[Haskell-cafe] OSX, ghci, dylib, what is the correct way?

[Simon Marlow]

On 15/06/2011 15:41, Jason Dagit wrote:
> On Wed, Jun 15, 2011 at 2:16 AM, Simon Marlow<marlowsd at gmail.com>  wrote:
>> On 14/06/2011 17:57, Jason Dagit wrote:
>>>
>>> On Tue, Jun 14, 2011 at 4:26 AM, Simon Marlow<marlowsd at gmail.com>    wrote:
>>>>
>>>> On 12/06/2011 20:17, Jason Dagit wrote:
>>>>>
>>>>> On Sun, Jun 12, 2011 at 11:45 AM, Brandon Allbery<allbery.b at gmail.com>
>>>>>   wrote:
>>>>>>
>>>>>> On Sun, Jun 12, 2011 at 14:31, Jason Dagit<dagitj at gmail.com>      wrote:
>>>>>>>
>>>>>>> If I build the C library as a .a, then ghci comlains that it cannot
>>>>>>> open the .dylib.  My first question is: Why does ghci need a .dylib
>>>>>>> and does it really use it?
>>>>>>
>>>>>> Static libraries are... static.  ghci would have to rebuild itself
>>>>>> against the static archive to use it; that's how static archives work.
>>>>>>   Dynamic libraries are dynamic because they can be loaded at runtime
>>>>>> instead of compile time.
>>>>>
>>>>> Interesting.  When I use dtruss to see what files ghci opens, it
>>>>> definitely opens .a files.  That gave me the impression it knows how
>>>>> to open a .a and use it at run-time.
>>>>
>>>> GHC as of version 7.0 can load .a files into GHCi.
>>>>
>>>>>>> When I build a dylib I get a [segfault when loading the code into
>>>>>>> ghci][2].
>>>>
>>>> I don't know what the cause of that is - when you load a .dylib into
>>>> GHCi,
>>>> the normal system dynamic linker is used.
>>>
>>> How would you track it down?  I'd really like to fix this and I don't
>>> mind debugging it, but I've tried all the things I could think of
>>> (valgrind, dtruss, gdb and printf).  Valgrind didn't help because ghci
>>> couldn't read from stdin.  gdb isn't so great because I was missing
>>> debug symbols for everything.
>>>
>>> I don't really believe it is an error in the RTS or the library code
>>> so it seems like gdb won't ever help here.
>>>
>>> Ideas?
>>
>> Can you build a simple .dylib, load it into GHCi and call it from Haskell?
>>   If that works, then see if you can gradually evolve the tiny example
>> towards the real failure case and see at which point it fails.
>
> I can try this.  I was hesitant to go down that road simply because
> this dylib does work if I remove the memset and any code that writes
> to that area of memory.
>
>> Can you build GHC yourself?  If so, you can link GHC with -debug, and that
>> will give you access to the debugging output from the linker (+RTS -Dl) and
>> gdb will have source information about the RTS.
>
> Building GHC myself is no problem.  I usually do that on OSX anyway so
> that I can link with iconv from macports.  This is the first time I've
> used the Haskell Platform version of GHC on osx.
>
>
>> I don't know who is generating those messages about "Reading symbols for
>> shared libraries ...", or the ones about "Could not find object file", maybe
>> those are generated by the system linker?
>
> I'm 99% sure those are from GDB.  I don't see them unless I run ghci inside gdb.
>
>> Did you compile the source files with -fPIC? (I presume that's necessary,
>> but I don't know much about OS X).
>
> I've tried with each -fPIC and -fno-common.  The makefile I use is
> linked in the original question, but here is the link again incase you
> want to look at it:
> https://github.com/dagit/GLFW-b/blob/master/Makefile
>
> The current flag configuration matches what is in the git repo for
> GLFW.  When I tried with -fPIC I didn't notice any difference.

The symptoms don't look quite right, but I wonder if it is related to 
this at all?

   http://hackage.haskell.org/trac/ghc/ticket/781

Cheers,
	Simon