[Haskell-cafe] LLVM: function pointer in global struct

[Tom Schouten]

Hi everyone,

Using the LLVM bindings, I'm trying to create an initialized global
struct variable containing a pointer to a function.

 > {-# LANGUAGE ScopedTypeVariables #-}
 > import LLVM.Core
 > import Data.Word
 > import LLVM.Util.File(writeCodeGenModule)

 > sm_module = do
 >  tick :: Function (Word32 -> IO Word32) <- createFunction 
ExternalLinkage $ \x -> ret x
 >  info <- createNamedGlobal False ExternalLinkage "sm_info" $ 
constStruct (tick & ())
 >  return info


I run into a complaint that this pointer isn't constant when it's part
of a global variable initializer.


     No instance for (llvm-0.10.0.1:LLVM.Core.CodeGen.IsConstStruct
                        (Function (Word32 -> IO Word32) :& ()) a0)
       arising from a use of `constStruct'
     Possible fix:
       add an instance declaration for
       (llvm-0.10.0.1:LLVM.Core.CodeGen.IsConstStruct
          (Function (Word32 -> IO Word32) :& ()) a0)
     In the second argument of `($)', namely `constStruct (tick & ())'
     In a stmt of a 'do' expression:
         info <- createNamedGlobal False ExternalLinkage "sm_info"
               $ constStruct (tick & ())
     In a stmt of a 'do' expression:
         tick :: Function (Word32 -> IO Word32) <- createFunction
                                                     ExternalLinkage
                                                 $ \ x -> ret x
I suppose this is because of

 > -- |A function is simply a pointer to the function.
 > type Function a = Value (Ptr a)

being a Value instead of ConstValue.  Is there a way around this?

Cheers
Tom