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 | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |