id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
3789,Segfault and -dstg-lint errors using FFI and -XEmptyDataDecls,judahj,,"I encountered a segfault when working with some FFI code.  I eventually discovered that this code also makes `-dstg-lint` complain.

With the below files, I can reproduce the segfault and `-dstg-lint` issues using ghc-6.12.1 and ghc-6.10.3 on OS X 10.6.2.  The segfault goes away if I use -fvia-C, -O, or if I build on OS X 10.5.7.

The segfault also goes away if I use a unit type `()` instead of -XEmptyDataDecls.

{{{
$ ghc --make test-segfault.hs foreign.c -XForeignFunctionInterface \
        -XEmptyDataDecls -fforce-recomp && ./test-segfault 
[1 of 2] Compiling Types            ( Types.hs, Types.o )
[2 of 2] Compiling Main             ( test-segfault.hs, test-segfault.o )
Linking test-segfault ...
About to create...
Segmentation fault
}}}

foreign.c:
{{{
#include <stdio.h>
#include <stdlib.h>

void *
c_createFoo (int x) {
    fprintf(stderr,""Creating foo...\n"");
    fflush(stderr);
    int *p = malloc(sizeof(int));
    *p = x;
    return p;
}
}}}
Types.hs:
{{{
module Types where

import Foreign.Ptr
import Foreign.C.Types

-- Replacing this line with the following one prevents the segfault,
-- but not the -dstg-lint error.
data Foo_
-- type Foo_ = ()

foreign import ccall safe c_createFoo :: CInt -> IO (Ptr Foo_)

createFoo :: Int -> IO (Ptr Foo_)
createFoo dtype = c_createFoo (toEnum dtype)
}}}
test-segfault.hs:
{{{
module Main where

import Types

main = do
    putStrLn ""About to create...""
    createFoo 1
    putStrLn ""Created.""
}}}

The `-dstg-lint` error is somewhat long, but I can paste it if you're unable to reproduce it.",bug,closed,high,6.12.2,Compiler (NCG),6.12.1,fixed,,,MacOS X,x86,Runtime crash,,,,,