linux-kernel - Re: [PATCH 2/4] tracing/eprobes: Do not hardcode $comm as a string

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Message-ID: <20220820084837.4d6a95e4@gandalf.local.home>
Date:   Sat, 20 Aug 2022 08:48:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tzvetomir Stoyanov <tz.stoyanov@...il.com>,
        Tom Zanussi <zanussi@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH 2/4] tracing/eprobes: Do not hardcode $comm as a string

On Sat, 20 Aug 2022 20:18:24 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:

> > Do not assume that comm is a string. Not to mention, it currently forces
> > comm fields to fault, as string processing for event probes is currently
> > broken.  
> 
> Indeed. There should be an event argument which names "comm".
> Eprobe might refer it. BTW, does eprobe use any special common fields?
> I originally introduced "$" variable for such special variables.

I used the '$' for denoting the fields, as it was the easiest way to
integrate with trace_probe.c. There's no special variables, but this patch
series now allows '@' as well as if $comm (or $COMM) is not a field, it
acts the same as $comm for kprobes. Filtering and histograms do the same
thing (use 'comm' as the event field, or has the current->comm if the event
does not have 'comm' as a field). I should probably make "$common_comm"
used too.

-- Steve