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 <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/147214228193.23638.12581984840822162131.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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::

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");

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");

tools/perf/util/symbol-elf.c

@@ -732,7 +732,7 @@ 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) {