linux-kernel - Re: Warnings from sched

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Message-ID: <20071221110336.GB29047@elte.hu>
Date:	Fri, 21 Dec 2007 12:03:37 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Meelis Roos <mroos@...ux.ee>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: Re: Warnings from sched_debug.c


* Meelis Roos <mroos@...ux.ee> wrote:

> This happens on sparc64 with 2.6.24-rc6 (gcc-4.2):
> 
>   CC      kernel/sched.o
> In file included from kernel/sched.c:879:
> kernel/sched_debug.c: In function 'nsec_high':
> kernel/sched_debug.c:38: warning: comparison of distinct pointer types lacks a cast
> kernel/sched_debug.c:41: warning: comparison of distinct pointer types lacks a cast
> kernel/sched_debug.c: In function 'nsec_low':
> kernel/sched_debug.c:51: warning: comparison of distinct pointer types lacks a cast

it should be harmless. Does the patch below fix the warnings?

	Ingo

-------------->
Subject: sched: fix gcc warnings
From: Ingo Molnar <mingo@...e.hu>

Meelis Roos reported these warnings on sparc64:

  CC      kernel/sched.o
  In file included from kernel/sched.c:879:
  kernel/sched_debug.c: In function 'nsec_high':
  kernel/sched_debug.c:38: warning: comparison of distinct pointer types lacks a cast

the debug check in do_div() is over-eager here, because the long long
is always positive in these places. Mark this by casting them to
unsigned long long.

no change in code output:

   text    data     bss     dec     hex filename
  51471    6582     376   58429    e43d sched.o.before
  51471    6582     376   58429    e43d sched.o.after

  md5:
   7f7729c111f185bf3ccea4d542abc049  sched.o.before.asm
   7f7729c111f185bf3ccea4d542abc049  sched.o.after.asm

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_debug.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux/kernel/sched_debug.c
===================================================================
--- linux.orig/kernel/sched_debug.c
+++ linux/kernel/sched_debug.c
@@ -31,9 +31,9 @@
 /*
  * Ease the printing of nsec fields:
  */
-static long long nsec_high(long long nsec)
+static long long nsec_high(unsigned long long nsec)
 {
-	if (nsec < 0) {
+	if ((long long)nsec < 0) {
 		nsec = -nsec;
 		do_div(nsec, 1000000);
 		return -nsec;
@@ -43,9 +43,9 @@ static long long nsec_high(long long nse
 	return nsec;
 }
 
-static unsigned long nsec_low(long long nsec)
+static unsigned long nsec_low(unsigned long long nsec)
 {
-	if (nsec < 0)
+	if ((long long)nsec < 0)
 		nsec = -nsec;
 
 	return do_div(nsec, 1000000);
--
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