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Date: Tue, 10 Sep 2013 18:15:27 +0200
From: Adrien Nader <adrien@notk.org>
To: oleg@okmij.org
Cc: alain@frisch.fr, Xavier.Leroy@inria.fr, caml-list@inria.fr
Message-ID: <20130910161527.GA11953@notk.org>
References: <522D8605.1050603@frisch.fr>
 <20130910020157.41613.qmail@www1.g3.pair.com>
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User-Agent: Mutt/1.5.20 (2009-06-14)
Subject: Re: [Caml-list] Accelerating compilation

On Tue, Sep 10, 2013, oleg@okmij.org wrote:
> The real problem in my view is the strange decision to load shared
> libraries at link time and force the resolution of their undefined
> references. This decision certainly makes linking slower, without
> providing much benefit, it seems. After all, if the resolution
> succeeded at link time, it may still fail at run time since the
> linked executable can be run in a different location or even a
> different computer.
> 
> So, the real problem to me is ocamlc using RTLD_NOW flag when loading
> shared library. Removing the flag would make linking faster, and less
> painful.
> 
> A few technical details: dlopen with the problematic flag occurs in
> the function caml_dlopen in the file byterun/unix.c
> 
> void * caml_dlopen(char * libname, int for_execution, int global)
> {
>   return dlopen(libname, RTLD_NOW | (global ? RTLD_GLOBAL : RTLD_LOCAL) | RTLD_NODELETE);
>   /* Could use RTLD_LAZY if for_execution == 0, but needs testing */
> }
> 
> That function caml_dlopen is used within caml_dynlink_open_lib,
> which, under alias dll_open, is called in Dll.open_dll. The latter
> function is invoked in Bytelink.link_bytecode.

That completely breaks for cross-compilation. No matter how hard you
try, you're going to have troubles loading a PE32 shared library from
your ELF executable (and even more if you try to load AArch64 on MIPS).
 :) 

And of course, right now I can't find what I've done for that. I guess
I'll have to find again soon though.

-- 
Adrien Nader