perf probe: Show accessible local variables

Add -V (--vars) option for listing accessible local variables at given probe
point. This will help finding which local variables are available for event
arguments.

e.g.)
 # perf probe -V call_timer_fn:23
 Available variables at call_timer_fn:23
         @<run_timer_softirq+345>
                 function_type*  fn
                 int     preempt_count
                 long unsigned int       data
                 struct list_head        work_list
                 struct list_head*       head
                 struct timer_list*      timer
                 struct tvec_base*       base

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20101021101323.3542.40282.stgit@ltc236.sdl.hitachi.co.jp>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-probe.txt

@@ -17,6 +17,8 @@ or
 'perf probe' --list
 or
 'perf probe' --line='FUNC[:RLN[+NUM|:RLN2]]|SRC:ALN[+NUM|:ALN2]'
+or
+'perf probe' --vars='PROBEPOINT'
 
 DESCRIPTION
 -----------
@@ -57,6 +59,11 @@ OPTIONS
 	Show source code lines which can be probed. This needs an argument
 	which specifies a range of the source code. (see LINE SYNTAX for detail)
 
+-V::
+--vars=::
+	Show available local variables at given probe point. The argument
+	syntax is same as PROBE SYNTAX, but NO ARGs.
+
 -f::
 --force::
 	Forcibly add events with existing name.

tools/perf/builtin-probe.c

@@ -50,6 +50,8 @@ static struct {
 	bool list_events;
 	bool force_add;
 	bool show_lines;
+	bool show_vars;
+	bool mod_events;
 	int nevents;
 	struct perf_probe_event events[MAX_PROBES];
 	struct strlist *dellist;
@@ -57,7 +59,6 @@ static struct {
 	int max_probe_points;
 } params;
 
-
 /* Parse an event definition. Note that any error must die. */
 static int parse_probe_event(const char *str)
 {
@@ -92,6 +93,7 @@ static int parse_probe_event_argv(int argc, const char **argv)
 	len = 0;
 	for (i = 0; i < argc; i++)
 		len += sprintf(&buf[len], "%s ", argv[i]);
+	params.mod_events = true;
 	ret = parse_probe_event(buf);
 	free(buf);
 	return ret;
@@ -100,9 +102,10 @@ static int parse_probe_event_argv(int argc, const char **argv)
 static int opt_add_probe_event(const struct option *opt __used,
 			      const char *str, int unset __used)
 {
-	if (str)
+	if (str) {
+		params.mod_events = true;
 		return parse_probe_event(str);
-	else
+	} else
 		return 0;
 }
 
@@ -110,6 +113,7 @@ static int opt_del_probe_event(const struct option *opt __used,
 			       const char *str, int unset __used)
 {
 	if (str) {
+		params.mod_events = true;
 		if (!params.dellist)
 			params.dellist = strlist__new(true, NULL);
 		strlist__add(params.dellist, str);
@@ -130,6 +134,25 @@ static int opt_show_lines(const struct option *opt __used,
 
 	return ret;
 }
+
+static int opt_show_vars(const struct option *opt __used,
+			 const char *str, int unset __used)
+{
+	struct perf_probe_event *pev = &params.events[params.nevents];
+	int ret;
+
+	if (!str)
+		return 0;
+
+	ret = parse_probe_event(str);
+	if (!ret && pev->nargs != 0) {
+		pr_err("  Error: '--vars' doesn't accept arguments.\n");
+		return -EINVAL;
+	}
+	params.show_vars = true;
+
+	return ret;
+}
 #endif
 
