Linker problem with HPC and TemplateHaskell

David Turner dct25-561bs at
Wed Dec 24 12:42:37 UTC 2014

Turns out this was already a known issue: and a fix is now on the
way for 7.10.1. In the meantime, adding -fomit-interface-pragmas works
for me.



On 19 December 2014 at 21:58, David Turner
<dct25-561bs at> wrote:
> Ok, I've opened
> I won't be able to repro on HEAD in the near future, I'm afraid.
> Many thanks,
> On 19 December 2014 at 21:32, Edward Z. Yang <ezyang at> wrote:
>> Sounds like a bug. File a ticket? If you can see if you can
>> repro on GHC HEAD that would also be helpful.
>> Edward
>> 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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