On Tue, Apr 29, 2025 at 9:10 AM Alan Maguire <alan.maguire@xxxxxxxxxx> wrote:
>
> Recently as a side-effect of
>
> commit ac053946f5c4 ("compiler.h: introduce TYPEOF_UNQUAL() macro")
>
> issues were observed in deduplication between modules and kernel BTF
> such that a large number of kernel types were not deduplicated so
> were found in module BTF (task_struct, bpf_prog etc). The root cause
> appeared to be a failure to dedup struct types, specifically those
> with members that were pointers with __percpu annotations.
>
> The issue in dedup is at the point that we are deduplicating structures,
> we have not yet deduplicated reference types like pointers. If multiple
> copies of a pointer point at the same (deduplicated) integer as in this
> case, we do not see them as identical. Special handling already exists
> to deal with structures and arrays, so add pointer handling here too.
>
> Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> tools/lib/bpf/btf.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
>
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 24fc71ce5631..eea7fc10d19c 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -4396,6 +4396,19 @@ static bool btf_dedup_identical_structs(struct btf_dedup *d, __u32 id1, __u32 id
> return true;
> }
>
> +static bool btf_dedup_identical_ptrs(struct btf_dedup *d, __u32 id1,
> +__u32 id2)
fixed up this unintended line wrap, applied to bpf-next, and I've
already synced all the pending libbpf changes to Github ([0]). Alan,
feel free to pull all that into pahole master, so it propagates to BPF
CI (and we can start testing GCC 14)
[0] https://github.com/libbpf/libbpf/pull/899
> +{
> + struct btf_type *t1, *t2;
> +
> + t1 = btf_type_by_id(d->btf, id1);
> + t2 = btf_type_by_id(d->btf, id2);
> +
> + if (!btf_is_ptr(t1) || !btf_is_ptr(t2))
> + return false;
> + return t1->type == t2->type;
> +}
> +
> /*
> * Check equivalence of BTF type graph formed by candidate struct/union (we'll
> * call it "candidate graph" in this description for brevity) to a type graph
> @@ -4528,6 +4541,9 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id,
> */
> if (btf_dedup_identical_structs(d, hypot_type_id, cand_id))
> return 1;
> + /* A similar case is again observed for PTRs. */
> + if (btf_dedup_identical_ptrs(d, hypot_type_id, cand_id))
> + return 1;
> return 0;
> }
>
> --
> 2.43.5
>
