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User can enable this > format by setting options/relative-stacktrace. > > Basically, this does not change anything for users who are using ftrace > with 'trace' text-formatted interface. This changes how each stacktrace > entry address is stored, so users who is using 'trace_pipe_raw' needs > to change how to decode the stacktrace. > > Currently, the stacktrace is stored as raw kernel address. Thus, for > decoding the binary trace data, we need to refer the kallsyms. But this > is not useful on the platform which prohibits to access /proc/kallsyms > for security reason. Since KASLR will change the kernel text address, > we can not decode symbols without kallsyms in userspace. > > On the other hand, if we record the stacktrace entries in the offset > from _stext, we can use System.map file to decode it. This is also good > for the stacktrace in the persistent ring buffer, because we don't need > to save the kallsyms before crash anymore. > > The problem is to decode the address in the modules because it will be > loaded in the different place. To solve this issue, I also introduced > 'module_text_offsets' event, which records module's text and init_text > info as the offset from _stext when loading it. User can store this > event in the (another) persistent ring buffer for decoding. This does not handle the situation where a module is already loaded before tracing starts. In LTTng we have a statedump facility for this, where we can iterate on all modules at trace start and dump the relevant information. You may want to consider a similar approach for other tracers. Thanks, Mathieu > > Thank you, > > --- > > Masami Hiramatsu (Google) (3): > tracing: Record stacktrace as the offset from _stext > tracing: Introduce "rel_stack" option > modules: tracing: Add module_text_offsets event > > > include/trace/events/module.h | 40 ++++++++++++++++++++++++++++++++++++++++ > kernel/module/main.c | 1 + > kernel/trace/trace.c | 11 ++++++++++- > kernel/trace/trace.h | 2 ++ > kernel/trace/trace_entries.h | 22 ++++++++++++++++++++++ > kernel/trace/trace_output.c | 35 +++++++++++++++++++++++++++++++---- > 6 files changed, 106 insertions(+), 5 deletions(-) > > -- > Signature -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com