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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 7 Sep 2021 21:55:08 -0700
Message-ID: <CAHk-=whVDMcg==vcOopR0Mci2FQ8bzJjufyCg+WPh003K2i2ww@mail.gmail.com>
Subject: Re: [PATCH] Enable '-Werror' by default for all kernel builds
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Christian Koenig <christian.koenig@amd.com>,
        Huang Rui <ray.huang@amd.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-sparc <sparclinux@vger.kernel.org>
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On Tue, Sep 7, 2021 at 9:28 PM Guenter Roeck <linux@roeck-us.net> wrote:
>
> It is seen with gcc 11.x whenever a memXXX or strXXX function parameter
> is a pointer to a fixed address.

I wonder why I don't see it with gcc 11.2 here on x86-64.

> gcc is happy if "(void *) 0xfffc1f2c"
> is passed to a global function which does nothing but return the address,
> such as:
>
> void *sanitize_address(void *address)
> {
>         return address;
> }

We have had reasons to do things like that before for somewhat similar
(well, opposite) reasons - trying to disassociate some pointer from
its originating symbol type.

Look at RELOC_HIDE().

It might be worth it having something similar for "absolute_pointer()".

Entirely untested "written-in-the-MUA" garbage:

   #define absolute_pointer(val) \
        ({ void *__res; __asm__("":"=r" (__res):"0" ((unsigned
long)(val))); __res; })

I dunno.

               Linus