[PATCH RFC bpf-next v2 1/4] bpf: Introduce BPF_HELPER_CALL

[Ilya Leoshkevich <iii@linux.ibm.com>]

Make the code more readable by introducing a symbolic constant
instead of using 0.

Suggested-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 include/uapi/linux/bpf.h       |  4 ++++
 kernel/bpf/disasm.c            |  2 +-
 kernel/bpf/verifier.c          | 12 +++++++-----
 tools/include/linux/filter.h   |  2 +-
 tools/include/uapi/linux/bpf.h |  4 ++++
 5 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 1503f61336b6..37f7588d5b2f 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -1211,6 +1211,10 @@ enum bpf_link_type {
  */
 #define BPF_PSEUDO_FUNC		4
 
+/* when bpf_call->src_reg == BPF_HELPER_CALL, bpf_call->imm == index of a bpf
+ * helper function (see ___BPF_FUNC_MAPPER below for a full list)
+ */
+#define BPF_HELPER_CALL		0
 /* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative
  * offset to another bpf function
  */
diff --git a/kernel/bpf/disasm.c b/kernel/bpf/disasm.c
index 7b4afb7d96db..c11d9b5a45a9 100644
--- a/kernel/bpf/disasm.c
+++ b/kernel/bpf/disasm.c
@@ -19,7 +19,7 @@ static const char *__func_get_name(const struct bpf_insn_cbs *cbs,
 {
 	BUILD_BUG_ON(ARRAY_SIZE(func_id_str) != __BPF_FUNC_MAX_ID);
 
-	if (!insn->src_reg &&
+	if (insn->src_reg == BPF_HELPER_CALL &&
 	    insn->imm >= 0 && insn->imm < __BPF_FUNC_MAX_ID &&
 	    func_id_str[insn->imm])
 		return func_id_str[insn->imm];
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 272563a0b770..427525fc3791 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2947,7 +2947,8 @@ static int backtrack_insn(struct bpf_verifier_env *env, int idx,
 			/* BPF helpers that invoke callback subprogs are
 			 * equivalent to BPF_PSEUDO_CALL above
 			 */
-			if (insn->src_reg == 0 && is_callback_calling_function(insn->imm))
+			if (insn->src_reg == BPF_HELPER_CALL &&
+			    is_callback_calling_function(insn->imm))
 				return -ENOTSUPP;
 			/* kfunc with imm==0 is invalid and fixup_kfunc_call will
 			 * catch this error later. Make backtracking conservative
@@ -7522,7 +7523,7 @@ static int __check_func_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 	}
 
 	if (insn->code == (BPF_JMP | BPF_CALL) &&
-	    insn->src_reg == 0 &&
+	    insn->src_reg == BPF_HELPER_CALL &&
 	    insn->imm == BPF_FUNC_timer_set_callback) {
 		struct bpf_verifier_state *async_cb;
 
@@ -14730,7 +14731,7 @@ static int do_check(struct bpf_verifier_env *env)
 				if (BPF_SRC(insn->code) != BPF_K ||
 				    (insn->src_reg != BPF_PSEUDO_KFUNC_CALL
 				     && insn->off != 0) ||
-				    (insn->src_reg != BPF_REG_0 &&
+				    (insn->src_reg != BPF_HELPER_CALL &&
 				     insn->src_reg != BPF_PSEUDO_CALL &&
 				     insn->src_reg != BPF_PSEUDO_KFUNC_CALL) ||
 				    insn->dst_reg != BPF_REG_0 ||
@@ -14740,7 +14741,8 @@ static int do_check(struct bpf_verifier_env *env)
 				}
 
 				if (env->cur_state->active_lock.ptr) {
-					if ((insn->src_reg == BPF_REG_0 && insn->imm != BPF_FUNC_spin_unlock) ||
+					if ((insn->src_reg == BPF_HELPER_CALL &&
+					     insn->imm != BPF_FUNC_spin_unlock) ||
 					    (insn->src_reg == BPF_PSEUDO_CALL) ||
 					    (insn->src_reg == BPF_PSEUDO_KFUNC_CALL &&
 					     (insn->off != 0 || !is_bpf_graph_api_kfunc(insn->imm)))) {
@@ -16933,7 +16935,7 @@ static struct bpf_prog *inline_bpf_loop(struct bpf_verifier_env *env,
 static bool is_bpf_loop_call(struct bpf_insn *insn)
 {
 	return insn->code == (BPF_JMP | BPF_CALL) &&
-		insn->src_reg == 0 &&
+		insn->src_reg == BPF_HELPER_CALL &&
 		insn->imm == BPF_FUNC_loop;
 }
 
diff --git a/tools/include/linux/filter.h b/tools/include/linux/filter.h
index 736bdeccdfe4..78dc208c8d88 100644
--- a/tools/include/linux/filter.h
+++ b/tools/include/linux/filter.h
@@ -261,7 +261,7 @@
 	((struct bpf_insn) {					\
 		.code  = BPF_JMP | BPF_CALL,			\
 		.dst_reg = 0,					\
-		.src_reg = 0,					\
+		.src_reg = BPF_HELPER_CALL,			\
 		.off   = 0,					\
 		.imm   = ((FUNC) - BPF_FUNC_unspec) })
 
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 1503f61336b6..37f7588d5b2f 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -1211,6 +1211,10 @@ enum bpf_link_type {
  */
 #define BPF_PSEUDO_FUNC		4
 
+/* when bpf_call->src_reg == BPF_HELPER_CALL, bpf_call->imm == index of a bpf
+ * helper function (see ___BPF_FUNC_MAPPER below for a full list)
+ */
+#define BPF_HELPER_CALL		0
 /* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative
  * offset to another bpf function
  */
-- 
2.39.1