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 <muri...@linux.ibm.com>
Cc: Kevin Wolf <kw...@redhat.com>
Cc: Hanna Reitz <hre...@redhat.com>
Cc: Markus Armbruster <arm...@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));
      }
  }