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

[Leo Yan]

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
>