Re: libbpf: failed to load program 'vxlan_get_tunnel_src'

[Shung-Hsi Yu <shung-hsi.yu@suse.com>]

On Thu, May 19, 2022 at 08:25:00AM -0700, Vincent Li wrote:
> Hi,
> 
> Here is my step to run bpf selftest on Ubuntu 20.04.2 LTS
> 
> git clone https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git
> cd bpf-next; cp /boot/config-5.10.0-051000-generic .config; yes "" |
> make oldconfig; make bzImage; make modules; cd
> tools/testing/selftests/bpf/; make

[snip...]

> ; bpf_printk("vxlan key %d local ip 0x%x remote ip 0x%x gbp 0x%x\n",
> 
> 46: (7b) *(u64 *)(r10 -88) = r2
> 
> 47: (7b) *(u64 *)(r10 -72) = r1
> 
> 48: (61) r1 = *(u32 *)(r10 -48)
> 
> 49: (7b) *(u64 *)(r10 -96) = r1
> 
> 50: (61) r1 = *(u32 *)(r10 -44)
> 
> 51: (7b) *(u64 *)(r10 -80) = r1
> 
> 52: (bf) r3 = r10
> 
> 53: (07) r3 += -96
> 
> 54: (18) r1 = 0xffffabaec02c82af
> 
> 56: (b4) w2 = 52
> 
> 57: (b4) w4 = 32
> 
> 58: (85) call unknown#177
> 
> invalid func unknown#177

This should be the reason that why vxlan_get_tunnel_src fails to load, the
kernel does not recognize the helper function that the program is trying to
call.

And that helper function is bpf_trace_vprintk (determined with v5.17.4
vmlinux).

 $ bpftool btf dump file /sys/kernel/btf/vmlinux format c | grep -e 'BPF_FUNC_.* 177,'
 	BPF_FUNC_trace_vprintk = 177,

Based on your description you're using a v5.10-based kernel, which explains
why it doesn't have bpf_trace_vprintk(), since it was not added until commit
10aceb629e19 ("bpf: Add bpf_trace_vprintk helper") in v5.16.

The call to bpf_trace_vprintk() comes from the bpf_printk() call, which is
actually a macro that uses either bpf_trace_printk() or bpf_trace_vprintk()
depending on the number of arguments given[1].

In general I think it'd make more sense to run bpf-next selftests on a
bpf-next kernel, either compile and install on the machine that you're
testing on or use tools/testing/selftests/bpf/vmtest.sh which spins up a VM
with suitable environment (though I haven't tried vmtest.sh myself).


Shung-Hsi

1: https://github.com/libbpf/libbpf/blob/master/src/bpf_helpers.h

> processed 64 insns (limit 1000000) max_states_per_insn 1 total_states
> 5 peak_states 5 mark_read 2
> 
> -- END PROG LOAD LOG --
> 
> libbpf: failed to load program 'vxlan_get_tunnel_src'
> 
> libbpf: failed to load object 'test_tunnel_kern'
> 
> libbpf: failed to load BPF skeleton 'test_tunnel_kern': -22
> 
> test_ip6vxlan_tunnel:FAIL:test_tunnel_kern__open_and_load unexpected error: -22
> 
> serial_test_tunnel:PASS:pthread_join 0 nsec
> 
> #198/2     tunnel/ip6vxlan_tunnel:FAIL
> 
> #198       tunnel:FAIL
> 
> Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
>