Re: [PATCH] hw/virtio/virtio-gpu: Fix compiler warning when compiling with -Wshadow

[Thomas Huth]

On 08/10/2023 10.57, Michael S. Tsirkin wrote:
> On Fri, Oct 06, 2023 at 06:45:08PM +0200, Thomas Huth wrote:
> > Avoid using trivial variable names in macros, otherwise we get
> > the following compiler warning when compiling with -Wshadow=local:
> >
> > In file included from ../../qemu/hw/display/virtio-gpu-virgl.c:19:
> > ../../home/thuth/devel/qemu/hw/display/virtio-gpu-virgl.c:
> >   In function ‘virgl_cmd_submit_3d’:
> > ../../qemu/include/hw/virtio/virtio-gpu.h:228:16: error: declaration of ‘s’
> >   shadows a previous local [-Werror=shadow=compatible-local]
> >    228 |         size_t s;
> >        |                ^
> > ../../qemu/hw/display/virtio-gpu-virgl.c:215:5: note: in expansion of macro
> >   ‘VIRTIO_GPU_FILL_CMD’
> >    215 |     VIRTIO_GPU_FILL_CMD(cs);
> >        |     ^~~~~~~~~~~~~~~~~~~
> > ../../qemu/hw/display/virtio-gpu-virgl.c:213:12: note: shadowed declaration
> >   is here
> >    213 |     size_t s;
> >        |            ^
> > cc1: all warnings being treated as errors
> >
> > Signed-off-by: Thomas Huth <thuth@redhat.com>
> > ---
> >   include/hw/virtio/virtio-gpu.h | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h
> > index 390c4642b8..8b7e3faf01 100644
> > --- a/include/hw/virtio/virtio-gpu.h
> > +++ b/include/hw/virtio/virtio-gpu.h
> > @@ -225,13 +225,13 @@ struct VhostUserGPU {
> >   };
> >   
> >   #define VIRTIO_GPU_FILL_CMD(out) do {                                   \
> > -        size_t s;                                                       \
> > -        s = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num, 0,          \
> > +        size_t s_;                                                      \
> > +        s_ = iov_to_buf(cmd->elem.out_sg, cmd->elem.out_num, 0,         \
> >                          &out, sizeof(out));                              \
> > -        if (s != sizeof(out)) {                                         \
> > +        if (s_ != sizeof(out)) {                                        \
> >               qemu_log_mask(LOG_GUEST_ERROR,                              \
> >                             "%s: command size incorrect %zu vs %zu\n",    \
> > -                          __func__, s, sizeof(out));                    \
> > +                          __func__, s_, sizeof(out));                   \
> >               return;                                                     \
> >           }                                                               \
> >       } while (0)
> This is not really enough I think. Someone might
> use another macro as parameter to this macro and we'll get
> a mess. We want something that's specific to this macro.
> How about VIRTIO_GPU_FILL_CMD_s ?
Sure, can do (also for the other patch).

 Thomas