[PATCH bpf-next v1 3/4] bpf: use KF_FASTCALL to mark kfuncs supporting fastcall contract

[Eduard Zingerman <eddyz87@gmail.com>]

In order to allow pahole add btf_decl_tag("bpf_fastcall") for kfuncs
supporting bpf_fastcall, mark such functions with KF_FASTCALL in
id_set8 objects.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
---
 include/linux/btf.h   | 1 +
 kernel/bpf/helpers.c  | 4 ++--
 kernel/bpf/verifier.c | 5 +----
 3 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/include/linux/btf.h b/include/linux/btf.h
index b8a583194c4a..631060e3ad14 100644
--- a/include/linux/btf.h
+++ b/include/linux/btf.h
@@ -75,6 +75,7 @@
 #define KF_ITER_NEXT    (1 << 9) /* kfunc implements BPF iter next method */
 #define KF_ITER_DESTROY (1 << 10) /* kfunc implements BPF iter destructor */
 #define KF_RCU_PROTECTED (1 << 11) /* kfunc should be protected by rcu cs when they are invoked */
+#define KF_FASTCALL     (1 << 12) /* kfunc supports bpf_fastcall protocol */
 
 /*
  * Tag marking a kernel function as a kfunc. This is meant to minimize the
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3956be5d6440..d80632405148 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3052,8 +3052,8 @@ BTF_ID(func, bpf_cgroup_release_dtor)
 #endif
 
 BTF_KFUNCS_START(common_btf_ids)
-BTF_ID_FLAGS(func, bpf_cast_to_kern_ctx)
-BTF_ID_FLAGS(func, bpf_rdonly_cast)
+BTF_ID_FLAGS(func, bpf_cast_to_kern_ctx, KF_FASTCALL)
+BTF_ID_FLAGS(func, bpf_rdonly_cast, KF_FASTCALL)
 BTF_ID_FLAGS(func, bpf_rcu_read_lock)
 BTF_ID_FLAGS(func, bpf_rcu_read_unlock)
 BTF_ID_FLAGS(func, bpf_dynptr_slice, KF_RET_NULL)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f35b80c16cda..80a9c73137b8 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -16199,10 +16199,7 @@ static u32 kfunc_fastcall_clobber_mask(struct bpf_kfunc_call_arg_meta *meta)
 /* Same as verifier_inlines_helper_call() but for kfuncs, see comment above */
 static bool is_fastcall_kfunc_call(struct bpf_kfunc_call_arg_meta *meta)
 {
-	if (meta->btf == btf_vmlinux)
-		return meta->func_id == special_kfunc_list[KF_bpf_cast_to_kern_ctx] ||
-		       meta->func_id == special_kfunc_list[KF_bpf_rdonly_cast];
-	return false;
+	return meta->kfunc_flags & KF_FASTCALL;
 }
 
 /* LLVM define a bpf_fastcall function attribute.
-- 
2.46.0