[v4] socket: Use may_alias on sockaddr structs (bug 19622)

This supports common coding patterns.  The GCC C front end before
version 7 rejects the may_alias attribute on a struct definition
if it was not present in a previous forward declaration, so this
attribute can only be conditionally applied.

This implements the spirit of the change in Austin Group issue 1641.

Suggested-by: Marek Polacek <polacek@redhat.com>
Suggested-by: Jakub Jelinek <jakub@redhat.com>

---
v2: Mention Austing Group issue 1641.  Correct the GCC version range.
    The C front end was changed early in the 7 release cycle.
v3: Require the GCC 7 release version based on feedback from Jakub.
v4: Fix typo in commit message.

 bits/socket.h                           | 4 ++--
 inet/netinet/in.h                       | 8 +++++---
 misc/sys/cdefs.h                        | 9 +++++++++
 socket/sys/un.h                         | 2 +-
 sysdeps/mach/hurd/bits/socket.h         | 4 ++--
 sysdeps/unix/sysv/linux/bits/socket.h   | 4 ++--
 sysdeps/unix/sysv/linux/net/if_packet.h | 2 +-
 sysdeps/unix/sysv/linux/netash/ash.h    | 2 +-
 sysdeps/unix/sysv/linux/neteconet/ec.h  | 2 +-
 sysdeps/unix/sysv/linux/netiucv/iucv.h  | 2 +-
 10 files changed, 25 insertions(+), 14 deletions(-)


base-commit: 143ef68b2aded7c794956beddad495af8c7d3251

On 5/10/24 2:24 AM, Florian Weimer wrote:
> This supports common coding patterns.  The GCC C front end before
> version 7 rejects the may_alias attribute on a struct definition
> if it was not present in a previous forward declaration, so this
> attribute can only be conditionally applied.
> 
> This implements the spirit of the change in Austin Group issue 1641.
> 
> Suggested-by: Marek Polacek <polacek@redhat.com>
> Suggested-by: Jakub Jelinek <jakub@redhat.com>
> 

Missing the RB from Same James? It hasn't changed substantially since then.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
> v2: Mention Austing Group issue 1641.  Correct the GCC version range.
>     The C front end was changed early in the 7 release cycle.
> v3: Require the GCC 7 release version based on feedback from Jakub.
> v4: Fix typo in commit message.
> 
>  bits/socket.h                           | 4 ++--
>  inet/netinet/in.h                       | 8 +++++---
>  misc/sys/cdefs.h                        | 9 +++++++++
>  socket/sys/un.h                         | 2 +-
>  sysdeps/mach/hurd/bits/socket.h         | 4 ++--
>  sysdeps/unix/sysv/linux/bits/socket.h   | 4 ++--
>  sysdeps/unix/sysv/linux/net/if_packet.h | 2 +-
>  sysdeps/unix/sysv/linux/netash/ash.h    | 2 +-
>  sysdeps/unix/sysv/linux/neteconet/ec.h  | 2 +-
>  sysdeps/unix/sysv/linux/netiucv/iucv.h  | 2 +-
>  10 files changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/bits/socket.h b/bits/socket.h
> index 13de124bac..772074d52a 100644
> --- a/bits/socket.h
> +++ b/bits/socket.h
> @@ -149,7 +149,7 @@ enum __socket_type
>  #include <bits/sockaddr.h>
>  
>  /* Structure describing a generic socket address.  */
> -struct sockaddr
> +struct __attribute_struct_may_alias__ sockaddr
>    {
>      __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
>      char sa_data[14];		/* Address data.  */
> @@ -166,7 +166,7 @@ struct sockaddr
>  #define _SS_PADSIZE \
>    (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
>  
> -struct sockaddr_storage
> +struct __attribute_struct_may_alias__ sockaddr_storage
>    {
>      __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
>      char __ss_padding[_SS_PADSIZE];
> diff --git a/inet/netinet/in.h b/inet/netinet/in.h
> index fa57b61079..f684be5beb 100644
> --- a/inet/netinet/in.h
> +++ b/inet/netinet/in.h
> @@ -244,7 +244,7 @@ extern const struct in6_addr in6addr_loopback;   /* ::1 */
>  
>  
>  /* Structure describing an Internet socket address.  */
> -struct sockaddr_in
> +struct __attribute_struct_may_alias__ sockaddr_in
>    {
>      __SOCKADDR_COMMON (sin_);
>      in_port_t sin_port;			/* Port number.  */
> @@ -257,9 +257,11 @@ struct sockaddr_in
>  			   - sizeof (struct in_addr)];
>    };
>  
> -#if !__USE_KERNEL_IPV6_DEFS
> +#if __USE_KERNEL_IPV6_DEFS
> +struct __attribute_struct_may_alias__ sockaddr_in6;
> +#else
>  /* Ditto, for IPv6.  */
> -struct sockaddr_in6
> +struct __attribute_struct_may_alias__ sockaddr_in6
>    {
>      __SOCKADDR_COMMON (sin6_);
>      in_port_t sin6_port;	/* Transport layer port # */
> diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
> index 2e8279a2c7..ab9620bd0d 100644
> --- a/misc/sys/cdefs.h
> +++ b/misc/sys/cdefs.h
> @@ -874,4 +874,13 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
>  # define __attribute_returns_twice__ /* Ignore.  */
>  #endif
>  
> +/* Mark struct types as aliasable.  Restricted to compilers that
> +   support forward declarations of structs in the presence of the
> +   attribute.  */
> +#if __GNUC_PREREQ (7, 1) || defined __clang__

