linux-kernel - Re: [PATCH v3 2/7] perf probe: Verify given line is a representive line

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Date:   Mon, 18 Nov 2019 18:59:09 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v3 2/7] perf probe: Verify given line is a representive
 line

Em Mon, Nov 18, 2019 at 05:12:00PM +0900, Masami Hiramatsu escreveu:
> Verify user given probe line is a representive line (which doesn't
> share the address with other lines or the line is the least line
> among the lines which shares same address), and if not, it shows
> what is the representive line.
> 
> Without this fix, user can put a probe on the lines which is not a
> a representive line. But since this is not a representive line,
> perf probe -l shows a representive line number instead of user given
> line number. e.g. (put kernel_read:3, but listed as kernel_read:2)
> 
>   # perf probe -a kernel_read:3
>   Added new event:
>     probe:kernel_read    (on kernel_read:3)
> 
>   You can now use it in all perf tools, such as:
> 
>   	perf record -e probe:kernel_read -aR sleep 1
> 
>   # perf probe -l
>     probe:kernel_read    (on kernel_read:2@...ux-5.0.0/fs/read_write.c)
> 
> With this fix, perf probe doesn't allow user to put a probe on
> a representive line, and tell what is the representive line.
> 
>   # perf probe -a kernel_read:3
>   This line is sharing the addrees with other lines.
>   Please try to probe at kernel_read:2 instead.
>     Error: Failed to add events.

Thanks, this fixes the problem I reported, applied.

- Arnaldo
 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  tools/perf/util/probe-finder.c |   36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
> index 9ecea45da4ca..ef1b320cedf8 100644
> --- a/tools/perf/util/probe-finder.c
> +++ b/tools/perf/util/probe-finder.c
> @@ -776,6 +776,39 @@ static Dwarf_Die *find_best_scope(struct probe_finder *pf, Dwarf_Die *die_mem)
>  	return fsp.found ? die_mem : NULL;
>  }
>  
> +static int verify_representive_line(struct probe_finder *pf, const char *fname,
> +				int lineno, Dwarf_Addr addr)
> +{
> +	const char *__fname, *__func = NULL;
> +	Dwarf_Die die_mem;
> +	int __lineno;
> +
> +	/* Verify line number and address by reverse search */
> +	if (cu_find_lineinfo(&pf->cu_die, addr, &__fname, &__lineno) < 0)
> +		return 0;
> +
> +	pr_debug2("Reversed line: %s:%d\n", __fname, __lineno);
> +	if (strcmp(fname, __fname) || lineno == __lineno)
> +		return 0;
> +
> +	pr_warning("This line is sharing the addrees with other lines.\n");
> +
> +	if (pf->pev->point.function) {
> +		/* Find best match function name and lines */
> +		pf->addr = addr;
> +		if (find_best_scope(pf, &die_mem)
> +		    && die_match_name(&die_mem, pf->pev->point.function)
> +		    && dwarf_decl_line(&die_mem, &lineno) == 0) {
> +			__func = dwarf_diename(&die_mem);
> +			__lineno -= lineno;
> +		}
> +	}
> +	pr_warning("Please try to probe at %s:%d instead.\n",
> +		   __func ? : __fname, __lineno);
> +
> +	return -ENOENT;
> +}
> +
>  static int probe_point_line_walker(const char *fname, int lineno,
>  				   Dwarf_Addr addr, void *data)
>  {
> @@ -786,6 +819,9 @@ static int probe_point_line_walker(const char *fname, int lineno,
>  	if (lineno != pf->lno || strtailcmp(fname, pf->fname) != 0)
>  		return 0;
>  
> +	if (verify_representive_line(pf, fname, lineno, addr))
> +		return -ENOENT;
> +
>  	pf->addr = addr;
>  	sc_die = find_best_scope(pf, &die_mem);
>  	if (!sc_die) {

-- 

- Arnaldo