x86_64 NCG goes via unsigned for FFI Int return types.

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.

Trac metadata

Trac field	Value
Version	6.4.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	high
Resolution	Unresolved
Component	Compiler (NCG)
Test case
Differential revisions
BlockedBy
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Blocking
CC
Operating system
Architecture