 static const char * const probe_usage[] = {
@@ -139,6 +162,7 @@ static const char * const probe_usage[] = {
 	"perf probe --list",
 #ifdef DWARF_SUPPORT
 	"perf probe --line 'LINEDESC'",
+	"perf probe --vars 'PROBEPOINT'",
 #endif
 	NULL
 };
@@ -180,6 +204,9 @@ static const struct option options[] = {
 	OPT_CALLBACK('L', "line", NULL,
 		     "FUNC[:RLN[+NUM|-RLN2]]|SRC:ALN[+NUM|-ALN2]",
 		     "Show source code lines.", opt_show_lines),
+	OPT_CALLBACK('V', "vars", NULL,
+		     "FUNC[@SRC][+OFF|%return|:RL|;PT]|SRC:AL|SRC;PT",
+		     "Show accessible variables on PROBEDEF", opt_show_vars),
 	OPT_STRING('k', "vmlinux", &symbol_conf.vmlinux_name,
 		   "file", "vmlinux pathname"),
 	OPT_STRING('s', "source", &symbol_conf.source_prefix,
@@ -217,7 +244,7 @@ int cmd_probe(int argc, const char **argv, const char *prefix __used)
 		usage_with_options(probe_usage, options);
 
 	if (params.list_events) {
-		if (params.nevents != 0 || params.dellist) {
+		if (params.mod_events) {
 			pr_err("  Error: Don't use --list with --add/--del.\n");
 			usage_with_options(probe_usage, options);
 		}
@@ -225,6 +252,10 @@ int cmd_probe(int argc, const char **argv, const char *prefix __used)
 			pr_err("  Error: Don't use --list with --line.\n");
 			usage_with_options(probe_usage, options);
 		}
+		if (params.show_vars) {
+			pr_err(" Error: Don't use --list with --vars.\n");
+			usage_with_options(probe_usage, options);
+		}
 		ret = show_perf_probe_events();
 		if (ret < 0)
 			pr_err("  Error: Failed to show event list. (%d)\n",
@@ -234,9 +265,13 @@ int cmd_probe(int argc, const char **argv, const char *prefix __used)
 
 #ifdef DWARF_SUPPORT
 	if (params.show_lines) {
-		if (params.nevents != 0 || params.dellist) {
-			pr_warning("  Error: Don't use --line with"
-				   " --add/--del.\n");
+		if (params.mod_events) {
+			pr_err("  Error: Don't use --line with"
+			       " --add/--del.\n");
+			usage_with_options(probe_usage, options);
+		}
+		if (params.show_vars) {
+			pr_err(" Error: Don't use --line with --vars.\n");
 			usage_with_options(probe_usage, options);
 		}
 
@@ -245,6 +280,18 @@ int cmd_probe(int argc, const char **argv, const char *prefix __used)
 			pr_err("  Error: Failed to show lines. (%d)\n", ret);
 		return ret;
 	}
+	if (params.show_vars) {
+		if (params.mod_events) {
+			pr_err("  Error: Don't use --vars with"
+			       " --add/--del.\n");
+			usage_with_options(probe_usage, options);
+		}
+		ret = show_available_vars(params.events, params.nevents,
+					  params.max_probe_points);
+		if (ret < 0)
+			pr_err("  Error: Failed to show vars. (%d)\n", ret);
+		return ret;
+	}
 #endif
 
 	if (params.dellist) {

tools/perf/util/probe-event.c

@@ -378,6 +378,72 @@ int show_line_range(struct line_range *lr)
 	return ret;
 }
 
+static int show_available_vars_at(int fd, struct perf_probe_event *pev,
+				  int max_vls)
+{
+	char *buf;
+	int ret, i;
+	struct str_node *node;
+	struct variable_list *vls = NULL, *vl;
+
+	buf = synthesize_perf_probe_point(&pev->point);
+	if (!buf)
+		return -EINVAL;
+	pr_debug("Searching variables at %s\n", buf);
+
+	ret = find_available_vars_at(fd, pev, &vls, max_vls);
+	if (ret > 0) {
+		/* Some variables were found */
+		fprintf(stdout, "Available variables at %s\n", buf);
+		for (i = 0; i < ret; i++) {
+			vl = &vls[i];
+			/*
+			 * A probe point might be converted to
+			 * several trace points.
+			 */
+			fprintf(stdout, "\t@<%s+%lu>\n", vl->point.symbol,
+				vl->point.offset);
+			free(vl->point.symbol);
+			if (vl->vars) {
+				strlist__for_each(node, vl->vars)
+					fprintf(stdout, "\t\t%s\n", node->s);
+				strlist__delete(vl->vars);
+			} else
+				fprintf(stdout, "(No variables)\n");
+		}
+		free(vls);
+	} else
+		pr_err("Failed to find variables at %s (%d)\n", buf, ret);
+
+	free(buf);
+	return ret;
+}
+
+/* Show available variables on given probe point */
+int show_available_vars(struct perf_probe_event *pevs, int npevs,
+			int max_vls)
+{
+	int i, fd, ret = 0;
+
+	ret = init_vmlinux();
+	if (ret < 0)
+		return ret;
+
+	fd = open_vmlinux();
+	if (fd < 0) {
+		pr_warning("Failed to open debuginfo file.\n");
+		return fd;
+	}
+
+	setup_pager();
+
+	for (i = 0; i < npevs && ret >= 0; i++)
+		ret = show_available_vars_at(fd, &pevs[i], max_vls);
+
+	close(fd);
+	return ret;
+}
+
 #else	/* !DWARF_SUPPORT */
 
