netdev - eBPF: verifier: back-edge

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Message-ID: <CAKPgXcFZ=jrVFTWEr99hxzcqE3A6hBWbyiQCKHz-jndPSJo52Q@mail.gmail.com>
Date:   Sun, 2 Sep 2018 16:52:54 +0300
From:   Sameeh Jubran <sameeh@...nix.com>
To:     netdev@...r.kernel.org
Subject: eBPF: verifier: back-edge

Hi all,

I am trying to insert instructions into the bpf using the bof syscall,
the instructions were generated using the following command line:

clang -I ~/Builds/bpf_rss/iproute2/include -Wall -target bpf -O2
-emit-llvm -c upstream/qemu/hw/net/rss_tap_bpf_program.c -o - | llc
-march=bpf -filetype=obj -o tap_bpf_program.o

and then were translated to bpf instructions using the BPFCparser tool

Every time I try to insert the array of instructions the verfier fails
with the following error:

back-edge from insn 363 to 364

I am not sure how to debug this error since the instructions are in
binary and the precompiled source code doesn't seem to contain any
weird loops or jump to instructions...

Is there a way to identify which line of source code is causing these errors?

Thanks!