Re: [PATCH] powerpc/boot: Use address-of operator on section symbols

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Segher,

On Mon, Jul 20, 2020 at 11:03 PM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
> On Sat, Jul 18, 2020 at 09:50:50AM +0200, Geert Uytterhoeven wrote:
> > On Wed, Jun 24, 2020 at 6:02 AM Nathan Chancellor
> > <natechancellor@gmail.com> wrote:
> > >         /* If we have an image attached to us, it overrides anything
> > >          * supplied by the loader. */
> > > -       if (_initrd_end > _initrd_start) {
> > > +       if (&_initrd_end > &_initrd_start) {
> >
> > Are you sure that fix is correct?
> >
> >     extern char _initrd_start[];
> >     extern char _initrd_end[];
> >     extern char _esm_blob_start[];
> >     extern char _esm_blob_end[];
> >
> > Of course the result of their comparison is a constant, as the addresses
> > are constant.  If clangs warns about it, perhaps that warning should be moved
> > to W=1?
> >
> > But adding "&" is not correct, according to C.
>
> Why not?
>
> 6.5.3.2/3
> The unary & operator yields the address of its operand.  [...]
> Otherwise, the result is a pointer to the object or function designated
> by its operand.
>
> This is the same as using the name of an array without anything else,
> yes.  It is a bit clearer if it would not be declared as array, perhaps,
> but it is correct just fine like this.

Thanks, I stand corrected.

Regardless, the comparison is still a comparison between two constant
addresses, so my fear is that the compiler will start generating
warnings for that in the near or distant future, making this change
futile.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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