Hi Steve, Thanks for looking at this.
I believe this path is reachable. field->system is set when a VAR_REF is created with an event-qualified reference. The assignment happens in init_var_ref(), which is called from create_var_ref(). The parser accepts fully qualified references of the form system.event.$var and parse_expr() passes the parsed system/event strings into create_var_ref(). trace_action_create() also accepts explicitly qualified action parameters in the same form and passes those strings into create_var_ref(). This is also documented in Documentation/trace/histogram.rst: fully-qualified name is of the form 'system.event_name.$var_name' or 'system.event_name.field'. The path is user-visible because reading back the trigger goes through event_hist_trigger_print() -> hist_field_print() -> hist_field_name() so creating a hist trigger that uses an inter-event variable reference in fully qualified form is enough to exercise it. So I don't think this is dead code. If you would prefer a different way of handling the printed name, I can respin accordingly, but I don't think the current branch is unreachable. Thanks, Pengpeng
