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> Changes in v2:
>   - Use __struct_group() instead of TRAILING_OVERLAP().
> 
> v1:
>   - Link: https://lore.kernel.org/linux-hardening/aLSCu8U62Hve7Dau@kspp/
> 
>   include/net/bluetooth/mgmt.h | 9 +++++++--
>   net/bluetooth/mgmt_config.c  | 4 ++--
>   2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/bluetooth/mgmt.h b/include/net/bluetooth/mgmt.h
> index 3575cd16049a..74edea06985b 100644
> --- a/include/net/bluetooth/mgmt.h
> +++ b/include/net/bluetooth/mgmt.h
> @@ -53,10 +53,15 @@ struct mgmt_hdr {
>   } __packed;
>   
>   struct mgmt_tlv {
> -	__le16 type;
> -	__u8   length;
> +	/* New members MUST be added within the __struct_group() macro below. */
> +	__struct_group(mgmt_tlv_hdr, __hdr, __packed,
> +		__le16 type;
> +		__u8   length;
> +	);
>   	__u8   value[];
>   } __packed;
> +static_assert(offsetof(struct mgmt_tlv, value) == sizeof(struct mgmt_tlv_hdr),
> +	      "struct member likely outside of __struct_group()");
>   
>   struct mgmt_addr_info {
>   	bdaddr_t	bdaddr;
> diff --git a/net/bluetooth/mgmt_config.c b/net/bluetooth/mgmt_config.c
> index 6ef701c27da4..c4063d200c0a 100644
> --- a/net/bluetooth/mgmt_config.c
> +++ b/net/bluetooth/mgmt_config.c
> @@ -13,13 +13,13 @@
>   
>   #define HDEV_PARAM_U16(_param_name_) \
>   	struct {\
> -		struct mgmt_tlv entry; \
> +		struct mgmt_tlv_hdr entry; \
>   		__le16 value; \
>   	} __packed _param_name_
>   
>   #define HDEV_PARAM_U8(_param_name_) \
>   	struct {\
> -		struct mgmt_tlv entry; \
> +		struct mgmt_tlv_hdr entry; \
>   		__u8 value; \
>   	} __packed _param_name_
>

Re: [PATCH v2][next] Bluetooth: Avoid a couple dozen -Wflex-array-member-not-at-end warnings

Posted by Paul Menzel 3 weeks, 1 day ago

Dear Gustavo,


Thank you for your patch.

Am 09.09.25 um 14:13 schrieb Gustavo A. R. Silva:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the __struct_group() helper to fix 31 instances of the following
> type of warnings:
> 
> 30 net/bluetooth/mgmt_config.c:16:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 1 net/bluetooth/mgmt_config.c:22:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

You could add an explanation, why the macro `__struct_group()` defined 
in `include/uapi/linux/stddef.h` fixes this, and why it is preferred 
over `TRAILING_OVERLAP()`. Also, the two underscores would suggest to 
me, it’s some kind of internal implementation.

> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> Changes in v2:
>   - Use __struct_group() instead of TRAILING_OVERLAP().
> 
> v1:
>   - Link: https://lore.kernel.org/linux-hardening/aLSCu8U62Hve7Dau@kspp/
> 
>   include/net/bluetooth/mgmt.h | 9 +++++++--
>   net/bluetooth/mgmt_config.c  | 4 ++--
>   2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/bluetooth/mgmt.h b/include/net/bluetooth/mgmt.h
> index 3575cd16049a..74edea06985b 100644
> --- a/include/net/bluetooth/mgmt.h
> +++ b/include/net/bluetooth/mgmt.h
> @@ -53,10 +53,15 @@ struct mgmt_hdr {
>   } __packed;
>   
>   struct mgmt_tlv {
> -	__le16 type;
> -	__u8   length;
> +	/* New members MUST be added within the __struct_group() macro below. */
> +	__struct_group(mgmt_tlv_hdr, __hdr, __packed,
> +		__le16 type;
> +		__u8   length;
> +	);
>   	__u8   value[];
>   } __packed;
> +static_assert(offsetof(struct mgmt_tlv, value) == sizeof(struct mgmt_tlv_hdr),
> +	      "struct member likely outside of __struct_group()");
>   
>   struct mgmt_addr_info {
>   	bdaddr_t	bdaddr;
> diff --git a/net/bluetooth/mgmt_config.c b/net/bluetooth/mgmt_config.c
> index 6ef701c27da4..c4063d200c0a 100644
> --- a/net/bluetooth/mgmt_config.c
> +++ b/net/bluetooth/mgmt_config.c
> @@ -13,13 +13,13 @@
>   
>   #define HDEV_PARAM_U16(_param_name_) \
>   	struct {\
> -		struct mgmt_tlv entry; \
> +		struct mgmt_tlv_hdr entry; \
>   		__le16 value; \
>   	} __packed _param_name_
>   
>   #define HDEV_PARAM_U8(_param_name_) \
>   	struct {\
> -		struct mgmt_tlv entry; \
> +		struct mgmt_tlv_hdr entry; \
>   		__u8 value; \
>   	} __packed _param_name_
>   


Kind regards,

Paul

Re: [PATCH v2][next] Bluetooth: Avoid a couple dozen -Wflex-array-member-not-at-end warnings

Posted by Simon Horman 3 weeks, 1 day ago

On Tue, Sep 09, 2025 at 02:13:35PM +0200, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
> 
> Use the __struct_group() helper to fix 31 instances of the following
> type of warnings:
> 
> 30 net/bluetooth/mgmt_config.c:16:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 1 net/bluetooth/mgmt_config.c:22:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> ---
> Changes in v2:
>  - Use __struct_group() instead of TRAILING_OVERLAP().
> 
> v1:
>  - Link: https://lore.kernel.org/linux-hardening/aLSCu8U62Hve7Dau@kspp/

Reviewed-by: Simon Horman <horms@kernel.org>