linux-kernel - Re: arch/arm/kernel/hibernate.c:29:40: warning: array subscript -1 is outside array bounds of 'const void[2147483647]'

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Date:   Mon, 20 Nov 2023 15:14:37 +0800
From:   Yujie Liu <yujie.liu@...el.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Kees Cook <keescook@...omium.org>
CC:     kernel test robot <lkp@...el.com>, <oe-kbuild-all@...ts.linux.dev>,
        <linux-kernel@...r.kernel.org>
Subject: Re: arch/arm/kernel/hibernate.c:29:40: warning: array subscript -1
 is outside array bounds of 'const void[2147483647]'

On Mon, Nov 06, 2023 at 02:19:33PM +0100, Linus Walleij wrote:
> Hi Robot,
> 
> On Wed, Oct 18, 2023 at 2:17 PM kernel test robot <lkp@...el.com> wrote:
> 
> >    arch/arm/kernel/hibernate.c: In function 'pfn_is_nosave':
> > >> arch/arm/kernel/hibernate.c:29:40: warning: array subscript -1 is outside array bounds of 'const void[2147483647]' [-Warray-bounds=]
> >       29 |         unsigned long nosave_end_pfn = virt_to_pfn(&__nosave_end - 1);
> >          |                                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> So the concern is that &__nosave_end  could be 0 and the -1 would make
> it wrap around?
> 
> It still has nothing to do with arrays, I don't get it.

Hi Linus Walleij, sorry that we couldn't explain this warning very
clearly. Let's consult Kees for more input.

Hi Kees, our robot has sent out several reports of "-Warray-bounds"
warnings. Thanks a lot for helping to analyze them. [1][2]

[1] https://lore.kernel.org/all/202309200904.CEED70DA33@keescook/
[2] https://lore.kernel.org/all/202311071521.099CAEA58@keescook/

As for some other reports, developers have some doubt about them that we
are not sure how to explain, such as the one in this report and
[3][4][5][6]. If it's not too much trouble, could you please help take a
look to see if these are valid warnings or false positives? Thanks a lot.

[3] https://lore.kernel.org/oe-kbuild-all/CACRpkdZ-1OcZ-cz0V218-VxAc07DMPvKWee3MHngs6Hrwv4zPA@mail.gmail.com/
[4] https://lore.kernel.org/oe-kbuild-all/20231019092258.c2cbwmmgffa33bro@vireshk-i7/
[5] https://lore.kernel.org/oe-kbuild-all/CANn89iKdMVNrV_0QienhpCJ98D7hj2sqOOYFhhSHBVHzvtkgWQ@mail.gmail.com/
[6] https://lore.kernel.org/oe-kbuild-all/CAOQ4uxjTv+5cB4z8TZQ02c5F3rags1HARoEQG9834A0+_+_twA@mail.gmail.com/

Best Regards,
Yujie