[PATCH v6 bpf-next 07/10] selftests/bpf: test kind encoding/decoding

Alan Maguire
2025-12-10T20:33:32Z

verify btf__new_empty_opts() adds kind 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 <alan.maguire@oracle.com>
---
.../selftests/bpf/prog_tests/btf_kind.c | 176 ++++++++++++++++++
1 file changed, 176 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..735ea0b588a5
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_kind.c
@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2025, 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_kind_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->kind_layout_off % 4, 0, "kind_layout aligned");
+ ASSERT_EQ(hdr->kind_layout_len, sizeof(struct btf_kind_layout) * NR_BTF_KINDS,
+ "kind_layout_len");
+ btf__free(btf);
+}
+
+static void write_raw_btf(const char *btf_path, void *raw_btf, size_t raw_size)
+{
+ int fd = open(btf_path, O_WRONLY | O_CREAT);
+
+ write(fd, raw_btf, raw_size);
+ close(fd);
+}
+
+/* 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)
+{
+ __s32 int_id, unrec_id, id, id2;
+ LIBBPF_OPTS(btf_new_opts, opts);
+ struct btf *btf, *new_btf;
+ struct btf_kind_layout *k;
+ struct btf_header *hdr;
+ const void *raw_btf;
+ struct btf_type *t;
+ char btf_path[64];
+ void *new_raw_btf;
+ __u32 raw_size;
+
+ opts.add_kind_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;
+
+ /* now 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(*k));
+ memcpy(new_raw_btf, raw_btf, raw_size);
+
+ /* add new layout description */
+ hdr = new_raw_btf;
+ hdr->kind_layout_len += sizeof(*k);
+ k = new_raw_btf + hdr->hdr_len + hdr->kind_layout_off;
+ k[NR_BTF_KINDS].info_sz = 0;
+ k[NR_BTF_KINDS].elem_sz = 0;
+
+ /* now modify our 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);
+
+ /* now write our BTF to a raw file, ready for parsing. */
+ snprintf(btf_path, sizeof(btf_path), "/tmp/btf_kind.%d", getpid());
+
+ write_raw_btf(btf_path, new_raw_btf, raw_size + sizeof(*k));
+
+ /* 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_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);
+
+ /* 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.
+ */
+ k[NR_BTF_KINDS].info_sz = sizeof(struct btf_type);
+ write_raw_btf(btf_path, new_raw_btf, raw_size + sizeof(*k));
+
+ 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);
+
+ /* next, 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.
+ */
+ k[NR_BTF_KINDS].info_sz = 0;
+ k[NR_BTF_KINDS].elem_sz = sizeof(struct btf_type)/2;
+ t->info |= 2;
+ write_raw_btf(btf_path, new_raw_btf, raw_size + sizeof(*k));
+
+ 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);
+ 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();
+}
--
2.43.5