linux-kernel - [PATCH v3] trace/kprobe: Display the actual notrace function when rejecting a probe

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Message-ID: <20231213143914.1591175-1-naveen@kernel.org>
Date:   Wed, 13 Dec 2023 20:09:14 +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 v3] 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>
---
v3: Remove tk parameter from within_notrace_func() as suggested by 
Masami

 kernel/trace/trace_kprobe.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 3d7a180a8427..dc36c6ed6131 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -449,9 +449,8 @@ static bool __within_notrace_func(unsigned long addr)
 	return !ftrace_location_range(addr, addr + size - 1);
 }
 
-static bool within_notrace_func(struct trace_kprobe *tk)
+static bool within_notrace_func(unsigned long addr)
 {
-	unsigned long addr = trace_kprobe_address(tk);
 	char symname[KSYM_NAME_LEN], *p;
 
 	if (!__within_notrace_func(addr))
@@ -471,12 +470,14 @@ static bool within_notrace_func(struct trace_kprobe *tk)
 	return true;
 }
 #else
-#define within_notrace_func(tk)	(false)
+#define within_notrace_func(addr)	(false)
 #endif
 
 /* Internal register function - just handle k*probes and flags */
 static int __register_trace_kprobe(struct trace_kprobe *tk)
 {
+	unsigned long addr = trace_kprobe_address(tk);
+	char symname[KSYM_NAME_LEN];
 	int i, ret;
 
 	ret = security_locked_down(LOCKDOWN_KPROBES);
@@ -486,9 +487,9 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 	if (trace_kprobe_is_registered(tk))
 		return -EINVAL;
 
-	if (within_notrace_func(tk)) {
+	if (within_notrace_func(addr)) {
 		pr_warn("Could not probe notrace function %s\n",
-			trace_kprobe_symbol(tk));
+			lookup_symbol_name(addr, symname) ? trace_kprobe_symbol(tk) : symname);
 		return -EINVAL;
 	}
 

base-commit: 4758560fa268cecfa1144f015aa9f2525d164b7e
-- 
2.43.0