netdev - ARM: BPF: xdpdump unknown opcode 21

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Date:   Fri, 11 Mar 2022 09:12:05 +0000
From:   Michael Graichen <michael.graichen@...mail.com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: ARM: BPF: xdpdump unknown opcode 21

Hey all,

I try to teach myself how BPF, XDP and JIT are working.
So, while doing this I started 'xdpdump' to attach to a running program on a 32-bit ARM (i.MX7)

xdpdump wants to load /lib/bpf/xdpdump_bpf.o but ends up with the error:

libbpf: prog 'trace_on_entry': failed to attach: ERROR: strerror_r(-524)=22
ERROR: Can't attach XDP trace fentry function: Unknown error 524

and dmesg tells me

"unknown opcode 21"

I have checked the Kernel source code under arch/arm/net/bpf_jit_32.c
and figured out that opcode 0x21 should be BPF_LDX | BPF_W | BPF_ABS but it is not implemented.
Well, it was in Kernel 4.1 until 4.13.

Can someone help me / guide me to reimplement this opcode?

Best regards
Michael