linux-kernel - Re: [PATCH] m68k: Fix virt_addr

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Date:   Fri, 5 Mar 2021 09:37:10 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Greg Ungerer <gerg@...ux-m68k.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>
Cc:     Lee Jones <lee.jones@...aro.org>, Arnd Bergmann <arnd@...db.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] m68k: Fix virt_addr_valid() W=1 compiler warnings

On Tue, Feb 23, 2021 at 11:50 AM Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> If CONFIG_DEBUG_SG=y, and CONFIG_MMU=y:
>
>     include/linux/scatterlist.h: In function ‘sg_set_buf’:
>     arch/m68k/include/asm/page_mm.h:174:49: warning: ordered comparison of pointer with null pointer [-Wextra]
>       174 | #define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
>           |                                                 ^~
>
> or CONFIG_MMU=n:
>
>     include/linux/scatterlist.h: In function ‘sg_set_buf’:
>     arch/m68k/include/asm/page_no.h:33:50: warning: ordered comparison of pointer with null pointer [-Wextra]
>        33 | #define virt_addr_valid(kaddr) (((void *)(kaddr) >= (void *)PAGE_OFFSET) && \
>           |                                                  ^~
>
> Fix this by doing the comparison in the "unsigned long" instead of the
> "void *" domain.
>
> Note that for now this is only seen when compiling btrfs, due to commit
> e9aa7c285d20a69c ("btrfs: enable W=1 checks for btrfs"), but as people
> are doing more W=1 compile testing, it will start to show up elsewhere,
> too.
>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> ---
> Probably we want this as a fix for v5.12, to avoid the build bots
> nagging about it all the time?
>
>  arch/m68k/include/asm/page_mm.h | 2 +-
>  arch/m68k/include/asm/page_no.h | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/m68k/include/asm/page_mm.h b/arch/m68k/include/asm/page_mm.h
> index 7f5912af2a52ea0a..9b1672f9b2e22cdf 100644
> --- a/arch/m68k/include/asm/page_mm.h
> +++ b/arch/m68k/include/asm/page_mm.h
> @@ -171,7 +171,7 @@ static inline __attribute_const__ int __virt_to_node_shift(void)
>  #include <asm-generic/memory_model.h>
>  #endif
>
> -#define virt_addr_valid(kaddr) ((void *)(kaddr) >= (void *)PAGE_OFFSET && (void *)(kaddr) < high_memory)
> +#define virt_addr_valid(kaddr) ((unsigned long)(kaddr) >= PAGE_OFFSET && ((unsigned long)kaddr) < (unsigned long)high_memory)

While preparing the pull request, I noticed I misplaced the braces in
the second part.
Will send a v2...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

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