#15933: Wrong size for int for callbacks into Haskell from foreign code -------------------------------------+------------------------------------- Reporter: iliastsi | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.4.3 (FFI) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The following code produces different results on amd64 (64-bit little endian) and s390x (64-bit big endian). `foo.h:` {{{#!c typedef void(*hs_callback)(int x); extern void function_in_c(hs_callback cb); }}} `foo.c:` {{{#!c #include "foo.h" void function_in_c(hs_callback cb) { int x = 10; cb(x); } }}} `Foo.hs:` {{{#!hs module Main(main) where import Foreign import Foreign.C type HsCallback = CInt -> IO () foreign import ccall "foo.h function_in_c" functionInC :: FunPtr HsCallback -> IO () foreign import ccall "wrapper" wrap :: HsCallback -> IO (FunPtr HsCallback) main = do f <- wrap $ \x -> print x functionInC f freeHaskellFunPtr f }}} On amd64 the output is 10, but on s390x is 0. On both machines, `sizeOf (undefined :: CInt) == sizeof(int) == 4`. When changing `HsCallback` to: {{{#!hs type HsCallback = Int -> IO () }}} both produce the same, correct result, but the above seems wrong, as `sizeOf (undefined :: Int) == 8`. This has been reproduced with both ghc-8.4 and ghc-8.2, and causes dbus to fail to build on s390x (https://github.com/rblaze/haskell-dbus/issues/26), as it relies on libxml-sax which contains the above (simplified) code. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15933 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler