Re: Gnulib needed in AC_CHECK_HEADERS

[Sylvain Beucler]

Hi,

I'm facing an issue with missing alloca.h + cross-compilation again:

On Sat, Oct 13, 2007 at 10:12:00PM +0200, Bruno Haible wrote:
> Sylvain Beucler wrote:
> > I'm cross-compiling an SDL application for i586-mingw32mscv.  I
> > imported the alloca module from Gnulib, as a dependency of strcasestr.
> 
> You mean the 'alloca-opt' module, I guess?
> 
> > When checking for SDL.h,
> > 
> >   AC_CHECK_HEADERS(SDL.h SDL_rotozoom.h SDL_framerate.h SDL_image.h,
> >     [], AC_MSG_ERROR([Could not find necessary SDL libs headers]))
> > 
> > ../configure fails checking for SDL.h, because SDL.h (more exactly
> > SDL_stdinc.h), seeing [HAVE_ALLOCA_H] set, tries to include <alloca.h>,
> > and fails (mingw doesn't have alloca.h).
> > 
> > How would you deal with this?
> 
> Indeed gnulib defines HAVE_ALLOCA_H always:
> 
>    2004-05-16  Paul Eggert  <address@hidden>
> 
>         * m4/alloca.m4 (gl_FUNC_ALLOCA): Define HAVE_ALLOCA_H always,
>         for backward compatibility with older code.
> 
> I think this is right. There are so many places in code which test
> HAVE_ALLOCA_H.
> 
> SDL_stdinc.h is also right: It can be used without or with gnulib.
> It would be very ugly if it #included different files at configure time
> than later, at build time.
> 
> Therefore I agree with you that adding some temporary -I options to
> CPPFLAGS while testing for SDL.h is the best workaround.


And I did it: CPPFLAGS now includes 'gnulib/lib' (src and build dirs)
during AC_CHECK_HEADERS tests.


However, it seems alloca.h is not yet present at ./configure time
(there's only gnulib/lib/alloca.in.h). So AC_CHECK_HEADERS fails
anyway:

configure:14417: checking SDL.h usability
configure:14434: i586-mingw32msvc-gcc -c -g -O2 
-I/usr/local/cross-tools/i386-mingw32/include/SDL -D_GNU_SOURCE=1 
-Dmain=SDL_main  -I/usr/local/cross-tools/i386-mingw32/include/SDL 
-D_GNU_SOURCE=1 -Dmain=SDL_main -I../gnulib/lib -I./gnulib/lib conftest.c >&5
In file included from 
/usr/local/cross-tools/i386-mingw32/include/SDL/SDL_main.h:26,
                 from /usr/local/cross-tools/i386-mingw32/include/SDL/SDL.h:28,
                 from conftest.c:117:
/usr/local/cross-tools/i386-mingw32/include/SDL/SDL_stdinc.h:169:22: error: 
alloca.h: No such file or directory


I guess I didn't clean my build directory correctly last time, I don't
see how I missed alloca.h's absence. I didn't cross-compile again
since then, hence why I only realize the problem now.


How would you deal with this? Can we generate Gnulib's alloca.h before
testing headers? Or should I just drop header tests?

Thanks!

-- 
Sylvain