Hmm, we're looking at this. However, I don't really know what
C is or is not supposed to do here. Given
char fooble ( ... )
{
return 'z';
}
on an x86, 'z' will be returned at the lowest 8 bits in %eax.
What I don't know is, is the C compiler obliged to clear the
upper 24 bits of %eax, or does that onus fall on the callee?
Also, I don't even know where to look for the specification of
details of the C calling conventions. Anyone got a clue?
J
| -----Original Message-----
| From: Ashley Yakeley [mailto:[EMAIL PROTECTED]]
| Sent: Monday, August 06, 2001 1:34 AM
| To: GHC List
| Subject: GHC FFI Return Type Bug
|
|
| Has anyone else come across this? I've only tried this with
| Word8 but I
| suspect this is a problem with all return types smaller than
| four bytes.
|
| I've entered this as GHC bug #448104.
| <http://sourceforge.net/tracker/index.php?func=detail&aid=4481
| 04&group_id=8
| 032&atid=108032>
|
| Here's the C code:
|
| extern "C"
| {
| unsigned char foo();
| }
|
| inline void use(const char* s)
| {
| }
|
| unsigned char foo()
| {
| const char* s = "";
| use(s);
| return 0;
| }
|
| ...and the Haskell looks something like this:
|
| foreign import foo :: IO Word8
|
| do {
| w8 <- foo;
| putStrLn (show (w8 :: Word8));
| }
|
| ...and the result is this:
| 1074803712
|
| Kind of an unusual Word8 value! But note that the low byte of
| this value
| is zero.
|
| My setup:
|
| $ ghc -v
| Glasgow Haskell Compiler, Version 5.00, for Haskell 98,
| compiled by GHC
| version 5.00
| Using package config file: /usr/lib/ghc-5.00/package.conf
| Hsc static flags: -static -fignore-interface-pragmas
| -fomit-interface-pragmas -fdo-lambda-eta-expansion -flet-no-escape
|
| $ uname -a
| Linux server 2.2.19pre17 #1 Tue Mar 13 22:37:59 EST 2001 i686 unknown
|
|
| --
| Ashley Yakeley, Seattle WA
|
|
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| Glasgow-haskell-users mailing list
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