[GHC] #7753: Profiling report broken with foreign exported functions

8 Mar 2013

      #7753: Profiling report broken with foreign exported functions
-------------------------+--------------------------------------------------
Reporter:  akio          |          Owner:                  
    Type:  bug           |         Status:  new             
Priority:  normal        |      Component:  Profiling       
 Version:  7.6.2         |       Keywords:                  
      Os:  Linux         |   Architecture:  Unknown/Multiple
 Failure:  None/Unknown  |      Blockedby:                  
Blocking:                |        Related:                  
-------------------------+--------------------------------------------------
 Save the following Haskell source as wrapper.hs:

 {{{
 import Foreign.Ptr
 import Control.Monad

 main = do
   fptr <- wrap wrapped
   replicateM 100 $ (return$!) =<< dyn fptr 4

 wrapped :: Double -> IO Double
 wrapped x = return $ f 10000 x

 f :: Int -> Double -> Double
 f 0 u = u
 f n u = (u / fromIntegral n) * f (n-1) u

 foreign import ccall "wrapper" wrap :: (Double -> IO Double) -> IO (FunPtr
 (Double -> IO Double))
 foreign import ccall "dynamic" dyn :: FunPtr (Double -> IO Double) ->
 Double -> IO Double
 }}}

 Then compile and run it with:

 {{{
 $ ghc -O2 wrapper.hs -fprof-auto -prof
 $ ./wrapper +RTS -p
 }}}

 It generates wrapper.prof (attached). The file contains the following
 lines:

 {{{
  CAF        GHC.IO.Encoding.Iconv    58           0    0.0    0.2     0.0
 0.2
   wrapped   Main                     80         100    0.0    1.1     0.0
 0.0
    f        Main                     81     1000100  100.0    0.0     0.0
 0.0
 }}}

 I see two problems here, (1) the inherited column is 0 for 'wrapped' and
 'f' but this is incorrect, and (2) 'wrapped' and 'f' belongs to the wrong
 cost center, 'GHC.IO.Encoding.Iconv'.

-- 
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7753
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