linux-kernel - Re: kprobes: get rid of distinct type warning

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Message-ID: <20100105084027.GA5480@osiris.boeblingen.de.ibm.com>
Date:	Tue, 5 Jan 2010 09:40:27 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: kprobes: get rid of distinct type warning

On Tue, Jan 05, 2010 at 09:15:41AM +1030, Rusty Russell wrote:
> On Tue, 5 Jan 2010 02:27:02 am Heiko Carstens wrote:
> > On Wed, Dec 30, 2009 at 01:29:45PM -0800, Andrew Morton wrote:
> > > The num_*() "functions" return unsigned on SMP and int on UP.  This is
> > > wrong.
> > > 
> > > The cpu_*() "functions" got lucky and return int in both cases.
> > > 
> > > Personally I think it's neatest if a quantity which can never be
> > > negative is held in an unsigned type.  Than includes anything starting
> > > with "num".  But for expediency's sake we could live with making these
> > > things consistently return "int".
> > > 
> > > Alas, changing those four num_*() "functions" to return int on SMP is a
> > > pretty wide-reaching change and will probably expose warts.
> > 
> > Looks like there are quite a lot of num_* function usages in the kernel.
> > Some seem to assume they return an int some assume an unsigned int.
> > Don't know if it's worth changing anything here.
> > Maybe Rusty has an opinion.
> 
> If we have to go one way or the other, go with unsigned.
> 
> What does such a patch look like?

Something like this, doesn't even trigger new warnings on an !SMP defconfig
build:

Subject: [PATCH] cpumask: let num_*_cpus() function always return unsigned values

From: Heiko Carstens <heiko.carstens@...ibm.com>

Dependent on CONFIG_SMP the num_*_cpus() functions return unsigned or
signed values.
Let them always return unsigned values to avoid strange casts.

Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
---
 include/linux/cpumask.h |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -90,10 +90,10 @@ extern const struct cpumask *const cpu_a
 #define cpu_present(cpu)	cpumask_test_cpu((cpu), cpu_present_mask)
 #define cpu_active(cpu)		cpumask_test_cpu((cpu), cpu_active_mask)
 #else
-#define num_online_cpus()	1
-#define num_possible_cpus()	1
-#define num_present_cpus()	1
-#define num_active_cpus()	1
+#define num_online_cpus()	1U
+#define num_possible_cpus()	1U
+#define num_present_cpus()	1U
+#define num_active_cpus()	1U
 #define cpu_online(cpu)		((cpu) == 0)
 #define cpu_possible(cpu)	((cpu) == 0)
 #define cpu_present(cpu)	((cpu) == 0)
--
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