Hi, Mark
Thank you for your suggestion.
I just compiled it sucessfuly.
It should be work.
I will do test it tomorrow.
Thanks
Atsushi SAKAI
Mark McLoughlin <markmc@xxxxxxxxxx> wrote:
> Hi,
> Thanks for that ...
>
> On Tue, 2007-02-20 at 13:51 +0900, Atsushi SAKAI wrote:
>
> > > > - ((struct sockaddr_in *)&ifr.ifr_addr)->sin_family = AF_INET;
> > > > - ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr = inaddr;
> > > > + ((struct sockaddr_in *)((void *)&ifr.ifr_addr))->sin_family = AF_INET;
> > > > + ((struct sockaddr_in *)((void *)&ifr.ifr_addr))->sin_addr = inaddr;
>
> > bridge.c: In function 'brSetInetAddr':
> > bridge.c:344: warning: cast increases required alignment of target type
> > bridge.c:345: warning: cast increases required alignment of target type
> > bridge.c: In function 'brGetInetAddr':
> > bridge.c:381: warning: cast increases required alignment of target type
>
> Okay, my understanding of this is that:
>
> - The warning is caused by -Wcast-align
>
> - Our problem is that we're casting between pointers to struct
> sockaddr and struct sockaddr_in, which look like
>
> struct sockaddr
> {
> unsigned short int sa_family;
> };
>
> struct sockaddr_in
> {
> unsigned short int sin_family;
> uint16_t sin_port;
> struct { uint32_t s_addr } sin_addr;
> };
>
> - Because of the uint32_t, struct sockaddr_in is required to be
> aligned to a 4 byte boundary, whereas on ia64 struct sockaddr is
> only required to be aligned to a 2 byte boundary
>
> - If we look at in the context of struct ifreq, though:
>
> struct ifreq
> {
> ....
> union {
> struct sockaddr ifru_addr;
> ....
> void *ifru_data;
> } ifr_ifru;
> };
> #define ifr_addr ifr_ifru.ifru_addr
> #define ifr_data ifr_ifru.ifru_data
>
> we see that because of the void pointer in the union, the struct
> sockaddr is actually guaranteed to be aligned to 8 bytes and so the
> warning can be ignored.
>
> - I'd prefer to avoid the void pointer cast as someone could come
> along and wonder whether the cast is hiding a genuine problem.
>
> - So, I think I'll go ahead and do it this way instead:
>
> - ((struct sockaddr_in *)&ifr.ifr_addr)->sin_family = AF_INET;
> - ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr = inaddr;
> + ((struct sockaddr_in *)&ifr.ifr_data)->sin_family = AF_INET;
> + ((struct sockaddr_in *)&ifr.ifr_data)->sin_addr = inaddr;
>
> Cheers,
> Mark.
>