Re: [Ocamlnet-devel] Re: How to make the library PCRE dynamically loadable

[Gerd S. <in...@ge...>]

Sorry for the small mistakes. I was a bit tired when writing
the instructions up.

On 2001.12.16 19:20 Markus Mottl wrote:
> Gerd Stolpmann schrieb am Sonntag, den 16. Dezember 2001:
> > because ocamlnet depends on PCRE, I have tried to compile PCRE (4.8-1) as 
> > DLL. It works as follows:
> 
> The newest version of PCRE for OCaml (4.10-1) uses an upgraded version
> of Phil Hazel's PCRE-library. I am not sure whether this can make a
> difference.
> 
> > This make will fail (it cannot make pcretest). Look into pcre-C/.libs,
> > and check if there is libpcre.so.0.0.1. If so, the part of the build we
> > need has succeeded.
> 
> Everything's fine up to here.
> 
> > Now:
> > 
> > cp .libs/libpcre.so.0.0.1 ../pcre-OCaml/dllpcre.so
> > cp .libs/libpcre.a ../pcre-OCaml
> > cd ../pcre-OCaml
> > ocamlc pcre.mli
> > ocamlc pcre.ml
> > ocamlopt pcre.ml
> 
> Shouldn't this be:
> 
>   ocamlc -c pcre.ml
>   ocamlopt -c pcre.ml

Yes, of course.
 
> > ocamlmklib -o pcre pcre.cma

ocamlmklib -o pcre pcre.cmo

is right. ocamlmklib has a strange interface. It appends the suffix (.cma
or .cmxa) to the output name.

> > ocamlmklib -o pcre pcre.cmx
> 
> This doesn't seem to work: pcre.cma would obviously be overwritten
> during reading.
> 
> I am not sure what mode of installation the users would prefer most.
> Maybe it would be better to have two separate shared libraries, one for
> the C-library and another for the stubs? I have just taken my first look
> at the documentation of the new ocamlmklib-tool and it would probably
> work more smoothly this way.

This may work, but see below. You can create dllpcre.so by

ocamlmklib -o pcre pcre_intf.o -lpcre

and this adds libpcre.so as dependent library. I think this is the reason
why Xavier changed the naming conventions between OCaml 3.03 and 3.04;
now all OCaml-specific libraries follow the name pattern dll*.<extension>
so you can have a OCaml library dllpcre.so and a generic library libpcre.so.

(Note that ocamlmklib -o pcre now creates dllpcre.so! It depends on the type 
of the other objects you give on the command line.)

But: Many people already have pcre on their disk (especially
the users of free OS), but probably the wrong version. It would not be a
good idea forcing them to replace the system-wide library, and it can
become difficult to have two shared libraries with the same name.

I don't really know whether the PCRE stubs only work for certain PCRE
versions, or whether they are generic enough such that they will work
with every installed system-wide PCRE library.

> If anybody manages to improve the build process such that a shared
> PCRE-library is built automatically (if possible) in a portable way,
> I'd be glad to add this to the PCRE-distribution... :)

I think there are only two choices:

- Have two libraries libpcre.so and dllpcre.so with the outlined problems

- Because it is not possible to add objects later to a shared library,
  pcre_intf.o must be added to the command creating the shared library.
  There are again two ways:
 
   * Keep the current Makefile in pcre-C and patch it

   * Replace the whole Makefile in pcre-C with a self-written one. Especially
     drop libtool, it is not really helpful. Compile the C files 
     with ocamlc -c; this will add the necessary -fPIC options, too.
     Make the shared library with ocamlmklib.

I think the last alternative is by far the simplest one. I am able to compile
PCRE and create the library with only two commands:

ocamlc -ccopt -I. -c maketables.c study.c get.c pcre.c pcre_intf.c
ocamlmklib -o pcre maketables.o study.o get.o pcre.o pcre_intf.o

And these commands work on all platforms that support shared libraries under
OCaml, so there is no need for libtool.

Gerd
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