[2/2] linux-user: Don't use CMSG_ALIGN(sizeof struct cmsghdr)

The Linux struct cmsghdr is already guaranteed to be sufficiently
aligned that CMSG_ALIGN(sizeof struct cmsghdr) is always equal
to sizeof struct cmsghdr. Stop doing the unnecessary alignment
arithmetic for host and target cmsghdr.

This follows kernel commit 1ff8cebf49ed9e9ca2 and brings our
TARGET_CMSG_* macros back into line with the kernel ones,
as well as making them easier to understand.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 linux-user/syscall_defs.h | 6 +++---
 linux-user/syscall.c      | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

Le 15/12/2017 à 14:52, Peter Maydell a écrit :
> The Linux struct cmsghdr is already guaranteed to be sufficiently
> aligned that CMSG_ALIGN(sizeof struct cmsghdr) is always equal
> to sizeof struct cmsghdr. Stop doing the unnecessary alignment
> arithmetic for host and target cmsghdr.
> 
> This follows kernel commit 1ff8cebf49ed9e9ca2 and brings our
> TARGET_CMSG_* macros back into line with the kernel ones,
> as well as making them easier to understand.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  linux-user/syscall_defs.h | 6 +++---
>  linux-user/syscall.c      | 4 ++--
>  2 files changed, 5 insertions(+), 5 deletions(-)

Reviewed-by: Laurent Vivier <laurent@vivier.eu>

Le 15/12/2017 à 14:52, Peter Maydell a écrit :
> The Linux struct cmsghdr is already guaranteed to be sufficiently
> aligned that CMSG_ALIGN(sizeof struct cmsghdr) is always equal
> to sizeof struct cmsghdr. Stop doing the unnecessary alignment
> arithmetic for host and target cmsghdr.
> 
> This follows kernel commit 1ff8cebf49ed9e9ca2 and brings our
> TARGET_CMSG_* macros back into line with the kernel ones,
> as well as making them easier to understand.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  linux-user/syscall_defs.h | 6 +++---
>  linux-user/syscall.c      | 4 ++--
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
> index bec3680..a35c52a 100644
> --- a/linux-user/syscall_defs.h
> +++ b/linux-user/syscall_defs.h
> @@ -303,9 +303,9 @@ struct target_cmsghdr {
>                                 __target_cmsg_nxthdr(mhdr, cmsg, cmsg_start)
>  #define TARGET_CMSG_ALIGN(len) (((len) + sizeof (abi_long) - 1) \
>                                 & (size_t) ~(sizeof (abi_long) - 1))
> -#define TARGET_CMSG_SPACE(len) (TARGET_CMSG_ALIGN (len) \
> -                               + TARGET_CMSG_ALIGN (sizeof (struct target_cmsghdr)))
> -#define TARGET_CMSG_LEN(len)   (TARGET_CMSG_ALIGN (sizeof (struct target_cmsghdr)) + (len))
> +#define TARGET_CMSG_SPACE(len) (sizeof(struct target_cmsghdr) + \
> +                                TARGET_CMSG_ALIGN(len))
> +#define TARGET_CMSG_LEN(len) (sizeof(struct target_cmsghdr) + (len))
>  
>  static __inline__ struct target_cmsghdr *
>  __target_cmsg_nxthdr(struct target_msghdr *__mhdr,
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index a1b9772..39553c8 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -1692,7 +1692,7 @@ static inline abi_long target_to_host_cmsg(struct msghdr *msgh,
>          void *target_data = TARGET_CMSG_DATA(target_cmsg);
>  
>          int len = tswapal(target_cmsg->cmsg_len)
> -                  - TARGET_CMSG_ALIGN(sizeof (struct target_cmsghdr));
> +            - sizeof(struct target_cmsghdr);
>  
>          space += CMSG_SPACE(len);
>          if (space > msgh->msg_controllen) {
> @@ -1773,7 +1773,7 @@ static inline abi_long host_to_target_cmsg(struct target_msghdr *target_msgh,
>          void *data = CMSG_DATA(cmsg);
>          void *target_data = TARGET_CMSG_DATA(target_cmsg);
>  
> -        int len = cmsg->cmsg_len - CMSG_ALIGN(sizeof (struct cmsghdr));
> +        int len = cmsg->cmsg_len - sizeof(struct cmsghdr);
>          int tgt_len, tgt_space;
>  
>          /* We never copy a half-header but may copy half-data;
> 

Applied to my linux-user branch.

Thanks,
Laurent