linux-kernel - [PATCH] tracing: fix "gfp_t" format for synthetic events

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Date:   Thu, 17 Oct 2019 16:38:13 +0800
From:   Zhengjun Xing <zhengjun.xing@...ux.intel.com>
To:     rostedt@...dmis.org, mingo@...hat.com, tom.zanussi@...ux.intel.com
Cc:     linux-kernel@...r.kernel.org, zhengjun.xing@...ux.intel.com
Subject: [PATCH] tracing: fix "gfp_t" format for synthetic events

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.xing@...ux.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++;
 		}
 	}
@@ -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;
 }
-- 
2.17.1