[RFC dwarves 2/2] btf_encoder: learn BTF_KIND_MAX value from base BTF when generating split BTF

[Alan Maguire <alan.maguire@oracle.com>]

When creating module BTF, the module likely will not have a DWARF
specificiation of BTF_KIND_MAX, so look for it in the base BTF.  For
vmlinux base BTF, the enumeration value is present, so the base BTF
can be checked to limit BTF kind representation.

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
---
 btf_encoder.c | 24 ++++++++++++++++++++++++
 btf_encoder.h |  2 ++
 pahole.c      |  2 ++
 3 files changed, 28 insertions(+)

diff --git a/btf_encoder.c b/btf_encoder.c
index 98c7529..269ed48 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -1901,3 +1901,27 @@ void dwarves__set_btf_kind_max(struct conf_load *conf_load, int btf_kind_max)
 	if (btf_kind_max < BTF_KIND_ENUM64)
 		conf_load->skip_encoding_btf_enum64 = true;
 }
+
+void btf__set_btf_kind_max(struct conf_load *conf_load, struct btf *btf)
+{
+	__u32 id, type_cnt = btf__type_cnt(btf);
+
+	for (id = 1; id < type_cnt; id++) {
+		const struct btf_type *t = btf__type_by_id(btf, id);
+		const struct btf_enum *e;
+		__u16 vlen, i;
+
+		if (!t || !btf_is_enum(t))
+			continue;
+		vlen = btf_vlen(t);
+		e = btf_enum(t);
+		for (i = 0; i < vlen; e++, i++) {
+			const char *name = btf__name_by_offset(btf, e->name_off);
+
+			if (!name || strcmp(name, "BTF_KIND_MAX"))
+				continue;
+			dwarves__set_btf_kind_max(conf_load, e->val);
+			return;
+		}
+	}
+}
diff --git a/btf_encoder.h b/btf_encoder.h
index 34516bb..e5e12ef 100644
--- a/btf_encoder.h
+++ b/btf_encoder.h
@@ -27,4 +27,6 @@ struct btf *btf_encoder__btf(struct btf_encoder *encoder);
 
 int btf_encoder__add_encoder(struct btf_encoder *encoder, struct btf_encoder *other);
 
+void btf__set_btf_kind_max(struct conf_load *conf_load, struct btf *btf);
+
 #endif /* _BTF_ENCODER_H_ */
diff --git a/pahole.c b/pahole.c
index 6fc4ed6..542921a 100644
--- a/pahole.c
+++ b/pahole.c
@@ -3462,6 +3462,7 @@ int main(int argc, char *argv[])
 				base_btf_file, libbpf_get_error(conf_load.base_btf));
 			goto out;
 		}
+		btf__set_btf_kind_max(&conf_load, conf_load.base_btf);
 		if (!btf_encode && !ctf_encode) {
 			// Force "btf" since a btf_base is being informed
 			conf_load.format_path = "btf";
@@ -3505,6 +3506,7 @@ try_sole_arg_as_class_names:
 					base_btf_file, libbpf_get_error(conf_load.base_btf));
 				goto out;
 			}
+			btf__set_btf_kind_max(&conf_load, conf_load.base_btf);
 		}
 	}
 
-- 
2.39.3