On 3/26/24 15:12, Luiz Augusto von Dentz wrote:
Hi Gustavo, On Tue, Mar 26, 2024 at 4:02 PM Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> wrote:-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[]; };Wouldn't it be better, more readable at least, to not define the l2cap_ecred_conn_rsp_hdr inside thought? Instead just do: struct_group_tagged(l2cap_ecred_conn_rsp_hdr, hdr, ... }; struct l2cap_ecred_conn_rsp { struct l2cap_ecred_conn_rsp_hdr hdr; __le16 dcid[]; }; Or was this done this way in order to maintain the same fields?
Exactly. But I can change it if people consider that's better.
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: https://github.com/KSPP/linux/issues/202 Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> --- 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(-) diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h index a4278aa618ab..92a143517d83 100644 --- a/include/net/bluetooth/l2cap.h +++ b/include/net/bluetooth/l2cap.h @@ -463,18 +463,22 @@ struct l2cap_le_credits { #define L2CAP_ECRED_MAX_CID 5 struct l2cap_ecred_conn_req { - __le16 psm; - __le16 mtu; - __le16 mps; - __le16 credits; + __struct_group(l2cap_ecred_conn_req_hdr, hdr, __packed, + __le16 psm; + __le16 mtu; + __le16 mps; + __le16 credits; + ); __le16 scid[]; } __packed; struct l2cap_ecred_conn_rsp { - __le16 mtu; - __le16 mps; - __le16 credits; - __le16 result; + struct_group_tagged(l2cap_ecred_conn_rsp_hdr, hdr, + __le16 mtu; + __le16 mps; + __le16 credits; + __le16 result; + ); __le16 dcid[]; }; diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 467b242d8be0..bf087eca489e 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -1257,7 +1257,7 @@ static void l2cap_le_connect(struct l2cap_chan *chan) struct l2cap_ecred_conn_data { struct { - struct l2cap_ecred_conn_req req; + struct l2cap_ecred_conn_req_hdr req; __le16 scid[5]; } __packed pdu;Can't we just use DEFINE_RAW_FLEX for the pdu field above?
No; DEFINE_FLEX() and DEFINE_RAW_FLEX() are for on-stack code only. Thanks -- Gustavo
struct l2cap_chan *chan; @@ -3737,7 +3737,7 @@ static void l2cap_ecred_list_defer(struct l2cap_chan *chan, void *data) struct l2cap_ecred_rsp_data { struct { - struct l2cap_ecred_conn_rsp rsp; + struct l2cap_ecred_conn_rsp_hdr rsp; __le16 scid[L2CAP_ECRED_MAX_CID]; } __packed pdu;Ditto.int count; @@ -3746,6 +3746,8 @@ struct l2cap_ecred_rsp_data { static void l2cap_ecred_rsp_defer(struct l2cap_chan *chan, void *data) { struct l2cap_ecred_rsp_data *rsp = data; + struct l2cap_ecred_conn_rsp *rsp_flex = + container_of(&rsp->pdu.rsp, struct l2cap_ecred_conn_rsp, hdr); if (test_bit(FLAG_ECRED_CONN_REQ_SENT, &chan->flags)) return; @@ -3755,7 +3757,7 @@ static void l2cap_ecred_rsp_defer(struct l2cap_chan *chan, void *data) /* Include all channels pending with the same ident */ if (!rsp->pdu.rsp.result) - rsp->pdu.rsp.dcid[rsp->count++] = cpu_to_le16(chan->scid); + rsp_flex->dcid[rsp->count++] = cpu_to_le16(chan->scid); else l2cap_chan_del(chan, ECONNRESET); } @@ -4995,10 +4997,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, u8 *data) { struct l2cap_ecred_conn_req *req = (void *) data; - struct { - struct l2cap_ecred_conn_rsp rsp; - __le16 dcid[L2CAP_ECRED_MAX_CID]; - } __packed pdu; + DEFINE_RAW_FLEX(struct l2cap_ecred_conn_rsp, pdu, dcid, L2CAP_ECRED_MAX_CID); struct l2cap_chan *chan, *pchan; u16 mtu, mps; __le16 psm; @@ -5017,7 +5016,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, cmd_len -= sizeof(*req); num_scid = cmd_len / sizeof(u16); - if (num_scid > ARRAY_SIZE(pdu.dcid)) { + if (num_scid > L2CAP_ECRED_MAX_CID) { result = L2CAP_CR_LE_INVALID_PARAMS; goto response; } @@ -5046,7 +5045,7 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, BT_DBG("psm 0x%2.2x mtu %u mps %u", __le16_to_cpu(psm), mtu, mps); - memset(&pdu, 0, sizeof(pdu)); + memset(pdu, 0, sizeof(*pdu)); /* Check if we have socket listening on psm */ pchan = l2cap_global_chan_by_psm(BT_LISTEN, psm, &conn->hcon->src, @@ -5072,8 +5071,8 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, BT_DBG("scid[%d] 0x%4.4x", i, scid); - pdu.dcid[i] = 0x0000; - len += sizeof(*pdu.dcid); + pdu->dcid[i] = 0x0000; + len += sizeof(*pdu->dcid); /* Check for valid dynamic CID range */ if (scid < L2CAP_CID_DYN_START || scid > L2CAP_CID_LE_DYN_END) { @@ -5107,13 +5106,13 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, l2cap_ecred_init(chan, __le16_to_cpu(req->credits)); /* Init response */ - if (!pdu.rsp.credits) { - pdu.rsp.mtu = cpu_to_le16(chan->imtu); - pdu.rsp.mps = cpu_to_le16(chan->mps); - pdu.rsp.credits = cpu_to_le16(chan->rx_credits); + if (!pdu->credits) { + pdu->mtu = cpu_to_le16(chan->imtu); + pdu->mps = cpu_to_le16(chan->mps); + pdu->credits = cpu_to_le16(chan->rx_credits); } - pdu.dcid[i] = cpu_to_le16(chan->scid); + pdu->dcid[i] = cpu_to_le16(chan->scid); __set_chan_timer(chan, chan->ops->get_sndtimeo(chan)); @@ -5135,13 +5134,13 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, l2cap_chan_put(pchan); response: - pdu.rsp.result = cpu_to_le16(result); + pdu->result = cpu_to_le16(result); if (defer) return 0; l2cap_send_cmd(conn, cmd->ident, L2CAP_ECRED_CONN_RSP, - sizeof(pdu.rsp) + len, &pdu); + sizeof(*pdu) + len, pdu); return 0; } @@ -7112,14 +7111,11 @@ EXPORT_SYMBOL_GPL(l2cap_chan_connect); static void l2cap_ecred_reconfigure(struct l2cap_chan *chan) { struct l2cap_conn *conn = chan->conn; - struct { - struct l2cap_ecred_reconf_req req; - __le16 scid; - } pdu; + DEFINE_RAW_FLEX(struct l2cap_ecred_reconf_req, pdu, scid, 1); - pdu.req.mtu = cpu_to_le16(chan->imtu); - pdu.req.mps = cpu_to_le16(chan->mps); - pdu.scid = cpu_to_le16(chan->scid); + pdu->mtu = cpu_to_le16(chan->imtu); + pdu->mps = cpu_to_le16(chan->mps); + pdu->scid[0] = cpu_to_le16(chan->scid); chan->ident = l2cap_get_ident(conn); -- 2.34.1
