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

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Date:   Tue, 19 Jul 2022 17:51:59 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 22/35] perf tools: Automatically use guest kcore_dir if present

On Mon, Jul 11, 2022 at 2:33 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>
> 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)

Is there a missing free for this in perf_data__close ?

Thanks,
Ian

> +               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
>