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selftests/bpf: Add btf dedup test covering module BTF dedup

Recently issues were observed with module BTF deduplication failures
[1]. Add a dedup selftest that ensures that core kernel types are
referenced from split BTF as base BTF types. To do this use bpf_testmod
functions which utilize core kernel types, specifically

ssize_t
bpf_testmod_test_write(struct file *file, struct kobject *kobj,
struct bin_attribute *bin_attr,
char *buf, loff_t off, size_t len);

__bpf_kfunc struct sock *bpf_kfunc_call_test3(struct sock *sk);

__bpf_kfunc void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb);

For each of these ensure that the types they reference -
struct file, struct kobject, struct bin_attr etc - are in base BTF.
Note that because bpf_testmod.ko is built with distilled base BTF
the associated reference types - i.e. the PTR that points at a
"struct file" - will be in split BTF. As a result the test resolves
typedef and pointer references and verifies the pointed-at or
typedef'ed type is in base BTF. Because we use BTF from
/sys/kernel/btf/bpf_testmod relocation has occurred for the
referenced types and they will be base - not distilled base - types.

For large-scale dedup issues, we see such types appear in split BTF and
as a result this test fails. Hence it is proposed as a test which will
fail when large-scale dedup issues have occurred.

[1] https://lore.kernel.org/dwarves/CAADnVQL+-LiJGXwxD3jEUrOonO-fX0SZC8496dVzUXvfkB7gYQ@mail.gmail.com/

Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20250430134249.2451066-1-alan.maguire@oracle.com

authored by

Alan Maguire and committed by
Andrii Nakryiko f263336a 86870d0b

+101
+101
tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c
··· 440 440 btf__free(btf1); 441 441 } 442 442 443 + /* Ensure module split BTF dedup worked correctly; when dedup fails badly 444 + * core kernel types are in split BTF also, so ensure that references to 445 + * such types point at base - not split - BTF. 446 + * 447 + * bpf_testmod_test_write() has multiple core kernel type parameters; 448 + * 449 + * ssize_t 450 + * bpf_testmod_test_write(struct file *file, struct kobject *kobj, 451 + * struct bin_attribute *bin_attr, 452 + * char *buf, loff_t off, size_t len); 453 + * 454 + * Ensure each of the FUNC_PROTO params is a core kernel type. 455 + * 456 + * Do the same for 457 + * 458 + * __bpf_kfunc struct sock *bpf_kfunc_call_test3(struct sock *sk); 459 + * 460 + * ...and 461 + * 462 + * __bpf_kfunc void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb); 463 + * 464 + */ 465 + const char *mod_funcs[] = { 466 + "bpf_testmod_test_write", 467 + "bpf_kfunc_call_test3", 468 + "bpf_kfunc_call_test_pass_ctx" 469 + }; 470 + 471 + static void test_split_module(void) 472 + { 473 + struct btf *vmlinux_btf, *btf1 = NULL; 474 + int i, nr_base_types; 475 + 476 + vmlinux_btf = btf__load_vmlinux_btf(); 477 + if (!ASSERT_OK_PTR(vmlinux_btf, "vmlinux_btf")) 478 + return; 479 + nr_base_types = btf__type_cnt(vmlinux_btf); 480 + if (!ASSERT_GT(nr_base_types, 0, "nr_base_types")) 481 + goto cleanup; 482 + 483 + btf1 = btf__parse_split("/sys/kernel/btf/bpf_testmod", vmlinux_btf); 484 + if (!ASSERT_OK_PTR(btf1, "split_btf")) 485 + return; 486 + 487 + for (i = 0; i < ARRAY_SIZE(mod_funcs); i++) { 488 + const struct btf_param *p; 489 + const struct btf_type *t; 490 + __u16 vlen; 491 + __u32 id; 492 + int j; 493 + 494 + id = btf__find_by_name_kind(btf1, mod_funcs[i], BTF_KIND_FUNC); 495 + if (!ASSERT_GE(id, nr_base_types, "func_id")) 496 + goto cleanup; 497 + t = btf__type_by_id(btf1, id); 498 + if (!ASSERT_OK_PTR(t, "func_id_type")) 499 + goto cleanup; 500 + t = btf__type_by_id(btf1, t->type); 501 + if (!ASSERT_OK_PTR(t, "func_proto_id_type")) 502 + goto cleanup; 503 + if (!ASSERT_EQ(btf_is_func_proto(t), true, "is_func_proto")) 504 + goto cleanup; 505 + vlen = btf_vlen(t); 506 + 507 + for (j = 0, p = btf_params(t); j < vlen; j++, p++) { 508 + /* bpf_testmod uses resilient split BTF, so any 509 + * reference types will be added to split BTF and their 510 + * associated targets will be base BTF types; for example 511 + * for a "struct sock *" the PTR will be in split BTF 512 + * while the "struct sock" will be in base. 513 + * 514 + * In some cases like loff_t we have to resolve 515 + * multiple typedefs hence the while() loop below. 516 + * 517 + * Note that resilient split BTF generation depends 518 + * on pahole version, so we do not assert that 519 + * reference types are in split BTF, as if pahole 520 + * does not support resilient split BTF they will 521 + * also be base BTF types. 522 + */ 523 + id = p->type; 524 + do { 525 + t = btf__type_by_id(btf1, id); 526 + if (!ASSERT_OK_PTR(t, "param_ref_type")) 527 + goto cleanup; 528 + if (!btf_is_mod(t) && !btf_is_ptr(t) && !btf_is_typedef(t)) 529 + break; 530 + id = t->type; 531 + } while (true); 532 + 533 + if (!ASSERT_LT(id, nr_base_types, "verify_base_type")) 534 + goto cleanup; 535 + } 536 + } 537 + cleanup: 538 + btf__free(btf1); 539 + btf__free(vmlinux_btf); 540 + } 541 + 443 542 void test_btf_dedup_split() 444 543 { 445 544 if (test__start_subtest("split_simple")) ··· 549 450 test_split_fwd_resolve(); 550 451 if (test__start_subtest("split_dup_struct_in_cu")) 551 452 test_split_dup_struct_in_cu(); 453 + if (test__start_subtest("split_module")) 454 + test_split_module(); 552 455 }