From: Samuel Thibault <samuel.thibault@eu.citrix.com>
Subject: [PATCH] [Mini-OS] Optimize get_current()
Date: Fri, 23 Nov 2007 15:58:00 +0000
Message-ID: <20071123155800.GA11663@implementation.uk.xensource.com>
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Let gcc perform the computation with SP itself, leading to yet better
code.

diff -r 2e05a6173be0 extras/mini-os/include/x86/arch_sched.h
--- a/extras/mini-os/include/x86/arch_sched.h	Fri Nov 23 11:58:11 2007 +0000
+++ b/extras/mini-os/include/x86/arch_sched.h	Fri Nov 23 15:53:18 2007 +0000
@@ -7,10 +7,11 @@
 {
     struct thread **current;
 #ifdef __i386__    
-    __asm__("andl %%esp,%0; ":"=r" (current) : "0" (~8191UL));
+    register unsigned long sp asm("esp");
 #else
-    __asm__("andq %%rsp,%0; ":"=r" (current) : "0" (~8191UL));
+    register unsigned long sp asm("rsp");
 #endif 
+    current = (void *)(sp & ~8191UL);
     return *current;
 }