Re: [PATCH] Enable '-Werror' by default for all kernel builds

[Guenter Roeck]

On 9/7/21 9:55 PM, Linus Torvalds wrote:
> On Tue, Sep 7, 2021 at 9:28 PM Guenter Roeck <linux@xxxxxxxxxxxx> 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.

I see the problem only on some architectures. No idea what triggers it,
but it is definitely architecture dependent.

> > 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; })

or:

#define absolute_pointer(val) RELOC_HIDE(val, 0)

or maybe:

#define absolute_pointer(val) RELOC_HIDE((void *)val, 0)

would do the same (though the first variant needs a pointer as argument).
All of those compile.

I tested the first and the last option on qemu:parisc and confirmed that
both work as expected.

I'd be happy to send a formal patch. Which one do you prefer, and where
should I put it ?

Thanks,
Guenter