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

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Date:   Wed, 15 Sep 2021 07:03:26 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
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

On 9/15/21 12:13 AM, Geert Uytterhoeven wrote:
> 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?
> 

No, we are not. It is quite similar to RELOC_HIDE() in that regard.

Guenter