OpenEuphoria

Re: C_FUNC in DOS

• Posted by Robert Craig <rds at EMAIL.MSN.COM> Jan 06, 1999
• 606 views

Ralf writes:
> Why not add support for using .OBJ files ?
> As a counterpart to the Win32-call_func () one that works with
> .OBJ files rather than .DLL files.

That would be a great feature, but I don't think there's
any practical way to implement it. Dynamic linking is supported by
the WIN32 O/S but not by DOS.

A couple of years ago a user provided me with a demo program
that would:
    - open a .OBJ file
    - read in the machine code for a C routine
    - call() the machine code

It looked pretty good. You could modify and recompile the
C function and then run the Euphoria demo program.
However:
    - the .OBJ had to be created by a specific C compiler (GNU I think)
    - a special compile option had to be supplied to that compiler
    - parameters could not be passed
    - the routine could not call any other routines, not even
       library routines
    - the routine could not reference any global C variables

Given these restrictions, and the difficulty in overcoming some of them,
I've never proceeded with DOS "DLL" support. Maybe a "third-party"
could try to improve on the demo above, for some specific C compiler.
I don't think this necessarily requires any support from ex.exe

Bernie Ryan writes:
> If I allocate memory at the begining of a program does that
> memory stay in scope throughout the whole program ?

Yes, you can use it until you free() it, or your
program terminates.

> When one eu function calls an eu function does it use the stack?

No. It uses an internal Euphoria "call-stack" in memory
which has nothing to do with the machine stack.

> Is there a way to locate the stack, and push something on the stack.
> and recover it without disturbing eu ?

You have to use PUSH and POP machine instructions in a section
of machine code.

> How does C_FUNC and C_proc work in win32lib ?
> I understand that it uses the DLL's but this same thing will work
> if define_c_function and define_c_proc were written to work on
> any hex sequence of code that was poked into memory as long
> as it was setup in the format of a dll.

define_c_func() and define_c_proc() call an O/S routine that returns
the machine address of the C routine. This address is
saved in a table, and a small integer value is returned to you.
Later, when you call c_func() or c_proc(), passing the small integer
value, Euphoria indexes into the table, gets the address,
the number and type of parameters etc., and makes the call.

There's a standard C calling convention on WIN32 for making such
calls, that requires the arguments to be pushed onto the machine
stack (the last arg is pushed first as I recall).

Regards,
     Rob Craig
     Rapid Deployment Software
     http://members.aol.com/FilesEu/