From: Li Huafei lihuafei1@huawei.com
[ 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@huawei.com Tested-by: Arnaldo Carvalho de Melo acme@redhat.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Frank Ch. Eigler fche@redhat.com Cc: Jianlin Lv jianlin.lv@arm.com Cc: Jiri Olsa jolsa@redhat.com Cc: Mark Rutland mark.rutland@arm.com Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Namhyung Kim namhyung@kernel.org Cc: Peter Zijlstra peterz@infradead.org Cc: Srikar Dronamraju srikar@linux.vnet.ibm.com Cc: Yang Jihong yangjihong1@huawei.com Cc: Zhang Jinhao zhangjinhao2@huawei.com http://lore.kernel.org/lkml/20210601092750.169601-1-lihuafei1@huawei.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 76dd349aa48d..fdafbfcef687 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);