linux-kernel - [PATCH v2 2/3] perf-probe: Ignore vmlinux buildid if offline kernel is given

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Date:   Fri, 26 Aug 2016 01:24:42 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>
Subject: [PATCH v2 2/3] perf-probe: Ignore vmlinux buildid if offline kernel is given

Ignore the buildid of running kernel when both of --definition and
--vmlinux is given because that kernel should be off-line.
This also skips post-processing of kprobe event for relocating
symbol and checking blacklist, because it can not be done on
off-line kernel.

E.g. without this fix perf shows an error as below
  ----
  $ perf probe --vmlinux=./vmlinux-arm --definition do_sys_open
  ./vmlinux-arm with build id 7a1f76dd56e9c4da707cd3d6333f50748141434b not found, continuing without symbols
  Failed to find symbol do_sys_open in kernel
    Error: Failed to add events.
  ----
with this fix, we can get the definition
  ----
  $ perf probe --vmlinux=./vmlinux-arm --definition do_sys_open
  p:probe/do_sys_open do_sys_open+0
  ----

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 Changes from v1:
  - Update the condition since --definition is introduced.
  - Skip post processing because this is not running kernel.
  - Update documentation too.
---
 tools/perf/Documentation/perf-probe.txt |    2 ++
 tools/perf/builtin-probe.c              |   10 +++++++++-
 tools/perf/util/probe-event.c           |    4 ++++
 tools/perf/util/symbol-elf.c            |    2 +-
 4 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Documentation/perf-probe.txt b/tools/perf/Documentation/perf-probe.txt
index 56db4d4..e6c9902 100644
--- a/tools/perf/Documentation/perf-probe.txt
+++ b/tools/perf/Documentation/perf-probe.txt
@@ -36,6 +36,8 @@ OPTIONS
 -k::
 --vmlinux=PATH::
 	Specify vmlinux path which has debuginfo (Dwarf binary).
+	Only when using this with --definition, you can give an offline
+	vmlinux file.
 
 -m::
 --module=MODNAME|PATH::
diff --git a/tools/perf/builtin-probe.c b/tools/perf/builtin-probe.c
index 7a3d8c4..b4220cd 100644
--- a/tools/perf/builtin-probe.c
+++ b/tools/perf/builtin-probe.c
@@ -654,8 +654,16 @@ __cmd_probe(int argc, const char **argv, const char *prefix __maybe_unused)
 			return ret;
 		}
 		break;
-	case 'a':
 	case 'D':
+		/*
+		 * If user gives offline vmlinux, ignore buildid, since
+		 * --definition doesn't change running kernel.
+		 */
+		if (symbol_conf.vmlinux_name)
+			symbol_conf.ignore_vmlinux_buildid = true;
+		/* fall through */
+	case 'a':
+
 		/* Ensure the last given target is used */
 		if (params.target && !params.target_used) {
 			pr_err("  Error: -x/-m must follow the probe definitions.\n");
diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index ad7094d..8dcec0c 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -674,6 +674,10 @@ post_process_kernel_probe_trace_events(struct probe_trace_event *tevs,
 	char *tmp;
 	int i, skipped = 0;
 
+	/* Skip post process if the target is an offline kernel */
+	if (symbol_conf.ignore_vmlinux_buildid)
+		return 0;
+
 	reloc_sym = kernel_get_ref_reloc_sym();
 	if (!reloc_sym) {
 		pr_warning("Relocated base symbol is not found!\n");
diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index a811c13..013cebf 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -685,7 +685,7 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
 	}
 
 	/* Always reject images with a mismatched build-id: */
-	if (dso->has_build_id) {
+	if (dso->has_build_id && !symbol_conf.ignore_vmlinux_buildid) {
 		u8 build_id[BUILD_ID_SIZE];
 
 		if (elf_read_build_id(elf, build_id, BUILD_ID_SIZE) < 0) {