bpf: emit map name in register state if applicable and available

In complicated real-world applications, whenever debugging some
verification error through verifier log, it often would be very useful
to see map name for PTR_TO_MAP_VALUE register. Usually this needs to be
inferred from key/value sizes and maybe trying to guess C code location,
but it's not always clear.

Given verifier has the name, and it's never too long, let's just emit it
for ptr_to_map_key, ptr_to_map_value, and const_ptr_to_map registers. We
reshuffle the order a bit, so that map name, key size, and value size
appear before offset and immediate values, which seems like a more
logical order.

Current output:

  R1_w=map_ptr(map=array_map,ks=4,vs=8,off=0,imm=0)

But we'll get rid of useless off=0 and imm=0 parts in the next patch.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231118034623.3320920-6-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

2 files changed, 23 insertions, 11 deletions

diff --git a/kernel/bpf/log.c b/kernel/bpf/log.c
index 97a1641e848e..c209ab1ec2b5 100644
--- a/kernel/bpf/log.c
+++ b/kernel/bpf/log.c
@@ -553,6 +553,17 @@ static void print_scalar_ranges(struct bpf_verifier_env *env,
 	}
 }
 
+static bool type_is_map_ptr(enum bpf_reg_type t) {
+	switch (base_type(t)) {
+	case CONST_PTR_TO_MAP:
+	case PTR_TO_MAP_KEY:
+	case PTR_TO_MAP_VALUE:
+		return true;
+	default:
+		return false;
+	}
+}
+
 static void print_reg_state(struct bpf_verifier_env *env, const struct bpf_reg_state *reg)
 {
 	enum bpf_reg_type t;
@@ -584,16 +595,17 @@ static void print_reg_state(struct bpf_verifier_env *env, const struct bpf_reg_s
 		verbose_a("ref_obj_id=%d", reg->ref_obj_id);
 	if (type_is_non_owning_ref(reg->type))
 		verbose_a("%s", "non_own_ref");
+	if (type_is_map_ptr(t)) {
+		if (reg->map_ptr->name[0])
+			verbose_a("map=%s", reg->map_ptr->name);
+		verbose_a("ks=%d,vs=%d",
+			  reg->map_ptr->key_size,
+			  reg->map_ptr->value_size);
+	}
 	if (t != SCALAR_VALUE)
 		verbose_a("off=%d", reg->off);
 	if (type_is_pkt_pointer(t))
 		verbose_a("r=%d", reg->range);
-	else if (base_type(t) == CONST_PTR_TO_MAP ||
-		 base_type(t) == PTR_TO_MAP_KEY ||
-		 base_type(t) == PTR_TO_MAP_VALUE)
-		verbose_a("ks=%d,vs=%d",
-			  reg->map_ptr->key_size,
-			  reg->map_ptr->value_size);
 	if (tnum_is_const(reg->var_off)) {
 		/* Typically an immediate SCALAR_VALUE, but
 		 * could be a pointer whose offset is too big
diff --git a/tools/testing/selftests/bpf/prog_tests/spin_lock.c b/tools/testing/selftests/bpf/prog_tests/spin_lock.c
index f29c08d93beb..ace65224286f 100644
--- a/tools/testing/selftests/bpf/prog_tests/spin_lock.c
+++ b/tools/testing/selftests/bpf/prog_tests/spin_lock.c
@@ -17,18 +17,18 @@ static struct {
 	  "R1_w=ptr_foo(id=2,ref_obj_id=2,off=0,imm=0) refs=2\n6: (85) call bpf_this_cpu_ptr#154\n"
 	  "R1 type=ptr_ expected=percpu_ptr_" },
 	{ "lock_id_global_zero",
-	  "; R1_w=map_value(off=0,ks=4,vs=4,imm=0)\n2: (85) call bpf_this_cpu_ptr#154\n"
+	  "; R1_w=map_value(map=.data.A,ks=4,vs=4,off=0,imm=0)\n2: (85) call bpf_this_cpu_ptr#154\n"
 	  "R1 type=map_value expected=percpu_ptr_" },
 	{ "lock_id_mapval_preserve",
 	  "[0-9]\\+: (bf) r1 = r0                       ;"
-	  " R0_w=map_value(id=1,off=0,ks=4,vs=8,imm=0)"
-	  " R1_w=map_value(id=1,off=0,ks=4,vs=8,imm=0)\n"
+	  " R0_w=map_value(id=1,map=array_map,ks=4,vs=8,off=0,imm=0)"
+	  " R1_w=map_value(id=1,map=array_map,ks=4,vs=8,off=0,imm=0)\n"
 	  "[0-9]\\+: (85) call bpf_this_cpu_ptr#154\n"
 	  "R1 type=map_value expected=percpu_ptr_" },
 	{ "lock_id_innermapval_preserve",
 	  "[0-9]\\+: (bf) r1 = r0                      ;"
-	  " R0=map_value(id=2,off=0,ks=4,vs=8,imm=0)"
-	  " R1_w=map_value(id=2,off=0,ks=4,vs=8,imm=0)\n"
+	  " R0=map_value(id=2,ks=4,vs=8,off=0,imm=0)"
+	  " R1_w=map_value(id=2,ks=4,vs=8,off=0,imm=0)\n"
 	  "[0-9]\\+: (85) call bpf_this_cpu_ptr#154\n"
 	  "R1 type=map_value expected=percpu_ptr_" },
 	{ "lock_id_mismatch_kptr_kptr", "bpf_spin_unlock of different lock" },