linux-kernel - RE: [PATCH v2 2/4] perf probe: Fix list result when address is zero

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Date:	Wed, 26 Aug 2015 09:29:42 +0000
From:	平松雅巳 / HIRAMATU，MASAMI 
	<masami.hiramatsu.pt@...achi.com>
To:	"'Wang Nan'" <wangnan0@...wei.com>,
	"acme@...nel.org" <acme@...nel.org>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"pi3orama@....com" <pi3orama@....com>,
	sysp-manager <cti.systems-productivity-manager.ts@...achi.com>
Subject: RE: [PATCH v2 2/4] perf probe: Fix list result when address is zero

> From: Wang Nan [mailto:wangnan0@...wei.com]
> 
> When manually added uprobe point with zero address, 'perf probe -l'
> reports error. For example:
> 
>  # echo p:probe_libc/abs_0 /path/to/lib.bin:0x0 arg1=%ax > \
>            /sys/kernel/debug/tracing/uprobe_events
> 
>  # perf probe -l
>  Error: Failed to show event list.
> 
> Probing at 0x0 is possible and useful when lib.bin is not a normal
> shared object but is manually mapped. However, in this case kernel
> report:
> 
>  # cat /sys/kernel/debug/tracing/uprobe_events
>  p:probe_libc/abs_0 /tmp/oxygen_root/lib64/libc-2.18.so:0x          (null) arg1=%ax
> 
> This patch supports the above kernel output.

Former part is OK to me.

> 
> In addition, this patch also fixes convert_to_perf_probe_point() that,
> if failed to find probe point from both of dwarf and map, in all cases
> pp->function should be filled with a strdup() result, or the following
> ENOMEM error code is incorrect. Remove !tp->module && !is_kprobe
> condition so always use address to build function name if symbol is not
> found.

No, I think this should be included in 3/4, since until that perf probe
doesn't support absolute address on kernel.

Thank you,

> 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> ---
>  tools/perf/util/probe-event.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
> index ef325a2..3ce223d 100644
> --- a/tools/perf/util/probe-event.c
> +++ b/tools/perf/util/probe-event.c
> @@ -1521,9 +1521,31 @@ int parse_probe_trace_command(const char *cmd, struct probe_trace_event *tev)
>  	} else
>  		p = argv[1];
>  	fmt1_str = strtok_r(p, "+", &fmt);
> -	if (fmt1_str[0] == '0')	/* only the address started with 0x */
> -		tp->address = strtoul(fmt1_str, NULL, 0);
> -	else {
> +	/* only the address started with 0x */
> +	if (fmt1_str[0] == '0')	{
> +		/*
> +		 * Fix a special case:
> +		 * if address == 0, kernel reports something like:
> +		 * p:probe_libc/abs_0 /lib/libc-2.18.so:0x          (null) arg1=%ax
> +		 * Newer kernel may fix that, but we want to
> +		 * support old kernel also.
> +		 */
> +		if (strcmp(fmt1_str, "0x") == 0) {
> +			if (!argv[2] || strcmp(argv[2], "(null)")) {
> +				ret = -EINVAL;
> +				goto out;
> +			}
> +			tp->address = 0;
> +
> +			free(argv[2]);
> +			for (i = 2; argv[i + 1] != NULL; i++)
> +				argv[i] = argv[i + 1];
> +
> +			argv[i] = NULL;
> +			argc -= 1;
> +		} else
> +			tp->address = strtoul(fmt1_str, NULL, 0);
> +	} else {
>  		/* Only the symbol-based probe has offset */
>  		tp->symbol = strdup(fmt1_str);
>  		if (tp->symbol == NULL) {
> @@ -1868,7 +1890,7 @@ static int convert_to_perf_probe_point(struct probe_trace_point *tp,
>  	if (tp->symbol) {
>  		pp->function = strdup(tp->symbol);
>  		pp->offset = tp->offset;
> -	} else if (!tp->module && !is_kprobe) {
> +	} else {
>  		ret = e_snprintf(buf, 128, "0x%" PRIx64, (u64)tp->address);
>  		if (ret < 0)
>  			return ret;
> --
> 1.8.3.4