linux-kernel - [PATCH v4] trace/kprobe: Display the actual notrace function when rejecting a probe

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Message-ID: <20231214051702.1687300-1-naveen@kernel.org>
Date:   Thu, 14 Dec 2023 10:47:02 +0530
From:   Naveen N Rao <naveen@...nel.org>
To:     <linux-kernel@...r.kernel.org>,
        <linux-trace-kernel@...r.kernel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Srikar Dronamraju <srikar@...ux.ibm.com>
Subject: [PATCH v4] trace/kprobe: Display the actual notrace function when rejecting a probe

Trying to probe update_sd_lb_stats() using perf results in the below
message in the kernel log:
	trace_kprobe: Could not probe notrace function _text

This is because 'perf probe' specifies the kprobe location as an offset
from '_text':
	$ sudo perf probe -D update_sd_lb_stats
	p:probe/update_sd_lb_stats _text+1830728

However, the error message is misleading and doesn't help convey the
actual notrace function that is being probed. Fix this by looking up the
actual function name that is being probed. With this fix, we now get the
below message in the kernel log:
	trace_kprobe: Could not probe notrace function update_sd_lb_stats.constprop.0

Signed-off-by: Naveen N Rao <naveen@...nel.org>
---
v4: Use printk format specifier %ps with probe address to lookup the 
symbol, as suggested by Masami.

 kernel/trace/trace_kprobe.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 3d7a180a8427..0017404d6e8d 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -487,8 +487,8 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 		return -EINVAL;
 
 	if (within_notrace_func(tk)) {
-		pr_warn("Could not probe notrace function %s\n",
-			trace_kprobe_symbol(tk));
+		pr_warn("Could not probe notrace function %ps\n",
+			(void *)trace_kprobe_address(tk));
 		return -EINVAL;
 	}
 

base-commit: 4758560fa268cecfa1144f015aa9f2525d164b7e
-- 
2.43.0