linux-kernel - Re: [PATCH 2/5] powerpc: ftrace, convert to new dynamic ftrace arch API

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Message-ID: <alpine.DEB.1.10.0811241256370.32561@gandalf.stny.rr.com>
Date:	Mon, 24 Nov 2008 13:00:36 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Paul Mackerras <paulus@...ba.org>
cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>, linuxppc-dev@...abs.org,
	Milton Miller <miltonm@....com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/5] powerpc: ftrace, convert to new dynamic ftrace arch
 API


On Mon, 24 Nov 2008, Paul Mackerras wrote:

> Steven Rostedt writes:
> 
> > Thanks to Paul Mackennas for pointing out the mistakes of my original
> 
> Mackerras

Heh, I have two reasons for that typo.

 1) I reference Paul McKenney a lot, and my fingers are programmed.
 2) I type with the dvorak layout, and the 'r' is just above the 'n'.
    qwerty 'o' == dvorak 'r'
    qwerty 'l' == dvorak 'n'

;-)

> 
> > +static int test_24bit_addr(unsigned long ip, unsigned long addr)
> > +{
> > +	long diff;
> > +
> > +	/*
> > +	 * Can we get to addr from ip in 24 bits?
> > +	 *  (26 really, since we mulitply by 4 for 4 byte alignment)
> > +	 */
> > +	diff = addr - ip;
> > +
> > +	/*
> > +	 * Return true if diff is less than 1 << 25
> > +	 *  and greater than -1 << 26.
> > +	 */
> > +	return (diff < (1 << 25)) && (diff > (-1 << 26));
> 
> I think this still isn't right, and the comment is one of those ones
> that is only useful to people who can't read C, as it's just a
> transliteration of the code.

Argh!!! That must be a misfold.  I fixed that code.  The final version 
ad the same shift for both.

> 
> The comment should say something like "Return true if diff can be
> represented as a 26-bit twos-complement binary number" and the second
> part of the test should be (diff >= (-1 << 25)).  However, since you
> define a test_offset() function in patch 4/5 that does the same test
> but using only one comparison instead of two, why don't you just say:
> 
> 	return !test_offset(diff);
> 
> (having first moved test_offset() before test_24bit_addr)?

OK, will fix. Thanks. Hmm, maybe I ment to do that, and miss the patch :-/

-- Steve

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