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Debugging C and OCaml
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Date: 2010-03-02 (00:52)
From: Jianzhou Zhao <jianzhou@s...>
Subject: Re: [Caml-list] Debugging C and OCaml
On Mon, Mar 1, 2010 at 7:48 PM, Jianzhou Zhao <jianzhou@seas.upenn.edu> wrote:
> On Mon, Mar 1, 2010 at 10:19 AM, Mark Shinwell <mshinwell@janestreet.com> wrote:
>> On Mon, Mar 01, 2010 at 10:10:44AM -0500, Jianzhou Zhao wrote:
>>> My main program is C++. It uses C functions to call
>>> OCaml functions, and these OCaml functions also call
>>> C functions and wrapped C++ functions sometimes.
>>> I can debug from C++, but it stops when it meets
>>> an OCaml binding. Does anyone know an efficient
>>> solution about how to debug across different languages?
>> Is this native code compilation?
> I compiled OCaml code into *.o by 'ocamlc -custom -output-obj...',
> and then linked it with *.o from C and C++ code.
> I think this isnt a native compilation.
> My main C++ program is eventually compiled into a shared library.
> If I do 'ocamlopt', ld reports:
> /usr/lib64/gcc/x86_64-suse-linux/4.3/../../../../x86_64-suse-linux/bin/ld:
> /mnt/eclipse/acg/users/jianzhou/tools/ocaml-3.11.2//lib/ocaml/libasmrun.a(amd64.o):
> relocation R_X86_64_PC32 against symbol `caml_last_return_address' can
> not be used when making a shared object; recompile with -fPIC
> So I am doing ''ocamlc -custom' for the time being.
>> If so, you should be able to use gdb to debug into the Caml bindings at the
>> assembly level -- does that work?  Unfortunately at the moment there is no Caml
>> compiler support for emitting the debug info required by gdb to debug at the
>> language level.  That said, ocamlopt-compiled assembly code is fairly easy to
>> read, and you should be able to get something resembling a backtrace using
>> "where".
> Now I can debug into OCaml assembly from C, and its stack frames.
> #0  0x00007ffff6cad3f4 in caml_interprete ()
> #1  0x00007ffff6caa54f in caml_callbackN_exn ()
> #2  0x00007ffff6caa64a in caml_callback_exn ()
> #3  0x00007ffff6caa658 in caml_callback ()
> ...
> It seems that OCaml runtime is interpreting via 'caml_interprete' the
> OCaml function which C
> calls at runtime. If this is true, we cannot really debug that OCaml
> function, but we can
> see how it is interpreted. But I guess we can debug the real assembly if I do
> native compilation.

If we do native compilation, will each OCaml function be assembled to
a function in assemly with a readable name? That will help a lot while
reading the assemly code.

>> Mark
> --
> Jianzhou