Re: New warning in linus/master

[Ricardo Ribalda <ribalda@chromium.org>]

Hi Thomas

On Wed, 22 Apr 2026 at 15:32, Thomas Weißschuh
<thomas.weissschuh@linutronix.de> wrote:
>
> On Wed, Apr 22, 2026 at 03:00:11PM +0800, Ricardo Ribalda wrote:
> > On Wed, 22 Apr 2026 at 13:57, Thomas Weißschuh
> > <thomas.weissschuh@linutronix.de> wrote:
> > > On Wed, Apr 22, 2026 at 11:51:45AM +0800, Ricardo Ribalda wrote:
> > > > Media-CI has found a couple of new warnings in the latest kernel
> > > > version for aarch64 and powerpc. They get fixed with this patch and
> > > > before moving I wanted to know if this was under your radar.
> > >
> > > Thanks for the report. I was not aware of these so far.
> > >
> > > > diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> > > > index 7dec05dd33b7..65914842fae0 100644
> > > > --- a/arch/arm64/kernel/vdso/Makefile
> > > > +++ b/arch/arm64/kernel/vdso/Makefile
> > > > @@ -50,7 +50,7 @@ CFLAGS_vgettimeofday.o = $(CC_FLAGS_ADD_VDSO)
> > > >  CFLAGS_vgetrandom.o = $(CC_FLAGS_ADD_VDSO)
> > > >
> > > >  ifneq ($(c-gettimeofday-y),)
> > > > -  CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> > > > +  CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)
> > > > -Wno-maybe-uninitialized
> > > >  endif
> > >
> > > (...)
> > >
> > > I'd like to know exactly what is going on before suppressing the warning.
> > > It is a non-standard warning, only enabled by *some* of the vDSO builds
> > > for some reason.
> > >
> > > > https://gitlab.freedesktop.org/linux-media/users/ribalda/-/pipelines/1649144/test_report?job_name=cross-gcc
> > >
> > > While I was able to download a configuration from this job and also use the
> > > same container image, I can not reproduce the issue. Is the configuration the
> > > full one or only the template?
> > >
> > > Could you provide full reproduction steps?
> >
> > You can try repro with:
> >
> > work/linux $ podman run -v .:/workdir/ --rm -it
> > registry.freedesktop.org/linux-media/media-ci/build:latest
> > $ cd /workdir
> > $ CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make allyesconfig
> > $ CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make
> > arch/arm64/kernel/vdso/vgettimeofday.o
> >
> > The gcc version discrepancy is because I the error was due to old gcc
> > version and I was playing around with that... but it fails in both
> > gcc14 and gcc15
>
> Ack.
>
> > You can try with debian testing with
> > work/linux$ podman run -v .:/workdir/ --rm -it debian:testing
> > $ apt-get update
> > $ apt-get install gcc-aarch64-linux-gnu build-essential flex bison libssl-dev bc
> > $ cd /workdir
> > $ CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make allyesconfig
> > $ CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make
> > arch/arm64/kernel/vdso/vgettimeofday.o
>
> Both reproducers do *not* reproduce the issue for me.
> (It is more or less exactly what I tried before)


Ok, I think I found what is going on. media-ci was forcing
KCFLAGS=-Wmaybe-uninitialized

https://gitlab.freedesktop.org/linux-media/media-ci/-/blob/main/test-build.sh?ref_type=heads#L29

And something has changed in the kernel in the last version that
triggers a (hopefully) false positive.

can you try with:

CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make
KCFLAGS=-Wmaybe-uninitialized  allyesconfig
CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make
KCFLAGS=-Wmaybe-uninitialized  prepare

?


>
> Please note that this line does not work in general:
> $ CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 make arch/arm64/kernel/vdso/vgettimeofday.o
>
> The vDSO object files can not be built in this way like regular kernel object
> files and will produce a compiler error, but not the one under discussion.
> Instead the vDSO on arm64 is built during the 'make prepare' phase.
> (Other architectures work differently, of course...)
>
> (...)
>
>
> Thomas



-- 
Ricardo Ribalda