From: Qian Cai

Sent: 30 July 2019 15:38

...

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 <redacted>

...

Although I suggested it needs a bit of tidy up.

Add a comment maybe:

/* 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 {
+		void *__align; /* implementation specific desired alignment */

Move the 'void *' below the struct so the first member is the 'public one.

+		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 */
+			};
+		};
+};

 #endif /* _UAPI_LINUX_SOCKET_H */
--
1.8.3.1

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)