On 15/03/10 23:54, Iavor Diatchki wrote:
Hi,
I think that one may view a "static_wrapper" import as a pair of an
export like the one you wrote and an import of the address of the
exported function (this is useful because usually it is convenient to
install the handler on the Haskell side). Perhaps that's a better way
to explain its meaning, rather then the long-winded example that I
wrote. Thanks!
In practice, the foreign export generates slightly less direct code,
because the C code follows 2 indirections: first we enter the closure
for "cbind", and then _that_ code enters the closure for the actual
Haskell function. Perhaps with sufficient optimization on the C side
this can be avoided although I don't think that it happens at the
moment.
In terms of notation, I like the directness of the "static_wrapper"
declaration (although not so much the "static_wrapper" name!) because
it avoids duplication, thus reducing clutter and potential errors.
It seems hard to justify adding this to GHC, since it's really just
syntactic convenience for a particular case. Traditionally syntactic
sugar for FFI declarations has been implemented in the preprocessing
tools: c2hs and hsc2hs, whereas the FFI extension itself is purposefully
minimal.
So at the moment we're slightly inclined not to put it in - but feel
free to make a compelling case. Note that as an extension in its own
right it would need its own flag, documentation etc.
Cheers,
Simon
-Iavor
On Mon, Mar 15, 2010 at 3:56 PM, Tyson Whitehead<[email protected]> wrote:
On March 15, 2010 12:48:02 Iavor Diatchki wrote:
I have implemented a small extension to the FFI which allows for
"static_wrapper" imports. These are a variation on "wrapper" imports
that do not use run-time code generation. This is important in
security sensitive contexts because it avoids executable data. While
"static_wrapper" imports are less general then "wrapper" imports, they
can be used to install Haskell handlers in many C libraries where
callbacks have an extra "user-data" parameter (e.g., GTK signal
handlers).
Hi Iavor,
Would not the following also do what you want
foreign export ccall "haskellCIntCInt" \
cbind :: CInt -> StablePtr (CInt -> IO CInt) -> IO CInt
cbind :: a -> StablePtr (a-> IO b) -> IO b
cbind x f = deRefStablePtr f>>= (\f_ -> f_ x)
On the C side you would then have something like
register_callback(haskellCIntInt,<wrapped haskell closure>)
where<wrapped haskell closure> would be a stable pointer of type StablePtr
(CInt -> IO CInt) generated on the haskell side via
newStablePtr<haskell closure>
and passed to the C code.
Cheers! -Tyson
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