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- From: "J. Grant" <jg-lists at jguk dot org>
- To: Doug Evans <dje at transmeta dot com>
- Cc: binutils <binutils at sources dot redhat dot com>, cgen at sources dot redhat dot com
- Date: Thu, 05 Dec 2002 00:13:57 +0000
- Subject: Re: Decompilation
- References: <3DE6AFF4.firstname.lastname@example.org> <email@example.com>
Doug Evans wrote:
J. Grant writes:
Thank you for the reply.
> I am currently working on some decompilation methods/ideas. I have been
> looking at the suitability of implementing using the GNU tools as a
> base. I realise this is a very complex process, so would like to ask
> peoples opinions before diving in and coding in all the wrong places.
> I would like to achive something similar to the way that gcc is the
> front end for compiling. For each of the stages below I would welcome
> sugested areas of binutils/GCC that I should focus my work on. I have
> been modifying objdump to produce the intermediate code. Clearly a lot
> of new code needs to be written to complete this work. If anyone has
> sugestions for the direction I should take this is welcome.
> Stage 1: Front end
> Input machine code binary
> Abstract intermediate code generation
> Intermediate code output
What if you used cgen for stage 1?
I've always wanted to add the rtl to the opcodes files of cgen (*1),
but haven't had a reason or impetus to.
With that (and some suitable cover/utility fns) I believe you could easily
go from binary to intermediate code (*2). Only for the targets that cgen
supports of course.
Having just checked cgen, I think it might be useful to use for this
purpose. It is a very interesting project.
Is the CPU description language complete? I have been working with
C--(http://cminusminus.org/) and modifying objdump currently. C-- seems
more of an intermediate code language than the cgen one (from reading
the docs). I am not sure of the exact organisation of GCC and binutils.
I notice the use of Scheme as the implementation language, I have been
leaning towards C for my research so far. Certainly for the first phase
it seems suitable IMO. I have not started on phase 2 or 3 yet (beyond
considerations of techniques).
Is there cgen Scheme source in binutils currently? I have not seen any
as part of the opcodes dir or other areas. Is it only available
separatly from the home page currently?
(*1): At some point I've been expecting binutils to want to boot cgen
out of libopcodes. I dunno. But I've always wanted to create libcgen too.
There's a lot more ISA utilities that can be provided with cgen and should
be made available in the form of a library, but whether they belong in
libopcodes and shipped with binutils is certainly debatable.
This should be feasible on architectures that separate data & code in
(*2): pedantic: insert all the usual caveats of determining what's code
and what's data.
different sections. Targets such as SH that I believe place const data
inline in .text would have to use some heuristics based on access of the
data I expect.
Comments or sugestions welcome