Ping issue in 1.20+

[Giovanni Vallesi - TeeBX]

Il 28/06/2013 1.04, Denys Vlasenko ha scritto:
>> Please add debugging prints to inet_cksum() function - for one,
>> >  let's find out the value of nleft, addr[0], and the return value.
>> >  (IOW, let's find out whether we checksum over the correct buffer,
>> >  and whether we produce the same xsum we see in tcpdump.)
> For example, this way:
>
>
> uint16_t FAST_FUNC inet_cksum(uint16_t *addr, int nleft)
> {
>          /*
>           * Our algorithm is simple, using a 32 bit accumulator,
>           * we add sequential 16 bit words to it, and at the end, fold
>           * back all the carry bits from the top 16 bits into the lower
>           * 16 bits.
>           */
>          unsigned sum = 0;
> char string[nleft*2 + 2];
> int z = nleft;
> bin2hex(string, (void*)addr, nleft)[0] = 0;
>          while (nleft>  1) {
>                  sum += *addr++;
>                  nleft -= 2;
>          }
>
>          /* Mop up an odd byte, if necessary */
>          if (nleft == 1) {
>                  if (BB_LITTLE_ENDIAN)
>                          sum += *(uint8_t*)addr;
>                  else
>                          sum += *(uint8_t*)addr<<  8;
>          }
>
>          /* Add back carry outs from top 16 bits to low 16 bits */
>          sum = (sum>>  16) + (sum&  0xffff);     /* add hi 16 to low 16 */
>          sum += (sum>>  16);                     /* add carry */
>
> bb_error_msg("inet_cksum(%s,%d)=0x%x", string, z, (unsigned)(uint16_t)~sum);
>          return (uint16_t)~sum;
> }
>
> When I run it, I see:
>
> # ./busybox ping -c2 10.0.0.138
> PING 10.0.0.138 (10.0.0.138): 56 data bytes
> ping: inet_cksum(080000001f29000038717f2500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000,64)=0x4021
> 64 bytes from 10.0.0.138: seq=0 ttl=254 time=3.116 ms
> ping: inet_cksum(080000001f29000117b48e2500000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000,64)=0xfc32
> 64 bytes from 10.0.0.138: seq=1 ttl=254 time=2.747 ms

Thanks Denys,
I patched ping.c source according to your suggestion... but I think the 
output is of little use because the (I guess) contains non printable 
chars so the terminals strips them:

~ # ping -c3 172.31.255.1
PING 172.31.255.1 (172.31.255.1): 56 data bytes
ping: inet_cksum(,64)=0xa786
64 bytes from 172.31.255.1: seq=0 ttl=62 time=1.097 ms
ping: inet_cksum(,64)=0xb851
ping: inet_cksum,64)=0x603c

--- 172.31.255.1 ping statistics ---
3 packets transmitted, 1 packets received, 66% packet loss
round-trip min/avg/max = 1.097/1.097/1.097 ms

What else I can do to help in debugging?

I tried also removing the endianess test, forcing le, same issue.
Also I tried changing if (nleft == 1) to if (nleft) like it was before 
1.20. I think its a big change because any integer >0 compare to true in 
the second case. No luck.

@Tito: you asked about the config.
No problem, no secrets, but because I am new here I'd like to know if is 
allowed to attach the file, put it inline or??

Thanks again to everyone.

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