linux-kernel - [PATCH 3/4] KVM: Clean up AMD SVM debug registers load and unload

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Message-Id: <20061210171142.7B0442500CF@il.qumranet.com>
Date:	Sun, 10 Dec 2006 17:11:42 -0000
From:	Avi Kivity <avi@...ranet.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org, mingo@...e.hu
Subject: [PATCH 3/4] KVM: Clean up AMD SVM debug registers load and unload

By letting gcc choose the temporary register for us, we lose arch
dependency and some ugliness.  Conceivably gcc will also generate
marginally better code.

Signed-off-by: Avi Kivity <avi@...ranet.com>

Index: linux-2.6/drivers/kvm/svm.c
===================================================================
--- linux-2.6.orig/drivers/kvm/svm.c
+++ linux-2.6/drivers/kvm/svm.c
@@ -1345,53 +1345,18 @@ static void kvm_reput_irq(struct kvm_vcp
 
 static void save_db_regs(unsigned long *db_regs)
 {
-#ifdef __x86_64__
-	asm ("mov %%dr0, %%rax \n\t"
-	     "mov %%rax, %[dr0] \n\t"
-	     "mov %%dr1, %%rax \n\t"
-	     "mov %%rax, %[dr1] \n\t"
-	     "mov %%dr2, %%rax \n\t"
-	     "mov %%rax, %[dr2] \n\t"
-	     "mov %%dr3, %%rax \n\t"
-	     "mov %%rax, %[dr3] \n\t"
-	     : [dr0] "=m"(db_regs[0]),
-	       [dr1] "=m"(db_regs[1]),
-	       [dr2] "=m"(db_regs[2]),
-	       [dr3] "=m"(db_regs[3])
-	     : : "rax");
-#else
-	asm ("mov %%dr0, %%eax \n\t"
-	     "mov %%eax, %[dr0] \n\t"
-	     "mov %%dr1, %%eax \n\t"
-	     "mov %%eax, %[dr1] \n\t"
-	     "mov %%dr2, %%eax \n\t"
-	     "mov %%eax, %[dr2] \n\t"
-	     "mov %%dr3, %%eax \n\t"
-	     "mov %%eax, %[dr3] \n\t"
-	     : [dr0] "=m"(db_regs[0]),
-	       [dr1] "=m"(db_regs[1]),
-	       [dr2] "=m"(db_regs[2]),
-	       [dr3] "=m"(db_regs[3])
-	     : : "eax");
-#endif
+	asm volatile ("mov %%dr0, %0" : "=r"(db_regs[0]));
+	asm volatile ("mov %%dr1, %0" : "=r"(db_regs[1]));
+	asm volatile ("mov %%dr2, %0" : "=r"(db_regs[2]));
+	asm volatile ("mov %%dr3, %0" : "=r"(db_regs[3]));
 }
 
 static void load_db_regs(unsigned long *db_regs)
 {
-	asm volatile ("mov %[dr0], %%dr0 \n\t"
-	     "mov %[dr1], %%dr1 \n\t"
-	     "mov %[dr2], %%dr2 \n\t"
-	     "mov %[dr3], %%dr3 \n\t"
-	     :
-	     : [dr0] "r"(db_regs[0]),
-	       [dr1] "r"(db_regs[1]),
-	       [dr2] "r"(db_regs[2]),
-	       [dr3] "r"(db_regs[3])
-#ifdef __x86_64__
-	     : "rax");
-#else
-	     : "eax");
-#endif
+	asm volatile ("mov %0, %%dr0" : : "r"(db_regs[0]));
+	asm volatile ("mov %0, %%dr1" : : "r"(db_regs[1]));
+	asm volatile ("mov %0, %%dr2" : : "r"(db_regs[2]));
+	asm volatile ("mov %0, %%dr3" : : "r"(db_regs[3]));
 }
 
 static int svm_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
-
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