Segmentation fault when running hs_init(0, 0) for ffi - haskell

Question

I am trying to call Haskell functions from python.
I have the following make file:
GHC=ghc
GHC_RUNTIME_LINKER_FLAG=-lHSrts-ghc7.4.1
libffi-example.so: Example.o wrapper.o
$(GHC) -o $# -shared -dynamic -fPIC $^ $(GHC_RUNTIME_LINKER_FLAG)
Example_stub.h Example.o: Example.hs
$(GHC) -c -dynamic -fPIC Example.hs
wrapper.o: wrapper.c Example_stub.h
$(GHC) -c -dynamic -fPIC wrapper.c
clean:
rm -f *.hi *.o *_stub.[ch]
clean-all:
rm -f *.hi *.o *_stub.[ch] *.so
# Runs the example Python program
example: libffi-example.so
python program.py
The only thing wrapper.c does it creating wrappers for hs_init by calling hs_init(0,0);. The wrapper is called example_init
I get a segmentation fault when running make example, in example_init (ie when calling hs_init(0,0)).
Can someone tell me why this is and/or how to fix it?
Thanks!

Answer 1

It ought to work:
"Moreover, hs_init() may be called with NULL for both argc and argv, signalling the absence of command line arguments."
It seems to be a bug in ghc-7.2.1 to ghc-7.4.1:
RFib.hs:
{-# LANGUAGE ForeignFunctionInterface #-}
module RFib where
fib :: Int -> Int
fib n
| n >= 0 = go 0 1 n
| even n = -go 0 1 (-n)
| otherwise = go 0 1 (-n)
where
go a _ 0 = a
go a b k = go b (a+b) (k-1)
foreign export ccall "rfib" fib :: Int -> Int
rfib.c:
#include <stdio.h>
#include <HsFFI.h>
int rfib(int);
int main(void) {
hs_init(0,0);
printf("%d\n", rfib(35));
hs_exit();
return 0;
}
Compile and run:
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc-7.0.2 -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
9227465
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc-7.0.4 -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
9227465
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc-7.2.1 -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
Speicherzugriffsfehler
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc-7.2.2 -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
Speicherzugriffsfehler
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc-7.4.1 -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
Speicherzugriffsfehler
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc-7.4.2 -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
9227465
$ rm rfib.o RFib.hi RFib.o a.out
$ ghc -O2 -Wall -no-hs-main RFib.hs rfib.c && ./a.out
[1 of 1] Compiling RFib ( RFib.hs, RFib.o )
Linking a.out ...
9227465
Changing two lines in rfib.c:
int main(int argc, char *argv[]) {
hs_init(&argc,&argv);
it works with all versions (>= 7.0 that I have installed).
So to fix it
pass &argc and &argv
upgrade GHC
are the two most obvious ways.