perf probe: Support "$vars" meta argument syntax for local variables

Support "$vars" meta argument syntax for tracing all local variables at
probe point.

Now you can trace all available local variables (including function
parameters) at the probe point by passing $vars.

 # perf probe --add foo $vars

This automatically finds all local variables at foo() and adds it as
probe arguments.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20131011071023.15557.51770.stgit@udc4-manage.rcp.hitachi.co.jp
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 89 insertions, 9 deletions

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index 779b2dacd43f..9c6989ca2bea 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -47,7 +47,6 @@
 #include "session.h"
 
 #define MAX_CMDLEN 256
-#define MAX_PROBE_ARGS 128
 #define PERFPROBE_GROUP "probe"
 
 bool probe_event_dry_run;       /* Dry run flag */
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index c09e0a9fdf4c..5a46be968c0b 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -1136,12 +1136,78 @@ found:
         return ret;
 }
 
+struct local_vars_finder {
+        struct probe_finder *pf;
+        struct perf_probe_arg *args;
+        int max_args;
+        int nargs;
+        int ret;
+};
+
+/* Collect available variables in this scope */
+static int copy_variables_cb(Dwarf_Die *die_mem, void *data)
+{
+        struct local_vars_finder *vf = data;
+        int tag;
+
+        tag = dwarf_tag(die_mem);
+        if (tag == DW_TAG_formal_parameter ||
+            tag == DW_TAG_variable) {
+                if (convert_variable_location(die_mem, vf->pf->addr,
+                                              vf->pf->fb_ops, NULL) == 0) {
+                        vf->args[vf->nargs].var = (char *)dwarf_diename(die_mem);
+                        if (vf->args[vf->nargs].var == NULL) {
+                                vf->ret = -ENOMEM;
+                                return DIE_FIND_CB_END;
+                        }
+                        pr_debug(" %s", vf->args[vf->nargs].var);
+                        vf->nargs++;
+                }
+        }
+
+        if (dwarf_haspc(die_mem, vf->pf->addr))
+                return DIE_FIND_CB_CONTINUE;
+        else
+                return DIE_FIND_CB_SIBLING;
+}
+
+static int expand_probe_args(Dwarf_Die *sc_die, struct probe_finder *pf,
+                             struct perf_probe_arg *args)
+{
+        Dwarf_Die die_mem;
+        int i;
+        int n = 0;
+        struct local_vars_finder vf = {.pf = pf, .args = args,
+                                .max_args = MAX_PROBE_ARGS, .ret = 0};
+
+        for (i = 0; i < pf->pev->nargs; i++) {
+                /* var never be NULL */
+                if (strcmp(pf->pev->args[i].var, "$vars") == 0) {
+                        pr_debug("Expanding $vars into:");
+                        vf.nargs = n;
+                        /* Special local variables */
+                        die_find_child(sc_die, copy_variables_cb, (void *)&vf,
+                                       &die_mem);
+                        pr_debug(" (%d)\n", vf.nargs - n);
+                        if (vf.ret < 0)
+                                return vf.ret;
+                        n = vf.nargs;
+                } else {
+                        /* Copy normal argument */
+                        args[n] = pf->pev->args[i];
+                        n++;
+                }
+        }
+        return n;
+}
+
 /* Add a found probe point into trace event list */
 static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
 {
         struct trace_event_finder *tf =
                         container_of(pf, struct trace_event_finder, pf);
         struct probe_trace_event *tev;
+        struct perf_probe_arg *args;
         int ret, i;
 
         /* Check number of tevs */
@@ -1161,21 +1227,35 @@ static int add_probe_trace_event(Dwarf_Die *sc_die, struct probe_finder *pf)
         pr_debug("Probe point found: %s+%lu\n", tev->point.symbol,
                  tev->point.offset);
 
-        /* Find each argument */
-        tev->nargs = pf->pev->nargs;
-        tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
-        if (tev->args == NULL)
+        /* Expand special probe argument if exist */
+        args = zalloc(sizeof(struct perf_probe_arg) * MAX_PROBE_ARGS);
+        if (args == NULL)
                 return -ENOMEM;
-        for (i = 0; i < pf->pev->nargs; i++) {
-                pf->pvar = &pf->pev->args[i];
+
+        ret = expand_probe_args(sc_die, pf, args);
+        if (ret < 0)
+                goto end;
+
+        tev->nargs = ret;
+        tev->args = zalloc(sizeof(struct probe_trace_arg) * tev->nargs);
+        if (tev->args == NULL) {
+                ret = -ENOMEM;
+                goto end;
+        }
+
+        /* Find each argument */
+        for (i = 0; i < tev->nargs; i++) {
+                pf->pvar = &args[i];
                 pf->tvar = &tev->args[i];
                 /* Variable should be found from scope DIE */
                 ret = find_variable(sc_die, pf);
                 if (ret != 0)
-                        return ret;
+                        break;
         }
 
-        return 0;
+end:
+        free(args);
+        return ret;
 }
 
 /* Find probe_trace_events specified by perf_probe_event from debuginfo */
diff --git a/tools/perf/util/probe-finder.h b/tools/perf/util/probe-finder.h
index 3f0c29dd6ac5..d6dab0e0a937 100644
--- a/tools/perf/util/probe-finder.h
+++ b/tools/perf/util/probe-finder.h
@@ -7,6 +7,7 @@
 
 #define MAX_PROBE_BUFFER        1024
 #define MAX_PROBES               128
+#define MAX_PROBE_ARGS           128
 
 static inline int is_c_varname(const char *name)
 {