Incremental linking

Incremental linking

[Dawid Toton]

I have lot of modules and they are compiled to native code.
So I have .cmx and .o files and want to link them faster.

Is is possible to make linking an associative operation acting on modules?

I would like to do something like the following:
Knowing the correct partial order of modules (that compiler requires) I
can create a tree that preserves that order. Leafs are modules. Other
nodes of the tree correspond to a result of linking all descendant
modules. Modules that are frequently recompiled are placed closer to the
root. This way I expect to execute less linking operations during
development.

Documentation of ld says that files produced with --relocatable can be
used as intermediate partially linked files. Can something like this be
done with object code produced by ocamlopt?
I don't know ocaml-specific details of linking, so maybe I overlook some
obvoius obstacle?

Dawid

Re: [Caml-list] Incremental linking

[Gerd Stolpmann]

Am Dienstag, den 29.09.2009, 20:39 +0200 schrieb Dawid Toton:
> I have lot of modules and they are compiled to native code.
> So I have .cmx and .o files and want to link them faster.

Well, you can link several .cmx files (and their accompanying .o files)
to a .cmxa file (and an accompanying .a file): ocamlopt -a

You cannot do the same again on the next level, i.e. link
several .cmxa/.a together to get another .cmxa/.a. (I don't remember why
this restriction exists.)

Gerd

> 
> Is is possible to make linking an associative operation acting on modules?
> 
> I would like to do something like the following:
> Knowing the correct partial order of modules (that compiler requires) I
> can create a tree that preserves that order. Leafs are modules. Other
> nodes of the tree correspond to a result of linking all descendant
> modules. Modules that are frequently recompiled are placed closer to the
> root. This way I expect to execute less linking operations during
> development.
> 
> Documentation of ld says that files produced with --relocatable can be
> used as intermediate partially linked files. Can something like this be
> done with object code produced by ocamlopt?
> I don't know ocaml-specific details of linking, so maybe I overlook some
> obvoius obstacle?
> 
> Dawid
> 
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-- 
------------------------------------------------------------
Gerd Stolpmann, Bad Nauheimer Str.3, 64289 Darmstadt,Germany 
gerd@gerd-stolpmann.de          http://www.gerd-stolpmann.de
Phone: +49-6151-153855                  Fax: +49-6151-997714
------------------------------------------------------------

Re: [Caml-list] Incremental linking

[Xavier Leroy]

Dawid Toton wrote:
> I have lot of modules and they are compiled to native code.
> So I have .cmx and .o files and want to link them faster.
> Is is possible to make linking an associative operation acting on modules?
> [...]
> Documentation of ld says that files produced with --relocatable can be 
> used as intermediate partially linked files. Can something like this be 
> done with object code produced by ocamlopt?

Yes.  "ocamlopt -pack" actually calls "ld -r" underneath to
consolidate several compilation units in a single .cmx/.o file.
"ld -r" will resolve references between these compilation units.

Gerd Stolpmann wrote:
> Well, you can link several .cmx files (and their accompanying .o files)
> to a .cmxa file (and an accompanying .a file): ocamlopt -a

 From a linking standpoint, "ocamlopt -a" is equivalent to "ar": it
does not resolve any references, just concatenates individual
.cmx/.o files in a single .cmxa/.a file.   That can still speed up
linking a bit, since reading one big .a file is faster than reading a
zillion small .o files.

Generally speaking, I'm somewhat surprised that linking time is an
issue for Dawid.  Modern Unix linkers are quite fast, and the
additional link-time work that OCaml does is small.  Let us know if
you manage to narrow the problem.

- Xavier Leroy