#4036: Compiled FFI static imports are invalid when imported in GHCI
-------------------------------+--------------------------------------------
Reporter: jmillikin | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (FFI)
Version: 6.12.1 | Keywords:
Os: Linux | Testcase:
Architecture: x86_64 (amd64) | Failure: Incorrect result at runtime
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When I try to use the FFI syntax for static storage, only modules running
in interpreted mode (ie GHCI) work properly. Compiled modules have invalid
pointers, and do not work. I asked in #haskell, and tommd suggested that
this might be an architecture-dependent error in GHC.
Here's the code used to reproduce the problem. I'm using {{{sys_siglist}}}
declared in {{{<signal.h>}}}, since it's similar to how I originally found
the problem, but I suspect this will occur for any static data.
Given the following modules:
{{{
-- A.hs
{-# LANGUAGE ForeignFunctionInterface #-}
module A where
import Foreign
import Foreign.C
foreign import ccall "&sys_siglist"
siglist_a :: Ptr CString
}}}
{{{
-- B.hs
{-# LANGUAGE ForeignFunctionInterface #-}
module B where
import Foreign
import Foreign.C
foreign import ccall "&sys_siglist"
siglist_b :: Ptr CString
}}}
{{{
-- Main.hs
{-# LANGUAGE ForeignFunctionInterface #-}
module Main where
import Foreign
import Foreign.C
import A
import B
foreign import ccall "&sys_siglist"
siglist_main :: Ptr CString
main = do
putStrLn $ "siglist_a = " ++ show siglist_a
putStrLn $ "siglist_b = " ++ show siglist_b
putStrLn $ "siglist_main = " ++ show siglist_main
peekSiglist "a " siglist_a
peekSiglist "b " siglist_b
peekSiglist "main" siglist_main
peekSiglist name siglist = do
ptr <- peekElemOff siglist 2
str <- maybePeek peekCString ptr
putStrLn $ "siglist_" ++ name ++ "[2] = " ++ show str
}}}
Running the application via GHCI gives correct output:
{{{
$ runhaskell Main.hs
siglist_a = 0x00007f53a948fe00
siglist_b = 0x00007f53a948fe00
siglist_main = 0x00007f53a948fe00
siglist_a [2] = Just "Interrupt"
siglist_b [2] = Just "Interrupt"
siglist_main[2] = Just "Interrupt"
}}}
However, if one of them is compiled, its pointer will be invalid:
{{{
$ ghc -c A.hs
$ runhaskell Main.hs
siglist_a = 0x0000000040378918
siglist_b = 0x00007fe7c029ce00
siglist_main = 0x00007fe7c029ce00
siglist_a [2] = Nothing
siglist_b [2] = Just "Interrupt"
siglist_main[2] = Just "Interrupt"
}}}
I thought this might be related to
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4036>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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