OK. Resolve's Jakub's suggestion to use 7.1.

> +# define __attribute_struct_may_alias__ __attribute__ ((__may_alias__))
> +#else
> +# define __attribute_struct_may_alias__
> +#endif
> +
>  #endif	 /* sys/cdefs.h */
> diff --git a/socket/sys/un.h b/socket/sys/un.h
> index bf03b7d6ce..ff9cbd6efa 100644
> --- a/socket/sys/un.h
> +++ b/socket/sys/un.h
> @@ -26,7 +26,7 @@
>  __BEGIN_DECLS
>  
>  /* Structure describing the address of an AF_LOCAL (aka AF_UNIX) socket.  */
> -struct sockaddr_un
> +struct __attribute_struct_may_alias__ sockaddr_un
>    {
>      __SOCKADDR_COMMON (sun_);
>      char sun_path[108];		/* Path name.  */
> diff --git a/sysdeps/mach/hurd/bits/socket.h b/sysdeps/mach/hurd/bits/socket.h
> index 3e72f9fa93..b5eeac3731 100644
> --- a/sysdeps/mach/hurd/bits/socket.h
> +++ b/sysdeps/mach/hurd/bits/socket.h
> @@ -153,7 +153,7 @@ enum __socket_type
>  #include <bits/sockaddr.h>
>  
>  /* Structure describing a generic socket address.  */
> -struct sockaddr
> +struct __attribute_struct_may_alias__ sockaddr
>    {
>      __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
>      char sa_data[14];		/* Address data.  */
> @@ -170,7 +170,7 @@ struct sockaddr
>  #define _SS_PADSIZE \
>    (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
>  
> -struct sockaddr_storage
> +struct __attribute_struct_may_alias__ sockaddr_storage
>    {
>      __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
>      char __ss_padding[_SS_PADSIZE];
> diff --git a/sysdeps/unix/sysv/linux/bits/socket.h b/sysdeps/unix/sysv/linux/bits/socket.h
> index 86444f0018..5ab19a8c08 100644
> --- a/sysdeps/unix/sysv/linux/bits/socket.h
> +++ b/sysdeps/unix/sysv/linux/bits/socket.h
> @@ -181,7 +181,7 @@ typedef __socklen_t socklen_t;
>  #include <bits/sockaddr.h>
>  
>  /* Structure describing a generic socket address.  */
> -struct sockaddr
> +struct __attribute_struct_may_alias__ sockaddr
>    {
>      __SOCKADDR_COMMON (sa_);	/* Common data: address family and length.  */
>      char sa_data[14];		/* Address data.  */
> @@ -194,7 +194,7 @@ struct sockaddr
>  #define _SS_PADSIZE \
>    (_SS_SIZE - __SOCKADDR_COMMON_SIZE - sizeof (__ss_aligntype))
>  
> -struct sockaddr_storage
> +struct __attribute_struct_may_alias__ sockaddr_storage
>    {
>      __SOCKADDR_COMMON (ss_);	/* Address family, etc.  */
>      char __ss_padding[_SS_PADSIZE];
> diff --git a/sysdeps/unix/sysv/linux/net/if_packet.h b/sysdeps/unix/sysv/linux/net/if_packet.h
> index 9ffb69b508..c17e1c23c5 100644
> --- a/sysdeps/unix/sysv/linux/net/if_packet.h
> +++ b/sysdeps/unix/sysv/linux/net/if_packet.h
> @@ -26,7 +26,7 @@
>     From Linux 2.1 the AF_PACKET interface is preferred and you should
>     consider using it in place of this one.  */
>  
> -struct sockaddr_pkt
> +struct __attribute_struct_may_alias__ sockaddr_pkt
>    {
>      __SOCKADDR_COMMON (spkt_);
>      unsigned char spkt_device[14];
> diff --git a/sysdeps/unix/sysv/linux/netash/ash.h b/sysdeps/unix/sysv/linux/netash/ash.h
> index 7d885d17cc..7a6ff50b17 100644
> --- a/sysdeps/unix/sysv/linux/netash/ash.h
> +++ b/sysdeps/unix/sysv/linux/netash/ash.h
> @@ -22,7 +22,7 @@
>  #include <features.h>
>  #include <bits/sockaddr.h>
>  
> -struct sockaddr_ash
> +struct __attribute_struct_may_alias__ sockaddr_ash
>    {
>      __SOCKADDR_COMMON (sash_);		/* Common data: address family etc.  */
>      int sash_ifindex;			/* Interface to use.  */
> diff --git a/sysdeps/unix/sysv/linux/neteconet/ec.h b/sysdeps/unix/sysv/linux/neteconet/ec.h
> index b07a107961..f3132f06ff 100644
> --- a/sysdeps/unix/sysv/linux/neteconet/ec.h
> +++ b/sysdeps/unix/sysv/linux/neteconet/ec.h
> @@ -28,7 +28,7 @@ struct ec_addr
>      unsigned char net;			/* Network number.  */
>    };
>  
> -struct sockaddr_ec
> +struct __attribute_struct_may_alias__ sockaddr_ec
>    {
>      __SOCKADDR_COMMON (sec_);
>      unsigned char port;			/* Port number.  */
> diff --git a/sysdeps/unix/sysv/linux/netiucv/iucv.h b/sysdeps/unix/sysv/linux/netiucv/iucv.h
> index f5fad81751..27151e8bbe 100644
> --- a/sysdeps/unix/sysv/linux/netiucv/iucv.h
> +++ b/sysdeps/unix/sysv/linux/netiucv/iucv.h
> @@ -23,7 +23,7 @@
>  
>  __BEGIN_DECLS
>  
> -struct sockaddr_iucv
> +struct __attribute_struct_may_alias__ sockaddr_iucv
>    {
>      __SOCKADDR_COMMON (siucv_);
>      unsigned short	siucv_port;		/* Reserved */
> 
> base-commit: 143ef68b2aded7c794956beddad495af8c7d3251
>

