[PATCH bpf-next v3 1/6] resolve_btfids: Deduplicate BTF after btf2btf transformations

[Ihor Solodrai <ihor.solodrai@linux.dev>]

btf2btf() adds new types to the BTF: the KF_IMPLICIT_ARGS transform
synthesizes an _impl FUNC together with its FUNC_PROTO and copies of the
kfunc's decl tags. Nothing deduplicates them afterwards. pahole runs
btf__dedup() on its own output, but that happens before resolve_btfids
sees the BTF, so any type the tool itself creates is emitted as-is, even
when a structurally identical type is already present.

Call btf__dedup() at the start of finalize_btf(), so that base
distillation and the by-name sort both operate on the canonical set of
types.

On an x86_64 build with the BPF selftests config this removes 17
duplicate FUNC_PROTOs from vmlinux BTF.

The dedup call increases runtime of resolve_btfids on vmlinux by 30-40%.
The performance hit is an acceptable cost to keep kernel BTF deduped [1].

[1] https://lore.kernel.org/bpf/986e6f4e-4b51-4440-a37c-9624906d7370@linux.dev/

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
 tools/bpf/resolve_btfids/main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/bpf/resolve_btfids/main.c b/tools/bpf/resolve_btfids/main.c
index 85488935909d..5d168c2a5ff5 100644
--- a/tools/bpf/resolve_btfids/main.c
+++ b/tools/bpf/resolve_btfids/main.c
@@ -1379,6 +1379,12 @@ static int finalize_btf(struct object *obj)
 	struct btf *base_btf = obj->base_btf, *btf = obj->btf;
 	int err;
 
+	err = btf__dedup(obj->btf, NULL);
+	if (err) {
+		pr_err("FAILED to dedup BTF: %s\n", strerror(errno));
+		goto out_err;
+	}
+
 	if (obj->base_btf && obj->distill_base) {
 		err = btf__distill_base(obj->btf, &base_btf, &btf);
 		if (err) {
-- 
2.55.0