KVM: emulate: put pointers in the fetch_cache

This simplifies the code a bit, especially the overflow checks.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/trace.h b/arch/x86/kvm/trace.h
index 33574c9..e850a7d 100644
--- a/arch/x86/kvm/trace.h
+++ b/arch/x86/kvm/trace.h
@@ -721,10 +721,10 @@
 		),
 
 	TP_fast_assign(
-		__entry->rip = vcpu->arch.emulate_ctxt.fetch.start;
 		__entry->csbase = kvm_x86_ops->get_segment_base(vcpu, VCPU_SREG_CS);
-		__entry->len = vcpu->arch.emulate_ctxt._eip
-			       - vcpu->arch.emulate_ctxt.fetch.start;
+		__entry->len = vcpu->arch.emulate_ctxt.fetch.ptr
+			       - vcpu->arch.emulate_ctxt.fetch.data;
+		__entry->rip = vcpu->arch.emulate_ctxt._eip - __entry->len;
 		memcpy(__entry->insn,
 		       vcpu->arch.emulate_ctxt.fetch.data,
 		       15);