linux-kernel - Re: [PATCH 1/3] ftrace: convert unsigned index to signed

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Date:	Tue, 6 Jan 2009 21:42:17 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, fweisbec@...il.com,
	roel.kluin@...il.com, pq@....fi, srostedt@...hat.com
Subject: Re: [PATCH 1/3] ftrace: convert unsigned index to signed


On Tue, 6 Jan 2009, Andrew Morton wrote:

> On Tue, 06 Jan 2009 17:33:38 -0500
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > From: Steven Rostedt <srostedt@...hat.com>
> > 
> > Impact: fix to unsigned compared to less than zero
> > 
> > Roel Kluin pointed out that there is a compare of an unsigned number
> > to less than zero. A previous clean up had the unsigned index set
> > to -1 for certain cases, but never converted it to signed.
> > 
> > Frederic Weisbecker noticed that another index is used to compare
> > the above index to and it also needs to be converted to signed.
> > 
> > Reported-by: Roel Kluin <roel.kluin@...il.com>
> > Reported-by: Frederic Weisbecker <fweisbec@...il.com>
> > Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> > ---
> >  kernel/trace/ftrace.c |    4 ++--
> >  1 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 2f32969..3576707 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -289,7 +289,7 @@ static DEFINE_MUTEX(ftrace_regex_lock);
> >  
> >  struct ftrace_page {
> >  	struct ftrace_page	*next;
> > -	unsigned long		index;
> > +	long			index;
> 
> Does that actually need to be a long type?

No, I think I just automatically typed "unsigned long" before, and here
I just removed the unsigned. It can also be an int. It only indexes what 
is on a page.


> 
> >  	struct dyn_ftrace	records[];
> >  };
> >  
> > @@ -786,7 +786,7 @@ enum {
> >  
> >  struct ftrace_iterator {
> >  	struct ftrace_page	*pg;
> > -	unsigned		idx;
> > +	int			idx;
> 
> because we have
> 
>         if (iter->idx >= iter->pg->index) {
> 
> Are 32-bit types actually more efficient than 64-bit types on any
> 64-bit hardware which we care about?  

They both should always be way less than 2^31, so they both can be int.

Thanks, I'll fix this one up. I don't think Ingo pulled it yet.

-- Steve

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