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Like many other functions that handle sockaddrs, realhostname_sa() takes a

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struct sockaddr * that it casts internally to the appropriate type based on
sa_family.  However, struct sockaddr has very lax alignment requirements,
which causes the compiler to complain when you cast a struct sockaddr * to,
say, a struct sockaddr_in6 *.

I find it reasonable to assume that the pointer we received is in fact
correctly aligned.  Therefore, we can work around the compiler warnings by
casting to void * before casting to the desired type.  For readability's
sake, this is done with macros.

The same technique should prove useful in other parts of the tree that
deal with socket addresses.

MFC after:	3 weeks
This commit is contained in:
Dag-Erling Smørgrav 2008-11-05 12:13:10 +00:00
parent 63c79eb71f
commit 31cfde7132
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=184683
1 changed files with 18 additions and 5 deletions
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23
lib/libutil/realhostname.c
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@ -83,6 +83,18 @@ realhostname(char *host, size_t hsize, const struct in_addr *ip)
return result;
}
/*
* struct sockaddr has very lax alignment requirements, since all its
* members are char or equivalent. This is a problem when trying to
* dereference a struct sockaddr_in6 * that was passed in as a struct
* sockaddr *. Although we know (or trust) that the passed-in struct was
* properly aligned, the compiler doesn't, and (rightly) complains. These
* macros perform the cast in a way that the compiler will accept.
*/
#define SOCKADDR_IN6(p) ((struct sockaddr_in6 *)(void *)(p))
#define SOCKADDR_IN(p) ((struct sockaddr_in *)(void *)(p))
#define SOCKINET(p) ((struct sockinet *)(void *)(p))
int
realhostname_sa(char *host, size_t hsize, struct sockaddr *addr, int addrlen)
{
@ -96,10 +108,10 @@ realhostname_sa(char *host, size_t hsize, struct sockaddr *addr, int addrlen)
/* IPv4 mapped IPv6 addr consideraton, specified in rfc2373. */
if (addr->sa_family == AF_INET6 &&
addrlen == sizeof(struct sockaddr_in6) &&
IN6_IS_ADDR_V4MAPPED(&((struct sockaddr_in6 *)addr)->sin6_addr)) {
IN6_IS_ADDR_V4MAPPED(&SOCKADDR_IN6(addr)->sin6_addr)) {
struct sockaddr_in6 *sin6;
sin6 = (struct sockaddr_in6 *)addr;
sin6 = SOCKADDR_IN6(addr);
memset(&lsin, 0, sizeof(lsin));
lsin.sin_len = sizeof(struct sockaddr_in);
@ -142,15 +154,16 @@ realhostname_sa(char *host, size_t hsize, struct sockaddr *addr, int addrlen)
}
if (sa->sa_len == addrlen &&
sa->sa_family == addr->sa_family) {
((struct sockinet *)sa)->si_port = ((struct sockinet *)addr)->si_port;
SOCKINET(sa)->si_port = SOCKINET(addr)->si_port;
#ifdef INET6
/*
* XXX: sin6_socpe_id may not been
* filled by DNS
*/
if (sa->sa_family == AF_INET6 &&
((struct sockaddr_in6 *)sa)->sin6_scope_id == 0)
((struct sockaddr_in6 *)sa)->sin6_scope_id = ((struct sockaddr_in6 *)addr)->sin6_scope_id;
SOCKADDR_IN6(sa)->sin6_scope_id == 0)
SOCKADDR_IN6(sa)->sin6_scope_id =
SOCKADDR_IN6(addr)->sin6_scope_id;
#endif
if (!memcmp(sa, addr, sa->sa_len)) {
result = HOSTNAME_FOUND;