linux-kernel - [PATCH] perf-probe: dso: Add symbols in .text.* subsections to text symbol map in kenrel modules

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Message-Id: <161406587251.969784.5469149622544499077.stgit@devnote2>
Date:   Tue, 23 Feb 2021 16:37:52 +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: dso: Add symbols in .text.* subsections to text symbol map in kenrel modules

The kernel modules have .text.* subsections such as .text.unlikely.
Since dso__process_kernel_symbol() only identify the symbols in the ".text"
section as the text symbols and inserts it in the default dso in the map,
the symbols in such subsections can not be found by map__find_symbol().

This adds the symbols in those subsections to the default dso in the map so
that map__find_symbol() can find them. This solves the perf-probe issue on
probing online module.

Without this fix, probing on a symbol in .text.unlikely fails.
  ----
  # perf probe -m nf_conntrack nf_l4proto_log_invalid
  Probe point 'nf_l4proto_log_invalid' not found.
    Error: Failed to add events.
  ----

With this fix, it works because map__find_symbol() can find the symbol
correctly.
  ----
  # perf probe -m nf_conntrack nf_l4proto_log_invalid
  Added new event:
    probe:nf_l4proto_log_invalid (on nf_l4proto_log_invalid in nf_conntrack)

  You can now use it in all perf tools, such as:

  	perf record -e probe:nf_l4proto_log_invalid -aR sleep 1

  ----

Reported-by: Evgenii Shatokhin <eshatokhin@...tuozzo.com>
Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 tools/perf/util/symbol-elf.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index 6dff843fd883..0c1113236913 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -985,7 +985,9 @@ static int dso__process_kernel_symbol(struct dso *dso, struct map *map,
 	if (strcmp(section_name, (curr_dso->short_name + dso->short_name_len)) == 0)
 		return 0;
 
-	if (strcmp(section_name, ".text") == 0) {
+	/* .text and .text.* are included in the text dso */
+	if (strncmp(section_name, ".text", 5) == 0 &&
+	    (section_name[5] == '\0' || section_name[5] == '.')) {
 		/*
 		 * The initial kernel mapping is based on
 		 * kallsyms and identity maps.  Overwrite it to