On 29/04/2009 23:48, Philip Hölzenspies wrote:
Dear GHC-ers,
From earlier questions, it seems no one wants to get down and dirty
with linker tricks in ghc. I'm now looking over an alternative solution.
I'm currently trying to use SDL. There's a wrapper on hackage, which
works fine under Linux, but it takes some tinkering under Mac OS X,
because OS X needs instantiated Cocoa stuff for the SDL entry point.
Long story short, to use SDL with ghc on the OS X, a little wrapper
c-file needs to be written, because the linker will find a 'main'
function in libSDLmain.a which expects a function 'SDL_main' as an entry
point into the user code.
I have written a small c file that can be used to wrap around any
haskell module (see below), based on the macro (cpp) definition of
MODNAME. I can compile this c file with gcc, for, let's say a module Foo
with entry point Foo.bar (so, if we could still have ghc make the entry
point, we would say ghc -main-is Foo.bar):
gcc -c -DMODNAME=Foo -D"ENTRYPOINT=bar();" -o Foo_entry.o entry.c
However, this only works after I explicitly add ghc's "include" dir to
my search path so that HsFFI.h can be found. Before I had this
pre-processor trick, I could simply feed the c file to ghc, together
with all my haskell files. Ghc then simply adds the correct includes and
feeds the c file to the c compiler. Unfortunately, giving ghc the above
-D options doesn't do much good.
The problem seems to lie with the suffix recognition ghc does. I took
this from [1]. With the -cpp switch, the c pre-processor is used, but
only when the file has a .hs suffix. The c compiler is only run when the
file has a .c suffix. Using -x .hs puts the file correctly through the c
pre-processor, but then fails to compile it, because it's not haskell
code. Using -x .c doesn't do pre-processing (even with -cpp). I tried to
compile this wrapper using this command (assume now that we have
Foo.hsMain as an entry point):
ghc -cpp -pgmP cc -optP-E -DMODNAME=Foo -o Foo_entry.o entry.c
(Notice that you can't just use cpp, because on OS X that's a shell
script that doesn't provide CPPs full strength, so you want "cc -E".)
This doesn't work:
entry.c:27:2: error: #error MODNAME undefined!
Trying to be more explicit as to where the -D should go:
ghc -cpp -pgmP cc -optP-E -optP-DMODNAME=Foo -o Foo_entry.o entry.c
does exactly the same. Now faking .hs:
ghc -cpp -pgmP cc -optP-E -optP-DMODNAME=Foo -o Foo_entry.o -x hs entry.c
which produces the error (coming from stdio.h inclusion):
/usr/include/i386/_types.h:37:28: parse error on input `;'
So, I guess my question is: Is it possible to let a c input file of ghc
pass through *both* the c pre-processor *and* the c compiler?
Maybe I'm missing something, but what's wrong with
ghc -c -optc-DMODNAME=Foo -o Foo_entry.o entry.c
Cheers,
Simon
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