import-trace: emit warning for malformed traces

The Fail* tools expect trace events to be ordered in a specific way:
memory-access events are supposed to come *after* the instruction
event for the instruction that caused them.  Using a different order
may cause subtle problems with both fault-space pruning and fast
forwarding.  This change introduces a warning message when such a
malformed trace is detected (i.e., when the instruction pointer of a
memory-access event does not match the preceding instruction event).

Change-Id: I8ae7420fd8ff26e2574590748bdcc5a63db76490

tools/import-trace/Importer.cc

@@ -68,6 +68,8 @@ bool Importer::copy_to_database(fail::ProtoIStream &ps) {
 	instruction_count_t instr = 0;
 	// instruction counter new memory access events belong to
 	instruction_count_t instr_memaccess = 0;
+	// absolute instruction address of the latest IP event
+	guest_address_t instr_memaccess_absolute = 0;
 
 	// the currently processed event
 	Trace_Event ev;
@@ -104,8 +106,15 @@ bool Importer::copy_to_database(fail::ProtoIStream &ps) {
 
 			// all subsequent mem access events belong to this dynamic instr
 			instr_memaccess = instr;
+			instr_memaccess_absolute = ev.ip();
 			instr++;
 		} else {
+			if (ev.ip() != instr_memaccess_absolute) {
+				LOG << "warning: mem-access IP 0x" << std::hex << ev.ip()
+					<< " differs from previous instruction IP 0x" << instr_memaccess_absolute
+					<< " at instr=" << std::dec << instr_memaccess
+					<< " (mem accesses must follow *after* their corresponding IP events in the trace!)" << std::endl;
+			}
 			if (!handle_mem_event(curtime, instr_memaccess, ev)) {
 				LOG << "error: handle_mem_event() failed at instr=" << instr_memaccess << std::endl;
 				return false;