Re: [Pkg-haskell-maintainers] libffi changes - help needed

[Steve McIntyre <steve@einval.com>]

On Wed, Apr 04, 2012 at 08:15:31PM +0200, Joachim Breitner wrote:
>Hi,
>
>am I understanding the problem correctly: If one calls a variadic C
>function with libffi, one should use ffi_prep_cif_variadic() instead of
>ffi_prep_cif(), otherwise bad things may happen. Whether the function is
>variadic or not might not be known when looking at the source that calls
>ffi_prep_cif(), e.g. in the implementation of the Haskell Foreign
>Function Interface.

Correct.

>In GHC itself, ffi_prep_cif is called
> * in ./rts/Adjustor.c when provding Haskell code to C calls; as Haskell
>functions are never variadic, this is not a problem.

OK, cool. That should make things much easier.

> * in ./compiler/ghci/LibFFI.hsc in the Haskell function
>prepForeignCall, called by generateCCall
>in ./compiler/ghci/ByteCodeGen.lhs. It seems that this is only relevant
>for ghci.
>
>This seems to imply that normal compiled Haskell code, even code that
>uses the Foreign Function Interface, does never call ffi_prep_cif and is
>therefore not affected by the problem at hand. Does this sound
>plausible?

If you're reasonably sure that there's no Haskell code calling C
through libffi (just C calling Haskell), then job done. :-)

-- 
Steve McIntyre, Cambridge, UK.                                steve@einval.com
Into the distance, a ribbon of black
Stretched to the point of no turning back