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

[Eugene Crosser]

Hello all,

I am new here, but I want to report what I suspect may be a problem.

I ran into it while using some third-party package from hackage on a
32bit Linux with ghc 7.4.1. I discovered that off_t fields in the .hsc
files in the package where interpreted as 32bit words. I suspected that
64bit offsets should be used because even 32bit Linux has "largefile"
support with 64bit offsets.

I found that earlier versions of hsc2hs included HsFFI.h into the
generated C code, and HsFFI.h in turn indirectly includes ghcautoconf.h
which has

#define _FILE_OFFSET_BITS 64

in it. So, if I build the .hsc files like this:

hsc2hs -i HsFFI.h filename.hsc

then off_t is 64bit and 64bit file manipulation syscalls are used. I did
not check it but I think that earlier versions of hsc2hs where creating
largefile-aware version of the code by default, because HsFFI.h was
included in the code by default.

This is a simple test program:

==== checktypes.hsc ====
-- run like this: hsc2hs checktypes.hsc && runhaskell checktypes.hs
module Main where
#include <sys/types.h>
main = do
  putStrLn $ show (#size off_t)
========================

$ hsc2hs checktypes.hsc && runhaskell checktypes.hs
4
$ hsc2hs -i HsFFI.h checktypes.hsc && runhaskell checktypes.hs
8

As I understand, this situation means that while the ghc itself and
haskell programs compiled by it are largefile-capable, any third party
modules that contain .hsc files are not. If I am right, this is probably
not a good thing.

Please can some guru take a look at this issue?

See also:
http://www.haskell.org/pipermail/glasgow-haskell-users/2009-February/016606.html
http://www.haskell.org/pipermail/cvs-ghc/2011-September/065848.html

Thanks,

Eugene

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