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Re: Decompilation

Doug Evans wrote:
J. Grant writes:
> 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
> Disassemble
> 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.
Thank you for the reply.

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--( 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).

(*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.
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?

(*2): pedantic: insert all the usual caveats of determining what's code
and what's data.
This should be feasible on architectures that separate data & code in
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


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