Linker problem with HPC and TemplateHaskell

Edward Z. Yang ezyang at
Fri Dec 19 21:32:08 UTC 2014

Sounds like a bug. File a ticket? If you can see if you can
repro on GHC HEAD that would also be helpful.


Excerpts from David Turner's message of 2014-12-19 16:24:25 -0500:
> Hi,
> I'm getting the following error message when compiling a Yesod
> application (which uses Template Haskell rather a lot) with -fhpc:
> /usr/bin/ld: ./Foundation.dyn_o: relocation R_X86_64_PC32 against
> undefined symbol `_hpc_tickboxes_Settings_hpc' can not be used when
> making a shared object; recompile with -fPIC
> Steps to reproduce:
> 1. Run 'yesod init' to make a new scaffold. Call it 'testsite' and
> select 'simple' for no database.
> 2. Run:
> cd testsite
> sed Settings.hs -i -e 's/staticRoot conf.*/staticRoot conf = "foo"/' #
> GHC doesn't like this line
> ghc --make app/main.hs  -XTemplateHaskell -XCPP -XOverloadedStrings
> -XMultiParamTypeClasses -XTypeFamilies -fhpc -O1
> Running the ghc line again completes successfully.
> It seems that there is a missing ./Settings.dyn_o in the gcc command
> line that ghc calls, the first time through. It's there the second
> time so the link succeeds. No idea what that might mean.
> It's not a problem at -O0.
> I'm using 7.8.3 so this might be fixed now.
> Not sure what else might help! Any advice gratefully received.
> Cheers,
> David

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