linux-kernel - [tip:perf/core] perf probe: Use right type to access array elements

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Date:   Mon, 19 Mar 2018 23:36:17 -0700
From:   tip-bot for Masami Hiramatsu <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rostedt@...dmis.org,
        shuah@...nel.org, acme@...hat.com, mingo@...nel.org,
        mhiramat@...nel.org, ravi.bangoria@...ux.vnet.ibm.com,
        tom.zanussi@...ux.intel.com, hpa@...or.com, tglx@...utronix.de,
        namhyung@...nel.org
Subject: [tip:perf/core] perf probe: Use right type to access array elements

Commit-ID:  d0461794a1dcaf552b507e23788777f718b736a1
Gitweb:     https://git.kernel.org/tip/d0461794a1dcaf552b507e23788777f718b736a1
Author:     Masami Hiramatsu <mhiramat@...nel.org>
AuthorDate: Sat, 17 Mar 2018 21:52:25 +0900
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Mon, 19 Mar 2018 13:51:53 -0300

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 <mhiramat@...nel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc: Shuah Khan <shuah@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Tom Zanussi <tom.zanussi@...ux.intel.com>
Cc: linux-kselftest@...r.kernel.org
Cc: linux-trace-users@...r.kernel.org
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 <acme@...hat.com>
---
 tools/perf/util/probe-finder.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index a5731de0e5eb..c37fbef1711d 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -423,20 +423,20 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 		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));
@@ -448,9 +448,6 @@ static int convert_variable_fields(Dwarf_Die *vr_die, const char *varname,
 				*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 */