diff mbox series

[v2] socket: Use may_alias on sockaddr structs (bug 19622)

Message ID 87h6f95rfd.fsf@oldenburg.str.redhat.com
State New
Headers show
Series [v2] socket: Use may_alias on sockaddr structs (bug 19622) | expand

Commit Message

Florian Weimer May 7, 2024, 7:54 p.m. UTC 
This supports common coding paddings.  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.

 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

Comments

Jakub Jelinek May 7, 2024, 7:57 p.m. UTC | #1 
On Tue, May 07, 2024 at 09:54:14PM +0200, Florian Weimer wrote:
> --- 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, 0) || defined __clang__

I'd use (7, 1) here, because pedantically there were some 7.0.0 snapshots
which didn't support it.
7.1.0 and later do support it though.

Otherwise LGTM.

Thanks.

	Jakub
diff mbox series

Patch

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..32fc70bf0e 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, 0) || defined __clang__
+# 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 */