linux-kernel - Re: [PATCH 9/9] tools lib traceevent: Honor operator priority

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Date:	Mon, 6 Apr 2015 10:45:04 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Joonsoo Kim <js1304@...il.com>, linux-mm@...ck.org
Subject: Re: [PATCH 9/9] tools lib traceevent: Honor operator priority

On Mon,  6 Apr 2015 14:36:16 +0900
Namhyung Kim <namhyung@...nel.org> wrote:

> Currently it ignores operator priority and just sets processed args as a
> right operand.  But it could result in priority inversion in case that
> the right operand is also a operator arg and its priority is lower.
> 
> For example, following print format is from new kmem events.
> 
>   "page=%p", REC->pfn != -1UL ? (((struct page *)(0xffffea0000000000UL)) + (REC->pfn)) : ((void *)0)
> 
> But this was treated as below:
> 
>   REC->pfn != ((null - 1UL) ? ((struct page *)0xffffea0000000000UL + REC->pfn) : (void *) 0)
> 
> In this case, the right arg was '?' operator which has lower priority.
> But it just sets the whole arg so making the output confusing - page was
> always 0 or 1 since that's the result of logical operation.
> 
> With this patch, it can handle it properly like following:
> 
>   ((REC->pfn != (null - 1UL)) ? ((struct page *)0xffffea0000000000UL + REC->pfn) : (void *) 0)

Nice catch. One nit.

> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/lib/traceevent/event-parse.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
> index 6d31b6419d37..604bea5c3fb0 100644
> --- a/tools/lib/traceevent/event-parse.c
> +++ b/tools/lib/traceevent/event-parse.c
> @@ -1939,7 +1939,22 @@ process_op(struct event_format *event, struct print_arg *arg, char **tok)
>  			goto out_warn_free;
>  
>  		type = process_arg_token(event, right, tok, type);
> -		arg->op.right = right;
> +
> +		if (right->type == PRINT_OP &&
> +		    get_op_prio(arg->op.op) < get_op_prio(right->op.op)) {
> +			struct print_arg tmp;
> +
> +			/* swap ops according to the priority */

This isn't really a swap. Better term to use is "rotate".

But other than that,

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> +			arg->op.right = right->op.left;
> +
> +			tmp = *arg;
> +			*arg = *right;
> +			*right = tmp;
> +
> +			arg->op.left = right;
> +		} else {
> +			arg->op.right = right;
> +		}
>  
>  	} else if (strcmp(token, "[") == 0) {
>  

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