Hi,　Mark It works fine. Thanks Atsushi SAKAI Atsushi SAKAI <sakaia@jp.fujitsu.com> wrote:
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@redhat.com> 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.
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