linux-kernel - Re: [PATCH] tracing/histograms: Fix parsing of "sym-offset" modifier

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Date:   Wed, 07 Jul 2021 11:30:46 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH] tracing/histograms: Fix parsing of "sym-offset" modifier

Hi Steve,

On Wed, 2021-07-07 at 11:08 -0400, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> With the addition of simple mathematical operations (plus and minus),
> the
> parsing of the "sym-offset" modifier broke, as it took the '-' part
> of the
> "sym-offset" as a minus, and tried to break it up into a mathematical
> operation of "field.sym - offset", in which case it failed to parse
> (unless the event had a field called "offset").
> 
> Both .sym and .sym-offset modifiers should not be entered into
> mathematical calculations anyway. If ".sym-offset" is found in the
> modifier, then simply make it not an operation that can be calculated
> on.
> 
> Cc: stable@...r.kernel.org
> Fixes: 100719dcef447 ("tracing: Add simple expression support to hist
> triggers")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  kernel/trace/trace_events_hist.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_hist.c
> b/kernel/trace/trace_events_hist.c
> index ba03b7d84fc2..0207aeed31e6 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1555,6 +1555,13 @@ static int contains_operator(char *str)
>  
>  	switch (*op) {
>  	case '-':
> +		/*
> +		 * Unfortunately, the modifier ".sym-offset"
> +		 * can confuse things.
> +		 */

Good catch.

> +		if (op - str >= 4 && !strncmp(op - 4, ".sym-offset",
> 11))
> +			return FIELD_OP_NONE;
> +
>  		if (*str == '-')
>  			field_op = FIELD_OP_UNARY_MINUS;
>  		else

Reviewed-by: Tom Zanussi <zanussi@...nel.org>