toolchain/53918: X crashes on pinebook and stack unwinding broken

[martin%NetBSD.org@localhost]

>Number:         53918
>Category:       toolchain
>Synopsis:       X crashes on pinebook and stack unwinding broken
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jan 28 13:55:00 +0000 2019
>Originator:     Martin Husemann
>Release:        NetBSD 8.99.32
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD painkiller.duskware.de 8.99.32 NetBSD 8.99.32 (GENERIC64) #32: Mon Jan 28 11:53:50 CET 2019 martin%seven-days-to-the-wolves.aprisoft.de@localhost:/work/src/sys/arch/evbarm/compile/GENERIC64 evbarm
Architecture: aarch64
Machine: evbarm
>Description:

Since my last update X does not start any more and the X process hangs 
apparently trying to log a backtrace:

[Switching to LWP 1 of process 437]
0x0000fffffb816e00 in memset () from /usr/lib/libc.so.12
(gdb) bt
#0  0x0000fffffb816e00 in memset () from /usr/lib/libc.so.12
#1  0x0000fffffb6d5218 in ?? () from /lib/libgcc_s.so.1
#2  0x0000fffffb6d68b8 in _Unwind_Backtrace () from /lib/libgcc_s.so.1
#3  0x0000fffffbe710b0 in backtrace (arr=<optimized out>, len=<optimized out>)
    at /work/src/lib/libexecinfo/unwind.c:67
#4  0x0000000200271d70 in xorg_backtrace ()
#5  0x000000020026dc6c in ?? ()
#6  0x0000fffffb79d750 in _opendir (name=<optimized out>)
    at /work/src/lib/libc/gen/opendir.c:72
Backtrace stopped: previous frame identical to this frame (corrupt stack?)

This failure to unwind is why this is in the toolchain category - real fixes
for the X issue would be nice too ;-)

>How-To-Repeat:

Set xdm=yes in /etc/rc.conf and boot a pinebook - does not happen always,
but quite often.

>Fix:
n/a