libbpf-rs is unable to load eBPF programs on older kernel versions

[olcarver]

Kernel version: 5.4.0-1125-aws
Distro: Ubuntu 18.04.6 LTS

After bumping our libbpf-rs version from 0.21.2->0.24.8, we ran into the following error when trying to run our program on a system running kernel 5.4

BPF map `bss` mmap pointer is NULL

The error is being thrown during the new function of the auto generated OpenXXXXMaps code in *.skel.rs. This error does not occur when we run our program but with libbpf-rs version 0.21.2.

How to reproduce:

Attempting to run the sample capable on a new EC2 instance with the same kernel/distro version yields the same error but for rodata.

$ sudo ./capable

thread 'main' panicked at /home/ssm-user/libbpf-rs/examples/capable/src/bpf/capable.skel.rs:165:26:
BPF map `rodata` mmap pointer is NULL
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[anakryiko]

On old kernel that do not support memory-mapped global variable maps, libbpf will just avoid doing mmap. So libbpf-rs doesn't seem to handle this condition. Not sure what would make the most sense, I'd rather wait for Daniel (libbpf-rs maintainer) to come back to decide on best ways to handle this.

[weitsochen]

Do we have any updates on this issue?

[d-e-s-o]

I suspect given this behavior we may have to make each <xxx>_data field an Option, as there is no way to correctly predict in advance what will happen at runtime.