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All this delta code has always been complete >> and utter garbage, and complete hacks. > > Actually, I think the proper model isn't even that "modify boot time > buffers in place" thing. > > The proper model was probably always to just do the "give the raw > data, and analyze the previous boot data in user mode". It appears that you just summarized the LTTng (out-of-tree) kernel tracer [1] model in one short sentence. If this can help in some way, within the LTTng model, here is how we're solving the problem of mapping addresses to symbols: 1- We have a statedump infrastructure, which dumps internal kernel state. It could dump the kernel and each module base addresses into the trace. (we do it for userspace tracing) 2- We can hook on module load/unload to insert event about insertion and removal of those base addresses into the trace buffers. (we do it for userspace tracing) 3- We augment the traces at post-processing with DWARF and ELF parsers in Babeltrace [2] to augment the trace with symbolic information using the ELF or DWARF files as inputs in addition to the traces. (this already exists, and is used for userspace traces) 4- We already have the integration of the LTTng Userspace tracer with PMEM and DAX to recover traces after a machine crash. Those buffers are self-described with an ABI which allows a userspace tool (lttng-crash) to extract well-formed Common Trace Format [3] traces from the buffers after reboot. We've never had the incentive to port this facility to the kernel tracer so far though. Thanks, Mathieu [1] https://lttng.org [2] https://babeltrace.org [3] https://diamon.org/ctf -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com