[Caml-list] Debugging mixed ocaml/C code

[Caml-list] Debugging mixed ocaml/C code

[Yaron M. Minsky]

Does anyone have any suggestions for debugging mixed ocaml/C code?  I 
have some code that uses a wrapper for the Berkeley DB.  When using some 
features of that wrapper (namely transaction support), I find that my 
app segfaults.  Unfortunately, it doesn't do the nice thing and segfault 
inside of the wrapper in a way that makes the bug findable with printfs. 
  Instead, it segfaults in a predictable place in the ocaml code 
instead.  (Surprisingly, it segfaults in the same place if I compile to 
native code or bytecode.)

My question is, does anyone have any suggestions as to how one might go 
about tracking down such a bug?  Are any of the standard debuggers (gdb, 
ocamldebug) useful for mixed ocaml/C code?

Thanks,
Yaron

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Re: [Caml-list] Debugging mixed ocaml/C code

[Olivier Andrieu]

 Yaron M. Minsky [Wednesday 11 September 2002] :
 >   Instead, it segfaults in a predictable place in the ocaml code 
 > instead.  (Surprisingly, it segfaults in the same place if I compile to 
 > native code or bytecode.)

Why is it surprising ? It probably means your C stub returns a
non-block value and caml thinks it's a block value (and when it tries
to access the block, it gets a segfault). Or it could be a block that
was allocated with a wrong size, etc.

You could use a generic function (using Obj) to print the actual
structure of the returned value (block/long, nb of fields, tag, etc).

-- 
   Olivier
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Re: [Caml-list] Debugging mixed ocaml/C code

[Yaron M. Minsky]

The wrappers are part of a larger project which will itself be released
publicly in the next few days.  In any case, I'll post a link to a copy of
just the Berkeley DB wrapper if I remember this evening.  I actually fixed
the bug in question, and the wrapper has decent support for the DB
environments, databases, cursors and transactions.  It's currently
compatible with Berkeley DB 3.3.11 and 3.2.9, but it could be updated for
the 4.x versions without too much work.
I'd be happy to have another pair of eyes on the code.  I find tracking
down bugs in C wrapper code much harder per loen of code than finding bugs
in Caml code proper.
y

> On 11 Sep 02, Yaron M. Minsky <yminsky@CS.Cornell.EDU> wrote:
>> Does anyone have any suggestions for debugging mixed ocaml/C code?  I
>> have some code that uses a wrapper for the Berkeley DB.
>
> Yaron,
>
> I unfortunately don't have any debugging hints for you, but I'm
> interested in hearing more about your BerkeleyDB module.  Do you need
> any help with it?  Will it be available to the public when you're
> done?  I have some projects coming up that will need BerkeleyDB
> access, and I've been putting them off because I didn't feel like
> writing an OCaml interface, but I would be more than happy to help you
> out!
>
> --
> ;; Erik Arneson <erik@aarg.net>      JD, Ashland Lodge No. 23 ;;
> ;; GPG Key ID: 2048R/8B4CBC9C    RAM, Siskiyou Chapter No. 21 ;;
> ;; <http://erik.arneson.org/>     <http://www.aarg.net/mason> ;;


-- 
|--------/            Yaron M. Minsky              \--------|
|--------\ http://www.cs.cornell.edu/home/yminsky/ /--------|

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Re: [Caml-list] Debugging mixed ocaml/C code

[Yaron M. Minsky]

It took me a while, but I just posted a version of my Berkeley DB 
wrapper.  Here's the URL:

   http://minsky-primus.homeip.net/ocaml/bdb.tar.gz

There are currently problems with the transactional support (it 
segfaults and I don't know why), but other than that seems to work 
pretty well.  There is currently good-but-not-complete support for 
dbenvs, dbs, cursors and transactions.

y

Erik Arneson wrote:
> On 11 Sep 02, Yaron M. Minsky <yminsky@CS.Cornell.EDU> wrote:
> 
>>Does anyone have any suggestions for debugging mixed ocaml/C code?  I 
>>have some code that uses a wrapper for the Berkeley DB.
> 
> 
> Yaron,
> 
> I unfortunately don't have any debugging hints for you, but I'm
> interested in hearing more about your BerkeleyDB module.  Do you need
> any help with it?  Will it be available to the public when you're
> done?  I have some projects coming up that will need BerkeleyDB
> access, and I've been putting them off because I didn't feel like
> writing an OCaml interface, but I would be more than happy to help you
> out!
> 

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