[PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

[PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

-Wflex-array-member-not-at-end was 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>
---
 .../chelsio/cxgb4/cxgb4_tc_u32_parse.h        |  2 +-
 include/uapi/linux/pkt_cls.h                  | 23 +++++++++++--------
 2 files changed, 14 insertions(+), 11 deletions(-)

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[];
 };
 
-- 
2.34.1

Re: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

[Simon Horman]

On Mon, Aug 05, 2024 at 10:24:30AM -0600, 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.
> 
> 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>

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

Re: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

[Jakub Kicinski]

On Mon, 5 Aug 2024 10:24:30 -0600 Gustavo A. R. Silva wrote:
> Subject: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning
> Date: Mon, 5 Aug 2024 10:24:30 -0600

>  .../chelsio/cxgb4/cxgb4_tc_u32_parse.h        |  2 +-
>  include/uapi/linux/pkt_cls.h                  | 23 +++++++++++--------

Took me a minute to realize you're changing uAPI.
Please fix the subject.
-- 
pw-bot: cr

Re: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

[Gustavo A. R. Silva]

>>   .../chelsio/cxgb4/cxgb4_tc_u32_parse.h        |  2 +-
>>   include/uapi/linux/pkt_cls.h                  | 23 +++++++++++--------
> 
> Took me a minute to realize you're changing uAPI.
> Please fix the subject.

What would be a preferred subject?

--
Gustavo

Re: [PATCH][next] cxgb4: Avoid -Wflex-array-member-not-at-end warning

[Jakub Kicinski]

On Thu, 8 Aug 2024 12:41:32 -0600 Gustavo A. R. Silva wrote:
> >>   .../chelsio/cxgb4/cxgb4_tc_u32_parse.h        |  2 +-
> >>   include/uapi/linux/pkt_cls.h                  | 23 +++++++++++--------  
> > 
> > Took me a minute to realize you're changing uAPI.
> > Please fix the subject.  
> 
> What would be a preferred subject?

The point is that include/uapi/linux/pkt_cls.h is the more important
change.

net/sched, based on:

git log --oneline -- include/uapi/linux/pkt_cls.h

11036bd7a0b3 net/sched: cls_flower: rework TCA_FLOWER_KEY_ENC_FLAGS usage
bfda5a63137b net/sched: flower: define new tunnel flags
6e5c85c003e4 net/sched: flower: refactor control flag definitions
1d17568e74de net/sched: cls_flower: add support for matching tunnel control flags
6dd514f48110 pfcp: always set pfcp metadata
82b2545ed9a4 net/sched: Remove uapi support for tcindex classifier
41bc3e8fc1f7 net/sched: Remove uapi support for rsvp classifier
ba24ea129126 net/sched: Retire ipt action
35b1b1fd9638 Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net
4c13eda757e3 tc: flower: support for SPI
4d50e50045aa net: flower: fix stack-out-of-bounds in fl_set_key_cfm()
7cfffd5fed3e net: flower: add support for matching cfm fields
1a432018c0cd net/sched: flower: Allow matching on layer 2 miss
8b189ea08c33 net/sched: flower: Add L2TPv3 filter
f86d1fbbe785 Merge tag 'net-next-6.0' of git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next
5008750eff5d net/sched: flower: Add PPPoE filter
94dfc73e7cf4 treewide: uapi: Replace zero-length arrays with flexible-array members
b40003128226 net/sched: flower: Add number of vlan tags filter
e3acda7ade0a net/sched: Allow flower to match on GTP options

You can throw in uAPI somewhere in the subject, too