bpf: Fix build when CONFIG_BPF_SYSCALL is disabled

When CONFIG_DEBUG_INFO_BTF is enabled and CONFIG_BPF_SYSCALL is
disabled, the following compilation error can be seen:

  GEN     .version
  CHK     include/generated/compile.h
  UPD     include/generated/compile.h
  CC      init/version.o
  AR      init/built-in.a
  LD      vmlinux.o
  MODPOST vmlinux.symvers
  MODINFO modules.builtin.modinfo
  GEN     modules.builtin
  LD      .tmp_vmlinux.btf
ld: net/ipv4/tcp_cubic.o: in function `cubictcp_unregister':
net/ipv4/tcp_cubic.c:545: undefined reference to `bpf_tcp_ca_kfunc_list'
ld: net/ipv4/tcp_cubic.c:545: undefined reference to `unregister_kfunc_btf_id_set'
ld: net/ipv4/tcp_cubic.o: in function `cubictcp_register':
net/ipv4/tcp_cubic.c:539: undefined reference to `bpf_tcp_ca_kfunc_list'
ld: net/ipv4/tcp_cubic.c:539: undefined reference to `register_kfunc_btf_id_set'
  BTF     .btf.vmlinux.bin.o
pahole: .tmp_vmlinux.btf: No such file or directory
  LD      .tmp_vmlinux.kallsyms1
.btf.vmlinux.bin.o: file not recognized: file format not recognized
make: *** [Makefile:1187: vmlinux] Error 1

'bpf_tcp_ca_kfunc_list', 'register_kfunc_btf_id_set()' and
'unregister_kfunc_btf_id_set()' are only defined when
CONFIG_BPF_SYSCALL is enabled.

Fix that by moving those definitions somewhere that doesn't depend on
the bpf() syscall.

Fixes: 14f267d ("bpf: btf: Introduce helpers for dynamic BTF set registration")
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>

kernel/bpf/btf.c

@@ -6344,33 +6344,8 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
 
 BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
 
-/* BTF ID set registration API for modules */
-
-struct kfunc_btf_id_list {
-	struct list_head list;
-	struct mutex mutex;
-};
-
 #ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 
-void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
-			       struct kfunc_btf_id_set *s)
-{
-	mutex_lock(&l->mutex);
-	list_add(&s->list, &l->list);
-	mutex_unlock(&l->mutex);
-}
-EXPORT_SYMBOL_GPL(register_kfunc_btf_id_set);
-
-void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
-				 struct kfunc_btf_id_set *s)
-{
-	mutex_lock(&l->mutex);
-	list_del_init(&s->list);
-	mutex_unlock(&l->mutex);
-}
-EXPORT_SYMBOL_GPL(unregister_kfunc_btf_id_set);
-
 bool bpf_check_mod_kfunc_call(struct kfunc_btf_id_list *klist, u32 kfunc_id,
 			      struct module *owner)
 {

kernel/bpf/core.c

@@ -2456,6 +2456,43 @@ int __weak bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
 DEFINE_STATIC_KEY_FALSE(bpf_stats_enabled_key);
 EXPORT_SYMBOL(bpf_stats_enabled_key);
 
+/* BTF ID set registration API for modules */
+
+struct kfunc_btf_id_list {
+	struct list_head list;
+	struct mutex mutex;
+};
+
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+
+void register_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+			       struct kfunc_btf_id_set *s)
+{
+	mutex_lock(&l->mutex);
+	list_add(&s->list, &l->list);
+	mutex_unlock(&l->mutex);
+}
+EXPORT_SYMBOL_GPL(register_kfunc_btf_id_set);
+
+void unregister_kfunc_btf_id_set(struct kfunc_btf_id_list *l,
+				 struct kfunc_btf_id_set *s)
+{
+	mutex_lock(&l->mutex);
+	list_del_init(&s->list);
+	mutex_unlock(&l->mutex);
+}
+EXPORT_SYMBOL_GPL(unregister_kfunc_btf_id_set);
+
+#endif
+
+#define DEFINE_KFUNC_BTF_ID_LIST(name)                                         \
+	struct kfunc_btf_id_list name = { LIST_HEAD_INIT(name.list),           \
+					  __MUTEX_INITIALIZER(name.mutex) };   \
+	EXPORT_SYMBOL_GPL(name)
+
+DEFINE_KFUNC_BTF_ID_LIST(bpf_tcp_ca_kfunc_list);
+DEFINE_KFUNC_BTF_ID_LIST(prog_test_kfunc_list);
+
 /* All definitions of tracepoints related to BPF. */
 #define CREATE_TRACE_POINTS
 #include <linux/bpf_trace.h>