[PATCH bpf-next v4 01/13] bpf: Rename 'early' BTF checking as a preparation phase

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

BTF processing is split around subprogram discovery. The first phase gets
program BTF and imports func_info because a BTF-tagged exception callback
may not be referenced by any instruction. Subprogram discovery needs this
metadata to find it.

The later phase validates func_info and line_info against the complete
subprogram table and applies CO-RE relocations. This split breaks a real
dependency cycle rather than merely running the same checks early.

Rename bpf_check_btf_info_early() and check_btf_func_early() to preparation
names that reflect this role. Add short call-site comments to make the two
phases and their responsibilities clear.

No functional change is intended.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf_verifier.h |  4 ++--
 kernel/bpf/check_btf.c       | 14 +++++++-------
 kernel/bpf/verifier.c        |  4 +++-
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index a2a40caca0a0..a9555d17fd8e 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -1177,8 +1177,8 @@ static inline void bpf_trampoline_unpack_key(u64 key, u32 *obj_id, u32 *btf_id)
 		*btf_id = key & 0x7FFFFFFF;
 }
 
-int bpf_check_btf_info_early(struct bpf_verifier_env *env,
-			     const union bpf_attr *attr, bpfptr_t uattr);
+int bpf_prepare_btf_info(struct bpf_verifier_env *env,
+			 const union bpf_attr *attr, bpfptr_t uattr);
 int bpf_check_btf_info(struct bpf_verifier_env *env,
 		       const union bpf_attr *attr, bpfptr_t uattr);
 
diff --git a/kernel/bpf/check_btf.c b/kernel/bpf/check_btf.c
index 93bebe6fe12e..0e8b3ccc7a5b 100644
--- a/kernel/bpf/check_btf.c
+++ b/kernel/bpf/check_btf.c
@@ -28,9 +28,9 @@ static int check_abnormal_return(struct bpf_verifier_env *env)
 #define MIN_BPF_FUNCINFO_SIZE	8
 #define MAX_FUNCINFO_REC_SIZE	252
 
-static int check_btf_func_early(struct bpf_verifier_env *env,
-				const union bpf_attr *attr,
-				bpfptr_t uattr)
+static int prepare_btf_func(struct bpf_verifier_env *env,
+			    const union bpf_attr *attr,
+			    bpfptr_t uattr)
 {
 	u32 krec_size = sizeof(struct bpf_func_info);
 	const struct btf_type *type, *func_proto;
@@ -407,9 +407,9 @@ static int check_core_relo(struct bpf_verifier_env *env,
 	return err;
 }
 
-int bpf_check_btf_info_early(struct bpf_verifier_env *env,
-			     const union bpf_attr *attr,
-			     bpfptr_t uattr)
+int bpf_prepare_btf_info(struct bpf_verifier_env *env,
+			 const union bpf_attr *attr,
+			 bpfptr_t uattr)
 {
 	struct btf *btf;
 	int err;
@@ -429,7 +429,7 @@ int bpf_check_btf_info_early(struct bpf_verifier_env *env,
 	}
 	env->prog->aux->btf = btf;
 
-	err = check_btf_func_early(env, attr, uattr);
+	err = prepare_btf_func(env, attr, uattr);
 	if (err)
 		return err;
 	return 0;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d925197c2e5f..129e50888b90 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -20317,7 +20317,8 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 		INIT_LIST_HEAD(&env->explored_states[i]);
 	INIT_LIST_HEAD(&env->free_list);
 
-	ret = bpf_check_btf_info_early(env, attr, uattr);
+	/* Prepare BTF and func_info needed to discover all subprograms. */
+	ret = bpf_prepare_btf_info(env, attr, uattr);
 	if (ret < 0)
 		goto skip_full_check;
 
@@ -20329,6 +20330,7 @@ int bpf_check(struct bpf_prog **prog, union bpf_attr *attr, bpfptr_t uattr,
 	if (ret < 0)
 		goto skip_full_check;
 
+	/* Validate BTF against the complete subprogram layout and apply CO-RE. */
 	ret = bpf_check_btf_info(env, attr, uattr);
 	if (ret < 0)
 		goto skip_full_check;
-- 
2.53.0