[PATCH bpf-next v3 4/7] bpf: Fix arg_track_join log to use sa prefix for stack arg slots

[Yonghong Song <yonghong.song@linux.dev>]

arg_track_join() logs state transitions at CFG merge points. For
stack arg slots (r >= MAX_BPF_REG), it printed "r11:", "r12:", etc.,
which is misleading since r11 is a special register (BPF_REG_PARAMS)
not meaningful to the user.

Fix it to print "sa0:", "sa1:", etc., matching the per-instruction
transition log in arg_track_log() which already uses the "sa" prefix.

Update the existing stack_arg_pruning_type_mismatch selftest to expect
the corrected format.

Fixes: 2af4e792773f ("bpf: Extend liveness analysis to track stack argument slots")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 kernel/bpf/liveness.c                                  | 4 +++-
 tools/testing/selftests/bpf/progs/verifier_stack_arg.c | 2 +-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/liveness.c b/kernel/bpf/liveness.c
index 7f4a0e4c2c49..0aadfbae0acc 100644
--- a/kernel/bpf/liveness.c
+++ b/kernel/bpf/liveness.c
@@ -806,7 +806,9 @@ static bool arg_track_join(struct bpf_verifier_env *env, int idx, int target, in
 		return true;
 
 	verbose(env, "arg JOIN insn %d -> %d ", idx, target);
-	if (r >= 0)
+	if (r >= MAX_BPF_REG)
+		verbose(env, "sa%d: ", r - MAX_BPF_REG);
+	else if (r >= 0)
 		verbose(env, "r%d: ", r);
 	else
 		verbose(env, "fp%+d: ", r * 8);
diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
index df0c3438529e..7e0ce5db28a0 100644
--- a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
@@ -117,7 +117,7 @@ __description("stack_arg: pruning with different stack arg types")
 __failure __log_level(2)
 __flag(BPF_F_TEST_STATE_FREQ)
 __msg("arg JOIN insn 9 -> 10 r1: fp0-8 + _ => fp0-8|fp0+0")
-__msg("arg JOIN insn 9 -> 10 r11: fp0-8 + _ => fp0-8|fp0+0")
+__msg("arg JOIN insn 9 -> 10 sa0: fp0-8 + _ => fp0-8|fp0+0")
 __msg("R{{[0-9]}} invalid mem access 'scalar'")
 __naked void stack_arg_pruning_type_mismatch(void)
 {
-- 
2.53.0-Meta