Re: [Qemu-devel] QEMU fails to configure on non-x86 hosts with recent SDL2

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Mar 05, 2018 at 10:24:41AM +0000, Peter Maydell wrote:
> On non-x86 hosts with SDL2 2.0.8, configure fails:
> 
> 
> config-host.mak is out-of-date, running configure
> 
> ERROR: configure test passed without -Werror but failed with -Werror.
>        This is probably a bug in the configure script. The failing command
>        will be at the bottom of config.log.
>        You can run configure with --disable-werror to bypass this check.
> 
> The relevant configure test is the SDL one:
> #include <SDL.h>
> #undef main /* We don't want SDL to override our main() */
> int main( void ) { return SDL_Init (SDL_INIT_VIDEO); }
> 
> and it fails because on non-x86 platforms one of the SDL headers
> triggers a -Wundef warning:
> 
> cc -Wundef -o zz9.o -I /usr/include/SDL2 -c qemu-conf.c
> In file included from /usr/include/SDL2/SDL.h:38:0,
>                  from qemu-conf.c:1:
> /usr/include/SDL2/SDL_cpuinfo.h:63:5: warning: "HAVE_IMMINTRIN_H" is
> not defined, evaluates to 0 [-Wundef]
>  #if HAVE_IMMINTRIN_H && !defined(SDL_DISABLE_IMMINTRIN_H)
>      ^~~~~~~~~~~~~~~~

Ewwww, even ignoring the -Wundef issue, this is a really unpleasant
approach from SDL.  All these HAVE_* symbols SDL2 tests & defines
are polluting the global header namespace and could easily clash
with symbols defined by QEMU / $APP's own configure.ac script :-(

> Any suggestions for how to do a workaround?

Drop -Wundef when running the configiure test, or override it with -Wno-undef

If the actual ui/sdl* files fail for same reason, we could use a gcc
pragma top disable -Wundef in just those files, or set -Wno-undef in
CFLAGS on a per-.o file basis in Makefile.objs

Regards,
Daniel
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