alloca and allocaArray do not respect alignment

When allocating memory with alloca or allocaArray the alignment of the Storable is not respected, alignment seems to be on 8 byte boundary. malloc and mallocArray seem to have the same problem. And because of this functions like withArray etc also break the alignment restriction of the array element.

Run this and look at the pointer.

import Foreign.Ptr
import Foreign.Storable
import Foreign.Marshal.Array
import Foreign.Marshal

data Foo = Foo

instance Storable Foo where
    sizeOf _ = 8
    alignment _ = 256

main =
    allocaArray 5 $ \ p -> do
    let _ = p :: Ptr Foo
    print p
    q <- mallocArray 5
    let _ = q :: Ptr Foo
    print q

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (FFI)
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	lennart@augustsson.net
Operating system
Architecture	x86