[Caml-list] Re: OCaml binary formats -- how are they linked?

[Dawid Toton <d0@wp.pl>]

On 06/14/2013 11:30 AM, Ömer Sinan Ağacan wrote:
> Hi all,
> 
> Let's say I have a C API called from OCaml. Bindings are compiled 
> to .cma, .cmx, .cmxa files.
> 
> What I'm wondering is that are those C objects linked to those 
> binary files statically or dynamically?
> 

Depending on what you do, some objects can be dynamically linked to an
OCaml program.

Since OCaml←→C interface requires the C code to follow the rules and
use the provided headers (like mlvalues.h), in practice an extra layer
of code is usually added:

---- normal OCaml stuff:
 a.ml → a.cmx + a.o
---- OCaml modules with "external" functions
 b.ml → b.cmx + b.o
---- the extra layer of C code:
 wrappers.c → wrappers.o
---- the actural C code that doesn't care about special OCaml needs:
 foo.c → foo.o
----

The OCaml compiler includes b.o and every other compiled OCaml module
in the executable.
wrappers.o and foo.o can end up as a part of dynamically linked
library, but you have choice. You can even call the linker directly
and play weird things with all the *.o files that C and OCaml
compilers produce.

Dawid