Re: [PATCH v2] m68k: Avoid -Wunused-but-set-parameter in clear_user_page()

[Geert Uytterhoeven]

Hi Andrew, Thomas,

On Mon, 25 May 2026 at 21:54, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 25 May 2026 10:33:52 +0200 Thomas Weißschuh <linux@xxxxxxxxxxxxxx> wrote:
> > The loop in clear_user_pages() iterates over all pages and calls
> > clear_user_page() for each of them. During the loop "vaddr" is modified.
> > However on m68k clear_user() is a macro which does not use "vaddr".
> > The compiler sees a variable which is modified but never used and emits
> > a warning for that:
> >
> > include/linux/highmem.h: In function 'clear_user_pages':
> > include/linux/highmem.h:234:63: warning: parameter 'vaddr' set but not used [-Wunused-but-set-parameter=]
> >     static inline void clear_user_pages(void *addr, unsigned long vaddr,
> >
> > Other architectures use an inline function for clear_user_page() which
> > avoids the warning. This is not possible on m68k, as dlush_dcache_page()
> > is another macro which is not yet defined where clear_user_page() is
> > defined. Including cacheflush_mm.h will trigger recursive and lots of
> > other issues.
> >
> > So hide the warning with a cast to (void) instead.
> >
> > While we are here, do the same for copy_user_page().
> >
>
> As with sparc, can this be addressed by converting these macros into
> static inline C functions?

That would fail for similar reasons as on sparc: flush_dcache_page() is
not yet defined, and trying to include <asm/page.h> causes include hell.

> > --- a/arch/m68k/include/asm/page_mm.h
> > +++ b/arch/m68k/include/asm/page_mm.h
> > @@ -55,10 +55,12 @@ static inline void clear_page(void *page)
> >  #define clear_user_page(addr, vaddr, page)   \
> >       do {    clear_page(addr);               \
> >               flush_dcache_page(page);        \
> > +             (void)(vaddr);                  \
> >       } while (0)
> >  #define copy_user_page(to, from, vaddr, page)        \
> >       do {    copy_page(to, from);            \
> >               flush_dcache_page(page);        \
> > +             (void)(vaddr);                  \
> >       } while (0)
> >
> >  extern unsigned long m68k_memoffset;

People are starting to report this, now gcc-16 is getting more
widespread use.

Andrew: can you please take this, or shall I queue it for m68k fixes
(I don't have any other fixes at the moment)?

Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>

Thanks!

Gr{oetje,eeting}s,

                        Geert


--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds