Re: [v3] Help wanted for enabling -Wshadow=local

[Thomas Huth <thuth@redhat.com>]

On 06/10/2023 21.08, Warner Losh wrote:
> 
> 
> On Fri, Oct 6, 2023, 11:55 AM Thomas Huth <thuth@redhat.com 
> <mailto:thuth@redhat.com>> wrote:
> 
>     On 06/10/2023 18.18, Thomas Huth wrote:
>      > On 06/10/2023 16.45, Markus Armbruster wrote:
>      >> Local variables shadowing other local variables or parameters make the
>      >> code needlessly hard to understand.  Bugs love to hide in such code.
>      >> Evidence: "[PATCH v3 1/7] migration/rdma: Fix save_page method to fail
>      >> on polling error".
>      >>
>      >> Enabling -Wshadow would prevent bugs like this one.  But we have to
>      >> clean up all the offenders first.
>      >>
>      >> Quite a few people responded to my calls for help.  Thank you so much!
>      >>
>      >> I'm collecting patches in my git repo at
>      >> https://repo.or.cz/qemu/armbru.git
>     <https://repo.or.cz/qemu/armbru.git> in branch shadow-next.  All but the
>      >> last two are in a pending pull request.
>      >>
>      >> My test build is down to seven files with warnings.  "[PATCH v2 0/3]
>      >> hexagon: GETPC() and shadowing fixes" takes care of four, but it needs a
>      >> rebase.
>      >>
>      >> Remaining three:
>      >>
>      >>      In file included from ../hw/display/virtio-gpu-virgl.c:19:
>      >>      ../hw/display/virtio-gpu-virgl.c: In function
>     ‘virgl_cmd_submit_3d’:
>      >>      /work/armbru/qemu/include/hw/virtio/virtio-gpu.h:228:16: warning:
>      >> declaration of ‘s’ shadows a previous local [-Wshadow=compatible-local]
>      >>        228 |         size_t
>      >> s;                                                       \
>      >>            |                ^
>      >>      ../hw/display/virtio-gpu-virgl.c:215:5: note: in expansion of
>     macro
>      >> ‘VIRTIO_GPU_FILL_CMD’
>      >>        215 |     VIRTIO_GPU_FILL_CMD(cs);
>      >>            |     ^~~~~~~~~~~~~~~~~~~
>      >>      ../hw/display/virtio-gpu-virgl.c:213:12: note: shadowed
>     declaration
>      >> is here
>      >>        213 |     size_t s;
>      >>            |            ^
>      >>
>      >>      In file included from ../contrib/vhost-user-gpu/virgl.h:18,
>      >>                       from ../contrib/vhost-user-gpu/virgl.c:17:
>      >>      ../contrib/vhost-user-gpu/virgl.c: In function
>     ‘virgl_cmd_submit_3d’:
>      >>      ../contrib/vhost-user-gpu/vugpu.h:167:16: warning: declaration
>     of ‘s’
>      >> shadows a previous local [-Wshadow=compatible-local]
>      >>        167 |         size_t
>      >> s;                                               \
>      >>            |                ^
>      >>      ../contrib/vhost-user-gpu/virgl.c:203:5: note: in expansion of
>     macro
>      >> ‘VUGPU_FILL_CMD’
>      >>        203 |     VUGPU_FILL_CMD(cs);
>      >>            |     ^~~~~~~~~~~~~~
>      >>      ../contrib/vhost-user-gpu/virgl.c:201:12: note: shadowed
>     declaration
>      >> is here
>      >>        201 |     size_t s;
>      >>            |            ^
>      >>
>      >>      ../contrib/vhost-user-gpu/vhost-user-gpu.c: In function
>      >> ‘vg_resource_flush’:
>      >>      ../contrib/vhost-user-gpu/vhost-user-gpu.c:837:29: warning:
>      >> declaration of ‘i’ shadows a previous local [-Wshadow=local]
>      >>        837 |             pixman_image_t *i =
>      >>            |                             ^
>      >>      ../contrib/vhost-user-gpu/vhost-user-gpu.c:757:9: note: shadowed
>      >> declaration is here
>      >>        757 |     int i;
>      >>            |         ^
>      >>
>      >> Gerd, Marc-André, or anybody else?
>      >>
>      >> More warnings may lurk in code my test build doesn't compile.  Need a
>      >> full CI build with -Wshadow=local to find them.  Anybody care to kick
>      >> one off?
>      >
>      > I ran a build here (with -Werror enabled, so that it's easier to see
>     where
>      > it breaks):
>      >
>      > https://gitlab.com/thuth/qemu/-/pipelines/1028023489
>     <https://gitlab.com/thuth/qemu/-/pipelines/1028023489>
>      >
>      > ... but I didn't see any additional spots in the logs beside the ones
>     that
>      > you already listed.
> 
>     After adding two more patches to fix the above warnings, things look pretty
>     good:
> 
>     https://gitlab.com/thuth/qemu/-/pipelines/1028413030
>     <https://gitlab.com/thuth/qemu/-/pipelines/1028413030>
> 
>     There are just some warnings left in the BSD code, as Warner already
>     mentioned in his reply to v2 of your mail:
> 
>     https://gitlab.com/thuth/qemu/-/jobs/5241420713
>     <https://gitlab.com/thuth/qemu/-/jobs/5241420713>
> 
> 
> I think I have fixes for these. I need to merge what just landed into 
> bsd-user fork, rebase, test, the apply them to qemu master branch, retest 
> and send them off...
> 
> My illness has hung on longer than I thought so I'm still behind...

Get well soon again! ... and no worries about the -Wshadow=local patches in 
the BSD code, there is no hurry - The BSDs are using Clang by default, so 
that option won't get enabled by default there anyway yet - I had to switch 
to GCC in the CI pipeline to trigger those, and I guess only very few people 
will use GCC to compile QEMU on FreeBSD.

  Thomas