linux-kernel - Re: [PATCH] tracing: don't macro-expand arguments before stringification in TP

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Message-ID: <20160222222308.12bdfeb3@grimm.local.home>
Date:	Mon, 22 Feb 2016 22:23:08 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: don't macro-expand arguments before
 stringification in TP_printk

On Wed, 16 Dec 2015 01:28:12 +0100
Rasmus Villemoes <linux@...musvillemoes.dk> wrote:

> Bah, just found 0462b5664b (ftrace: Output REC->var instead of
> __entry->var for trace format). There's some magic here I don't
> understand, but I'm wondering if '__entry' wouldn't do just as well as
> 'REC' for the tools that try to parse these strings.
> 
>

Sorry for the late reply, but I just found this in my INBOX :-)

Several tools already exist that use REC to parse. It would be ABI
breakage to suddenly convert it to __entry.

Not to mention, even in your example of:

  ((unsigned int) ((REC->dev) >> 20)), ((unsigned int) ((REC->dev) & ((1U << 20) - 1)))

which came from

  MAJOR(__entry->dev), MINOR(__entry->dev),


The parsing tools don't know how to parse MAJOR or MINOR but they do
know how to do the above macro expansions.

Just an FYI,

-- Steve