libbpf
libbpf-cargo: Build fails when a C struct contains an empty union
I am using libbpf-cargo version 0.24.6. I'm trying to use struct bio like this in my .bpf.c:
SEC("fentry/submit_bio")
int BPF_PROG(submit_bio, struct bio *bio)
{
...
vcnt = bio->bi_vcnt;
...
}
However cargo build fails with:
thread 'main' panicked at /home/jrc/.cargo/registry/src/index.crates.io-6f17d22bba15001f/libbpf-cargo-0.24.6/src/gen/btf.rs:769:49:
index out of bounds: the len is 0 but the index is 0
The error refers to this line, which is part of the code to "write a Default implementation for a union".
At vmlinux_601.h#L7735, we find this:
struct bio {
...
union {};
...
};
It looks like empty unions cause problems for libbpf-cargo. Arguably this is an issue of vmlinux.h, and I am aware that the vmlinux.h repo is advertised as "Development-only". This issue could be fixed by removing the empty union in vmlinux.h. However, it seems more convenient to me to add support for empty unions to libbpf-cargo. Is that reasonable?
Thanks for the report.
However, it seems more convenient to me to add support for empty unions to libbpf-cargo. Is that reasonable?
Yes, that seems reasonable to me. Will you take a look at fixing this problem?
