Sun Jan 29 18:33:07 2012 UTC ()

Allow using CMSG_NXTHDR with -Wcast-align.

If various checks are omitted, the CMSG_NXTHDR macro expands to
(struct cmsghdr *)((char *)(cmsg) + \
_ALIGN(((struct cmsghdr *)(cmsg))->cmsg_len))

Although there is no alignment problem (assuming cmsg is properly aligned
and _ALIGN is correct), this violates -Wcast-align on strict-alignment
architectures. Therefore an intermediate cast to void * is appropriate here.

There is no workaround other than not using -Wcast-align.

Taken from FreeBSD commit r220742 by jilles


(roy)

diff -r1.105 -r1.106 src/sys/sys/socket.h

--- src/sys/sys/socket.h 2012/01/25 00:28:35	1.105
+++ src/sys/sys/socket.h 2012/01/29 18:33:07	1.106

 @@ -1,14 +1,14 @@
-/*	$NetBSD: socket.h,v 1.105 2012/01/25 00:28:35 christos Exp $	*/
+/*	$NetBSD: socket.h,v 1.106 2012/01/29 18:33:07 roy Exp $	*/
 /*
  * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
  * All rights reserved.
+ *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
 @@ -534,27 +534,27 @@ struct cmsghdr {
  * changes in ALIGNBYTES.
  */
 #define __CMSG_ALIGN(n)	(((n) + __ALIGNBYTES) & ~__ALIGNBYTES)
 #ifdef _KERNEL
 #define CMSG_ALIGN(n)	__CMSG_ALIGN(n)
 #endif
 /* given pointer to struct cmsghdr, return pointer to next cmsghdr */
 #define	CMSG_NXTHDR(mhdr, cmsg)	\
 	(((char *)(cmsg) + __CMSG_ALIGN((cmsg)->cmsg_len) + \
 			    __CMSG_ALIGN(sizeof(struct cmsghdr)) > \
 	    (((char *)(mhdr)->msg_control) + (mhdr)->msg_controllen)) ? \
 	    (struct cmsghdr *)0 : \
-	    (struct cmsghdr *)((char *)(cmsg) + \
+	    (struct cmsghdr *)(void *)((char *)(cmsg) + \
 	        __CMSG_ALIGN((cmsg)->cmsg_len)))
 /*
  * RFC 2292 requires to check msg_controllen, in case that the kernel returns
  * an empty list for some reasons.
  */
 #define	CMSG_FIRSTHDR(mhdr) \
 	((mhdr)->msg_controllen >= sizeof(struct cmsghdr) ? \
 	 (struct cmsghdr *)(mhdr)->msg_control : \
 	 (struct cmsghdr *)0)
 #define CMSG_SPACE(l)	(__CMSG_ALIGN(sizeof(struct cmsghdr)) + __CMSG_ALIGN(l))
 #define CMSG_LEN(l)	(__CMSG_ALIGN(sizeof(struct cmsghdr)) + (l))