[PW_SID:838554] [next] Bluetooth: L2CAP: Avoid -Wflex-array-member-not-at-end warnings

[tedd-an]

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

There are currently a couple of objects (req and rsp), in a couple
of structures, that contain flexible structures (struct l2cap_ecred_conn_req
and struct l2cap_ecred_conn_rsp), for example:

struct l2cap_ecred_rsp_data {
struct {
struct l2cap_ecred_conn_rsp rsp;
__le16 scid[L2CAP_ECRED_MAX_CID];
} __packed pdu;
int count;
};

in the struct above, struct l2cap_ecred_conn_rsp is a flexible
structure:

struct l2cap_ecred_conn_rsp {
__le16 mtu;
__le16 mps;
__le16 credits;
__le16 result;
__le16 dcid[];
};

So, in order to avoid ending up with a flexible-array member in the
middle of another structure, we use the struct_group_tagged() (and
__struct_group() when the flexible structure is __packed) helper
to separate the flexible array from the rest of the members in the
flexible structure:

struct l2cap_ecred_conn_rsp {
struct_group_tagged(l2cap_ecred_conn_rsp_hdr, hdr,

... the rest of members

    );
    __le16 dcid[];

};

With the change described above, we now declare objects of the type of
the tagged struct, in this example struct l2cap_ecred_conn_rsp_hdr,
without embedding flexible arrays in the middle of other structures:

struct l2cap_ecred_rsp_data {
struct {
struct l2cap_ecred_conn_rsp_hdr rsp;
__le16 scid[L2CAP_ECRED_MAX_CID];
} __packed pdu;
int count;
};

Also, when the flexible-array member needs to be accessed, we use
container_of() to retrieve a pointer to the flexible structure.

We also use the DEFINE_RAW_FLEX() helper for a couple of on-stack
definitions of a flexible structure where the size of the flexible-array
member is known at compile-time.

So, with these changes, fix the following warnings:
net/bluetooth/l2cap_core.c:1260:45: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
net/bluetooth/l2cap_core.c:3740:45: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
net/bluetooth/l2cap_core.c:4999:45: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
net/bluetooth/l2cap_core.c:7116:47: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: KSPP/linux#202
Signed-off-by: Gustavo A. R. Silva gustavoars@kernel.org

Hi!

I wonder if struct l2cap_ecred_conn_rsp should also be __packed.

Thanks

• Gustavo

include/net/bluetooth/l2cap.h | 20 +++++++++------
net/bluetooth/l2cap_core.c | 46 ++++++++++++++++-------------------
2 files changed, 33 insertions(+), 33 deletions(-)