tracing: Fix TASK_COMM_LEN in trace event format file

After commit 3087c61ed2c4 ("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: 3087c61ed2c4 ("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>

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index 4342e996bcdb76d985391eebc1b5a2817acd5fc5..0e373222a6df8a983f19238239e51954e5bf1535 100644 (file)
--- 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 affd541fd25eac239e24d826273d8deaac312a5f..b6f679ae21aa77bb43abc2c466d48f78c3f69b84 100644 (file)
--- 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 4eb6d6b97a9fd952115cac736bc49cc729a7bfe2..085a31b978a56e8812c25e667936b3d65d0c5a66 100644 (file)
--- 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 33e0b4f8ebe6265e60b7f9659846267250c4781d..6a46967192975b0c90fb8df0bd36f49ffb44c24f 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -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;

diff --git a/kernel/trace/trace_export.c b/kernel/trace/trace_export.c
index d960f6b11b5e51a9bbefe0f6169eeecb0bb3783b..58f3946081e21ae5998205f1171407ca5420e09e 100644 (file)
--- a/kernel/trace/trace_export.c
+++ b/kernel/trace/trace_export.c
@@ -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)