[PATCH] tracing: precise log info for kretprobe addr err

[Jianlin Lv]

When trying to create kretprobe with the wrong function symbol in tracefs;
The error is triggered in the register_trace_kprobe() and recorded as
FAIL_REG_PROBE issue,

Example:
  $ cd /sys/kernel/debug/tracing
  $ echo 'r:myprobe ERROR_SYMBOL_XXX ret=%x0' >> kprobe_events
    bash: echo: write error: Invalid argument
  $ cat error_log
    [142797.347877] trace_kprobe: error: Failed to register probe event
    Command: r:myprobe ERROR_SYMBOL_XXX ret=%x0
                       ^

This error can be detected in the parameter parsing stage, the effect of
applying this patch is as follows:

  $ echo 'r:myprobe ERROR_SYMBOL_XXX ret=%x0' >> kprobe_events
    bash: echo: write error: Invalid argument
  $ cat error_log
    [415.89]trace_kprobe: error: Retprobe address must be an function entry
    Command: r:myprobe ERROR_SYMBOL_XXX ret=%x0
                       ^

Signed-off-by: Jianlin Lv <Jianlin.Lv@xxxxxxx>
---
 kernel/trace/trace_kprobe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index e6fba1798771..3dfd1b6711a3 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -830,7 +830,7 @@ static int trace_kprobe_create(int argc, const char *argv[])
 			flags |= TPARG_FL_RETURN;
 		if (kprobe_on_func_entry(NULL, symbol, offset))
 			flags |= TPARG_FL_FENTRY;
-		if (offset && is_return && !(flags & TPARG_FL_FENTRY)) {
+		if (is_return && !(flags & TPARG_FL_FENTRY)) {
 			trace_probe_log_err(0, BAD_RETPROBE);
 			goto parse_error;
 		}
-- 
2.25.1