[copied to Sigbjorn]
> We're groping around in the dark here
Sorry, yes we are. It is a bit cheeky of me to always punt and say
"I'll bet it is a GHC problem" when I haven't even seen the bug myself
on a machine whose configuration I know. Sorry about that.
In fact, it turns out that you've uncovered a bug in the ffi backend
of GreenCard. The ghc backend (and GHC itself) is fine though so I'd
guess that Sigbjorn tested this release with the ghc backend but since
then the Makefile (or something in the hslibs Makefile hierarchy)
switched to using the ffi backend.
I'll set about fixing this right away.
In the meantime, adding this line:
SRC_GC_OPTS += --target ghc
to hslibs/win32/Makefile may fix the problem (but I haven't been able
to test this myself).
I'm attaching details for those who want them.
--
Alastair Reid
[Explanation of how word8 is currently marshalled by GreenCard deleted]
> On a big-endian machine I'd expect this to break. Does it?
Digging deeper into my memory of GreenCard, the answer should be no
and the could should be perfectly safe (the word "should" is key here).
Greencard is supposed to turn each %fun into a pair of functions - one
Haskell, one C. They are supposed to comminucate with each other
through a common set of types which includes Word32 but excludes
Word8. To send a Word8 from one to the other we:
Convert the word8 to word32.
Hand the word32 across the border.
Convert the word32 back into a word8.
This is what happens in the Hugs backend
primFun(prim_foo_rgb)
{ BYTE arg1; BYTE arg2; BYTE arg3;DWORD res1;;
arg1 = (BYTE)(hugs->getWord()); // THESE 3 LINES
arg2 = (BYTE)(hugs->getWord()); // THESE 3 LINES
arg3 = (BYTE)(hugs->getWord()); // THESE 3 LINES
{ res1 = RGB(arg1,arg2,arg3);
hugs->putWord((DWORD)(res1));
hugs_returnIO(1);
}
}
and, through the magic of _casm_, in the ghc backend
rgb :: BYTE -> BYTE -> BYTE -> COLORREF
rgb gc_arg1 gc_arg2 gc_arg3 =
unsafePerformIO(
case ( word8ToWord32 gc_arg1) of { arg1 ->
case ( word8ToWord32 gc_arg2) of { arg2 ->
case ( word8ToWord32 gc_arg3) of { arg3 ->
_casm_ ``do {BYTE arg1; BYTE arg2; BYTE arg3;DWORD res1;
arg1 = (BYTE)%0; arg2 = (BYTE)%1; arg3 = (BYTE)%2;
do { res1 = RGB(arg1,arg2,arg3);
%r = (DWORD)(res1);} while(0);} while(0);'' arg1 arg2 arg3
>>= \ res1 ->
(return (res1))}}})
but not in the ffi backend
DWORD prim_rgb(BYTE arg1,BYTE arg2,BYTE arg3)
{ DWORD res1;
do { res1 = RGB(arg1,arg2,arg3);
return((DWORD)(res1));} while(0);
}
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