Created attachment 1476812 [details]
Testing source code file

Description of problem:

clang -target bpf generates unknown opcode 8d.
It doesn't generate this opcode when run with -O2.

Version-Release number of selected component (if applicable):

clang-6.0.1-1.fc28.x86_64
kernel-4.16.12-300.fc28.x86_64

How reproducible: 100%

Steps to reproduce:

Compile attached C source code file using:
$ clang -target bpf -c -o kprobes_kern.o kprobes_kern.c

Then use bpf_load.c from Linux source code tree to load it. BPF in-kernel verifier declines to load this file with following error:

# ./kprobes 
bpf_load_program() err=Invalid argument
unknown opcode 8d
unknown opcode 8d

This problem goes away when the same code is compiled with -O2.