Re: [PATCH] compiler.h: Avoid the usage of __typeof_unqual__() when __GENKSYMS__ is defined

[Uros Bizjak]

On Fri, Apr 4, 2025 at 9:14 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
>
> On Fri, Apr 4, 2025 at 11:37 PM Uros Bizjak <ubizjak@xxxxxxxxx> wrote:
> >
> > On Fri, Apr 4, 2025 at 4:06 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
> >
> > > > > > Current version of genksyms doesn't know anything about __typeof_unqual__()
> > > > > > operator.  Avoid the usage of __typeof_unqual__() with genksyms to prevent
> > > > > > errors when symbols are versioned.
> > > > > >
> > > > > > There were no problems with gendwarfksyms.
> > > > > >
> > > > > > Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
> > > > > > Fixes: ac053946f5c40 ("compiler.h: introduce TYPEOF_UNQUAL() macro")
> > > > > > Reported-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
> > > > > > Closes: https://lore.kernel.org/lkml/81a25a60-de78-43fb-b56a-131151e1c035@xxxxxxxxxxxxx/
> > > > > > Cc: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > > > > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > > > > ---
> > > > >
> > > > >
> > > > > Why don't you add it to the genksyms keyword table?
> > > >
> > > > It doesn't work, even if I patch it with an even more elaborate patch
> > > > (attached).
> > > >
> > > > I guess some more surgery will be needed, but for now a fallback works
> > > > as expected.
> > > >
> > > > Uros.
> > >
> > > The attached patch looks good to me.
> >
> > FAOD - do you refer to the submitted one for compiler.h or to the one
> > for scripts/genksyms/keywords.c? (The latter doesn't fix the warning,
> > though).
>
>
>
> You are still seeing the warnings because __typeof_unqual__
> is not only the issue.
>
> Hint:
>
> $ make -s KCFLAGS=-D__GENKSYMS__  arch/x86/kernel/setup_percpu.i
> $ grep  'this_cpu_off;'  arch/x86/kernel/setup_percpu.i

I see.

With my workaround, this_cpu_off is declared as:

extern __attribute__((section(".data..percpu" "..hot.."
"this_cpu_off"))) __typeof__(unsigned long) this_cpu_off;

while without workaround, the same variable is declared as:

extern __seg_gs __attribute__((section(".data..percpu" "..hot.."
"this_cpu_off"))) __typeof__(unsigned long) this_cpu_off;

It looks that genksyms should be extended to handle (or ignore)
__seg_gs/__seg_fs named address prefix. Somewhat surprising, because
genksyms can process:

extern __attribute__((section(".data..percpu" "..hot.."
"const_current_task"))) __typeof__(struct task_struct * const
__seg_gs) const_current_task

without problems.

I'm sorry, but I'm not able to extend genksyms with a new keyword by myself...

Uros.