Shared GHC libraries and the runtime system

[Lennart Augustsson]

The usual way to do this would be to include the dependency on the RTS
in the library and then vary the RTS by using LD_PRELOAD.
I think ghc does it the wrong way.

  -- Lennart

On Mon, Feb 22, 2010 at 10:00 PM, Max Bolingbroke
<batterseapower at hotmail.com> wrote:
> Hi Tyson,
>
> This blog post (http://blog.well-typed.com/2009/05/buildings-plugins-as-haskell-shared-libs/)
> might help explain the  motivation (actually there are a few relevant
> posts on the well-typed site).
>
> Essentially, I believe that this is done so that you can vary the RTS
> by changing LD_LIBRARY_PATH. I've never used this facility so I'm
> unable to say how useful this actually is (or if it actually works at
> the moment).
>
> Cheers,
> Max
>
> On 22 February 2010 21:34, Tyson Whitehead <twhitehead at gmail.com> wrote:
>> I was working on a shared library that loads up the GHC runtime (via hs_init)
>> and have been running into a bunch of undefined stg symbols.
>>
>> A bit of digging and it seems that GHC doesn't embed
>>
>>  - the dependency libHSrts-ghc6.12.1.so, and
>>  - the associated rpath /usr/lib/ghc-6.12.1
>>
>> into shared libraries that it builds.  Thus, if your main executable isn't GHC
>> generated (and hence has these), you run into unresolved symbols.
>>
>> I can work around this by manually adding them myself.  Is there any reason
>> GHC can't put this information by default into shared libraries though?
>>
>> Thanks!  -Tyson
>>
>> PS:  Further digging into the various shared libraries packaged with GHC
>> (Debian GHC package 6.12.1-2) reveal that they are actually missing
>>
>>  - the dependency libHSrts-ghc6.12.1.so, and
>>  - all rpaths (i.e., there are absolutely no rpaths in any of them)
>>
>> $ objdump -p /usr/lib/ghc-6.12.1/base-4.2.0.0/libHSbase-4.2.0.0-ghc6.12.1.so
>> ...
>> Dynamic Section:
>>  NEEDED      libHSinteger-gmp-0.2.0.0-ghc6.12.1.so
>>  NEEDED      libgmp.so.3
>>  NEEDED      libHSghc-prim-0.2.0.0-ghc6.12.1.so
>>  NEEDED      libc.so.6
>>  SONAME      libHSbase-4.2.0.0-ghc6.12.1.so
>> ...
>>
>>
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