Thanks Yonghong, I'd like to know more about the BPF compiler backend, let me know if there is anything I can help to do or test. William
On Tue, Apr 18, 2017 at 10:09 PM, Y Song <[email protected]> wrote: > Hi, William, > > Your analysis is correct. In this case, the error message could be improved. > In general, a message like this "back-edge from insn 240 to 219" indicates a > loop (back-edge ...). > > Compiler probably should give a warning if it is BPF backend to indicate > there > are loops in the byte code. I will look into this. > > Yonghong > > > On Tue, Apr 18, 2017 at 9:00 PM, William Tu via iovisor-dev > <[email protected]> wrote: >> >> Hi Mauricio, >> >> Thanks! Yes, I think like you said the compiler couldn't unroll in >> this case. Because we are passing memory address of i (&i) to a >> function, the function might change the value of 'i', which might >> change the number of loops. So compiler should disable unrolling. >> >> Regards, >> William >> >> On Tue, Apr 18, 2017 at 6:22 PM, Mauricio Vasquez >> <[email protected]> wrote: >> > Hi William, >> > >> > On 04/18/2017 06:54 PM, William Tu via iovisor-dev wrote: >> >> >> >> Hi, >> >> >> >> I found that if the loop variable "int i" is used in the map lookup as >> >> below: >> >> #pragma clang loop unroll(full) >> >> for (i = 0; i < 8; ++i) { >> >> struct bpf_flow_keys *mask; >> >> mask = bpf_map_lookup_elem(&flow_mask, &i); >> >> if (!mask) >> >> break; >> >> } >> >> Then the compiled BPF code does not unrolled the loop, causing errors: >> >> "back-edge from insn 240 to 219" >> >> >> >> A workaround for that is to declare another variable "int j", then I >> >> can pass the verifier. >> >> >> >> #pragma clang loop unroll(full) >> >> for (i = 0; i < 8; ++i) { >> >> int j = i; >> >> struct bpf_flow_keys *mask; >> >> mask = bpf_map_lookup_elem(&flow_mask, &j); // ---> use "j" >> >> if (!mask) >> >> break; >> >> } >> >> >> >> Does anyone hit similar issue? >> > >> > >> > Yes, we hit exactly the same problem [1], at that time we thought it was >> > because of the missing "const" qualifier in the bpf_map_* helpers [2], >> > however we added it and the result was the same. >> > >> > Until now we don't know what is the cause of the problem, we continue to >> > use >> > that workaround. >> > >> > Mauricio V, >> > >> > [1] >> > >> > https://lists.iovisor.org/pipermail/iovisor-dev/2016-December/000560.html >> > [2] >> > >> > https://lists.iovisor.org/pipermail/iovisor-dev/2016-December/000559.html >> >> >> >> Regards, >> >> William >> >> _______________________________________________ >> >> iovisor-dev mailing list >> >> [email protected] >> >> https://lists.iovisor.org/mailman/listinfo/iovisor-dev >> >> >> > >> _______________________________________________ >> iovisor-dev mailing list >> [email protected] >> https://lists.iovisor.org/mailman/listinfo/iovisor-dev > > _______________________________________________ iovisor-dev mailing list [email protected] https://lists.iovisor.org/mailman/listinfo/iovisor-dev
