linux-kernel - Re: Duplicate fields in event format of `regcache

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Message-ID: <76339068-99fe-53f8-c292-8b73900159b5@efficios.com>
Date:   Fri, 20 Nov 2020 14:03:00 -0500
From:   Philippe Duplessis-Guindon <pduplessis@...icios.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-trace-devel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Dimitris Papastamos <dp@...nsource.wolfsonmicro.com>,
        Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: Duplicate fields in event format of `regcache_sync `

Sorry Steven I forgot to reply all.
This is the original message:
Perfect,

I can prepare a patch, I think this would be a good learning opportunity 
for me.


Thank you,

Philippe

On 2020-11-20 1:47 p.m., Steven Rostedt wrote:
> On Fri, 20 Nov 2020 12:50:33 -0500
> Philippe Duplessis-Guindon <pduplessis@...icios.com> wrote:
> 
>> Hi,
>>
>> I am doing an ftrace plugin for Babeltrace 2 [1], and while I was
>> parsing the event fields I had an error saying that `regcache_sync` has
>> 2 fields named `type`. The problem seems to come from the
>> drivers/base/regmap/trace.h file [2]. This is the patch where this was
>> added: [3]. The `int field` type is not assigned, so I was wondering if
>> it is normal that the field is there.
>>
>> This is the format of this event:
>>
>> $ sudo cat /sys/kernel/debug/tracing/events/regmap/regcache_sync/format
>> name: regcache_sync
>> ID: 1216
>> 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:__data_loc char[] name;    offset:8;    size:4;    signed:1;
>>     field:__data_loc char[] status;    offset:12;    size:4;    signed:1;
>>     field:__data_loc char[] type;    offset:16;    size:4;    signed:1;
>>     field:int type;    offset:20;    size:4;    signed:1;
>>
>>     print fmt: "%s type=%s status=%s", __get_str(name), __get_str(type),
>> __get_str(status)
>>
> 
> It looks like dumb luck that this ever worked. :-/
> 
> The correct fix is to nuke that "int type" field. It's not even assigned.
> 
> Thanks for pointing this out.
> 
> -- Steve
> 
> 
>> Thank you,
>>
>> Philippe
>>
>>
>> [1] https://babeltrace.org/
>>
>> [2]
>> https://github.com/torvalds/linux/blob/master/drivers/base/regmap/trace.h#L129
>>
>> [3]
>> https://github.com/torvalds/linux/commit/593600890110c02eb471cf844649dee213870416
>