perf probe: Use right type to access array elements

Current 'perf probe' converts the type of array-elements incorrectly. It
always converts the types as a pointer of array. This passes the "array"
type DIE to the type converter so that it can get correct "element of
array" type DIE from it.

E.g.
====
$ cat hello.c
#include <stdio.h>

void foo(int a[])
{
printf("%d\n", a[1]);
}

void main()
{
int a[3] = {4, 5, 6};
printf("%d\n", a[0]);
foo(a);
}

$ gcc -g hello.c -o hello
$ perf probe -x ./hello -D "foo a[1]"
====

Without this fix, above outputs
====
p:probe_hello/foo /tmp/hello:0x4d3 a=+4(-8(%bp)):u64
====
The "u64" means "int *", but a[1] is "int".

With this,
====
p:probe_hello/foo /tmp/hello:0x4d3 a=+4(-8(%bp)):s32
====
So, "int" correctly converted to "s32"

Signed-off-by: Masami Hiramatsu <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Ravi Bangoria <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Tom Zanussi <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Fixes: b2a3c12b7442 ("perf probe: Support tracing an entry of array")
Link: http://lkml.kernel.org/r/152129114502.31874.2474068470011496356.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/probe-finder.c

···
 		pr_warning("Failed to get the type of %s.\n", varname);
 		return -ENOENT;
 	}
-	pr_debug2("Var real type: (%x)\n", (unsigned)dwarf_dieoffset(&type));
+	pr_debug2("Var real type: %s (%x)\n", dwarf_diename(&type),
+		  (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));
+		/* Save original type for next field or type */
+		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",
+		pr_debug2("Array real type: %s (%x)\n", dwarf_diename(&type),
 			 (unsigned)dwarf_dieoffset(&type));
 		if (tag == DW_TAG_pointer_type) {
 			ref = zalloc(sizeof(struct probe_trace_arg_ref));
···
 				*ref_ptr = ref;
 		}
 		ref->offset += dwarf_bytesize(&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 */