linux-kernel - [PATCH 22/35] perf tools: Automatically use guest kcore

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Date:   Mon, 11 Jul 2022 12:32:05 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: [PATCH 22/35] perf tools: Automatically use guest kcore_dir if present

When registering a guest machine using machine_pid from the id index,
check perf.data for a matching kcore_dir subdirectory and set the
kallsyms file name accordingly. If set, use it to find the machine's
kernel symbols and object code (from kcore).

Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
---
 tools/perf/util/data.c    | 19 +++++++++++++++++++
 tools/perf/util/data.h    |  1 +
 tools/perf/util/machine.h |  1 +
 tools/perf/util/session.c |  2 ++
 tools/perf/util/symbol.c  |  6 ++++--
 5 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
index 9782ccbe595d..a7f68c309545 100644
--- a/tools/perf/util/data.c
+++ b/tools/perf/util/data.c
@@ -518,6 +518,25 @@ char *perf_data__kallsyms_name(struct perf_data *data)
 	return kallsyms_name;
 }
 
+char *perf_data__guest_kallsyms_name(struct perf_data *data, pid_t machine_pid)
+{
+	char *kallsyms_name;
+	struct stat st;
+
+	if (!data->is_dir)
+		return NULL;
+
+	if (asprintf(&kallsyms_name, "%s/kcore_dir__%d/kallsyms", data->path, machine_pid) < 0)
+		return NULL;
+
+	if (stat(kallsyms_name, &st)) {
+		free(kallsyms_name);
+		return NULL;
+	}
+
+	return kallsyms_name;
+}
+
 bool is_perf_data(const char *path)
 {
 	bool ret = false;
diff --git a/tools/perf/util/data.h b/tools/perf/util/data.h
index 7de53d6e2d7f..173132d502f5 100644
--- a/tools/perf/util/data.h
+++ b/tools/perf/util/data.h
@@ -101,5 +101,6 @@ unsigned long perf_data__size(struct perf_data *data);
 int perf_data__make_kcore_dir(struct perf_data *data, char *buf, size_t buf_sz);
 bool has_kcore_dir(const char *path);
 char *perf_data__kallsyms_name(struct perf_data *data);
+char *perf_data__guest_kallsyms_name(struct perf_data *data, pid_t machine_pid);
 bool is_perf_data(const char *path);
 #endif /* __PERF_DATA_H */
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 5d7daf7cb7bc..d40b23c71420 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -48,6 +48,7 @@ struct machine {
 	bool		  single_address_space;
 	char		  *root_dir;
 	char		  *mmap_name;
+	char		  *kallsyms_filename;
 	struct threads    threads[THREADS__TABLE_SIZE];
 	struct vdso_info  *vdso_info;
 	struct perf_env   *env;
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 7ea0b91013ea..98e16659a149 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -2772,6 +2772,8 @@ static int perf_session__register_guest(struct perf_session *session, pid_t mach
 		return -ENOMEM;
 	thread__put(thread);
 
+	machine->kallsyms_filename = perf_data__guest_kallsyms_name(session->data, machine_pid);
+
 	return 0;
 }
 
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index f72baf636724..a4b22caa7c24 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -2300,11 +2300,13 @@ static int dso__load_kernel_sym(struct dso *dso, struct map *map)
 static int dso__load_guest_kernel_sym(struct dso *dso, struct map *map)
 {
 	int err;
-	const char *kallsyms_filename = NULL;
+	const char *kallsyms_filename;
 	struct machine *machine = map__kmaps(map)->machine;
 	char path[PATH_MAX];
 
-	if (machine__is_default_guest(machine)) {
+	if (machine->kallsyms_filename) {
+		kallsyms_filename = machine->kallsyms_filename;
+	} else if (machine__is_default_guest(machine)) {
 		/*
 		 * if the user specified a vmlinux filename, use it and only
 		 * it, reporting errors to the user if it cannot be used.
-- 
2.25.1