Removal of #include <HsFFI.h> from template-hsc.h breaks largefile support on 32bit Linux

John Meacham john at
Fri Feb 17 23:51:35 CET 2012

On Fri, Feb 17, 2012 at 2:12 PM, Simon Marlow <marlowsd at> wrote:
> On 17/02/12 19:36, John Meacham wrote:
>> It isn't local to a file though because it changes the ABI, for instance
>> void foo(off_t *x);
>> it will blow up if called from a file with a differently sized off_t.
> But we're talking about Haskell code here, not C code.  There's no way for
> something to "blow up", the typechecker will catch any discrepancies.
> Perhaps I don't understand what problem you're thinking of - can you give
> more detail?

Someone writes a C function that returns an off_t * that is foreign
imported by a haskell
program using Ptr COff, the haskell program then writes to the output
pointer with the COff
Storable instance. However the imported function was compiled  without
64 bit off_t's so it
only allocated 32 bits to be written into so some other memory gets
overwritten with garbage.
64 bit off_t's change the ABI of called C functions
much like passing -m32 or -mrtd does so should be considered a
all-or-nothing sort of thing. In
particular, when ghc compiles C code, it should make sure it does it
with the same ABI flags
as the rest of the thing being compiled.

environment as the rest of the code.

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