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

tip-bot for Masami Hiramatsu
2018-03-20T06:36:41Z

Commit-ID: d0461794a1dcaf552b507e23788777f718b736a1
Gitweb: https://git.kernel.org/tip/d0461794a1dcaf552b507e23788777f718b736a1
Author: Masami Hiramatsu <mhiramat@kernel.org>
AuthorDate: Sat, 17 Mar 2018 21:52:25 +0900
Committer: Arnaldo Carvalho de Melo <acme@redhat.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@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: linux-kselftest@vger.kernel.org
Cc: linux-trace-users@vger.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@redhat.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 */