linux-kernel - [PATCH 4.9 14/25] perf probe: Fix to probe on gcc generated symbols for offline kernel

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Message-Id: <20170713154002.501005401@linuxfoundation.org>
Date:   Thu, 13 Jul 2017 17:40:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Krister Johansen <kjlx@...pleofstupid.com>
Subject: [PATCH 4.9 14/25] perf probe: Fix to probe on gcc generated symbols for offline kernel

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Masami Hiramatsu <mhiramat@...nel.org>

commit 8a937a25a7e3c19d5fb3f9d92f605cf5fda219d8 upstream.

Fix perf-probe to show probe definition on gcc generated symbols for
offline kernel (including cross-arch kernel image).

gcc sometimes optimizes functions and generate new symbols with suffixes
such as ".constprop.N" or ".isra.N" etc. Since those symbol names are
not recorded in DWARF, we have to find correct generated symbols from
offline ELF binary to probe on it (kallsyms doesn't correct it).  For
online kernel or uprobes we don't need it because those are rebased on
_text, or a section relative address.

E.g. Without this:

  $ perf probe -k build-arm/vmlinux -F __slab_alloc*
  __slab_alloc.constprop.9
  $ perf probe -k build-arm/vmlinux -D __slab_alloc
  p:probe/__slab_alloc __slab_alloc+0

If you put above definition on target machine, it should fail
because there is no __slab_alloc in kallsyms.

With this fix, perf probe shows correct probe definition on
__slab_alloc.constprop.9:

  $ perf probe -k build-arm/vmlinux -D __slab_alloc
  p:probe/__slab_alloc __slab_alloc.constprop.9+0

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/148350060434.19001.11864836288580083501.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Krister Johansen <kjlx@...pleofstupid.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 tools/perf/util/probe-event.c |   48 +++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -618,6 +618,51 @@ error:
 	return ret ? : -ENOENT;
 }
 
+/*
+ * Rename DWARF symbols to ELF symbols -- gcc sometimes optimizes functions
+ * and generate new symbols with suffixes such as .constprop.N or .isra.N
+ * etc. Since those symbols are not recorded in DWARF, we have to find
+ * correct generated symbols from offline ELF binary.
+ * For online kernel or uprobes we don't need this because those are
+ * rebased on _text, or already a section relative address.
+ */
+static int
+post_process_offline_probe_trace_events(struct probe_trace_event *tevs,
+					int ntevs, const char *pathname)
+{
+	struct symbol *sym;
+	struct map *map;
+	unsigned long stext = 0;
+	u64 addr;
+	int i;
+
+	/* Prepare a map for offline binary */
+	map = dso__new_map(pathname);
+	if (!map || get_text_start_address(pathname, &stext) < 0) {
+		pr_warning("Failed to get ELF symbols for %s\n", pathname);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < ntevs; i++) {
+		addr = tevs[i].point.address + tevs[i].point.offset - stext;
+		sym = map__find_symbol(map, addr);
+		if (!sym)
+			continue;
+		if (!strcmp(sym->name, tevs[i].point.symbol))
+			continue;
+		/* If we have no realname, use symbol for it */
+		if (!tevs[i].point.realname)
+			tevs[i].point.realname = tevs[i].point.symbol;
+		else
+			free(tevs[i].point.symbol);
+		tevs[i].point.symbol = strdup(sym->name);
+		tevs[i].point.offset = addr - sym->start;
+	}
+	map__put(map);
+
+	return 0;
+}
+
 static int add_exec_to_probe_trace_events(struct probe_trace_event *tevs,
 					  int ntevs, const char *exec)
 {
@@ -694,7 +739,8 @@ post_process_kernel_probe_trace_events(s
 
 	/* Skip post process if the target is an offline kernel */
 	if (symbol_conf.ignore_vmlinux_buildid)
-		return 0;
+		return post_process_offline_probe_trace_events(tevs, ntevs,
+						symbol_conf.vmlinux_name);
 
 	reloc_sym = kernel_get_ref_reloc_sym();
 	if (!reloc_sym) {