From 943fd378a1324ca60da72b271769fea4a86e36cb Mon Sep 17 00:00:00 2001
From: rsc <rsc>
Date: Mon, 1 Oct 2007 20:43:15 +0000
Subject: Incorporate new understanding of/with Intel SMP spec.

Dropped cmpxchg in favor of xchg, to match lecture notes.

Use xchg to release lock, for future protection and to
keep gcc from acting clever.
---
 x86.h | 29 +++++------------------------
 1 file changed, 5 insertions(+), 24 deletions(-)

(limited to 'x86.h')

diff --git a/x86.h b/x86.h
index a1c66b5..1f2c881 100644
--- a/x86.h
+++ b/x86.h
@@ -96,35 +96,16 @@ write_eflags(uint eflags)
   asm volatile("pushl %0; popfl" : : "r" (eflags));
 }
 
-// XXX: Kill this if not used.
-static inline void
-cpuid(uint info, uint *eaxp, uint *ebxp, uint *ecxp, uint *edxp)
-{
-  uint eax, ebx, ecx, edx;
-
-  asm volatile("cpuid" :
-               "=a" (eax), "=b" (ebx), "=c" (ecx), "=d" (edx) :
-               "a" (info));
-  if(eaxp)
-    *eaxp = eax;
-  if(ebxp)
-    *ebxp = ebx;
-  if(ecxp)
-    *ecxp = ecx;
-  if(edxp)
-    *edxp = edx;
-}
-
 static inline uint
-cmpxchg(uint oldval, uint newval, volatile uint* lock_addr)
+xchg(volatile uint *addr, uint newval)
 {
   uint result;
   
   // The + in "+m" denotes a read-modify-write operand.
-  asm volatile("lock; cmpxchgl %2, %0" :
-                       "+m" (*lock_addr), "=a" (result) :
-                       "r"(newval), "1"(oldval) :
-                       "cc");
+  asm volatile("lock; xchgl %0, %1" :
+               "+m" (*addr), "=a" (result) :
+               "1" (newval) :
+               "cc");
   return result;
 }
 
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