### Change order of complement & filtering

master Nico Schottelius 3 years ago
parent
commit
26c27cefa8
3 changed files with 25 additions and 13 deletions
1. 4
bin/checksum_delta_diff_test.py
2. 10
doc/plan.org
3. 24
p4src/actions_delta_checksum.p4

#### 4 bin/checksum_delta_diff_test.py Unescape Escape View File

 `@ -13,16 +13,20 @@ def checksum_scapy(pkt):` ` if len(pkt) % 2 == 1:` ` pkt += b"\0"` ``` ``` ` # P4: ABOVE not needed (always even)` ``` ``` ` # array: create an array of 16 bit values from the input` ` # and then sum it up -> this might be sligthly/much higher` ` # than 16 bit (additions!)` ` s = sum(array.array("H", pkt))` ` # P4: summing manually into 32bit` ``` ``` ` # add the (right shift 16) and the 16 right bits` ` # basically: assuming 32 bit (?): add the two 16 bit "words"` ` # together` ` # This might still exceed 16 bit!` ` s = (s >> 16) + (s & 0xffff)` ` # P4:` ``` ``` ` # right shift 16 -> zero least significant bits,` ` # and add the upper bits to it`

#### 10 doc/plan.org Unescape Escape View File

 `@ -5245,6 +5245,16 @@ likely this is the cause for the main error:` ``` ``` `**** go through all steps again and try to understand why it (silently) fails later` `*** 2019-07-13: fix overflow error` `*** 2019-07-15: fix off-by-one-sometimes` ` - scapy shift code / return does not work` `**** scapy code results` `Using meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff)` `;` ``` ``` `we get on the wire:` ``` ``` `sum 0x324a (incorrect -> 0x5429),` ``` ``` `** The NetPFGA saga` `Problems encountered:` `- The logfile for a compile run is 10k+ lines`

#### 24 p4src/actions_delta_checksum.p4 Unescape Escape View File

 `@ -13,13 +13,12 @@ action v4sum() {` ` tmp = tmp + (bit<32>) hdr.ipv4.totalLen -20; // 16 bit` ` tmp = tmp + (bit<32>) hdr.ipv4.protocol; // 8 bit` ``` ``` ` carryover = tmp >> 16; /* maximum is 6*(2**16) >> 16 == 6 */` ` tmp = (tmp & 0xffff) + carryover; /* Now tmp contains at maximum 65541 */` ` carryover = tmp >> 16; /* Now carryover contains at maximum 1 */` ` tmp = tmp + carryover; /* No overrun possible anymore */` ``` ``` ` /* filtering code copied from scapy */` ` meta.v4sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;` ` tmp = (tmp >> 16) + (tmp & 0xffff);` ` tmp = tmp + (tmp >> 16);` ` tmp = ~tmp;` ` meta.v4sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff);` ``` ``` `}` ``` ``` `action v6sum() {` `@ -47,15 +46,14 @@ action v6sum() {` ` tmp = tmp + (bit<32>) hdr.ipv6.payload_length; // 16 bit` ` tmp = tmp + (bit<32>) hdr.ipv6.next_header; // 8 bit` ``` ``` ` carryover = tmp >> 16; /* maximum is 18*(2**16) >> 16 == 18 */` ` tmp = (tmp & 0xffff) + carryover; /* Now tmp contains at maximum 65554*/` ` carryover = tmp >> 16; /* Now carryover contains at maximum 1 */` ` tmp = tmp + carryover; /* No overrun possible anymore */` ``` ``` ` /* filtering code copied from scapy */` ` tmp = (tmp >> 16) + (tmp & 0xffff);` ` tmp = tmp + (tmp >> 16);` ` tmp = ~tmp;` ` meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;` `}` ``` ``` ``` ``` `action delta_prepare()` `{` ` v4sum();` `@ -70,13 +68,13 @@ action delta_prepare()` `action delta_udp_from_v4_to_v6()` `{` ` delta_prepare();` ` hdr.udp.checksum = hdr.udp.checksum + ~meta.headerdiff;` ` hdr.udp.checksum = hdr.udp.checksum + meta.headerdiff;` `}` ``` ``` `action delta_tcp_from_v4_to_v6()` `{` ` delta_prepare();` ` hdr.tcp.checksum = hdr.tcp.checksum + ~meta.headerdiff;` ` hdr.tcp.checksum = hdr.tcp.checksum + meta.headerdiff;` `}` ``` ``` `action delta_ipv4_from_v6_to_v4()`