Compile time assertions

[Steffen Daode Nurpmeso]

Hi,

my dhclient.c patch was very wrong.
And it (falsely) removed a runtime check of some struct member
size.  But this very hunk (while wrong) led me to a question.
Since saving even some bytes in shell scripts counts so much,
i wonder why compile-time assertions are not used at all (AFAIK).
I.e., the simple change in that POC patch below saves 76 bytes on
a i386.  (And that is only on-disk.)

Is there a reason not to use CTASSERT (and some kind of
member_sizeof())?  I couldn't find just any discussion on that in
marc and gmane.

--steffen

Index: sys/sys/cdefs.h
===================================================================
RCS file: /cvs/src/sys/sys/cdefs.h,v
retrieving revision 1.31
diff -a -p -u -r1.31 cdefs.h
--- sys/sys/cdefs.h     1 Oct 2010 04:51:49 -0000       1.31
+++ sys/sys/cdefs.h     14 Nov 2011 17:21:49 -0000
@@ -86,6 +86,18 @@
 #define        __CONCAT(x,y)   x/**/y
 #define        __STRING(x)     "x"
 
+/*
+ * Compile time assertion
+ */
+#define __CTASSERT(X)          __CTASSERT1((X), __LINE__)
+#define __CTASSERT1(X,L)       __CTASSERT2((X), L)
+#define __CTASSERT2(X,L)       typedef char __CTASSERT_bail_ ## L[(X) ? 1 : -1]
+
+/*
+ * __member_sizeof(T,M) - 0x8 to avoid cc warnings and too aggr. optimization
+ */
+#define __member_sizeof(T,M)   sizeof(((T *)0x8)->M)
+
 #if !defined(__GNUC__) && !defined(lint)
 #define        __const                         /* delete pseudo-ANSI C 
keywords */
 #define        __inline
Index: sbin/dhclient/dhcpd.h
===================================================================
RCS file: /cvs/src/sbin/dhclient/dhcpd.h,v
retrieving revision 1.73
diff -a -p -u -r1.73 dhcpd.h
--- sbin/dhclient/dhcpd.h       11 May 2011 14:38:36 -0000      1.73
+++ sbin/dhclient/dhcpd.h       14 Nov 2011 17:21:49 -0000
@@ -189,6 +189,8 @@ struct interface_info {
        int                      rdomain;
 };
 
+__CTASSERT(__member_sizeof(struct interface_info, name) >= IFNAMSIZ);
+
 struct timeout {
        struct timeout  *next;
        time_t           when;
Index: sbin/dhclient/dhclient.c
===================================================================
RCS file: /cvs/src/sbin/dhclient/dhclient.c,v
retrieving revision 1.141
diff -a -p -u -r1.141 dhclient.c
--- sbin/dhclient/dhclient.c    11 May 2011 14:38:36 -0000      1.141
+++ sbin/dhclient/dhclient.c    14 Nov 2011 17:21:49 -0000
@@ -2103,8 +2103,7 @@ get_ifname(char *ifname, char *arg)
                        arg = ifg->ifgrq_member;
                }
 
-               if (strlcpy(ifi->name, arg, IFNAMSIZ) >= IFNAMSIZ)
-                       error("Interface name too long: %m");
+               (void)strlcpy(ifi->name, arg, IFNAMSIZ);
 
                free(ifgr.ifgr_groups);
                close(s);