Add custom per object before-free hook function

[yairlenga]

Is it possible to define a custom function that will be called whenever allocated block is called ?

Motivation: I have existing project, where large objects with fixed arrays in them are allocated (objects can be >1mb). I would like to replace some of the fixed size array with malloced arrays. I hope to be able to attach custom free function to those objects, which will free the malloced arrays, when the main object is freed. I cannot change all the code base to replace the free, with ‘custom-free’ - to much work. I can fix the allocators - they are few of them.

Conceptually a destructor, similar to c++ delete or the gcc/clang cleanup attribute extension, for dynamically allocated memory.

Basically, I want to replace:

Struct big {
    Double x,y,Z ;
    Double a[1000000] ;   // max value, but usually much smaller.
}

With:

Struct big {
    Double x,y,Z ;
    Double *a ;   // max value, but usually much smaller.
}

allocator will be:

Struct big *alloc-big()
{
        Struct big *p= callow(…);
        Mi-set-free(p, free-big);  // free big will be called when free(p) is called
         P->a = calloc(actual size);
}