btf_prepare_func_args() indexes sub->args[] by BTF parameter, so a
parameter can only ever stand for a single argument register. Give the
loop a second index: 'i' keeps walking the BTF parameters while
'slots_used' walks the argument slots, and sub->arg_slot_cnt becomes the
number of slots, so that a later patch can give a parameter two of them.

No functional change: every parameter still takes exactly one slot.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/btf.c | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 01ec2b40f376..35eaa28c85b5 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -8037,7 +8037,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 	const struct btf_param *args;
 	const struct btf_type *t, *ref_t, *fn_t;
 	int err;
-	u32 i, nargs, btf_id;
+	u32 i, slots_used, nargs, btf_id;
 	const char *tname;
 
 	if (sub->args_cached)
@@ -8122,8 +8122,9 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 	/* Convert BTF function arguments into verifier types.
 	 * Only PTR_TO_CTX and SCALAR are supported atm.
 	 */
-	for (i = 0; i < nargs; i++) {
+	for (i = 0, slots_used = 0; i < nargs; i++) {
 		u32 tags = 0;
+
 		err = btf_scan_decl_tags(env, btf, fn_t, i, is_global, &tags);
 		if (err)
 			return err;
@@ -8145,7 +8146,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			    btf_validate_prog_ctx_type(log, btf, t, i, prog_type,
 						       prog->expected_attach_type))
 				return -EINVAL;
-			sub->args[i].arg_type = ARG_PTR_TO_CTX;
+			sub->args[slots_used++].arg_type = ARG_PTR_TO_CTX;
 			continue;
 		}
 		if (btf_is_dynptr_ptr(btf, t)) {
@@ -8153,7 +8154,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 				bpf_log(log, "arg#%d has invalid combination of tags\n", i);
 				return -EINVAL;
 			}
-			sub->args[i].arg_type = ARG_PTR_TO_DYNPTR;
+			sub->args[slots_used++].arg_type = ARG_PTR_TO_DYNPTR;
 			continue;
 		}
 		if (tags & ARG_TAG_TRUSTED) {
@@ -8168,10 +8169,11 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			if (kern_type_id < 0)
 				return kern_type_id;
 
-			sub->args[i].arg_type = ARG_PTR_TO_BTF_ID | PTR_TRUSTED;
+			sub->args[slots_used].arg_type = ARG_PTR_TO_BTF_ID | PTR_TRUSTED;
 			if (tags & ARG_TAG_NULLABLE)
-				sub->args[i].arg_type |= PTR_MAYBE_NULL;
-			sub->args[i].btf_id = kern_type_id;
+				sub->args[slots_used].arg_type |= PTR_MAYBE_NULL;
+			sub->args[slots_used].btf_id = kern_type_id;
+			slots_used++;
 			continue;
 		}
 		if (tags & ARG_TAG_UNTRUSTED) {
@@ -8185,8 +8187,10 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 
 			ref_t = btf_type_skip_modifiers(btf, t->type, NULL);
 			if (btf_type_is_void(ref_t) || btf_type_is_primitive(ref_t)) {
-				sub->args[i].arg_type = ARG_PTR_TO_MEM | MEM_RDONLY | PTR_UNTRUSTED;
-				sub->args[i].mem_size = 0;
+				sub->args[slots_used].arg_type = ARG_PTR_TO_MEM | MEM_RDONLY |
+								 PTR_UNTRUSTED;
+				sub->args[slots_used].mem_size = 0;
+				slots_used++;
 				continue;
 			}
 
@@ -8202,8 +8206,9 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 					i, btf_type_str(ref_t), tname);
 				return -EINVAL;
 			}
-			sub->args[i].arg_type = ARG_PTR_TO_BTF_ID | PTR_UNTRUSTED;
-			sub->args[i].btf_id = kern_type_id;
+			sub->args[slots_used].arg_type = ARG_PTR_TO_BTF_ID | PTR_UNTRUSTED;
+			sub->args[slots_used].btf_id = kern_type_id;
+			slots_used++;
 			continue;
 		}
 		if (tags & ARG_TAG_ARENA) {
@@ -8211,7 +8216,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 				bpf_log(log, "arg#%d arena cannot be combined with any other tags\n", i);
 				return -EINVAL;
 			}
-			sub->args[i].arg_type = ARG_PTR_TO_ARENA;
+			sub->args[slots_used++].arg_type = ARG_PTR_TO_ARENA;
 			continue;
 		}
 		if (is_global) { /* generic user data pointer */
@@ -8231,10 +8236,11 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 				return -EINVAL;
 			}
 
-			sub->args[i].arg_type = ARG_PTR_TO_MEM | PTR_MAYBE_NULL;
+			sub->args[slots_used].arg_type = ARG_PTR_TO_MEM | PTR_MAYBE_NULL;
 			if (tags & ARG_TAG_NONNULL)
-				sub->args[i].arg_type &= ~PTR_MAYBE_NULL;
-			sub->args[i].mem_size = mem_size;
+				sub->args[slots_used].arg_type &= ~PTR_MAYBE_NULL;
+			sub->args[slots_used].mem_size = mem_size;
+			slots_used++;
 			continue;
 		}
 
@@ -8244,7 +8250,7 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 			return -EINVAL;
 		}
 		if (btf_type_is_int(t) || btf_is_any_enum(t)) {
-			sub->args[i].arg_type = ARG_ANYTHING;
+			sub->args[slots_used++].arg_type = ARG_ANYTHING;
 			continue;
 		}
 		if (!is_global)
@@ -8254,6 +8260,8 @@ int btf_prepare_func_args(struct bpf_verifier_env *env, int subprog)
 		return -EINVAL;
 	}
 
+	sub->arg_slot_cnt = slots_used;
+
 	sub->args_cached = true;
 
 	return 0;
-- 
2.52.0