linux-kernel - Re: Reason for unused flags argument in trace_raw_output

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Date:   Thu, 7 Oct 2021 09:20:26 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     William Cohen <wcohen@...hat.com>
Cc:     mingo@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Reason for unused flags argument in trace_raw_output_*
 function?

On Wed, 6 Oct 2021 23:49:22 -0400
William Cohen <wcohen@...hat.com> wrote:

> Hi,
> 
> I have some code that analyzes x86_64 binaries
> (https://developers.redhat.com/articles/2021/08/09/debugging-function-parameters-
> dyninst#liveness_analysis) and list which function parameters are unused.
>  I noticed that trace_raw_output_* functions have an unused flags
> argument.  I assume this is is to make the argument list match up with
> some other function, but I couldn't see which function(s) the
> trace_raw_output_* functions are trying to match up with.  Which
> functions are the trace_raw_output_* function's arguments trying to match?
> 

The match of other printing functions is in kernel/trace/trace_output.c

And is called from kernel/trace/trace.c where one place it does pass in
flags:

static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
{
	[..]
	if (event)
		return event->funcs->trace(iter, sym_flags, event);

Now if they are still used, is something we should investigate.

This code has changed a lot over the years when that "flags" parameter was
introduced. It could now just be a relic from the old implementations.

Thanks for pointing this out. If I get time I'll look deeper into it, but
feel free to look at it yourself.

-- Steve