Re: [Qemu-devel] [PATCH] configure: add -Wno-format-truncation to QEMU_CFLAGS

[Daniel P. Berrange]

On Thu, Jul 20, 2017 at 04:57:29PM +0200, Eduardo Otubo wrote:
> Compilation breaks on GCC 7.1.1 20170622 (Fedora 26), thus adding
> -Wno-format-truncation to QEMU_CFLAGS on configure script is neecssary.
> 
>     hw/usb/bus.c: In function ‘usb_port_location’:
>     hw/usb/bus.c:410:66: error: ‘%d’ directive output may be truncated 
> writing between 1 and 11 bytes into a region of size between 0 and 15 
> [-Werror=format-truncation=]
>              snprintf(downstream->path, sizeof(downstream->path), "%s.%d",
>                                                                       ^~
>     In file included from /usr/include/stdio.h:939:0,
>                      from 
> /home/otubo/develop/qemu/otubo/include/qemu/osdep.h:68,
>                      from hw/usb/bus.c:1:
>     /usr/include/bits/stdio2.h:64:10: note: ‘__builtin___snprintf_chk’ output 
> between 3 and 28 bytes into a destination of size 16
>        return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
>               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>             __bos (__s), __fmt, __va_arg_pack ());
>             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>     cc1: all warnings being treated as errors
>     make: *** [/home/otubo/develop/qemu/otubo/rules.mak:66: hw/usb/bus.o] 
> Error 1
>     make: *** Waiting for unfinished jobs....
> 
> Signed-off-by: Eduardo Otubo <address@hidden>
> ---
> This warning looks pretty much bogus to me. Since building with -Werror is
> essential, we should add this flag to configure. If someone thinks this 
> warning
> is not a false positive, feel free to drop this patch.

This particular case of the warning may be a false positive, but the
-Wformat-truncation warning *can* detect serious real bugs so turning
it off is not appropriate. In any case there's a patch this problem
queued for merge already:

https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg06455.html


Regards,
Daniel
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