Re: [PATCH 1/2] perf expr: Force encapsulation on expr_id_data

[Jiri Olsa]

On Tue, Aug 25, 2020 at 09:29:09PM -0700, Ian Rogers wrote:
> This patch resolves some undefined behavior where variables in
> expr_id_data were accessed (for debugging) without being defined. To
> better enforce the tagged union behavior, the struct is moved into
> expr.c and accessors provided. Tag values (kinds) are explicitly
> identified.
> 
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/util/expr.c        | 64 ++++++++++++++++++++++++++++++-----
>  tools/perf/util/expr.h        | 17 +++-------
>  tools/perf/util/expr.y        |  2 +-
>  tools/perf/util/metricgroup.c |  4 +--
>  4 files changed, 62 insertions(+), 25 deletions(-)
> 
> diff --git a/tools/perf/util/expr.c b/tools/perf/util/expr.c
> index 53482ef53c41..1ca0992db86b 100644
> --- a/tools/perf/util/expr.c
> +++ b/tools/perf/util/expr.c
> @@ -17,6 +17,25 @@
>  extern int expr_debug;
>  #endif
>  
> +struct expr_id_data {
> +	union {
> +		double val;
> +		struct {
> +			double val;
> +			const char *metric_name;
> +			const char *metric_expr;
> +		} ref;
> +		struct expr_id	*parent;
> +	};
> +
> +	enum {
> +		EXPR_ID_DATA__VALUE,
> +		EXPR_ID_DATA__REF,
> +		EXPR_ID_DATA__REF_VALUE,
> +		EXPR_ID_DATA__PARENT,
> +	} kind;

I like that, it's more clear than current state ;-)

could you still put a small comment for each enum above,
as a hint what it's used for?

thanks,
jirka