Re: [RFC PATCH 6/6] perf cs-etm: Add warnings for missing DSOs

From: Leo Yan
Date: Mon Aug 02 2021 - 11:41:57 EST


On Thu, Jul 29, 2021 at 04:58:05PM +0100, James Clark wrote:
> Currently decode will silently fail if no binary data is available for
> the decode. This is made worse if only partial data is available because
> the decode will appear to work, but any trace from that missing DSO will
> silently not be generated.
>
> Add a UI popup once if there is any data missing, and then warn in the
> bottom left for each individual DSO that's missing.
>
> Signed-off-by: James Clark <james.clark@xxxxxxx>
> ---
> tools/perf/util/cs-etm.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 32ad92d3e454..e6851260d059 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -746,8 +746,16 @@ static u32 cs_etm__mem_access(struct cs_etm_queue *etmq, u8 trace_chan_id,
>
> len = dso__data_read_offset(al.map->dso, machine, offset, buffer, size);
>
> - if (len <= 0)
> + if (len <= 0) {
> + ui__warning_once("CS ETM Trace: Missing DSO. Use 'perf archive' to export data from the traced system.\n");
> + if (!al.map->dso->auxtrace_warned) {
> + pr_err("CS ETM Trace: Debug data not found for address %#"PRIx64" in %s\n",
> + address,
> + al.map->dso->long_name ? al.map->dso->long_name : "Unknown");
> + al.map->dso->auxtrace_warned = true;
> + }

This is very useful.

Just one comment: in particularly if the perf fails to find the kernel
symbols, the user needs to enable config "CONFIG_PROC_KCORE=y" or
specify option "-k /path/to/vmlinux". In this case, using 'perf
archive' is not helpful. So I think the UI warning can be imporved
like:

ui__warning_once("CS ETM Trace: Missing DSO. Use 'perf archive' to export data from the traced system.\n"
" Enable CONFIG_PROC_KCORE or use option '-k /path/to/vmlinux' for kernel symbols\n");

With this improvement, the patch looks good to me:

Reviewed-by: Leo Yan <leo.yan@xxxxxxxxxx>

> return 0;
> + }
>
> return len;
> }
> --
> 2.28.0
>