[Qemu-devel] -Werror=tautological-compare error with -save-temps on fedora 24 gcc 6.2.1

[Qemu-devel] -Werror=tautological-compare error with -save-temps on fedora 24 gcc 6.2.1

[Anand J]

Hi,

I'm using gcc 6.2.1 for compiling qemu with following options in Fedora 24

../../../configure --enable-debug --extra-cflags="-save-temps"
make

and getting following error.

*  CC      ui/gtk.o*
*qemu/ui/gtk.c: In function ‘gd_map_keycode’:*
*qemu/ui/gtk.c:1030:21: error: self-comparison always evaluates to true
[-Werror=tautological-compare]*
*     } else if (GDK_IS_X11_DISPLAY(dpy) && gdk_keycode < 158) {*
*                     ^~*
*qemu/ui/gtk.c: In function ‘gd_set_keycode_type’:*
*qemu/ui/gtk.c:2123:18: error: self-comparison always evaluates to true
[-Werror=tautological-compare]*
*     if (GDK_IS_X11_DISPLAY(display)) {*
*                  ^~*
*cc1: all warnings being treated as errors*
*qemu/rules.mak:60: recipe for target 'ui/gtk.o' failed*
*make: *** [ui/gtk.o] Error 1*



Build works fine without -save-temps options. Does anybody know how to fix
this?

Thanks,
Anand

Re: [Qemu-devel] -Werror=tautological-compare error with -save-temps on fedora 24 gcc 6.2.1

[John Snow]

On 10/16/2016 03:08 AM, Anand J wrote:
> Hi,
>
> I'm using gcc 6.2.1 for compiling qemu with following options in Fedora 24
>
> ../../../configure --enable-debug --extra-cflags="-save-temps"
> make
>
> and getting following error.
>
> *  CC      ui/gtk.o*
> *qemu/ui/gtk.c: In function ‘gd_map_keycode’:*
> *qemu/ui/gtk.c:1030:21: error: self-comparison always evaluates to true
> [-Werror=tautological-compare]*
> *     } else if (GDK_IS_X11_DISPLAY(dpy) && gdk_keycode < 158) {*
> *                     ^~*
> *qemu/ui/gtk.c: In function ‘gd_set_keycode_type’:*
> *qemu/ui/gtk.c:2123:18: error: self-comparison always evaluates to true
> [-Werror=tautological-compare]*
> *     if (GDK_IS_X11_DISPLAY(display)) {*
> *                  ^~*
> *cc1: all warnings being treated as errors*
> *qemu/rules.mak:60: recipe for target 'ui/gtk.o' failed*
> *make: *** [ui/gtk.o] Error 1*
>
>
>
> Build works fine without -save-temps options. Does anybody know how to fix
> this?
>
> Thanks,
> Anand
>

Reminds me of a CCACHE + clang problem. Try disabling ccache to see if 
that improves matters for you. Otherwise, I'd just start disabling 
errors as long as you want to be using the save temps option with 
-Wno-tautological-compare for now.