[Qemu-devel] Qemu build failure with uninitialized variables when "-Wmaybe-uninitialized" is open

[Qemu-devel] Qemu build failure with uninitialized variables when "-Wmaybe-uninitialized" is open

[Wei, Danmei]

Hi,

When we build qemu with "-Wmaybe-uninitialized" on, and got the following error information.
  CC      qobject/json-streamer.o
  CC      qobject/json-parser.o
  CC      qobject/block-qdict.o
qobject/block-qdict.c: In function 'qdict_array_split':
qobject/block-qdict.c:259:25: error: 'subqdict' may be used uninitialized in this function [-Werror=maybe-uninitialized]
         qlist_append_obj(*dst, subqobj ?: QOBJECT(subqdict));
                         ^
cc1: all warnings being treated as errors
make: *** [qobject/block-qdict.o] Error 1

It is because of the uninitialized variable subqdict function qdict_array_split.
Thanks to confirm it.

Below is the ENV Setting:
OS: RHEL OS 7.6
Qemu Version: commit c102d9471f8f02d9fbea72ec4505d7089173f470
CFLAGS Setting in env: export CFLAGS="-g -O3 -Wmaybe-uninitialized"

Thanks,
               Danmei

Re: [Qemu-devel] Qemu build failure with uninitialized variables when "-Wmaybe-uninitialized" is open

[Thomas Huth]

On 28/02/2019 04.00, Wei, Danmei wrote:
> Hi,
> 
> When we build qemu with "-Wmaybe-uninitialized" on, and got the following error information.
>   CC      qobject/json-streamer.o
>   CC      qobject/json-parser.o
>   CC      qobject/block-qdict.o
> qobject/block-qdict.c: In function 'qdict_array_split':
> qobject/block-qdict.c:259:25: error: 'subqdict' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>          qlist_append_obj(*dst, subqobj ?: QOBJECT(subqdict));
>                          ^
> cc1: all warnings being treated as errors
> make: *** [qobject/block-qdict.o] Error 1
> 
> It is because of the uninitialized variable subqdict function qdict_array_split.
> Thanks to confirm it.
> 
> Below is the ENV Setting:
> OS: RHEL OS 7.6
> Qemu Version: commit c102d9471f8f02d9fbea72ec4505d7089173f470
> CFLAGS Setting in env: export CFLAGS="-g -O3 -Wmaybe-uninitialized"

Don't build QEMU with -O3 and -Wmaybe-uninitialized and -Werror
together. -O3 produces lots of false warnings with
-Wmaybe-uninitialized, so we currently don't support building QEMU with
that combination. You should at least add
"-Wno-error=maybe-uninitialized" if you want to build that way.

 Thomas

Re: [Qemu-devel] Qemu build failure with uninitialized variables when "-Wmaybe-uninitialized" is open

[Wei, Danmei]

I got it. Many thanks.

Thanks,
	Danmei

-----Original Message-----
From: Thomas Huth [mailto:thuth@redhat.com] 
Sent: Friday, March 1, 2019 12:42 AM
To: Wei, Danmei <danmei.wei@intel.com>; qemu-devel@nongnu.org
Cc: Hao, Xudong <xudong.hao@intel.com>
Subject: Re: [Qemu-devel] Qemu build failure with uninitialized variables when "-Wmaybe-uninitialized" is open

On 28/02/2019 04.00, Wei, Danmei wrote:
> Hi,
> 
> When we build qemu with "-Wmaybe-uninitialized" on, and got the following error information.
>   CC      qobject/json-streamer.o
>   CC      qobject/json-parser.o
>   CC      qobject/block-qdict.o
> qobject/block-qdict.c: In function 'qdict_array_split':
> qobject/block-qdict.c:259:25: error: 'subqdict' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>          qlist_append_obj(*dst, subqobj ?: QOBJECT(subqdict));
>                          ^
> cc1: all warnings being treated as errors
> make: *** [qobject/block-qdict.o] Error 1
> 
> It is because of the uninitialized variable subqdict function qdict_array_split.
> Thanks to confirm it.
> 
> Below is the ENV Setting:
> OS: RHEL OS 7.6
> Qemu Version: commit c102d9471f8f02d9fbea72ec4505d7089173f470
> CFLAGS Setting in env: export CFLAGS="-g -O3 -Wmaybe-uninitialized"

Don't build QEMU with -O3 and -Wmaybe-uninitialized and -Werror together. -O3 produces lots of false warnings with -Wmaybe-uninitialized, so we currently don't support building QEMU with that combination. You should at least add "-Wno-error=maybe-uninitialized" if you want to build that way.

 Thomas