bpf: Fix configuration-dependent BTF function references

These BTF functions are not available unconditionally,
only reference them when they are available.

Avoid the following build warnings:

  BTF     .tmp_vmlinux1.btf.o
btf_encoder__tag_kfunc: failed to find kfunc 'bpf_send_signal_task' in BTF
btf_encoder__tag_kfuncs: failed to tag kfunc 'bpf_send_signal_task'
  NM      .tmp_vmlinux1.syms
  KSYMS   .tmp_vmlinux1.kallsyms.S
  AS      .tmp_vmlinux1.kallsyms.o
  LD      .tmp_vmlinux2
  NM      .tmp_vmlinux2.syms
  KSYMS   .tmp_vmlinux2.kallsyms.S
  AS      .tmp_vmlinux2.kallsyms.o
  LD      vmlinux
  BTFIDS  vmlinux
WARN: resolve_btfids: unresolved symbol prog_test_ref_kfunc
WARN: resolve_btfids: unresolved symbol bpf_crypto_ctx
WARN: resolve_btfids: unresolved symbol bpf_send_signal_task
WARN: resolve_btfids: unresolved symbol bpf_modify_return_test_tp
WARN: resolve_btfids: unresolved symbol bpf_dynptr_from_xdp
WARN: resolve_btfids: unresolved symbol bpf_dynptr_from_skb

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20241213-bpf-cond-ids-v1-1-881849997219@weissschuh.net

kernel/bpf/helpers.c

@@ -3104,7 +3104,9 @@ BTF_ID_FLAGS(func, bpf_task_get_cgroup1, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_from_pid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_task_from_vpid, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, bpf_throw)
+#ifdef CONFIG_BPF_EVENTS
 BTF_ID_FLAGS(func, bpf_send_signal_task, KF_TRUSTED_ARGS)
+#endif
 BTF_KFUNCS_END(generic_btf_ids)
 
 static const struct btf_kfunc_id_set generic_kfunc_set = {
@@ -3150,7 +3152,9 @@ BTF_ID_FLAGS(func, bpf_dynptr_is_null)
 BTF_ID_FLAGS(func, bpf_dynptr_is_rdonly)
 BTF_ID_FLAGS(func, bpf_dynptr_size)
 BTF_ID_FLAGS(func, bpf_dynptr_clone)
+#ifdef CONFIG_NET
 BTF_ID_FLAGS(func, bpf_modify_return_test_tp)
+#endif
 BTF_ID_FLAGS(func, bpf_wq_init)
 BTF_ID_FLAGS(func, bpf_wq_set_callback_impl)
 BTF_ID_FLAGS(func, bpf_wq_start)

kernel/bpf/verifier.c

@@ -5681,15 +5681,19 @@ static bool in_rcu_cs(struct bpf_verifier_env *env)
 
 /* Once GCC supports btf_type_tag the following mechanism will be replaced with tag check */
 BTF_SET_START(rcu_protected_types)
+#ifdef CONFIG_NET
 BTF_ID(struct, prog_test_ref_kfunc)
+#endif
 #ifdef CONFIG_CGROUPS
 BTF_ID(struct, cgroup)
 #endif
 #ifdef CONFIG_BPF_JIT
 BTF_ID(struct, bpf_cpumask)
 #endif
 BTF_ID(struct, task_struct)
+#ifdef CONFIG_CRYPTO
 BTF_ID(struct, bpf_crypto_ctx)
+#endif
 BTF_SET_END(rcu_protected_types)
 
 static bool rcu_protected_object(const struct btf *btf, u32 btf_id)
@@ -11722,8 +11726,10 @@ BTF_ID(func, bpf_rdonly_cast)
 BTF_ID(func, bpf_rbtree_remove)
 BTF_ID(func, bpf_rbtree_add_impl)
 BTF_ID(func, bpf_rbtree_first)
+#ifdef CONFIG_NET
 BTF_ID(func, bpf_dynptr_from_skb)
 BTF_ID(func, bpf_dynptr_from_xdp)
+#endif
 BTF_ID(func, bpf_dynptr_slice)
 BTF_ID(func, bpf_dynptr_slice_rdwr)
 BTF_ID(func, bpf_dynptr_clone)
@@ -11751,8 +11757,10 @@ BTF_ID(func, bpf_rcu_read_unlock)
 BTF_ID(func, bpf_rbtree_remove)
 BTF_ID(func, bpf_rbtree_add_impl)
 BTF_ID(func, bpf_rbtree_first)
+#ifdef CONFIG_NET
 BTF_ID(func, bpf_dynptr_from_skb)
 BTF_ID(func, bpf_dynptr_from_xdp)
+#endif
 BTF_ID(func, bpf_dynptr_slice)
 BTF_ID(func, bpf_dynptr_slice_rdwr)
 BTF_ID(func, bpf_dynptr_clone)