[Caml-list] Byte code and dynamic linking of C libraries

[Caml-list] Byte code and dynamic linking of C libraries

[Yaron Minsky]

I've got some code that dynamically links in a C library.  The code works
just fine when I compile to native code, but blows up when I compile to
bytecode.  Just to be clear, the dynamic linking I'm doing happens
entirely on the C side:  I've got a c library that is linked in
statically, and the dlopen and dlclose calls all happen within that C
library.  When I try this trick in bytecode, I get a segfault.

So, any ideas as to what I need to do to make dynamic linking and byte
code to play nicely together?

Yaron


|--------/            Yaron M. Minsky              \--------|
|--------\ http://www.cs.cornell.edu/home/yminsky/ /--------|

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Re: [Caml-list] Byte code and dynamic linking of C libraries

[Nicolas Cannasse]

> I've got some code that dynamically links in a C library.  The code works
> just fine when I compile to native code, but blows up when I compile to
> bytecode.  Just to be clear, the dynamic linking I'm doing happens
> entirely on the C side:  I've got a c library that is linked in
> statically, and the dlopen and dlclose calls all happen within that C
> library.  When I try this trick in bytecode, I get a segfault.
>
> So, any ideas as to what I need to do to make dynamic linking and byte
> code to play nicely together?

Is the C library you're dynlinking is using Caml API ?
I got such problems, because when linking (under windows) to ocamlrun.lib,
your C dll is referencing ocamlrun.dll wich is the caml api library for the
bytecode interpreter (before it was ocamlrun.exe but now it's a separate dll
so the custom mode works well since both the exe and the dll are using the
same code).
The solution I know is to link staticly all the C librairies in native code.
One other is that your dynlinked C library redirects its calls to the Caml
API through the C library which is loading it.

Regards,
Nicolas Cannasse

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Re: [Caml-list] Byte code and dynamic linking of C libraries

[Markus Mottl]

On Wed, 28 Apr 2004, Yaron Minsky wrote:
> I've got some code that dynamically links in a C library.  The code
> works just fine when I compile to native code, but blows up when I
> compile to bytecode.

Hm, this may indicate that one of your C-functions accessed from OCaml
takes more than five arguments.  In this case you'll have to write a
wrapper that uses argument vectors.  E.g.:

  CAMLprim value pcre_exec_stub_bc(value *argv, int argn)
  {
    return pcre_exec_stub(argv[0], argv[1], argv[2], argv[3],
                          argv[4], argv[5], argv[6]);
  }

The external declaration in OCaml then looks as follows (note the two
entry points for byte- and native code):

  external unsafe_pcre_exec :
    irflag -> regexp -> int -> string ->
    int -> int array -> callout option
    -> unit = "pcre_exec_stub_bc" "pcre_exec_stub"
              ------------------- ----------------

Earlier OCaml-releases didn't check the number of arguments, but I'm not
sure whether you'll have to grab a CVS-version to be warned about this
(if this is the cause of the problem)?

> Just to be clear, the dynamic linking I'm doing happens
> entirely on the C side:  I've got a c library that is linked in
> statically, and the dlopen and dlclose calls all happen within that C
> library.  When I try this trick in bytecode, I get a segfault.
> 
> So, any ideas as to what I need to do to make dynamic linking and byte
> code to play nicely together?

I can't imagine any good reason why dynamic linking performed at runtime
by C-code should have an effect on the byte code interpreter.  But maybe
there are bad ones?

Markus

-- 
Markus Mottl          http://www.oefai.at/~markus          markus@oefai.at

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