On Sun, 12 Feb 2023 15:13:03 +0000
Yafang Shao <laoar.shao@xxxxxxxxx> wrote:
> 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>
> Suggested-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
> 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: Qais Yousef <qyousef@xxxxxxxxxxx>
> Cc: John Stultz <jstultz@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v5.17+
This looks good to me.
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Thanks!
> ---
> include/linux/trace_events.h | 1 +
> include/trace/stages/stage4_event_fields.h | 3 ++-
> kernel/trace/trace.h | 1 +
> kernel/trace/trace_events.c | 39 +++++++++++++++++++++++-------
> kernel/trace/trace_export.c | 3 ++-
> 5 files changed, 36 insertions(+), 11 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..b6f679a 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..6a46967 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 +151,28 @@ 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 @@ 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;
>
> @@ -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 @@ 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,
> + 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 d960f6b..58f3946 100644
> --- a/kernel/trace/trace_export.c
> +++ b/kernel/trace/trace_export.c
> @@ -111,7 +111,8 @@ struct ____ftrace_##name { \
> #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)
> --
> 1.8.3.1
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
