avahi-core socket.c's input cmsghdr msg->msg_control buffers are misaligned on ia64 linux

Patch against 0.6.5/6 socket.c to fix issue

Mmm, this patch contains two errors and introduces a new compiler warning I don't understand.

The two errors: once you mistyped "cmsghdr" as "msghdr". And once you wrote "in_addr" instead of "in_pktinfo".

When I apply the patch i Get the followign compiler warnings:

socket.c: In function 'avahi_send_dns_packet_ipv4': socket.c:459: warning: invalid use of structure with flexible array member socket.c: In function 'avahi_send_dns_packet_ipv6': socket.c:545: warning: invalid use of structure with flexible array member socket.c: In function 'avahi_recv_dns_packet_ipv4': socket.c:599: warning: invalid use of structure with flexible array member socket.c: In function 'avahi_recv_dns_packet_ipv6': socket.c:729: warning: invalid use of structure with flexible array member

I wonder what they mean, do you have any idea and could supply me with a patch that doesn't produce these warnnings?

Thank you very much,

Lennart

updated patch to fix issue

OK, I fixed the typos with the updated patch just uploaded.

The compiler warnings are generated ONLY with the '-pedantic' gcc argument, and occur because the cmsghdr structures are declared:

struct cmsghdr

{

size_t cmsg_len;

int cmsg_level; int cmsg_type;

extension unsigned char cmsg_data [];

};

ie. they end with a "flexible array" of zero size, so in -pedantic mode, the compiler will complain about a vector of such structures. You can avoid this declaration using the -ansi gcc flag.

Possibly using 'size_t' instead of 'struct cmsghdr' for the type of the array would work just as well - the important thing is that the compiler must allocate an address on an 8-byte boundary for the buffers - ie. you could do:

size_t aux[1024 / sizeof(size_t)]; /* for alignment on ia64 ! */

and that would ensure that the array gets an 8-byte aligned address, since size_t is a U64 on ia64 .

Updated patch using size_t instead of 'struct cmsghdr' for buffers

OK, I just uploaded the latest version of the patch, which declares the buffers as 'size_t' vectors instead of 'struct cmsghdr' vectors, and tested the new patched avahi-daemon on ia64 - no unaligned access faults occurred, and the 'invalid use of structure with flexible array member' warnings have disappeared.

When you compile socket.c on ia64, you still get these warnings with -pedantic:

socket.c: In function 'avahi_send_dns_packet_ipv4': socket.c:498: warning: cast increases required alignment of target type socket.c: In function 'avahi_send_dns_packet_ipv6': socket.c:577: warning: cast increases required alignment of target type socket.c: In function 'avahi_recv_dns_packet_ipv4': socket.c:667: warning: cast increases required alignment of target type socket.c:673: warning: cast increases required alignment of target type socket.c: In function 'avahi_recv_dns_packet_ipv6': socket.c:786: warning: cast increases required alignment of target type socket.c:793: warning: cast increases required alignment of target type

These are for all expressions such as on line 498:

pkti = (struct in_pktinfo*) CMSG_DATA(cmsg);

But now the cmsghdr buffers are aligned correctly on 8 byte boundaries, these warnings do not matter.

I commited this in revision 1130.

Thank you for your contribution!