Messages in this thread | | | From | Eric Dumazet <> | Date | Wed, 24 Nov 2021 18:56:31 -0800 | Subject | Re: [tip:x86/core 1/1] arch/x86/um/../lib/csum-partial_64.c:98:12: error: implicit declaration of function 'load_unaligned_zeropad' |
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On Wed, Nov 24, 2021 at 5:59 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: >
> > Hi, I'm not sure if this is intentional or not, but I noticed that the output > of 'csum_partial' is different after this patch. I figured that the checksum > algorithm is fixed so just wanted mention it incase its a bug. If not sorry > for the spam. > > Example on x86_64: > > Buff: [ 87, b3, 92, b7, 8b, 53, 96, db, cd, 0f, 7e, 7e ] > len : 11 > sum : 0 > > csum_partial new : 2480936615 > csum_partial HEAD: 2472089390
No worries.
skb->csum is 32bit, but really what matters is the 16bit folded value.
So make sure to apply csum_fold() before comparing the results.
A minimal C and generic version of csum_fold() would be something like
static unsigned short csum_fold(u32 csum) { u32 sum = csum; sum = (sum & 0xffff) + (sum >> 16); sum = (sum & 0xffff) + (sum >> 16); return ~sum; }
I bet that csum_fold(2480936615) == csum_fold(2472089390)
It would be nice if we had a csum test suite, hint, hint ;)
Thanks !
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