From: Li Huafei <lihuafei1@xxxxxxxxxx>
[ Upstream commit 3cb17cce1e76ccc5499915a4d7e095a1ad6bf7ff ]
If we just check whether the variable can be converted, 'tvar' should be
a null pointer. However, the null pointer check is missing in the
'Constant value' execution path.
The following cases can trigger this problem:
$ cat test.c
#include <stdio.h>
void main(void)
{
int a;
const int b = 1;
asm volatile("mov %1, %0" : "=r"(a): "i"(b));
printf("a: %d\n", a);
}
$ gcc test.c -o test -O -g
$ sudo ./perf probe -x ./test -L "main"
<main@/home/lhf/test.c:0>
0 void main(void)
{
2 int a;
const int b = 1;
asm volatile("mov %1, %0" : "=r"(a): "i"(b));
6 printf("a: %d\n", a);
}
$ sudo ./perf probe -x ./test -V "main:6"
Segmentation fault
The check on 'tvar' is added. If 'tavr' is a null pointer, we return 0
to indicate that the variable can be converted. Now, we can successfully
show the variables that can be accessed.
$ sudo ./perf probe -x ./test -V "main:6"
Available variables at main:6
@<main+13>
char* __fmt
int a
int b
However, the variable 'b' cannot be tracked.
$ sudo ./perf probe -x ./test -D "main:6 b"
Failed to find the location of the 'b' variable at this address.
Perhaps it has been optimized out.
Use -V with the --range option to show 'b' location range.
Error: Failed to add events.
This is because __die_find_variable_cb() did not successfully match
variable 'b', which has the DW_AT_const_value attribute instead of
DW_AT_location. We added support for DW_AT_const_value in
__die_find_variable_cb(). With this modification, we can successfully
track the variable 'b'.
$ sudo ./perf probe -x ./test -D "main:6 b"
p:probe_test/main_L6 /home/lhf/test:0x1156 b=\1:s32
Fixes: 66f69b219716 ("perf probe: Support DW_AT_const_value constant value")
Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
Tested-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Frank Ch. Eigler <fche@xxxxxxxxxx>
Cc: Jianlin Lv <jianlin.lv@xxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
Cc: Yang Jihong <yangjihong1@xxxxxxxxxx>
Cc: Zhang Jinhao <zhangjinhao2@xxxxxxxxxx>
http://lore.kernel.org/lkml/20210601092750.169601-1-lihuafei1@xxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
tools/perf/util/dwarf-aux.c | 8 ++++++--
tools/perf/util/probe-finder.c | 3 +++
2 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index 7b2d471a6419..4343356f3cf9 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -975,9 +975,13 @@ static int __die_find_variable_cb(Dwarf_Die *die_mem, void *data)
if ((tag == DW_TAG_formal_parameter ||
tag == DW_TAG_variable) &&
die_compare_name(die_mem, fvp->name) &&
- /* Does the DIE have location information or external instance? */
+ /*
+ * Does the DIE have location information or const value
+ * or external instance?
+ */
(dwarf_attr(die_mem, DW_AT_external, &attr) ||
- dwarf_attr(die_mem, DW_AT_location, &attr)))
+ dwarf_attr(die_mem, DW_AT_location, &attr) ||
+ dwarf_attr(die_mem, DW_AT_const_value, &attr)))
return DIE_FIND_CB_END;
if (dwarf_haspc(die_mem, fvp->addr))
return DIE_FIND_CB_CONTINUE;
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index 1b118c9c86a6..bba61b95a37a 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -190,6 +190,9 @@ static int convert_variable_location(Dwarf_Die *vr_die, Dwarf_Addr addr,
immediate_value_is_supported()) {
Dwarf_Sword snum;
+ if (!tvar)
+ return 0;
+
dwarf_formsdata(&attr, &snum);
ret = asprintf(&tvar->value, "\\%ld", (long)snum);
--
2.30.2
