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SubjectRe: [PATCH] net/sctp: fix GCC8+ -Wpacked-not-aligned warnings
On Fri, Jul 26, 2019 at 04:57:39PM -0400, Qian Cai wrote:
> There are a lot of those warnings with GCC8+ 64bit,
>
> In file included from ./include/linux/sctp.h:42,
> from net/core/skbuff.c:47:
> ./include/uapi/linux/sctp.h:395:1: warning: alignment 4 of 'struct
> sctp_paddr_change' is less than 8 [-Wpacked-not-aligned]
> } __attribute__((packed, aligned(4)));
> ^
> ./include/uapi/linux/sctp.h:728:1: warning: alignment 4 of 'struct
> sctp_setpeerprim' is less than 8 [-Wpacked-not-aligned]
> } __attribute__((packed, aligned(4)));
> ^
> ./include/uapi/linux/sctp.h:727:26: warning: 'sspp_addr' offset 4 in
> 'struct sctp_setpeerprim' isn't aligned to 8 [-Wpacked-not-aligned]
> struct sockaddr_storage sspp_addr;
> ^~~~~~~~~
> ./include/uapi/linux/sctp.h:741:1: warning: alignment 4 of 'struct
> sctp_prim' is less than 8 [-Wpacked-not-aligned]
> } __attribute__((packed, aligned(4)));
> ^
> ./include/uapi/linux/sctp.h:740:26: warning: 'ssp_addr' offset 4 in
> 'struct sctp_prim' isn't aligned to 8 [-Wpacked-not-aligned]
> struct sockaddr_storage ssp_addr;
> ^~~~~~~~
> ./include/uapi/linux/sctp.h:792:1: warning: alignment 4 of 'struct
> sctp_paddrparams' is less than 8 [-Wpacked-not-aligned]
> } __attribute__((packed, aligned(4)));
> ^
> ./include/uapi/linux/sctp.h:784:26: warning: 'spp_address' offset 4 in
> 'struct sctp_paddrparams' isn't aligned to 8 [-Wpacked-not-aligned]
> struct sockaddr_storage spp_address;
> ^~~~~~~~~~~
> ./include/uapi/linux/sctp.h:905:1: warning: alignment 4 of 'struct
> sctp_paddrinfo' is less than 8 [-Wpacked-not-aligned]
> } __attribute__((packed, aligned(4)));
> ^
> ./include/uapi/linux/sctp.h:899:26: warning: 'spinfo_address' offset 4
> in 'struct sctp_paddrinfo' isn't aligned to 8 [-Wpacked-not-aligned]
> struct sockaddr_storage spinfo_address;
> ^~~~~~~~~~~~~~
> Fix them by aligning the structures and fields to 8 bytes instead.
>
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> include/uapi/linux/sctp.h | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h
> index b8f2c4d56532..e7bd71cde882 100644
> --- a/include/uapi/linux/sctp.h
> +++ b/include/uapi/linux/sctp.h

These changes gotta be more careful, if possible at all. As is, it's breaking UAPI.

-before
+after patch

struct sctp_paddrparams {
sctp_assoc_t spp_assoc_id; /* 0 4 */
- struct __kernel_sockaddr_storage spp_address __attribute__((__aligned__(1))); /* 4 128 */
- /* --- cacheline 2 boundary (128 bytes) was 4 bytes ago --- */
- __u32 spp_hbinterval; /* 132 4 */
- __u16 spp_pathmaxrxt; /* 136 2 */
- __u32 spp_pathmtu; /* 138 4 */
- __u32 spp_sackdelay; /* 142 4 */
- __u32 spp_flags; /* 146 4 */
- __u32 spp_ipv6_flowlabel; /* 150 4 */
- __u8 spp_dscp; /* 154 1 */

