[GHC] #2917: alloca and allocaArray do not respect alignment

[GHC]

#2917: alloca and allocaArray do not respect alignment
-----------------------------+----------------------------------------------
Reporter:  guest             |          Owner:                
    Type:  bug               |         Status:  new           
Priority:  normal            |      Component:  Compiler (FFI)
 Version:  6.10.1            |       Severity:  normal        
Keywords:                    |       Testcase:                
      Os:  Unknown/Multiple  |   Architecture:  x86           
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 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
 }}}

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2917>
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