| Message ID | 1564431838-23051-1-git-send-email-cai@lca.pw |
|---|---|
| State | Superseded |
| Delegated to: | David Miller |
| Headers | show |
| Series | net/socket: fix GCC8+ Wpacked-not-aligned warnings | expand |
From: Qian Cai > Sent: 29 July 2019 21:24 .. > 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. > > One option is use typedef between "sockaddr_storage" and > "__kernel_sockaddr_storage" but it needs to change 35 or 370 lines of > codes. The other option is to duplicate this simple 2-field structure to > have a separate "struct sockaddr_storage" so it can use a different > alignment than "__kernel_sockaddr_storage". Also the structure seems > stable enough, so it will be low-maintenance to update two structures in > the future in case of changes. Does it all work if the 8 byte alignment is implicit, not explicit? For instance if unnamed union and struct are used eg: struct sockaddr_storage { union { void * __ptr; /* Force alignment */ 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 */ }; }; }; I suspect unnamed unions and structs have to be allowed by the compiler. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
On Tue, 2019-07-30 at 09:01 +0000, David Laight wrote: > From: Qian Cai > > Sent: 29 July 2019 21:24 > > .. > > 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. > > > > One option is use typedef between "sockaddr_storage" and > > "__kernel_sockaddr_storage" but it needs to change 35 or 370 lines of > > codes. The other option is to duplicate this simple 2-field structure to > > have a separate "struct sockaddr_storage" so it can use a different > > alignment than "__kernel_sockaddr_storage". Also the structure seems > > stable enough, so it will be low-maintenance to update two structures in > > the future in case of changes. > > Does it all work if the 8 byte alignment is implicit, not explicit? > For instance if unnamed union and struct are used eg: > > struct sockaddr_storage { > union { > void * __ptr; /* Force alignment */ > 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 */ > }; > }; > }; > > I suspect unnamed unions and structs have to be allowed by the compiler. I believe this will suffer the same problem in that will break UAPI, https://lore.kernel.org/lkml/20190726213045.GL6204@localhost.localdomain/
From: Qian Cai > Sent: 30 July 2019 14:18 > On Tue, 2019-07-30 at 09:01 +0000, David Laight wrote: > > From: Qian Cai > > > Sent: 29 July 2019 21:24 > > > > .. > > > 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. > > > > > > One option is use typedef between "sockaddr_storage" and > > > "__kernel_sockaddr_storage" but it needs to change 35 or 370 lines of > > > codes. The other option is to duplicate this simple 2-field structure to > > > have a separate "struct sockaddr_storage" so it can use a different > > > alignment than "__kernel_sockaddr_storage". Also the structure seems > > > stable enough, so it will be low-maintenance to update two structures in > > > the future in case of changes. > > > > Does it all work if the 8 byte alignment is implicit, not explicit? > > For instance if unnamed union and struct are used eg: > > > > struct sockaddr_storage { > > union { > > void * __ptr; /* Force alignment */ > > 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 */ > > }; > > }; > > }; > > > > I suspect unnamed unions and structs have to be allowed by the compiler. > > I believe this will suffer the same problem in that will break UAPI, > > https://lore.kernel.org/lkml/20190726213045.GL6204@localhost.localdomain/ You are missing the bit where the UAPI structure is packed. If the compiler won't let you 'pack' a structure that contains structures (rather than just integers) then the compiler is broken! The hope here was that it would be ok is the alignment was implicit not explicit. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
diff --git a/include/linux/socket.h b/include/linux/socket.h index 97523818cb14..301119657125 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -38,7 +38,13 @@ struct linger { int l_linger; /* How long to linger for */ }; -#define sockaddr_storage __kernel_sockaddr_storage +struct sockaddr_storage { + __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 */ +} __aligned(4); /* force desired alignment */ /* * As we do 4.4BSD message passing we use a 4.4BSD message passing
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. One option is use typedef between "sockaddr_storage" and "__kernel_sockaddr_storage" but it needs to change 35 or 370 lines of codes. The other option is to duplicate this simple 2-field structure to have a separate "struct sockaddr_storage" so it can use a different alignment than "__kernel_sockaddr_storage". Also the structure seems stable enough, so it will be low-maintenance to update two structures in the future in case of changes. Signed-off-by: Qian Cai <cai@lca.pw> --- include/linux/socket.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)