On 2023-02-10 10:59, Yafang Shao 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@google.com Debugged-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Suggested-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Signed-off-by: Yafang Shao laoar.shao@gmail.com Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Alexei Starovoitov alexei.starovoitov@gmail.com Cc: Kajetan Puchalski kajetan.puchalski@arm.com Cc: Steven Rostedt rostedt@goodmis.org Cc: John Stultz jstultz@google.com Cc: stable@vger.kernel.org # 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;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, \
Just out of curiosity, is the content of __stringify(_len) ever used after this patch ? Perhaps we could remove it and just leave:
.type = #_type"[]"
considering that f_show appears to use the opening square bracket to detect arrays. This would remove a few useless bytes of data.
Thanks,
Mathieu
.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)@@ -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);#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); \@@ -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); \@@ -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;