perf probe: Support tracing an entry of array

Add array-entry tracing support to perf probe. This enables to trace an entry
of array which is indexed by constant value, e.g. array[0].

For example:

  $ perf probe -a 'bio_split bi->bi_io_vec[0]'

Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20100519195742.2885.5344.stgit@localhost6.localdomain6>
Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 42 insertions, 6 deletions

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index aaea16b1c60b..308664deb857 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -485,6 +485,9 @@ static int convert_variable_type(Dwarf_Die *vr_die,
                 return -ENOENT;
         }
 
+        pr_debug("%s type is %s.\n",
+                 dwarf_diename(vr_die), dwarf_diename(&type));
+
         if (cast && strcmp(cast, "string") == 0) {      /* String type */
                 ret = dwarf_tag(&type);
                 if (ret != DW_TAG_pointer_type &&
@@ -553,16 +556,44 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
         struct kprobe_trace_arg_ref *ref = *ref_ptr;
         Dwarf_Die type;
         Dwarf_Word offs;
-        int ret;
+        int ret, tag;
 
         pr_debug("converting %s in %s\n", field->name, varname);
         if (die_get_real_type(vr_die, &type) == NULL) {
                 pr_warning("Failed to get the type of %s.\n", varname);
                 return -ENOENT;
         }
-
-        /* Check the pointer and dereference */
-        if (dwarf_tag(&type) == DW_TAG_pointer_type) {
+        pr_debug2("Var real type: (%x)\n", (unsigned)dwarf_dieoffset(&type));
+        tag = dwarf_tag(&type);
+
+        if (field->name[0] == '[' &&
+            (tag == DW_TAG_array_type || tag == DW_TAG_pointer_type)) {
+                if (field->next)
+                        /* Save original type for next field */
+                        memcpy(die_mem, &type, sizeof(*die_mem));
+                /* Get the type of this array */
+                if (die_get_real_type(&type, &type) == NULL) {
+                        pr_warning("Failed to get the type of %s.\n", varname);
+                        return -ENOENT;
+                }
+                pr_debug2("Array real type: (%x)\n",
+                         (unsigned)dwarf_dieoffset(&type));
+                if (tag == DW_TAG_pointer_type) {
+                        ref = zalloc(sizeof(struct kprobe_trace_arg_ref));
+                        if (ref == NULL)
+                                return -ENOMEM;
+                        if (*ref_ptr)
+                                (*ref_ptr)->next = ref;
+                        else
+                                *ref_ptr = ref;
+                }
+                ref->offset += die_get_byte_size(&type) * field->index;
+                if (!field->next)
+                        /* Save vr_die for converting types */
+                        memcpy(die_mem, vr_die, sizeof(*die_mem));
+                goto next;
+        } else if (tag == DW_TAG_pointer_type) {
+                /* Check the pointer and dereference */
                 if (!field->ref) {
                         pr_err("Semantic error: %s must be referred by '->'\n",
                                field->name);
@@ -588,10 +619,15 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
                         *ref_ptr = ref;
         } else {
                 /* Verify it is a data structure  */
-                if (dwarf_tag(&type) != DW_TAG_structure_type) {
+                if (tag != DW_TAG_structure_type) {
                         pr_warning("%s is not a data structure.\n", varname);
                         return -EINVAL;
                 }
+                if (field->name[0] == '[') {
+                        pr_err("Semantic error: %s is not a pointor nor array.",
+                               varname);
+                        return -EINVAL;
+                }
                 if (field->ref) {
                         pr_err("Semantic error: %s must be referred by '.'\n",
                                field->name);
@@ -618,6 +654,7 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
         }
         ref->offset += (long)offs;
 
+next:
         /* Converting next field */
         if (field->next)
                 return convert_variable_fields(die_mem, field->name,
@@ -667,7 +704,6 @@ static int find_variable(Dwarf_Die *sp_die, struct probe_finder *pf)
         char buf[32], *ptr;
         int ret;
 
-        /* TODO: Support arrays */
         if (pf->pvar->name)
                 pf->tvar->name = strdup(pf->pvar->name);
         else {