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Using OCaml's run-time from LLVM-generated native code
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Date: 2008-02-01 (21:29)
From: Jon Harrop <jon@f...>
Subject: Using OCaml's run-time from LLVM-generated native code

I would like to use OCaml's run-time in code that is run-time generated by 
LLVM as simply as possible (i.e. with no regard for efficiency yet). There 
are two main motivations for this:

1. Write a native-code compiler for MiniML as an educational exercise but 
without having to implement a GC.

2. Write a tool that autogenerates bindings to native-code libraries that are 
immediately usable from OCaml without having to go via C or use external 
tools (just LLVM).

I believe the easiest solution is to autogenerate equivalents of the CAML* 
macros from OCaml's C FFI. For example, the LLVM backend can then generate 
native code equivalent to (from [1]):

CAMLprim value
create_tuple( value a, value b, value c )
    CAMLparam3( a, b, c );
    CAMLlocal1( abc );

    abc = caml_alloc(3, 0);

    Store_field( abc, 0, a );
    Store_field( abc, 1, b );
    Store_field( abc, 2, c );

    CAMLreturn( abc );

This raises several questions for me:

. Is this even possible?

. Has anyone written any self-contained toy C programs that use OCaml's 
run-time for garbage collection?

. Do I need to worry about what the C program puts on the stack or will this 
take care of itself?

. Has anyone already done this?

For anyone who hasn't already used LLVM and its excellent OCaml bindings, I 
cannot recommend it highly enough: it is a tremendous achievement.

[1] - http://www.linux-nantes.org/~fmonnier/OCaml/ocaml-wrapping-c.php

Many thanks,
Dr Jon D Harrop, Flying Frog Consultancy Ltd.