Re: SIGBUS on octeon for my program

On Wed, Nov 27, 2019 at 03:30:23PM +0100, Peter J. Philipp wrote:
> Hi David,
>
> I'm going to upgrade to -current and then report back.. it'll take me a few
> days to do that (I'm super slow).
>
> ...
> I'll see if this sort of issue repeats after I upgrade the octeon router
> to -current.
>
> Thanks!
> -peter

Hi David and Misc@,

OK this is weird. For people who are just reading this thread it's about
OpenBSD/octeon SIGBUS'ing my program with an unalignment error.

I upgraded to -current (very pleased that pppoe0 works now, as an aside),
and got the debug right after the fork. Here is the output of gdb

debug.1--->
Continuing.

Program received signal SIGBUS, Bus error.
lookup_axfr (f=0x2c6274db78, so=6, zonename=0x2c6b3d2130 "words.",
mysoa=0xfffffe7920, format=20, tsigkey=0x2c37b083d0 "pass",
tsigpass=0xfffffe7b60 "*censored*=",
segment=0xfffffe7b40, answers=0xfffffe7b3c, additionalcount=0xfffffe7b38)
at util.c:1842
1842 *type = htons(DNS_TYPE_AXFR);
(gdb) list
1837
1838 memcpy(p, name, len);
1839 totallen += len;
1840
1841 type = (u_int16_t *)&query[totallen];
1842 *type = htons(DNS_TYPE_AXFR);
1843 totallen += sizeof(u_int16_t);
1844
1845 class = (u_int16_t *)&query[totallen];
1846 *class = htons(DNS_CLASS_IN);
(gdb) print type
$1 = (u_int16_t *) 0xfffffe763d
<-----

So I point a pointer of type u_int16_t to a memory address (which may be
unaligned) and then load it with a value. I've always done it this way
throughout my program, but just to be sure that it isn't caused by the stack
somehow I moved query variable to the heap (or it's equivalent) and tried
again.

debug.2--->
Loaded symbols for /usr/libexec/ld.so
pull_remote_zone (lrz=0x216549d000) at parse.y:3605
3605 while (debugger == 1)
(gdb) set debugger=0
Current language: auto; currently minimal
(gdb) cont
Continuing.

Program received signal SIGBUS, Bus error.
lookup_axfr (f=0x21b8dfdb78, so=6, zonename=0x22041a4a10 "words.",
mysoa=0xffffff9050, format=20, tsigkey=0x22052c35b0 "pass",
tsigpass=0xffffff9290 "*censored*=",
segment=0xffffff9270, answers=0xffffff926c, additionalcount=0xffffff9268)
at util.c:1849
1849 *type = htons(DNS_TYPE_AXFR);
(gdb) print type
$1 = (u_int16_t *) 0x21d57f1015
(gdb) print query
$2 = 0x21d57f1000 ""
(gdb) print (char*)type - query
$3 = 21
<-------

So now I have a true offset of variable type it's not aligned. What can I
do here? Does this need fixing in OpenBSD/octeon or do I have to fix my
code for this? I don't really know what to use instead of this other than
memcpy'ing this value instead of (overloading?) the 16 bit integer.

Any help is welcomed!

Best regards,
-peter