[PATCH v14 bpf-next 08/10] selftests/bpf: test kind encoding/decoding

verify btf__new_empty_opts() adds layouts for all kinds supported,
and after adding kind-related types for an unknown kind, ensure that
parsing uses this info when that kind is encountered rather than
giving up.

Signed-off-by: Alan Maguire <[email protected]>
---
 .../selftests/bpf/prog_tests/btf_kind.c       | 224 ++++++++++++++++++
 1 file changed, 224 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/btf_kind.c

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_kind.c b/tools/testing/selftests/bpf/prog_tests/btf_kind.c
new file mode 100644
index 000000000000..c9f5fd4a0783
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_kind.c
@@ -0,0 +1,224 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026, Oracle and/or its affiliates. */
+
+#include <test_progs.h>
+#include <bpf/btf.h>
+#include <bpf/libbpf.h>
+
+/* Verify kind encoding exists for each kind */
+static void test_btf_kind_encoding(void)
+{
+	LIBBPF_OPTS(btf_new_opts, opts);
+	const struct btf_header *hdr;
+	const void *raw_btf;
+	struct btf *btf;
+	__u32 raw_size;
+
+	opts.add_layout = true;
+	btf = btf__new_empty_opts(&opts);
+	if (!ASSERT_OK_PTR(btf, "btf_new"))
+		return;
+
+	raw_btf = btf__raw_data(btf, &raw_size);
+	if (!ASSERT_OK_PTR(raw_btf, "btf__raw_data"))
+		return;
+
+	hdr = raw_btf;
+
+	ASSERT_EQ(hdr->layout_off % 4, 0, "layout_aligned");
+	ASSERT_EQ(hdr->layout_len, sizeof(struct btf_layout) * NR_BTF_KINDS,
+		  "layout_len");
+	ASSERT_EQ(hdr->str_off, hdr->layout_off + hdr->layout_len, "str_after_layout");
+	btf__free(btf);
+
+	opts.add_layout = false;
+	btf = btf__new_empty_opts(&opts);
+	if (!ASSERT_OK_PTR(btf, "btf_new"))
+		return;
+
+	raw_btf = btf__raw_data(btf, &raw_size);
+	if (!ASSERT_OK_PTR(raw_btf, "btf__raw_data"))
+		return;
+
+	hdr = raw_btf;
+
+	ASSERT_EQ(hdr->layout_off, 0, "no_layout_off");
+	ASSERT_EQ(hdr->layout_len, 0, "no_layout_len");
+	ASSERT_EQ(hdr->str_off, hdr->type_off + hdr->type_len, "strs_after_types");
+	btf__free(btf);
+}
+
+static int write_raw_btf(const char *btf_path, void *raw_btf, size_t raw_size)
+{
+	int fd = open(btf_path, O_WRONLY | O_CREAT | O_TRUNC | O_CLOEXEC, 0644);
+	ssize_t n;
+
+	if (!ASSERT_OK_FD(fd, "open_raw_btf"))
+		return -1;
+	n = write(fd, raw_btf, raw_size);
+	close(fd);
+	if (!ASSERT_EQ(n, (ssize_t)raw_size, "write_raw_btf"))
+		return -1;
+	return 0;
+}
+
+/*
+ * Fabricate an unrecognized kind at BTF_KIND_MAX + 1, and after adding
+ * the appropriate struct/typedefs to the BTF such that it recognizes
+ * this kind, ensure that parsing of BTF containing the unrecognized kind
+ * can succeed.
+ */
+void test_btf_kind_decoding(void)
+{
+	struct btf *btf = NULL, *new_btf = NULL;
+	__s32 int_id, unrec_id, id, id2;
+	LIBBPF_OPTS(btf_new_opts, opts);
+	struct btf_layout *l;
+	struct btf_header *hdr;
+	const void *raw_btf;
+	struct btf_type *t;
+	char btf_path[64];
+	void *new_raw_btf;
+	void *str_data;
+	__u32 raw_size;
+
+	opts.add_layout = true;
+	btf = btf__new_empty_opts(&opts);
+	if (!ASSERT_OK_PTR(btf, "btf_new"))
+		return;
+
+	int_id = btf__add_int(btf, "test_char", 1, BTF_INT_CHAR);
+	if (!ASSERT_GT(int_id, 0, "add_int_id"))
+		return;
+
+	/*
+	 * Create our type with unrecognized kind by adding a typedef kind
+	 * we will overwrite it with our unrecognized kind value.
+	 */
+	unrec_id = btf__add_typedef(btf, "unrec_kind", int_id);
+	if (!ASSERT_GT(unrec_id, 0, "add_unrec_id"))
+		return;
+
+	/*
+	 * Add an id after it that we will look up to verify we can parse
+	 * beyond unrecognized kinds.
+	 */
+	id = btf__add_typedef(btf, "test_lookup", int_id);
+	if (!ASSERT_GT(id, 0, "add_test_lookup_id"))
