Idea on system-level debugging solution

[Norman Feske]

Hi Johannes,

thanks for posting your idea. I share your sentiment that the debugging
challenges increasingly move from individual programs to entire
compositions of components. Here, the classical tools like GDB start to
become inefficient.

On the other hand, I made some interesting observations while developing
the GUI stack, which consists of many components that interact with each
other. As you said, each of those components is typically quite simple.
In fact, from a high-level view, a component like the window layouter is
merely a state machine that consumes 'ROM' data and produces 'Report'
data. Since I realized the propagation of state between the components
via the report_rom server, a new opportunity for debugging appeared: By
configuring the report_rom server to be verbose, each incoming report is
being printed to the LOG. Since all the components report their internal
states as reports, the output is a nice sequence of state transitions.
Most problems turned out to be very easy to spot in this trace.

I can think of several ways to make this style of debugging even more
usable for interactive scenarios. For example, a graphical tool could
consume those reports and produce a graphical view of each report
presented as the internal state of the originating component. Since the
report_rom server also knows the consumers of each report (the ROM
session clients), we could even show the information flow between the
components graphically. This view could be dynamic, depending on clients
known by the report_rom service.

> The debug logic can probably be implemented as a debug library that
> implements the hooks. A component is being instrumented by adding
> calls to the library functions and registering callback functions
> that print the debug information. Debugging is disabled by linking
> against a dummy library. Maybe this could also be implemented as a
> trace policy.

Leveraging the tracing mechanism sounds like a very cool idea.

Cheers
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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