Description of problem:
Was working on F37 and started crashing on F38. Here are some relevant parts of the VM config:

<memory unit="KiB">25165824</memory>
  <currentMemory unit="KiB">16777216</currentMemory>
  <vcpu placement="auto">12</vcpu>
  <numatune>
    <memory mode="strict" placement="auto"/>
  </numatune>
<features>
    <acpi/>
    <apic/>
    <hyperv mode="custom">
      <relaxed state="on"/>
      <vapic state="on"/>
      <spinlocks state="on" retries="8191"/>
    </hyperv>
    <vmport state="off"/>
    <smm state="on"/>
  </features>
<cpu mode="host-passthrough" check="none" migratable="on"/>
  <clock offset="localtime">
    <timer name="rtc" tickpolicy="catchup"/>
    <timer name="pit" tickpolicy="delay"/>
    <timer name="hpet" present="no"/>
    <timer name="hypervclock" present="yes"/>
  </clock>
<memballoon model="virtio">
      <address type="pci" domain="0x0000" bus="0x05" slot="0x00" function="0x0"/>
    </memballoon>

Version-Release number of selected component:
numad-0.5-38.20150602git.fc38

Additional info:
reporter:       libreport-2.17.10
type:           CCpp
reason:         numad killed by SIGABRT
journald_cursor: s=f205fceb5ad34d5c9fa69ba9ec1d8936;i=241142;b=452539ae96394dac8987a32a0f22ad10;m=97d0d6af3;t=5fdf40b321d76;x=32f404c20f561156
executable:     /usr/bin/numad
cmdline:        /usr/bin/numad -w 12:24576
cgroup:         0::/system.slice/libvirtd.service
rootdir:        /
uid:            0
kernel:         6.3.6-200.fc38.x86_64
package:        numad-0.5-38.20150602git.fc38
runlevel:       N 5
backtrace_rating: 4
crash_function: vsnprintf

Truncated backtrace:
Thread no. 1 (2 frames)
 #8 vsnprintf at /usr/include/bits/stdio2.h:68
 #9 numad_log at /usr/src/debug/numad-0.5-38.20150602git.fc38.x86_64/numad.c:156