* Carlos O'Donell:

> On 5/10/24 2:24 AM, Florian Weimer wrote:
>> This supports common coding patterns.  The GCC C front end before
>> version 7 rejects the may_alias attribute on a struct definition
>> if it was not present in a previous forward declaration, so this
>> attribute can only be conditionally applied.
>> 
>> This implements the spirit of the change in Austin Group issue 1641.
>> 
>> Suggested-by: Marek Polacek <polacek@redhat.com>
>> Suggested-by: Jakub Jelinek <jakub@redhat.com>
>> 
>
> Missing the RB from Sam James? It hasn't changed substantially since then.
>
> Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Sam, does your Reviewed-by: still stand?

Thanks,
Florian

Florian Weimer <fweimer@redhat.com> writes:

> * Carlos O'Donell:
>
>> On 5/10/24 2:24 AM, Florian Weimer wrote:
>>> This supports common coding patterns.  The GCC C front end before
>>> version 7 rejects the may_alias attribute on a struct definition
>>> if it was not present in a previous forward declaration, so this
>>> attribute can only be conditionally applied.
>>> 
>>> This implements the spirit of the change in Austin Group issue 1641.
>>> 
>>> Suggested-by: Marek Polacek <polacek@redhat.com>
>>> Suggested-by: Jakub Jelinek <jakub@redhat.com>
>>> 
>>
>> Missing the RB from Sam James? It hasn't changed substantially since then.
>>
>> Reviewed-by: Carlos O'Donell <carlos@redhat.com>
>
> Sam, does your Reviewed-by: still stand?

Yes, thanks!

thanks,
sam