--- /dev/null
+Deterministic Automata Monitor Synthesis
+========================================
+
+The starting point for the application of runtime verification (RV) technics
+is the *specification* or *modeling* of the desired (or undesired) behavior
+of the system under scrutiny.
+
+The formal representation needs to be then *synthesized* into a *monitor*
+that can then be used in the analysis of the trace of the system. The
+*monitor* connects to the system via an *instrumentation* that converts
+the events from the *system* to the events of the *specification*.
+
+
+In Linux terms, the runtime verification monitors are encapsulated inside
+the *RV monitor* abstraction. The RV monitor includes a set of instances
+of the monitor (per-cpu monitor, per-task monitor, and so on), the helper
+functions that glue the monitor to the system reference model, and the
+trace output as a reaction to event parsing and exceptions, as depicted
+below::
+
+ Linux +----- RV Monitor ----------------------------------+ Formal
+ Realm | | Realm
+ +-------------------+ +----------------+ +-----------------+
+ | Linux kernel | | Monitor | | Reference |
+ | Tracing | -> | Instance(s) | <- | Model |
+ | (instrumentation) | | (verification) | | (specification) |
+ +-------------------+ +----------------+ +-----------------+
+ | | |
+ | V |
+ | +----------+ |
+ | | Reaction | |
+ | +--+--+--+-+ |
+ | | | | |
+ | | | +-> trace output ? |
+ +------------------------|--|----------------------+
+ | +----> panic ?
+ +-------> <user-specified>
+
+DA monitor synthesis
+--------------------
+
+The synthesis of automata-based models into the Linux *RV monitor* abstraction
+is automated by the dot2k tool and the rv/da_monitor.h header file that
+contains a set of macros that automatically generate the monitor's code.
+
+dot2k
+-----
+
+The dot2k utility leverages dot2c by converting an automaton model in
+the DOT format into the C representation [1] and creating the skeleton of
+a kernel monitor in C.
+
+For example, it is possible to transform the wip.dot model present in
+[1] into a per-cpu monitor with the following command::
+
+ $ dot2k -d wip.dot -t per_cpu
+
+This will create a directory named wip/ with the following files:
+
+- wip.h: the wip model in C
+- wip.c: the RV monitor
+
+The wip.c file contains the monitor declaration and the starting point for
+the system instrumentation.
+
+Monitor macros
+--------------
+
+The rv/da_monitor.h enables automatic code generation for the *Monitor
+Instance(s)* using C macros.
+
+The benefits of the usage of macro for monitor synthesis are 3-fold as it:
+
+- Reduces the code duplication;
+- Facilitates the bug fix/improvement;
+- Avoids the case of developers changing the core of the monitor code
+ to manipulate the model in a (let's say) non-standard way.
+
+This initial implementation presents three different types of monitor instances:
+
+- ``#define DECLARE_DA_MON_GLOBAL(name, type)``
+- ``#define DECLARE_DA_MON_PER_CPU(name, type)``
+- ``#define DECLARE_DA_MON_PER_TASK(name, type)``
+
+The first declares the functions for a global deterministic automata monitor,
+the second for monitors with per-cpu instances, and the third with per-task
+instances.
+
+In all cases, the 'name' argument is a string that identifies the monitor, and
+the 'type' argument is the data type used by dot2k on the representation of
+the model in C.
+
+For example, the wip model with two states and three events can be
+stored in an 'unsigned char' type. Considering that the preemption control
+is a per-cpu behavior, the monitor declaration in the 'wip.c' file is::
+
+ DECLARE_DA_MON_PER_CPU(wip, unsigned char);
+
+The monitor is executed by sending events to be processed via the functions
+presented below::
+
+ da_handle_event_$(MONITOR_NAME)($(event from event enum));
+ da_handle_start_event_$(MONITOR_NAME)($(event from event enum));
+ da_handle_start_run_event_$(MONITOR_NAME)($(event from event enum));
+
+The function ``da_handle_event_$(MONITOR_NAME)()`` is the regular case where
+the event will be processed if the monitor is processing events.
+
+When a monitor is enabled, it is placed in the initial state of the automata.
+However, the monitor does not know if the system is in the *initial state*.
+
+The ``da_handle_start_event_$(MONITOR_NAME)()`` function is used to notify the
+monitor that the system is returning to the initial state, so the monitor can
+start monitoring the next event.
+
+The ``da_handle_start_run_event_$(MONITOR_NAME)()`` function is used to notify
+the monitor that the system is known to be in the initial state, so the
+monitor can start monitoring and monitor the current event.
+
+Using the wip model as example, the events "preempt_disable" and
+"sched_waking" should be sent to monitor, respectively, via [2]::
+
+ da_handle_event_wip(preempt_disable_wip);
+ da_handle_event_wip(sched_waking_wip);
+
+While the event "preempt_enabled" will use::
+
+ da_handle_start_event_wip(preempt_enable_wip);
+
+To notify the monitor that the system will be returning to the initial state,
+so the system and the monitor should be in sync.
+
+Final remarks
+-------------
+
+With the monitor synthesis in place using the rv/da_monitor.h and
+dot2k, the developer's work should be limited to the instrumentation
+of the system, increasing the confidence in the overall approach.
+
+[1] For details about deterministic automata format and the translation
+from one representation to another, see::
+
+ Documentation/trace/rv/deterministic_automata.rst
+
+[2] dot2k appends the monitor's name suffix to the events enums to
+avoid conflicting variables when exporting the global vmlinux.h
+use by BPF programs.
projects / platform / kernel / linux-starfive.git / commitdiff