dc(4) related misalignment trap

All,

On alpha this time:

	:
swapon: adding /dev/da0b as swap device
Starting file system checks:
/dev/da0a: 38800 files, 486252 used, 3308480 free (41816 frags,  
408333 blocks, 1.1% fragmentation)
Setting hostname: ds10.pn.xcllnt.net.

fatal kernel trap:

     trap entry     = 0x4 (unaligned access fault)
     faulting va    = 0xfffffc000096b73b
     opcode         = 0xc
     register       = 0x1
     pc             = 0xfffffc0000389cd8
     ra             = 0xfffffc0000389c98
     sp             = 0xfffffe001a581800
     usp            = 0x11ffe4f8
     curthread      = 0xfffffc003eb1d340
         pid = 165, comm = ifconfig

[thread pid 165 tid 100034 ]
Stopped at      dc_setfilt_21143+0x368: stl     t0,0x9c(s3)  
<0xfffffc000095879c>         
<t0=0xfffffc000096b733,s3=0xfffffc0000958700>
db> bt
Tracing pid 165 tid 100034 td 0xfffffc003eb1d340
dc_setfilt_21143() at dc_setfilt_21143+0x368
dc_setfilt() at dc_setfilt+0x58
dc_init_locked() at dc_init_locked+0x9c8
dc_init() at dc_init+0x78
ether_ioctl() at ether_ioctl+0xd8
dc_ioctl() at dc_ioctl+0x370
in6_ifinit() at in6_ifinit+0x11c
in6_update_ifa() at in6_update_ifa+0x604
in6_ifattach_linklocal() at in6_ifattach_linklocal+0x198
in6_ifattach() at in6_ifattach+0x110
in6_if_up() at in6_if_up+0xa8
if_route() at if_route+0xa4
if_up() at if_up+0x1c
ifhwioctl() at ifhwioctl+0x3a8
ifioctl() at ifioctl+0x178
soo_ioctl() at soo_ioctl+0x6e4
ioctl() at ioctl+0x6e8
syscall() at syscall+0x458
XentSys() at XentSys+0x64
--- syscall (54, FreeBSD ELF64, ioctl) ---


Note that the faulting instruction is really the instruction before
the one shown. In kgdb:

0xfffffc0000389cd4 <dc_setfilt_21143+868>:      ldwu    t0,8(t0)
0xfffffc0000389cd8 <dc_setfilt_21143+872>:      stl     t0,156(s3)

ldwu = load word unsigned.


(kgdb) l *dc_setfilt_21143+0x368
0xfffffc0000389cd8 is in dc_setfilt_21143 (../../../dev/dc/if_dc.c: 
1129).
1124                    h = dc_mchash_le(sc, ifp->if_broadcastaddr);
1125                    sp[h >> 4] |= htole32(1 << (h & 0xF));
1126            }
1127
1128            /* Set our MAC address */
1129            sp[39] = DC_SP_MAC(((u_int16_t *)IF_LLADDR(sc- 
 >dc_ifp))[0]);
1130            sp[40] = DC_SP_MAC(((u_int16_t *)IF_LLADDR(sc- 
 >dc_ifp))[1]);
1131            sp[41] = DC_SP_MAC(((u_int16_t *)IF_LLADDR(sc- 
 >dc_ifp))[2]);
1132
1133            sframe->dc_status = htole32(DC_TXSTAT_OWN);

(kgdb) f 12
#12 0xfffffc0000389cd8 in dc_setfilt_21143 (sc=0xfffffc0000842000)  
at ../../../dev/dc/if_dc.c:1129
1129            sp[39] = DC_SP_MAC(((u_int16_t *)IF_LLADDR(sc- 
 >dc_ifp))[0]);
(kgdb) p sp
$2 = (u_int32_t *) 0xfffffc0000958700
(kgdb) p sc->dc_ifp->if_addr->ifa_addr
$5 = (struct sockaddr *) 0xfffffc000096b730
(kgdb) p *(struct sockaddr_dl *)$5
$6 = {sdl_len = 56 '8', sdl_family = 18 '\022', sdl_index = 1,  
sdl_type = 6 '\006', sdl_nlen = 3 '\003', sdl_alen = 6 '\006',  
sdl_slen = 0 '\0', sdl_data = "dc0\b\000+\206\"J", '\0' <repeats 36  
times>}
(kgdb) p $6.sdl_data + $6.sdl_nlen
$7 = 0xfffffc000096b73b "\b"

Register s3 holds the sp variable ($2 in kgdb)
Register t0 holds the result the left-hand side of the statement, which
is not properly aligned for a 16-bit load ($7 = register t0 + 8).

Rough patch to fix the problem attached:


FYI,

-- 
  Marcel Moolenaar         USPA: A-39004          marcel_at_xcllnt.net