Re: [Caml-list] Error with and Proper Library Usage

[Kenneth Adam Miller <kennethadammiller@gmail.com>]

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I actually got it down to as little as this:

let x = Bap_memory.create Bap_common.LittleEndian
(Bap_types.Std.Word.of_int 32 0) (Core_kernel.Bigstring.of_string "\xc3")
in
let y = ok_exn x in
let d = Bap_disasm.disassemble `x86_64 y in
Bap_disasm.Disasm.insn_at_mem d y;;

- : insn option = None

I don't understand; c3 is the opcode for return. I tried it with both `x86
and 64 as in the example. Both return none...

On Sat, Mar 7, 2015 at 12:28 AM, Kenneth Adam Miller <
kennethadammiller@gmail.com> wrote:

> So, I want to use CMU's BAP to do some internal processing for a task that
> I have been assigned. One of the pertinent parts is transforming assembler
> representations of CPU instructions into the BAP Intermediate Language, or
> BIL. It's kind of difficult, because there's only so much documentation
> that is really anything more than just the MLI interface and the OCaml Doc
> generated stuff. I have a lot of questions about how to proceed, but before
> I begin eliciting the problem and all, let me explain about how I got where
> I am.
>
> You can install BAP through opam, but you don't get the documentation I
> don't think. So,
>
> git clone github.com/BinaryAnalysisPlatform/bap/
>
> and then just follow the instructions on how to build it, it's not hard at
> all, I got it going on Ubuntu 14.04. The only thing I ran into was an error
> on a llvm dependency, which required that I edit the opam file so that I do
> "--with-llvm-version=3.4" on the configure command line as an option. After
> that everything ran smoothly.
>
> Once you run bapbuild and make and all that, if you read the Makefile you
> can see that you can generate all the documentation with:
>
> make doc
>
> which will place the HTML files at:
>
> _build/bap.docdir
>
> Opening up the index file at _build/bap.docdir/index.html, you can see
> that the documentation starts off with a note about using Bap.Std as
> everything else is interface files. What confused me is the seeming
> repetition of the documentation that is generated. It seems that some of
> the documentation on some of the very same pages is duplicated for certain
> sections. Why does it do so much duplication?
>
> The next question I have has to do with code organization. It seems that
> ocamldoc derives the documentation from MLI files, and I know, I know-you
> can limit or edit the exposure and type definition of your ml files so that
> they form modules that control access from the outside. But I don't see how
> to combine usage of the modules that the BAP author has done (I haven't
> read the BAP code itself in terms of the ml, just searched around, consumed
> the documentation, the examples directory contents (meager) and read over
> readbin.ml and bap_mc.ml
>
> Most important regarding proper consumption of the code that I have is are
> the two avenues that I think would have made it the easiest for me to make
> use of the library.
>
> First, using the toplevel I tried to construct a BIL set of statements.
> But the way the code works, you actually have to compose a disassembler
> that is specific to your architecture (x32/64 and ARM vs Intel or
> whatever). You then have to construct memory, and from that memory
> construct an Insn type, which is meant to be the canonical, cross
> disassembler type representation of an instruction. I can see how module
> use makes for great reusability of code. Problem is, the type definitions
> that the toplevel reports (baptop) and those of which are reported in the
> documentation seem to differ often. TL;DR here, I tried to get as close to
> the front page mention of how to use module Disasm, which meant
> Disasm.insn_at_mem function, but I had a hard time navigating the modules
> to create what I wanted. It seems like each one thing depends on some other
> portion of the library, and at one point I hit a dead end. The
> documentation mentions the same functions being exposed copiously, but
> that's when the type definitions wouldn't match up or something.
>
> Lastly, and ultimately even more confusing is that of bap_mc.ml, which I
> saw as my second easiest avenue for usage of the BAP library. I saw
> bap_mc.ml line 55 as my chance;
>
>
> https://github.com/BinaryAnalysisPlatform/bap/blob/master/src/bap_mc/bap_mc.ml#L55
>
> If I just were to modify it so that it, instead of watering down the
> string constructed, were to just pipe the insn object to a BIL constructor,
> and then use the sexp_of_bil transformer, then I could just drop it from
> there to be printed or converted to string and then printed.
>
> Naturally, I tried with several different module's bil constructor. But
> most notably I think that the Std bil constructor blew up, so here's what I
> replaced that line with:
>
>   let s = (* Sexp.to_string @@ Sexp.List (List.rev res) in*)
>     sexp_of_bil (Bap.Std.Insn.bil insn) in
>
> But then even that blew up with:
>
> Error: This expression has type ('a, 'b) Insn.t
>        but an expression was expected of type insn
>
> Anyway that describes the past two days of jumping into the biggest ocaml
> project that I've even been into. I'm really excited to become more
> proficient, but I think there's something I'm missing about OCaml library
> organization strategies writ large.
>

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