add support for split BTF to gen min_core_btf

Signed-off-by: Bryce Kahle <bryce.kahle@datadoghq.com>

src/gen.c

@@ -1695,14 +1695,14 @@ btfgen_new_info(const char *targ_btf_path)
 	if (!info)
 		return NULL;
 
-	info->src_btf = btf__parse(targ_btf_path, NULL);
+	info->src_btf = btf__parse_split(targ_btf_path, base_btf);
 	if (!info->src_btf) {
 		err = -errno;
 		p_err("failed parsing '%s' BTF file: %s", targ_btf_path, strerror(errno));
 		goto err_out;
 	}
 
-	info->marked_btf = btf__parse(targ_btf_path, NULL);
+	info->marked_btf = btf__parse_split(targ_btf_path, base_btf);
 	if (!info->marked_btf) {
 		err = -errno;
 		p_err("failed parsing '%s' BTF file: %s", targ_btf_path, strerror(errno));
@@ -2139,12 +2139,18 @@ static int btfgen_remap_id(__u32 *type_id, void *ctx)
 /* Generate BTF from relocation information previously recorded */
 static struct btf *btfgen_get_btf(struct btfgen_info *info)
 {
+	const struct btf *base;
 	struct btf *btf_new = NULL;
 	unsigned int *ids = NULL;
 	unsigned int i, n = btf__type_cnt(info->marked_btf);
 	int err = 0;
+	int start_id = 1;
 
-	btf_new = btf__new_empty();
+	base = btf__base_btf(info->src_btf);
+	if (base)
+		start_id = btf__type_cnt(base);
+
+	btf_new = btf__new_empty_split((struct btf *)base);
 	if (!btf_new) {
 		err = -errno;
 		goto err_out;
@@ -2157,7 +2163,7 @@ static struct btf *btfgen_get_btf(struct btfgen_info *info)
 	}
 
 	/* first pass: add all marked types to btf_new and add their new ids to the ids map */
-	for (i = 1; i < n; i++) {
+	for (i = start_id; i < n; i++) {
 		const struct btf_type *cloned_type, *type;
 		const char *name;
 		int new_id;
@@ -2213,7 +2219,7 @@ static struct btf *btfgen_get_btf(struct btfgen_info *info)
 	}
 
 	/* second pass: fix up type ids */
-	for (i = 1; i < btf__type_cnt(btf_new); i++) {
+	for (i = start_id; i < btf__type_cnt(btf_new); i++) {
 		struct btf_type *btf_type = (struct btf_type *) btf__type_by_id(btf_new, i);
 
 		err = btf_type_visit_type_ids(btf_type, btfgen_remap_id, ids);