Re: Guidance needed: hi-level steps to track an object until its destruction

[Basile Starynkevitch <basile@starynkevitch.net>]

On Thu, 2010-08-26 at 18:16 -0700, Jeff Saremi wrote:
> I'm hoping someone here could take the time to outline what I need to do (i'm not looking for code but if you point me to some i'd appreciate it).
> 
> I'd like to track an object from the it's created until it's destroyed (in C++). And then see if a certain method of it is called or not. To keep it short we can limit this to one function at the beginning of which an object gets created and at the end of it the object goes out of scope.
> And i'm guessing this can be done via one a pass at the right time. I guess before gimplification or being converted to RTL and such.


I am not sure that is easily feasible. I would believe it is impossible.

Within the compiler (or inside a GCC plugin, or inside a GCC extension
coded in MELT), you probably are able change/inspect C++ classes & every
other declaration any compiler is tracking. You are also able to find
every occurrence of variables containing a pointer to such classes.

However, you are apparently willing to track a single *instance* of such
a class, and this instance is in the execution of the compiled program
[not inside the compiler]. This means that you are able to deal with all
the aliasing & pointer equivalence issues (a task known to be
impossible). How can the compiler surely know that pointer p in [a
particular instruction of] method YourClass::foo() is never (or
sometimes, or always) pointing to the same instance -in the running
process of the compiled program- as pointer q in method yourclass::bar()

Or perhaps my English is so weak that I misunderstood you. If that is
the case, apologies.

Or maybe you want to instrument your compiler so that for every code
emitted for method yourclass::gee() you add a first block which checks
that the this reciever is not a given pointer.

In other words & C++ parlance, you could (this is doable, but not
trivial) hack the compiler so that at the start of every method (i.e.
member function in C++) the equivalent of the following C++ code has
been magically added

  extern "C" YourClass* hunted_yourclass_pointer;
  extern "C" void some_error_routine(void);

  if (this == hunted_yourclass_pointer) 
    some_error_routine();

But I am not sure you want to do that.

Cheers.
-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/
email: basile<at>starynkevitch<dot>net mobile: +33 6 8501 2359
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