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To: Jan-Benedict Glaw <jbglaw@microdata-pos.de>
Cc: linux-kernel@vger.kernel.org
Subject: Re: xchg and GCC's optimisation:-(
In-Reply-To: <20011217134526.A31801@microdata-pos.de>
From: Momchil Velikov <velco@fadata.bg>
In-Reply-To: <20011217134526.A31801@microdata-pos.de>
Date: 17 Dec 2001 15:18:45 +0200
Message-ID: <87wuzmq91m.fsf@fadata.bg>
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>>>>> "Jan-Benedict" == Jan-Benedict Glaw <jbglaw@microdata-pos.de> writes:
Jan-Benedict> I've looked at ./include/asm-i386/system.h which does some black
Jan-Benedict> magic with it, and I don't really understand that. However, the
Jan-Benedict> result is that the xchg gets optimized away, rendering at least

Can you try with this patch ...

--- system.h.orig.0	Mon Dec 17 15:03:38 2001
+++ system.h	Mon Dec 17 15:16:58 2001
@@ -205,21 +205,15 @@ static inline unsigned long __xchg(unsig
 	switch (size) {
 		case 1:
 			__asm__ __volatile__("xchgb %b0,%1"
-				:"=q" (x)
-				:"m" (*__xg(ptr)), "0" (x)
-				:"memory");
+				     :"+q" (x),"=m" (*__xg(ptr)));
 			break;
 		case 2:
 			__asm__ __volatile__("xchgw %w0,%1"
-				:"=r" (x)
-				:"m" (*__xg(ptr)), "0" (x)
-				:"memory");
+				     :"+r" (x),"=m" (*__xg(ptr)));
 			break;
 		case 4:
 			__asm__ __volatile__("xchgl %0,%1"
-				:"=r" (x)
-				:"m" (*__xg(ptr)), "0" (x)
-				:"memory");
+				     :"+r" (x), "=m" (*__xg(ptr)));
 			break;
 	}
 	return x;
-
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