id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
765,x86_64 NCG goes via unsigned for FFI Int return types.,duncan.coutts@…,,"With ghc-6.4.2 on x86_64 and using the -fasm NCG we get the wrong answer for this FFI test case:

cbit.c:
{{{
int c_id (int n) {
        return n;
}
}}}

hsbit.hs:
{{{
module Foo where
foreign import ccall unsafe ""c_id"" c_id :: Int -> IO Int
}}}

{{{
ghc -c cbit.c
ghc -fffi --make test.hs cbit.o
./a.out
4294967295
}}}

Going via C we get the correct answer:

{{{
ghc -fvia-C -fffi --make test.hs cbit.o
/tmp/ghc32363.hc:135: warning: implicit declaration of function `c_id'
./a.out
-1
}}}

Obviously what's going on is that we're converting to an unsigned int value at some point so negative values are wrapping round.",bug,closed,high,,Compiler (NCG),6.4.2,invalid,,,Linux,x86_64 (amd64),,Unknown,,,,