Handle EPERM everywhere

[addisoncrump]

Sometimes, aya programs are executed without xtask -- and require sudo to execute properly, otherwise there are insufficient permissions. Aya does not currently have good error output in this case, e.g.:

Error: error relocating function

Caused by:
    0: error relocating `...`
    1: section `6` not found, referenced by symbol `` #11

For each of the BPF calls, the error should be checked if EPERM and handled explicitly.

[alessandrod]

For context

[2023-11-29T09:31:41Z DEBUG aya::bpf] BPF Feature Detection: Features {
        bpf_name: false,
        bpf_probe_read_kernel: false,
        bpf_perf_link: false,
        bpf_global_data: false,
        bpf_cookie: false,
        cpumap_prog_id: false,
        devmap_prog_id: false,
        btf: None,
    }
[2023-11-29T09:31:41Z DEBUG aya_obj::relocation] failed relocating map by section index 6

The relocation errors happens because the target map - in this case .rodata - is skipped during load as bpf_global_data is set to false. bpf_global_data is set to false like all the other features because all the probes failed with EPERM.

[dave-tucker]

Can we be 100% sure that we won't get EPERM from syscalls under any other circumstance than failing the capabilities check?

[alessandrod]

Can we be 100% sure that we won't get EPERM from syscalls under any other circumstance than failing the capabilities check?

Oh no we definitely will. The point is that we need to handle those cases and output meaningful error messages. From the error you get right now if you run without sudo it gives the impression that there is some kind of relocation bug 😅