On Tue, Jan 25, 2022 at 04:28:59PM -0500, Steven Rostedt wrote: > On Tue, 25 Jan 2022 16:23:26 -0500 > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > > > > #undef __get_rel_dynamic_array > > > > -#define __get_rel_dynamic_array(field) \ > > > > - ((void *)(&__entry->__rel_loc_##field) + \ > > > > - sizeof(__entry->__rel_loc_##field) + \ > > > > +#define __get_rel_dynamic_array(field) \ > > > > + ((void *)__entry + \ > > > > + offsetof(typeof(*__entry), __rel_loc_##field) + \ > > > > + sizeof(__entry->__rel_loc_##field) + \ > > > > (__entry->__rel_loc_##field & 0xffff)) > > > > > > > > #undef __get_rel_dynamic_array_len > > > > > I also do not like the the inconsistency between > sizeof(__entry->__rel_loc_##field) and sizeof(u32) that is used in the > calculation part: > > > #define __rel_dynamic_array(type, item, len) \ > __item_length = (len) * sizeof(type); \ > __data_offsets->item = __data_size + \ > offsetof(typeof(*entry), __data) - \ > offsetof(typeof(*entry), __rel_loc_##item) - \ > sizeof(u32); \ > __data_offsets->item |= __item_length << 16; \ > __data_size += __item_length; > > Why is one using sizeof(u32) and the other using the size of the field? It might make more sense to calculate everything as an offset within __data[] instead of from the start of __entry. The patch I sent just did in perf.h exactly what Masami did in trace_event.h. That worked. I had an earlier version that did this horrible thing which could probably be significantly improved, since I just subtract the offset of __data: #undef __get_rel_dynamic_array #define __get_rel_dynamic_array(field) \ - ((void *)(&__entry->__rel_loc_##field) + \ - sizeof(__entry->__rel_loc_##field) + \ - (__entry->__rel_loc_##field & 0xffff)) + ((void *)&__entry->__data[ \ + offsetof(typeof(*__entry), __rel_loc_##field) \ + + sizeof(__entry->__rel_loc_##field) \ + + (__entry->__rel_loc_##field & 0xffff) \ + - offsetof(typeof(*__entry), __data) \ + ]) > Just to let you know what is happening. As dynamic elements of the trace > event needs to be appended at the end of the event, the above macros are > defined and then run through the TRACE_EVENT() macro, where the > TP_STRUCT__entry() is parsed to calculate where each item will be for that > event. > > static inline notrace int trace_event_get_offsets_##call( \ > struct trace_event_data_offsets_##call *__data_offsets, proto) \ > { \ > int __data_size = 0; \ > int __maybe_unused __item_length; \ > struct trace_event_raw_##call __maybe_unused *entry; \ > \ > tstruct; \ > \ > return __data_size; \ > } > > > The tstruct is the TP_STRUCT__entry() and for each __rel_dynamic_array() or > __dynamic_array(), the __data_size gets updated and saved into the > __data_offsets that holds where each item is. > > The rel versions sets the offset from its location to the data, where as > the non rel versions sets the offset from the beginning of the event to the > data. Could this just be #define __get_rel_dynamic_array(field) \ ((void *)(&__entry->data[__entry->__rel_loc_##field & 0xffff]) ? -- Kees Cook