- FFI - Haskell.org

Advice on diagnosing segfaults?
by Adrian Cochrane 02 Oct '23

02 Oct '23

Hi, I've got a segfault in one of the language bindings I'm developing (fontconfig-pure), and I'm struggling to locate it. I see it occur in another project calling the language binding (so unfortunately I don't know what exactly is causing it), but GDB tells me that it occurs within a particular function I'm language binding to (and nothing more). I've attempted a few theoretical fixes without improvement (beyond triggering an infinite loop instead). And setting a breakpoint on the wrapper-function I added to create a better ABI to language bind to shows that dozens (if not more) of these calls successfully before I hit the segfault. I'm not sure how to diagnose this issue, any help would be appreciated! Cheers, Adrian Cochrane OpenWork Ltd libdggs spatial analysis Rhapsode & Haphaestus web browsers

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Re: Most efficient way to decode large C array of 32bit words?
by adrian＠openwork.nz 21 Sep '23

21 Sep '23

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Most efficient way to decode large C array of 32bit words?
by adrian＠openwork.nz 21 Sep '23

21 Sep '23

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header intact
by cori nur isa 23 Mar '17

23 Mar '17

ill join with u

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Re: [Haskell-cafe] managing embedded structs
by Henning Thielemann 29 Aug '16

29 Aug '16

On Sun, 28 Aug 2016, Alexey Khudyakov wrote: > On 27 August 2016 at 13:23, Henning Thielemann > <lemming(a)henning-thielemann.de> wrote: >> >> I want to write a Haskell interface to a C library that provides two data >> structures A and B, where B is contained in A. That is, if A is freed, then >> B is automatically freed, too. >> > I don't quite understand. Do A and B live in the same buffer and problem in > keeping buffer alive as long as there're pointers to A or B. If so > it's easy problem > and vector solves exactly this problem for storable vectors. Check > implementation > of basicUnsafeSlice. Idea is to share finalizer between ForeignPtr Sharing finalizer between ForeignPtr A and ForeignPtr B might indeed be a solution. It would require dependence on the ghc package (and thus GHC), though. > If they live in different buffers and B should not be collected as > long as A lives... This would be true in another situation, where I create a finalizer by the LLVM-JIT and need to finalize the finalizer's code if it is no longer needed. https://ghc.haskell.org/trac/ghc/ticket/12547

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managing embedded structs
by Henning Thielemann 27 Aug '16

27 Aug '16

I want to write a Haskell interface to a C library that provides two data structures A and B, where B is contained in A. That is, if A is freed, then B is automatically freed, too. There are two ways to obtain a Ptr B. Either construct it separately or as part of A, i.e. b0 :: Ptr B b0 <- createB b1 :: Ptr B b1 <- getBofA =<< createA Now I want to let the garbage collector manage the resources for B in a ForeignPtr. The first case is easy: fb0 :: ForeignPtr B fb0 <- newForeignPtr deleteB =<< createB But how to create an fb1? fa1 :: ForeignPtr A fa1 <- newForeignPtr deleteA =<< createA fb1 :: ForeignPtr B fb1 <- newForeignPtr ??? =<< withForeignPtr fa1 getBofA Obviously, there is nothing I can insert for ???. fb1 must not have its own finalizer, because fa1 already has one. But I have to make sure that fa1 lives at least as long as fb1. How to do that?

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type synonyms for dynamic imports and wrappers
by Henning Thielemann 18 Aug '16

18 Aug '16

The Haskell FFI report says that imports and exports of dynamic functions always have those types: foreign import ccall "dynamic" mkFun :: FunPtr fun -> fun foreign import ccall "wrapper" mkCallback :: fun -> IO (FunPtr fun) where 'fun' is an IO function. Since 'fn' can be a considerably large type expression I usually define type Importer fun = FunPtr fun -> fun type Exporter fun = fun -> IO (FunPtr fun) How about adding these type synonyms to Foreign?

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non-ASCII filepaths in a C function
by Henning Thielemann 25 Jul '15

25 Jul '15

In my 'soxlib' package I have written a binding to sox_format_t * sox_open_read( char const * path, sox_signalinfo_t const * signal, sox_encodinginfo_t const * encoding, char const * filetype); I construct the C filepath "path" from a Haskell FilePath using Foreign.C.String.withCString. This works for ASCII and non-ASCII characters in Linux. However, non-ASCII characters let sox_open_read fail on Windows. What is the correct way to convert FilePath to "char *"?

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allocate memory to Char **
by Lamine 29 Apr '14

29 Apr '14

Hi, I want to do write this C code in haskell code, but i have some pb: int w ; char **varnames = ccl_new_array (char *, w); int i; for (i = 0; i < w; i++) { varnames[i] = ccl_new_array (char, 100); sprintf (varnames[i], "x%d", i); } I try this code unsing mallocList to (http://lpaste.net/report/712) mallocList :: [CString] -> IO (Ptr CString) mallocList xs = do let n = Prelude.length xs p <- mallocBytes (n*100) forM_ (Prelude.zip [0..] xs) (uncurry (pokeByteOff p)) return p let n = sizeOf(undefined :: CString) allocaArray w $ \var -> do xs <- peekArray (w*n) var varnames <- mallocList xs I have an error "segmentation fault(core dumped)". can someone please help me? Thank you. Lamine

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Re: allocate memory to Char **
by Lamine 29 Apr '14

29 Apr '14

I try pokeElemOff but i have same error "segmentation fault(core dumped)". Thank for your response! On 04/29/2014 01:30 PM, Henning Thielemann wrote: > Am 29.04.2014 13:11, schrieb Lamine: > >> I try this code unsing mallocList to (http://lpaste.net/report/712) >> mallocList :: [CString] -> IO (Ptr CString) >> mallocList xs = do let n = Prelude.length xs >> p <- mallocBytes (n*100) >> forM_ (Prelude.zip [0..] xs) >> (uncurry (pokeByteOff p)) > > I guess this must be pokeElemOff. > >> return p >> >> let n = sizeOf(undefined :: CString) >> allocaArray w $ \var -> do >> xs <- peekArray (w*n) var >> varnames <- mallocList xs >> >> I have an error "segmentation fault(core dumped)". >> can someone please help me? Thank you. > -- « Chaque génération doit, dans un état relatif de captivité, découvrir sa mission. Elle a le choix de la remplir ou la trahir». Frantz Fanon

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