Low-level Tracing¶

Event and parameter tracing¶

As part of the SocTrace project, we implemented an initial support of low-level (i.e. raw) tracing of the model events required for building the model-centric representation of the application.

In practice, this means that, for all the events (i.e. breakpoints) caught my mcGDB, we log the parameters we had to read to update our internal representation.

All these information are machine and environment-implementation dependent, hence the tracing is done from the capture modules, based on a simple convention:

class clCreateBufferBP(mcgdb.capture.FunctionBreakpoint):
    [...]

    def prepare_before (self):
       data = {}
       data["mode"] = my_archi.nth_arg(2, my_archi.INT)
       data["retcode_p"] = my_archi.nth_arg(5, my_archi.INT_P)
       [...]

       return (False, True, data)

   def prepare_after(self, data):
       data["ret"] =  my_archi.return_value(my_archi.VOID_P)
       [...]

in mcgdb.capture.FunctionBreakpoint.prepare_before(), the third parameter returned by the function, corresponding to the data transmitted to the prepare_after(), has to be a dict object. If this is the case, then the breakpoint classname and the content of this dictionary will be sent to the tracing module. Likewise, method prepare_after() can extend the content of the dictionary with new values, and the function finish event and parameters will be passed to the tracing module.

Tracing Implementation¶

The trace generation is implemented in mcGDB mcgdb.toolbox.paje module. This module exports two public methods, before() and after(), that are hooked into mcgdb.capture.FunctionBreakpoint.stop() and mcgdb.capture.FunctionFinishBreakpoint.stop(), respectively.

Module mcgdb.toolbox.paje, as the name suggests, generated traces in the Paje format, thanks to libpoti shared library.

Tracing Command-line Interface¶

In GDB, run paje_print [filename] to dump the current content of the tracer.