| Message ID | ZrY1d01+JrX/SwqB@cute (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | [v2,next] UAPI: net/sched: Avoid -Wflex-array-member-not-at-end warning | expand |
On Fri, 9 Aug 2024 09:27:51 -0600 "Gustavo A. R. Silva" <gustavoars@kernel.org> wrote: > -Wflex-array-member-not-at-end has been introduced in GCC-14, and we > are getting ready to enable it, globally. > > So, in order to avoid ending up with a flexible-array member in the > middle of multiple other structs, we use the `__struct_group()` > helper to create a new tagged `struct tc_u32_sel_hdr`. This structure > groups together all the members of the flexible `struct tc_u32_sel` > except the flexible array. > > As a result, the array is effectively separated from the rest of the > members without modifying the memory layout of the flexible structure. > We then change the type of the middle struct member currently causing > trouble from `struct tc_u32_sel` to `struct tc_u32_sel_hdr`. > > This approach avoids having to implement `struct tc_u32_sel_hdr` > as a completely separate structure, thus preventing having to maintain > two independent but basically identical structures, closing the door > to potential bugs in the future. > > So, with these changes, fix the following warning: > drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h:245:27: 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> Tested this with iproute2-next and clang and no problem. The patch might be better split into two parts?
On Fri, 9 Aug 2024 09:42:03 -0700 Stephen Hemminger wrote: > Tested this with iproute2-next and clang and no problem. > > The patch might be better split into two parts? Fair point, a small two-patch series would be ideal.
diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h index 9050568a034c..64663112cad8 100644 --- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h +++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h @@ -242,7 +242,7 @@ struct cxgb4_next_header { * field's value to jump to next header such as IHL field * in IPv4 header. */ - struct tc_u32_sel sel; + struct tc_u32_sel_hdr sel; struct tc_u32_key key; /* location of jump to make */ const struct cxgb4_match_field *jump; diff --git a/include/uapi/linux/pkt_cls.h b/include/uapi/linux/pkt_cls.h index d36d9cdf0c00..2c32080416b5 100644 --- a/include/uapi/linux/pkt_cls.h +++ b/include/uapi/linux/pkt_cls.h @@ -246,16 +246,19 @@ struct tc_u32_key { }; struct tc_u32_sel { - unsigned char flags; - unsigned char offshift; - unsigned char nkeys; - - __be16 offmask; - __u16 off; - short offoff; - - short hoff; - __be32 hmask; + /* New members MUST be added within the __struct_group() macro below. */ + __struct_group(tc_u32_sel_hdr, hdr, /* no attrs */, + unsigned char flags; + unsigned char offshift; + unsigned char nkeys; + + __be16 offmask; + __u16 off; + short offoff; + + short hoff; + __be32 hmask; + ); struct tc_u32_key keys[]; };
-Wflex-array-member-not-at-end has been introduced in GCC-14, and we are getting ready to enable it, globally. So, in order to avoid ending up with a flexible-array member in the middle of multiple other structs, we use the `__struct_group()` helper to create a new tagged `struct tc_u32_sel_hdr`. This structure groups together all the members of the flexible `struct tc_u32_sel` except the flexible array. As a result, the array is effectively separated from the rest of the members without modifying the memory layout of the flexible structure. We then change the type of the middle struct member currently causing trouble from `struct tc_u32_sel` to `struct tc_u32_sel_hdr`. This approach avoids having to implement `struct tc_u32_sel_hdr` as a completely separate structure, thus preventing having to maintain two independent but basically identical structures, closing the door to potential bugs in the future. So, with these changes, fix the following warning: drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_u32_parse.h:245:27: 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: - Update subject line. (Jakub) .../chelsio/cxgb4/cxgb4_tc_u32_parse.h | 2 +- include/uapi/linux/pkt_cls.h | 23 +++++++++++-------- 2 files changed, 14 insertions(+), 11 deletions(-)