Re: Making a variable addressable in GIMPLE

[Yoav Etsion <etsman at gmail dot com>]

Frank Ch. Eigler wrote:
> Yoav Etsion <etsman@gmail.com> writes:
>
>
> > The pointer variable's address is used as the pointer's unique ID in
> > a database, collecting information about each pointer variable -
> > mostly its legal bounds.  That way I can test when a pointer crosses
> > its object's bounds.
...
> But I may misunderstand the nature of checking you intend.  Could you
> summarize your intended overall algorithm?
(I'll answer this first, hoping it will also answer the previous two 
comments)
My approach is simple: during dereference we have to check whether the 
pointer points within its legal boundaries, which should be those of the 
object assigned to it before any pointer arithmetic.
Question is how do we know what the legal boundaries are, as pointer 
arithmeric might have caused our pointer to jump into an adjacent object?
Now, think of the boundaries as attributes that can only change in 
pointer assignments (not arithmetic). We need to keep a database mapping 
pointers to boundaries, that is updated with each pointer assignment.
So the three operations I need to intercept are pointer dereferences 
(code which already exists in mudflap2), pointer assignments, and 
pointer declarations to get the variable's address as the unique 
database ID (my current predicament). Since I assume automatically 
generated variables do not induce bugs (hopefully) I don't have to track 
them (come to think of it, maybe I can do with only assignments and 
dereferences).
Using such database I can both check bounds, and more important to my 
current research to better understand programming habits and pointer flow.

Hope this clears things up, and obviously any comments and suggestions 
are more than welcome.

Yoav


> - FChE