Bytecode object files structure - fa.caml

Message from discussion Bytecode object files structure

Pierre-Etienne Meunier

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More options Nov 13 2006, 6:41 am

Newsgroups: fa.caml

From: Pierre-Etienne Meunier <pierreetienne.meun...@ens-lyon.fr>

Date: Mon, 13 Nov 2006 11:41:53 UTC

Local: Mon, Nov 13 2006 6:41 am

Subject: Re: [Caml-list] Bytecode object files structure

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Hello,

I'd like to write an assembler, to be able to understand how the vm really
works. I've to work on this for a school project (a compiler, I want it to
output caml bytecode object files).

I've understood that the data part, after the code itself, was generated using
output_value (I didn't know this function before). What I don't get now are
the cu_reloc, cu_primitives and cu_imports fields of the compilation_unit
type.

If you can help on this,
Thanks
P.E. Meunier

On Monday 13 November 2006 11:53, Xavier Clerc wrote:

> Hello,

> As I read a substancial part of the ocaml source code, I may help you
> understanding file formats.
> Could you be more precise about what you are particularly interested
> in :
> - file type : bytecode file, cmo file, cmi file ?
> - code or data section of these files ?

> May I also ask you what you are trying to do using these elements ?

> Cordially,

> Xavier Clerc

> Le 12 nov. 06 à 15:42, Pierre-Etienne Meunier a écrit :
> > Hi,

> > I'm trying to decrypt .cmo files produced by simple programs, such as
> > 1+1;;
> > or
> > print_string "string";;
> > or
> > List.length [1;2;3;4;5];;

> > According to the source of Ocaml, there's something called the
> > "cmo_magic_number", systematically written at the beginning of
> > all .cmo
> > files. Does it have a real function for executing the programs, or
> > is it just
> > a way to make sure the file contains ocaml bytecode ?

> > Then, there's the address of what seems to be the last bytecode
> > instruction.
> > Then, the bytecode instructions, as documented in opcodes.ml.

> > After that, I can't understand anything : there vaguely seems to be
> > some
> > information related to linking or so... What is the precise
> > structure of this
> > part ? Is there some kind of a bytecode assembler ?

> > Thanks,
> > P.E. Meunier (pierreetienne.meun...@ens-lyon.fr)

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