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tracing: Fix TASK_COMM_LEN in trace event format file

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After commit 3087c61ed2 ("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN"),
the content of the format file under
/sys/kernel/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/tracing/events/task/task_newtask/format
        field:char comm[16];    offset:12;      size:16;        signed:0;

Link: https://lore.kernel.org/lkml/Y+QaZtz55LIirsUO@google.com/
Link: https://lore.kernel.org/linux-trace-kernel/20230210155921.4610-1-laoar.shao@gmail.com/
Link: https://lore.kernel.org/linux-trace-kernel/20230212151303.12353-1-laoar.shao@gmail.com

Cc: stable@vger.kernel.org
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Kajetan Puchalski <kajetan.puchalski@arm.com>
CC: Qais Yousef <qyousef@layalina.io>
Fixes: 3087c61ed2 ("tools/testing/selftests/bpf: replace open-coded 16 with TASK_COMM_LEN")
Reported-by: John Stultz <jstultz@google.com>
Debugged-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
This commit is contained in:
Yafang Shao 2023-02-12 15:13:03 +00:00 committed by Steven Rostedt (Google)
parent 3e46d910d8
commit b6c7abd1c2
5 changed files with 36 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/trace_events.h
View File

@ -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 *);
};

3
include/trace/stages/stage4_event_fields.h
View File

@ -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) { \

1
kernel/trace/trace.h
View File

@ -1282,6 +1282,7 @@ struct ftrace_event_field {
int offset;
int size;
int is_signed;
int len;
};
struct prog_entry;

39
kernel/trace/trace_events.c
View File

@ -114,7 +114,7 @@ trace_find_event_field(struct trace_event_call *call, char *name)
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 +151,28 @@ 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);
int trace_define_field_ext(struct trace_event_call *call, const char *type,
const char *name, int offset, int size, int is_signed,
int filter_type, int len)
{
struct list_head *head;
if (WARN_ON(!call->class))
return 0;
head = trace_get_fields(call);
return __trace_define_field(head, type, name, offset, size,
is_signed, filter_type, len);
}
#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 +181,7 @@ EXPORT_SYMBOL_GPL(trace_define_field);
"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;
@ -1588,12 +1603,17 @@ static int f_show(struct seq_file *m, void *v)
seq_printf(m, "\tfield:%s %s;\toffset:%u;\tsize:%u;\tsigned:%d;\n",
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",
else if (field->len)
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);
else
seq_printf(m, "\tfield:%.*s %s[];\toffset:%u;\tsize:%u;\tsigned:%d;\n",
(int)(array_descriptor - field->type),
field->type, field->name,
field->offset, field->size, !!field->is_signed);
return 0;
}
@ -2379,9 +2399,10 @@ event_define_fields(struct trace_event_call *call)
}
offset = ALIGN(offset, field->align);
ret = trace_define_field(call, field->type, field->name,
ret = trace_define_field_ext(call, 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;

3
kernel/trace/trace_export.c
View File

@ -111,7 +111,8 @@ static void __always_unused ____ftrace_check_##name(void) \
#define __array(_type, _item, _len) { \
.type = #_type"["__stringify(_len)"]", .name = #_item, \
.size = sizeof(_type[_len]), .align = __alignof__(_type), \
is_signed_type(_type), .filter_type = FILTER_OTHER },
is_signed_type(_type), .filter_type = FILTER_OTHER, \
.len = _len },
#undef __array_desc
#define __array_desc(_type, _container, _item, _len) __array(_type, _item, _len)