aya-obj: fix variable length array index check

[fatemender]

The variable length array access check in aya_obj::btf::relocation::AccessSpec::new is wrong: index is the array index, not the field index. A similar but correct check can be found in match_candidate.

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[vadorovsky]

Good catch! Do you by any chance have a program that triggered the issue? If yes, it would be great to add it as an integration test.

[fatemender]

It's actually as simple as this:

SEC("raw_tracepoint/sys_enter")
int
var_len_array_access(const struct bpf_raw_tracepoint_args *ctx) {
    unsigned long nr = BPF_CORE_READ(ctx, args[1]);
    return 0;
}

[vadorovsky]

Mind adding that as an integration test? Would be great to write the test program in Rust.

[tamird]

Needs integration test.