KVM: selftests: Add proper helper for advancing RIP in debug_regs

Replace MOVE_RIP+SET_RIP with a proper helper, vcpu_skip_insn(), that is
more descriptive, doesn't subtly access local variables, and provides
type safety.
Signed-off-by: NSean Christopherson <seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/x86_64/debug_regs.c

@@ -65,19 +65,21 @@ static void guest_code(void)
 }
 
 #define  CAST_TO_RIP(v)  ((unsigned long long)&(v))
-#define  SET_RIP(v)  do {				\
-		vcpu_regs_get(vm, vcpu->id, &regs);	\
-		regs.rip = (v);				\
-		vcpu_regs_set(vm, vcpu->id, &regs);	\
-	} while (0)
-#define  MOVE_RIP(v)  SET_RIP(regs.rip + (v));
+
+static void vcpu_skip_insn(struct kvm_vcpu *vcpu, int insn_len)
+{
+	struct kvm_regs regs;
+
+	vcpu_regs_get(vcpu->vm, vcpu->id, &regs);
+	regs.rip += insn_len;
+	vcpu_regs_set(vcpu->vm, vcpu->id, &regs);
+}
 
 int main(void)
 {
 	struct kvm_guest_debug debug;
 	unsigned long long target_dr6, target_rip;
 	struct kvm_vcpu *vcpu;
-	struct kvm_regs regs;
 	struct kvm_run *run;
 	struct kvm_vm *vm;
 	struct ucall uc;
@@ -112,7 +114,7 @@ int main(void)
 		    "INT3: exit %d exception %d rip 0x%llx (should be 0x%llx)",
 		    run->exit_reason, run->debug.arch.exception,
 		    run->debug.arch.pc, CAST_TO_RIP(sw_bp));
-	MOVE_RIP(1);
+	vcpu_skip_insn(vcpu, 1);
 
 	/* Test instruction HW BP over DR[0-3] */
 	for (i = 0; i < 4; i++) {
@@ -134,7 +136,7 @@ int main(void)
 			    run->debug.arch.dr6, target_dr6);
 	}
 	/* Skip "nop" */
-	MOVE_RIP(1);
+	vcpu_skip_insn(vcpu, 1);
 
 	/* Test data access HW BP over DR[0-3] */
 	for (i = 0; i < 4; i++) {
@@ -156,15 +158,14 @@ int main(void)
 			    run->debug.arch.pc, CAST_TO_RIP(write_data),
 			    run->debug.arch.dr6, target_dr6);
 		/* Rollback the 4-bytes "mov" */
-		MOVE_RIP(-7);
+		vcpu_skip_insn(vcpu, -7);
 	}
 	/* Skip the 4-bytes "mov" */
-	MOVE_RIP(7);
+	vcpu_skip_insn(vcpu, 7);
 
 	/* Test single step */
 	target_rip = CAST_TO_RIP(ss_start);
 	target_dr6 = 0xffff4ff0ULL;
-	vcpu_regs_get(vm, vcpu->id, &regs);
 	for (i = 0; i < (sizeof(ss_size) / sizeof(ss_size[0])); i++) {
 		target_rip += ss_size[i];
 		memset(&debug, 0, sizeof(debug));