- /* size: 156, cachelines: 3, members: 9 */
+ /* XXX 4 bytes hole, try to pack */
+
+ struct __kernel_sockaddr_storage spp_address __attribute__((__aligned__(8))); /* 8 128 */
+ /* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */
+ __u32 spp_hbinterval; /* 136 4 */
+ __u16 spp_pathmaxrxt; /* 140 2 */
+ __u32 spp_pathmtu; /* 142 4 */
+ __u32 spp_sackdelay; /* 146 4 */
+ __u32 spp_flags; /* 150 4 */
+ __u32 spp_ipv6_flowlabel; /* 154 4 */
+ __u8 spp_dscp; /* 158 1 */
+
+ /* size: 160, cachelines: 3, members: 9 */
+ /* sum members: 155, holes: 1, sum holes: 4 */
/* padding: 1 */
- /* forced alignments: 1 */
- /* last cacheline: 28 bytes */
-} __attribute__((__aligned__(4)));
+ /* forced alignments: 1, forced holes: 1, sum forced holes: 4 */
+ /* last cacheline: 32 bytes */
+} __attribute__((__aligned__(8)));


> @@ -392,7 +392,7 @@ struct sctp_paddr_change {
> int spc_state;
> int spc_error;
> sctp_assoc_t spc_assoc_id;
> -} __attribute__((packed, aligned(4)));
> +} __attribute__((packed, aligned(8)));
>
> /*
> * spc_state: 32 bits (signed integer)
> @@ -724,8 +724,8 @@ struct sctp_assocparams {
> */
> struct sctp_setpeerprim {
> sctp_assoc_t sspp_assoc_id;
> - struct sockaddr_storage sspp_addr;
> -} __attribute__((packed, aligned(4)));
> + struct sockaddr_storage sspp_addr __attribute__((aligned(8)));
> +} __attribute__((packed, aligned(8)));
>
> /*
> * 7.1.10 Set Primary Address (SCTP_PRIMARY_ADDR)
> @@ -737,8 +737,8 @@ struct sctp_setpeerprim {
> */
> struct sctp_prim {
> sctp_assoc_t ssp_assoc_id;
> - struct sockaddr_storage ssp_addr;
> -} __attribute__((packed, aligned(4)));
> + struct sockaddr_storage ssp_addr __attribute__((aligned(8)));
> +} __attribute__((packed, aligned(8)));
>
> /* For backward compatibility use, define the old name too */
> #define sctp_setprim sctp_prim
> @@ -781,7 +781,7 @@ enum sctp_spp_flags {
>
> struct sctp_paddrparams {
> sctp_assoc_t spp_assoc_id;
> - struct sockaddr_storage spp_address;
> + struct sockaddr_storage spp_address __attribute__((aligned(8)));
> __u32 spp_hbinterval;
> __u16 spp_pathmaxrxt;
> __u32 spp_pathmtu;
> @@ -789,7 +789,7 @@ struct sctp_paddrparams {
> __u32 spp_flags;
> __u32 spp_ipv6_flowlabel;
> __u8 spp_dscp;
> -} __attribute__((packed, aligned(4)));
> +} __attribute__((packed, aligned(8)));
>
> /*
> * 7.1.18. Add a chunk that must be authenticated (SCTP_AUTH_CHUNK)
> @@ -896,13 +896,13 @@ struct sctp_stream_value {
> */
> struct sctp_paddrinfo {
> sctp_assoc_t spinfo_assoc_id;
> - struct sockaddr_storage spinfo_address;
> + struct sockaddr_storage spinfo_address __attribute__((aligned(8)));
> __s32 spinfo_state;
> __u32 spinfo_cwnd;
> __u32 spinfo_srtt;
> __u32 spinfo_rto;
> __u32 spinfo_mtu;
> -} __attribute__((packed, aligned(4)));
> +} __attribute__((packed, aligned(8)));
>
> /* Peer addresses's state. */
> /* UNKNOWN: Peer address passed by the upper layer in sendmsg or connect[x]
> --
> 1.8.3.1
>

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