 static int kprobe_convert_to_perf_probe(struct probe_trace_point *tp,
@@ -409,6 +475,12 @@ int show_line_range(struct line_range *lr __unused)
 	return -ENOSYS;
 }
 
+int show_available_vars(struct perf_probe_event *pevs __unused,
+			int npevs __unused, int max_probe_points __unused)
+{
+	pr_warning("Debuginfo-analysis is not supported.\n");
+	return -ENOSYS;
+}
 #endif
 
 int parse_line_range_desc(const char *arg, struct line_range *lr)

tools/perf/util/probe-event.h

@@ -90,6 +90,12 @@ struct line_range {
 	struct list_head	line_list;	/* Visible lines */
 };
 
+/* List of variables */
+struct variable_list {
+	struct probe_trace_point	point;	/* Actual probepoint */
+	struct strlist			*vars;	/* Available variables */
+};
+
 /* Command string to events */
 extern int parse_perf_probe_command(const char *cmd,
 				    struct perf_probe_event *pev);
@@ -115,6 +121,8 @@ extern int add_perf_probe_events(struct perf_probe_event *pevs, int npevs,
 extern int del_perf_probe_events(struct strlist *dellist);
 extern int show_perf_probe_events(void);
 extern int show_line_range(struct line_range *lr);
+extern int show_available_vars(struct perf_probe_event *pevs, int npevs,
+			       int max_probe_points);
 
 
 /* Maximum index number of event-name postfix */

tools/perf/util/probe-finder.h

@@ -25,17 +25,22 @@ extern int find_probe_trace_events(int fd, struct perf_probe_event *pev,
 extern int find_perf_probe_point(int fd, unsigned long addr,
 				 struct perf_probe_point *ppt);
 
+/* Find a line range */
 extern int find_line_range(int fd, struct line_range *lr);
 
+/* Find available variables */
+extern int find_available_vars_at(int fd, struct perf_probe_event *pev,
+				  struct variable_list **vls, int max_points);
+
 #include <dwarf.h>
 #include <libdw.h>
 #include <version.h>
 
 struct probe_finder {
 	struct perf_probe_event	*pev;		/* Target probe event */
-	struct probe_trace_event *tevs;		/* Result trace events */
-	int			ntevs;		/* Number of trace events */
-	int			max_tevs;	/* Max number of trace events */
+
+	/* Callback when a probe point is found */
+	int (*callback)(Dwarf_Die *sp_die, struct probe_finder *pf);
 
 	/* For function searching */
 	int			lno;		/* Line number */
@@ -53,6 +58,20 @@ struct probe_finder {
 	struct probe_trace_arg	*tvar;		/* Current result variable */
 };
 
+struct trace_event_finder {
+	struct probe_finder	pf;
+	struct probe_trace_event *tevs;		/* Found trace events */
+	int			ntevs;		/* Number of trace events */
+	int			max_tevs;	/* Max number of trace events */
+};
+
+struct available_var_finder {
+	struct probe_finder	pf;
+	struct variable_list	*vls;		/* Found variable lists */
+	int			nvls;		/* Number of variable lists */
+	int			max_vls;	/* Max no. of variable lists */
+};
+
 struct line_finder {
 	struct line_range	*lr;		/* Target line range */