linux-kernel - Re: [PATCH v2 1/4] compiler.h: Introduce absolute

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Date:   Wed, 15 Sep 2021 09:13:11 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Parisc List <linux-parisc@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, linux-sparse@...r.kernel.org
Subject: Re: [PATCH v2 1/4] compiler.h: Introduce absolute_pointer macro

Hi Günter,

On Wed, Sep 15, 2021 at 5:52 AM Guenter Roeck <linux@...ck-us.net> wrote:
> absolute_pointer() disassociates a pointer from its originating symbol
> type and context. Use it to prevent compiler warnings/errors such as
>
> drivers/net/ethernet/i825xx/82596.c: In function 'i82596_probe':
> ./arch/m68k/include/asm/string.h:72:25: error:
>         '__builtin_memcpy' reading 6 bytes from a region of size 0
>                 [-Werror=stringop-overread]
>
> Such warnings may be reported by gcc 11.x for string and memory operations
> on fixed addresses.
>
> Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> v2: No change
>
>  include/linux/compiler.h | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index b67261a1e3e9..3d5af56337bd 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -188,6 +188,8 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
>      (typeof(ptr)) (__ptr + (off)); })
>  #endif
>
> +#define absolute_pointer(val)  RELOC_HIDE((void *)(val), 0)

I guess we're not worried about "val" being evaluated multiple
times inside RELOC_HIDE(), as this is mainly intended for constants?

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