After commit 3087c61ed2c4 ("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN"),
the content of the format file under
/sys/kernel/debug/tracing/events/task/task_newtask was changed from
field:char comm[16]; offset:12; size:16; signed:0;
to
field:char comm[TASK_COMM_LEN]; offset:12; size:16; signed:0;
John reported that this change breaks older versions of perfetto.
Then Mathieu pointed out that this behavioral change was caused by the
use of __stringify(_len), which happens to work on macros, but not on enum
labels. And he also gave the suggestion on how to fix it:
:One possible solution to make this more robust would be to extend
:struct trace_event_fields with one more field that indicates the length
:of an array as an actual integer, without storing it in its stringified
:form in the type, and do the formatting in f_show where it belongs.
The result as follows after this change,
$ cat /sys/kernel/debug/tracing/events/task/task_newtask/format
field:char comm[16]; offset:12; size:16; signed:0;
Fixes: 3087c61ed2c4 ("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN")
Reported-by: John Stultz <jstultz@xxxxxxxxxx>
Debugged-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>
Cc: Kajetan Puchalski <kajetan.puchalski@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: John Stultz <jstultz@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.17+
---
include/linux/trace_events.h | 1 +
include/trace/stages/stage4_event_fields.h | 3 ++-
kernel/trace/trace.h | 1 +
kernel/trace/trace_events.c | 24 ++++++++++++++++--------
4 files changed, 20 insertions(+), 9 deletions(-)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 4342e99..0e37322 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -270,6 +270,7 @@ struct trace_event_fields {
const int align;
const int is_signed;
const int filter_type;
+ const int len;
};
int (*define_fields)(struct trace_event_call *);
};
diff --git a/include/trace/stages/stage4_event_fields.h b/include/trace/stages/stage4_event_fields.h
index affd541..306f39a 100644
--- a/include/trace/stages/stage4_event_fields.h
+++ b/include/trace/stages/stage4_event_fields.h
@@ -26,7 +26,8 @@
#define __array(_type, _item, _len) { \
.type = #_type"["__stringify(_len)"]", .name = #_item, \
.size = sizeof(_type[_len]), .align = ALIGN_STRUCTFIELD(_type), \
- .is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER },
+ .is_signed = is_signed_type(_type), .filter_type = FILTER_OTHER, \
+ .len = _len},
#undef __dynamic_array
#define __dynamic_array(_type, _item, _len) { \
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index e46a492..19caf15 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1282,6 +1282,7 @@ struct ftrace_event_field {
int offset;
int size;
int is_signed;
+ int len;
};
struct prog_entry;
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 33e0b4f..70f6725 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -114,7 +114,7 @@ struct ftrace_event_field *
static int __trace_define_field(struct list_head *head, const char *type,
const char *name, int offset, int size,
- int is_signed, int filter_type)
+ int is_signed, int filter_type, int len)
{
struct ftrace_event_field *field;
@@ -133,6 +133,7 @@ static int __trace_define_field(struct list_head *head, const char *type,
field->offset = offset;
field->size = size;
field->is_signed = is_signed;
+ field->len = len;
list_add(&field->link, head);
@@ -150,14 +151,14 @@ int trace_define_field(struct trace_event_call *call, const char *type,
head = trace_get_fields(call);
return __trace_define_field(head, type, name, offset, size,
- is_signed, filter_type);
+ is_signed, filter_type, 0);
}
EXPORT_SYMBOL_GPL(trace_define_field);
#define __generic_field(type, item, filter_type) \
ret = __trace_define_field(&ftrace_generic_fields, #type, \
#item, 0, 0, is_signed_type(type), \
- filter_type); \
+ filter_type, 0); \
if (ret) \
return ret;
@@ -166,7 +167,7 @@ int trace_define_field(struct trace_event_call *call, const char *type,
"common_" #item, \
offsetof(typeof(ent), item), \
sizeof(ent.item), \
- is_signed_type(type), FILTER_OTHER); \
+ is_signed_type(type), FILTER_OTHER, 0); \
if (ret) \
return ret;
@@ -1589,10 +1590,10 @@ static int f_show(struct seq_file *m, void *v)
field->type, field->name, field->offset,
field->size, !!field->is_signed);
else
- seq_printf(m, "\tfield:%.*s %s%s;\toffset:%u;\tsize:%u;\tsigned:%d;\n",
+ seq_printf(m, "\tfield:%.*s %s[%d];\toffset:%u;\tsize:%u;\tsigned:%d;\n",
(int)(array_descriptor - field->type),
field->type, field->name,
- array_descriptor, field->offset,
+ field->len, field->offset,
field->size, !!field->is_signed);
return 0;
@@ -2371,6 +2372,7 @@ static int ftrace_event_release(struct inode *inode, struct file *file)
if (list_empty(head)) {
struct trace_event_fields *field = call->class->fields_array;
unsigned int offset = sizeof(struct trace_entry);
+ struct list_head *head;
for (; field->type; field++) {
if (field->type == TRACE_FUNCTION_TYPE) {
@@ -2379,9 +2381,15 @@ static int ftrace_event_release(struct inode *inode, struct file *file)
}
offset = ALIGN(offset, field->align);
- ret = trace_define_field(call, field->type, field->name,
+ if (WARN_ON(!call->class)) {
+ offset += field->size;
+ continue;
+ }
+ head = trace_get_fields(call);
+ ret = __trace_define_field(head, field->type, field->name,
offset, field->size,
- field->is_signed, field->filter_type);
+ field->is_signed, field->filter_type,
+ field->len);
if (WARN_ON_ONCE(ret)) {
pr_err("error code is %d\n", ret);
break;
--
1.8.3.1
