Hi,

I am trying to build a very simple Haskell function (foo) which I can then

call from C, using an example I got from the GHC FFI Wiki. The problem is that

the resulting program fails to run with a seg fault.

Here is the code:

---Haskell Module start (Foo.hs)

module Foo where

foreign export ccall foo :: Int -> IO Int

foo :: Int -> IO Int

foo n = return (length (f n))

f :: Int -> [Int]

f 0 = []

f n = n:(f (n-1))

---Haskell Module end

/*- C module start foo.c*/

#include <stdio.h>

#include "Foo_stub.h"

int main(void)

{

int x = foo(100);

//printf("x = %d\n", x);

return 0;

}

/*- C module end */

The I build the a.out with the commands:

ghc -fglasgow-exts -fffi -c Foo.hs

ghc -fglasgow-exts -fffi Foo.o Foo_stub.o foo.c

Now if I run the resulting a.out then I get:

Segmentation fault

Quickly putting this through GDB I get:

gdb ./a.out

GNU gdb Red Hat Linux (6.5-16.el5rh)

GDB is free software, covered by the GNU General Public License, and you are

welcome to change it and/or distribute copies of it under certain conditions.

Type "show copying" to see the conditions.

There is absolutely no warranty for GDB. Type "show warranty" for details.

This GDB was configured as "i386-redhat-linux-gnu"...

(no debugging symbols found)

Using host libthread_db library "/lib/libthread_db.so.1".

run

Starting program: /home/brg/dev/haskell/ffi/a.out

(no debugging symbols found)

[Thread debugging using libthread_db enabled]

[New Thread 7870144 (LWP 22448)]

Program received signal SIGSEGV, Segmentation fault.

[Switching to Thread 7870144 (LWP 22448)]

0x0805c313 in allocateLocal ()

(gdb) where

#0 0x0805c313 in allocateLocal ()

#1 0x0000005c in ?? ()

#2 0x08075c97 in base_DataziTypeable_zdLr42klvl4_srt ()

#3 0x4ee1dca0 in _dl_argv_internal () from /lib/ld-linux.so.2

#4 0x0807c920 in last_free_capability ()

#5 0x4ee1dca0 in _dl_argv_internal () from /lib/ld-linux.so.2

#6 0x00000000 in ?? ()

I am using GHC 6.6.1 built from sources on RHE5.

Many regards,

Ben

Benedict R. Gaster
S/W Architecture Team Lead
ClearSpeed Technology Plc
3110 Great Western Court
Hunts Ground Road
Stoke Gifford
Bristol
BS34 8HP

Phone: + 44 117 3172016
Fax: + 44 117 3172002
brg@clearspeed.com
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