If there's an existing tap device on the system, runqemu takes a different path that essentially leaves the trailing colon on the tap device name e.g. tap0: instead of what it should be: tap0.  Stripping the colon off the name it finds should fix the problem, but the runqemu* scripts should be audited for similar kind of problems with this and other devices.

If there isn't a tap device found, the script uses the output of:

tap=`sudo $QEMUIFUP $USERID $GROUPID $OECORE_NATIVE_SYSROOT

which doesn't cause a problem, which is why the problem isn't normally seen (i.e. everybody must be using Ubuntu).

Details: my system has the following ifconfig output:

[trz@empanada build]$ ifconfig
em1: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        ether 08:2e:5f:74:a0:a0  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 48  base 0x6000  

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 16436
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 103  bytes 5852 (5.7 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 103  bytes 5852 (5.7 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

tap0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 192.168.7.1  netmask 255.255.255.255  broadcast 192.168.7.255
        inet6 fe80::707d:5fff:fe24:2343  prefixlen 64  scopeid 0x20<link>
        ether 72:7d:5f:24:23:43  txqueuelen 500  (Ethernet)
        RX packets 50  bytes 16387 (16.0 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 21  bytes 3461 (3.3 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

which produces the error below:

Continuing with the following parameters:
KERNEL: [/home/trz/yocto/systemtap-ext/build/tmp/deploy/images/bzImage-qemux86.bin]
ROOTFS: [/home/trz/yocto/systemtap-ext/build/tmp/deploy/images/core-image-sato-qemux86.ext3]
FSTYPE: [ext3]
Acquiring lockfile for tap0:...
Using preconfigured tap device 'tap0:'
/home/trz/yocto/systemtap-ext/scripts/runqemu-internal: line 219: 0: * 2 + 1: syntax error in expression (error token is ": * 2 + 1")
WARNING: distccd not present, no distcc support loaded.
Running qemu...
/home/trz/yocto/systemtap-ext/build/tmp/sysroots/x86_64-linux/usr/bin/qemu -kernel /home/trz/yocto/systemtap-ext/build/tmp/deploy/images/bzImage-qemux86.bin -net nic,vlan=0 -net tap,vlan=0,ifname=tap0:,script=no,downscript=no -hda /home/trz/yocto/systemtap-ext/build/tmp/deploy/images/core-image-sato-qemux86.ext3 -show-cursor -usb -usbdevice wacom-tablet -vga vmware -no-reboot -m 128 --append "vga=0 root=/dev/hda rw mem=128M ip=192.168.7.1::192.168.7.:255.255.255.0 oprofile.timer=1 "
qemu: -net tap,vlan=0,ifname=tap0:,script=no,downscript=no: could not configure /dev/net/tun (tap0:): Operation not permitted
qemu: -net tap,vlan=0,ifname=tap0:,script=no,downscript=no: Device 'tap' could not be initialized
Set 'tap0:' nonpersistent
Releasing lockfile of preconfigured tap device 'tap0:'
[trz@empanada build]$ emacs -nw