[GHC] #4899: Non-standard compile plus Template Haskell produces spurious "unknown symbol" linker error

[GHC]

#4899: Non-standard compile plus Template Haskell produces spurious "unknown
symbol" linker error
-------------------------------------------+--------------------------------
    Reporter:  jepst                       |        Owner:  simonmar                 
        Type:  bug                         |       Status:  new                      
    Priority:  normal                      |    Milestone:  7.4.1                    
   Component:  Compiler                    |      Version:  7.0.1                    
    Keywords:  template link prof dynamic  |     Testcase:                           
   Blockedby:                              |   Difficulty:                           
          Os:  Unknown/Multiple            |     Blocking:                           
Architecture:  Unknown/Multiple            |      Failure:  GHC rejects valid program
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Changes (by simonpj):

  * owner:  => simonmar


Comment:

 Jeff's script is wrong. The desired thing is
  * `ghc --make Main`
  * `ghc --make -prof -osuf p_o -hisuf p_hi`
 and he wasn't doing that.
  * The error message didn't make it clear that's what to do
  * There was no mention of `hisuf`, which is bad

 However there is something deeper wrong.  When compiling a TH splice
 `$(Foo.f 3)` with `-prof`, we compile the byte-code non-profiled, and link
 against the ''non-profiled'' `Foo.o`.  But which hi file will we use for
 `Foo`.  Really we should use `Foo.hi` for the TH stuff and `Foo.p_hi` for
 the stuff outside TH splices.  But GHC has no mechanism for two
 simultaneous interface files!

 It probably just about works at the moment because TH only uses the types
 of exported symbols, which don't really vary between `.p_hi` and `.hi`
 files.  The ice is pretty thin though.

 We'd also like a better error report for when you link against a `.o` file
 that (say) was compiled with profiling.  `ghc: ./Bug1.o: unknown symbol
 era` doesn't help much!

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4899#comment:2>
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