linux-kernel - Re: [PATCH] perf machine: Fix load kernel symbol with '-k' option

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Date:   Wed, 7 Mar 2018 14:09:24 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Leo Yan <leo.yan@...aro.org>, Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perf machine: Fix load kernel symbol with '-k' option

Hi Leo,

On 27 February 2018 at 00:17, Leo Yan <leo.yan@...aro.org> wrote:
> On Hikey arm64 octa A53 platform, when use command './perf report -v
> -k vmlinux --stdio' it outputs below error info, and it skips to load
> kernel symbol and doesn't print symbol for event:
> Failed to open [kernel.kallsyms]_text, continuing without symbols.
>
> The regression is introduced by commit ("8c7f1bb37b29 perf machine: Move
> kernel mmap name into struct machine"), which changes the logic for
> machine mmap_name by removing function machine__mmap_name() and always
> use 'machine->mmap_name'.  Comparing difference between
> machine__mmap_name() and 'machine->mmap_name', the later one includes
> the string for specified kernel vmlinux string with option '-k' in
> command, but the old function machine__mmap_name() ignores vmlinux
> path string.  As result, event's mmap file name doesn't match with
> machine mmap file name anymore and it skips to load kernel symbol from
> vmlinux file.
>
> To resolve this issue, this patch adds extra checking for
> 'machine->mmap_name', when its start char is not '[' then we can know
> it includes vmlinux path string specified for option '-k'. For this
> case it sets 'is_kernel_mmap = true' and run into flow to load kernel
> symbol from vmlinux.
>
> This patch has been verified with two commands: './perf report -v
> -k vmlinux --stdio' and './perf script -v -F cpu,event,ip,sym,symoff
> -k vmlinux'.
>
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/machine.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
> index 12b7427..ffd709d 100644
> --- a/tools/perf/util/machine.c
> +++ b/tools/perf/util/machine.c
> @@ -1299,9 +1299,18 @@ static int machine__process_kernel_mmap_event(struct machine *machine,
>         else
>                 kernel_type = DSO_TYPE_GUEST_KERNEL;
>
> -       is_kernel_mmap = memcmp(event->mmap.filename,
> -                               machine->mmap_name,
> -                               strlen(machine->mmap_name) - 1) == 0;
> +       /*
> +        * If machine mmap_name doesn't start with char '[', it includes
> +        * the specified kernel vmlinux name with option '-k'.  So set
> +        * is_kernel_mmap as true to create machine symbol map.
> +        */
> +       if (machine->mmap_name[0] != '[')

I have tested your patch and it indeed solves the problem but I
suggest to replace the above with:

    if (symbol_conf.vmlinux_name)

That is consistent with the test in function machine__set_mmap_name()
and doesn't rely on a user specified input to operate properly.

Thanks,
Mathieu

> +               is_kernel_mmap = true;
> +       else
> +               is_kernel_mmap = memcmp(event->mmap.filename,
> +                                       machine->mmap_name,
> +                                       strlen(machine->mmap_name) - 1) == 0;
> +
>         if (event->mmap.filename[0] == '/' ||
>             (!is_kernel_mmap && event->mmap.filename[0] == '[')) {
>                 map = machine__findnew_module_map(machine, event->mmap.start,
> --
> 2.7.4
>