linux-kernel - Re: [PATCH 2/3] perf alias: Rebuild alias expression string to make it comparable

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Date:   Thu, 14 Jun 2018 08:53:14 -0500
From:   Paul Clarke <pc@...ibm.com>
To:     Thomas Richter <tmricht@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org, jolsa@...hat.com
Cc:     brueckner@...ux.vnet.ibm.com, schwidefsky@...ibm.com,
        heiko.carstens@...ibm.com
Subject: Re: [PATCH 2/3] perf alias: Rebuild alias expression string to make
 it comparable

On 06/14/2018 06:48 AM, Thomas Richter wrote:
> PMU alias definitions in sysfs files may have spaces, newlines
> and number with leading zeroes. Same alias definitions may
> also appear in JSON files without spaces, etc.
> 
> Scan alias definitions and remove leading zeroes, spaces,
> newlines, etc and rebuild string to make alias->str member
> comparable.
> 
> s390 for example  has terms specified as
> event=0x0091 (read from files ../<PMU>/events/<FILE>
> and terms specified as event=0x91 (read from JSON files).
> 
> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
> ---
>  tools/perf/util/pmu.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
> index 26c79a9c4142..da8f243743d3 100644
> --- a/tools/perf/util/pmu.c
> +++ b/tools/perf/util/pmu.c
> @@ -241,9 +241,11 @@ static int __perf_pmu__new_alias(struct list_head *list, char *dir, char *name,
>  				 char *metric_expr,
>  				 char *metric_name)
>  {
> +	struct parse_events_term *term;
>  	struct perf_pmu_alias *alias;
>  	int ret;
>  	int num;
> +	char newval[256];

How was 256 chosen?

> 
>  	alias = malloc(sizeof(*alias));
>  	if (!alias)
> @@ -262,6 +264,27 @@ static int __perf_pmu__new_alias(struct list_head *list, char *dir, char *name,
>  		return ret;
>  	}
> 
> +	/* Scan event and remove leading zeroes, spaces, newlines, some
> +	 * platforms have terms specified as
> +	 * event=0x0091 (read from files ../<PMU>/events/<FILE>
> +	 * and terms specified as event=0x91 (read from JSON files).
> +	 *
> +	 * Rebuild string to make alias->str member comparable.
> +	 */
> +	memset(newval, 0, sizeof(newval));
> +	ret = 0;
> +	list_for_each_entry(term, &alias->terms, list) {
> +		if (ret)
> +			ret += scnprintf(newval + ret, sizeof(newval) - ret,
> +					 ",");
> +		if (term->type_val == PARSE_EVENTS__TERM_TYPE_NUM)
> +			ret += scnprintf(newval + ret, sizeof(newval) - ret,
> +					 "%s=%#x", term->config, term->val.num);
> +		else if (term->type_val == PARSE_EVENTS__TERM_TYPE_STR)
> +			ret += scnprintf(newval + ret, sizeof(newval) - ret,
> +					 "%s=%s", term->config, term->val.str);

If we exceed 256, we just suddenly terminate the rebuilding without reporting any issues.

> +	}
> +
>  	alias->name = strdup(name);
>  	if (dir) {
>  		/*
> @@ -285,7 +308,7 @@ static int __perf_pmu__new_alias(struct list_head *list, char *dir, char *name,
>  		snprintf(alias->unit, sizeof(alias->unit), "%s", unit);
>  	}
>  	alias->per_pkg = perpkg && sscanf(perpkg, "%d", &num) == 1 && num == 1;
> -	alias->str = strdup(val);
> +	alias->str = strdup(newval);
> 
>  	list_add_tail(&alias->list, list);
> 

PC