On Mon, Aug 14, 2017 at 07:40:51PM -0700, David Miller wrote:
> From: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> Date: Mon, 14 Aug 2017 22:58:14 -0300
>
> > On Tue, Aug 15, 2017 at 10:43:59AM +0900, 吉藤英明 wrote:
> >> > diff --git a/net/sctp/ipv6.c b/net/sctp/ipv6.c
> >> > index 2a186b201ad2..a15d691829c6 100644
> >> > --- a/net/sctp/ipv6.c
> >> > +++ b/net/sctp/ipv6.c
> >> > @@ -513,6 +513,8 @@ static void sctp_v6_to_addr(union sctp_addr *addr, struct in6_addr *saddr,
> >> > addr->sa.sa_family = AF_INET6;
> >> > addr->v6.sin6_port = port;
> >> > addr->v6.sin6_addr = *saddr;
> >> > + addr->v6.sin6_flowinfo = 0;
> >> > + addr->v6.sin6_scope_id = 0;
> >>
> >> Please set flowinfo between port and addr.
> >
> > Why?
>
> Store buffer compression.
>
> You want to always initialize structure member in the order
> they are in memory.
Thanks.
>
> No, the compiler won't do this automatically.
Ok, but I should see a difference in the generated code, right?
union sctp_addr is a union of sockaddr_in structs, for easy reference
ipv6 being:
struct sockaddr_in6 {
short unsigned int sin6_family; /* 0 2 */
__be16 sin6_port; /* 2 2 */
__be32 sin6_flowinfo; /* 4 4 */
struct in6_addr sin6_addr; /* 8 16 */
__u32 sin6_scope_id; /* 24 4 */
Current code:
12a1: ba 0a 00 00 00 mov $0xa,%edx
12a6: 49 8b 5f 68 mov 0x68(%r15),%rbx
12aa: 66 89 55 a0 mov %dx,-0x60(%rbp)
union/struct start -----^
12ae: 4d 8d 4f 68 lea 0x68(%r15),%r9
12b2: 49 8b 55 40 mov 0x40(%r13),%rdx
12b6: 66 c1 c0 08 rol $0x8,%ax (htons)
12ba: 4c 39 cb cmp %r9,%rbx
12bd: 48 89 55 b0 mov %rdx,-0x50(%rbp)
thus this ---^
12c1: 66 89 45 a2 mov %ax,-0x5e(%rbp)
^-------- port number
12c5: 49 8b 45 38 mov 0x38(%r13),%rax
12c9: 48 89 45 a8 mov %rax,-0x58(%rbp)
and this are the ipv6 addr bytes ---^
12cd: 74 30 je 12ff <sctp_v6_get_dst+0x37f>
Alexander's:
12a1: ba 0a 00 00 00 mov $0xa,%edx
12a6: 49 8b 5f 68 mov 0x68(%r15),%rbx
12aa: 66 89 55 a0 mov %dx,-0x60(%rbp)
12ae: 4d 8d 4f 68 lea 0x68(%r15),%r9
12b2: 49 8b 55 40 mov 0x40(%r13),%rdx
12b6: c7 45 a4 00 00 00 00 movl $0x0,-0x5c(%rbp)
12bd: c7 45 b8 00 00 00 00 movl $0x0,-0x48(%rbp)
12c4: 66 c1 c0 08 rol $0x8,%ax
12c8: 4c 39 cb cmp %r9,%rbx
12cb: 48 89 55 b0 mov %rdx,-0x50(%rbp)
12cf: 66 89 45 a2 mov %ax,-0x5e(%rbp)
12d3: 49 8b 45 38 mov 0x38(%r13),%rax
12d7: 48 89 45 a8 mov %rax,-0x58(%rbp)
12db: 74 30 je 130d <sctp_v6_get_dst+0x38d>
Hideaki's:
12a1: ba 0a 00 00 00 mov $0xa,%edx
12a6: 49 8b 5f 68 mov 0x68(%r15),%rbx
12aa: 66 89 55 a0 mov %dx,-0x60(%rbp)
12ae: 4d 8d 4f 68 lea 0x68(%r15),%r9
12b2: 49 8b 55 40 mov 0x40(%r13),%rdx
12b6: c7 45 a4 00 00 00 00 movl $0x0,-0x5c(%rbp)
12bd: c7 45 b8 00 00 00 00 movl $0x0,-0x48(%rbp)
12c4: 66 c1 c0 08 rol $0x8,%ax
12c8: 4c 39 cb cmp %r9,%rbx
12cb: 48 89 55 b0 mov %rdx,-0x50(%rbp)
12cf: 66 89 45 a2 mov %ax,-0x5e(%rbp)
12d3: 49 8b 45 38 mov 0x38(%r13),%rax
12d7: 48 89 45 a8 mov %rax,-0x58(%rbp)
12db: 74 30 je 130d <sctp_v6_get_dst+0x38d>
They are the same, and messed up by the compiler breaking the copy of
the ipv6 addr (which was copied backwards) with the port number copy.
Marcelo
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