Turns out this was already a known issue: https://ghc.haskell.org/trac/ghc/ticket/9762 and a fix is now on the way for 7.10.1. In the meantime, adding -fomit-interface-pragmas works for me. Thanks, David On 19 December 2014 at 21:58, David Turner wrote:

Ok, I've opened https://ghc.haskell.org/trac/ghc/ticket/9909

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 wrote:

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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:

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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