| Message ID | 1564500633-7419-1-git-send-email-cai@lca.pw |
|---|---|
| State | Accepted |
| Delegated to: | David Miller |
| Headers | show |
| Series | [v3] net/socket: fix GCC8+ Wpacked-not-aligned warnings | expand |
From: Qian Cai <cai@lca.pw> Date: Tue, 30 Jul 2019 11:30:33 -0400 > There are a lot of those warnings with GCC8+ 64-bit, ... > This is because the commit 20c9c825b12f ("[SCTP] Fix SCTP socket options > to work with 32-bit apps on 64-bit kernels.") added "packed, aligned(4)" > GCC attributes to some structures but one of the members, i.e, "struct > sockaddr_storage" in those structures has the attribute, > "aligned(__alignof__ (struct sockaddr *)" which is 8-byte on 64-bit > systems, so the commit overwrites the designed alignments for > "sockaddr_storage". > > To fix this, "struct sockaddr_storage" needs to be aligned to 4-byte as > it is only used in those packed sctp structure which is part of UAPI, > and "struct __kernel_sockaddr_storage" is used in some other > places of UAPI that need not to change alignments in order to not > breaking userspace. > > Use an implicit alignment for "struct __kernel_sockaddr_storage" so it > can keep the same alignments as a member in both packed and un-packed > structures without breaking UAPI. > > Suggested-by: David Laight <David.Laight@ACULAB.COM> > Signed-off-by: Qian Cai <cai@lca.pw> Ok, this just changes how the alignment is declared from using the aligned attribute to using a union member which requires the same alignment. Applied.
diff --git a/include/uapi/linux/socket.h b/include/uapi/linux/socket.h index 8eb96021709c..c3409c8ec0dd 100644 --- a/include/uapi/linux/socket.h +++ b/include/uapi/linux/socket.h @@ -6,17 +6,24 @@ * Desired design of maximum size and alignment (see RFC2553) */ #define _K_SS_MAXSIZE 128 /* Implementation specific max size */ -#define _K_SS_ALIGNSIZE (__alignof__ (struct sockaddr *)) - /* Implementation specific desired alignment */ typedef unsigned short __kernel_sa_family_t; +/* + * The definition uses anonymous union and struct in order to control the + * default alignment. + */ struct __kernel_sockaddr_storage { - __kernel_sa_family_t ss_family; /* address family */ - /* Following field(s) are implementation specific */ - char __data[_K_SS_MAXSIZE - sizeof(unsigned short)]; + union { + struct { + __kernel_sa_family_t ss_family; /* address family */ + /* Following field(s) are implementation specific */ + char __data[_K_SS_MAXSIZE - sizeof(unsigned short)]; /* space to achieve desired size, */ /* _SS_MAXSIZE value minus size of ss_family */ -} __attribute__ ((aligned(_K_SS_ALIGNSIZE))); /* force desired alignment */ + }; + void *__align; /* implementation specific desired alignment */ + }; +}; #endif /* _UAPI_LINUX_SOCKET_H */
There are a lot of those warnings with GCC8+ 64-bit, 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; ^~~~~~~~~~~~~~ This is because the commit 20c9c825b12f ("[SCTP] Fix SCTP socket options to work with 32-bit apps on 64-bit kernels.") added "packed, aligned(4)" GCC attributes to some structures but one of the members, i.e, "struct sockaddr_storage" in those structures has the attribute, "aligned(__alignof__ (struct sockaddr *)" which is 8-byte on 64-bit systems, so the commit overwrites the designed alignments for "sockaddr_storage". To fix this, "struct sockaddr_storage" needs to be aligned to 4-byte as it is only used in those packed sctp structure which is part of UAPI, and "struct __kernel_sockaddr_storage" is used in some other places of UAPI that need not to change alignments in order to not breaking userspace. Use an implicit alignment for "struct __kernel_sockaddr_storage" so it can keep the same alignments as a member in both packed and un-packed structures without breaking UAPI. Suggested-by: David Laight <David.Laight@ACULAB.COM> Signed-off-by: Qian Cai <cai@lca.pw> --- v3: Add some comments and rearrange the public member first per David. v2: Use an implicit alignment for "struct __kernel_sockaddr_storage". include/uapi/linux/socket.h | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-)