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 <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260326145444.2076244-9-alan.maguire@oracle.com

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 (file)
index 0000000..f61afe6
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/btf_kind.c
@@ -0,0 +1,226 @@
+// 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(void *raw_btf, size_t raw_size, char *file)
+{
+       int fd = mkstemp(file);
+       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)
+{
+       char btf_kind_file1[] = "/tmp/test_btf_kind.XXXXXX";
+       char btf_kind_file2[] = "/tmp/test_btf_kind.XXXXXX";
+       char btf_kind_file3[] = "/tmp/test_btf_kind.XXXXXX";
+       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;
+       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. */
+       if (write_raw_btf(new_raw_btf, raw_size, btf_kind_file1))
+               goto out;
+
+       /*
+        * Verify parsing succeeds, and that we can read type info past
+        * the unrecognized kind.
+        */
+       new_btf = btf__parse_raw(btf_kind_file1);
+       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(new_raw_btf, raw_size, btf_kind_file2))
+               goto out;
+
+       new_btf = btf__parse_raw(btf_kind_file2);
+       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) and set vlen
+        * associated with unrecognized type to 1; 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);
+       t->info |= 1;
+       if (write_raw_btf(new_raw_btf, raw_size, btf_kind_file3))
+               goto out;
+
+       new_btf = btf__parse_raw(btf_kind_file3);
+       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_kind_file1);
+       unlink(btf_kind_file2);
+       unlink(btf_kind_file3);
+       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();
+}