Re: [PATCH v2] block-qdict: Fix -Werror=maybe-uninitialized build failure

[Philippe Mathieu-Daudé]

On 11/3/22 23:16, Murilo Opsfelder Araujo wrote:
> Building QEMU on Fedora 37 (Rawhide Prerelease) ppc64le failed with the
> following error:
>
>      $ ../configure --prefix=/usr/local/qemu-disabletcg 
> --target-list=ppc-softmmu,ppc64-softmmu --disable-tcg --disable-linux-user
>      ...
>      $ make -j$(nproc)
>      ...
>      FAILED: libqemuutil.a.p/qobject_block-qdict.c.o

This part >>>

>      cc -m64 -mlittle-endian -Ilibqemuutil.a.p -I. -I.. 
> -Isubprojects/libvhost-user -I../subprojects/libvhost-user -Iqapi -Itrace -Iui 
> -Iui/shader -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include 
> -I/usr/include/sysprof-4 -I/usr/include/lib
>      mount -I/usr/include/blkid -I/usr/include/gio-unix-2.0 
> -I/usr/include/p11-kit-1 -I/usr/include/pixman-1 -fdiagnostics-color=auto -Wall 
> -Winvalid-pch -Werror -std=gnu11 -O2 -g -isystem /root/qemu/linux-headers 
> -isystem linux-headers -iquote
>       . -iquote /root/qemu -iquote /root/qemu/include -iquote 
> /root/qemu/disas/libvixl -pthread -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 
> -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstrict-prototypes 
> -Wredundant-decls -Wundef -Wwrite
>      -strings -Wmissing-prototypes -fno-strict-aliasing -fno-common -fwrapv 
> -Wold-style-declaration -Wold-style-definition -Wtype-limits -Wformat-security 
> -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body -Wnested-externs 
> -Wendif-label
>      s -Wexpansion-to-defined -Wimplicit-fallthrough=2 
> -Wno-missing-include-dirs -Wno-shift-negative-value -Wno-psabi 
> -fstack-protector-strong -fPIE -MD -MQ libqemuutil.a.p/qobject_block-qdict.c.o 
> -MF libqemuutil.a.p/qobject_block-qdict.c.o.d -
>      o libqemuutil.a.p/qobject_block-qdict.c.o -c ../qobject/block-qdict.c

<<< is noise (doesn't provide any value) and could be stripped.

>      In file included from /root/qemu/include/qapi/qmp/qdict.h:16,
>                       from /root/qemu/include/block/qdict.h:13,
>                       from ../qobject/block-qdict.c:11:
>      /root/qemu/include/qapi/qmp/qobject.h: In function ‘qdict_array_split’:
>      /root/qemu/include/qapi/qmp/qobject.h:49:17: error: ‘subqdict’ may be used 
> uninitialized [-Werror=maybe-uninitialized]
>         49 |     typeof(obj) _obj = (obj);                                   \
>            |                 ^~~~
>      ../qobject/block-qdict.c:227:16: note: ‘subqdict’ declared here
>        227 |         QDict *subqdict;
>            |                ^~~~~~~~
>      cc1: all warnings being treated as errors
>
> Fix build failure by expanding the ternary operation.
> Tested with `make check-unit` (the check-block-qdict test passed).
>
> Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Cc: Hanna Reitz <hreitz@redhat.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> ---
> v1: https://lists.nongnu.org/archive/html/qemu-devel/2022-03/msg03224.html
>
>   qobject/block-qdict.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/qobject/block-qdict.c b/qobject/block-qdict.c
> index 1487cc5dd8..4a83bda2c3 100644
> --- a/qobject/block-qdict.c
> +++ b/qobject/block-qdict.c
> @@ -251,12 +251,12 @@ void qdict_array_split(QDict *src, QList **dst)
>           if (is_subqdict) {
>               qdict_extract_subqdict(src, &subqdict, prefix);
>               assert(qdict_size(subqdict) > 0);
> +            qlist_append_obj(*dst, QOBJECT(subqdict));
>           } else {
>               qobject_ref(subqobj);
>               qdict_del(src, indexstr);
> +            qlist_append_obj(*dst, subqobj);
>           }
> -
> -        qlist_append_obj(*dst, subqobj ?: QOBJECT(subqdict));
>       }
>   }
>