linux-kernel - [PATCH][GIT PULL] ring-buffer: typecast cmpxchg to fix PowerPC warning

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Date:	Mon, 14 Sep 2009 09:43:43 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: [PATCH][GIT PULL] ring-buffer: typecast cmpxchg to fix PowerPC
 warning


Ingo,

Please pull the latest tip/tracing/core tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
tip/tracing/core


Steven Rostedt (1):
      ring-buffer: typecast cmpxchg to fix PowerPC warning

----
 kernel/trace/ring_buffer.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---------------------------
commit 08a408161749d2406f94f4e3d47cfdbc826ad1cc
Author: Steven Rostedt <srostedt@...hat.com>
Date:   Mon Sep 14 09:31:35 2009 -0400

    ring-buffer: typecast cmpxchg to fix PowerPC warning
    
    The cmpxchg used by PowerPC does the following:
    
      ({									 \
         __typeof__(*(ptr)) _o_ = (o);					 \
         __typeof__(*(ptr)) _n_ = (n);					 \
         (__typeof__(*(ptr))) __cmpxchg((ptr), (unsigned long)_o_,		 \
    				    (unsigned long)_n_, sizeof(*(ptr))); \
      })
    
    This does a type check of *ptr to both o and n.
    
    Unfortunately, the code in ring-buffer.c assigns longs to pointers
    and pointers to longs and causes a warning on PowerPC:
    
    ring_buffer.c: In function 'rb_head_page_set':
    ring_buffer.c:704: warning: initialization makes pointer from integer without a cast
    ring_buffer.c:704: warning: initialization makes pointer from integer without a cast
    ring_buffer.c: In function 'rb_head_page_replace':
    ring_buffer.c:797: warning: initialization makes integer from pointer without a cast
    
    This patch adds the typecasts inside cmpxchg to annotate that a long is
    being cast to a pointer and a pointer is being casted to a long and this
    removes the PowerPC warnings.
    
    Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
    Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 8786c35..6eef389 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -701,8 +701,8 @@ static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
 
 	val &= ~RB_FLAG_MASK;
 
-	ret = (unsigned long)cmpxchg(&list->next,
-				     val | old_flag, val | new_flag);
+	ret = cmpxchg((unsigned long *)&list->next,
+		      val | old_flag, val | new_flag);
 
 	/* check if the reader took the page */
 	if ((ret & ~RB_FLAG_MASK) != val)
@@ -794,7 +794,7 @@ static int rb_head_page_replace(struct buffer_page *old,
 	val = *ptr & ~RB_FLAG_MASK;
 	val |= RB_PAGE_HEAD;
 
-	ret = cmpxchg(ptr, val, &new->list);
+	ret = cmpxchg(ptr, val, (unsigned long)&new->list);
 
 	return ret == val;
 }


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