Hi Zhengjun,
On Thu, 2019-10-17 at 16:38 +0800, Zhengjun Xing wrote:
> In the format of synthetic events, the "gfp_t" is shown as
> "signed:1",
> but in fact the "gfp_t" is "unsigned", should be shown as "signed:0".
> The offset should be increased by the real size of each field, rather
> than by the size of "u64".
>
> The issue can be reproduced by the following commands:
>
> echo 'memlatency u64 lat; unsigned int order; gfp_t gfp_flags; int
> migratetype' > /sys/kernel/debug/tracing/synthetic_events
> cat /sys/kernel/debug/tracing/events/synthetic/memlatency/format
>
> name: memlatency
> ID: 2233
> format:
> field:unsigned short
> common_type; offset:0; size:2; signed:0;
> field:unsigned char
> common_flags; offset:2; size:1; signed:0;
> field:unsigned char
> common_preempt_count; offset:3; size:1; signed:0;
> field:int common_pid; offset:4; size:4; signed:1;
>
> field:u64 lat; offset:8; size:8; signed:0;
> field:unsigned int order; offset:16; size:4;
> signed:0;
> field:gfp_t gfp_flags; offset:24; size:4; signed:1;
> field:int migratetype; offset:32; size:4; signed:1;
>
> print fmt: "lat=%llu, order=%u, gfp_flags=%x, migratetype=%d", REC-
> >lat, REC->order, REC->gfp_flags, REC->migratetype
>
> Signed-off-by: Zhengjun Xing <zhengjun.x...@linux.intel.com>
> ---
> kernel/trace/trace_events_hist.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace_events_hist.c
> b/kernel/trace/trace_events_hist.c
> index 57648c5aa679..7d70321d03b1 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -665,7 +665,7 @@ static int synth_event_define_fields(struct
> trace_event_call *call)
> offset += STR_VAR_LEN_MAX;
> n_u64 += STR_VAR_LEN_MAX / sizeof(u64);
> } else {
> - offset += sizeof(u64);
> + offset += size;
> n_u64++;
> }
> }
This part isn't correct - currently, all the synthetic event fields are
u64, so doing this alone will mess things up. The synthetic fields
were defined to be u64 in order to simplify event generation - if we
want to use the actual sizes, it would take a more extensive patch
including the generation code as well. Not sure the added complexity
is worth it to save a few bytes in the ring buffer.
> @@ -679,6 +679,8 @@ static bool synth_field_signed(char *type)
> {
> if (str_has_prefix(type, "u"))
> return false;
> + if (strcmp(type, "gfp_t") == 0)
> + return false;
>
> return true;
> }
This part is fine and makes sense.
Thanks,
Tom