+		return;
+	id2 = btf__add_typedef(btf, "test_lookup2", int_id);
+	if (!ASSERT_GT(id2, 0, "add_test_lookup_id2"))
+		return;
+
+	raw_btf = (void *)btf__raw_data(btf, &raw_size);
+	if (!ASSERT_OK_PTR(raw_btf, "btf__raw_data"))
+		return;
+
+	new_raw_btf = calloc(1, raw_size + sizeof(*l));
+	if (!ASSERT_OK_PTR(new_raw_btf, "calloc_raw_btf"))
+		return;
+	memcpy(new_raw_btf, raw_btf, raw_size);
+
+	hdr = new_raw_btf;
+
+	/* Move strings to make space for one new layout description */
+	raw_size += sizeof(*l);
+	str_data = new_raw_btf + hdr->hdr_len + hdr->str_off;
+	memmove(str_data + sizeof(*l), str_data, hdr->str_len);
+	hdr->str_off += sizeof(*l);
+
+	/* Add new layout description */
+	hdr->layout_len += sizeof(*l);
+	l = new_raw_btf + hdr->hdr_len + hdr->layout_off;
+	l[NR_BTF_KINDS].info_sz = 0;
+	l[NR_BTF_KINDS].elem_sz = 0;
+	l[NR_BTF_KINDS].flags = 0;
+
+	/* Now modify typedef added above to be an unrecognized kind. */
+	t = (void *)hdr + hdr->hdr_len + hdr->type_off + sizeof(struct btf_type) +
+		sizeof(__u32);
+	t->info = (NR_BTF_KINDS << 24);
+
+	/* Write BTF to a raw file, ready for parsing. */
+	snprintf(btf_path, sizeof(btf_path), "/tmp/btf_kind.%d", getpid());
+
+	if (write_raw_btf(btf_path, new_raw_btf, raw_size))
+		goto out;
+
+	/*
+	 * Verify parsing succeeds, and that we can read type info past
+	 * the unrecognized kind.
+	 */
+	new_btf = btf__parse_raw(btf_path);
+	if (ASSERT_OK_PTR(new_btf, "btf__parse_raw")) {
+		ASSERT_EQ(btf__find_by_name(new_btf, "unrec_kind"), unrec_id,
+			  "unrec_kind_found");
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup",
+						 BTF_KIND_TYPEDEF), id,
+			  "verify_id_lookup");
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup2",
+						 BTF_KIND_TYPEDEF), id2,
+			  "verify_id2_lookup");
+	}
+	btf__free(new_btf);
+	new_btf = NULL;
+
+	/*
+	 * Next, change info_sz to equal sizeof(struct btf_type); this means the
+	 * "test_lookup" kind will be reinterpreted as a singular info element
+	 * following the unrecognized kind.
+	 */
+	l[NR_BTF_KINDS].info_sz = sizeof(struct btf_type);
+	if (write_raw_btf(btf_path, new_raw_btf, raw_size))
+		goto out;
+
+	new_btf = btf__parse_raw(btf_path);
+	if (ASSERT_OK_PTR(new_btf, "btf__parse_raw")) {
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup",
+						 BTF_KIND_TYPEDEF), -ENOENT,
+			  "verify_id_not_found");
+		/* id of "test_lookup2" will be id2 -1 as we have removed one type */
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup2",
+						 BTF_KIND_TYPEDEF), id2 - 1,
+			  "verify_id_lookup2");
+
+	}
+	btf__free(new_btf);
+	new_btf = NULL;
+
+	/*
+	 * Change elem_sz to equal sizeof(struct btf_type)/2 and set vlen
+	 * associated with unrecognized type to 2; this allows us to verify
+	 * vlen-specified BTF can still be parsed.
+	 */
+	l[NR_BTF_KINDS].info_sz = 0;
+	l[NR_BTF_KINDS].elem_sz = sizeof(struct btf_type)/2;
+	t->info |= 2;
+	if (write_raw_btf(btf_path, new_raw_btf, raw_size))
+		goto out;
+
+	new_btf = btf__parse_raw(btf_path);
+	if (ASSERT_OK_PTR(new_btf, "btf__parse_raw")) {
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup",
+						 BTF_KIND_TYPEDEF), -ENOENT,
+			  "verify_id_not_found");
+		/* id of "test_lookup2" will be id2 -1 as we have removed one type */
+		ASSERT_EQ(btf__find_by_name_kind(new_btf, "test_lookup2",
+						 BTF_KIND_TYPEDEF), id2 - 1,
+			  "verify_id_lookup2");
+
+	}
+out:
+	btf__free(new_btf);
+	free(new_raw_btf);
+	unlink(btf_path);
+	btf__free(btf);
+}
+
+void test_btf_kind(void)
+{
+	if (test__start_subtest("btf_kind_encoding"))
+		test_btf_kind_encoding();
+	if (test__start_subtest("btf_kind_decoding"))
+		test_btf_kind_decoding();
+}
-- 
2.39.3