10.0-RC1: net/mpd5 crashes in NgMkSockNode due to stack alignment on ARM EABI

[John-Mark Gurney]

Guy Yur wrote this message on Sat, Dec 21, 2013 at 19:24 +0200:
> I am running 10.0-RC1 on the BeagleBone Black and the net/mpd5 port is
> crashing in libnetgraph NgMkSockNode due to stack alignment.
> 
> 10.0-RC1 World and kernel were compiled in a VirtualBox VM running
> 9.2-RELEASE-p2 i386.
> clang and ARM_EABI used as the default make options.
> 
> Added prints in NgMkSockNode show rbuf is aligned on 2-byte and not
> 4-byte which is needed to access ni->id (a uint32_t).
> 
> ni = 0xbfffe87a
> rbuf = 0xbfffe842
> sizeof(resp->header) = 56
> 
> 
> (gdb) bt
> #0  0x201529a0 in NgMkSockNode (name=<value optimized out>, csp=0xbfffe95c,
>     dsp=0xbfffe958) at /usr/src/lib/libnetgraph/sock.c:134
> #1  0x00037b9c in MppcTestCap () at ccp_mppc.c:754
> #2  0x0007c1f4 in main (ac=4, av=0xbfffeb90) at main.c:248
> #3  0x0000d1b0 in __start (argc=4, argv=0xbfffeb90, env=0xbfffeba4,
>     ps_strings=<value optimized out>, obj=<value optimized out>,
>     cleanup=<value optimized out>) at /usr/src/lib/csu/arm/crt1.c:115
> #4  0x203e9dc0 in _thr_ast (curthread=0x200fd000)
>     at /usr/src/lib/libthr/thread/thr_sig.c:265
> 
> 
> Putting rbuf in a union with struct ng_mesg sorted the alignment to
> 4-byte and mpd5 didn't crash.
> I attached the changes I used to test mpd5 doesn't crash with correct alignment.

The patch looks correct, but lets make sure that the -net people don't
have an issue with it...

I've reattached Guy's patch for review.

Guy, bug me in a week or so if I haven't committed it, and I will...

Thanks for tracking this down.

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."
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