Re: [Caml-list] What's the purpose of the static library?

[Richard Jones <rich@annexia.org>]

On Tue, Sep 23, 2008 at 05:09:58PM +0800, bill yan wrote:
> Thanks a lot for your information. And we'd like to know more about the 
> OCaml library architectures, like on what situation dynamic libraries 
> are used, and when static libraries are used, and so on.. Really 
> appreciate if you could point me to a document that can help on this topic.

It's not particularly well-documented, and it changes a little in
3.11, but below is my understanding.  There are probably errors in
what follows.  If someone can correct the errors then I'll publish a
corrected document.

File: module.cmi ------------------------------

Contains the compiled interface for Module, essentially equivalent to
the contents of the *.mli file but in a compiled/binary form which the
compiler can load easily.

Created by: 'ocamlc -c module.mli', or if module.mli doesn't exist
then 'ocamlc -c module.ml' (also by 'ocamlopt -c module.ml').

Used: Whenever the toplevel or compiler uses any symbol Module.foo,
this file is consulted.

File: module.cmo ------------------------------

Contains the bytecode of the implementation of Module.

Created by: 'ocamlc -c module.ml'

Used: When linking bytecode programs, or creating bytecode libraries
(*.cma), or by the toplevel when you use #load, or by Dynlink.

File: library.cma ------------------------------

This is just a set of *.cmo files combined together.

Created by: 'ocamlc -a'

Used: Same as for module.cmo

Files: module.o and module.cmx --------------------

These two files go together.  The *.o file contains compiled native
code in the normal system object file format.  The *.cmx file contains
metainformation about the machine code in the *.o file.

Created by: 'ocamlopt -c module.ml'

Used: When linking native code programs, or creating native code
libraries.

Note(1): You normally never need to specify the *.o files by hand.  On
the command line when the compiler sees a *.cmx file, it looks for the
corresponding *.o file if it needs it.

Note(2): It is thought that the *.cmx file needs to be around even
when linking a library (*.cmxa) file in order to do cross-module
function inlining.  Both the Debian & Fedora packaging rules specify
that *.cmx files be kept around for this reason.  Whether this is
really true or not is not certain.

File: library.a and library.cmxa --------------------

These files go together.  The *.a file contains compiled native code
in the normal system archive format.  The *.cmxa file contains
metainformation.

Created by: 'ocamlopt -a'

Used: Same as for *.o/*.cmx

Note: You normally never need to specify the *.a files by hand.

File: dlllibrary.so and liblibrary.a --------------------

These files are created and used when a bytecode or native library
contains some C code.  'dllXXX.so' is created for use by the toplevel
and contains the compiled C code.  'libXXX.a' is created for use by
compiled standalone programs and also contains the same compiled C
code.

Created by: 'ocamlmklib -o library *.o *.cmo'
        or: 'ocamlmklib -o library *.o *.cmx'

Used: dlllibrary.so is dlopen(2)'d by the toplevel.
      liblibrary.a is linked in standalone programs.

Note: You normally never need to specify these files by hand.  The
*.cma/*.cmxa file contains the necessary information to find these
files if necessary.

----------------------------------------------------------------------

Rich.

-- 
Richard Jones
Red Hat