Why xor() does not work on openwrt

We are porting openwrt to our device which is a mips platform. But we found the service "dnsmasq" can't be started correctly on our device.

Then we found the root cause, "/etc/init.d/dnsmasq" used the script "/bin/ipcalc.sh" generating the wrong configuration for "dnsmasq" and "dnsmasq" failed to parse the configuration.

Here is the link to the original code of "/bin/ipcalc.sh" in github https://github.com/respeaker/openwrt/blob/master/package/base-files/files/bin/ipcalc.sh

Then we replace all the invoke of compl32() with compl(), then it works. As we investigate the script, and find compl32() is a very simple function, which just invoke xor(). But looks like xor() can't produce what we were expecting.

Here is the code of /bin/ipcalc.sh that we are using, and I add some debug in it:

#!/bin/sh

awk -f - $* <<EOF
function bitcount(c) {
    c=and(rshift(c, 1),0x55555555)+and(c,0x55555555)
    c=and(rshift(c, 2),0x33333333)+and(c,0x33333333)
    c=and(rshift(c, 4),0x0f0f0f0f)+and(c,0x0f0f0f0f)
    c=and(rshift(c, 8),0x00ff00ff)+and(c,0x00ff00ff)
    c=and(rshift(c,16),0x0000ffff)+and(c,0x0000ffff)
    return c
}

function ip2int(ip) {
    for (ret=0,n=split(ip,a,"\."),x=1;x<=n;x++)    ret=or(lshift(ret,8),a[x])
    return ret
}

function int2ip(ip,ret,x) {
    ret=and(ip,255)
    ip=rshift(ip,8)
    for(;x<3;ret=and(ip,255)"."ret,ip=rshift(ip,8),x++);
    return ret
}

function compl32(v) {
    ret=xor(v, 0xffffffff)
    return ret
}

BEGIN {
    print "var1="compl32(255)
    print "var2="compl(0xff)
    print "var3="xor(0xff,0xffffffff)
    print "var4="xor(255,0xffffffff)
    slpos=index(ARGV[1],"/")
    if (slpos == 0) {
            ipaddr=ip2int(ARGV[1])
            dotpos=index(ARGV[2],".")
            if (dotpos == 0)
                    netmask=compl(2**(32-int(ARGV[2]))-1)
            else
                    netmask=ip2int(ARGV[2])
    } else {
            ipaddr=ip2int(substr(ARGV[1],0,slpos-1))
            netmask=compl(2**(32-int(substr(ARGV[1],slpos+1)))-1)
            ARGV[4]=ARGV[3]
            ARGV[3]=ARGV[2]
    }

    network=and(ipaddr,netmask)
    broadcast=or(network,compl(netmask))

    start=or(network,and(ip2int(ARGV[3]),compl(netmask)))
    limit=network+1
    if (start<limit) start=limit

    end=start+ARGV[4]
    limit=or(network,compl(netmask))-1
    if (end>limit) end=limit

    print "IP="int2ip(ipaddr)
    print "NETMASK="int2ip(netmask)
    print "BROADCAST="int2ip(broadcast)
    print "NETWORK="int2ip(network)
    print "PREFIX="32-bitcount(compl(netmask))

    # range calculations:
    # ipcalc <ip> <netmask> <start> <num>

    if (ARGC > 3) {
            print "START="int2ip(start)
            print "END="int2ip(end)
    }
}
EOF

Here is the running result:

root@OpenWrt:/tmp# ipcalc.sh 192.168.1.1/24 100 50
var1=255
var2=4294967295
var3=0
var4=255
IP=192.168.1.1
NETMASK=255.255.255.0
BROADCAST=192.168.1.255
NETWORK=192.168.1.0
PREFIX=32
START=192.168.1.100
END=192.168.1.150
root@OpenWrt:/tmp#

This is very strange. Why xor() does not work?

Your expression in BEGIN for var3 produces var3=4294967040 on my system (GNU Awk 4.1.4). Looks like you are using an broken Awk- please try a different version.