I'd just sent mail to [email protected] and he replied.
> I know nothing abnout ELF format, and I have not worked on GCC since
> 1991. Thus, I simply am not in a position to judge the merits of your
> suggestion. How about writing to [email protected], which is the discussion
> list for GCC?
My original message is below. I'd like to hear your opinion.
> Hello.
>
> This is the 3rd time to send email in this topic. My first
> purpose in 1994 was to make a simple and lightweight OO language
> which can run on 32bit native DOS. I planned the implementation
> of C structure which has the first variable of a pointer to its
> class. And I considered about the class which contains a pointer
> table for instance methods.
>
> ------------------------------------------------------------------------
> class Object {
> int a, b; /* instance variable */
> void do0 (); /* instance method */
> void do1 ();
> void do2 ();
> void do3 ();
> void do4 ();
> };
>
> Object obj;
>
> ------------------------------------------------------------------------
> [MEMORY IMAGE]
>
> Object
> +-----------+
> | Ptr super |
> | Ptr do0 |
> | Ptr do1 |
> | Ptr do2 |
> | Ptr do3 |
> | Ptr do4 |
> +-----------+
>
> obj
> +-----------+
> | Ptr class |---> Object
> | int a |
> | int b |
> +-----------+
>
> ------------------------------------------------------------------------
> class Point extends Object {
> int x, y, z; /* instance variable */
> void do2 (); /* instance method (override) */
> void do5 (); /* instance method */
> void do6 (); /* instance method */
> };
>
> Point pt;
>
> ------------------------------------------------------------------------
> [MEMORY IMAGE]
>
> Point
> +--------------------+
> | Ptr super |---> Object
> | Ptr do0 |
> | Ptr do1 |
> | Ptr do2 |
> | Ptr do3 |
> | Ptr do4 |
> | Ptr do5 |
> | Ptr do6 |
> +--------------------+
>
> pt
> +-----------+
> | Ptr class |---> Point
> | int a |
> | int b |
> | int x |
> | int y |
> | int z |
> +-----------+
>
> ------------------------------------------------------------------------
>
> Even with this simple plan, trying to implement was very difficult
> because I was going to keep the principle "What is necessary is to
> re-compile only the source files you touched".
>
> Consider the class, for example, which has 5 instance methods.
> The derived class adds 2 methods and overrides 1 method. The
> object files are separate into two. The symbols of indices (in
> asm file) will be something like the below.
>
> Object_super .define 0
> Object_do0 .define 4
> Object_do1 .define 8
> Object_do2 .define 12
> Object_do3 .define 16
> Object_do4 .define 20
> Object_MMAX .define 24 /* Method MAX */
>
> Object_class .define 0
> Object_a .define 4
> Object_b .define 8
> Object_VMAX .define 12 /* Variable MAX */
>
>
> Point_super .define Object_super
> Point_do0 .define Object_do0
> Point_do1 .define Object_do1
> Point_do2 .define Object_do2
> Point_do3 .define Object_do3
> Point_do4 .define Object_do4
> Point_do5 .define Object_MMAX .+ 0
> Point_do6 .define Object_MMAX .+ 4
> Point_MMAX .define Object MMAX .+ 8
>
> Point_a .define Object_a
> Point_b .define Object_b
> Point_x .define Object_VMAX .+ 0
> Point_y .define Object_VMAX .+ 4
> Point_z .define Object_VMAX .+ 8
> Point_VMAX .define Object_VMAX .+ 12
>
>
> The object file of the derived class doesn't know the length of
> the method table of the super class, nor the index of the method
> to override. The calculation of constants to generate a suitable
> method table must be ld's job as long as we keep the principle.
> Take care this is not about the method dispatch. This is about
> the classes as global variables which is generated by ld. It
> contains a flat pointer table of instance methods. How do you
> think about this principle?
>
> I suspect we should make decision of solving all symbols by the
> calculation. That is, all symbols should be solved by the
> calculation of the information that stored in Reverse Polish which
> consists of constants, other symbols, and their arithmetic. It
> also contains the information of shared libraries possibly. I
> suppose this decision gives unified implementation of object
> files, static libraries, and shared libraries. In fact it will be
> the extended ELF.
>
> Please forgive me because I'm not any linker expert. I don't know
> very much the details of ELF format. I know m68k asm, but I only
> regards ld as a kind of constant resolver. I even don't know
> really well about dynamic linking. But I believe this kind of
> solution will be the best infrastructure (binutils, and the
> mechanism of shared library) for the object oriented languages.
> I'm not interested in designing OO language, I'm just talking
> about infrastructure. I imagine the goal of this infrastructure
> is to provide seamless linking of OO language's object files, C's
> object files, and Asm's object files.
>
> I had read the article of the interview to Straustrap so many
> years ago and he had said "My work is to design the language, I'm
> not interested in implementations" or something like it. In
> contrast with it, my interest is implementations. How do you
> think about the great effects which he brought with his stance?
>
