[PATCH] 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@qumranet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/kvm/svm.c

@@ -1345,53 +1345,18 @@ static void kvm_reput_irq(struct kvm_vcpu *vcpu)
 
 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)