linux-kernel - [PATCH] perf-probe: Failback to symbol-base probe for probes on module

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Date:   Tue, 23 Feb 2021 10:48:30 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Evgenii Shatokhin <eshatokhin@...tuozzo.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        live-patching@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Konstantin Khorenko <khorenko@...tuozzo.com>
Subject: [PATCH] perf-probe: Failback to symbol-base probe for probes on module

If an error occurs on post processing (this converts probe point to
_text relative address for identifying non-unique symbols) for the
probes on module, failback to symbol-base probe.

There are many non-unique name symbols (local static functions can
be in the different name spaces) in the kernel. If perf-probe uses
a symbol-based probe definition, it can be put on an unintended
symbol. To avoid such mistake, perf-probe tries to convert the
address to the _text relative address expression.

However, such symbol duplication is rare for only one module. Thus
even if the conversion fails, perf probe can failback to the symbol
based probe.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/probe-event.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index a9cff3a50ddf..af946f68e32e 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -779,16 +779,16 @@ post_process_module_probe_trace_events(struct probe_trace_event *tevs,
 
 	map = get_target_map(module, NULL, false);
 	if (!map || debuginfo__get_text_offset(dinfo, &text_offs, true) < 0) {
-		pr_warning("Failed to get ELF symbols for %s\n", module);
-		return -EINVAL;
+		pr_info("NOTE: Failed to get ELF symbols for %s. Use symbol based probe.\n", module);
+		return 0;
 	}
 
 	mod_name = find_module_name(module);
 	for (i = 0; i < ntevs; i++) {
-		ret = post_process_probe_trace_point(&tevs[i].point,
-						map, (unsigned long)text_offs);
-		if (ret < 0)
-			break;
+		if (post_process_probe_trace_point(&tevs[i].point,
+				map, (unsigned long)text_offs) < 0)
+			pr_info("NOTE: %s is not in the symbol map. Use symbol based probe.\n",
+				   tevs[i].point.symbol);
 		tevs[i].point.module =
 			strdup(mod_name ? mod_name : module);
 		if (!tevs[i].point.module) {